Nursing: Epidemiology and Health
U N I T Concepts of Health and Disease arly peoples were considered long-lived if they reached 30 years of age—that is, if they survived infancy. For many centuries, infant mortality was so great that large families became the tradition; many children in a family ensured that at least some would survive. Life expectancy has increased over the centuries, and today an individual in a developed country can expect to live about 71 to 79 years. Although life expectancy has increased radically since ancient times, human longevity has remained fundamentally unchanged.
The quest to solve the mystery of human longevity, which appears to be genetically programmed, began with Gregor Mendel (1822–1884), an Augustinian monk. Mendel laid the foundation of modern genetics with the pea experiments he performed in a monastery garden. Today, geneticists search for the determinant, or determinants, of the human life p. Up to this time, scientists have failed to identify an aging gene that would account for a limited life p. However, they have found that cells have a ? nite reproductive capacity. As they age, genes are increasingly unable to perform their functions.
The cells become poorer and poorer at making the substances they need for their own special tasks or even for their own maintenance. Free radicals, mutation in a cell’s DNA, and the process of programmed cell death are some of the factors that work together to affect a cell’s functioning. I E CHAPTER Concepts of Health and Disease Georgianne H. Heymann Carol M. Porth 1 ogy. There has been an increased knowledge of immune mechanisms; the discovery of antibiotics to cure infections; and the development of vaccines to prevent disease, chemotherapy to attack cancers, and drugs to control the manifestations of mental illness.
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The introduction of the birth control pill and improved prenatal care have led to decreased birth rates and declines in infant and child mortality. The bene? ts of science and technology also have increased the survival of infants born prematurely and of children with previously untreatable illnesses, such as immunode? ciency states and leukemia. There also has been an increase in the survival of very seriously ill and critically injured persons of all age groups.
Consequently, there has been an increase in longevity, a shift in the age distribution of the population, and an increase in age-related diseases. Coronary heart disease, stroke, and cancer have now replaced pneumonia, tuberculosis, and diarrhea and enteritis—the leading causes of death in the 1900s. This chapter, which is intended to serve as an introduction to the book, is organized into four sections: health and society, historical perspectives on health and disease, perspectives on health and disease in individuals, and perspectives on health and disease in populations.
The chapter is intended to provide the reader with the ability to view within a larger framework the historical aspects of health and disease and the relationship of health and disease to individuals and populations, and to introduce the reader to terms, such as etiology and pathogenesis, that are used throughout this text. HEALTH AND SOCIETY HEALTH AND DISEASE: A HISTORICAL PERSPECTIVE The In? ence of Early Scholars The Nineteenth Century The Twentieth Century The Twenty-First Century PERSPECTIVES ON HEALTH AND DISEASE IN INDIVIDUALS Health Health and Disease as States of Adaptation Disease Etiology Pathogenesis Morphology Clinical Manifestations Diagnosis Clinical Course PERSPECTIVES ON HEALTH AND DISEASE IN POPULATIONS Epidemiology and Patterns of Disease Prevalence and Incidence Morbidity and Mortality Determination of Risk Factors The Framingham Study The Nurses’ Health Study Natural History Levels of Prevention Evidence-Based Practice and Practice Guidelines e concepts of what constituted health and disease at the beginning of the last century were far different from those of this century. In most of the industrialized nations of the world, people now are living longer and enjoying a healthier lifestyle. Much of this has been made possible by recent advances in science and technol- T Health and Society Everyone who is born holds dual citizenship in the kingdom of the well and in the kingdom of the sick. Although we all prefer to use only the good passport, sooner or later each of us is obligated, at least for a spell, to identify ourselves as citizens of that other place. 3 4 UNIT I Concepts of Health and Disease After completing this section of the chapter, you should be able to meet the following objectives: ? Describe the concepts used to establish belief systems within a community and the effects on its health care practices ? Identify a disease believed to be generated by speci? c emotions and the characteristics ascribed to it ? Explain how mythologizing disease can be detrimental to individuals in a society There is a long history that documents the concern of humans for their own health and well-being and that of their community.
It is not always evident what particular beliefs were held by early humans concerning health and disease. Still, there is evidence that whenever humans have formed social groups, some individuals have taken the role of the healer, responsible for the health of the community by preventing disease and curing the sick. In prehistoric times, people believed that angry gods or evil spirits caused ill health and disease. To cure the sick, the gods had to be paci? ed or the evil spirits driven from the body. In time, this task became the job of the ealers, or tribal priests. They tried to pacify the gods or drive out the evil spirits using magic charms, spells, and incantations. There also is evidence of surgical treatment. Trephining involved the use of a stone instrument to cut a hole in the skull of the sick person. It is believed that this was done to release spirits responsible for illness. Prehistoric healers probably also discovered that many plants can be used as drugs. The community as a whole also was involved in securing the health of its members.
It was the community that often functioned to take care of those considered ill or disabled. The earliest evidence of this comes from an Old Stone Age cave site, Riparo del Romio, in southern Italy. There the remains of an adolescent dwarf were found. Despite his severe condition, which must have greatly limited his ability to contribute to either hunting or gathering, the young man survived to the age of 17 years. He must have been supported throughout his life by the rest of the community, which had incorporated compassion for its members into its belief system. Communities such as this probably existed throughout prehistory; separated from each other and without any formal routes of communication, they relied on herbal medicines and group activity to maintain health. Throughout history, peoples and cultures have developed their health practices based on their belief systems. Many traditions construed sickness and health primarily in the context of an understanding of the relations of human beings to the planets, stars, mountains, rivers, spirits, and ancestors, gods and demons, the heavens and underworld.
Some traditions, such as those re? ected in Chinese and Indian cultures, although concerned with a cosmic scope, do not pay great attention to the supernatural. Over time, modern Western thinking has shed its adherence to all such elements. Originating with the Greek tradition—which dismissed supernatural powers, although not environmental in? uences—and further shaped by the In? uences of zodiac signs on the human body. (Courtesy of the National Library of Medicine) ourishing anatomic and physiologic programs of the Renaissance, the Western tradition was created based on the belief that everything that needed to be known essentially could be discovered by probing more deeply and ever more minutely into the ? esh, its systems, tissues, cells, and DNA. 3 Through Western political and economic domination, these health beliefs now have powerful in? uence worldwide. Every society has its own ideas and beliefs about life, death, and disease. It is these perceptions that shape the concept of health in a society.
