Elevated End-Tidal CO₂ in Trained Underwater Swimmers

¹ From the National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Maryland

A comparison of the response of trained and untrained swimmers to the exercise involved in underwater swimming revealed that end-tidal CO₂ levels were elevated in the trained swimmers. The breathing pattern in the trained swimmers (slow deep breaths with long postinspiratory pauses) might have accentuated the large cyclic variation in alveolar CO₂ accompanying the respiratory cycle during exercise thus resulting in an elevated end-tidal CO₂ without an elevated average alveolar or arterial CO₂ tension. It was also suggested that an increase in the average alveolar CO₂ tension might have been partially the result of a significantly lower oxygen ventilation equivalent in the trained swimmers as compared to the nontrained subjects.

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