Factors limiting maximal O2 consumption: effects of acute changes in ventilation

The response of the O2 transport system to acute changes in alveolar ventilation (V̇A) was analysed. The fractional limitations to maximal O2 consumption (V̇Ojavax.xml.bind.JAXBElement@30c9a41max) imposed by the lungs (ventilation, Fv, and lung-blood transfer, Fl), the cardiovascular system (Fq), and peripheral O2 diffusion (Fp) were calculated according to a multifactorial model. A reference set of data, describing the status of O2 transport at maximal exercise in normoxia was used. The effects of V̇A on V̇Ojavax.xml.bind.JAXBElement@63011e1dmax were assessed on the assumption of a constant reference O2 flow in mixed venous blood Q̇V̄Ojavax.xml.bind.JAXBElement@8e04a96). The changes in reference data after given independent changes in V̇A were calculated by an iterative procedure, until the V̇Ojavax.xml.bind.JAXBElement@36417926max value compatible with the constant reference QV̄Ojavax.xml.bind.JAXBElement@51f8233d was found, at PiOjavax.xml.bind.JAXBElement@3a623ee9 values of 150 (normoxia), 130, 110 and 90 Torr. The VOjavax.xml.bind.JAXBElement@305c67c9max changes in normoxia were less than expected assuming a linear O2 transport system, because of the flatness of the O2 dissociation curve around normoxic POjavax.xml.bind.JAXBElement@d69a0ad. This affected the cardiovascular resistance to O2 flow, and its changes counterbalanced the effects on V̇Ojavax.xml.bind.JAXBElement@1d989bf6max of induced changes in V̇A. This phenomenon was reversed in hypoxia, as the steep part of the O2 dissociation curve was approached. The fractional limitations to V̇Ojavax.xml.bind.JAXBElement@36a66bdamax in normoxia resulted as follows: Fv and Fl provided between 5 and 12%, Fq between 59 and 78%, and Fp between 13 and 19% of the overall V̇Ojavax.xml.bind.JAXBElement@651720e8max limitation. In hypoxia, Fv and Fl increased and Fq decreased. At PiOjavax.xml.bind.JAXBElement@25bb982f = 90 Torr, when V̇A was halved, Fv, Fl, Fq and Fp amounted to 0.35, 0.31, 0.20 and 0.14, respectively. © 1995.