The following blog post was written by Dr. Pamela Peacock, Museum Curator.
April 7th marks World Health Day, a day that celebrates the birthday of the World Health Organization (WHO) by drawing attention to a significant health problem affecting the world today. The focus in 2013 is high blood pressure.
The WHO evolved out of a tradition, first begun in the nineteenth century, of international conferences and organizations that sought to facilitate disease prevention and control through cooperation. In 1945, the United Nations Conference on International Organizations voted in favour of a new international health organization and, in 1946, the International Health Conference approved a constitution for the WHO. Between 1946 and 1948 signatures were collected to ratify this constitution and, finally, in 1948 the WHO was established. The organization established as its priorities malaria, tuberculosis, maternal and child health, nutrition, sanitary engineering, and venereal diseases. Many of these continue to be priorities for the WHO today. Additionally, new diseases, such as AIDS, have received sustained focus, as have ‘lifestyle diseases,’ such as heart disease and Type II diabetes.
Hypertension, or high blood pressure, is a growing problem with significant health risks. Today, one in three adults worldwide has high blood pressure. More than 25% of Canadians have hypertension, and 90% will develop it at some point in their lifetime. Hypertension is the leading risk of premature death in the world.
High blood pressure occurs when blood vessels narrow or become rigid, often because of plaque build up. This causes the heart to work harder to pump the blood through the narrowed channels, which can lead to heart attack. If the vessels become weakened or blocked the result can be aneurism, stroke, or dementia. The health risks of hypertension are serious and life-threatening.
The most common causes of high blood pressure are related to lifestyle choices. Eating high calorie diets with too much sodium and saturated fats, not getting enough exercise, smoking, and drinking more than the recommended weekly limit all contribute to hypertension. Genes also factor into the equation. Luckily, we can all make choices to decrease the risk of high blood pressure, by getting at least thirty minutes of exercise a day, eating a low fat, low sodium diet, and managing our stress more effectively. Medicine may also be prescribed to help individuals manage their high blood pressure.
Hypertension is sometimes referred to as the “silent killer” because there are often no outward signs or symptoms until a dangerous health incident, such as stroke, occurs. Knowing your blood pressure measurement and taking this reading on a regular basis is a key tool in managing risk. Normal blood pressure is 120/80, while 140/90 is considered high for the average adult. The first number represents the systolic pressure, the pressure exerted on the walls of the arteries as the heart contracts, while the second is the diastolic pressure, the pressure exerted when the heart relaxes.
Although blood pressure machines are fairly ubiquitous in today’s world, found not only in the doctor’s office but in the pharmacy section of many national chain stores, this important diagnostic instrument only emerged in the late nineteenth century. The ability to measure blood pressure took over two hundred years to develop.
The measurement of blood pressure began in 1733 when Stephen Hales demonstrated that the amount of pressure generated by the heart could be measured through the displacement of blood. Using a horse as his subject, he inserted a pipe into an artery and attached this to a glass tube, into which blood would flow and could be measured. The invasive nature of this procedure meant that it had little clinical application with humans.
In 1828, Jean Leonard Marie Poiseuille introduced the mercury manometer, or as he called it the haemodynamometer, as a key tool for measuring blood pressure. Manometers, first invented in the seventeenth century to measure pressure, were typically U-shaped tubes containing mercury or some other liquid. In Poiseuille’s experiment, a cannula, or hollow tube with retractable inner core, was inserted into an artery and attached to a manometer on the other end. With each pulse, the movement of blood displaced mercury inside the manometer. Blood pressure was identified by measuring the amount of mercury displacement.
In 1847 this technique was advanced when Carl Ludwig invented the kymograph, an instrument that allowed for the graphic representation of data. Essentially, the manometer was attached to a float pen connected to a revolving drum. As the mercury moved with each pulse, so too the pen moved, creating a wave chart depicting each pulse on the drum.
The problem with both of these methods was that they required invasive measures, tubes being inserted into arteries. Beginning in 1855 new indirect and non-invasive methods of assessing blood pressure were attempted, based primarily on the idea of assessing the counter-pressure needed to stop circulation. In 1860 Etienne Jules Marey measured blood pressure by enclosing the arm in a water-filled glass chamber and increasing the water pressure until no circulation occurred. The pressure at this point was identified as the systolic pressure. In 1881, Samuel Siegfried Karl Ritter von Basch improved upon the method. He placed a rubber bag around a manometer bulb and inflated the bag with water. As the water pressure increased, the mercury in the manometer was displaced enabling the measurement of the pressure. The bag was placed over the distal pulse and inflated until the pulse was no longer recorded; the pressure at this point was noted as the systolic pressure. In 1889 Pierre Potain altered this method by using air rather than water in the compression bag.
Blood pressure measurement evolved again in 1896, becoming much more familiar to today’s patients. Scipione Riva-Rocci initiated the use of a cuff placed around the arm’s circumference, which was inflated by an attached bulb. The pressure in the cuff was increased until the radial pulse (at the wrist) was no longer present. At this point, the pressure in the cuff was released. The pressure at which the radial pulse reappeared was noted as the systolic pressure.
At the turn of the twentieth century it was possible to calculate systolic pressure, but diastolic pressure remained elusive. The ability to measure diastolic pressure was first achieved in 1905 by Nikolai Korotkoff. He identified certain sounds, now known as Korotkof sounds, made by the blood in the arteries and associated with changes in pressure that doctors and nurses now use to read blood pressure. These sounds are what your physician is listening for when they hold a stethoscope to your inner elbow when taking your blood pressure. They read the pressure gage on the sphygmomanometer when they hear Korotkoff sounds to identify your systolic and diastolic readings. When the blood pressure cuff is inflated and occluding blood flow no sounds are heard. The first sound is heard when systolic pressure is reached and some blood is able to pass through the artery, but does so in spurts as the pressure varies from being above to below the pressure in the cuff with each heart beat. This variance causes the blood to flow turbulently and make audible sounds. As the pressure in the cuff continues to lower, the sounds diminish and ultimately disappear once a consistent blood flow is established. The pressure reading at this moment is considered the diastolic pressure.
Luckily for us, a long list of physicians and researchers has advanced blood pressure measurement techniques. There is almost no excuse for not checking your blood pressure. Armed with this knowledge, and in consultation with your health care provider, you can make lifestyle choices that will decrease your risk of hypertension.
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Zanchetti, Alberto and Giuseppe Mancia. “The centenary of blood pressure measurement: a tribute to Scipione Riva-Rocci.” Journal of Hypertension 14 (1996): 1-12.
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