The measurement of total respiratory resistance in small children

Assessment of airway reversibility in asthmatic children using forced oscillation technique - A single-center experience from North India

Background:

Lung function testing is recommended for the management of asthma. Due to certain limitations of conventional spirometry in vulnerable patients, forced oscillation technique (FOT) has been studied with promising results. As there is a paucity of data from developing world, we planned to conduct this study in children using FOT. To assess airway reversibility after inhaled salbutamol in asymptomatic children with suspected asthma.

Settings:

This study was conducted at pediatric asthma clinic of a tertiary care referral hospital in North India.

Design:

This was a prospective interventional study over 1-year period.

Subjects and Methods:

Asymptomatic children between 2 and 18 years of age, with history suggestive of asthma, were eligible for participation. Baseline and postbronchodilator pulmonary functions were assessed using FOT. Airway resistance and reactance were monitored at various frequencies. SPSS version 17 was used for statistical analysis.

Results:

Among the 345 enrolled children, baseline mean ± standard deviation total airway resistance (R₅), central airway resistance (R₁₉), peripheral airway resistance (R₅–R₁₉), reactance (X₅), and resonant frequency (Fres) were 6.85 ± 2.60, 5.23 ± 1.93, 1.6 ± 1.16, and − 2.54 ± 1.36 cmH₂O/L/s and 17.28 ± 3.06 Hz. The median (interquartile range) percentage change after inhaled salbutamol was 19.9 (11.40, 29.12), 22.86 (6.88, 38.76), 14.08 (3.40, 22.62), 39.20 (8.20, 62.39), and 15.79 (8.33, 27.27) in respective parameters. All changes were statistically significant. The studied respiratory variables were in maximum negative correlation with height, followed by body mass index.

Conclusions:

FOT is a simple technique for monitoring lung functions in children during asthma management.

Defining 'healthy' in preschool-aged children for forced oscillation technique reference equations

BACKGROUND AND OBJECTIVE

Selecting 'healthy' preschool-aged children for reference ranges may not be straightforward. Relaxing inclusion criteria for normative data does not affect spirometry z-scores. We therefore investigated the effect of similarly relaxing inclusion criteria in preschoolers on reference ranges for respiratory impedance (Zrs) using a modified forced oscillation technique (FOT).

METHODS

The International Study of Asthma and Allergies in Childhood questionnaire classified 585 children into a healthy and five mutually exclusive groups. Zrs was measured between 4 and 26 Hz and resistance (R) and compliance (C) obtained by model fitting. Prediction models were determined using mixed effect models and z-scores compared between healthy children and the five groups.

RESULTS

Zrs data were obtained for 494 participants (4.30 ± 0.7 years) on 587 occasions. Comparison of the Zrs z-scores between the healthy children and the health groups found significant differences in children with asthma, current wheeze and respiratory symptoms, but not in children born preterm or with early-life wheeze. Adding these two groups to the healthy dataset had no significant effect on the distribution of z-scores and increased the size of the dataset by 22.3%.

CONCLUSION

Our data suggest that preschool-aged children born preterm or with early-life wheeze can be included in FOT reference equations, while those with asthma, current wheeze and respiratory symptoms within 4 weeks of testing should be excluded. This more inclusive approach results in more robust FOT reference ranges.

Impulse oscillometry in the evaluation of diseases of the airways in children

OBJECTIVE

To provide an overview of impulse oscillometry and its application to the evaluation of children with diseases of the airways.

DATA SOURCES

Medline and PubMed search, limited to English language and human disease, with keywords forced oscillation, impulse oscillometry, and asthma.

STUDY SELECTIONS

The opinions of the authors were used to select studies for inclusion in this review.

RESULTS

Impulse oscillometry is a noninvasive and rapid technique requiring only passive cooperation by the patient. Pressure oscillations are applied at the mouth to measure pulmonary resistance and reactance. It is employed by health care professionals to help diagnose pediatric pulmonary diseases such asthma and cystic fibrosis; assess therapeutic responses; and measure airway resistance during provocation testing.

CONCLUSIONS

Impulse oscillometry provides a rapid, noninvasive measure of airway impedance. It may be easily employed in the diagnosis and management of diseases of the airways in children.

