A Deep Dive into Korotkoff Sounds: How Are Systolic and Diastolic Blood Pressures Measured? The Foundation, Evolution, and Historical Reach of the Auscultatory Method

When told “Your blood pressure is 130/85” during a health checkup, or when seeing two numbers displayed on a home blood pressure monitor, we rarely think about why those two numbers are necessary or how they are measured.

However, the non-invasive measurement of these “two numbers” became possible only 120 years ago. The catalyst for this discovery was the insight of a single Russian military physician who placed a stethoscope on the arms of wounded soldiers on the battlefield.

In this article, we delve deeply into the principles behind the measurement of the two blood pressure values—systolic blood pressure and diastolic blood pressure—from their physical foundation to their historical widespread adoption.

1. What Are Systolic and Diastolic Blood Pressures?

First, let’s confirm the formal definitions of the two numerical values obtained in blood pressure measurement.

Systolic Blood Pressure (Maximum Blood Pressure)

This is the maximum pressure exerted on the artery walls at the moment the heart contracts and pumps blood into the aorta. It represents the pressure at the moment the heart’s pumping function is exerted most strongly, and is simply called systolic blood pressure in English.

Diastolic Blood Pressure (Minimum Blood Pressure)

This is the minimum pressure remaining in the artery walls while the heart relaxes and prepares for the next contraction (while it receives blood from the lungs and the rest of the body). Even while the heart is resting, a certain pressure is maintained due to the elasticity of the blood vessels. This is called diastolic blood pressure.

Why Are Two Values Necessary?

Because the heart constantly repeats the cycle of “contraction → relaxation → contraction…”, the pressure within the blood vessels is not constant, but fluctuates, undulating between a maximum and minimum value with each heartbeat. Knowing these two extreme values allows for a comprehensive understanding of the cardiovascular system’s state, including the heart’s pumping power, vessel elasticity, and peripheral resistance.

However, “measuring these two values simultaneously” was impossible for a long time.

2. The Pre-Korotkoff World: Why Only Systolic Blood Pressure Could Be Measured

The Era of the Palpatory Method

At the end of the 19th century, methods for measuring blood pressure from outside the body already existed. In 1881, Austrian physician Samuel von Basch developed the sphygmomanometer, and in 1896, Italian physician Scipione Riva-Rocci invented the cuff-based mercury sphygmomanometer¹.

All these devices measured blood pressure using a method called the “palpatory method”. The procedure was as follows:

1. Wrap the cuff around the arm and pump air into it to completely compress the artery.
2. Place a finger on the pulse at the wrist (radial artery).
3. Slowly decrease the cuff pressure.
4. Read the pressure at the exact moment the pulse completely returns to the finger = Systolic blood pressure.

Why Only Systolic Blood Pressure Was Measurable

The reason why only systolic blood pressure could be measured with the palpatory method is simple. When the cuff pressure drops even slightly below the systolic pressure, blood forcefully breaches the cuff’s compression only at the moment the heart contracts, resulting in a clear tactile change: “the pulse returns.” The fingers could sensitively detect this change.

However, there is no corresponding tactile change for diastolic blood pressure.

As the cuff pressure is further decreased, the cuff eventually stops compressing the artery altogether. However, the pulse felt by the finger simply changes continuously from “present” to “stronger,” and there is no clear moment to determine “this is the boundary.”

This was the fundamental limitation of the palpatory method. The fingers only had the sensitivity to distinguish between the binary choice of “pulse present / absent,” and could not detect the boundary between a “partially compressed state” and a “completely relaxed state” of the blood vessel—namely, the diastolic blood pressure.

The idea of “listening with the ears” instead of “touching with the fingers” was a completely new concept that broke through this barrier.

3. Nikolai Korotkoff: A Discovery Born on the Battlefield

Life as a Military Physician

Nikolai Sergeevich Korotkoff was born in Kursk, Russia, in 1874². He entered Kharkiv University and later transferred to Moscow University, graduating from the medical faculty with honors in 1898.

Korotkoff’s career as a physician was tied to military medicine from the very beginning. During the Boxer Rebellion in 1900, he was dispatched to China under the Red Cross to treat wounded soldiers. For his achievements, he was awarded the Order of Saint Anna.

