title: Evidence for an alveolar-arterial PO2 gradient threshold during incremental exercise.
abstract: Examination of the alveolar-to-arterial O2 tension (A-a PO2 difference) provides a method of examining the efficiency of pulmonary gas exchange during exercise. At present, considerable confusion exists as to the exact pattern of the A-a PO2 difference during incremental exercise. We tested the hypothesis that the A-a PO2 difference during incremental exercise is alinear with respect to metabolic rate. Measurements of the A-a PO2 difference were made on six healthy male subjects during incremental exercise under sea level conditions (PIO2 = 149 torr). An alinear model best described the relationship between the A-a PO2 difference and metabolic rate; only small increases in the A-a PO2 difference occurred at low work rates followed by a rapid increase at higher work rates. The existence of a "A-a PO2 difference threshold" was mathematically confirmed by the use of a computer algorithm to define inflection points. These data provide evidence that the relationship between the A-a PO2 difference and metabolic rate is alinear and that a metabolic threshold exists for a rapid increase in the A-a PO2 difference. We conclude that the efficiency of pulmonary gas exchange during exercise is unaltered from rest during low-to-moderate power outputs, however, high intensity exercise compromises pulmonary gas exchange efficiency as evidenced by a significant widening of the A-a PO2 difference.
authors.affiliation: Department of Physical Therapy, University of Florida, Gainesville 32611.
authors.forename: S K
authors.initials: SK
authors.lastname: Powers
authors.forename: S
authors.initials: S
authors.lastname: Dodd
authors.forename: D D
authors.initials: DD
authors.lastname: Criswell
authors.forename: J
authors.initials: J
authors.lastname: Lawler
authors.forename: D
authors.initials: D
authors.lastname: Martin
authors.forename: S
authors.initials: S
authors.lastname: Grinton
mesh_terms: D000328:Adult; D015308:Anaerobic Threshold; D001784:Blood Gas Analysis; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D007773:Lactates / Q000097:blood; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012119:Respiration
chemical_list: D007773:Lactates