Blood pressure was first directly measured in 1733, when an English clergyman and natural philosopher named Stephen Hales inserted a brass tube into the artery of a live horse and watched the blood rise more than eight feet up a glass column. That dramatic experiment gave the world its first quantitative reading of the force blood exerts on vessel walls, but the intellectual groundwork had been laid a century earlier, and it took another 170 years after Hales before doctors had a practical way to check a patient’s blood pressure without cutting them open. The full story spans horses, mercury, rubber cuffs, and a Russian military surgeon who changed medicine with a three-paragraph report.
Harvey, Malpighi, and the Idea That Blood Moves in a Loop
Before anyone could measure blood pressure, someone had to prove that blood actually circulates. For most of Western medical history, physicians followed Galen’s model from the second century, which held that blood was continuously produced in the liver and consumed by the body’s tissues. There was no concept of blood traveling in a closed loop, so the idea of measuring the force behind that loop had no reason to exist.
William Harvey upended this in 1628 with his landmark work on the circulation of the blood, demonstrating through careful experiments and dissections that the heart pumps blood outward through arteries and that it returns through veins in a continuous circuit.1PubMed Central. William Harvey and the discovery of the circulation of the blood Harvey’s argument was elegant but incomplete. He could show that blood flowed from arteries toward veins, but he could not explain how it got from one to the other, because the connecting vessels were too small to see with the naked eye.
That gap was filled in 1661 by Marcello Malpighi, an Italian biologist who was among the first to put the newly invented microscope to serious scientific use. Examining frog lungs under magnification, Malpighi discovered the capillaries, the tiny vessels that bridge arteries and veins, confirming Harvey’s hypothesis that blood flows in a complete circuit.2PubMed. Malpighi and the discovery of capillaries He also identified the pulmonary capillaries and alveoli, giving the first microscopic picture of how blood picks up air in the lungs.3PubMed. Marcello Malpighi and the discovery of the pulmonary capillaries and alveoli With Harvey’s circulation theory now visually confirmed, the question shifted from whether blood moves in a loop to how forcefully the heart pushes it.
Stephen Hales and the First Measurement
Stephen Hales was a parish vicar in Teddington, England, but he spent much of his time on scientific pursuits, from studying plant physiology to investigating the mechanics of animal blood flow. In a series of experiments described in his 1733 publication Haemastaticks, Hales performed the first direct measurement of blood pressure by connecting a long glass tube to the crural artery of a horse.4PubMed. Stephen Hales and the measurement of blood pressure When he released the ligature, blood surged upward in the tube, and Hales carefully noted the height to which it rose and the way it pulsed with each heartbeat.
The experiment was crude by modern standards but remarkably informative. Hales observed that the blood column’s height fluctuated in rhythm with the heart, establishing for the first time that blood pressure has both a peak and a trough with each beat. Invasive arterial measurement of this kind remains, to this day, the most direct way to read blood pressure and is still used in intensive care units as the reference standard.5PubMed Central. History and evolution of blood pressure measurement Hales also tested other animals, building the first comparative picture of how blood pressure differs across species. His work was brilliant, but it was obviously impractical for human patients. Nobody was going to tolerate having a glass tube jammed into an artery for a routine checkup.
From Glass Tubes to Mercury Columns
For roughly a century after Hales, researchers looked for ways to measure blood pressure that were less dramatic and more precise. The French physician Jean-Léonard-Marie Poiseuille made a major contribution by inventing a U-tube mercury manometer, which replaced Hales’s unwieldy glass column with a compact device that translated blood pressure into the height of a mercury column. Mercury is about 13 times denser than blood, so the column needed to be far shorter, making the instrument portable enough for laboratory use.6PubMed. Blood pressure measurement: lessons learned from our ancestors The unit “millimeters of mercury” (mmHg) that we still use today is a direct legacy of Poiseuille’s design.
These early manometers still required inserting a tube into an artery, though. The push toward noninvasive measurement took a step forward with the French physiologist Étienne-Jules Marey, who in 1860 devised the first portable sphygmograph, a spring-loaded gadget strapped to the wrist that could record the pulse wave on a strip of smoked paper without breaking the skin.6PubMed. Blood pressure measurement: lessons learned from our ancestors Marey later introduced an oscillometric method of blood pressure measurement in 1876, which detected tiny pulsations transmitted through an inflated cuff, a principle that underpins the automatic blood pressure monitors billions of people use today.7PubMed Central. History of blood pressure measurement in newborns and infants Still, these devices could track the shape of a pulse wave but could not reliably pin down a specific systolic or diastolic number. Clinicians needed something simpler and more standardized.
