Physiological effects of chronic exposure to carbon monoxide

¹ Department of Physiology and Biophysics, School of Aviation Medicine, USAF, Randolph Air Force Base, Texas

A group of seven dogs was given a daily 6–8 hour exposure to CO levels of 0.08 to 0.10% for a period of 36 weeks and their tolerance to CO was compared with that of normal dogs, altitude-acclimatized dogs and dogs transfused with blood from normal dogs. The observed increased tolerance to CO was attributed primarily to the increase in concentration of the hemoglobin pigments of the blood. With this increased hemoglobin there was a greater reserve of the pigment for O₂ transport at a given concentration level of HbCO. The time required to reach an equilibrium level with a given Pco was greater for the acclimatized than for the normal animals. The Pa_OO2 was always lower than Pa_OO2 during the acclimatization period. There was no evidence of factors, other than hematologic, which increased the tolerance of the dogs to CO. Animals subjected to other hypoxic stress such as altitude, or normal animals transfused with normal blood to increase the hematocrit level, showed increased tolerance similar to that accomplished by chronic exposure to low CO levels.