Strange is it that our bloods,
Of colour, weight, and heat, pour’d all together,
Would quite confound distinction, yet stand off
In differences so mighty.
All’s Well That Ends Well, shakespeare
Blood is one of the most important constituents of the human body. The importance of this precious fluid in the human physiological system cannot be exaggerated. It transports life-giving oxygen to the tissues, carries food stuffs, mineral substances and harmones to the cells and protects tissues and vital organs from infection. A reduction in the total blood volume below a certain level due to heavy bleeding from gross injuries or after severe water loss due to diarrhoea would trigger off irreversible and fatal complications.
‘Blood Pressure’ is the pressure of blood in the arteries and is a measure of the tension in the arterial wall produced by the blood forced from the heart. It depends on the output of the heart and the resistance to the flow provided by the smaller arteries and arterioles. Blood pressure can be measured by an instrument called the sphygmomanometer. There are several models available all over the world including some sophisticated electronic devices but the one commonly seen in India has an inflatable cloth cuff which is connected by a rubber tube to a glass column containing mercury. The level of mercury indicates the pressure (in millimetres of mercury) that is exerted by the cuff which is wrapped around the upper arm of a patient. A rubber bulb is squeezed to inflate the cuff so as to stop the blood flowing through the brachial artery (running along the length of the arm). By gradually releasing the air in the cuff and simultaneously listening through a stethescope applied to the arm, the doctor can measure two sounds, the readings corresponding to which indicate the systolic and the diastolic. The systolic is produced when the heart contracts and is the highest pressure in the circulatory system. The diastolic is the pressure within the circulatory system between heart beats. It reveals how much the heart has to work to overcome resistance in the arteries. So when a doctor’s instrument registers a reading of say 130/80 (the ideal level at which most health conscious people try to keep their blood pressure) it means that the systolic is 130 and the diastolic is 80.
Hypertension would never have occurred as a disturbing phenomenon in human physiological processes, if the human body had been programmed to maintain the systolic and the diastolic within a safe range by some internal regulating system. But high blood pressure is required at least temporarily as a defence mechanism in certain psychological and physiological states. During exercise it is necessary to provide increased blood flow to the heart and other muscles; it also shoots up when one is either emotionally upset or tense. But the problem arises if this high blood pressure continues to linger after its purpose is served, for having outlived its utility it begins to behave like an unwelcome guest who does a lot of damage to the household. Continued excessive blood pressure can cause serious damage to the brain or the heart inducing strokes or heart attacks. It can also harm the kidney which in turn once again can worsen the hypertension.
The two elements which regulate blood pressure are the total volume of blood in the human body and the resistance offered by the arteries to the flow of blood. An increase in either can raise the blood pressure. The volume of blood increases when fluid is retained in the body. Similarly, arterial resistance increases when the walls of the arteries constrict and their diameter decreases or if cholesterol deposits effectively reduce the space available in the arteries.
Both these factors are regulated by complex biochemical signals. The role of the enzyme renin which is secreted by the kidney appears to be vital in this connection. Whenever the kidney detects a fall in the blood pressure its immediate response is to secrete renin and this triggers off a series of actions that raise the blood pressure back to normal. A substance called angiotensin II which increases the blood pressure in different ways also seems to play a prominent part. It makes the arterial walls contract and enhances the heart rate as well as the force of heart contraction. It makes the adrenal glands release aldosterone, a harmone that causes the body to retain salt and water, increasing the blood volume. Whenever the blood pressure increases in a normal healthy person, an alarm signal is sent to the kidneys which stop the secretion of renin. But a failure of the feedback mechanism would prevent the kidneys from getting this message and would lead to hypertension. A study of the renin level in the body enables doctors to prescribe a suitable drug for any particular patient. Several agents other than renin also seem to have an effect on the blood pressure; prominent among these are the naturally occurring chemicals, prostaglandins and the kinins which make the arterial walls dilate. Deficiencies of these two substances could, according to some scientists, lead to hypertension.
The habits, lifestyle and behaviour patterns of people also seem to influence hypertension in a significant manner. A few contributory factors are—excessive salt intake, over weight, smoking, consumption of alcohol, sedentary habits, physchological tension, an aggressive dominant personality, and in women, the use of birth control pills.
One of the greatest villains in this context is common table salt used by people all over the world. The sodium in the salt (sodium chloride) causes retention of fluid in the body, particularly in people whose kidneys are unable to get rid of the sodium into the urine. Against a daily requirement of about 3 to 5 grams for the human body, people consume on an average, about 12 to 20 grams which is almost four times the permissible limit. This is particularly relevant in countries where people are used to taking hot and spicy pickles or curries with a high salt content. Scientific studies have confirmed that a reduction in salt intake lowers the blood pressure and an increase in salt intake elevates blood pressure. It has become routine practice all over the world for physicians to advise people with a tendency to develop hypertension to cut down on their salt1 intake.
Some scientists are trying to analyse the reasons for the adverse effects of salt. They argue that many human societies had evolved, in low salt regions of the earth where it had been necessary to have for survival, the ability to retain sodium as a genetic trait. Thus, in the arid dry regions of Africa the intake of salt would have been necessary for the people as a survival measure whereas it is not required for their descendents who now live in America where the salt glut does not call for a salt retaining apparatus. Having been biologically programmed to retain this apparatus, the latter seem to be more prone to hypertension than the rest of the population.
