Journey to Understand Blood Vessels and Flow: From Ancient Pulse Diagnosis to Modern Functional Diagnostics

“A man is as old as his arteries.”

As this famous saying suggests, knowing the state of one’s blood vessels has been synonymous with “knowing the state of life” for humanity since ancient times. However, the methods of confirmation have changed dramatically over time.

How did ancient people think about blood vessels, and what did they rely on to confirm that someone was alive? And what are we trying to see today?

Let’s take a journey to understand blood vessels and blood flow, from records remaining in ancient literature to modern precision diagnostics and future personalized medicine.

1. Ancient Times: The Age of Senses and Philosophy (“Why are we alive?”)

In an era without scientific measuring instruments, people perceived blood vessels through keen senses and philosophical interpretations.

Egypt: Canals of Soul and Fluids

In the ancient Egyptian medical text “Ebers Papyrus” (written around 1550 BCE), the concept of “Metu” appears¹. This was a concept that treated blood vessels, tendons, and nerves indiscriminately as “tubes running through the body.” They believed that these tubes carried not only blood but also air (breath), mucus, and even evil spirits that caused disease. The heart was believed to be the center of the “Soul (Ib)” and “Body (Haty),” and it was thought that life force was sent to the whole body through the tubes extending from it.

China: A Microcosm of “Qi and Blood” Read by Fingertips

In the classic of Chinese medicine “Huangdi Neijing” (Yellow Emperor’s Inner Canon), the foundation of pulse diagnosis is recorded². “Pulse Diagnosis” is a technique to read the state of “Qi” and “Blood” in the body from the rhythm, strength, and depth of the pulsation by placing fingers on the artery of the wrist (radial artery). For them, blood vessels were written not just as a passage for blood, but as a network where the body’s energy (Qi) circulated. The beating pulse was the very “proof of life,” and they sensed signs of disease from its subtle changes.

Greece: Burning Fuel and Spirit (Pneuma)

Galen (around 2nd century AD), often called the father of Western medicine, developed his own theories in his books such as “On the Natural Faculties”³. He believed that blood was made in the liver and was like “fuel that is consumed and disappears” as nutrition in various parts of the body. And he preached that “Pneuma (Spirit)”, the source of life, flowed in the arteries. This “blood consumption theory” continued to be believed for nearly 1500 years thereafter.

2. 17th Century: Scientific Revolution and Proof of Circulation (Elucidation of “Mechanism”)

It was the English physician William Harvey who broke the long-standing spell of Galen.

“Blood Circulates”

In 1628, Harvey published his masterpiece “Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus” (An Anatomical Exercise on the Motion of the Heart and Blood in Living Beings)⁴. He performed a simple calculation. “If blood is consumed, the amount of blood the heart pumps out in an hour would be several times the body weight. It is impossible to continue making such an amount of blood every day.” Furthermore, he performed a ligature experiment in which he tied the arm to make the blood vessels stand out, visually proving that the valves of the veins are one-way streets to the heart. With this, it became clear that blood is not consumed but “Circulates” in a closed circuit.

The Micro Missing Link: Discovery of Capillaries

Harvey’s theory had one weakness. He could not see how arteries and veins were connected at the ends. It was the Italian Marcello Malpighi who solved that mystery. After Harvey’s death, he observed the lungs of frogs using a microscope and discovered the capillaries, the fine network connecting arteries and veins. With this, the circulatory system as a closed circuit was finally completed.

3. 18th-19th Century: The Age of Measurement and Quantification (Discovery of “Pressure”)

Once the mechanism of circulation was understood, the next interest turned to “the force flowing within it.”

Inserting a Glass Tube into a Horse’s Neck: The First Blood Pressure Measurement

In 1733, the English clergyman Stephen Hales reported a shocking experiment in his book “Haemastaticks” in which he directly connected a long glass tube to the carotid artery of a horse⁵. The blood rushed up the glass tube for several meters. This was humanity’s first blood pressure measurement. It was the moment when it was visualized that blood was not just flowing, but pressing against the vessel walls with strong “pressure.”

