Noninvasive ambulatory assessment of cardiac function in healthy men exposed to carbon monoxide during upper and lower body exercise

Very little is known about the cardiovascular responses of exercising individuals when exposed to carbon monoxide (CO). Sixteen healthy nonsmoking men aged 18–29 years participated in the study. Using a combination of exposures to CO by breathing from a bag or in an environmental chamber, subjects performed a randomized sequence of brief (5 min) multi-level treadmill and hand-crank exercises on different days at less than 2% carboxyhemoglobin (COHb) and after attaining target levels of 5%, 10%, 15%, and 20% COHb. To assess cardiac function changes we employed noninvasive impedance cardiography (ICG) and three-lead electrocardiograms (ECG). The ICG was used to estimate cardiac output, stroke volume, heart rate, cardiac contractility, and time-to-peak ejection time. The ECG was used to assess myocardial irritability and ischemia, and changes in cardiac rhythm. The results showed that the cardiovascular system compensated for the reduced O2-carrying capacity of the blood by augmenting heart rate, cardiac contractility, and cardiac output for both upper-body and lower-body exercise. While this mechanism served well in submaximal exercise, the enhanced cardiovascular response to exercise was not without physiological costs because it began to fail at moderate levels of CO exposure and exercise. We concluded that young, apparently healthy men can perform submaximal upper and lower-body exercise without overt impairment of cardiovascular function after CO exposures attaining 20% COHb.