BLOOD PRESSURE

In pumping the blood to different parts of the body, the heart creates a certain pre ure on the arteries, in exactly the same manner as a2 pump will create pre ure in a pipe through which it is forcing water. The first to measure the pre ure thus produced was Stephen Hales, who, in 1733, measured the blood pre ure of a horse by inserting into one of its arteries a small bra pipe which he connected to a long gla tube, held perpendicular. He found that the blood rose, in this tube, to a height of eight feet, rising and falling to some extent with the pulsations of the heart. On inserting this tube into a vein he found that the blood rose only about twelve inches, thus demonstrating the much greater pre ure in the artery than in the vein. About one hundred years later the French doctor, Poisenille, used a mercury manometer in the place of the gla tube, and thus paved the way for the instruments used to-day for determining blood pre ure in human beings. The sphygmometer, as it is called, consists, in its simplest form of a rubber bag, covered with sill, which is pre ed against an art until the pulse is obliterated. The is connected with a mercury manometer, and the pre ure of blood in the artery compre es the air in the bag, which, in turn, forces down the mercury in one arm of the manometer, causing it to rise in the other. Many refinements exist in the more modern sphygmometers, and instruments of great precision and delicacy are now manufactured, but the principle in all of them remains the same. As an indication of obscure disease the blood pre ure is of much importance, and the test now forms part of the routine investigation made into the physical condition of applicants for life insurance, and in other general health examinations. The normal blood pre ure varies with age, being lower in the young than in the old, and ranges from 110 to 140 millimeters of mercury. In certain diseases of the kidneys the pre ure rises, and high pre ure is also an indication of hardening of the arteries, and of a tendency to gout or apoplexy. During physical exertion or mental excitement, the pre ure rises, and athletes in perfect health have been found to show & blood pre ure as high as 190 m.m, at the end of a long race.