Although some customs and beliefs tend to safeguard human communities from disease, others invite and provoke disease outbreaks. The beliefs that people have concerning health and disease can change the destiny of nations. The conquering of the Aztec empire may be one example. Historians have speculated how Hernando Cortez, starting off with fewer than 600 men, could conquer the Aztec empire, whose subjects numbered millions. Historian William H. McNeill suggests a sequence of events that may explain how a tiny handful of men could subjugate a nation of millions.
Although the Aztecs ? rst thought the mounted, gunpowered Spaniards were gods, experience soon showed CHAPTER 1 Concepts of Health and Disease 5 otherwise. Armed clashes revealed the limitations of horse? esh and of primitive guns, and the Aztecs were able to drive Cortez and his men from their city. Unbeknownst to the Aztecs, the Spaniards had a more devastating weapon than any ? rearm: smallpox. An epidemic of smallpox broke out among the Aztecs after their skirmishes with the Spaniards.
Because the population lacked inherited or acquired immunity, the results were catastrophic. It is presumed that a quarter to a third of the population died from the initial onslaught. Even more devastating were the psychological implications of the disease: it killed only American Indians and left Spaniards unharmed. A way of life built around the old Indian gods could not survive such a demonstration of the superior power of the God the Spaniards worshipped. It is not hard to imagine then that the Indians accepted Christianity and submitted meekly to Spanish control. Although we live in an age of science, science has not eliminated fantasies about health; the stigmas of sickness and the moral meanings that they carry continue. Whereas people in previous centuries wove stories around leprosy, plague, and tuberculosis to create fear and guilt, the modern age has created similar taboos and mythologies about cancer and acquired immunode? ciency syndrome (AIDS). The myth of tuberculosis (TB) was that a person who suffered from it was of a melancholy, superior character— sensitive, creative, a being apart.
Melancholy, or sadness, made one “interesting” or romantic. The general perception of TB as “romantic” was not just a literary device. It was a way of thinking that insinuated itself into the sensibilities and made it possible to ignore the social conditions, such as overcrowding and poor sanitation and nutrition, that helped breed tuberculosis. The infusion of beliefs into public awareness often is surreptitious. Just as tuberculosis often had been regarded sentimentally, as an enhancement of identity, cancer was regarded with irrational revulsion, as a diminution of the self. Current accounts of the psychological aspects of cancer often cite old authorities, starting with the Greek physician Galen, who observed that “melancholy women” are more likely to get breast cancer than “sanguine women. ” Grief and anxiety were cited as causes of cancer, as well as personal losses. Public ? gures such as Napoleon, Ulysses S. Grant, Robert A. Taft, and Hubert Humphrey have all had their cancers diagnosed as the reaction to political defeat and the end to their political ambitions. Although distress can affect immunologic responsiveness, there is no scienti? evidence to support the view that speci? c emotions, or emotions in general, can produce speci? c diseases—or that cancer is the result of a “cancer personality,” described as emotionally withdrawn, lacking self-con? dence, and depressive. These disease mythologies contribute to the stigmatizing of certain illnesses and, by extension, of those who are ill. The beliefs about health and disease have the power to trap or empower people. They may inhibit people from seeking early treatment, diminish personal responsibility for practicing healthful behaviors, or encourage fear and social isolation.
Conversely, they also can be the impetus for compassion to those who are ill, for commitment to improving one’s own health, and for support of efforts to improve the health status of others. In summary, what constitutes health and disease changes over time. Prehistoric times were marked by beliefs that angry gods or evil spirits caused ill health and disease. To cure the sick, the gods had to be paci? ed or the evil spirits driven from the body. Tribal healers, or priests, emerged to accomplish this task. Prehistoric healers used a myriad of treatments, including magic charms, spells, and incantations; surgical treatment; and plant medicines.
Throughout history, the concept of health in a society has been shaped by its beliefs about life, death, and disease. Some beliefs and customs, such as exhibiting compassion for disabled community members, tend to safeguard human communities and increase the quality of life for all community members. Others invite and provoke disease outbreaks, such as myths about the causes of disease. Even though science and technology have advanced the understanding and treatment of disease, misconceptions and fantasies about disease still arise.
In previous centuries, diseases such as leprosy, plague, and tuberculosis were fodder for taboos and mythologies; today, it is cancer and AIDS. The psychological effects of disease mythologies can be positive or negative. At their worst, they can stigmatize and isolate those who are ill; at their best, they can educate the community and improve the health of its members. Health and Disease: A Historical Perspective After completing this section of the chapter, you should be able to meet the following objectives: Describe the contributions of the early Greek, Italian, and English scholars to the understanding of anatomy, physiology, and pathology ? State two important advances of the nineteenth century that helped to pave the way for prevention of disease ? State three signi? cant advances of the twentieth century that have revolutionized diagnosis and treatment of disease ? Propose developments that will both hamper and contribute to the promotion of health and the elimination of disease in the twenty-? rst century It has been said that those who do not know history are condemned to repeat it.
There are many contributors to the understanding of how the body is constructed and how it works, and what disease is and how it can be treated, which in turn leads to an understanding of what health is and how can it be maintained. Much of what we take for granted in terms of treating the diseases that af? ict humankind has had its origin in the past. Although they are seemingly small contributions in terms of today’s scienti? c advances, it is the knowledge 6 UNIT I Concepts of Health and Disease produced by the great thinkers of the past that has made possible the many things we now take for granted.
THE INFLUENCE OF EARLY SCHOLARS Knowledge of anatomy, physiology, and pathology as we now know it began to emerge with the ancient Greeks. They were the ? rst to recognize the distinction between internal and external causes of illness. To Hippocrates and his followers, we owe the foundations of the clinical principles and the ethics that grew into modern medical science. Hippocrates (460–377 BC) was a blend of scientist and artist. He believed that disease occurred when the four humors—blood from the heart, yellow bile from the liver, black bile from the spleen, and phlegm from the brain—became out of balance.
