USING LOW-FREQUENCY OSCILLATION TO DETECT BRONCHODILATOR RESPONSIVENESS IN INFANTS

The potential of the low-frequency forced oscillation technique (FOT) to measure the response to inhaled salbutamol was studied in 13 infant s with a history of recurrent wheeze and nine healthy infants. The inp ut impedance of the respiratory system (Zrs) between 0.5 and 20 Hz was measured at a transrespiratory pressure of 20 cm H2O during a brief H ering-Breuer reflex-induced pause in breathing. Parameters representin g the airway resistance (Raw) and inertance (law), and a constant-phas e tissue damping (G) and elastance (H) were estimated from the Zrs spe ctra. Lung function was measured before and after the administration o f 500 mu g of salbutamol via a small-volume metal spacer. Six of these infants also received a placebo aerosol. A fall in Raw (13% for the e ntire group) occurred following treatment with salbutamol (p < 0.008) but not placebo. There was no significant difference in the response t o salbutamol between the normal infants (7.65% +/- 5.49%) and those wi th recurrent wheeze (17.58% +/- 8.67%). On grouped data, the fall in G just failed to reach statistical significance (p = 0.05) after correc ting the significance level for multiple tests. No significant change occurred in law or H. We conclude that the low-frequency FOT is a suit able methodology for studying bronchodilator responsiveness in infants .