Maximal Cardiorespiratory Responses During Acute Exposure to 4300 M; Challenging Previous Research Using a Multi-Study Database

Abstract

Maximal oxygen uptake (VO2max) decreases ∼ 27% during an acute (< 24 h) exposure to 4300 m in direct relation to the decline in arterial oxygen saturation at maximal effort (SaO2max). However, previous research suggests that maximal heart rate (HRmax) and pulmonary ventilation (VEmax) are not changed from sea level (SL) during an acute exposure to 4300 m (Reeves, 2002; Wolfel and Levine, 2001) and thus unlikely to contribute to the decline in VO2max. PURPOSE: Investigate possible relationships between the change in VO2max, SaO2max, HRmax, and VEmax from SL during an acute (< 24 h) exposure to 4300 m altitude (AA) using an USARIEM database encompassing 7 studies from 1992 to 2004. METHODS: Data were retrospectively analyzed in 88 male lowlanders (27±5 yr, 76±11 kg; ±SD) that performed a VO2max test on a cycle ergometer or treadmill at SL and within 24-h exposure to either Pikes Peak (4300 m) or the hypobaric chamber (4300 m, 446 mmHg). At maximal effort, VO2max, SaO2max, HRmax, and VEmax were measured. Pearson-product correlations were calculated for the relationships between the change in VO2max, SaO2max, HRmax, and VEmax from SL to AA. RESULTS: From SL to AA, there was a 27% decrease(P=0.0001) in VO2max (4.0±0.7 to 2.9±0.5 1·min-1) and SaO2max(96±2 to 71±8%), a 5% decrease (P=0.0001) in HRmax (186±10 to 177±10 beats·min−1), and 6% increase (P=0.0001) in VEmax (BTPS) (146±30 to 155±33 1·min−1). The change in VO2max was correlated with change in SaO2max (r=0.29; p=0.04) and VEmax (r=0.29, p=0.007) but not HRmax (r=0.07, p=0.62). CONCLUSIONS: These results confirm the ∼27% decrease in VO2max and SaO2max during an acute exposure to 4300 m. In contrast to previous research, there was a highly significant decrease in HRmax and increase in VEmax during maximal effort. It appears that lowlanders who demonstrate a greater increase in VEmax from SL to 4300 m also have less of a decline in VO2max from SL to 4300 m whereas the decline in HRmax had little impact on the decrement in VOmax.