INTERACTION BETWEEN CHEST-WALL MOTION AND LUNG-MECHANICS IN NORMAL INFANTS AND INFANTS WITH BRONCHOPULMONARY DYSPLASIA

Asynchronous or paradoxic motion between the rib cage and abdomen may be seen in infants with lung disease. We have recently shown that after bronchodilator administration, the degree of asynchrony decreases proportionately to the improvement in lung mechanics. However, whether such thoraco-abdominal asynchrony (TAA) is a useful indicator of lung function in a cross-sectional population, i.e., whether asynchrony correlates with baseline lung mechanics, is unknown. Therefore, we quantitated the degree of TAA using respiratory inductive plethysmography during quiet sleep in ten infants with bronchopulmonary dysplasia (BPD) and six weight-matched control infants. We displayed abdominal wall (AB) and rib cage (RC) motion on an X-Y recorder, and from the tidal breathing loop we calculated a phase angle PHI, between 0-degrees and 180-degrees as an index of asynchrony (synchronous RC/AB motion = 0-degrees, paradox = 180-degrees). Lung resistance (R(L)) and compliance/kg (C(L)/kg) were calculated from esophageal and mouth pressure, tidal volume, and tidal flow. As expected, BPD infants had abnormally high R(L), and low C(L)/kg when compared to controls. All infants with BPD displayed marked thoraco-abdominal asynchrony (PHI = 102 +/- 16-degrees, mean +/- SEM; range 35-degrees-160-degrees) while controls displayed synchronous chest wall motion (PHI = 8 +/- 3-degrees, range 0-degrees-15-degrees) (P < 0.001). The degree of TAA was significantly correlated with R(L) (r = 0.773, P < 0.001) and inversely correlated with C(L)/kg (r = -0.67, P < 0.01). We conclude that in infants of similar weight, TAA may be used as a cross-sectional index reflecting both resistive and elastic properties of the lungs.