These humors were said to govern character as well as health, producing phlegmatic, sanguine, choleric, and melancholic personalities. This belief paralleled the even older Chinese tradition, which was founded on the complementary principles of yin (female principle) and yang (male), whose correct proportions were essential for health. Hippocrates is identi? ed with an approach to health that dictated plenty of healthy exercise, rest in illness, and a moderate, sober diet. It was Aristotle (384–322 BC) who, through his dissection of small animals and description of their internal Hippocrates: A blend of scientist and scholar. Courtesy of the National Library of Medicine) anatomy, laid the foundations for the later scrutiny of the human body. For Aristotle, the heart was the most important organ. He believed it to be the center of the blood system as well as the center of the emotions. However, Aristotle’s main contributions were made to science in general. The person who took the next major step was Galen (AD 129–199), a physician to the emperors and gladiators of ancient Rome. Galen expanded on the Hippocratic doctrines and introduced experimentation into the study of healing. His work came to be regarded as the encyclopedia of anatomy and physiology.
He demoted the heart—in his view, the liver was primary for venous blood, whereas the seat of all thought was the brain. He described the arteries and veins and even revealed the working of the nervous system by severing a pig’s spinal cord at different points and demonstrating that corresponding parts of the body became paralyzed. According to Galen, the body carried three kinds of blood that contained spirits charged by various organs: the veins carried “natural spirit” from the liver; the arteries, “vital spirit” from the lungs; the nerves, “animal spirit” from the brain. The heart merely warmed the blood.
After Galen’s death, however, anatomic research ceased, and his work was considered infallible for almost 1400 years. As the great medical schools of universities reformed the teaching of anatomy in the early 1500s and integrated it into medical studies, it became apparent to anatomists that Galen’s data—taken from dogs, pigs, and apes—often were riddled with error. It was only with the work of Andreas Vesalius (1514–1564) that Galen’s ideas truly were challenged. Vesalius, professor of anatomy and surgery at Padua, Italy, dedicated a lifetime to the study of the human body.
Vesalius carried out some unprecedentedly scrupulous dissections and used the latest in artistic techniques and printing for the more than 200 woodcuts in his De Humani Corporis Fabrica (“On the Fabric [Structure] of the Human Body”). He showed not only what bodily parts looked like but also how they worked. The book, published in 1543, set a new standard for the understanding of human anatomy. With this work, Vesalius became a leading ? gure in the revolt against Galen’s teachings. One of the most historically significant discoveries was made by William Harvey (1578–1657), an English physician and physiologist.
He established that the blood circulates in a closed system impelled mechanically by a “pumplike” heart. He also measured the amount of blood in the circulatory system in any given unit of time—one of the ? rst applications of quantitative methods in biology. Harvey’s work, published in On the Motion of the Heart and Blood in Animals (1628), provided a foundation of physiologic principles that led to an understanding of blood pressure and set the stage for innovative techniques such as cardiac catheterization. With the re? ement of the microscope by the Dutch lens maker Anton van Leeuwenhoek (1632–1723), the stage was set for the era of cellular biology. Another early user of the microscope, English scientist Robert Hooke (1635–1703), published his Micrographia in 1665 in which CHAPTER 1 Concepts of Health and Disease 7 William Harvey’s most eminent patient, King Charles I, and the future King Charles II look on as Harvey displays a dissected deer heart. (Courtesy of the National Library of Medicine) he formally described the plant cells in cork and presented his theories of light and combustion and his studies of insect anatomy.
His book presented the great potential of the microscope for biologic investigation. In it, he inaugurated the modern biologic usage of the word cell. A century later, German-born botanist Mathias Schleiden (1804–1881) and physiologist Theodor Schwann (1810–1882) observed that animal tissues also were composed of cells. Although Harvey contributed greatly to the understanding of anatomy and physiology, he was not interested in the chemistry of life. It was not until French chemist Antoine Lavoisier (1743–1794), who was schooled as a lawyer but devoted to scienti? pursuits, overturned 100year-old theories of chemistry and established the basis of modern chemistry that new paths to examine body processes, such as metabolism, opened up. His restructured chemistry also gave scientists, including Louis Pasteur, the tools to develop organic chemistry. In 1796, Edward Jenner (1749–1823) conducted the ? rst vaccination by injecting the ? uid from a dairymaid’s cowpox lesion into a young boy’s arm. The vaccination by this English country doctor successfully protected the child from smallpox. Jenner’s discovery led to the development of vaccines to prevent many other diseases as well.
Jenner’s classic experiment was the ? rst of? cially recorded vaccination. Painting by Georges-Gaston Melingue (1894). The ? rst vaccination. Here Dr. Jenner introduces cowpox taken from dairymaid Sarah Nelmes (right) and introduces it into two incisions on the arm of James Phipps, a healthy 8-year-old boy. The boy developed cowpox, but not smallpox, when Jenner introduced the organism into his arm 48 days later. (Courtesy of the National Library of Medicine) THE NINETEENTH CENTURY The nineteenth century was a time of spectacular leaps forward in the understanding of infectious diseases.
For many centuries, rival epidemiologic theories associated disease and epidemics like cholera with poisonous fumes given off from dung heaps and decaying matter (poisons in the air, exuded from rotting animal and vegetable material, the soil, and standing water) or with contagion (person-to-person contact). In 1865, English surgeon Joseph Lister (1827–1912) concluded that microbes caused wound infections. He began to use carbolic acid on wounds to kill microbes and reduce infection after surgery. However, Lister was not alone in identifying hazards in the immediate environment as detrimental to health.
English nurse Florence Nightingale (1820–1910) was a leading proponent of sanitation and hygiene as weapons against disease. It was at the English base at Scutari during the Crimean War (1854–1856) that Nightingale waged her battle. Arriving at the army hospital with a party of 38 nurses, Nightingale found nearly 2000 wounded and sick inhabiting foul, rat-infested wards. The war raged on, deluging the hospital with wounded as Nightingale not only organized the nursing care of the wounded but also provided meals, supplied bedding, and saw to the laundry.
