Influence of carbon dioxide on venous gas emboli production during altitude decompression in goats

Goats (N = 7) were decompressed from 1,500 m to 9,150, 9,750, or 10,400 m simulated altitude while breathing CO2 tensions of 0, 15, 30, or 46 mm Hg in O2 during 15-min prebreathing and 30-min peak altitude exposures. Risk of decompression sickness was determined by detecting venous gas emboli (VGE) in the pulmonary artery with an implanted Doppler cuff. VGE scores were calculated using the ratio of cardiac cycles containing VGE to total cardiac cycles. The VGE scoring methodology proved sensitive to standard treatment effects (air versus O2 prebreathing). No significant change in VGE scores as a result of varying the inspired CO2 level was detected. Further, no significant change in cardiac index occurred during the various CO2 exposures, and VGE scores were not correlated with cardiac index. Ground-level studies revealed the tension of end-tidal CO2 was significantly elevated at all three levels of inspired CO2, but no change in cardiac index was observed. Short-duration breathing of CO2 in oxygen failed to significantly reduce the risk of decompression sickness as assessed by VGE production.