Effects of enhanced human chemosensitivity on ventilatory responses to exercise

It is not clear what the effects of different types of intermittent hypoxia have on human exercise ventilation. The purpose of this study was to determine whether short-duration intermittent hypoxia, and the subsequent augmentation of the hypoxic ventilatory response (HVR), would lead to an increase in ventilatory responses during exercise at sea level. It was hypothesized that subjects exposed to short-duration intermittent hypoxia would have a greater increase in the ventilatory response to exercise compared to those exposed to long-duration intermittent hypoxia. Subjects (n = 17, male) were randomly assigned to short-duration intermittent hypoxia (SDIH: 5 min of 12% O2 separated by 5 min of normoxia for 1 h) or long-duration intermittent hypoxia (LDIH: 30 min of 12% O2). Both groups had 10 exposures over a 12 day period. The HVR was measured on days 1 and 12. Maximal oxygen consumption (VO2max) was determined using a ramped cycle exercise test. Maximal exercise data were not different (P > 0.05) between SDIH and LDIH groups or following intermittent hypoxia. Minute ventilation, tidal volume and respiratory frequency were compared at 20, 40, 60, 80 and 100% of VO2max . There was no difference in the ventilatory responses at any intensity of exercise following the intermittent hypoxia period. The HVR was significantly increased following the intermittent hypoxia intervention (P < 0.05) but was not different between SDIH and LDIH (P > 0.05). The relationships between HVR and VO2max were non-significant on day 1 (r = 0.30) and day 12 (r = 0.47; P > 0.05). Our findings point to a lack of functional significance of increasing HVR via intermittent hypoxia on ventilatory responses to exercise at sea level.