Respiratory exchange

Alveolar ventilation supplies O2 to the bloodstream while alveolar capillary perfusion provides alveolar gas with COj. Resting individuals consume approximately 250 mL 02/min and produce approximately 200 ml. COi/min because, stoichiometrically, metabolic processes require a greater supply of O, than the quantity of CO2 produced. Defining the respiratory exchange ratio, R, as... 

Respiratory exchange ration Ratio of carbon dioxide production to oxygen... 

The respiratory exchange ratio (usually abbreviated, RQ or R) should be known but, in practice, it makes little difference unless very high accuracy is required. 

DEWAR STRUCTURES KEKULE STRUCTURES RESONANCE STABILIZATION ENERGY RESPIRATORY BURST OXIDASE NADPH OXIDASE RESPIRATORY EXCHANGE RATIO Restricted rotation,... 

Studies of the respiratory quotient or respiratory exchange ratio (RER) indicate a metabolic shift in CR rats depending on food availability, while there is little change in AL rats [21,42]. Figure 7 illustrates daily variations of RER with dietary regimen. Analysis of the food composition indicates an expected average value of RER of 0.89. RER in AL rats is 0.89 0.02 over a 24-hour period and is relatively more constant than that in CR rats, indicating that AL rats metabolize a constant ratio of carbohydrate and lipid over 24 hours [21, 42]. In contrast, CR animals metabolize more carbohydrate... 

Fig. 7. Respiratory exchange ratio of male F344 rats at 18 months of age. Calorically restricted rats were fed just before turning off the light (arrow). The light was off from hours 0 to 12 and on from hours 12 to 24. Adapted from reference 21.

Johanson G. 1991a. Modelling of respiratory exchange of polar solvents. AnnOccupHyg... 

The quantitative analysis of oxidation of fuels shows that when most carbohydrates are oxidized, the ratio of carbon dioxide produced to oxygen consumed is 1. On the other hand, this ratio, which is called the respiratory quotient (RQ) or the respiratory exchange ratio, is -0.7 when fatty acids are oxidized. The measurements of O2 consumption and CO2 emission only indicate which fuels are being oxidized on average by the whole body and do not necessarily reflect which fuel is being used selectively by particular cell types or tissues. As noted in Chap. 11, the synthesis of triglycerides raises the RQ above 1. 

A footballer on a treadmill, showing the equipment used to measure the respiratory exchange of oxygen and carbon dioxide. 

The effect of thyroid hormones on oxidative processes has long been considered to be their most fundamental action in adult mammals. In 1895, Magnus-Levy made the classic observation that respiratory exchange is depressed in hypothyroidism and elevated in hyperthyroidism. Many factors modify the effect of thyroid hormones in the intact animal, such as nutrition, other endocrine secretions, and the general health of the animal (cf. Boothby and Sandiford, 1924 Sundaram el al., 1956 Money, 1956) a consideration of these fa( tors is beyond the scope of this review. It should be noted that the thyroid hormones appear to exert no calorigenic activity in lower vertebrates (cf. Fromm and Reineke, 1956). 

Respiratory exchange measurements, namely, oxygen consumption ( 02) and the concentration of oxygen and carbon dioxide in expired gases, were monitored throughout rest, exercise, and recovery. Blood samples taken at the end of the rest, exercise, and recovery periods, were analyzed for glucose, lactate, and pyruvate. Blood samples were obtained during the exercise sessions only in study 2. 

Equation 4.7 uses the definition of the respiratory exchange ratio, R = VcqjA qj. which usually has a value of /f 0.8 for VJQ = 1. It also replaces the end capillary concentration with the systemic arterial value, assuming equilibration. From Eq. 4.7, the extreme limits of VJ Q, men-... 

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