Another explanation for the cause of hypertension in modern society could be the effect that high blood pressure has as a tranquilizer and as an analgesic. There is evidence to show that patients with hypertension are less sensitive to pain as compared to normal people. According to some researchers when fear or pain causes a rise in the blood pressure, special nerves in the region of the aorta and the carotid arteries of the neck known as baroreceptors are stimulated to deaden the pain centres of the brain, thus producing relief. They believe that there is a special link between the brain and the baroreceptor nerves which is necessary as a survival measure. When there is threat of danger, a person cannot afford to be slowed down by fear or- pain for he has to act swiftly. He is, therefore, spurred on to achieve feats of bravery to save himself, which otherwise would not have been possible. Wounded soldiers who defy the enemy with courage or a mother leaping into the flames to save her child are motivated by such stimuli. However, there is an inherent drawback in this mechanism. Since the body soon learns that blood pressure is a useful mechanism in times of stress to get immediate relief, it gets habituated to take recourse to this subterfuge in stress situations like job problems, marital conflicts, etc. The whole exercise then becomes counter-productive as an elevation of blood pressure if brought on repeatedly in this manner would only serve to cause injury to ones health. However, one saving grace is the fact that just as elevation in blood pressure can become a habit that is ‘learned’; one could also ‘unlearn’ it by a process called ‘bio-feedback’ in which a patient can keep a track of his blood pressure and brain waves. He is taught to identify actions or thoughts that had brought about a reduction in blood pressure. Relaxation exercises fall under this category. Doctors, however, feel that bio-feedback techniques cannot replace regular drug therapy but can only be effective when used along with them. In such cases, there could be a proportionate reduction in the dosage of medicines.
Until very recently doctors had attached importance only to the diastolic. A reading greater than 95 had been considered as ‘hypertension’ and people with diastolic reading of 90-90 had been considered as ‘borderline’ cases. However, doctors are now inclined to believe that a reading of 90 measured at least on two occasions would warrant classification under ‘hypertension’ thus eliminating the borderline category. People who have a diastolic of 80 to 89 would be considered as being at intermediate risk. Such people are usually advised to restrict salt intake, control their weight, stop smoking, etc. This new approach had been found to be justified by recent findings that the risk of death rate had more than doubled when the diastolic had increased from 80 to 89. The latest trend in treating high blood pressure is to take treatment even in the early stages when mild hypertension is suspected. In a method known as ‘stepped care’ a hypertension drug is given and blood pressure is monitored for a fixed period by a process of trial and error till the most suitable drug for the condition is identified. Studies in one place in the United States have indicated that this method had considerably reduced the death rate and stroke rate in patients who had received ‘stepped care’ compared to people who had received only routine medical treatment. Doctors now feel that sporadic high blood pressure readings which had been dismissed in the past as ‘labile hypertension’ should be regarded as early warning signals and treated.
There is a controversy over the question of treating children, considered to be hypertensive either by prescribing drugs or by subjecting them to dietary and other restrictions. Doctors are now generally reluctant to rush in for drug therapy which is usually a lifetime proposition as some drugs could have undesirable side-effects such as raising the level of fat in the blood and actually inducing the cardiovascular disease, which they are meant to prevent. The real solution would be to work out a compromise between the two alternatives, i.e. to prescribe drugs for hypertensive children so as to check the condition in the early stages or to help them by recommending proper exercises and diet and to resort to drugs only when they are absolutely necessary.
There are more than twenty classes of drugs available for treating hypertension and doctors can always find one or a combination of drugs suitable for a particular patient. Hypertension drugs work usually either by reducing the blood volume or dilating the arteries. Either goal can be accomplished in a variety of ways. The wise physician would first prescribe a low salt diet along with a diuretic which enables the kidney to excrete excess salt and water. If these are not enough, other drugs are added, such as those which act on the brain and influence blood pressure or those that prevent the walls of the blood vessels from constricting. Unfortunately, most of these drugs have undesirable side-effects such as nausea, fatigue, impotence, etc. A new group of drugs known as beta-blockers and a drug called captopril which acts by preventing the formation of angiotensin II, lower the blood pressure with very few uncomfortable side-effects. At the Harward Medical School, attempts are being made to produce two types of antibodies—one that will inactivate renin and another that will prevent arteries from constricting. Studies are also on the way in the University of Iowa where researchers had identified a region in the brain of animals that seems to be responsible for hypertension. Destruction of that site eliminates the possibility of blood pressure being induced. Researches are on to see whether this trend would make it possible for producing new kind of drugs to treat hypertension.
In this age of anxiety, hypertension has proved to be one of the major killers, taking away the lives of millions of people every year all over the world. However, science has shown that it is not only easy to detect blood pressure but that it can also be treated successfully. The reduction in the mortality rate due to blood pressure by means of therapy which involves a judicious mixture of medication and dietary and other restrictions could be regarded as one of the triumphs of modern medicine.
Some Hints to Lower Your Blood Pressure
- SALT: Reducing salt intake would lower blood pressure. Heavily salted foods such as pickles must be avoided.
- WEIGHT: Losing weight would reduce the load on the cardiovascular system.
- SMOKING: If smoking is reduced there is less likelihood of tar and nicotine contributing to the formation of clots in blood vessels or leading to constriction of arteries.
- EXERCISE: Aerobic exercises such as jogging, swimming, etc., make the body adapt itself to increased physical demands and consequently readjust itself to a lower blood pressure level.
- ALCOHOL: Reduction in alcohol consumption would prevent hardening of arteries due to cholesterol.
- STRESS: Reduction in mental tension by developing a relaxed approach to various problems.
- PILL: In some women it could raise the blood pressure. However, it is wise to have the blood pressure monitored regularly while taking the pill.
- People suffering from diabetes which can in the long run increase the risk of a heart attack must keep their sugar levels under control under medical supervision.