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The effects of a six week sea level exposure on the cardiac output of high altitude Quechua natives Davidson, Robert Bruce


Six healthy males (mean age 34 +/- 1.9) from La Raya, Peru served as subjects in a study of the effects of a six week sea level exposure on the cardiac output of high altitude natives. The subjects had resided, as had their ancestors, at or above 13,000 ft for their entire lives. Cardiac output was measured upon exposure to sea level, three weeks later, and after six weeks at sea level using a CO₂ rebreathing protocol, and also upon exposure and six weeks later using a nuclear ventriculogram protocol. Measurements of cardiac output, stroke volume, and heart rate, were taken at rest and then workloads corresponding to 40%, 60%, (and in the case of the ventriculograms) 90% of maximal oxygen consumption. The results were analyzed using repeated measures ANOVA to determine if significant changes occurred over time. Stroke volume increased 21% and cardiac output increased 28% averaged across intensity, for the nuclear ventriculogram protocol, but neither of these changes were found to be significant (p=.089 and .095 respectively). For the CO₂ rebreathing protocol cardiac output was found to increase significantly over time (p=.042), while the increase in stroke volume was non significant (p=.073). Non significant changes were also found in HR (p=.291), and O₂ delivery (p=.342), while significant changes were found in Hgb (which decreased an average of 16%) and VO₂ (which decreased an average of 23%) (p=.0001 and .023 respectively). It was found that over time at sea level slight in most cases non significant, increases in cardiac output, stroke volume, and heart rate all had the additive effect of compensating for the significant decrease found in the haemoglobin values. These contrary changes had the net effect of allowing the oxygen delivery to the tissues to remain essentially constant.

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