Assessing bronchodilator responsiveness in infants using partial expiratory flow-volume curves

Bronchodilator response in wheezing infants assessed by the raised volume rapid thoracic compression technique

BACKGROUND

Bronchodilator response (BDR) analyzed by the raised volume rapid thoracic compression (RVRTC) in wheezing infants is not yet well described, although bronchodilators (BD) are routine in the treatment of this population.

OBJECTIVE

To evaluate BDR by RVRTC technique in infants with recurrent wheezing and compare to control group.

METHOD

Cross sectional study, 45 infants, age 56 weeks (38-67 weeks). Two groups: wheezing group (WG: history of recurrent wheezing) and control group (CG). RVRTC was evaluated, FVC, FEV_0.5, FEF₅₀, FEF₇₅, FEF_85, FEF_25-75 were measured. Salbutamol was delivered to infants and RVRTC evaluated again. BDR was determined by the increase greater than two standard deviation from the mean change in the CG.

RESULTS

In WG (n = 32) lung function was worse than in CG (n = 13): FEV_0.5: 0.0(-0.9-0.9z score) vs 0.8(0.2-1.4z score); FEF₅₀: 0.2(-0.3-1.1z score) vs 0.9(0.5-1.4z score); and FEF_25-75: 0.2(-0.5-1.1z score) vs 1.1(0.6-1.6z score), respectively, p < 0.05. Both groups had similar increase after BD. In WG 11 patients (34%) were responder and these had worse lung function compared to nonresponder (n = 21) (p < 0.05). The increase in lung function after BD in responder was higher than in nonresponder: FEV_0.5: 6.5(2.1-7.1%) vs -0.5(-2.5-0.7%), FEF₅₀: 5.1(2.7-11.7%) vs 0.4(-1.1-2.8%), FEF₇₅: 20.7(4.7-23.6%) vs -1.3(-6.4-3.9%), FEF_25-75: 9.9(3.8-16.4%) vs 0.0(-1.5-1.0%), respectively, p < 0.05.

CONCLUSION

34% WG showed BDR measured by the RVRTC. The best variables to detect BDR were FEF₇₅, FEF_25-75 and FEV_0.5. Patients with worse lung function showed better response to BD.

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.