Abstract
Purpose: Positive expiratory pressure (PEP) breathing has been shown to increase arterial oxygenation during acute hypoxic exposure but the underlying mechanisms and consequences on symptoms during prolonged high-altitude exposure remain to be elucidated.Methods: Twenty-four males (41 ± 16 years) were investigated, at sea level and at 5,085 m after 18 days of trekking from 570 m. Participants breathed through a face-mask with PEP = 0 cmH2O (PEP0, 0–45th min) and with PEP = 10 cmH2O (PEP10, 46–90th min). Arterial (SpO2), quadriceps and prefrontal (near infrared spectroscopy) oxygenation was measured continuously. Middle cerebral artery blood velocity (MCAv, transcranial Doppler), cardiac function (2D-echocardiography), extravascular lung water accumulation (UsLC, thoracic ultrasound lung comets) and acute mountain sickness (Lake Louise score, LLS) were assessed during PEP0 and PEP10.Results: At 5,085 m with PEP0, SpO2 was 78 ± 4%, UsLC was 8 ± 5 (a.u.) and the LLS was 2.3 ± 1.7 (all P < 0.05 versus sea level). At 5,085 m, PEP10 increased significantly SpO2 (+9 ± 5%), quadriceps (+2 ± 2%) and prefrontal cortex (+2 ± 2%) oxygenation (P < 0.05), and decreased significantly MCAv (−16 ± 14 cm.s–1) and cardiac output (−0.7 ± 1.2 L.min–1) together with a reduced stroke volume (−9 ± 15 mL, all P < 0.05) and no systemic hypotension. PEP10 decreased slightly the number of UsLC (−1.4 ± 2.7, P = 0.04) while the incidence of acute mountain sickness (LLS ≥ 3) fell from 42% with PEP0 to 25% after PEP10 (P = 0.043).Conclusion: PEP10 breathing improved arterial and tissue oxygenation and symptoms of acute mountain sickness after trekking to very high altitude, despite reduced cerebral perfusion and cardiac output. Further studies are required to establish whether PEP-breathing prophylactic mechanisms also occur in participants with more severe acute mountain sickness.
Highlights
At high-altitude, the low barometric pressure reduces inspired oxygen partial pressure (PiO2) in mountaineers, workers and travellers, leading to reduced arterial oxygenation that can be responsible for symptoms of acute mountain sickness (AMS)
SpO2 was decreased at high altitude base camp (HABC) compared to SL (P < 0.001, Table 1) and increased with PEP10 compared to PEP0 at HABC (+8.8 to 9.4% on average depending on the time point throughout the 45 min, P < 0.001; Figure 2A)
DABP and MABP were both higher at HABC compared to SL and increased with PEP10 compared to PEP0, whatever the altitude condition
Summary
At high-altitude, the low barometric pressure reduces inspired oxygen partial pressure (PiO2) in mountaineers, workers and travellers, leading to reduced arterial oxygenation that can be responsible for symptoms of acute mountain sickness (AMS). Under heterogeneous experimental designs (e.g., subject characteristics, altitude level, exposure duration, day-time/nighttime evaluation, level/type of PEP, simulated vs terrestrial altitude), 0–23% increase in SpO2 have been reported with PEP breathing (Savourey et al, 1998; Tannheimer et al, 2009; Nespoulet et al, 2013; Lipman et al, 2015; Rupp et al, 2019). Whether PEP breathing would be a safe and efficient method to improve SpO2 and AMS symptoms remains to be assessed in participants reaching very high altitude (>5,000 m) after several days of trekking, as performed nowadays by an increasing amount of people in the Himalaya and Andean Cordillera
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