V_ESTPD as a measure of ventilatory acclimatization to hypobaric hypoxia

Abstract

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 (≈4,350 m altitude) in eight male cyclists and runners. At 455 mmHg, the V E STPD at RER <1.0 was significantly lower and the V E BTPS was higher because of higher breathing frequency; at VO 2 max, both V E STPD and V E BTPS were not significantly different. As percent of VO 2 max, the V E BTPS was nearly identical and V E STPD was 30% lower throughout the exercise at 455 mmHg. The lower V E STPD at lower pressure differs from two classical studies of acclimatized subjects (Silver Hut and OEII), where V E STPD at submaximal workloads was maintained or increased above that at sea level. The lower V E STPD at 455 mmHg in unacclimatized subjects at submaximal workloads results from acute respiratory alkalosis due to the initial fall in HbO 2 (≈0.17 pHa units), reduction in PACO 2 (≈5 mmHg) and higher PAO 2 throughout the exercise, which are partially pre-established during acclimatization. Regression equations from these studies predict V E STPD from VO 2 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 V E STPD at low workloads after arrival at altitude.

Variations in exercise ventilation in hypoxia will affect oxygen uptake

“…These data were obtained during a research study previously reported with a different focus (21)(22)(23). Eight male volunteers were cyclists and runners consistently performing an average of 6 hr/ wk of moderate and 2-3 hr/wk of vigorous exercise during the year prior to, and during the study.…”

“…Each 35-W work rate increment was divided into four quarters to coincide with the 15-s measurement intervals. The average number of recorded points for the 16 tests was 22 (range: [16][17][18][19][20][21][22][23][24][25][26]. The measured values for the tests at 633 and 455 mmHg were then superimposed and compared at identical work rates.…”