Carboxyhemoglobin Levels in Humans: Effects of Altitude

Abstract

These studies were conducted to determine the effects of altitude on endogenous blood carboxyhemoglobin (COHb) concentrations and on COHb concentrations produced by breathing carbon monoxide (CO). COHb concentrations were determined at sea level (SL) and at altitude (HA) in human volunteers breathing ambient air (group I) or 9 ppm CO for 1 hr (group II). Breath CO measurements were also made in both groups. The first measurements were made at College Station, Texas (elevation 330 ft) and the second at Hoosier Pass, Colorado (elevation 11,540 ft) after 20 hr at altitude. Blood drawn from the finger was immediately frozen for COHb and hemoglobin analysis in Lubbock, Texas. Alveolar air samples, collected in aluminized Mylar bags, were analyzed for CO in Warren, Michigan. In group 1 subjects, COHb levels increased significantly (p <.05) from 0.790% and 0.795%, respectively, in males and females at SL to 0.947% and 0.945% at HA. The overall increase for both groups was approximately 20%. In group 2 subjects breathing 9 ppm CO for 1 hr, COHb levels increased from 0.780% to 1.464% at SL and from 0.959% to 1.982% at HA. The increase in COHb concentration in subjects breathing CO was significantly (p <.05) greater at HA (1.024% COHb at HA vs. 0.684% at SL). Breath CO concentrations tended to increase at HA but were more variable and not statistically significant. These results suggest that COHb concentrations are higher at altitude due in part to alterations in the mechanisms by which the body excretes CO produced endogenously and to a more rapid uptake of CO at altitude.