White Mountain Expedition 2019: The Impact of Sustained Hypoxia on Cerebral Blood Flow Responses and Tolerance to Simulated Hemorrhage

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2021

Authors

Rosenberg, Alexander
Anderson, Garen K.
Barnes, Haley J.
Bird, Jordan D.
Pentz, Brandon
Byman, Britta
Jendzjowsky, Nicholas
Wilson, Richard
Day, Trevor
Rickards, Caroline

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Abstract

Trauma-induced hemorrhage can occur at high altitude (HA) from a variety of causes, including battlefield injuries, vehicle/air accidents, and major falls. As the partial pressure of oxygen decreases with ascent to altitude, compensatory increases in cerebral blood flow (CBF) and oxygen delivery occur to preserve cerebral tissue oxygenation (ScO2). Accordingly, we hypothesized that tolerance to simulated hemorrhage (via lower body negative pressure, LBNP) following sustained exposure to HA would be similar compared to low altitude (LA) due to compensatory increases in CBF and oxygen delivery, and the subsequent preservation of ScO2. Healthy adults (N=8;4F/4M) participated in LBNP protocols to presyncope at LA (1045m) and at HA (3800m) following 5-7 days of acclimatization. Arterial pressure, heart rate (HR), stroke volume (SV), internal carotid artery blood flow (ICA BF), and ScO2 were measured continuously. Time to presyncope was similar between conditions (LA:1276±304s vs. HA:1208±306s;P=0.58). Similar maximal responses to LBNP were observed at LA and HA in mean arterial pressure (LA:-16±6% vs. HA:-16±6%;P=0.85), SV (LA:-57±14% vs. HA:-60±13%;P=0.39), and HR (LA:+69±33% vs. HA:+65±23%;P=0.71). ICA BF was elevated at baseline at HA vs. LA (P=0.04) and decreased with LBNP under both conditions (P< 0.0001). There was no effect of altitude (P=0.59) on ScO2, which decreased with LBNP under both conditions (P=0.09). Sustained exposure to hypoxia at an altitude of 3800m does not affect tolerance to simulated hemorrhage in adults, which may be due to 1) similar cardiovascular reflex responses, and 2) compensatory increases in CBF and subsequent preservation of ScO2.

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Research Appreciation Day Award Winner - 2021 Graduate School of Biomedical Sciences Postdoctoral Oral Presentations - 1st Place
Research Appreciation Day Award Winner - 2021 Graduate School of Biomedical Sciences Postdoctoral Oral Presentations - 1st Place

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