Cardio-respiratory, oxidative stress and acute mountain sickness responses to normobaric and hypobaric hypoxia in prematurely born adults.

Abstract

We compared the effects of hypobaric and normobaric hypoxia on select cardio-respiratory responses, oxidative stress and acute mountain sickness (AMS) severity in prematurely born individuals, known to exhibit blunted hypoxic ventilatory response. Sixteen prematurely born but otherwise healthy males underwent two 8-h hypoxic exposures under: (1) hypobaric hypoxic [HH; terrestrial altitude 3840m; PiO2:90.2 (0.5) mmHg; BP: 478 (2) mmHg] and (2) normobaric hypoxic [NH; PiO2:90.6 (0.9) mmHg; FiO2:0.142 (0.001)] condition. Resting values of capillary oxyhemoglobin saturation (SpO2), heart rate (HR) and blood pressure were measured before and every 2h during the exposures. Ventilatory responses and middle cerebral artery blood flow velocity (MCAv) were assessed at rest and during submaximal cycling before and at 4 and 8h. Plasmatic levels of selected oxidative stress and antioxidant markers and AMS symptoms were also determined at these time points. HH resulted in significantly lower resting (P = 0.010) and exercise (P = 0.004) SpO2 as compared to NH with no significant differences in the ventilatory parameters, HR or blood pressure. No significant differences between conditions were found in resting or exercising MCAv and measured oxidative stress markers. Significantly lower values of ferric-reducing antioxidant power (P = 0.037) were observed during HH as opposed to NH. AMS severity was higher at 8h compared to baseline (P = 0.002) with no significant differences between conditions. These data suggest that, in prematurely born adults, 8-h exposure to hypobaric, as opposed to normobaric hypoxia, provokes greater reductions in systemic oxygenation and antioxidant capacity. Further studies investigating prolonged hypobaric exposures in this population are warranted. NCT02780908 (ClinicalTrials.gov).