A Four-Way Comparison of Cardiac Function with Normobaric Normoxia, Normobaric Hypoxia, Hypobaric Hypoxia and Genuine High Altitude.
BACKGROUND
There has been considerable debate as to whether different modalities of simulated hypoxia induce similar cardiac responses.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Department of Cardiology, Poole Hospital NHS Foundation trust, Poole, United Kingdom.|Dept of Postgraduate Medical Education, Bournemouth University, Bournemouth, United Kingdom.|Research Institute, for Sport, Physical Activity and Leisure, Leeds Beckett University, Leeds, United Kingdom.
Christopher John
CJ
Boos
Research Institute, for Sport, Physical Activity and Leisure, Leeds Beckett University, Leeds, United Kingdom.
John Paul
JP
O'Hara
Research Institute, for Sport, Physical Activity and Leisure, Leeds Beckett University, Leeds, United Kingdom.|James Cook University Hospital, Middlesbrough, TS4 3BW, United Kingdom.|Defence Medical Services, Lichfield, United Kingdom.
Adrian
A
Mellor
Defence Medical Services, Lichfield, United Kingdom.|RAF Centre of Aviation Medicine, RAF Henlow, Beds, SG16 6DN, United Kingdom.|Division of Anaesthesia, University of Cambridge, Box 93, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, United Kingdom.
Peter David
PD
Hodkinson
Research Institute, for Sport, Physical Activity and Leisure, Leeds Beckett University, Leeds, United Kingdom.
Costas
C
Tsakirides
Research Institute, for Sport, Physical Activity and Leisure, Leeds Beckett University, Leeds, United Kingdom.
Nicola
N
Reeve
Research Institute, for Sport, Physical Activity and Leisure, Leeds Beckett University, Leeds, United Kingdom.
Liam
L
Gallagher
Defence Medical Services, Lichfield, United Kingdom.|RAF Centre of Aviation Medicine, RAF Henlow, Beds, SG16 6DN, United Kingdom.
Nicholas Donald Charles
ND
Green
Research Institute, for Sport, Physical Activity and Leisure, Leeds Beckett University, Leeds, United Kingdom.|Defence Medical Services, Lichfield, United Kingdom.|Northumbria and Newcastle NHS Trusts, Wansbeck General and Royal Victoria Infirmary, Newcastle, United Kingdom.|University of Newcastle, Newcastle upon Tyne, United Kingdom.
David Richard
DR
Woods
D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D000531:Altitude; D000532:Altitude Sickness / Q000503:physiopathology*; D001274:Atmospheric Pressure; D002302:Cardiac Output / Q000502:physiology; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D010100:Oxygen / Q000378:metabolism; D011446:Prospective Studies; D014655:Vascular Resistance / Q000502:physiology; D016278:Ventricular Function, Right / Q000502:physiology*; D055815:Young Adult
D010100:Oxygen