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

Abstract

Purpose 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. Methods Sixteen prematurely born but otherwise healthy males underwent two 8-h hypoxic exposures under: (1) hypobaric hypoxic [HH; terrestrial altitude 3840 m; P i O 2 :90.2 (0.5) mmHg; BP: 478 (2) mmHg] and (2) normobaric hypoxic [NH; P i O 2 :90.6 (0.9) mmHg; F i O 2 :0.142 (0.001)] condition. Resting values of capillary oxyhemoglobin saturation (SpO 2 ), heart rate (HR) and blood pressure were measured before and every 2 h 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 8 h. Plasmatic levels of selected oxidative stress and antioxidant markers and AMS symptoms were also determined at these time points. Results HH resulted in significantly lower resting (P = 0.010) and exercise (P = 0.004) SpO 2 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 8 h compared to baseline (P = 0.002) with no significant differences between conditions. Conclusion 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. Registration NCT02780908 (ClinicalTrials.gov).

Similar Supine Heart Rate Variability Changes During 24-h Exposure to Normobaric vs. Hypobaric Hypoxia

“…Our study confirmed a higher oxygen saturation in NH vs. HH after 24 h of hypoxic exposure. This is already well described for shorter exposition times ( Aebi et al, 2020 ; Debevec et al, 2020 ) and logically was also already reported in the three support experiments of the present study. However, the latter was still debated for exposures longer than 8 h ( Coppel et al, 2015 ).…”

“…However, recent research suggested that NH and HH are not interchangeable (Fulco et al, 2011;Millet et al, 2012;Saugy et al, 2014Saugy et al, , 2016aCoppel et al, 2015;DiPasquale et al, 2015a;Conkin, 2016) although the differences between HH and NH are still debated (Millet and Debevec, 2020;Richalet, 2020). The following differences were already reported for a matched inspired oxygen pressure (P I O 2 ) in HH vs. NH, respectively: (1) lower pulse oximeter oxygen saturation (S p O 2 ) (Saugy et al, 2016c;Aebi et al, 2020;Debevec et al, 2020); (2) greater performance impairment (Beidleman et al, 2014;Saugy et al, 2016a), both recently confirmed in a study with perfectly controlled environmental factors (Takezawa et al, 2021); (3) higher oxidative stress (Faiss et al, 2013;Ribon et al, 2016); (4) impaired nitric oxide bioavailability (Faiss et al, 2013); (5) greater fluid retention (Loeppky et al, 2005;Conkin and Wessel, 2008), and (6) sleep structure perturbation (Heinzer et al, 2016;Saugy et al, 2016b). In addition, breathing patterns are affected as well: lower tidal volume, lower minute ventilation, higher physiological dead space, and higher respiratory frequency during HH exposure compared to NH (Savourey et al, 2003;Conkin and Wessel, 2008;Saugy et al, 2014).…”

Oxidative Stress and Diseases Associated with High-Altitude Exposure

“…Additionally, a study by Irarrázaval et al [ 41 ] showed glutathione peroxidase (GPx) activity decreased under hypobaric hypoxia conditions; this study emphasized the relationship between oxidative stress and AMS severity. Moreover, adults who had been born prematurely and were later exposed to hypobaric hypoxia (3840 m; 8 h) showed a decrease in antioxidant capacity and an increase in AMS severity [ 42 ].…”

Alterations in acid–base balance and high-intensity exercise performance after short-term and long-term exposure to acute normobaric hypoxic conditions

“…With regard to hypoxia-induced changes in [HCO 3 − ] after several hours of altitude exposure, the kidney responds to a decline in PCO 2 and an increase in pH b through excretion of HCO 3 − known as compensation of respiratory alkalosis. According to the literature, we expected a reduction in [HCO 3 − ] by 1.8 ± 2.5 mmol/L and an [HCO 3 − ] of 21.7 ± 2.5 mmol/L for acute 12-h exposure to an altitude of 3,000 m 5 , regardless of a normobaric or hypobaric acute hypoxic exposure 43 , 44 . However, in Study A, after 12 h of hypoxic exposure, there was a significant reduction in [HCO 3 − ] of only 1.4 ± 0.3 mmol/L and [HCO 3 − ] was 23.3 ± 1.3 mmol/L.…”