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Variability of pulmonary function tests in cystic fibrosis
P J Cooper1, C F Robertson, I L Hudson
1Professional Department of Thoracic Medicine Royal Children's Hospital, Melbourne, Australia.
Pediatric Pulmonology
|January 1, 1990
Summary
This study defines respiratory function test variability in cystic fibrosis (CF) patients. Understanding individual variability is crucial for accurately interpreting lung function changes in CF patients.
Area of Science:
- Pulmonary Medicine
- Medical Physiology
- Pediatric Respiratory Health
Background:
- Cystic Fibrosis (CF) necessitates precise monitoring of respiratory function.
- Variability in pulmonary function tests (PFTs) can complicate the assessment of disease progression and treatment efficacy in CF patients.
- Establishing reliable within-subject variability metrics is essential for accurate clinical interpretation.
Purpose of the Study:
- To quantify the within-subject variability of various respiratory function tests in patients with cystic fibrosis (CF) across different timeframes (within-day, day-to-day, week-to-week).
- To compare variability metrics between CF patients and healthy controls.
- To provide reference values for interpreting serial PFT results in CF.
Main Methods:
- Twenty-eight CF patients (9-19 years) and 23 healthy controls (9-18 years) underwent repeated measurements of spirometry, lung volumes, maximal flows, and respiratory pressures.
- Testing was conducted on nine occasions over consecutive weeks, with three assessments per day.
- Within-subject variability was summarized using within-subject standard deviation (WSD) and within-subject coefficient of variation (WCV).
Main Results:
- Within-subject standard deviation (WSD) was more appropriate for assessing variability in vital capacity (VC), forced expiratory volume in 1 second (FEV1), total lung capacity (TLC), residual volume (RV), and RV/TLC.
- CF patients exhibited significantly higher WSD for VC and FEV1 compared to controls.
- Within-subject coefficient of variation (WCV) better summarized variability for FEF25-75, FRC, V25, V50max, and V75max, with CF subjects showing significantly greater variability.
- Individual variability was consistent, supporting personalized assessment over group data.
Conclusions:
- Individualized variability assessment is superior to group data for detecting significant changes in lung function for CF patients.
- Increased day-to-day and week-to-week variability in PFTs must be considered when interpreting lung function in CF.
- Reference values for WSD and WCV are provided to enhance the accuracy of serial pulmonary function test interpretation in CF.