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document
The effects of hypoxemia on cardiac output . A dose-response curve . To establish a dose-response curve for the effects of isocapnic hypoxemia on cardiac output ( CO ) , we studied 20 healthy men , aged 20 to 34 years , using a tight-fitting face mask and an isocapnic partial rebreathing system ( a modified anesthesia machine ) . We blended oxygen and hypoxic gas to achieve arterial oxygen saturations ( SaO2 ) of 80 , 85 , and 90 percent ; subjects also breathed 100 percent oxygen and room air ( RA ) . Target SaO2 and end-tidal carbon dioxide were continuously monitored using an ear oximeter and CO2 gas analyzer . Subjects experienced the five SaO2 measurements in random order . CO was measured noninvasively at approximately two-minute intervals , using continuous-wave Doppler echocardiography . Mean cardiac output increased with increasing hypoxemia from 6.84 L/min at FIo2 1.0 to 8.44 L/min at SaO2 80 percent ( p less than 0.0005 ) ; the increase was entirely due to increased heart rate . We concluded that cardiac output increases significantly in a dose-response manner in response to acute isocapnic hypoxemia in normal persons .
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Intervention_Other
tight-fitting face mask and an isocapnic partial rebreathing system
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Intervention_Control
room air
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Outcome_Physical
cardiac output ( CO )
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Outcome_Physical
CO
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Outcome_Physical
Mean cardiac output
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Outcome_Physical
heart rate
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Outcome_Physical
cardiac output
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Participant_Condition
hypoxemia
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Participant_Sample-size
20
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Participant_Condition
healthy
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Participant_Sex
men
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Participant_Age
aged 20 to 34 years