The Physiology and Pharmacology of Hypertension
An academic edit of an essay concerned with the physiology and pharmacology of hypertension. The ‘flow’ and sense have been improved, references added where necessary, and the style amended to an appropriate academic one.
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The following essay looks at the physiology and pharmacology of hypertension. First, the nature of the condition is examined, together with risk factors and current statistics on its occurrence. Next, the possible ways of treating the condition, particularly through drugs, is considered.
2. Hypertension: its Physiology and other Aspects
The definition of hypertension has attracted controversy over the last 50 years or so, but is currently generally seen as blood pressure which is over 140 over 90mmHg (Gotto and Toth 2006). This can be translated as the heart beating pressure or systolic pressure being 140 mmHg and the relaxing pressure or Diastolic pressure at 90mmHg. Blood pressure can vary considerably from person to person (Brubaker et al 2002). There is a concern to reduce high blood pressure, as it has been associated with cardiovascular disease, stroke, diabetes, and other serious conditions (Edlin and Golanty 2009).In terms of diagnosis, this is done over several readings at a given period, and these must be give regular high readings to confirm that there is a problem. These readings should be taken during and after normal activities, and also when relaxing (Bricker et al 1994).
The cause of high blood pressure in most cases is unknown, but it is widely thought that the pressure in the arteries depends on how hard the heart pumps blood and how much resistance there is in the arteries. A slight narrowing of the arteries will increase the resistance of blood flow. Many factors will contribute to this occurrence (Sherwood 2012). Whatever the cause or causes might be, the condition is common: in the UK well over half the people aged 65 or over suffer from high blood pressure, and 25% of those in middle age (Woods and Clare 2008). High blood pressure is particularly common in the following groups:
People with diabetes (type 1 and type two)
People of Afro-Caribbean descent
People from the Indian subcontinent
Those with a family history of high blood pressure
People who consume a lot of salt
People with a high caffeine and alcohol intake
People who consumer Insufficient fruits and vegetables or do not take enough exercise
(Patient.co.uk [online] 2012)
High blood pressure is not always apparent to the sufferer. It might be years before the condition is discovered, and by then a considerable amount of damage may already have been done. Therefore, regular checks are important, to ensure that any excess strain on the arteries is detected and risk reduced (Rhoden and Schein 2010). At some point, most people develop atherosclerosis, so the aim is to slow it down and halt any acceleration.While a number of causes associated with high blood pressure cannot be altered, including:
Heart disease or strokes before 55
Early Menopause in females
For people falling into these categories, there is extra reason to take extra precautions and deal with any lifestyle risk associated with high blood pressure. By doing so, the development of hypertension can be slowed down considerably reducing the chances of cardiovascular disease in the future (Edlin and Golanty 2009). Estimates show that a reduced diastolic blood pressure by 6mmHg can reduce the risk of having a stroke in the future by 35-40% and heart attacks by 20-25% (Warrell et al 2003). The higher the blood pressure, the higher the risk. However, there are several treatments and therapies to help reduce high blood pressure. Lifestyle changes including weight loss, increased physical activity, change of diet cutting down on alcohol intake, less smoking, low salt and caffeine consumption can all help (Kaplan et al 2002). If lifestyle changes are not effective, medication can help.
3. Medical Treatment of High Blood Pressure
There are several classes of medicines used in the treatment of lowering blood pressure, and each class contains many different drugs. For the purpose of this essay l will use a couple of examples in each section, to give a picture of what is currently available on the market, which are in use, and the available research about them, class by class. It should be noted that all drug therapies normally have side effects. Calcium-channel blockers, for example can sometimes cause dizziness, swollen ankles, facial flushing and constipation (Ascheim and Ascheim 2009).
3.1 Calcium-Channel Blockers
Calcium-Channel blockers include the drugs amlodipine and felodipine, which are also used in the treatment of angina (Hughes and Hughes 2001). They act through
selective inhibitors of calcium influx through the cell membrane or on the release and binding of calcium in the cells (Frishman and Sica 2011). They are also referred to as inducers of vascular and other smooth muscle relaxation (Raffa 2004). They are used in the drug therapy of hypertension and cerebrovascular spasms as myocardial protective agents, and for the relaxation of uterine spasms (McKenzie and Porter 2011). Amlodipine and Valsartan is a drug of this class, a single–pill combination which is used in hypertension management in the US. Valsartan is an Angiotensin II receptor blocker (Alexander 2008). The combination pill is used in the management of patients with mild to moderate blood pressure over trials of 8-16 weeks. Results showed the combination therapy is more effective than the monotherapy of amlodipine and Valsartan solely (Sureshkumar 2008). This combination pill is more acceptable, and also works well for the many who will need more than one drug to help them reach their target of lowering their blood pressure.
