COMPARISON OF RESPIRATORY INDUCTANCE PLETHYSMOGRAPHY WITH THORACOABDOMINAL COMPRESSION IN BRONCHIAL CHALLENGES IN INFANTS AND YOUNG-CHILDREN

Respiratory inductance plethysmography measuring thoracoabdominal asyn chrony (TAA) has been claimed to be a useful tool for measuring change s in airway resistance in infants. In this study we evaluated the resp onse to methacholine by thoracoabdominal compression and respiratory i nductance plethysmography. Seventeen infants (mean age, 13.1 +/- 4.7 m o) with recurrent episodes of cough or wheeze underwent bronchial chal lenge with inhaled methacholine. Lung function was evaluated by measur ing maximal expiratory flow at resting lung volume (VmaxFRC), and the deg ree of TAA was measured by phase angle (theta). Methacholine was i nhaled for 1 min during tidal breathing using increasing doubling conc entrations until a fall of at least 40% in VmaxFRC was achieved (final concentration). All infants responded to the final concentration of m ethacholine by a significant fall in VmaxFRC (from 31 +/- 10 to 12 +/- 5 ml/s/kg, p < 0.001). All but one infant responded to methacholine a t the final concentration with a significant increase in phase angle ( median a increased from 11.7 to 31.7 degrees, p < 0.001). In two other infants there was an early response in theta compared with the respon se in VmaxFRC. Phase angle increase after methacholine was expressed a s Z-scores (the difference between postmethacholine theta and postbuff er theta divided by the standard deviation of postbuffer theta). An in crease of at least 2.0 Z-scores in theta was observed at the same conc entration of methacholine when VmaxFRC fell by at least 40% in 15 of t he 17 infants (88%). We conclude that respiratory inductance plethysmo graphy is a sensitive method to measure bronchial reactivity to methac holine in most of the infants studied (14 of 17, 82%). A concentration of methacholine causing an increase in theta of at least 2.0 standard deviations above baseline is equivalent to the concentration causing a 40% fall in VmaxFRC.