Journal of Applied Physiology, Vol 56, Issue 1 97-101, Copyright © 1984 by American Physiological Society
Effect of posture on thoracoabdominal movements during CO2 rebreathing
K. R. Chapman and A. S. Rebuck
To determine whether the rib cage and abdomen-diaphragm contributions to
tidal volume (VT) during CO2 rebreathing are affected by postural change,
using respiratory inductive plethysmography, we measured in eight healthy
volunteers the compartmental VT responses to progressive hypercapnia in
both seated and supine postures. The ventilatory, frequency, and VT
responses to CO2 of the total respiratory system were not significantly
different between postures. VT responses, corrected for body size, ranged
from 1.67 to 3.71% vital capacity (VC) X Torr-1 (mean 2.27) in seated
subjects and from 1.08 to 3.79% VC X Torr-1 (mean 2.06), in supine
subjects. In both postures, the VT response of the abdominal compartment
was nearly uniform among subjects and independent of the total respiratory
system VT response (slope = 0.091, r = 0.210 P greater than 0.3 seated;
slope = 0.043, r = 0.077, P greater than 0.3 supine), whereas the VT
response of the rib cage varied among subjects and was significantly
correlated to the total VT response (slope = 0.815, r = 0.84, P less than
0.01, seated; slope = 1.125, r = 0.859, P less than 0.01, supine). Thus
high tidal volume responses to CO2 rebreathing are determined largely by
recruitment of the rib cage compartment in both seated and supine postures.
