Re-examination of the incidence of exercise-induced hypoxaemia in highly trained subjects.

The purpose of this study was to examine the occurrence of exercise-induced hypoxaemia (EIH) during maximal exercise in highly trained athletes. Eleven trained cyclists (mean(s.d.) age 23(3.5) years; mean(s.d.) VO2max 66.9(4.8) ml kg-1min-1) performed a continuous, multistage (270 kpm min-1) cycle ergometer test to exhaustion. Measurements of arterial oxygen-haemoglobin saturation (%HbO2) were obtained simultaneously at rest, every 2 min during exercise, and at maximum exercise capacity from arterial blood sampling (%SaO2) and ear oximetry (%SpO2). Exercise induced hypoxaemia (%HbO2 < or = 91%) was present in 64% of the athletes examined when EIH was determined using pulse oximetry, whereas none of the subjects exhibited EIH when %HbO2 was determined using arterial blood. At rest the values for %HbO2 were similar with mean(s.d.) %SaO2 being 97.3(0.6)% and mean(s.d.) %SpO2 being 96.5(1.6)%. During exercise, statistically significant differences were found for %HbO2 between arterial blood and ear oximetry at the 6-min, 8-min, and maximal exercise sampling times (repeated measures analysis of variance, P < 0.05). The results indicate that ear oximetry overestimates the incidence of EIH and underestimates the oxyhaemoglobin saturation in highly trained cyclists during exercise in comparison with those measurements made from arterial blood.