Diuretics, or water tablets, work by promoting the excretion of salt and fluid through the urine. This brings about reduced circulation of fluid and a reduction in blood pressure. The blood vessels within the circulatory system relax, which has an effect on blood pressure. The most commonly used diuretic in the United Kingdom, for the treatment of high blood pressure are thiazides (Bullock et al 2007). Examples of this class are bendroflumethiazide and hydrochlorothiazide. A low dose of these is often prescribed for the treatment of high blood pressure, with the proviso that blood and kidney tests are advisable before treatment is started, with follow up tests at 4-6 weeks to check potassium levels, then an annual blood test is normal (Rubin 2007). Diuretics have a number of side effects, including gout in a small number of users, and impotence in others (Souhami and Moxham 2002). These drugs are also often used in combination. Combining them with other drugs is often preferred, as it allows a more rapid and intensive control of high blood pressure, for example the combination of a diuretic and an Angiotensin converting enzyme (ACE) and thiazides. Zofenpril, for example, is a strong ACE inhibitor and the combination of Hydrochlorothiazide given to patients with acute myocardial infarction over long term improves the risk of major cardiovascular disease (Khan 2005). The fixed combination of Zofenpril and Hydrochlorothiades (HCTZ), 30/12.5mg/ day has been approved for mild to moderate management in several Europeans countries (Borghi and Cicero 2006).
3.3 Beta Blockers
Beta blockers come in various brands and types, typical examples being are propranolol and atenolol. They work by slowing the heart rate and reducing the force of the heart. They are also used are used to treat angina and some other conditions. They are not recommended for asthma sufferers, and those with chronic obstructive pulmonary disease (COPD) (Arcangelo and Peterson 2006).
They do have some side effects, including cold feet and hands, poor sleep and tiredness. Propranolol is also used in the treatment of Haemangioma related high blood pressure. Haemangioma is , a vascular swelling forming a tumour- like mass which forms anywhere in the body (Stedman 2002), and has shown to be effective for this in a study of 39 children, where Propranolol therapy showed a reduction of haemangioma within 2 days to 2 weeks.. Propranolol therapy has been proved more effective for infantile head and neck haemangioma, provided it is given to the patient early, when it first appears (Stedman 2002), and more patients are now being treated with propranolol therapy rather than corticosteroid therapy, although the best dosage and age when to stop treatment is still under discussion.
3.3 Angio Tensin Receptor Blockers
These are known as receptor antagonists drugs. The brands available include Candesartan and Eprosartan. All work by blocking the Angiotensin 11 on the walls of the blood vessel, and hence reduce the amount of this substance in the bloodstream. They are similar to the ACE inhibitors (Moini 2004).
The chemical effect narrows the blood vessels forcing it to relax and widen which reducing the blood vessel in the process. The most popular of these are captopril and Cilazapril, however these are contra-indicated where the patient has underlying kidney problems. Captopril was first discovered in 1898, however it was only used for treating high blood pressure fairly recently. An ACE inhibitor is beneficial to patients with heart failure and diabetes (Johnson and Morgan 2000)
While the mechanisms whereby high blood pressure is caused are not fully understood, it is associated with a number of hereditary conditions as well as lifestyle factors. If moderating consumption of salt, alcohol and other changes to lifestyle are ineffective in bringing down blood pressure, a variety of medical approaches are possible. The exact type of treatment suitable for individual patients depends on a number of factors including medical history, ethnic origin and age.The UK guidelines set out suitable treatments for various classes of patients. However it should be remembered that individuals vary a great deal in regards to blood pressure; occasionally treatment does not work and may have side effects too, in such cases switching to a different class of medication is recommended. Generally, high blood pressure treatment is for life, but some individuals may respond so well that treatment could stop after three or so years.
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