Impaired pulmonary mechanics can cause thoraco-abdominal asynchrony during spontaneous breathing so that work of breathing is wasted by chest wall distortion. We hypothesized that elastic unloading by Volume-Proportional Assist Ventilation (VPAV) would reduce chest wall distortion in animals with stiff lungs. Respiratory inductive plethysmography was used to quantitate asynchrony in five young adult rabbits with meconium injured, low-compliance lungs (median 0.95, range 0.7-1.4 mL/cmH2O/kg). We aimed at unloading three fourth of lung elastance. The phase shift between the rib cage (RC) and abdominal compartment (AB) movements (degrees of the total respiratory cycle), and the total compartmental displacement ratio (TCD) were used as indexes of asynchrony and chest wall distortion. (The TCD increases above 1.0 with distortion.) The RC and AB excursion amplitudes were measured at end-inspiratory zero flow. Compared to CPAP, VPAV significantly reduced asynchrony and RC paradoxical movement With VPAV, the outward RC excursion increased while the AB excursion decreased significantly. We conclude that thoraco-abdominal synchrony improved during VPAV in spontaneously breathing animals with stiff lungs. We speculate that the decrease in chest wall distortion increased ventilatory efficiency for a given diaphragmatic effort and hence improved diaphragmatic effectiveness.Table

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