The mechanics of the chest wall was studied in seven asthmatic patients bef
ore and during histamine-induced bronchoconstriction (B). The volume of the
chest wall (VCW) was calculated by three-dimensional tracking of 89 chest
wall markers. Pleural (Ppl) and gastric (Pga) pressures were simultaneously
recorded. VCW was modeled as the sum of the volumes of the pulmonary-appos
ed rib cage (VRC,p), diaphragm-apposed rib cage (VRC,a), and abdomen (VAB).
During B, hyperinflation was due to the increase in end-expiratory volume
of the rib cage (0.63 +/- 0.09 L, p < 0.01), whereas change in VAB was inco
nsistent (0.09 +/- 0.07 L, NS) because of phasic recruitment of abdominal m
uscles during expiration. Changes in end-expiratory VRC,p and VRC,a were al
ong the rib cage relaxation configuration, indicating that both compartment
s shared proportionally the hyperinflation. VRC,p-Ppl plot during B was dis
placed leftward of the relaxation curve, suggesting persistent activity of
rib cage inspiratory muscles throughout expiration. Changes in end-expirato
ry VCW during B did not relate to changes in FEV1 or time and volume compon
ents of the breathing cycle. We concluded that during B in asthmatic patien
ts: (1) rib cage accounts largely for the volume of hyperinflation, whereas
abdominal muscle recruitment during expiration limits the increase in VAR;
(2) hyperinflation is influenced by sustained postinspiratory activity of
the inspiratory muscles; (3) this pattern of respiratory muscle recruitment
seems to minimize volume distortion of the rib cage at end-expiration and
to preserve diaphragm length despite hyperinflation.