Interactive effects of hypoxia, carbon monoxide and acute lung injury on oxygen transport and aerobic capacity.

This study determined how breathing hypoxic gas, reducing circulatory capacitance for O2 by breathing CO, and impairing pulmonary gas exchange by acutely injuring the lungs interact to limit cardiopulmonary O2 delivery, O2 extraction and maximal aerobic capacity (VO2max). Five goats ran on a treadmill at VO2max following oleic-acid induced acute lung injury that impaired pulmonary gas exchange, after partial recovery or with no acute lung injury. Goats breathed normoxic or hypoxic inspired gas fractions (FIO2 0.21 or 0.12) with and without small amounts of CO to maintain carboxyhemoglobin fractions (FHbCO) of 0.02 or 0.30. With the exception of elevated FHbCO with acute lung injury (P=0.08), all combinations of hypoxia, elevated FHbCO and acute lung injury attenuated the reduction in VO2max by 15-27% compared to the sum of each treatment's individual reduction in VO2max when administered separately. Simultaneous administration of two treatments attenuated the reduction in VO2max by attenuating the decrease in cardiopulmonary O2 delivery, not synergistically increasing O2 extraction.