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Inherent variability of pulmonary function tests in infants with bronchiolitis
J Mallol1, M E Hibbert, C F Robertson
1Department of Thoracic Medicine, Royal Children's Hospital, Parkville, Victoria, Australia.
Insights
Infant pulmonary function tests show high variability, especially when infants are repositioned. This increased variability can impact studies on inhaled medications, necessitating individual test assessments before therapeutic intervention studies.
Area of Science:
- Pediatric Pulmonology
- Respiratory Physiology
- Clinical Trial Methodology
Background:
- New infant pulmonary function assessment methods have emerged, yet their use in evaluating inhaled medications remains controversial.
- Existing variability data for infant pulmonary function tests may not apply to drug efficacy studies due to time intervals and repositioning.
Purpose of the Study:
- To investigate the variability of infant pulmonary function tests when infants are repositioned between measurements.
- To assess the impact of repositioning on measurements of thoracic gas volume, passive respiratory mechanics, and forced expiration.
Main Methods:
- Measurements of thoracic gas volume (TGV), passive respiratory mechanics, and forced expiration were performed.
- Infants were either removed from the plethysmograph or repositioned within it between measurement sets.
- Between-test coefficients of variation were calculated for various pulmonary function parameters.
Main Results:
- Variability of TGV, respiratory system resistance, respiratory system compliance, and maximal flow measurements approximately doubled with infant repositioning.
- Between-test coefficients of variation ranged from 4.8% to 36.1% across different pulmonary function tests.
- Significant variability was observed in commonly used infant pulmonary function tests in infants with acute wheezing.
Conclusions:
- Commonly employed infant pulmonary function tests exhibit wide variability in infants with acute wheezing illnesses.
- Establishing individual test variability under study conditions is crucial before investigating therapeutic interventions in these infants.
- Failure to account for individual variability may lead to erroneous conclusions in drug efficacy studies.
Abstract:
During the last decade, many new methods of assessing pulmonary function in infants have been introduced. However, considerable controversy has arisen when these different techniques are used to assess the efficacy of various inhaled medications. The currently employed measures of pulmonary function have been reported to have coefficients of variation of less than 10%. However, these figures refer to repeated measurements made in individual babies over a short period of time, with the infant in a constant position. They may not be applicable to studies on the effects of drugs when a significant time interval elapses between measurements, particularly if the infant is repositioned during this time. In the present study, we found that the variability of measurements of thoracic gas volume (TGV), passive respiratory mechanics, and forced expiration approximately doubled if the infant was taken out of the plethysmograph, or repositioned within the plethysmograph, between sets of measurements. The between-test coefficients of variation ranged from 4.8% to 18.9% for TGV, 7.8% to 23.5% for respiratory system resistance, from 5.0% to 24.1% for respiratory system compliance, and from 10.8% to 36.1% for maximal flow at functional residual capacity. These results demonstrate that the commonly employed infant pulmonary function tests have wide variability in infants with acute wheezing illnesses. Before studying the efficacy of therapeutic interventions in such infants, it is necessary to establish the individual variability of the tests in the infants under the conditions of the study. Failure to do so may result in erroneous conclusions and recommendations.