Peripheral hypercapnic chemosensitivity at rest and progressive exercise intensities in males and females.

Peripheral hypercapnic chemosensitivity (PHC) is the ventilatory response to hypercapnia and is enhanced with acute whole-body exercise. However, little is known about the mechanism(s) responsible for the exercise related increase in PHC and if progressive exercise leads to further augmentation. We hypothesized that unloaded cycle exercise (0W) would increase PHC but progressively increasing the intensity would not further augment the response. Twenty healthy subjects completed 2 testing days. Day 1 was a maximal exercise test on a cycle ergometer to determine peak power output (Wmax ). Day 2 consisted of six 12-minute stages: (i) rest on chair, (ii) rest on bike, (iii) 0W unloaded cycling, (iv) 25% Wmax , (v) 50% Wmax , and (vi) ~70% Wmax with ~10 min of rest between each exercise stage. In each stage, PHC was assessed via 2 breaths of 10% CO2 (~21% O2 ) repeated 5 times with ~45s between each to ensure end-tidal CO2 (PET CO2 ) and ventilation returned to baseline. Pre-stimulus PET CO2 was not different between rest and unloaded cycling ( p =0.478). There was a significant increase in PHC between seated rest and 25% Wmax (0.71±0.37 vs. 1.03±0.52 LmmHg-1 min-1 , respectively p =0.0006), and between seated rest and unloaded cycling (0.71±0.37 vs. 1.04±0.4 LmmHg-1 min-1 , respectively p =0.0017). There was no effect of exercise intensity on PHC (1.03±0.52 vs. 0.95±0.58 vs. 1.01±0.65 LmmHg-1 min-1 for 25, 50 and 70% Wmax , p =0.44). The increased PHC response from seated rest to unloaded and 25% Wmax , but no effect of exercise intensity suggests a possible feedforward/feedback mechanism causing increased PHC sensitivity through the act of cycling.