Measurement of cardiopulmonary performance during acute exposure to a 2440-m equivalent atmosphere

Each of 20 subjects was given two Bruce Protocol symptom-limited maximum treadmill stress tests breathing sea-level compressed air (20.9% 02) for one test and a 2440-m equivalent (15.5% 02) for the other. Subjects ranged from 18-38 years of age; 15 were male and 5 female. Half of the population was tested first on the sea-level air, the other half on the altitude mixture. Real time measurements included heart rate, blood pressure, exercise time, oxygen consumption, carbon dioxide production, respiratory rate and volume, CO2 production, and several other derived parameters. A significant difference existed between measured VO2 max (p less than 0.002) and exercise time (p less than 0.004) for the two conditions. Mean differences were 8.3% and 6.7%, respectively. No significant differences were observed in heart rate or the recovery time to a respiratory quotient of less than 1. Hemoglobin saturation, as measured by an ear oximeter, averaged 95% for sea-level and 91% for the 2440-m equivalent gases. These results support a 2440-m equivalent contingency atmosphere in the NASA Space Shuttle prior to donning a low pressure suit for the purpose of reducing nitrogen washout times.