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Out of France and the Science of Heat to Extracorporeal Support and Transplantation

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Vincent Valentine, MD
University of Alabama Birmingham
Birmingham, AL, USA

Let's warm things up about our upcoming ISHLT meeting in France by exploring some of the early 19th century ideas about heat. Not so much what heat was thought to be, but instead how heat behaves with the "Laws" it follows. This is important because of the central role heat plays among nature's many forces, i.e. motive, magnetic or electrical force. Let's be sure to stay away from all the recent heated topical news in the workplace related to perhaps, the Descent of Man or Men of Power, or more aptly named - Man and His Nature and those "Laws" not followed.

Heat is important because it is ubiquitous. Whenever one force is used to produce another, almost without exception heat will be produced. Heat has important characteristics. Think about electromagnetism exemplifying the interrelationships among forces like a generator. Turning a coil of wire mechanically in a magnetic field interrupts that field giving us electrical current. Is the mechanical force used to turn the coil made use of to produce the electrical force of a current or is the mechanical force converted to electrical force? What about an electric motor that starts with electrical current and ends with the rotating mechanical motion of the armature. Is the electrical force of the current made use of to produce the mechanical rotation or is the electrical force converted to mechanical force? Note, the first posits that mechanical or electrical force is made use of to produce the alternative, then these forces are made use of or used but not used up. Therefore, the initial force is recoverable and can be used again. The latter posits that mechanical or electrical force is converted to electrical or mechanical force respectively, then the initial mechanical or electrical force has been used up and is no longer around.

Early attempts to understand the behavior of heat were proposed by French natural philosophers from the early decades of the 19th century who began to explore the relationship between heat and motive force. In the early 1800s society was keenly aware of the use of heat to obtain motive force, the steam engine. The invention of the steam engine, the most important symbol of the industrial revolution, represented the major shift away from animal power to inanimate power. Falling water was another favorite use of power to turn the wheels of a mill. Pause here if you will about the steam engine and reflect on the ventricular assist devices and other extracorporeal devices and circuits of today. Consider the inefficiencies and efficiencies. Think about heat.

Now let's turn to the direction of influence on science and technology. The usual direction is from science to technology, theory to application, such as the aftermath of the discovery of electromagnetism. On the other hand, technology precedes science as occurred with the steam engine. Effective steam engines were built well before how they worked was understood. The steam engine set the stage for the birth of thermodynamics. In this instance, science learned a lot more from the steam engine than the steam engine learned from science. So how did the science of heat come about?

One of the first natural philosophers to consider the behavior of heat from a theoretical as opposed to a practical point of view was the French mathematician Jean-Baptiste Joseph Fourier who is also credited with the discovery of the greenhouse effect - again let's stay away from politics, men of power and global warming. Because Fourier was born into humble surroundings, this enthusiastic and driven youth with amazing mathematical abilities had natural sympathies for the French Revolution. He survived the Reign of Terror and acquired an important position at the École Polytechnique. Indirectly from the influence on Napoleon, Fourier devoted himself to the study of heat and asked the question, how does heat flow through solid bodies? Can this be described mathematically? Fourier had developed an unconventional aspect on the treatment of heat. It was the introduction of a nonnewtonian element into physics showing the way heat flowed. The Laws Fourier had formulated for the conduction of heat implied that heat flow was not reversible. For the early 19th Century, this was in opposition to the mechanical laws that Newton had formulated to describe how the machinery of nature ran were reversible. Nature's laws should not be reversible as predicted by Newtonian laws.

Now there was another Frenchmen also fascinated by the theoretical study of heat as it appeared in the steam engine. His name was Nicolas Leonard Sadi Carnot. Unlike Fourier, Carnot came from an important family in France. Carnot completed his studies at the increasingly famous École Polytechnique in Engineering, Mathematics and Science. He developed an important curiosity about heat engines which enabled him to ask an intriguing and fundamental set of questions about the way heat is used to produce motive force. One of his questions was whether there was a maximal amount of motive force that could be obtained using a certain amount of heat. For example, a steam engine puts out a certain amount of heat. Is there a limit to the amount of motive force produced from heat? Were some substances better than others in producing a given amount of motive force. Is coal better than wood?

Those who worked steam engines used trial and error to answer these questions. From experience they can determine if different engines could produce different amounts of force from the same quantity of heat. Carnot focused on the theoretical side of these questions. He knew very little about working on or with steam engines. In his pursuit of these theoretical questions, Carnot discovered something that took years to appreciate. He recognized that if heat were used to produce motive force, then the only way that could occur was when heat from a higher temperature fell to a lower temperature, ΔH. These ideas were put down in his only publication in 1824 entitled Reflections on the Motive Power of Fire. This became a key work in the history of physics.

