Early onset of pulmonary gas exchange disturbance during progressive exercise in healthy active men

1 HYLAB, Clinique du Mail, F-38100 Grenoble, France; 2 Laboratoire de physiologie de l'exercice, 69921 Lyon Sud, France; and 3 Department of Kinesiology and Physical Education, McGill University, Montreal, Canada H2W IS4 10.1152/japplphysiol.00630.1999. Some recent studies of competitive athletes have shown exercise-induced hypoxemia to begin in submaximal exercise. We examined the role of ventilatory factors in the submaximal exercise gas exchange disturbance (GED) of healthy men involved in regular work-related exercise but not in competitive activities. From the 38 national mountain rescue workers evaluated (36 ± 1 yr), 14 were classified as GED and were compared with 14 subjects matched for age, height, weight, and maximal oxygen uptake ( O 2 max ; 3.61 ± 0.12 l/min) and showing a normal response (N). Mean arterial P O 2 was already lower than N ( P = 0.05) at 40% O 2 max and continued to fall until O 2 max (GED: 80.2 ± 1.6 vs. N: 91.7 ± 1.3 Torr). A parallel upward shift in the alveolar-arterial oxygen difference vs. % O 2 max relationship was observed in GED compared with N from the onset throughout the incremental protocol. At submaximal intensities, ideal alveolar P O 2 , tidal volume, respiratory frequency, and dead space-to-tidal volume ratio were identical between groups. As per the higher arterial P CO 2 of GED at O 2 max , subjects with an exaggerated submaximal alveolar-arterial oxygen difference also showed a relative maximal hypoventilation. Results thus suggest the existence of a common denominator that contributes to the GED of submaximal exercise and affects the maximal ventilatory response. alveolar-arterial oxygen difference; exercise ventilation, arterial hypoxemia