Thoracoabdominal asynchrony (TAA) has long been thought clinically useful in the assessment of airflow obstruction (AO) in infants. To test the hypothesis that the measurement of TAA is useful in the assessment of lung mechanics in infants with AO, we have used respiratory inductive plethysmography (RIP) to quantity TAA. We compared changes in TAA to changes in lung mechanics before and after aerosolized bronchodilator (BD) administration in 13 infants. Abdominal wall (AB) and rib cage (RC) motion were displayed on an X-Y recorder in a Lissajous figure. Asynchrony between RC and AB motion was quantified by comparing the width m of the Lissajous figure (difference between AB inspiratory and expiratory positions) at mid-RC excursion with the total AB excursion at its extremes (s). Phase angle phi ws computed as sin phi = m/s (or phi = 180 degrees - mu, where sin mu = m/s for phase angles greater than 90 degrees) and was taken as a measure of TAA. Lung resistance RL and elastance EL were calculated from esophageal pressure (Pes), mouth pressure, tidal volume, and tidal flow. All infants displayed TAA at baseline. After BD administration, TAA decreased in those infants in whom RL decreased. The percentage decrease in the phase angle from baseline after BD administration was significantly correlated with the decrease in peak-to-peak Pes (delta Pes) and the percentage decrease in RL and EL. We conclude that AO in infants leads to TAA through altered pleural pressure swings acting on the compliant chest wall. Changes in lung mechanics induced by bronchodilators are reflected in changes in TAA.(ABSTRACT TRUNCATED AT 250 WORDS)