Ventilatory Responsiveness during Exercise and Performance Impairment in Acute Hypoxia

Introduction: An adequate increase in minute ventilation to defend arterial oxyhemoglobin saturation (SpO(2)) during hypoxic exercise is commonly viewed as an important factor contributing to large inter-individual variations in the degree of exercise performance impairment in hypoxia. Although the hypoxic ventilatory response (HVR) could provide insight into the underpinnings of such impairments, it is typically measured at rest under isocapnic conditions. Thus, we aimed to determine whether 1) HVR at rest and during exercise are similar and 2) exercise HVR is related to the degree of impairment in cycling time trial (TT) performance from normoxia to acute hypoxia (Delta TT). Methods: Sixteen endurance-trained men ((V)over dotO(2peak), 62.5 +/- 5.8 mL.kg(-1).min(-1)) performed two poikilocapnic HVR tests: one during seated rest (HVRREST) and another during submaximal cycling (HVREX). On two separate visits, subjects (n = 12) performed a 10-km cycling TT while breathing either room air (FiO2 = 0.21) or hypoxic gas mixture (FiO2 = 0.16) in a randomized order. Results: HVREX was significantly (P < 0.001) greater than HVRREST (1.52 +/- 0.47 and 0.22 +/- 0.13 L.min(-1).%SpO(2)(-1), respectively), and these measures were not correlated (r = -0.16, P = 0.57). Delta TT was not correlated with HVRREST (P = 0.70) or HVREX (P = 0.54), but differences in ventilation and end-tidal CO2 between hypoxic and normoxic TT and the ventilatory equivalent for CO2 during normoxic TT explained similar to 85% of the variance in performance impairment in acute hypoxia (P < 0.01). Conclusion: We conclude that 1) HVR is not an appropriate measure to predict the exercise ventilatory response or performance impairments in acute hypoxia and 2) an adequate and metabolically matched increase in exercise ventilation, but not the gain in the ventilatory response to hypoxia, is essential for mitigating hypoxia-induced impairments in endurance cycling performance.

Automated summary

The study found that the hypoxic ventilatory response at rest and during exercise are not correlated, and in acute hypoxia, factors such as ventilation and CO2 release play a significant role in performance impairment.