These last several weeks I have been absolutely overwhelmed with science, meetings, writing, and reviews. I might complain, but I should also be flattered that I am as busy as I am. Mama is in demand, little muffin. Still, things are beginning to slow down to a tolerable level on my end, which means I will be back to blogging.
Today I was working on some writing when I had cause to review some historical texts. It gives me pause to stop and consider things that we take for granted. For example, think about how blood flows through the heart and lungs…
I can’t tell you how many times a day I look at a heart and take for granted that blood should flow from the venous circulation, into the right side of the heart, across the lungs, back to the left side of the heart, and out to the arterial circulation. When all is right with the world, such is the way it should be.
But, we didn’t always know that. The experiments that provided evidence that blood flows in a single direction across the lungs were done by medical student William Harvey at the University of Padua in the early 1600s. In 1628, Dr. Harvey published his findings in the now classic tome Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (translated as An Anatomical Study of the Motion of the Heart and of the Blood in
Animals). As most revolutionary studies are, Dr. Harvey’s work was hugely controversial, probably the result of both the novelty of his findings and his use of human subjects and cadavers.
In a letter written after the publication of his work, Dr. Harvey wrote:
I have pleasure in describing here an experiment, tried out recently in the presence of several colleagues, and from the implications of which there is no escape. The pulmonary artery and pulmonary vein and the aorta were ligated in the cadaver of a throttled human being, and the left ventricle of the heart was opened. I then introduced a small tube through the vena cava into the right ventricle and at the same time fastened on to the tube an ox’s bladder as is usually done in the injection of clysters.
This I filed almost full of warm water, and injected it with great force into the ventricle mentioned so that almost a pound of fluid passed over into it and its neighbouring auricle. What happened? The ventricle in question (together with its auricle) swelled up violently, but not even a small drop of water or blood escaped through the gap in the left ventricle. When the aforementioned ligatures had been released, the same tube was introduced into the pulmonary artery, and after a tight ligature had been made to prevent the water from getting back into the right ventricle, I attempted to drive this water into the lungs. At once it shot forward, mixed with a large amount of blood, from the cut in the left ventricle in such a way that as much water came out from this cut in question as was pushed into the lungs at the individual compressions of the bladder. You can try it as often as you wish and discover that it is so.
As similar preparation, although refined a bit, is still used in basic cardiopulmonary research to investigate the effects of various substances on the pulmonary circulation.
Figure 2: The Harvard Isolated Lung Apparatus.
If you’ve ever had a doctor, nurse, or technician place a tourniquet on your arm to help facilitate drawing blood from a vein, you can thank Dr. Harvey for that bit of technology too. Dr. Harvey first noted that when a ligature was placed around the forearm, it because warm and swollen as blood flowed into the limb, but was unable to escape. He observed swelling in the veins and noted small varicosities that he identified as the valves that maintain unidirectional flow.
Figure 3: From Harvey’s original work.
Dr. Harvey hypothesized that there must be some intermediate between arteries and veins, although he failed to visualize his hypothetical “porosities” during his lifetime. Four years after William Harvey died, Marcello became the first to visualize capillaries by looking at a living frog lung under the microscope. By the time of his death in 1694, Malpighi had also become the first to visualize red blood cells, completing Harvey’s description of the circulatory system.
Figure 4: Malpighi’s drawing of the microvascular network on the surface of inflated frog lungs.
*This blog post was originally published at On Becoming a Domestic and Laboratory Goddess*