BREATHING - HOMEOSTATIC FUNCTION AND VOLUNTARY MOTOR-ACTIVITY

In a magnitude production test, subjects of both sexes rated their bre ath depth under different conditions. In the first group, 50 subjects were examined at rest in the supine position and breathing spontaneous ly or assisted by a respirator. The second group, consisting of 33 sub jects, was tested in the sitting position at rest and during mild bicy cle exercise (females 35 W, males 40 W). Subjectively quantified breat h depths and corresponding tidal volumes were compared and their relat ions were described by Stevens power function. The assessment of breat h depth in spontaneous breathing at rest was remarkably precise (mean Stevens exponent 0.94+/-0.02). During assisted ventilation, rating was less accurate and tended to underestimate breath depth. Noticeable un der both conditions was a tendency to overestimate voluntary tidal vol ume reductions. This was more pronounced in young (up to 35 years) wom en than in men or elderly women. During exercise, the subjects (men an d women) overestimated both increases and reductions of tidal volume. Each voluntary tidal volume modification was accompanied immediately b y involuntary changes of inspiration and expiration times, thus, parti ally compensating disturbances of ventilation. In addition, voluntaril y reduced tidal volumes were quantitatively compensated within the fir st breath subsequent to the voluntary manoeuver. We conclude that brea th depth sensation is more strongly related to proprioceptive signals than to visceroceptive signals and is influenced by the autonomous res piratory drive. Furthermore, proprioception is assumed to participate in the control of the autonomous respiratory drive.