Journal Article

A Four-Way Comparison of Cardiac Function with Normobaric Normoxia, Normobaric Hypoxia, Hypobaric Hypoxia and Genuine High Altitude

Mellor, Adrian, Hodkinson, Peter David, Gallagher, Liam, Woods, David Richard, Green, Nicholas Donald Charles, Tsakirides, Costas, O’Hara, John Paul, Boos, Christopher John, Reeve, Nicola

2016

Overview

There has been considerable debate as to whether different modalities of simulated hypoxia induce similar cardiac responses. This was a prospective observational study of 14 healthy subjects aged 22-35 years. Echocardiography was performed at rest and at 15 and 120 minutes following two hours exercise under normobaric normoxia (NN) and under similar PiO2 following genuine high altitude (GHA) at 3,375 m, normobaric hypoxia (NH) and hypobaric hypoxia (HH) to simulate the equivalent hypoxic stimulus to GHA. All 14 subjects completed the experiment at GHA, 11 at NN, 12 under NH, and 6 under HH. The four groups were similar in age, sex and baseline demographics. At baseline rest right ventricular (RV) systolic pressure (RVSP, p = 0.0002), pulmonary vascular resistance (p = 0.0002) and acute mountain sickness (AMS) scores were higher and the SpO2 lower (p<0.0001) among all three hypoxic groups (GHA, NH and HH) compared with NN. At both 15 minutes and 120 minutes post exercise, AMS scores, Cardiac output, septal S', lateral S', tricuspid S' and A' velocities and RVSP were higher and SpO2 lower with all forms of hypoxia compared with NN. On post-test analysis, among the three hypoxia groups, SpO2 was lower at baseline and 15 minutes post exercise with GHA (89.3±3.4% and 89.3±2.2%) and HH (89.0±3.1 and (89.8±5.0) compared with NH (92.9±1.7 and 93.6±2.5%). The RV Myocardial Performance (Tei) Index and RVSP were significantly higher with HH than NH at 15 and 120 minutes post exercise respectively and tricuspid A' was higher with GHA compared with NH at 15 minutes post exercise. GHA, NH and HH produce similar cardiac adaptations over short duration rest despite lower SpO2 levels with GHA and HH compared with NH. Notable differences emerge following exercise in SpO2, RVSP and RV cardiac function.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Acclimatization - physiology / Adaptation / Adult / Aerospace medicine / Altitude / Altitude sickness / Altitude Sickness - physiopathology / Atmospheric Pressure / Aviation / Biology and Life Sciences / Blood pressure / Cardiac output / Cardiac Output - physiology / Cardiology / Comparative analysis / Complications and side effects / Demographics / Demography / Echocardiography / Edema / Exercise / Exercise - physiology / Female / Heart / Heart diseases / Heart failure / Heart rate / High altitude / High-altitude environments / Hospitals / Humans / Hypoxia / Hypoxia - physiopathology / Leisure / Male / Medicine and Health Sciences / Observational studies / Oxygen - metabolism / Physical fitness / Physiological aspects / Physiology / Prospective Studies / Research and Analysis Methods / Rest / Sea level / Studies / Systolic pressure / Vascular Resistance - physiology / Ventricle / Ventricular Function, Right - physiology / Young Adult