Physiological mechanisms dissociating pulmonary CO2 and O2 exchange dynamics during exercise in humans

Beskriver hvordan forholdet mellom CO2 og O2 endrer seg unde trening, og spesielt over melkesyreterskel hvor bikarbonat også begynner å spille inn i homeosasen av pH i blod.

«During incremental exercise, the increased rate of Graphic relative to pulmonary O2 uptake (Graphic) can be used to quantify θL validly if aerobic and hyperventilatory sources can be ruled out, i.e. θL is then attributable to the decrease in muscle and blood [HCO3]. In many cases, however, very rapid incrementation of work rate and/or prior depletion of CO2 stores (by volitional or anticipatory hyperventilation) can yield a ‘false positive’ non-invasive estimation of θL(‘pseudo-threshold’) resulting from a slowing of the rate of wash-in of transient CO2stores.»

«Since the tissue capacitance for CO2 is appreciably greater than for O2 (Farhi & Rahn, 1955), this means that the respiratory exchange ratio (R), i.e. the ratio of the volumes of CO2and O2 exchanged across the tissue of interest per unit time, will differ from that of the respiratory quotient (RQ), i.e. the ratio of the amounts of metabolic CO2 and O2 produced and consumed, respectively, by the tissue per unit time not only across the lung, where it is most typically determined and from which inferences are most typically drawn, but also across the muscle vascular bed itself. »

«But, in addition, skeletal muscle contraction results in a transient metabolic alkalosis in the force-generating units (Steinhagen et al. 1976; Kemp, 2005) and in the venous effluent of the exercising muscle (Wasserman et al. 1997) as a result of the net proton (H+) trapping associated with the high-energy phosphate utilization, i.e. H+ release as ATP is split, and H+ uptake consequent to phosphocreatine (PCr) splitting (Kushmerick, 1997).»

«This transient alkalosis therefore results in a component of the metabolically produced CO2 being retained within the muscle.»

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