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 before dental procedures.

The measurement of BP and the meaning of BP 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 BP — once thought to be a normal part of aging — increased risk for heart disease. In 1970, high BP was also linked to stroke.

An early sphygmomanometer of the von Basch design. Photo courtesy of: The National Library of Medicine

Early instruments

The earliest methods of measuring BP 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 BP. Invented in 1860 by Étienne Jules Marey, the sphygmograph determined BP 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 BP measurement was made by Samuel Siegfried 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. BP 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 discussed the methods for using it to measure BP. 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 BP, not diastolic.

Korotkoff’s new technique

The measurement of both diastolic and systolic BP is most often credited to Nicolai Korotkoff. In 1905, he presented a paper to the Imperial Military Academy detailing a new technique for measuring BP 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 BP.

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 BP cuff’s popularity in the United States.

Cushing introduced cuff in US

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 BP 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 BP measurements replaced pulse palpation as the standard practice for assessing the force of blood flow.

After this, BP 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 BP came from a US insurance company in 1917 and from the US 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. – by Leah Lawrence

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.