October 21, 2017

Mysteries Of The Heart

I had never been a fun of non-fictional books but as the years went by I found myself picking up more books that fall under this category and finding them an enjoyable read. Most of these books were read on recommendation and one such great read was “The Ten Most Beautiful Experiments” by George Johnson, describing experiments that discovered what we may now consider basic science. Some of the experiments described were new to me, all the experiments were indeed beautiful and I couldn’t help but acknowledge the intricate and delicate designs of these experiments. So here is my take on one such experiment or series of experiments by William Harvey as described by George Johnson in the chapter “Mysteries of the heart“.

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The man

Probably no one has ever studied so many different kinds of hearts; from dogs and pigs to snails, crabs and shrimps like Harvey did. William Harvey begun his studies in Cambridge at the age of 16 and went on to one of the most prestigious medical schools in Europe at the time, the University of Padua where he must have met another great scientist Galileo. Following his return to England, he took up a lecturing position and set up his own practise where he attended to kings (I mean literally, King James I and King Charles I). It was his exposure to human anatomy, keen mind and dissection of smaller creatures that led him to redefine a long standing school of thought about blood circulation in the human body and the function of the heart.

The problem

Back in the second century, a great Physician to Roman gladiators and emperors by name Galen had written that there was two types of blood carried by two systems in the body. First was an elixir of growth made in the liver and transported through bluish colored veins. Secondly was a bright red liquid transported through arteries and necessary to stimulate motion. In Galen’s line of work he came across a lot of injured bodies since he treated gladiators, so his understanding of human physiology was held in high esteem and his theories went unchallenged until the 17th century (So that is 1400 years of doctors learning that in the brain some of this vital red fluid was converted into an ethereal essence).

The beauty

Knowing that the blood that was pumped through to the body was the same that returned was not intuitive as it had previously been stated (By Galen) that both kinds of blood were constantly created form the ingestion of food and depleted in the growth and locomotion of the body. However by measuring how much blood the heart could hold and pump out and working out how many beats there were, Harvey concluded that we would have to synthesis an impossible amount of blood to keep the system running if it was all one way. He also chose to observe the contractions and relaxations of the heart muscles in cold blooded animals because the process was too rapid in warm blooded animals. This helped him reach the conclusion that blood was pumped to the body by the left side of the heart via the arteries and returned to the right side of the heart via the veins.

A simple circulation diagram showing oxygenated blood in red and de-oxygenated blood in blue (william-harvey.org)

Over two decades of research into the workings of the human heart and circulatory system, he performed a number of beautiful experiments such as inserting a long probe into a dissected vein to prove that veins allowed blood flow in one direction and the in built valves were meant to prevent a reverse flow. His experiments and observations also led to the following conclusions amongst others:

  • Arterial blood was pushed out of the heart to the body and venous blood flowed from the body back to the heart
  • Purpose of the left side of the heart is to pump blood to the extremities
  • The right side of the heart pumped blood through the lungs

It may all seem common knowledge now but at the time it was a radical new hypothesis to suggest that blood circulated. This was the experiment that sealed the deal on his hypothesis;

Opening up a snake with a still beating heart he showed that pinching the main vein of the vena cava just before it entered the heart would quickly empty the space downstream of blood. The heart then grows paler and beats more slowly. Alternatively, pinching the main artery just before it leaves the heart the space upstream of that becomes distended assuming a deep livid colour

The legacy

Most of Harvey’s findings were published in a short book in 1628 titled, “On the motion of the heart and blood in animals”. It contains a summary of all his conclusions after two decades of research. During the English civil war which broke out in 1642, and Harvey had his room ransacked with most of his papers burnt and losing many records of his documented works. Nonetheless, his legacy remains in everything we now accept as the basic function of the heart and the circulation of blood.

Future scientist would build on his work and by the use of microscopes show capillaries that connect the arteries to the veins and also explain the osmotic process that allowed transfer of blood between the two networks.


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