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Repeatability of airway resistance measurements made using the interrupter technique
E Y Chan1, P D Bridge, I Dundas
1Department of Respiratory Paediatrics, Fielden House, The Royal London Hospital, Barts, London E1 1BB, UK.
Insights
Airway resistance measurements using the interrupter technique (Rint) show good within-occasion repeatability in children. However, between-occasion repeatability is too poor to confidently assess changes after bronchodilator use.
Area of Science:
- Pediatric Pulmonology
- Respiratory Physiology
- Clinical Measurement Science
Background:
- Accurate interpretation of physiological measurements requires knowledge of their repeatability.
- The interrupter technique provides a method for measuring airway resistance.
- Repeatability data for airway resistance measurements in children is essential for clinical interpretation.
Purpose of the Study:
- To determine the within-occasion and between-occasion repeatability of airway resistance measurements using the interrupter technique (Rint).
- To assess the repeatability in healthy children and those with respiratory symptoms like cough or wheeze.
- To evaluate the clinical significance of Rint measurements in relation to bronchodilator response.
Main Methods:
- Children aged 2-10 years (healthy, cough, wheeze) underwent three Rint measurements 15 minutes apart.
- Measurements were taken before and after placebo and salbutamol administration.
- Between-occasion repeatability was assessed over 2-20 weeks.
Main Results:
- Within-occasion repeatability showed limits of agreement of 20% expected resistance, irrespective of age or health status.
- Between-occasion repeatability had wider limits of agreement (32-53%) depending on health status.
- Bronchodilator response exceeded within-occasion limits in a significant proportion of children with cough or wheeze.
Conclusions:
- Within-occasion repeatability of Rint is clinically meaningful for assessing bronchodilator response.
- Between-occasion repeatability is insufficient for confidently evaluating changes in airway resistance over time.
- The interrupter technique is useful for short-term assessments but not for tracking changes between visits.
Background:
To be able to interpret any measurement, its repeatability should be known. This study reports the repeatability of airway resistance measurements using the interrupter technique (Rint) in children with and without respiratory symptoms.
Methods:
Children aged 2-10 years who were healthy, had persistent isolated cough, or who had previous wheeze were studied. On the same occasion, three Rint measurements were made 15 minutes apart, before and after placebo and salbutamol given in random order. Results from those given placebo first were analysed for within-occasion repeatability. Between-occasion repeatability measurements were made 2-20 weeks apart (median 3 weeks).
Results:
For 85 pairs of measurements before and after placebo the limits of agreement were 20% expected resistance and were unaffected by age or health status. The change in resistance following bronchodilator in one of 18 healthy children, 12 of 28 with cough, and 22 of 39 with wheeze exceeded this threshold. For between-occasion measurements the limits of agreement were 32% in 72 healthy subjects, 49% in 57 with cough, and 53% in 95 with previous wheeze.
Conclusion:
The measurement of airways resistance by the interrupter technique is clinically meaningful when change following an intervention such as the administration of bronchodilator is greater than its within-occasion repeatability. Between-occasion repeatability is too poor to judge change confidently.