Within 6 months, she had brought about a transformation and slashed the death rate from approximately 40% to 2%. 3 8 UNIT I Concepts of Health and Disease Florence Nightingale caring for wounded at Scutari, Turkey, during the Crimean War. (Courtesy of the National Library of Medicine) From the 1860s, the rise of bacteriology, associated especially with chemist and microbiologist Louis Pasteur in France and bacteriologist Robert Koch in Germany, established the role of microorganismal pathogens. Almost for the ? rst time in medicine, bacteriology led directly to dramatic new cures.
The technique of pasteurization is named after Louis Pasteur (1822–1895). He introduced the method in 1865 to prevent the souring of wine. Pasteur’s studies of fermentation convinced him that it depended on the presence of microscopic forms of life, with each fermenting medium serving as a unique food for a speci? c microorganism. He developed techniques for culturing microbes in liquid broths. Through his work, he was able to dispel the disease theory that predominated in the mid-nineteenth century, attributing fevers to “miasmas,” or fumes, and laid the foundation for the germ theory of disease.
The anthrax bacillus, discovered by Robert Koch (1843–1910), was the ? rst microorganism identi? ed as a cause of illness. Koch’s trailblazing work also included identifying the organism responsible for tuberculosis and the discovery of a tuberculosis skin-testing material. In 1895, German physicist Wilhelm Rontgen (1845– 1923) discovered X rays. For the ? rst time without a catastrophic event, the most hidden parts of a human body were revealed. Even though he understood that it was a signi? cant discovery, Rontgen did not initially recognize the amazing diagnostic potential of the process he had discovered.
THE TWENTIETH CENTURY The twentieth century was a period of revolutionary industry in the science and politics of health. Concerns about the care of infants and children and the spread of infectious disease became prevailing themes in public and political arenas alike. It was during this time that private duty and public health nursing emerged as the means of delivering health care to people in their homes and in their communities. Social service agencies like the Henry Street Settlement in New York, founded by Lillian Wald, sent nurses into tenements to care for the sick. The placement of nurses in schools began in New York City in 1902 at the urging of Wald, who offered to supply a Henry Street nurse for 1 month without charge. 5 Efforts to broaden the delivery of health care from the city to rural areas also were initiated during the early 1900s. The American Red Cross, which was reorganized and granted a new charter by Congress in 1905, established a nursing service for the rural poor that eventually expanded to serve the small town poor as well. 5 Scienti? c discoveries and innovations abounded in the twentieth century.
In the early 1900s, German bacteriologist Paul Ehrlich (1854–1915) theorized that certain substances could act as “magic bullets,” attacking disease-causing microbes but leaving the rest of the body undamaged. In 1910, he introduced his discovery: using the arsenic compound Salvarsan, he had found an effective weapon against syphilis. Through his work, Ehrlich launched the science of chemotherapy. CHAPTER 1 Concepts of Health and Disease 9 The operating room. With the advent of anesthesia, knowledge of how microbes cause disease, and availability of incandescent lighting in the operating room, surgery became an option for treating disease.
Rubber gloves had not yet been invented and the surgical team worked with bare hands to perform surgery. (Hahnemann Hospital, Chicago, IL. Courtesy Bette Clemons, Phoenix, AZ) The ? rst antibiotic was discovered in 1928 by English bacteriologist Sir Alexander Fleming (1881–1955). As he studied the relationship between bacteria and the mold Penicillium, he discovered its ability to kill staphylococci. However, it was not until the 1940s that later researchers, who were searching for substances produced by one microorganism that might kill other microorganisms, produced penicillin as a clinically useful antibiotic.
By the 1930s, innovative researchers had produced a cornucopia of new drugs that could be used to treat many of the most common illnesses that left their victims either severely disabled or dead. The medical community now had at its disposal medications such as digoxin to treat heart failure; sulfa drugs, which produced near-miraculous cures for infections such as scarlet fever; and insulin to treat diabetes. At the turn of the century, social service agencies like Henry Street Settlement in New York sent nurses into tenements to care for the sick. (Schorr T. M. , Kennedy S.
M. [1999]. 100 years of American nursing [p. 12]. Philadelphia: Lippincott Williams & Wilkins) 10 UNIT I Concepts of Health and Disease With the discovery of insulin, a once-fatal disease known from antiquity no longer carried a death sentence. Working together, Canadian physician Sir Frederick Banting (1891–1941) and physiologist Charles Best (1899–1978) isolated insulin from the pancreas of a dog in 1921. The extract, when given to diabetic dogs, restored their health. In January 1922, they successfully treated a young boy dying of diabetes with their pancreatic extracts.
Although still incurable, it became possible to live with diabetes. One disease that remained not only incurable but untreatable through much of the twentieth century was tuberculosis. With no cure or preventive vaccine forthcoming, efforts at the turn of the century were dedicated to controlling the spread of tuberculosis. It was then that an alliance between organized medicine and the public resulted in the formation of voluntary local organizations to battle the disease. These organizations focused on education to counteract the fear of tuberculosis; at the same time, they warned against the disease.
In 1904, the local organizations joined together to form a national organization, the National Association for the Study and Prevention of Tuberculosis. In 1918, the name was changed to the National Tuberculosis Association, which was renamed the American Lung Association in 1973. 6 The national and local tuberculosis associations played a vital role in educating the public by running campaigns urging people to have skin tests and chest x-rays as a means of diagnosing tuberculosis. Once tuberculosis was diagnosed, an individual was likely to be sent to a sanatorium or tuberculosis hospital.
There, good nourishment, fresh air, and bed rest were prescribed in the belief that if the body’s natural defenses were strengthened, they would be able to overcome the tuberculosis bacillus. For almost half a century, this would be the prevailing treatment. It was not until 1945, with the introduction of chemotherapy, that streptomycin was used to treat tuberculosis. Outbreaks of poliomyelitis, which had increased in the early decades of the 1900s, served as the impetus for the work of American microbiologist Jonas Salk (1914–1995).
