High Blood Pressure

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.