Am. J. Respir. Crit. Care Med., Volume 157, Number 2, February 1998, 574-579

Using Low-frequency Oscillation to Detect Bronchodilator Responsiveness in Infants

MARK J. HAYDEN, FERENC PETAK, ZOLTAN HANTOS, GRAHAM HALL, and PETER D. SLY

Department of Respiratory Medicine, Princess Margaret Hospital, Division of Clinical Sciences, Institute of Child Health Research, and Department of Paediatrics, University of Western Australia, Perth, Western Australia, Australia; and Department of Medical Informatics and Engineering, Albert Szent-Györgyi Medical University, Szeged, Hungary

The potential of the low-frequency forced oscillation technique (FOT) to measure the response to inhaled salbutamol was studied in 13 infants with a history of recurrent wheeze and nine healthy infants. The input 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 Hering-Breuer reflex-induced pause in breathing. Parameters representing the airway resistance (Raw) and inertance (Iaw), and a constant-phase tissue damping (G) and elastance (H) were estimated from the Zrs spectra. Lung function was measured before and after the administration of 500 µg of salbutamol via a small-volume metal spacer. Six of these infants also received a placebo aerosol. A fall in Raw (13% for the entire group) occurred following treatment with salbutamol (p < 0.008) but not placebo. There was no significant difference in the response to salbutamol between the normal infants (7.65% ± 5.49%) and those with recurrent wheeze (17.58% ± 8.67%). On grouped data, the fall in G just failed to reach statistical significance (p = 0.05) after correcting the significance level for multiple tests. No significant change occurred in Iaw or H. We conclude that the low-frequency FOT is a suitable methodology for studying bronchodilator responsiveness in infants.

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