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

Abstract

BackgroundThere has been considerable debate as to whether different modalities of simulated hypoxia induce similar cardiac responses.Materials and MethodsThis 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 3,375m, normobaric hypoxia (NH) and hypobaric hypoxia (HH) to simulate the equivalent hypoxic stimulus to GHA.ResultsAll 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.ConclusionsGHA, 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.

The Effect of Sex on Heart Rate Variability at High Altitude

“…For example, Karinen et al defined AMS as a LLS of >3 in their study whereas in the study by Willie they a LLS ≥4 was used to define AMS (10,24). In our study we used the Lake Louise Consensus definition (1992) for AMS, which is refers to LLS score of >3 in the presence of headache (4,8,12).…”

The effect of high altitude on central blood pressure and arterial stiffness

“…HA exposure leads to a wide range of complex effects on both the pulmonary and systolic circulation which have been well described. 2,4,5,22 Hypobaric hypoxia leads to widespread sympathetic activation leading to an increase in resting heart rate . [23][24][25] The reported effects on BP are variable and are highly dependent on the degree of hypoxia and speed and duration of exposure.…”

High Altitude Affects Nocturnal Non-linear Heart Rate Variability: PATCH-HA Study

“…These include increases in resting minute ventilation and pulmonary artery systolic pressure (West, 2006). Resting cardiac output increases which is principally driven by a rise in resting heart with little change in stroke volume (Boos et al, 2016b). …”