At its peak, the virus was claiming 50,000 victims annually in the United States. 3 Test trials of Salk’s vaccine with inactivated virus began in 1953, and it proved to prevent the development of polio. By 1955, the massive testing was complete, and the vaccine was quickly put into wide use. Surgical techniques also flourished during this time. A single technical innovation was responsible for opening up the last surgical frontier—the heart. Up to this time, the heart had been out of bounds; surgeons did not have the means to take over the function of the heart for long enough to get inside and operate. American surgeon John Gibbon (1903–1973) addressed this problem when he developed the heart-lung machine. Dramatic advances followed its successful use in 1953—probably none more so than the ? rst successful heart transplantation performed in 1967 by South African surgeon Christiaan Barnard (1922–2001). For centuries, the inheritance of traits had been explained in religious or philosophical terms. Although English naturalist Charles Darwin’s (1809–1882) work dispelled long-held beliefs about inherited traits, it was Austrian bo-
A tuberculosis skin testing clinic. (Schorr T. M. , Kennedy S. M. [1999]. 100 years of American nursing [p. 49]. Philadelphia: Lippincott Williams & Wilkins) CHAPTER 1 Concepts of Health and Disease 11 The “iron lung,” which used negative pressure to draw air into the lungs, was used to provide ventilatory support for persons with “bulbar polio. ” (Schorr T. M. , Kennedy S. M. [1999]. 100 years of American nursing [p. 91]. Philadelphia: Lippincott Williams & Wilkins) anist Gregor Mendel’s (1822–1884) revolutionary theories on the segregation of traits, largely ignored until 1902, that laid the groundwork for establishing the chromosome as the structural unit of heredity. Many other scientists and researchers contributed to the storehouse of genetic knowledge. With the work by American geneticist James Watson (1928–) and British biophysicists Francis Crick (1916–) and Maurice Wilkins (1916–) in the early 1950s, which established the double-helical structure of DNA, the way to investigating and understanding our genetic heritage was opened.
It is dif? cult, if not impossible, to single out all the landmark events of the twentieth century that contributed to the health of humankind. Among the other notable achievements are the development of kidney dialysis, oral contraceptives, transplant surgery, the computed axial tomography (CAT) scanner, and coronary angioplasty. Not all of the important advances in modern medicine are as dramatic as open-heart surgery. Often, they are the result of dogged work by many people and yield results only after a number of years, and then they frequently go unheralded.
For example, vaccination programs, control of infectious diseases through improvements in sanitation of water and waste disposal, safer and healthier foods free from microbial contamination, identi? cation of health risks from behaviors such as smoking, and improved prenatal care all have saved many lives in the twentieth century. THE TWENTY-FIRST CENTURY The twenty-? rst century reveals new horizons, but also new problems. In greater numbers than ever, goods and people travel the world. There is unprecedented physical mobility—travel and migration from villages to cities and country to country—and interconnectedness.
However, the bene? ts of physical mobility and interconnectedness are accompanied by risks. Diseases such as AIDS remind us that nothing is regional, local, or limited in its reach: contagious illness has a worldwide arena. The challenges of maintaining health and well-being in this global community are increasingly apparent. The inadvertent introduction of pathogens poses an unrelenting threat to public health, as does the deliberate use of microorganisms as weapons (see Chapter 18 for a discussion of bioterrorism and emerging global infectious diseases).
In February 2003, the viral respiratory illness named severe acute respiratory syndrome (SARS) by the World Health Organization was ? rst recognized in China. 8 In the next few months, the illness swept through parts of Asia and spread to more than two dozen countries in North America, South America, and Europe. The disease was characterized by rapid onset and variable severity, ranging from mild illness to death. The prevention of SARS was a particular challenge because preventive interventions (e. g. , vaccines and antibiotics) were unavailable.
Containment became a global collaboration, with public health authorities utilizing isolation and quarantine to focus delivery of health care to people who were ill and to protect healthy people from getting sick. During the February to July outbreak, more than 8000 people worldwide became infected, and more than 900 died. Commerce also is an integral part of the growing world community, bringing goods and services once unobtainable into the global marketplace. Expanded international trade also provides the vehicle for the unwitting introduction or transmission of disease. One such instance occurred in the spring of 2003 in the United States. A multistate outbreak of human monkeypox, ? rst identi? ed in the Democratic Republic of the Congo in 1970, was traced by investigators to pet prairie dogs. The prairie dogs became infected when they were housed or transported along with infected Gambian giant rats, dormice, and rope squirrels that were part of a shipment of small mammals from Ghana. Spread of nonindigenous zoonotic pathogens to indigenous susceptible animal populations can be rapid and deadly. With such outbreaks lurks an additional danger—the potential for interspecies exchange, including between humans and animals such as pets.
The widespread distribution of infected and potentially infected animals allowed epizootic spread of monkeypox through several states before effective interventions could be put into place. One of the challenges to the world health community will be to study the role of international travel and commerce in the emergence of infectious diseases through the dissemination of pathogens and their vectors throughout the world and then to develop long-term strategies of surveillance and intervention with the ultimate goal of curtailing their occurrence.
In 1976, the World Health Organization (WHO) actually succeeded in eliminating smallpox from the face of the earth. 10 This triumph gave substance to the idea that other infections, like measles, also might disappear if suf? cient efforts were directed at worldwide campaigns to isolate and cure them. However, new infectious diseases, such as Lyme disease and Legionnaire’s disease, and new forms of old diseases, such as resistant strains of tuberculosis and malaria, have emerged and are readily spread 12 UNIT I Concepts of Health and Disease ing on Hippocratic doctrines and introducing experimentation into the study of healing.
His work, gleaned through his role as physician to the emperors and gladiators of Rome and animal dissections, came to be regarded as the encyclopedia of anatomy and physiology and was considered infallible for almost 1400 years. Signi? cant challenges to long-held beliefs began with the work of Andreas Vesalius (1514–1564), professor of anatomy and surgery at Padua, Italy. His published work, On the Fabric [Structure] of the Human Body, showing how the parts of the body looked and worked, set a new standard for the understanding of human anatomy.
Other significant early contributions were made by scholars such as William Harvey (1578–1657), the English physician and physiologist, who in his book, On the Motion of the Heart and Blood in Animals, provided a physiologic framework for the circulation of blood; Anton van Leeuwenhoek (1632–1723), the Dutch lens maker who refined the microscope and set the stage for the era of cellular biology; and Edward Jenner (1749–1823), the English country physician who conducted the first successful vaccination. The nineteenth century was a time of major discoveries that paved the way for understanding infectious diseases.
