Do cardiopulmonary exercise tests predict summit success and acute mountain sickness? A prospective observational field study at extreme altitude.

Objective: During a high-altitude expedition, the association of cardiopulmonary exercise testing (CPET) parameters with the risk of developing acute mountain sickness (AMS) and the chance of reaching the summit were investigated.

Methods: Thirty-nine subjects underwent maximal CPET at lowlands and during ascent to Mount Himlung Himal (7126 m) at 4844 m, before and after 12 days of acclimatisation, and at 6022 m. Daily records of Lake-Louise-Score (LLS) determined AMS. Participants were categorised as AMS+ if moderate to severe AMS occurred.

Results: Maximal oxygen uptake (V̇O) decreased by 40.5%±13.7% at 6022 m and improved after acclimatisation (all p<0.001). Ventilation at maximal exercise (VE) was reduced at 6022 m, but higher VE was related to summit success (p=0.031). In the 23 AMS+ subjects (mean LLS 7.4±2.4), a pronounced exercise-induced oxygen desaturation (ΔSpO) was found after arrival at 4844 m (p=0.005). ΔSpO >-14.0% identified 74% of participants correctly with a sensitivity of 70% and specificity of 81% for predicting moderate to severe AMS. All 15 summiteers showed higher V̇O (p<0.001), and a higher risk of AMS in non-summiteers was suggested but did not reach statistical significance (OR: 3.64 (95% CI: 0.78 to 17.58), p=0.057). V̇O ≥49.0 mL/min/kg at lowlands and ≥35.0 mL/min/kg at 4844 m predicted summit success with a sensitivity of 46.7% and 53.3%, and specificity of 83.3% and 91.3%, respectively.

Conclusion: Summiteers were able to sustain higher VE throughout the expedition. Baseline V̇O below 49.0 mL/min/kg was associated with a high chance of 83.3% for summit failure, when climbing without supplemental oxygen. A pronounced drop of SpO at 4844 m may identify climbers at higher risk of AMS.