Breathing Pattern and Ventilatory Response to CO₂ during Exercise

Abstract

The aim of this study was to determine during moderate exercise whether response to the CO₂ rebreathing test was dependent on differences in breathing pattern components among individuals recorded before the test and whether differences in tidal volume response and/or breathing frequency response to CO₂ during the test could influence their ventilatory response to CO2. Ten healthy, sedentary male subjects, 20 to 34 years old, participated in the study. Ventilatory response to CO2 was measured by the CO₂ rebreathing method (7% CO₂, 50% O₂). The measure-ments of breathing pattern components and CO₂ rebreathing were made during mild steady State exercise: V̇CO₂ = 20 ml·kg^-1min^-1. We measured the following: 1) tidal volume (VTex) and breathing frequency (fex) before CO₂ rebreathing and 2) ventilatory response to CO₂ (SVEex), tidal volume response to CO₂ (SVTex), and breathing frequency response to CO₂ (Sfex) during the CO₂ rebreathing test. The results showed that SVEex was correlated with VTex (r = 0.89, p < 0.001), fex (r = -0.79, p < 0.01), and Sfex (r = 0.83, p < 0.01). There was no correlation between SVEex and SVTex. A curvilinear relationship existed between SVEex and alveolar ventilation calculated during exercise (r = 0.87, p < 0.001), but there was no correlation with dead space. Sfex was positively correlated with VTex (r = 0.68, p < 0.05) and negatively with fex (r = -0.70, p < 0.05). We concluded that, during moderate exercise, higher tidal volumes measured before CO₂ rebreathing were associated with higher response to the CO₂ rebreathing test and consequently with higher ventilatory response to CO₂. The breathing frequency response to CO₂ measured during CO₂ rebreathing also influenced the ventilatory response to CO₂. Differences in breathing pattern components thus could play a part in the differences in ventilatory response to CO₂ among individuals as measured by the CO₂ rebreathing test during exercise. If the CO₂ rebreathing test is used to measure ventilatory response to CO₂ during exercise, it seems necessary to take into consideration differences in breathing pattern among subjects.

Key words

Breathing pattern - exercise - ventilatory response to CO₂