Peak inspiratory flows in children with cystic fibrosis

To show that in children with moderately severe cystic fibrosis lung disease: (i). inspiratory flow may be reduced; and (ii). peak inspiratory flow may be predicted from height, expiratory flow analysis or body mass index.

All children attending the Royal Children's Hospital, Melbourne, between May and July, 2001 who had cystic fibrosis, were aged > 5 years, were able to perform spirometry reproducibly and who had a forced expiratory volume in 1 s < 60% predicted were prospectively enrolled. Height, weight, peak inspiratory flow, forced expiratory volume in 1 s and forced vital capacity were recorded. Linear regression analysis was performed.

The age range was 9.4-19.9 years. Sixteen boys and 11 girls were studied. All children had a peak inspiratory flow > 0.5 L/s. There was a significant relationship between peak inspiratory flow and forced vital capacity (R2 = 0.50) especially in boys (R2 = 0.65). In boys, peak inspiratory flow was significantly related to forced expiratory volume in 1 s (R2 = 0.47). There was no relationship between peak inspiratory flow and predicted values of expiratory flow, age, height, weight or body mass index. Logistic regression was used to predict the probability that peak inspiratory flow was < 2.0 L/s for a given forced vital capacity. If the forced vital capacity is > 2.5 L, peak inspiratory flow is likely to be > 2.0 L/s.

In children with significant cystic fibrosis lung disease, peak inspiratory flow is likely to be > 0.5 L/s, which is required to activate dry powder inhalers. If the forced vital capacity is < 2.5 L, the peak inspiratory flow may be < 2.0 L/s, and a metered dose inhaler and spacer should be considered. Further studies that investigate the relationship between expiratory flow and peak inspiratory flow against an internal resistance are needed.