VESTPD as a measure of ventilatory acclimatization to hypobaric hypoxia

This study compared the ventilation response to an incremental ergometer exercise at two altitudes: 633 mmHg (resident altitude = 1,600 m) and following acute decompression to 455 mmHg (approximate to 4,350 m altitude) in eight male cyclists and runners. At 455 mmHg, the VESTPD at RER < 1.0 was significantly lower and the VEBTPS was higher because of higher breathing frequency; at VO(2)max, both VESTPD and VEBTPS were not significantly different. As percent of VO(2)max, the VEBTPS was nearly identical and VESTPD was 30% lower throughout the exercise at 455 mmHg. The lower VESTPD at lower pressure differs from two classical studies of acclimatized subjects (Silver Hut and OEII), where VESTPD at submaximal workloads was maintained or increased above that at sea level. The lower VESTPD at 455 mmHg in unacclimatized subjects at submaximal workloads results from acute respiratory alkalosis due to the initial fall in HbO(2) (approximate to 0.17 pHa units), reduction in PACO2 (approximate to 5 mmHg) and higher PAO(2) throughout the exercise, which are partially pre-established during acclimatization. Regression equations from these studies predict VESTPD from VO2 and P-B in unacclimatized and acclimatized subjects. The attainment of ventilatory acclimatization to altitude can be estimated from the measured vs. predicted difference in VESTPD at low workloads after arrival at altitude.