Effect of Altered Levels of Carbon Dioxide on the Incidence of Altitude Decompression Sickness

摘要

Goats were exposed to 30,000, 32,000 or 34,000 ft simulated altitude while breathing carbon dioxide tensions of 15, 30, or 46 tor in oxygen during 15-min prebreathing and 30-min peak altitude exposures. Risk of decompression was determi ned 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 other treatment effects (air versus oxygen prebreathing); however, no significant change in VGE scores occurred as a result of varying the carbon dioxide level in the inspired air. Furthermore, there was no significant change in cardiac index during the various carbon dioxide exposures and the VGE scores were not correlated with cardiac index. Ground level studies revealed that end-tidal carbon dioxide tensions were significantly elevated at all three levels of inspired carbon dioxide, but no change in cardiac index was observed. In a trial involving one animal, conditions producing high VGE scores did not produce arterial emboli. Short duration prebreathing of carbon dioxide in oxygen does not appear to affect DCS incidence. Longer periods of prebreathing with carbon dioxide supplementation should be investigated.