Riva-Rocci’s Inflatable Cuff
The breakthrough came in 1896 from Scipione Riva-Rocci, an Italian physician working in Turin. His innovation was disarmingly simple: an inflatable rubber cuff wrapped around the upper arm, connected to a mercury column manometer. By inflating the cuff until the pulse at the wrist disappeared, then slowly deflating it until the pulse returned, Riva-Rocci could read the systolic pressure off the mercury column.8PubMed Central. From Concept to Cure: The Life and Legacy of Scipione Riva-Rocci Earlier devices had tried to compress arteries at the finger or wrist, but those readings were unreliable because smaller arteries respond differently to compression. Riva-Rocci’s key insight was to compress the brachial artery of the upper arm, which gave a much more stable and reproducible measurement.9PubMed. Riva-Rocci and blood pressure
Riva-Rocci’s device was the first noninvasive blood pressure instrument accurate enough for clinical use, and its basic layout, an inflatable cuff, a pressure gauge, and a way to detect blood flow, remains the template for every cuff-based monitor sold today. There was one limitation, though: Riva-Rocci’s technique could detect only systolic pressure, the peak force when the heart contracts. It could not identify diastolic pressure, the baseline force between beats. That required someone to listen more carefully.
Korotkoff and the Sounds That Changed Everything
In 1905, Nikolai Korotkoff, a Russian military surgeon, presented a brief report describing a new way to use Riva-Rocci’s cuff. Instead of simply feeling for the return of a pulse at the wrist, Korotkoff placed a stethoscope on the brachial artery just below the cuff and listened as the cuff pressure was slowly released. He discovered a series of distinct sounds corresponding to different stages of blood flow through the partially compressed artery.10PubMed. A centenary of auscultatory blood pressure measurement: a tribute to Nikolai Korotkoff
The first tapping sound appeared when cuff pressure dropped just enough for a small jet of blood to squeeze through. That point marked systolic pressure. As the cuff continued to deflate, the sounds went through several phases, changing from sharp taps to softer murmurs. When the sounds disappeared entirely, the artery was fully open and blood flowed smoothly again; that silence marked diastolic pressure. Korotkoff described four distinct phases of sound, and his method gave clinicians both numbers, systolic and diastolic, from a single noninvasive measurement.11PubMed. How Korotkoff, the surgeon, discovered the auscultatory method of measuring arterial pressure The underlying physics is straightforward: when the cuff partly squeezes the artery shut, blood rushing through the narrowed opening becomes turbulent and creates audible vibrations. Once the artery is wide open again, the turbulence stops and so do the sounds.12PubMed Central. Using Korotkoff Sounds to Detect the Degree of Vascular Compliance in Different Age Groups
Korotkoff’s auscultatory method, using a cuff and a stethoscope, became the global standard for blood pressure measurement and remained virtually unchallenged for most of the twentieth century. The mercury sphygmomanometer used with this method has long been considered the gold standard, even as concerns about mercury toxicity have gradually pushed it out of routine clinical use.13PubMed Central. Agreement of Automated Oscillometric Blood Pressure Measurement Device with the Manual Mercury Sphygmomanometer
The Rise of Automated Oscillometric Devices
Automated oscillometric blood pressure monitors were developed in the 1970s to replace the manual auscultatory technique.14PubMed Central. Automated ‘oscillometric’ blood pressure measuring devices: how they work and what they measure Rather than relying on a trained listener to identify Korotkoff sounds, these devices detect the tiny pressure oscillations transmitted to the cuff itself as the artery pulses beneath it, a concept that traces back to Marey’s work in the 1870s. A microprocessor inside the device analyzes the pattern of oscillations as the cuff deflates and uses a proprietary algorithm to estimate systolic and diastolic values.
These machines made blood pressure measurement something any person could do at home without training. That shift was enormous for public health, because hypertension is notoriously symptomless. Before home monitors existed, the only way most people discovered they had high blood pressure was during a doctor’s visit, which itself introduced a well-known complication.
White Coat Hypertension and Its Mirror Image
Not long after ambulatory and home monitors became available, researchers documented a phenomenon most patients had always suspected: blood pressure readings taken in a medical setting tend to run higher than readings taken at home. The anxiety of a clinical visit can temporarily spike a person’s numbers. This pattern, called white coat hypertension, is common enough that ambulatory blood pressure monitoring (wearing a cuff that takes readings throughout the day) has become a standard tool for distinguishing genuinely elevated pressure from a stress-related bump. One study found that the first and last readings during ambulatory monitoring could identify white coat hypertension with high agreement compared to traditional diagnostic criteria.15PubMed. Diagnosis of white coat hypertension by ambulatory blood pressure monitoring
The more worrying flip side is masked hypertension, where a person’s pressure looks normal in the clinic but runs high the rest of the time. A long-term Japanese study found that people with masked hypertension had roughly double the risk of cardiovascular death and stroke compared to people with consistently normal readings, while people with white coat hypertension had no significantly higher risk than truly normotensive individuals.16PubMed. Prognosis of “masked” hypertension and “white-coat” hypertension detected by 24-h ambulatory blood pressure monitoring 10-year follow-up from the Ohasama study A meta-analysis of multiple studies supported the same pattern: white coat hypertension carries little extra cardiovascular risk compared to normal blood pressure, but masked hypertension is genuinely dangerous.17American Journal of Hypertension. Prognostic Value of White-Coat and Masked Hypertension Diagnosed by Ambulatory Monitoring in Initially Untreated Subjects: An Updated Meta Analysis These discoveries only became possible because measurement moved outside the clinic. The history of blood pressure is, in part, a story about where and how often you take the reading mattering as much as the reading itself.
