Notes concerning The Dynamic Heart and Circulation, edited by Craig Holdrege, translations by Katherine Creeger (Fair Oaks CA: AWSNA, 2002).
What follows is not a broad review of the book, but rather a narrow selection of notes drawn mostly on a single theme. The book contains wide-ranging essays by five European scientists, with an introduction by my colleague at The Nature Institute, Craig Holdrege. I will refer to the text using page numbers and authors’ last names. For chapter titles and full identification of the authors, together with ordering information, see the end of this article.
Not so long ago, if I had been asked to visualize and describe the human circulatory system, my natural impulse would probably have been, first, to talk about how the blood consisted of plasma and various cells, such as red and white blood cells. Then I would have pictured a network of pipelines, larger or smaller, for transporting the blood in a complex loop throughout the body. And, of course, I would have told how the heart, with its tireless and wonderfully consistent pumping action, drives this entire, life-sustaining circulation throughout its course.
Unfortunately, my description would, in spirit and in substance, have been hopelessly misconceived. It would also have been quite respectable. Why? Because it is an essentially mechanical description, and mechanical descriptions of organisms, however misconceived, tend to get respect today. Even if we recognize their inadequacy in a particular case, we can’t help thinking they give us the “right sort” of understanding.
For now, let’s take a look at the idea that the heart is a pump, propelling the blood around the body. You can decide for yourself how well the metaphor fits the reality.
Here is an elaboration of the heart-pump idea by a blood specialist who appears perfectly happy with it. The description occurs under the chapter heading, “Pumps and Pipes” in a 1973 book called Blood, by Earle Hackett, who at the time was a Fellow of the Royal Australian College of Physicians and President of the Royal College of Pathologists of Australia.
Go to a good engineering firm and ask them to make you a reliable, compact, automatic pump about 1/250th of a horsepower, as big as a man’s fist and weighing rather less than a pound (about 450 grams). It must have an output which can be varied from one gallon to eight gallons (five to thirty-five liters) of thickish fluid per minute. For the most part it must idle smoothly along at the lower rate, beating about forty million strokes a year. It will work usually against a head equivalent to six feet (two meters) of water, but at times this may be doubled, and then it must automatically increase its force. Similarly it must be sensitive to any increase or decrease in the pool of fluid from which it is pumping, responding immediately by acceleration or deceleration, or by increased or decreased stroke as the case may be. It must also accept signals which may reach it electrically from other pieces of machinery or from control centers elsewhere. It must react, too, to signals in the form of dissolved substances reaching it in the fluid being pumped. Its valve closures must not damage millions of suspended cells which will form almost half the volume of this fluid. It must never stop in an average run of sixty to eighty years, during which time each of its chambers will pump sixty-five million gallons (about three hundred million liters) of blood.
An impressive description. So impressive that it almost seems to require too much of the heart, thereby raising questions about the mechanical metaphor it celebrates. But the quickest way to get much clearer about the metaphor is by looking not only at the heart, but also at the “pipeline” it supplies.
There are 6,000 miles of blood vessels in the human body — arteries, arterioles, capillaries, venules, and veins. (You will encounter estimates up to at least 60,000 miles, but I’m being extremely conservative.) That’s enough pipeline to reach from New York to the west coast and back. So with my early, naive picture of the heart-pump, I was requiring less than a pound of specialized muscle to propel blood through tiny tubes running along one side of Interstate 80 from New York to the California shore, and then back again along the other side of the highway. Anyone who has experienced the muscular exertion required to drive a little bit of liquid through a few feet of narrow tubing (say, by blowing on one end of the tube) knows that the heart’s New York to Pacific Ocean round trip is not only impossible, but impossible by many orders of magnitude. Of course, in the body many of these pipes run in parallel, but this does not change the amount of work required.
But let’s look a little closer. How narrow is our transcontinental pipeline? Very narrow. Most of its length consists of capillaries 0.3 millimeters or less in diameter. Some of these are so small that the donut-shaped red blood cells must flatten themselves in order to squeeze through. But this is not all. Our pipeline has the unfortunate habit of leaking. “Leaking” is an oddly mild word for it, however, since every day the pipeline loses about eighty times the total volume of blood plasma it contains (Lauboeck, p. 70). So our one-pound muscle not only has to overcome the astronomical resistance of a microscopic, 6,000-mile pipeline to the California beaches and back, but it also has to irrigate the Great Plains along the way. Some pump!
You might be thinking, “If eighty times the total volume of blood plasma is being lost to the pipeline every day, this loss must be replaced somehow". So it must, and this is our first hint of all the other things going on quite unrelated to the idea of a pump. But this needs to wait. First, a quick listing of a few other observations that just don’t fit a simplistic, mechanical image of the heart:
William DeVries, the creator of the first implanted artificial heart, made an unexpected observation after implanting the device into four different patients. He observed that when systolic, diastolic, and mean blood pressures are increased, the cardiac output actually decreases. This is the opposite of what one would expect if the circulation is impelled by an artificial pump. (Lauboeck, p. 55)Similarly, once the body has reasonably adapted to the artificial heart, you can increase the device’s pumping rate, and yet there will be no sustained increase in blood pressure or cardiac output. This is because the blood vessels respond by dilating, thereby holding the blood flow at a level that the body has found to be optimal. So the mechanical device is “subverted” and not allowed to act as a central controller; the circulatory system as a whole counters it in order to maintain a desirable state.
