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Clinical Investigations: CYSTIC FIBROSIS |

Expiratory Airflow Patterns in Children and Adults With Cystic Fibrosis*

E. Mark Williams, PhD; Richard G. Madgwick; Anne H. Thomson, MD; M. Jocelyn Morris, MD
Author and Funding Information

*From the Osler Chest Unit (Drs. Williams and Morris and Mr. Madgwick), Churchill Hospital, and Department of Paediatrics (Dr. Thomson), John Radcliffe Hospital, Oxford, United Kingdom.

Correspondence to: M. Jocelyn Morris, MD, Osler Chest Unit, Churchill Hospital, Oxford, OX3 7LJ, UK; e-mail: Jmorris@radius.jr2.ox.ac.uk



Chest. 2000;117(4):1078-1084. doi:10.1378/chest.117.4.1078
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Study objective: To determine whether tidal expiratory airflow patterns change with increasing airways obstruction in patients with cystic fibrosis.

Design: An observational study.

Setting: Lung function laboratory.

Patients: Sixty-four children and young adults with cystic fibrosis.

Measurements: After measuring FEV1 and airways resistance using body plethysmography, each subject was seated and asked to mouth breathe through a pneumotachograph for 2 min. The collected data were analyzed, and three expiratory airflow pattern-sensitive indexes were computed. The first index was derived from the ratio of the time to reach peak expiratory flow to the total expiratory time (tptef/te). The second index, Trs, was an estimate of the time constant of the passive portion of expiration. The third index, S̄, describes the slope of the whole post-peak expiratory flow pattern after scaling.

Results: Compared with FEV1, the index tptef/te was a poor indicator of airways obstruction (r2 = 0.15, p = 0.002). Trs showed a strong relationship with the severity of airways obstruction (r2 = 0.46, p < 0.001). Using S̄, the postexpiratory profile could be categorized into three shapes, and provided a good indicator of airways obstruction when linear and concave-shaped profiles occurred (r2 = 0.42, p < 0.001). Convex-shaped flow profiles had to be treated separately and were indicative of normal lung function.

Conclusions: In a cross-sectional study of patients with cystic fibrosis, increase in airways resistance above normal is reflected by quantifiable changes in the expiratory airflow pattern.

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