MEDEX 2015: Prophylactic Effects of Positive Expiratory Pressure in Trekkers at Very High Altitude

Thomas Rupp; Claire Maufrais; Guillaume Walther; François Esteve; Jamie Hugo Macdonald; Pierre Bouzat; Samuel Verges

doi:10.3389/fphys.2021.710622

MEDEX 2015: Prophylactic Effects of Positive Expiratory Pressure in Trekkers at Very High Altitude

Front Physiol. 2021 Sep 21:12:710622. doi: 10.3389/fphys.2021.710622. eCollection 2021.

Authors

Thomas Rupp¹, Claire Maufrais^{2

3}, Guillaume Walther², François Esteve⁴, Jamie Hugo Macdonald⁵, Pierre Bouzat⁶, Samuel Verges³

Affiliations

¹ Inter-University Laboratory of Human Movement Science (LIBM), University Savoie Mont Blanc, Chambéry, France.
² Laboratoire de Pharm-Ecologie Cardiorespiratoire (LAPEC EA4278), Avignon University, Avignon, France.
³ HP2 Laboratory, INSERM, Grenoble Alpes University, Grenoble, France.
⁴ RSRM EA7442, ID17-ESRF, Grenoble Alpes University, Grenoble, France.
⁵ Extremes Research Group, School of Sport, Health and Exercise Sciences, Bangor University, Bangor, United Kingdom.
⁶ Pôle Anesthésie Réanimation, Grenoble Alpes University Hospital, Grenoble, France.

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, 0-45^th min) and with PEP = 10 cmH₂O (PEP₁₀, 46-90^th 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.

Keywords: PEP breathing; altitude illness; cardiac function; cerebral perfusion; extreme environment; hypoxia; medical expedition; tissue oxygenation.