Introduction of High Blood Pressure
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‘Blood Pressure’ is a mysterious word for lay people. However, it is not really so. Blood pressure is merely the pressure that the blood exerts on the blood vessels, while circulating.
Blood pressure is essential for
(1) the return of the blood to the heart, after making its way through more than 60,000 miles along blood vessels of our body.
(2) the exchange of nutrients and waste products between the various cells of the body and the blood capillaries.
(3) the filtering ( and therefore purification) of blood in the kidneys and the lungs.
Stephen Hales, an English clergyman was the first person to try to measure the blood pressure. He used to securely tie a horse upside down and insert a long glass tube into its chief artery, the aorta. He observed that because of the pressure, the blood rose inside the tube, to a height of almost nine feet. That was in the fourth decade of the eighteenth century, 1733, AD to be precise.
Almost a hundred years later, in 1828 AD, a French medical student Jean Leonard Poiseuille thought of connecting a mercury – filled U-tube to the aorta. Since mercury is 13.6 times heavier than blood or water, the column in the tube was raised to a much smaller height and indoor measurement of blood pressure became feasible. Even then, the method was obviously unsuitable to measure human blood pressure because an artery of a living person cannot be punctured. However, it should be noted that Poiseuille’s idea of using mercury while measuring blood pressure is taken advantage of, even today. Almost all accurate instruments for measuring blood pressure incorporate mercury. Since Poiseuille’s time, millimeters of mercury, or mm Hg, have been the standard units of blood pressure measurement.
It was to be almost 70 years before an Italian physician Scipion Rivorokki
invented a measuring instrument which had an arm-cuff. This solved the problem
of artery-puncture. Rivorokki argued, and rightly so, that the pressure of the
arm-cuff that stops the flow of blood into the forearm, should be equivalent
to the blood pressure. The arm-cuff was connected to two things : to an
air-pump and to a mercury filled tube. Rivorokki first snugly tied the cuff
around a person’s arm. He then placed his fingers on the wrist of the
person, where he could feel the pulsations ( of the blood) in the ‘radial’
artery. Finally, with the air-pump he used to build up pressure inside the
arm-cuff. He would consider that pressure ( as observed in the mercury-filled
tube) as the blood pressure which made the pulsations in the radial artery to
stop. Rivorokki did not realize that this was only the pressure of the blood
while the heart was contracting.
Finally in 1905 AD, a Russian physician Nicolai Korotcoff, using the
stethoscope ( the instrument which decorates the doctors’ ears or necks),
measured both the pressures i.e., when the heart was fully contracted and when
the heart was fully relaxed.
When the rhythmically beating heart contracts, it forcefully drives the blood
into the arteries. The pressure at such a time is high and is termed
‘systolic blood pressure’. When the heart relaxes, the pressure is
comparatively low and is termed ‘diastolic blood pressure’. The instrument
used to measure blood pressure is called a ‘sphygmomanometer’. A systolic
blood pressure of 120mm Hg and a diastolic blood pressure of 80 mm Hg are
considered normal. These pressures are denoted as 120/80.
Blood pressure does not remain the same throughout the day; it undergoes
slight variations (termed diurnal variations). The pressure is least during
the early hours of the day, when a person is deep asleep. At around 9.00 –
9.30 am, the pressure is usually the maximum. Besides, the blood pressure is
temporarily raised ( many a time markedly so ) by physical labour, mental
strain, acute pain or fear. It is essential that before measuring the blood
pressure, the person should be made to rest for a while.
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