Sphygmomanometer

A visit to a doctor’s surgery often involves a check on blood pressure. To do that one of the patient’s arms is put inside an inflatable cuff which collapses and releases the artery under the cuff in a controlled manner and is attached to a mercury or aneroid manometer which measures the pressure. The machine is technically known as a sphygmomanometer.

The heart pumps blood to all parts of the body and as the blood flows through the arteries and veins, it presses up against the walls with varying degrees of strength. The strength or weakness of this pressure is what is known as blood pressure and readings comprise of two elements. The systolic measures the pressure when the heart squeezes blood through an artery and the diastolic the pressure when it relaxes after each contraction. The reading is represented as systolic over diastolic and the outcome can either produce a nod of approval from the doctor or a sharp intake of breath.

The ancient Chinese had recognized that blood flowed around the body through blood vessels and developed theories on how the blood system worked. Similarly, scholars in India had gleaned some knowledge of the circulatory system and, in particular, the importance of the pulse. However, a more systematic and, dare I say it, a more scientific understanding of circulation and the circulatory system had to wait until the early 17th century.

William Harvey, who began teaching about circulation in 1615 and published in 1628 his tome, Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus, which became the foundation stone of the study of circulation and is still widely regarded today. Having established the correlation between heart rate and pulse, it was possible to determine blood volume and blood pressure, which the Reverend Stephen Hales was the first to do, in 1733. He measured the blood pressure of a horse by inserting a long glass tube upright into an artery and noting the increase in pressure as blood was forced up the tube.        

However, it was another 150 years before the first sphygmomanometer appeared. Devised by Samuel Siegfried Karl Ritter von Basch in 1881, it consisted of a rubber bulb that was filled with water to restrict blood flow in the artery and a mercury column, to which the bulb was attached, which translated the pressure required to obscure the pulse completely into millilitres of mercury. In 1896 Scipione Riva-Rocci added a cuff that would go round the arm to ensure that even pressure could be applied to the artery.

In 1905 Dr Nikolai Korotkoff discovered the intrinsic difference between systolic and diastolic blood pressure, which corresponded to the sounds within the arteries as pressure was applied and then released. Known as Korotkoff sounds, the use of systolic and diastolic sounds is now standard in blood pressure measurement.

So now we know!