Effects of exercise on peripheral hypercapnic chemosensitivity during high altitude acclimatization.

Abstract

Hypercapnic sensitivity of the peripheral chemoreceptors can be enhanced by sustained exposure to high altitude, leading to a greater ventilatory response to hypercapnic stimulus. Exercise is known to also increase peripheral hypercapnic chemosensitivity (PHC) in an intensity-independent manner. We sought to determine how sustained exposure to hypobaric hypoxia influences exercise-induced potentiation of PHC. Twenty-one healthy participants were recruited to complete a maximal and submaximal exercise test at both low altitude (LA; Calgary, Canada, 1100m) and high altitude (HA; La Paz, Bolivia, 3500m). Both tests were conducted on a cycle ergometer with submaximal tests following 2-5 days post arrival at LA and 6-10 days post arrival at HA. The PHC was assessed at rest and throughout two 10-minute submaximal exercise bouts by giving two breaths of a hypercapnic inspirate (10% CO₂, 21%O₂) and was repeated 5 times each separated by 40-60s. The PHC response was quantified as the quotient of the change in ventilation (⩒_I) over the change in end-tidal PCO₂ (P_ETCO₂) following each hypercapnic stimulus. At HA, compared to LA, there was a greater resting ⩒_I (15±3 vs 12±2 l•min^-1, p=0.0016) and lower resting P_ETCO₂ (27±3 vs 37±4 mmHg, p<0.0001). Resting PHC at HA was greater than LA (1.8±0.7 vs 0.9±0.4 l•min^-1•mmHg^-1, p<0.0001). The increase in PHC induced by exercise was not different between LA and HA (+38±60% vs +24±51%, p=0.18). Sustained high-altitude exposure increases resting PHC, and exercise at HA sensitizes the peripheral chemoreceptors to a similar extent as LA.