Influence of exercise and CO2 on breathing pattern of normal man

Abstract

Ventilatory patterns during rest, CO2 inhalation (2, 3 and 4%) and 3 levels of exercise were analyzed in supine men using a canopy system for noninvasive measurements. Changes in tidal volume (VT) and breathing frequency (f) with equal increases in minute ventilation (.ovrhdot.VE) differed significantly during exercise and CO2 inhalation. Increases in .ovrhdot.VE during exercise were accompanied by increases in VT and f. During CO2 inhalation the change in frequency was less than during exercise. When analyzed in terms of inspiratory flow (VT/TI) [inspiratory time] and inspiratory duty cycle (TI/Tot), [inspiratory time plus expiratory time], the response to both stimuli was similar. With increases to 2 .times. control .ovrhdot.VE both TI and Ttot and VT/TI increased. Thereafter only VT/TI increased with increasing .ovrhdot.VE. At rest inspiratory time on a breath by breath basis increased minimally with VT; changes in inspiratory flow accounted for the variability in VT. These 2 respiratory stimulants appear to increase ventilation through different mechanisms when analyzed in terms of VT and f. However, changes in inspiratory flow and duty cycle are similar in both.