Then, in 1904, the Russo-Japanese War broke out. Korotkoff was appointed as the chief surgeon of the Second Saint George Red Cross Unit and stationed in Harbin, Manchuria.

The Question Posed by the Battlefield

On the battlefields of the Russo-Japanese War, soldiers with arteries damaged by bullets and artillery shrapnel were consistently brought in. As a vascular surgeon, Korotkoff spent his days treating these wounds.

When an artery was damaged, military physicians first ligated the artery—tying it with a thread to stop the blood flow and control the bleeding. Or, if applicable, they would suture and repair the damaged blood vessel.

However, the biggest problem military physicians faced after completing an operation was this:

“Is there sufficient blood flow remaining in this arm (or leg)? Can it be saved, or will gangrene progress, making amputation the only option?”

If sufficient blood flow remained in the tissues beyond the ligated artery, the tissue could survive through collateral circulation (a detour pathway). But if the blood flow was insufficient, gangrene (tissue necrosis) would progress, leading to life-threatening infections. A decision to amputate had to be made early on.

In making this judgment, Korotkoff acutely felt the limitations of the palpatory method. Extremely weak blood flow couldn’t be detected merely by feeling the pulse with a finger. Even if a pulse couldn’t be felt, a slight amount of blood flow might still remain—or conversely, even if a weak pulse was felt, it might actually be insufficient to nourish the tissue.

The Idea of “Listening for Sounds”

Korotkoff arrived at a particular idea.

Could blood flow that is too weak to be felt by the fingers be detected as a sound instead?

He wrapped the cuff of Riva-Rocci’s sphygmomanometer around an arm and placed a stethoscope on the inside of the elbow (over the path of the brachial artery). After increasing the cuff pressure to completely compress the artery, he slowly released the pressure. And then—

A characteristic sound began to be heard through the stethoscope.

As the cuff pressure was lowered further, the quality of the sound changed, and eventually, it completely disappeared.

Korotkoff realized that the appearance and disappearance of this sound corresponded accurately with the pressure inside the blood vessel. And this discovery would fundamentally change the history of blood pressure measurement.

A 281-Word Presentation

In November 1905, Korotkoff delivered a short report of just 281 words at the Imperial Military Medical Academy in St. Petersburg³.

The title was “On the question of methods of determining the blood pressure.”

Although it was one of the shortest reports in medical history, it was one of the most impactful presentations ever made. The method he described in this report—later called the auscultatory method—revolutionized blood pressure measurement.

4. The 5 Phases of Korotkoff Sounds: What is Happening?

The sounds discovered by Korotkoff—Korotkoff sounds—change through five stages (phases) during the process of reducing cuff pressure. To understand these sound changes, it is first necessary to understand the fluid dynamics concepts of laminar flow and turbulent flow.

Laminar and Turbulent Flow

Normally, blood inside an artery flows as laminar flow. Laminar flow is a state where the fluid flows orderly in parallel layers and does not produce sound. This is why normally nothing is heard when a stethoscope is placed on a healthy blood vessel.

However, if a part of the tube is compressed and narrowed, the blood must pass through that narrow gap at high speed. When the flow velocity exceeds a certain limit, the orderly flow breaks down and turns into turbulent flow. Turbulence creates eddies, vibrates the vessel walls, and generates sounds that can be heard with a stethoscope.

This is the true nature of Korotkoff sounds.

Details of the 5 Phases

As the cuff pressure is slowly reduced, Korotkoff sounds change as follows:

Why Phase 1 Indicates Systolic Blood Pressure

When the cuff pressure is still high, the artery is completely compressed, and blood cannot flow.

As the cuff pressure drops, it eventually falls slightly below the systolic blood pressure at a certain point. At this precise moment, only the pressure peaks generated each time the heart contracts exceed the external pressure of the cuff, and blood momentarily fountains through the narrow gap.

This jet of blood causes turbulence, and the first tapping sounds are heard.

In other words, the cuff pressure at the exact moment the first sound is heard perfectly matches the maximum pressure exerted by the heart on the vessel walls (systolic blood pressure).

Why Phase 5 Indicates Diastolic Blood Pressure

As the cuff pressure is further decreased, it eventually falls below the diastolic blood pressure as well.

When this happens, regardless of whether the heart is contracting or relaxing, the pressure inside the blood vessel always exceeds the cuff pressure. The artery is never compressed by the cuff and remains completely open at all times.