The Appearance of Painless Sphygmomanometers

However, the method of inserting a tube cannot be used on humans. In 1896, the Italian Scipione Riva-Rocci invented a mercury sphygmomanometer that uses a cuff wrapped around the arm, which is still used today, and published it in a paper⁶. Furthermore, in 1905, the Russian military doctor Nikolai Korotkoff discovered the “auscultatory method (Korotkoff sounds)” to measure blood pressure by listening to vascular sounds with a stethoscope⁷. This made it possible for anyone to safely measure blood pressure = “load on blood vessels” without pain, opening the way to the treatment of hypertension.

4. 20th Century: The Age of Visualization and Structure (Seeing the “Form”)

Since the discovery of X-rays, medicine has immersed itself in technology to “see through the body.” With the advent of angiography using catheters, and then CT and MRI, it became possible to capture stenosis (narrowing) and aneurysms (bulges) of blood vessels as clear images. Diagnosis of “Structure”, such as “where is it clogged” and “what is the shape,” became the leading role in emergency medicine.

5. Modern Era: The Age of Function and Quality (Seeing the “Function” and “Signs”)

Diagnostic imaging is powerful, but it only looks at what happens after the “form” has changed (= arteriosclerosis is complete). “There are people who die suddenly even though their blood vessel shape looks clean.” To challenge this mystery, modern researchers have developed tests one after another to measure the invisible health of blood vessels, that is, “Function” and “Quality”.

Seeing Stiffness: PWV / CAVI

If you compare blood vessels to a rubber hose, they become hard and easy to burst as they get old. PWV (Pulse Wave Velocity) and CAVI measure the “speed” at which the heartbeat reaches the hands and feet. Utilizing the physical law that vibration travels faster as the blood vessel is harder, it quantifies the “stiffness (suppleness)” of the blood vessel.

Seeing the Degree of Clogging: ABI

Blood vessels in the legs are one of the places prone to clogging. ABI (Ankle-Brachial Index) looks at the ratio of blood pressure in the arms and legs. Usually, blood pressure in the legs is higher, but if leg blood pressure is lower, there is a possibility that flow is poor due to clogging somewhere.

Seeing Wall Thickness: Carotid Ultrasound (IMT)

By applying ultrasound to the blood vessels of the neck (carotid arteries), the thickness of the blood vessel wall (intima-media thickness: IMT) is directly measured. This is a site prone to arteriosclerosis and serves as a window to estimate the aging degree of blood vessels throughout the body.

Seeing “Function”: FMD (Flow-Mediated Dilation)

FMD is a test that measures the “Function” of how much endothelial cells can release nitric oxide (NO) to dilate blood vessels. Based on the importance of “endothelium-derived relaxing factor (EDRF, later identified as NO)” discovered by pharmacologist Furchgott et al. in the 1980s⁸, it is being studied as a method to evaluate the condition of blood vessels at a stage before structural changes occur.

6. Future: From Average to “You” (Dawn of Personalized Medicine)

Medical care until now has been based on “statistical averages” based on large-scale epidemiological surveys. Uniform standards such as “take medicine if blood pressure is 140 or higher” were useful, but there were limits to covering individual differences.

Future vascular testing is about to steer significantly towards “Personalized Medicine.”

From “Points” to “Lines”: Continuous Monitoring by Wearables

Tests until now were “point” data at the moment of visiting the hospital. In the future, with the evolution of smartwatches and ring-type devices, continuous monitoring 24 hours a day, 365 days a year of blood pressure, pulse waves, heart rate variability, etc., will become commonplace. Diagnoses based on individual biorhythms invisible in hospitals, such as “you are the type whose blood pressure rises sharply while sleeping” or “blood vessels become stiff under specific stress,” will become possible.

“Future Prediction” by AI and Omics Analysis

Furthermore, in addition to image data and physiological data, AI will integrate and analyze detailed biological information such as genes (genome) and metabolites (metabolome). This is making possible precise future prediction optimized for individuals, not “statistically, people of your age will become like this,” but “your blood vessels have a high probability of becoming like this in 3 years if you continue your current life”⁹.

Tests of the future will evolve from tools to “find diseases” to tools to obtain “your own compass of health” and correct the trajectory before becoming ill.

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