When the pacemaker induces excessively rapid beating...both aortic pressure and the strength of the heart contractions increase. However, the volume of blood flowing through the heart per minute (the cardiac output) remains the same. Even when the heart rate is doubled or tripled, cardiac output remains the same.... (Lauboeck, p. 57)When the heart rate is increased in this way, the amount of blood ejected during each heartbeat diminishes.
the body does not behave like a plumber, first connecting the water pipes in a house and then turning the water on....the first blood-like liquid...simply trickles through gaps in the tissues....Preferred channels develop only very gradually as blood cells are deposited along the edges and eventually merge into the beginnings of vessel walls. (Schad, p. 80)Moreover, “when blood vessels first start to form, the heart does not yet exist ... early blood flow stimulates the development of the heart” (Schad, pp. 82-83). As we see everywhere in the world, fixed form not only shapes movement, but also results from it. (Novalis remarked that the human body is a formed stream.) Thus, the spiraling fibers of the heart muscle that help to direct the blood in its flow are themselves a congealed image of the swirling vortex of blood within. This kind of mutuality holds even for the heart’s basic structural divisions:
Before the heart has developed walls (septa) separating the four chambers from each other, the blood already flows in two distinct “currents” through the heart. The blood flowing through the right and left sides of the heart do not mix, but stream and loop by each other, just as two currents in a body of water. In the “still water zone” between the two currents, the septum dividing the two chambers forms. Thus the movement of the blood gives the parameters for the inner differentiation of the heart, just as the looping heart redirects the flow of blood. (Holdrege, p. 12)
The prevailing science takes mechanism as the given and everything else, including movement, as the result. The truth may be more like the reverse of this.
By now you can surmise that, in asking what drives the circulation, we are up against a complex and organic set of interrelationships. The idea of a mechanical pump is not only hopelessly simplistic, but also flat-out misconceived. Certainly it’s true that the muscular contractions of the left ventricle play a key role in the blood’s movement through the arterial portion of the circulatory system (which accounts for about twelve percent of the blood volume as a whole). But, as we have seen, even here the pressure, volume, and heartbeat relationships are not at all characteristic of a typical pump. Nor is the phase of reverse flow. Moreover, the arteries themselves play a substantial role, dilating or shrinking as physiological conditions require, so as to accommodate more or less blood. The arteries also assist blood flow through the pulsing, wavelike muscular contractions of their walls.
On the other hand, approximately eighty-five percent of the body’s blood flows without being under significant pressure. This “low-pressure system" — which includes the capillaries, veins, right side of the heart, pulmonary (lung) circulation, and left atrium of the heart — absorbs nearly all of a one-liter transfusion without causing any increase in blood pressure. The system counteracts pressure changes by relaxing in response to increased pressure and contracting in response to a pressure drop (Brettschneider, p. 27).
And what drives the blood through this low-pressure system? The factors are many, including lung movement, muscular exertion, and suction from the heart, but the central fact emerging from the book under review is that the metabolism as a whole propels the blood. While the heart’s output volume is not directly proportional to heartbeat rate or blood pressure, it is proportional to the oxygen consumed in all the body’s tissues. “Cardiac output is...determined by the metabolic demands of the tissues” (Lauboeck, p. 65).
To understand this, recall that the capillaries are open to their surroundings. The fluids moving outside the blood vessels through the “extracellular matrix” make up a volume twice that of the total blood plasma. Fluid is continually passing in both directions between the primary circulatory system and the extracellular matrix, and also, for example, between the primary circulatory system and the kidneys — so much so that, as we saw, the total volume of blood plasma must be replenished eighty times each day.
So it is this metabolically driven flow from the tissues into the blood vessels that sustains the greatest part of our circulation. “The force that causes the blood to flow into the heart is the result of work performed by the tissues continually replenishing the fluid volume of the blood” (Lauboeck, p. 70). It is therefore no more accurate to say a “central mechanism” drives the blood than to say “everything else does". All of which explains why a weakened heart results in greater pressure in the veins returning blood to the heart: the heart cannot cope with the volume of blood being driven to it. One of the key functions of the heart, according to the authors of this book, is momentarily to stop or dam up the flow of blood, bringing its motion into the kind of harmonious rhythm that seems so essential in all our bodily activity.
None of this is to belittle the heart’s central importance in the body! Quite the opposite. It’s just a matter of striving to grasp the complex realities of the matter — realities that mechanical metaphors make invisible. To take an example not touched on above: the heart plays a significant role in regulating the body’s warmth. Only about 20 percent of the oxygen it consumes is used for basal metabolism, and 5 to 20 percent is used for muscular contraction (beating):
Surprisingly, 60 to 70 percent of oxygen consumed is turned into heat. Thus we see that most of the heart’s work does not result in mechanical force but in the production of warmth. The warmth infuses into the bloodstream and helps to warm the rest of the body. (Lauboeck, p. 68)
How many of those who “know” that the heart is a pump also know that our hearts help to warm us?
Mechanical metaphors not only conceal many things from us; they also lead to dangerously unrealistic expectations. When Robert Tools, the first recipient of an AbioCor artificial heart, died on November 30, 2001, his doctors assured journalists that the experiment had not failed. As the Los Angeles Times reported, “Tools’ doctors noted that the heart continued to beat flawlessly even as he died".
Yes, that’s exactly what we want of a mechanism; anything else would indeed have been a mechanical failure. But this only shows how alien the mechanism remains in relation to the organism: it fails to become an organic expression of the body as a whole. As Holdrege notes (p. 20), the “flawless” beating in Robert Tools’ chest testifies to the fact that the AbioCor heart was a mere mechanism, operating in grotesque disconnection from the dying person of whom it was intended to be an integral part. And there was nothing in the AbioCor’s operation to make this disconnection a less fundamental reality for the living patient than for the dying one.
The AbioCor remains an engineering marvel, worthy of our admiration. But we will make the best use of such mechanisms only when we are less mesmerized by the engineering feat and more attuned to the organisms in which we try to deploy them.
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Steve Talbott :: On Being Wholehearted