Blood flows smoothly through the fully open artery, returning to laminar flow. Laminar flow produces no sound. Therefore, the cuff pressure at the exact moment the sound completely disappears precisely matches the pressure inside the blood vessel while the heart is relaxed and resting—namely, the diastolic blood pressure.

The Debate Between Phase 4 and Phase 5

In clinical practice, there was a long-standing debate over whether Phase 4 (the point where the sound becomes muffled) or Phase 5 (the point where the sound disappears) should be considered the diastolic blood pressure.

Particularly in pregnant women, where cardiac output is increased, sounds may not disappear even at Phase 5, continuing to be heard down to very low pressures. Similar phenomena occur in children and patients with hyperthyroidism.

In current global consensus, Phase 5 (point of sound disappearance) is the standard indicator for diastolic blood pressure⁴. Phase 4 is used as an alternative indicator only when it is difficult to detect Phase 5.

5. The Impact of the “Listening” Measurement: Why Was It Revolutionary?

The innovation brought about by Korotkoff’s auscultatory method can be summarized in three points.

1. The First Non-invasive Measurement of Diastolic Blood Pressure

As discussed in Section 2, the palpatory method before Korotkoff could only measure systolic blood pressure. The auscultatory method, using the clear indicator of the sound disappearing, provided the first method to measure diastolic blood pressure without physically cutting the body.

This allowed doctors to simultaneously obtain both “systolic blood pressure” and “diastolic blood pressure.” From these two values, it became possible to calculate pulse pressure (Systolic Blood Pressure - Diastolic Blood Pressure), opening new avenues for evaluating vascular elasticity and the progression of arteriosclerosis.

2. A Dramatic Increase in Reproducibility

The palpatory method heavily relied on the specific sensations of the practitioner’s fingertips. The assessment of when the “pulse had returned” varied significantly from person to person, causing measurements to fluctuate between different practitioners even for the same patient.

The auscultatory method uses much clearer, objective criteria: “the sound has started being heard” and “the sound has disappeared.” This significantly increased the reproducibility of the measurements, enabling fair comparisons of data among different doctors and across different facilities.

3. Implementable Using Existing Equipment Alone

The most astonishing aspect of Korotkoff’s method was that it required no new equipment whatsoever. Simply by combining the already-widespread Riva-Rocci cuff sphygmomanometer with the stethoscope routinely used by doctors, entirely new diagnostic information could be obtained.

This “simplicity” was the biggest reason why the auscultatory method spread incredibly rapidly around the world.

6. From Discovery to Worldwide Standard: The Historical Adoption of the Auscultatory Method

1905–1910s: Acceptance in Russia

Korotkoff’s announcement was initially received within the context of military medicine. However, its usefulness was quickly recognized, and it quickly spread to civilian hospitals in Russia. Korotkoff himself obtained his medical doctorate in 1910 and continued to serve as a military surgeon during World War I.

Unfortunately, Korotkoff passed away from tuberculosis on March 14, 1920, at the age of 46². It was an untimely death, occurring before the true global significance of his discovery was widely recognized.

Harvey Cushing and the Arrival of Sphygmomanometers in America

Prior to Korotkoff’s discovery, in 1901, the renowned American neurosurgeon Harvey Cushing encountered the Riva-Rocci sphygmomanometer during a trip across Europe and brought it back to the American medical field⁵. Cushing advocated the importance of blood pressure monitoring during surgery and contributed to the widespread use of blood pressure monitors.

However, during Cushing’s time, only the palpatory method could be used, meaning only systolic pressure could be measured. By incorporating Korotkoff’s auscultatory method, it could be said that Riva-Rocci’s blood pressure monitor truly became “complete.”

1920s–1930s: Penetration into European and American Medical Practice

Between the 1920s and the 1930s, Korotkoff’s auscultatory method rapidly infiltrated clinical settings in Europe and the United States. As the recognition that blood pressure was a risk factor for cardiovascular disease spread, the demand for accurate blood pressure measurement only continued to grow.

The auscultatory method could be implemented using just the “Riva-Rocci sphygmomanometer + stethoscope”—instruments already present in virtually every hospital—meaning it could be introduced without any special medical equipment investments. This helped fuel its rapid expansion.