Where You Measure Matters Too
A subtlety that even many healthcare professionals overlook is that blood pressure is not the same everywhere in the body. The pressure in your aorta, the large vessel leaving the heart, is typically lower than the pressure measured at your upper arm by a standard cuff. This difference exists because of the way pressure waves amplify as they travel through progressively smaller and stiffer arteries toward the limbs. In one study of patients with hypertension on medication, brachial cuff readings overestimated how well blood pressure was controlled in about 40% of patients when compared to central aortic pressure.18PubMed Central. Comparsion of central aortic pressure to brachial artery pressure in hypertensive patients on drug treatment: An observational study In other words, the arm reading looked fine, but the pressure closer to the heart was still too high.
Research comparing invasive measurements taken during cardiac catheterization with noninvasive cuff readings has shown that cuff-based brachial systolic pressure can underestimate the true invasive brachial value by a substantial margin as well, with one study finding a mean underestimation of about 22 mmHg.19Hypertension Research. Comparison of invasive and brachial cuff-based noninvasive measurements for the assessment of blood pressure amplification The direction and size of the discrepancy varies depending on the device, the calibration method, and the individual patient’s vascular stiffness. This is a practical reason why researchers and some clinicians are increasingly interested in measuring central aortic pressure rather than relying solely on arm readings, especially when making treatment decisions for high-risk patients.
Cuffless and Wearable Monitors
The latest frontier in blood pressure measurement aims to ditch the cuff entirely. In recent years, cuffless devices have entered the market that promise continuous, beat-to-beat blood pressure monitoring. These devices use a range of principles, including pulse transit time (how quickly a pulse wave travels between two body points), pulse wave analysis, volume clamping, and applanation tonometry.20PubMed Central. Validating cuffless continuous blood pressure monitoring devices
Wearable sensors built into smartwatches and patches use optical, electrical, mechanical, and even ultrasonic methods to pick up signals related to blood flow and arterial stiffness. Machine learning algorithms then convert these signals into blood pressure estimates.21PubMed Central. Wearable blood pressure sensors for cardiovascular monitoring and machine learning algorithms for blood pressure estimation The appeal is obvious: a watch that tracks your blood pressure around the clock could catch masked hypertension, nocturnal spikes, and other patterns that occasional cuff readings miss. Some emerging platforms combine flexible sensor designs with sophisticated signal processing to push toward better wearability and accuracy.22npj Digital Medicine. Emerging sensing and modeling technologies for wearable and cuffless blood pressure monitoring
The challenge is accuracy. Cuffless devices still need to be validated against cuff-based or invasive standards, and many commercial products have not been through rigorous independent testing. The technology is promising but not yet at the point where a cardiologist would base a treatment decision solely on a smartwatch reading. If cuffless monitors do reach clinical-grade reliability, though, they will represent the biggest shift in blood pressure measurement since Korotkoff picked up a stethoscope in 1905.
What Giraffes Reveal About Blood Pressure
One of the more fascinating chapters in blood pressure research involves an animal that operates at pressures that would be catastrophic in a human. Giraffes have a mean arterial blood pressure of about 200 mmHg, roughly double a healthy human’s, which appears necessary to push blood up their extraordinarily long necks and maintain adequate perfusion pressure at the brain.23PubMed. The Remarkable Cardiovascular System of Giraffes In humans, sustained pressure at that level would shred small blood vessels and destroy the kidneys within years. Giraffes manage it through a suite of cardiovascular adaptations, including uniquely thick-walled blood vessels and specialized kidney architecture.
Genomic studies have identified giraffe-specific mutations in genes related to cardiovascular function and bone growth. When researchers introduced one such mutation, in a gene called FGFRL1, into mice, those mice showed exceptional resistance to hypertension and higher bone mineral density, both traits tightly connected to how giraffes handle their extreme blood pressure.24PubMed Central. A towering genome: Experimentally validated adaptations to high blood pressure and extreme stature in the giraffe Even the act of drinking, which requires a giraffe to splay its legs and lower its head far below heart level, triggers a complex hemodynamic response: blood pressure at the heart drops initially, heart rate falls, and small cerebral arteries constrict sharply to prevent a dangerous surge of blood into the brain.25PubMed Central. Hemodynamics and Drinking in the Giraffe Studying how giraffes handle pressures that would kill a human offers a window into the mechanics of vascular damage and hypertension resistance that researchers hope could eventually inform treatments for people with dangerously high blood pressure.