Contribution of central and reflex nervous activity to the rapid increase in pulmonary ventilation at the start of muscular exercise in man

Summary

To investigate the relative contributions of the central and peripheral neural drive to hyperventilation at the onset of muscular exercise, five volunteers were tested during the first ten breaths while performing both voluntary (VM) and passive (PM) ankle rotations with a frequency of 1 Hz and through an angle of 10°. Resulting breathing patterns for the two movements were compared. Hypocapnic hyperventilation, found in both PM and VM, indicated its neural origin. Respiratory changes were higher in VM than in PM. In both experimental conditions, increases in ventilation ($\dot V_E$) depended more on respiratory frequency (f) than on tidal volume (V _T). Moreover, increases inV _T adapted, breath-by-breath, to values lower than the initial ones, while increases inf rose progressively. Expiratory time was reduced more than inspiratory time (T _I); increases in inspiratory flow (V _T/T _I) depended to the same extent on changes in bothT _I andV _T. Increases in expiratory tidal volume were initially higher than in inspiratory tidal volume, thereby producing a reduction in functional residual capacity. Because PM respiratory changes could be considered to be of nervous reflex origin only, the identical breathing patterns in PM and VM indicated that the hyperventilation found also in VM was mainly of reflex origin. The increase in$\dot V_E$ was considered to be dependent on a greater stimulus from muscle proprioreceptors.