MINI-SYMPOSIUM: LUNG FUNCTION IN PRESCHOOL CHILDRENThe measurement of airways resistance using the interrupter technique (Rint)
Section snippets
BACKGROUND
Although the measurement of airways resistance using the interrupter technique (Rint) was first described by Von Neergaard in 1927,1 it is only in the last 10 years that portable, affordable equipment has facilitated its wider use as a research and clinical tool. As Rint is effort-independent, non-invasive and requires minimal subject co-operation, it is ideally placed for use in preschool children where traditional measurements of lung function may be unreliable or unachievable. Unfortunately,
WHAT DOES RINT MEASURE?
Direct measurements of airways resistance (Raw) are traditionally obtained using whole-body plethysmography. Here, changes in alveolar pressure, caused by breathing, are recorded as pressure changes within the sealed plethysmograph (Palv) and Raw is calculated from the ratio between the change in Palv and the airflow at the mouth. In contrast, rather than measuring alveolar pressure itself, the interrupter technique is based on the assumption that during transient occlusion of the airway at the
HOW IS RINT MEASURED?
Rint measurements may be obtained using plethysmography or portable equipment such as the MicroRint machine (Micro Medical Ltd, Rochester, Kent, UK; Fig. 2). As with traditional Raw measurements, plethysmographic methods require expiration against a transiently closed valve in a body box and may be difficult or impossible for some young children. Portable devices also require valve closure, but have the advantage that children need not sit in a body box, nor be separated from their parents.
As
EFFECT OF AGE AND SIZE ON SUCCESS RATES AND RINT MEASUREMENTS
Although Rint measurements from younger children tend to have a slightly higher coefficient of variation, repeatable results can be obtained from over 95% of Rint-naïve children aged 4 years or more and from a smaller percentage aged 2–3 years.4, 6, 12 These success rates may be improved with practice. Inter-observer variability is low and is influenced only marginally by the experience of the investigator.4, 5, 13
The patient characteristic most consistently correlated with Rint is height,
CLINICAL APPLICABILITY
As with any lung function test, Rint can be used both to obtain baseline data and to measure the effect of specific interventions. Not surprisingly, most of the paediatric literature has concentrated on its use in the assessment of children with cough, wheeze and asthma, with a smaller number of studies including children with cystic fibrosis. Although each centre should ideally produce its own normal ranges, a number of similar, but subtly different, reference equations are now available in
SUMMARY
Portable Rint machines provide a quick, simple and cost-effective alternative to plethysmographic measurements of airways resistance in children as young as 2 years. Normative data are available and recent studies have improved standardisation of the methodology. Unfortunately, due to the variability of the data obtained, single Rint measurements cannot reliably be used to separate children with normal and increased bronchial tone, nor is Rint helpful in the assessment of long-term
PRACTICE POINTS
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Easy, cheap, non-invasive, effort-independent
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Reproducible in children as young as 2–3 years
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Helpful in assessing bronchodilator responsiveness
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Limited applicability in assessing longer-term interventions
RESEARCH DIRECTIONS
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Standardised methodology and reporting of results
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Clinical studies of the role of Rint in the management of the preschool child with respiratory disease
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Total specific airway resistance vs spirometry in asthma evaluation in children in a large real-life population
2015, Annals of Allergy, Asthma and ImmunologyCitation Excerpt :One study found that Rtot was more sensitive than FEV1, forced oscillation technique, and resistance by the interrupter technique in detecting bronchoconstriction in normal subjects.10 As described by Child,11 sRtot is an easy, cheap, noninvasive, and effort-independent measurement that is reproducible in children as young as 2 to 3 years old and is helpful in assessing bronchodilator responsiveness. Most recently, Beydon et al12 found that interrupter resistance had poor sensitivity to detect baseline obstruction but fairly good sensitivity and specificity to detect reversibility in schoolchildren with asthma.
Lung function testing in pre-school children
2010, Allergologia et ImmunopathologiaApplied physiology: Lung function tests in children
2006, Current PaediatricsLung function in preschool children: Aplications in clinical and epidemiological research
2006, Paediatric Respiratory ReviewsIntroduction and overview of preschool lung function testing
2006, Paediatric Respiratory Reviews