1939: Official Approval as the Global Standard

In 1939, a joint committee of the American Heart Association (AHA) and the British Cardiac Society endorsed Korotkoff’s auscultatory method as the official global standard for blood pressure measurement⁶.

This endorsement signified that the auscultatory method had, in both name and reality, become the “common language” of global medicine, some 34 years after its initial discovery. Subsequently, it continued to be used throughout the 20th century as the standard blood pressure measurement method in hospitals, clinics, and health screening facilities worldwide.

7. The Limitations of the Auscultatory Method and the Bridge to the Present Day

Limitations of the Auscultatory Method

Even the auscultatory method, which had become the global standard, faced several limitations.

Dependence on the Measurer’s Skill: Karena the auscultatory method relies on the act of “listening to sounds,” human factors such as the measurer’s hearing ability, how the stethoscope is positioned, and the speed at which the cuff pressure is released influence the results.

Auscultatory Gap: In some patients—especially those with severe hypertension or arteriosclerosis—a phenomenon occurs where the sound temporarily disappears between Phase 2 and Phase 3, only to reappear later. Failing to notice this runs the risk of underestimating the systolic pressure or overestimating the diastolic pressure.

Impact of Arteriosclerosis: In elderly individuals with advanced arteriosclerosis, calcified arterial walls can prevent compression by the cuff, leading to “pseudohypertension,” where artificially high values are measured.

The Shift to the Oscillometric Method

From the 1970s onward, electronic blood pressure monitors based on the oscillometric method were developed to overcome these limitations⁷.

The oscillometric method is an approach that automatically detects minute vibrations (oscillations) in the air pressure within the cuff to calculate blood pressure. Because it doesn’t require the use of a stethoscope, anyone can measure it accurately, even without specialized medical knowledge.

In particular, companies like Omron and Terumo in Japan have contributed significantly to the development and popularization of home electronic blood pressure monitors, paving the way for an era where “anyone can easily measure their blood pressure at home.”

However, the Auscultatory Method Remains

Even now, with the widespread availability of home electronic blood pressure monitors, the auscultatory method has retained its position as the gold standard in clinical settings.

When verifying the accuracy of electronic blood pressure monitors, the values measured using the auscultatory method serve as the benchmark. Furthermore, the design of the algorithms in electronic blood pressure monitors—specifically, how blood pressure values are calculated from the vibration patterns within the cuff—is fundamentally structured with the systolic and diastolic blood pressure values derived from the auscultatory method defined as the “correct answer.”

In other words, Korotkoff’s discovery still lives on today as the fundamental foundation of modern electronic blood pressure monitors.

Conclusion: The Insight of a Military Physician 120 Years Ago

In 1905, a young Russian military physician returning from the battlefields of the Russo-Japanese War delivered an incredibly brief, 281-word report at the Imperial Military Medical Academy.

What he discovered was a phenomenon where, by listening to an artery with a stethoscope while reducing the pressure of a cuff, distinctive sounds would appear and then eventually vanish. And the points at which these sounds appeared and vanished matched precisely with the systolic and diastolic blood pressures.

The essence of this discovery lies in its the application of the principles of fluid dynamics to clinical practice:

• Turbulent flow creates sound — When blood passes through a partially compressed artery, turbulent flow occurs and becomes sound.
• Laminar flow returns to silence — When the artery is fully open, the blood flow returns to laminar flow, and the sound disappears.
• This appearance and disappearance of sound accurately reflects the maximum and minimum values of intravascular pressure.

The desperate question of a military physician trying to determine if blood was still flowing in an arm by placing a stethoscope over the wounds of a soldier on the battlefield. The answer to that question has been passed down seamlessly, right up to the modern home blood pressure monitors we use today.

The next time a blood pressure monitor cuff tightens around your arm, we hope you’ll briefly recall the profound insights of Korotkoff and the incredible 120-year history of medical progress encapsulated within that simple action.

Related Articles

• A Journey of Measuring Blood Pressure: Why Did Humanity Try to Measure Blood Pressure?
• A Journey to Understand Blood Vessels and Blood Flow: From Ancient Pulse Diagnosis to Diverse Modern Testing
• Exercise and Vascular Health: The Effects and Mechanisms of Physical Activity on Vascular Function

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