Use of tidal breathing curves for evaluating expiratory airway obstruction in infants.

OBJECTIVE: To evaluate tidal breathing (TB) flow-volume and flow-time curves for identification of expiratory airway obstruction in infants. METHODS: Pulmonary function tests were analyzed retrospectively in 156 infants aged 3-24 months with persistent or recurrent respiratory complaints. Parameters derived from TB curves were compared to maximal expiratory flow at functional residual capacity ( V˙ maxFRC) measured by rapid thoracoabdominal compression technique. Analyzed parameters were: inspiratory time (tI), expiratory time (tE), tidal volume, peak tidal expiratory flow (PTEF), time to peak tidal expiratory flow (tPTEF), expiratory flow when 50% and 25% of tidal volume remains in the lungs (FEF50, FEF25, respectively), and the ratios tPTEF/tE, tI/tE, FEF50/PTEF, and FEF25/PTEF. Statistical comparisons between flow indices and TB parameters were performed using mean squared error and Pearson's sample correlation coefficient. The study population was also divided into two groups based on severity of expiratory obstruction (above or below z-score for V˙ maxFRC of -2) to generate receiver operating characteristic (ROC) curves and calculate discriminatory values between the groups. RESULTS: TB parameters that were best correlated to V˙ maxFRC were: tPTEF/tE, FEF50/PTEF, and FEF25/PTEF, with r = 0.61, 0.67, 0.65, respectively (p < 0.0001 for all). ROC curves for FEF50/PTEF, FEF25/PTEF and tPTEF/tE showed areas under the curve of 0.813, 0.797, and 0.796, respectively. Cutoff value z-scores of -0.35, -0.34, and -0.43 for these three parameters, respectively, showed an 86% negative predictive value for severe airway obstructions. CONCLUSION: TB curves can assist in ruling out severe expiratory airway obstruction in infants.

Bronchodilator responsiveness in wheezy infants predicts continued early childhood respiratory morbidity.

OBJECTIVE: Spirometry including bronchodilator responsiveness is considered routine in the workup of asthma in older children. However, in wheezy infants the existence of bronchodilator responsiveness and its prognostic significance remain unclear. METHODS: Infants (< 2 years) with chronic or recurrent wheezing or coughing were evaluated by infant pulmonary function testing (PFT). Maximal expiratory flow at the point of functional residual capacity (V̇maxFRC) was measured before and 20 minutes after salbutamol administration. Only infants with an obstructive profile (V̇maxFRC < 80% predicted) were included. The infants were divided into two groups with regard to whether or not a response to salbutamol was observed on PFT. A response was defined as a mean V̇maxFRC after salbutamol administration exceeding the upper confidence interval limit of individual pre-bronchodilator V̇maxFRC measurements. Follow-up data was gathered after a mean of 2 years. MEASUREMENTS AND MAIN RESULTS: Sixty infants were included in the study of which 32 (53%) demonstrated responsiveness to bronchodilators. The infants in the responsive group had a significantly higher frequency of physician visits for wheezing than the non-responders (3.0 mean visits/yr vs. 1.5 respectively, P = 0.03), and had a higher likelihood of having received asthma medication in the last year of the follow-up period (84% vs. 50% respectively, RR: 1.68[1.10-2.56]). At the end of the follow-up period, more parents in the responsive group reported continued respiratory disease (71% vs. 22%, RR:3.21[1.30-7.95]). CONCLUSIONS: Bronchodilator responsiveness can be demonstrated by infant PFT in infants with recurrent wheezing and can predict increased respiratory morbidity until 3 years of age.