Signi? cant contributions were made by such scientists as Joseph Lister, the English surgeon who concluded that microbes caused wound infections; German bacteriologist Robert Koch, who discovered the anthrax bacillus, thus identifying for the ? rst time a microorganism and the illness it caused; and French chemist and microbiologist Louis Pasteur, who developed the technique of pasteurization. Perhaps the most notable technical innovation of the century was the discovery of X rays by German physicist Wilhelm Rontgen. The scienti? undertakings and discoveries of the twentieth century were revolutionary. In 1910, Paul Ehrlich introduced chemotherapy, and in 1928, Sir Alexander Fleming discovered the ? rst antibiotic as he studied the relationship between bacteria and the mold Penicillium. Diseases that had once been fatal or crippling were managed or prevented by new advances, such as the discovery of insulin by Sir Frederick Banting and Charles Best in 1922 and the development of the polio vaccine by Jonas Salk in 1953. Technical innovations set the stage for new surgical techniques.
The creation of the heartlung machine by American surgeon John Gibbon paved the way for coronary bypass surgery and the ? rst successful heart transplantation in 1967, which was performed by Christiaan Barnard, a South African surgeon. Other important advances included kidney dialysis, oral contraceptives, the CAT scanner, and coronary angioplasty. Public health programs also were responsible for greatly affecting the health of populations, such as those dedicated to increasing vaccination, improving sanitation of water and waste disposal, and identifying health risks.
Knowledge about the in? uence of heredity on health and disease originated with Charles Darwin’s (1809–1882) evolutionary theories about inherited traits and with Gregor Mendel’s (1822–1884) theories on the segregation of traits, which laid the groundwork for establishing the chromosome as the structural unit of heredity. In the early 1950s, geneticist James Watson of the United States and British biophysicists Francis Crick and Maurice Wilkins presented their ? ndings on the double-helical structure of DNA. worldwide.
The powerful interventions used to ? ght these infections have had the unexpected effect of accelerating their biologic evolution and making them impervious to one after another form of chemical attack. Pathogens also can be introduced into the food chain and travel worldwide. The discovery that beef from cattle infected with bovine spongiform encephalopathy (BSE) may be the source of Creutzfeldt-Jakob disease led many countries to ban beef products from the United Kingdom when BSE was found to be prevalent in English herds.
The introduction of such pathogens can be the result of ignorance, carelessness, or greed. Tobacco is a product that serves as a pathogen. In a quest for ever-increasing pro? ts, the tobacco industry created a demand for its product by arti? cially raising the nicotine content of cigarettes so as to increase their addictive potential. This was done with the knowledge of the health risks of tobacco products, thanks to experiments conducted by the tobacco companies’ own medical scientists, but kept secret.
If there is a blueprint for future advances, it is in the genes. The twenty-? rst century is destined to be dominated by advances in genetics. With the mapping of the human genome comes hope of cure for some of the most dreaded crippling and fatal diseases. The mapping of the human genome also has posed new ethical dilemmas, for with it comes the potential to predict the future health of persons based on their genes. It soon may be possible to differentiate between persons who will develop certain debilitating diseases and those who will not.
Although advances in science and technology will continue to provide new treatments for many diseases, it has become apparent that there are more impressive rewards to be had by preventing diseases from becoming established in the ? rst place. Ultimately, maintaining health is more resource conservative and cost effective than relying on the treatment of disease. Many decades ago, we learned that even though the “magic bullets” such as antibiotics had the ability to cure what was once considered incurable, much of our freedom from communicable disease is due to clean water, ef? ient sanitation, and good nutrition. We have become increasingly aware of the importance of preventive measures against noninfectious conditions, especially cancer and coronary heart disease. There is no better way to prevent disease and maintain health than by leading a healthy life, and increasingly, it will be the individual who is responsible for ensuring a healthy passage through life. In summary, Greek scholars were responsible for establishing the fundamentals of anatomy, physiology, and pathology that served as the earliest knowledge base for understanding health and disease.
It was Hippocrates (460–377 BC) and his followers who laid the foundations of the clinical principles and ethics that grew into modern science. Although his belief that disease occurred when the four humors—blood, yellow and black bile, and phlegm—became out of balance was disproved, his approach to health that dictated plenty of healthy exercise, rest in illness, and a moderate, sober diet remains valid. Galen (AD 129–199) took the next major step, expand- CHAPTER 1 The twenty-? rst century is predicted to be a time of great advances in the ? ld of genetics, already evidenced by the substantial mapping of the human genome that has taken place. Scientists look to genetic research to provide advances that not only will predict who may develop disease but also will provide new treatments for those diseases. However promising future advances may appear, it is readily apparent that prevention is an equally important tool in maintaining health. Concepts of Health and Disease 13 Perspectives on Health and Disease in Individuals
After completing this section of the chapter, you should be able to meet the following objectives: ? State the World Health Organization de? nition of health ? Describe the function of adaptation as it relates to health and disease ? State a de? nition of pathophysiology ? Characterize the disease process in terms of etiology, pathogenesis, morphology, clinical manifestations, and prognosis ? Explain the meanings of reliability, validity, sensitivity, speci? city, and predictive value as they relate to observations and tests used in the diagnosis of disease
What constitutes health and disease often is dif? cult to determine because of the way different people view the topic. What is de? ned as health is determined by many factors, including heredity, age and sex, cultural and ethnic differences, as well as individual, group, and governmental expectations. HEALTH The World Health Organization (WHO) in 1948 de? ned health as a “state of complete physical, mental, and social well-being and not merely the absence of disease and in? rmity. ”10 Although ideal for many people, this was an unrealistic goal.
At the World Health Assembly in 1977, representatives of the member governments of WHO agreed that their goal was to have all citizens of the world reach a level of health by the year 2000 that allows them to live a socially and economically productive life. 10 The U. S. Department of Health and Human Services in Healthy People 2010 described the determinants of health as an interaction between an individual’s biology and behavior, physical and social environments, government policies and interventions, and access to quality health care. 1 with which the need to adapt occurs (see Chapter 9). Generally speaking, adaptation affects the whole person. When adapting to stresses that are threats to health, the body uses those behaviors that are the most ef? cient and effective. It does not use long-term mechanisms when short-term adaptation is suf? cient. The increase in heart rate that accompanies a febrile illness is a temporary response designed to deliver additional oxygen to tissues during the short period that the elevated temperature increases metabolic needs.
