Calorimetry and metabolic knowledge.

David Frankenfield’s review, ‘‘On Heat, Respiration, and Calorimetry,’’ traces the studies on human respiration, heat, and oxygen consumption over a long period. The story offers interlocking benefits. In the first place, one can trace the research on gas exchange and an understanding of the relatedness of oxygen and carbon dioxide. In the second place, one can see the evolution of a clinical measurement tool evolve as each question raised is answered. In the third place, one can trace the changes in hypotheses about metabolism emerging as studies were directed at the questions raised. In the fourth and last place, one can anticipate improvements in calculations of catabolic losses and a future potential to perhaps limit the size of the measurement technology for future use. The biggest challenge, however, is the fact that the science is dependent on the assumption of an equilibrium state that does not apply in acute illness. In addition, variations in body composition and surface area may limit the use of regression equations. The leading question is how animals maintain a constant internal temperature that links internal heat to breathing. In the late 17th century, John Mayow demonstrated that animals consume air and die without it, but there was no explanation of how the air taken in could generate heat. A flurry of experimentation followed for measuring heat production using the latent heat of transformation (ice to water). A novel hypothesis was introduced in the 18th century. The exchange of oxygen and carbon dioxide in the lungs associated with liberation of heat in respiration was hypothesized after the discovery of carbon dioxide by Joseph Black (a colleague of Adam Smith) and of oxygen by Joseph Priestly and the discovery by Antoine Lavoisier that exhaled air is depleted of oxygen. These scientists were very exacting in their scientific measurements and developed the calorimeter just before the 19th century. However, there was a 20% gap in heat production that needed explanation. At about the same time, Adair Crawford designed a calorimeter using water instead of ice to absorb heat and achieved a 90% agreement between heat production and oxygen consumption. The context of these discoveries is two centuries after the end of the Italian Renaissance, highlighted by Leonardo da Vinci and Galileo Galilei. The awakening of European science outside England was led by Baruch Spinoza and Gottfried Leibnitz. The 17th century was a period of great scientific awakening in England with the leadership of Christopher Wren, Isaac Newton, and William Harvey’s discovery of the circulation, paving the way to modern anatomic studies. In the 18th century, a dominance in English medical education coincided with the work of John Hunter and those mentioned, which preceded the work of Charles Darwin by less than a century. It remained for Gustavus Magnus in Germany to determine in 1837 by way of an arteriovenous oxygen gradient for oxygen and carbon dioxide that gas exchange occurs in the lungs, extending the study of calorimetry into the 19th century. This coincides with the rise of the Viennese anatomic studies led by Baron Carl von Rokitansky. The story is carried forward to the modern calorimetry of the 20th century with a rebirth in the 1970s to the present.