The Relationship of Acute Mountain Sickness to Arterial Oxygen Saturation at Altitudes of 3,324 to 5,176 m

Abstract

Compensation for hypoxia at altitude through increased blood flow helps maintain oxygen delivery (Wolff, Adv Exp Med Biol 599:169–182, 2007). However, the relationship of acute mountain sickness (AMS) to the hypoxia of altitude is poorly understood. In the present study arterial oxygen saturation (SaO₂) and heart rate (HR) were measured twice daily at altitude in eight subjects both at rest (SaO₂rest; HRrest) and separately during exercise (SaO₂ex; HRex). Seven subjects completed a 28-day expedition (one subject only 20 days) at altitudes 3,324–5,176 m (55–68 kPa). The AMS score (Hackett PH, Oeltz O (1992) The Lake Louis Consensus on the definition and quantification of altitude illness. In: Sutton JR, Coates G, Houston SC (eds) Hypoxia and mountain medicine. Queen City Printers, Burlington, pp 327–330) was recorded daily. In seven of the eight subjects HRrest correlated with SaO₂rest (p ≤ 0.01). HR × SaO₂ a surrogate for oxygen delivery (DO₂) remained constant. Individual mean SaO₂rest, HRrest, SaO₂ex, HRex and AMS scores were calculated (SaO₂rest 81.3–93.2%; HRrest 70–106 bpm. Mean individual SaO₂ values for exercise (SaO₂ex) correlated with, but were significantly lower than SaO₂rest (SaO₂ex = 1.3363 × SaO₂rest – 33.734, r = 0.975, p < 0.001). Mean AMS scores correlated with mean SaO₂rest (r = 0.926, p = 0.002) and SaO₂ex (r = 0.917, p = 0.003) in the seven 28-day subjects. AMS is therefore related to SaO₂, which, in turn, indicates (inversely) the degree of respiratory compensation for ambient hypoxia. An earlier version of this work was presented to the UK Physiological Society (Parks et al., Proc Physiol Soc 14:PC2, 2009).