Blood pressure (BP) is the physical force exerted by circulating blood against the walls of the major arteries. This measurement is a fundamental gauge of circulatory function used worldwide to assess health and disease risk. The ability to measure this force accurately resulted from a long history of scientific inquiry. The development of BP measurement progressed from dangerous, direct observation to sophisticated, non-invasive techniques that underpin modern medicine.
The Foundational Concept and First Invasive Measurement
The conceptual foundation for measuring blood pressure was established by the English physician William Harvey in 1628. He demonstrated that blood circulates continuously throughout the body, driven by the heart’s pumping action. Harvey’s work proved the heart was a pump, creating a quantifiable pressure, setting the stage for the first attempt to measure the force of blood flow.
The first documented measurement of arterial pressure was performed nearly a century later in 1733 by the Reverend Stephen Hales, an English clergyman and physiologist. Hales experimented on a living horse by inserting a brass pipe into the femoral artery and connecting it to a vertical glass tube approximately nine feet long. The blood rose in the tube to a height of about eight feet and three inches, demonstrating the force of the blood ejected from the heart.
Hales observed that the column of blood did not remain static but rose and fell by several inches with each heartbeat, providing the first physical evidence of systolic and diastolic pressure variations. Although Hales’s experiment established the principle that blood pressure was a measurable physiological quantity, the method was obviously invasive, traumatic, and unsuitable for human subjects. It was a proof of concept that quantified the “force of the blood” but required an entirely new approach for clinical application.
Developing Indirect Measurement Techniques
After Hales’s direct method, the next major step involved developing more accurate instruments, even if they remained invasive, and then shifting the focus to external, non-invasive estimation. The French physician Jean Léonard Marie Poiseuille introduced the mercury manometer in 1828, which was a U-shaped tube containing mercury. Poiseuille connected this manometer to an artery, allowing the pressure of the blood to displace the mercury column, providing the first readings reliably calibrated in millimeters of mercury (mmHg), a unit still used today.
The crucial intellectual leap toward non-invasive measurement occurred with the German physiologist Karl von Vierordt, who in 1855 invented the first external device, the sphygmograph. Vierordt’s device was designed to estimate blood pressure by applying a measured external counter-pressure to obliterate the pulse in the radial artery. The apparatus used weights and levers to press against the artery, recording the pulse wave’s trace on paper.
The sphygmograph was cumbersome and provided only an estimate of systolic pressure, but it solidified the mechanical principle of external pulse detection. French physiologist Étienne-Jules Marey significantly improved this design in 1860, creating a much more portable version that used a spring and a lever to record the pulse waves more accurately. These early devices were critical for analyzing the pulse waveform and recording its rhythm, moving the field away from direct arterial puncture toward external compression and detection.
The Birth of the Modern Sphygmomanometer
The principles of external compression and pulse detection were finally synthesized into a clinically viable tool by the Italian physician Scipione Riva-Rocci in 1896. Riva-Rocci’s innovation was the mercury sphygmomanometer, which introduced the use of an inflatable rubber cuff wrapped around the upper arm. The cuff was inflated to a pressure high enough to completely stop blood flow, and then the pressure was slowly released.
Riva-Rocci’s method determined the systolic pressure by watching the mercury column and noting the pressure at which the radial pulse, felt at the wrist, first reappeared as the cuff deflated. This device was a breakthrough because it was relatively simple, consistent, and safe for patients, replacing the complex mechanical instruments of the past. However, this method, known as the palpatory method, could only reliably measure the higher, systolic pressure.
The technique became complete in 1905 when the Russian surgeon Nikolai Korotkoff added the crucial element of auscultation, or listening. Korotkoff used a stethoscope over the artery just below the cuff and listened for distinct sounds as the pressure was slowly released. He found that the first sound—a sharp tapping—indicated the systolic pressure.
The point where all sounds disappeared marked the diastolic pressure, the lower pressure when the heart rests. Korotkoff’s discovery of these sounds, now known as Korotkoff sounds, combined with Riva-Rocci’s cuff and manometer, created the auscultatory method that became the gold standard for non-invasive blood pressure measurement worldwide.