Cigarette smokers exhibit partial adaptation to hypoxia, maintaining similar cardiovascular responses to altitude and carbon monoxide exposure compared to nonsmokers. However, smokers showed less physiological adjustment to combined altitude and carbon monoxide stress.
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Carbon monoxide (CO) exposure and altitude exposure independently affect oxygen transport and utilization.
The combined effects of CO and hypoxia on exercise physiology in cigarette smokers are not well understood.
Cigarette smoking is associated with chronic CO exposure, potentially leading to adaptations.
Purpose of the Study:
To investigate the physiological responses of cigarette smokers and nonsmokers to exercise under simulated sea level and altitude conditions with varying levels of carbon monoxide.
To determine if chronic CO exposure from smoking confers an advantage or disadvantage during hypoxic exercise.
Main Methods:
Six healthy adult smokers and six nonsmokers (22-34 years old) performed 30-minute bicycle ergometry at 53% of sea level VO2 max.
Four environmental conditions were tested: simulated sea level (SL) with 0.5% carboxyhemoglobin (HbCO), SL with 4.2% HbCO (SLCO), altitude with 0.5% HbCO (A), and altitude with 4.2% HbCO (ACO).
Cardiovascular and ventilatory parameters including heart rate (HR), cardiac output (Qc), stroke volume (SV), arterial-mixed venous oxygen difference (a-vO2), minute ventilation, tidal volume, and finger temperature were measured.
Main Results:
During altitude exposure (A and ACO), smokers and nonsmokers showed similar baseline responses in Qc, SV, and a-vO2.
Under combined altitude and 4.2% HbCO (ACO), nonsmokers increased Qc and SV and decreased a-vO2, indicating enhanced oxygen delivery to tissues.
Smokers did not show these compensatory increases in Qc and SV at ACO, but exhibited a graded increase in HR and reduced finger temperatures, suggesting vasoconstriction and potential partial adaptation to hypoxia.
Conclusions:
Cigarette smokers may possess partial adaptations to hypoxic conditions, as evidenced by their cardiovascular responses during exercise under simulated altitude and carbon monoxide exposure.
Smokers' blunted physiological adjustments in cardiac output and stroke volume at combined altitude and high carboxyhemoglobin levels suggest a different compensatory strategy compared to nonsmokers.
Further research is needed to elucidate the long-term physiological implications of these adaptations in smokers.