On the other hand, hypertrophy of the left ventricle is a long-term adaptive response that occurs in persons with chronic hypertension. Adaptation is further affected by the availability of adaptive responses and the ability of the body to select the most appropriate response. The ability to adapt is dependent on the availability of adaptive responses—the greater number of available responses, the more effective the capacity to adapt. Adaptive capacity is decreased with extremes of age and with disease conditions that limit the availability of adaptive responses.
The immaturity of the infant impairs the ability to adapt, as does the decline in functional reserve that occurs in the elderly. For example, infants have dif? culty concentrating urine because of the immaturity of their renal tubular structures and therefore are less able than an older child or adult to cope with decreased water intake or exaggerated water losses. Similarly, persons with preexisting heart disease are less able to adapt to health problems that require recruitment of cardiovascular responses. Adaptation also is less effective when changes in health status occur suddenly rather than gradually.
For instance, it is possible to lose a liter of blood through chronic gastrointestinal bleeding without developing signs of shock. On the other hand, a sudden hemorrhage that causes the loss of an equal amount of blood is apt to produce hypotension and circulatory shock. Even in advanced disease states, the body retains much of its adaptive capacity and is able to maintain the internal environment within relatively normal limits. DISEASE The term pathophysiology, which is the focus of this book, may be de? ned as the physiology of altered health. The term combines the words pathology and physiology.
Pathology (from the Greek pathos, meaning “disease”) deals with the study of the structural and functional changes in cells, tissues, and organs of the body that cause or are caused by disease. Physiology deals with the functions of the human body. Thus, pathophysiology deals not only with the cellular and organ changes that occur with disease but also with the effects that these changes have on total body function. Pathophysiology also focuses on the mechanisms of the underlying disease and provides the background for preventive as well as therapeutic health care measures and practices.
A disease has been de? ned as any deviation from or interruption of the normal structure or function of a part, organ, or system of the body that is manifested by a characteristic set of symptoms or signs; the etiology, pathology, and prognosis may be known or unknown. 12 The aspects HEALTH AND DISEASE AS STATES OF ADAPTATION The ability of the body to adapt both physically and psychologically to the many stresses that occur in both health and disease is affected by a number of factors, including age, health status, psychosocial resources, and the rapidity 14 UNIT I Concepts of Health and Disease f the disease process include the etiology, pathogenesis, morphologic changes, clinical manifestations, diagnosis, and clinical course. ity, the progression from fatty streak to the occlusive vessel lesion seen in persons with coronary heart disease represents the pathogenesis of the disorder. The true etiology of atherosclerosis remains largely uncertain. Etiology The causes of disease are known as etiologic factors. Among the recognized etiologic agents are biologic agents (e. g. , bacteria, viruses), physical forces (e. g. , trauma, burns, radiation), chemical agents (e. g. , poisons, alcohol), and nutritional excesses or de? its. At the molecular level, it is important to distinguish between sick molecules and molecules that cause disease. 13 This is true of diseases such as cystic ? brosis, sickle cell anemia, and familial hypercholesterolemia, in which genetic abnormality of a single amino acid, transporter molecule, or receptor protein produces widespread effects on health. Most disease-causing agents are nonspeci? c, and many different agents can cause disease of a single organ. For example, lung disease can result from trauma, infection, exposure to physical and chemical agents, or neoplasia.
With severe lung involvement, each of these agents has the potential to cause respiratory failure. On the other hand, a single agent or traumatic event can lead to disease of a number of organs or systems. For example, severe circulatory shock can cause multiorgan failure. Although a disease agent can affect more than a single organ, and a number of disease agents can affect the same organ, most disease states do not have a single cause. Instead, most diseases are multifactorial in origin. This is particularly true of diseases such as cancer, heart disease, and diabetes.
The multiple factors that predispose to a particular disease often are referred to as risk factors. One way to view the factors that cause disease is to group them into categories according to whether they were present at birth or acquired later in life. Congenital conditions are defects that are present at birth, although they may not be evident until later in life. Congenital malformation may be caused by genetic in? uences, environmental factors (e. g. , viral infections in the mother, maternal drug use, irradiation, or intrauterine crowding), or a combination of genetic and environmental factors.
Not all genetic disorders are evident at birth. Many genetic disorders, such as familial hypercholesterolemia and polycystic kidney disease, take years to develop. Acquired defects are those that are caused by events that occur after birth. These include injury, exposure to infectious agents, inadequate nutrition, lack of oxygen, inappropriate immune responses, and neoplasia. Many diseases are thought to be the result of a genetic predisposition and an environmental event or events that serve as a trigger to initiate disease development. Morphology
Morphology refers to the fundamental structure or form of cells or tissues. Morphologic changes are concerned with both the gross anatomic and microscopic changes that are characteristic of a disease. Histology deals with the study of the cells and extracellular matrix of body tissues. The most common method used in the study of tissues is the preparation of histologic sections that can be studied with the aid of a microscope. Because tissues and organs usually are too thick to be examined under a microscope, they must be sectioned to obtain thin, translucent sections.
Histologic sections play an important role in the diagnosis of many types of cancer. A lesion represents a pathologic or traumatic discontinuity of a body organ or tissue. Descriptions of lesion size and characteristics often can be obtained through the use of radiographs, ultrasonography, and other imaging methods. Lesions also may be sampled by biopsy and the tissue samples subjected to histologic study. Clinical Manifestations Disease can be manifest in a number of ways. Sometimes, the condition produces manifestations, such as fever, that make it evident that the person is sick.
Other diseases are silent at the onset and are detected during examination for other purposes or after the disease is far advanced. Signs and symptoms are terms used to describe the structural and functional changes that accompany a disease. A symptom is a subjective complaint that is noted by the person with a disorder, whereas a sign is a manifestation that is noted by an observer. Pain, dif? culty in breathing, and dizziness are symptoms of a disease. An elevated temperature, a swollen extremity, and changes in pupil size are objective signs that can be observed by someone other than the person with the disease.
