The mercury sphygmomanometer: end of an era?
Invented 110 years ago, the instrument was used decades before the significance of blood pressure numbers was well understood.
Taking blood pressure measurements is a routine part of medical visits, regardless of the reason for the visit. Most patients are well accustomed to having a Velcro cuff placed and inflated around their arm. In fact, blood pressure machines are available to give readings at many local pharmacies or drug stores, and blood pressure is even sometimes taken prior to dental procedures.
The measurement of blood pressure and the meaning of blood pressure both have a long history. Although methods to measure the force of circulating blood on blood vessel walls had their earliest days in the late 1800s and early 1900s, the meaning behind the numbers did not become clear until well into the second half of the 20th century.
In 1943, the National Heart, Lung, and Blood Institute launched the Framingham Heart Study to discover the cause of heart disease and stroke. At that time, mortality due to heart disease and stroke had been steadily rising for years. In 1961, the researchers discovered that high blood pressure — once thought to be a normal part of aging —increased risk for heart disease. In 1970, high blood pressure was also linked to stroke.
The earliest methods of measuring blood pressure required arterial puncture. These methods are largely traced back to the work of Hales, Ludwig, Faivre and Poiseuille, who introduced the measurement mm Hg. The sphygmograph was the first noninvasive instrument used to measure blood pressure. Invented in 1860 by Étienne Jules Marey, the sphygmograph determined blood pressure by discovering the weight at which the radial pulse was obliterated.
Despite some adaption and modification of the instrument by different researchers, it proved to have little clinical utility and was never adopted throughout medical practice. Many physicians believed the finger to be just as useful an instrument.
The next major milestone in blood pressure measurement was made by Samuel Siegfriend Ritter von Basch in 1880. It was then that he first described the sphygmomanometer, which consisted of a water-filled bulb connected to a manometer. The manometer was used to determine the amount of pressure required to obliterate the pulse, done by hand above the placed instrument. Again, although a useful advance in science, the instrument was difficult to use in day-to-day clinical practice.
Unlike many earlier attempts, a breakthrough came in 1896 when Scipione Riva-Rocci introduced the mercury sphygmomanometer. Blood pressure instruments today are only slightly different from Riva-Rocci’s early designs.
Riva-Rocci published four articles in the Gazzetta Medica Di Torino; two discussed his new sphygmomanometer and two, the methods for using it to measure blood pressure. His new instrument used an inflatable cuff to obliterate the brachial artery and incorporated a mercury manometer.
Despite this breakthrough in design, all of these instruments could only provide physicians with readings of systolic blood pressure, not diastolic.
Korotkoff’s new technique
The measurement of both diastolic and systolic blood pressure is most often credited to Nicolai Korotkoff. In 1905, he presented a paper to the Imperial Military Academy detailing a new technique for measuring blood pressure that incorporated the use of the newly popularized stethoscope.
Later, reprinted in the Reports of the Imperial Military Medical Academy, Korotkoff wrote, “The cuff of Riva-Rocci is placed on the middle third of the upper arm; the pressure within the cuff is quickly raised up to complete cessation of circulation below the cuff. Then, letting the mercury of the manometer fall one listens to the artery just below the cuff with a children’s stethoscope.” He further described the tones, or lack of, that one could recognize to measure systolic and diastolic blood pressure.
Courtesy of The National Library of Medicine
Korotkoff’s new method required much more skill on the part of the physician, but it also seemed to be a turning point for the blood pressure cuff’s popularity in the United States.
Cushing introduced cuff in U.S.
Harvey Cushing first brought a Riva-Rocci cuff to the United States in 1901 as a method to reduce mortality while patients were under anesthesia during his early experiments with intracranial surgeries. Although Cushing had been promoting the cuff’s use for almost a decade, more widespread adoption of the blood pressure cuff did not occur until about 1910 with the introduction of Korotkoff’s method. This new method, which required knowledge of auscultation, was deemed much more worthy of a physician’s skill set.
Unlike the thermometer, a tool that was quickly passed to nurses, the sphygmomanometer joined the ranks of other new instruments, such as the stethoscope, that required the much more practiced skills of a physician. Soon blood pressure measurements replaced pulse palpation as the standard practice for assessing the force of blood flow.
After this, blood pressure measurements began to appear with more regularity in clinical case reports and on patient charts. However, it took years for a standardization of methods to be established and adopted by physicians in the United States. In fact, physicians measured diastolic pressure for many years by different sounds: either the “muffling” of pulse sounds or the disappearance of pulse sounds.
The call for a standardized definition of diastolic blood pressure came from a U.S. insurance company in 1917 and from the U.S. Bureau of Standards in 1924. However, it was not until the 1970s that one was established.
Despite its widespread use, the mercury sphygmomanometer’s days may be numbered. The use of mercury in hospitals is slowly being banned due to the element’s toxicity. In addition, more accurate digital or automated devices are now available for use.
For more information:
- Crenner CW. Ann Intern Med. 1998;128:488-493.
- Laher M. BMJ. 1982;285:1796-1798.
- Lawrence C. Medical History. 1979;23:474-478.
- O’Brien E. Lancet. 1996;348:1569-1570.