Carnot thought of the production of motive force from heat as nature's response to a disturbance from a normally balanced state, not unlike the production of electricity or the perturbation of a pendulum from its equilibrium. Carnot viewed the steam engine as another way of disturbing a normal state which gives nature an opportunity to restore the disturbance back to its the original state. This heat engine Carnot imagined was the "ideal heat engine," one which is considered weightless with no heat loss to friction or conduction. Most of his readers interpreted his description of heat as a weightless "subtle fluid" that Lavoisier had called caloric. Caloric was one of those imponderable substances. (see Editor's Corner, September 2017 Links) When these imponderable substances were combined with material bodies or matter, these bodies were warmed. How much caloric was present was a measure of the matters temperature. The temperature of the air in the chamber of a steam engine depended on how caloric was present in the volume of the chamber. With these assumptions, Carnot was able to explain how disturbing and restoring an equilibrium state could tell us how a steam engine is able to produce motive force. Imagine a cylinder with a movable piston that expands the volume of the cylinder on its upstroke then compresses the volume on its downstroke. In the equilibrium state, there is no movement. Carnot assumed that nature would maintain that equilibrium. Now bring on the heat, extra caloric into the cylinder. This is done by bringing the cylinder into contact with a body made hot by steam. Nature maintains the equilibrium by expansion, moving the chamber up as it was disturbed by the increasing temperature. Now remove the cylinder from its contact with the hot body, no more steam flows in, at this point the piston continues up expanding the volume of the chamber briefly resulting in another unstable situation. The temperature now drops from the increasing temperature. The amount of caloric has been reduced. Nature restores equilibrium by bringing the cylinder into contact with a cold body. Nature allows the caloric to flow to the cold body thus contracting the volume of the cylinder and moving the piston down. The downward movement of the piston continues beyond the equilibrium which perpetuates the cycle similar to the simple harmonic motion or oscillation of a pendulum, spring or in this case a piston under ideal circumstances. From this analysis, Carnot learned that the motive power of the engine depended on two factors: the amount of heat produced and the availability of cold - that is the size of the fall in temperature or the delta ΔH - "without the latter, the heat is useless."

This brings us back to the original questions about the relationships among forces, electrical and mechanical as pointed out above. Is heat made use of to produce motive force or is heat used up to produce motive force. Carnot states that "the production of motive power is then due in steam engines not to an actual consumption of caloric but due to its transportation from a warm body to a cold body," in its reestablishment to equilibrium. He believes heat was conserved. Most importantly to produce a motive force there must be a drop in temperature akin to Norman Shumway's great quote, "all water flows downhill." To answer the question about which substances are better at producing a given motive force, if motive power depended on the difference in temperature of the hot body and the cold body, then the substance used to supply the heat was not important. He concluded that all ideal reversible heat engines must have the same efficiency. This was just the beginning of the new science of thermodynamics. For this, Carnot is considered the father of thermodynamics.

Now fast forward to the technological explosion of extracorporeal life support systems where such systems assume the work of the heart and/or the lungs. Consider the production of heat and its effect on clot formation. What about the sources of energy necessary for ventricular assist devices? When the energy is "used up" where does it go other than producing a motive force for circulation? What about the heat? What effect does this heat from motion and friction have on our patients and on ourselves? Think not just about how hot or if it clots, but think about "sudden" changes in temperature. Of course, is the energy perpetual, renewable or when batteries or back up batteries must be changed? Imponderable questions?

Before we finish here, rethink or reflect on heat, France and Carnot, then think about sewing two vascular structures together successfully to allow blood flow with the least amount of friction, resistance or heat. Let's not confuse Nicolas Leonard Sadi Carnot (1796 - 1832) - Father of Thermodynamics with Marie François Sadi Carnot (1837 - 1894), the President of France from 1887 until he was assassinated in 1894. Nicolas Carnot was Marie Carnot's uncle. Anyway, a fatal stab wound to the abdomen of the nephew Carnot in 1894 profoundly influenced a French surgeon, Dr Alexis Carrel (1873 - 1944), to consider the possibility of repairing the severed abdominal vessels. Carrel's pioneering vascular surgical techniques paved the way to his Nobel Prize in 1912. Further, with the assistance of Charles Lindbergh, Carrel in his effort to keep tissues and organs alive, extracorporeally, invented the "perfusion pump" in the 1930's which unlocked the door to open heart surgery and organ transplantation.

Need we simply end here with all these "links" related to France, heat, motion, rotaries, propulsion, travel, transplantation, replacement therapies and extracorporeal life support? Or should we go in circles and swing back and forth like a pendulum in a frictionless vacuum like an idealized steam engine in perpetuity. What came first? The chicken or the egg, science or technology, or the theory or the application? Where are we today? Soon it will be Nice. ■

Disclosure Statement: The author has no conflicts of interest to disclose.

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