Signs and symptoms may be related to the primary disorder, or they may represent the body’s attempt to compensate for the altered function caused by the pathologic condition. Many pathologic states are not observed directly—one cannot see a sick heart or a failing kidney. Instead, what can be observed is the body’s attempt to compensate for changes in function brought about by the disease, such as the tachycardia that accompanies blood loss or the increased respiratory rate that occurs with pneumonia. It is important to recognize that a single sign or symptom may be associated with a number of different disease states.
For example, an elevated temperature can indicate the presence of an infection, heat stroke, brain tumor, or any number of other disorders. A differential diagnosis that describes the origin of a disorder usually requires information regarding a number of signs and symptoms. For example, the presence of fever, a reddened sore throat, and positive throat culture describe a “strep throat” infection. A syndrome is a compilation of signs and symptoms (e. g. , chronic fatigue syndrome) that are characteristic of a speci? c disease state. Complications are possible adverse ex-
Pathogenesis Pathogenesis is the sequence of cellular and tissue events that take place from the time of initial contact with an etiologic agent until the ultimate expression of a disease. Etiology describes what sets the disease process in motion, and pathogenesis, how the disease process evolves. Although the two terms often are used interchangeably, their meanings are quite different. For example, atherosclerosis often is cited as the cause or etiology of coronary heart disease. In real- CHAPTER 1 Concepts of Health and Disease 15 ensions of a disease or outcomes from treatment. Sequelae are lesions or impairments that follow or are caused by a disease. Diagnosis A diagnosis is the designation as to the nature or cause of a health problem (e. g. , bacterial pneumonia or hemorrhagic stroke). The diagnostic process usually requires a careful history and physical examination. The history is used to obtain a person’s account of his or her symptoms, their progression, and the factors that contribute to a diagnosis. The physical examination is done to observe for signs of altered body structure or function.
The development of a diagnosis involves weighing competing possibilities and selecting the most likely one from among the conditions that might be responsible for the person’s clinical presentation. The clinical probability of a given disease in a person of a given age, sex, race, lifestyle, and locality often is in? uential in arriving at a presumptive diagnosis. Laboratory tests, radiologic studies, CT scans, and other tests often are used to con? rm a diagnosis. Normality. An important factor when interpreting diagnostic test results is the determination of whether they are normal or abnormal.
Is a blood count above normal, within the normal range, or below normal? Normality usually determines whether further tests are needed or if interventions are necessary. What is termed a normal value for a laboratory test is established statistically from test results obtained from a selected sample of people. The normal values refer to the 95% distribution (mean plus or minus two standard deviations [mean ± 2 SD]) of test results for the reference population. 14 Thus, the normal levels for serum sodium (135 to 145 mEq/L) represent the mean serum level for the reference population ± 2 SD.
The normal values for some laboratory tests are adjusted for sex or age. For example, the normal hemoglobin range for women is 12. 0 to 16. 0 g/dL and for men, 14. 0 to 17. 4 g/dL. 15 Serum creatinine level often is adjusted for age in the elderly (see Chapter 36), and normal values for serum phosphate differ between adults and children. Reliability, Validity, Sensitivity, Speci? city, and Predictive Value. The quality of data on which a diagnosis is based may be judged for its reliability, validity, sensitivity, speci? city, and predictive value. 6,17 Reliability refers to the extent to which an observation, if repeated, gives the same result. A poorly calibrated blood pressure machine may give inconsistent measurements of blood pressure, particularly of pressures in either the high or low range. Reliability also depends on the persons making the measurements. For example, blood pressure measurements may vary from one observer to another because of the technique that is used (e. g. , different observers may de? ate the cuff at a different rate, thus obtaining different values), the way the numbers on the manometer are read, or differences in hearing acuity.
Validity refers to the extent to which a measurement tool measures what it is intended to measure. This often is assessed by comparing a measurement method with the best possible method of measure that is available. For example, the validity of blood pressure measurements ob- tained by a sphygmomanometer might be compared with those obtained by intraarterial measurements. Measures of sensitivity and speci? city are concerned with determining how well the test or observation identi? es people with the disease and people without the disease.
Sensitivity refers to the proportion of people with a disease who are positive for that disease on a given test or observation (called a true-positive result). Speci? city refers to the proportion of people without the disease who are negative on a given test or observation (called a true-negative result). A test that is 95% speci? c correctly identi? es 95 of 100 normal people. The other 5% are false-positive results. A false-positive test result, particularly for conditions such as human immunodeficiency virus (HIV) infection, can be unduly stressful for the person being tested (see Chapter 22).
In the case of HIV testing, a positive result on the initial antibody test is followed up with a more sensitive test. On the other hand, false-negative test results in conditions such as cancer can delay diagnosis and jeopardize the outcome of treatment. Predictive value is the extent to which an observation or test result is able to predict the presence of a given disease or condition. A positive predictive value refers to the proportion of true-positive results that occurs in a given population.
In a group of women found to have “suspect breast nodules” in a cancer-screening program, the proportion later determined to have breast cancer would constitute the positive predictive value. A negative predictive value refers to the true-negative observations in a population. In a screening test for breast cancer, the negative predictive value represents the proportion of women without suspect nodules who do not have breast cancer. Although predictive values rely in part on sensitivity and speci? city, they depend more heavily on the prevalence of the condition in the population. Despite unchanging sensitivity and speci? ity, the positive predictive value of an observation rises with prevalence, whereas the negative predictive value falls. Clinical Course The clinical course describes the evolution of a disease. A disease can have an acute, subacute, or chronic course. An acute disorder is one that is relatively severe, but selflimiting. Chronic disease implies a continuous, long-term process. A chronic disease can run a continuous course, or it can present with exacerbations (aggravation of symptoms and severity of the disease) and remissions (a period during which there is a lessening of severity and a decrease in symptoms).
Subacute disease is intermediate or between acute and chronic: it is not as severe as an acute disease and not as prolonged as a chronic disease. The spectrum of disease severity for infectious diseases such as hepatitis B can range from preclinical to persistent chronic infection. During the preclinical stage, the disease is not clinically evident but is destined to progress to clinical disease. As with hepatitis B, it is possible to
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