Reference equations for pulmonary function tests in preschool children: a review

Recent developments in pulmonary function tests (PFTs) in preschool children (2-5 years of age) have meant that objective assessments of respiratory function are now possible for this age group. However, the application and interpretation of these tests may be limited by the relative paucity of appropriate reference equations. This review summarizes available preschool reference equations, identifies the current gaps and limitations in the methodologies and statistics used and proposes future directions for improving reference data. A PubMed search which included the MeSH terms (preschool [2-5years]), (respiratory function test), and (reference value) yielded 214 publications which were screened to identify 34 publications presenting 36 reference equations for seven techniques. There were considerable differences with respect to population characteristics, recruitment strategies, equipment and methodologies and reported parameters both within and between each measurement technique. Despite an increasing number of reference equations for PFT for preschool children, the extent to which these can be generalized to other populations may be limited in some cases by inclusion of relatively few children less than 5 years of age, a lack of details regarding the sample populations and measurement techniques and/or inappropriate statistical analysis. A fresh approach based on large sample sizes, clearly documented population characteristics, equipment and protocols, and more rigorous modern statistical methods both for developing reference equations and interpreting results could enhance clinical application of these tests. This in turn would maximize the tremendous opportunities to detect early lung disease offered by the recent surge in developing suitable tests for preschool children.

The use of oscillometry as a measure of airway responsiveness in asthmatic children after histamine and methacholine bronchoprovocation with dosimeter-MedicAid and DeVilbiss nebulizers

To explore the use of oscillometry as a measure of airway responsiveness, 69 asthmatic children underwent histamine and methacholine bronchoprovocation using dosimeter-MedicAid (Jaeger Co.; Germany) and DeVilbiss nebulizers (DeVilbiss, Bornemouth; England). The mean increase in R5 resistance in challenge testing measured after methacholine with the dosimeter-MedicAid nebulizer was 77.14% compared with 65.05% using histamine. Using the dosimeter-DeVilbiss nebulizer, the mean increases in R5 resistance following methacholine and histamine testing were 57.50% and 59.36%, respectively. The resistance R5 over R20 significantly correlated with forced expiratory volume in 1 second (FEV1). The MedicAid produced a more aggressive challenge than the DeVilbliss nebulizer. Oscillometry can be used to monitor the level of airway hyperresponsiveness following bronchoprovocation tests.

Pediatric reference values for respiratory resistance measured by forced oscillation

OBJECTIVES

To determine, in North American children, reference values for respiratory resistance measurements by the forced oscillation (Rfo) technique and to examine whether sitting height, as index of truncal length, is a better determinant of resistance, less influenced by race and gender, than standing height.

DESIGN/SETTING

A prospective cross-sectional study of healthy nonobese children, carefully selected for absence of atopy, exposure to tobacco smoke, and recent upper respiratory tract infection.

MEASUREMENTS

Three measurements of respiratory resistance by forced oscillation were obtained at the fixed frequencies of 8 Hz (Rfo8), 12 Hz (Rfo12), and at 16 Hz (Rfo16) using the Custo Vit R (Custo Med GMBH; Munich, Germany). In cooperative children, routine spirometry (FEV1, FVC, and peak expiratory flow rate [PEFR]) was also performed.

RESULTS

We recruited 217 healthy children aged 3 to 17 years. Reproducible measurements of Rfo8 were obtained for 206 children, Rfo12 for 197 children, and Rfo16 for 209 children. Normal FEV1, FVC, and PEFR values were documented in all 69 subjects who were able to reproducibly cooperate with spirometry. Multiple linear regression identified measurements of either sitting or standing height as the best, and equally strong, determinants of respiratory resistance at all three frequencies. Gender and race were not important factors once either sitting or standing height measurement was considered. Our regression equations at 8 Hz are comparable to published reference values obtained at fixed frequencies of 6, 8, and 10 Hz using other instruments. However, in comparison to our results, prior values tended to underestimate resistance in the shortest children or to overestimate it in the tallest ones. Our regression equation for Rfo12 is similar to the only previously published one, while no reference values at 16 Hz were available for comparison.

CONCLUSIONS

Height is the best predictor for total respiratory resistance at 8, 12, and 16 Hz in children aged > or = 3 years. Use of sitting height does not appear to be a stronger determinant of resistance than standing height.