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Respirometry
Description
Respirometry is the quantitative measurement of respiration. Respiration is therefore a combustion, a very slow one to be precise (Lavoisier and Laplace 1783). Thus the basic idea of using calorimetry to explore the sources and dynamics of heat changes was present in the origins of bioenergetics (Gnaiger 1983). Respirometry provides an indirect calorimetric approach to the measurement of metabolic heat changes, by measuring oxygen uptake (and carbon dioxide production and nitrogen excretion in the form of ammonia, urea or uric acid) and converting the oxygen consumed into an enthalpy change, using the oxycaloric equivalent. Liebig (1842) showed that the substrate of oxidative respiration was protein, carbohydrates, and fat. The sum of these chemical changes of materials under the influence of living cells is known as metabolism (Lusk 1928). The amount (volume STP) of carbon dioxide expired to the amount (volume STP) of oxygen inspired simultaneously is the respiratory quotient, which is 1.0 for the combustion of carbohydrate, but less for lipid and protein. Voit (1901) summarized early respirometric studies carried out by the Munich school on patients and healthy controls, concluding that the metabolism in the body was not proportional to the combustibility of the substances outside the body, but that protein, which burns with difficulty outside, metabolizes with the greatest ease, then carbohydrates, while fats, which readily burns outside, is the most difficultly combustible in the organism. Extending these conclusion on the sources of metabolic heat changes, the corresponding dynamics or respiratory control was summarized (Lusk 1928): The absorption of oxygen does not cause metabolism, but rather the amount of the meabolism determines the amount of oxygen to be absorbed. .. metabolism regulates the respiration.
Abbreviation: n.a.
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Respirometry
External and internal respiration
The brief historical summary on respirometry and respiration in the description (above) illustrates that early concepts on respiration focussed on the mechanism of respiration in living systems. This integrated systems view is different from the notion of respiration separating the external mode of respiration (inhaling and exhaling gas through the lungs, gills or body surface) from the internal mode of respiration related to metabolism. The integrated concept of respirometry and respiration thus unifies respirometry applied to ecological systems, whole organims, organs and tissues, living cells, and mitochondria.
