Topic Areas: Health Effects of Air Pollution
The primary objective of this study was to determine whether carbon monoxide (CO) exposure at simulated high altitude in human volunteers known to be at risk to CO-induced health effects caused greater changes in respiratory physiological, cardiological or hemodynamic parameters than CO exposures at sea level. A secondary objective was to measure the rate of endogenous CO production in order to refine physiologic models for computing COHb values from CO exposure data. The secondary objective was not fully I realized because the available methods for COHb determination were able to accurately measure the washout of CO from selected exposed subjects, however the small incremental change in the washout slope which would have been attributed to endogenous production was not large enough to reliably detect. On the other hand the physiologic models did accurately predict the COHb concentrations in the subjects exposed under the conditions of this study, suggesting that they could be useful for estimating effects of environmental CO exposures. The National Ambient Air Quality Standard for CO is equivalent to 9 ppm averaged over an 8 hr period. The State of California has established the same standard for sea level areas as the NAAQS, but in addition has established a more stringent 6 ppm standard (averaged over 8 hr) for areas at high altitude, such as Lake Tahoe. Individuals with coronary artery disease were exposed to carbon monoxide (CO) at sea level and at simulated high altitude (2.1 km or 7000 ft). Control exposures were performed with subjects breathing clean air at sea level and simulated high altitude. At conditions which were designed to reduce oxygen delivery to metabolizing tissues by about the same degree (reducing percent of oxygen saturation of arterial blood by 4%) both CO and simulated high altitude reduced time to onset of angina during exercise and increased the amount of cardiac effort to accomplish the same amount of work, compared to sea level, clean air conditions. The effects of CO and increased altitude were additive; statistical analyses using repeated measures analysis of variance did not demonstrate any significant interactions between carbon monoxide and altitude, although there were significant main effects of both factors, The lack of statistical interactions for any of the endpoints examined is consistent with an additive but not a synergistic effect of CO exposure at high altitude.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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