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1 Fondazione Don C. Gnocchi-ONLUS,
We studied chest wall kinematics and
respiratory muscle action in five untrained healthy men walking on a
motor-driven treadmill at 2 and 4 miles/h with constant grade (0%).
The chest wall volume (Vcw), assessed by using the ELITE system, was
modeled as the sum of the volumes of the lung-apposed rib cage (Vrc,p),
diaphragm-apposed rib cage (Vrc,a), and abdomen (Vab). Esophageal and
gastric pressures were measured simultaneously. Velocity of shortening
(Vdi) and power
[
di = diaphragm pressure (Pdi) × Vdi] of the
diaphragm were also calculated. During walking, the progressive
increase in end-inspiratory Vcw (P < 0.05) resulted from an increase in end-inspiratory Vrc,p and Vrc,a
(P < 0.01). The progressive decrease (P < 0.05) in end-expiratory Vcw was
entirely due to the decrease in end-expiratory Vab
(P < 0.01). The increase in Vrc,a
was proportionally slightly greater than the increase in Vrc,p,
consistent with minimal rib cage distortion (2.5 ± 0.2% at 4 miles/h). The Vcw end-inspiratory increase and end-expiratory decrease
were accounted for by inspiratory rib cage (RCM,i) and abdominal (ABM)
muscle action, respectively. The pressure developed by RCM,i and ABM
and Pdi progressively increased (P < 0.05) from rest to the highest workload. The increase in
Vdi, more than
the increase in the change in Pdi, accounted for the increase in
di. In conclusion, we found that, in
walking healthy humans, the increase in ventilatory demand was met by the recruitment of the inspiratory and expiratory reserve volume. ABM
action accounted for the expiratory reserve volume recruitment. We have
also shown that the diaphragm acts mainly as a flow generator. The rib
cage distortion, although measurable, is minimized by the coordinated
action of respiratory muscles.
respiratory kinematics; walking; diaphragm; power; velocity of shortening
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