Chest

Chest

Volume 125, Issue 1, January 2004, Pages 150-155
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Clinical Investigations
CYSTIC LUNG DISEASE
The Repeatability of Forced Expiratory Volume Measurements in Adults With Cystic Fibrosis

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Study objective

To determine the repeatability of measurements of FEV1 in adults with lung disease due to cystic fibrosis (CF).

Design

Single cohort study nested within a randomized controlled trial.

Setting

Adult CF of a university teaching hospital. Subjects were participants in a randomized trial of an experimental mucolytic drug.

Patients

Twenty-one adults (mean age, 27.5 ± 9.2 years [± SD]) with CF and mild-to-moderate airflow obstruction (FEV1 70 ± 15% predicted). Patients were in clinically stable condition prior to and during the study.

Interventions

Repeated FEV1 measurements were obtained at specific times of the day for 9 consecutive days, for a total of 31 measurements from each subject. Statistical measures of repeatability were calculated. Variation over the course of 1 day and variation from 1 day to the next were examined separately.

Measurements and results

For day-to-day FEV1 measurements, the within-subject SD was 0.145 L (4.5% of predicted), indicating greater variation compared to values previously established in normal subjects. The coefficient of repeatability indicated that day-to-day measurements could differ by as much as 13% of predicted in the absence of clinical change. For measurements within a single day, variation was not observed to be greater than normal.

Conclusions

In adults with CF, day-to-day variation in FEV1 measurements is greater than normal and similar to that seen in other obstructive lung diseases. Changes in FEV1 over time in adults with CF can likely be interpreted using the same criteria that apply to asthma or COPD.

Section snippets

Subjects

Subjects were outpatients of the Toronto Adult Cystic Fibrosis Program. Eligible subjects were ≥ 16 years old, had a diagnosis of CF as defined by a positive sweat chloride test result, had an FEV1 between 40% and 80% of predicted, and had an oxygen saturation of at least 92% on room air. To be enrolled, subjects had to be able to perform pulmonary function testing satisfactorily. Written informed consent was obtained from all enrolled subjects. The study protocol received official ethics

Results

A total of 21 subjects were enrolled in the study (7 men and 14 women). Baseline demographic variables are shown in Table 1. With the exception of body mass index (BMI), all baseline variables were normally distributed across the study population. Subjects were adequately nourished, with only three subjects having a BMI < 20. The severity of airflow obstruction3 at baseline was mild in eight subjects (38%), moderate in eight subjects (38%), and moderately severe or severe in five subjects

Discussion

Using a unique data set of FEV1 measurements made repeatedly for several days, this study was able to provide estimates of the variation of FEV1 in adults with lung disease due to CF. Technical and disease-related variation were minimized through rigorous attention to established laboratory standards for quality control8 and by ensuring that participants were clinically stable during the study period, respectively. The variation measured should therefore reflect the physiologic variation that

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Cited by (0)

Data for the present study were derived from a study originally funded by a grant from Biogen Inc., but Biogen had no financial or other involvement with the present study itself.

Dr. Stanbrook is supported by a fellowship from the Canadian Institutes of Health Research and by the Clinician-Scientist Program of the Department of Medicine, University of Toronto.

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Copyright © 2004 The American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.