Effects of exercise on peripheral hypercapnic chemosensitivity during high altitude acclimatization

Hypercapnic sensitivity of the peripheral chemoreceptors can be enhanced by sustained exposure to high altitude (HA), 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, 1,100 m) and high altitude (HA; La Paz, Bolivia, 3,500 m). Both tests were conducted on a cycle ergometer with submaximal tests following 2-5 days after arrival at LA and 6-10 days after arrival at HA. The PHC was assessed at rest and throughout two 10-min submaximal exercise bouts by giving two breaths of a hypercapnic inspirate (10% CO₂, 21% O₂) and was repeated five times each separated by 40-60 s. The PHC response was quantified as the quotient of the change in ventilation (V̇_I) over the change in end-tidal PCO₂ ([Formula: see text]) following each hypercapnic stimulus. At HA, compared with LA, there was a greater resting V̇_I (15 ± 3 vs. 12 ± 2 L·min^-1, <i>P</i> = 0.0016) and lower resting [Formula: see text] (27 ± 3 vs. 37 ± 4 mmHg, <i>P</i> < 0.0001). Resting PHC at HA was greater than LA (1.8 ± 0.7 vs. 0.9 ± 0.4 L·min^-1·mmHg^-1, <i>P</i> < 0.0001). The increase in PHC induced by exercise was not different between LA and HA (+38 ± 60% vs. +24 ± 51%, <i>P</i> = 0.18). Sustained high-altitude exposure increases resting PHC, and exercise at HA sensitizes the peripheral chemoreceptors to a similar extent as LA.<b>NEW & NOTEWORTHY</b> Temporary residence at 3,500 m resulted in a greater resting peripheral hypercapnic chemosensitivity than at 1,100 m. Exercise increases hypercapnic sensitivity of the peripheral chemoreceptors from rest at both 1,100 m and 3,500 m, but the magnitude of increase from rest was not different between altitudes. The mechanism for the increased peripheral hypercapnic chemosensitivity induced by exercise is likely unaffected by altitude exposure.