Repeatability of airway resistance measurements made using the interrupter technique

Bronchodilator response by interrupter technique to guide management of preschool wheeze

OBJECTIVE

We examined relationships between clinical features and pulmonary function before and after inhaled corticosteroid (ICS) treatment in wheezy preschool children, and specifically, whether measuring bronchodilator response (BDR) could predict benefit from ICS.

DESIGN

Clinical non-randomised intervention study SETTING: Secondary care.

PATIENTS

Preschool children (2 years to <6 years) with recurrent wheeze.

INTERVENTIONS

Inhaled beta-agonist, ICS.

OUTCOME MEASURES

We measured prebronchodilator and postbronchodilator interrupter resistance (Rint) and symptom scores at 0 (V1), 4 (V2) and 12 (V3) weeks. At V2, those with a predetermined symptom level commenced ICS. Modified Asthma Predictive Index (mAPI) and parental perception of response to bronchodilator were recorded. Response to ICS was defined as a reduction in daily symptom score of >0.26. Positive BDR was defined as fall in Rint of ≥0.26 kPa.s/L, ≥35% predicted or ≥1.25 Z Scores.

RESULTS

Out of 138 recruited children, 67 completed the full study. Mean (SD) prebronchodilator Rint at V2 was 1.22 (0.35) kPa.s/L, and fell after starting ICS (V3) to 1.09 (0.33) kPa.s/L (p<0.001), while mean (SD) daily symptom score fell from 0.56 (0.36) to 0.28 (0.36) after ICS (p<0.001). Positive Rint BDR before ICS (at V1 and/or V2), using all three threshold criteria, was significantly associated with response to ICS on symptom scores at V3 (p<0.05). mAPI was not significantly associated with response to ICS, and parents' perception of response to bronchodilator was not related to measured Rint BDR .

CONCLUSIONS

Rint BDR may be helpful in selecting which wheezy preschool children are likely to benefit from ICS.

Interrupter resistance to measure dose-response to salbutamol in wheezy preschool children

AIM

Using a non-invasive lung function technique (interrupter resistance, Rint), we aimed to determine whether a dose-response to salbutamol could be detected in wheezy preschool children and if so, which dose of salbutamol should be administered to routinely evaluate bronchial reversibility.

METHOD

Wheezy children (3 to <7 years) were enrolled in a prospective multicenter study. Rint was measured at baseline, and after random assignment to a first dose (100 or 200 μg) and a second dose (cumulative dose: 400, 600, or 800 μg) of salbutamol. Data were analyzed using mixed modeling approach with an inhibitory maximal effect (I_max ) model, to account for a sparse sampling design. Simulations were performed to predict the percentage of children with significant Rint reversibility at several doses.

RESULTS

Final results were available in 99 children out of 106 children included. The model adequately fitted the data, showing satisfactory goodness-of-fit plots and a low residual error of 8%. Children with uncontrolled symptoms had lower I_max (ie, showed less reversibility) compared to children with totally/partly controlled symptoms (0.23 vs. 0.31, P < 0.001). Dose to reach 50% of I_max (D₅₀ ) was 51 μg. According to simulations, 88.1% of children with significant reversibility at dose 800 μg would already show significant reversibility at 400 μg.

CONCLUSION

Interrupter resistance was able to measure a dose-response curve to salbutamol in wheezy preschool children, which was similar to that of older patients. Young children require a high dose of salbutamol to correctly assess airway bronchodilator response, especially these with poor symptom control.

Interrupter technique in infancy: Higher airway resistance and lower short-term variability in preterm versus term infants

BACKGROUND

In preschool children, measurement of airway resistance using interrupter technique (Rint) is feasible to assess the degree of bronchial obstruction. Although some studies measured Rint in infancy, values of Rint and its variability in preterm infants are unknown. In this study, Rint and its variability was measured at infancy and compared between healthy term and preterm infants.

METHODS

High quality Rint measurements in term (n = 50) and preterm (n = 48) infants were obtained at postmenstrual age of 42-50 weeks in two study centers in Switzerland. Intra-measurement variability of Rint in one measurement and inter-measurement variability between two subsequent measurements was assessed by coefficient of variation (CV).

RESULTS

Mean Rint in term infants was 4.2 ± (SD; 1.9) kPa · s · L^-1 and in preterm infants was 5.6 ± (2.8) kPa · s · L^-1 . Mean CV in term infants was 29.6 ± (14.9)% and in preterm infants was 20.2 ± (8.4)%. Rint was significantly lower (95%CI -2.31 to -0.38; P = 0.007) and CV significantly higher (95%CI 4.53-14.3; P < 0.001) in term compared to preterm infants. There were no differences in mean Rint and mean CV between the first and the second measurement obtained in a subgroup of term (n = 24, 48%) and preterm (n = 22, 45%) infants.

CONCLUSIONS

Our results suggest that differences in airway mechanics between term and preterm infants can be assessed with the interrupter technique during early infancy. Before clinical application of Rint measurements in this age group, reasons underlying the variability of measurements should be further investigated.

Feasibility of spirometry testing in preschool children

RATIONALE

The primary purpose of this study was to evaluate the feasibility of obtaining acceptable and reproducible spirometry data in preschool aged children (3-5 years) by technicians without prior experience with spirometry.

METHODS

Two technicians were trained to perform spirometry testing (ndd Easy on-PC) and to administer standardized questionnaires. Preschool aged children were enrolled from two Head Start centers and a local primary care clinic. Subjects were trained in proper spirometry technique and tested until at least two acceptable efforts were obtained or the subject no longer produced acceptable efforts.

RESULTS

200 subjects were enrolled: mean age 4.0 years (± 0.7 SD); age distribution: 51 (25.5%) 3 years old, 103 (51.5%) 4 years old, and 46 (23%) 5 years old. Fifty-six percent male and 75% Hispanic. One hundred thirty (65%) subjects produced at least one acceptable effort on their first visit: 23 (45%) for 3 years old, 67 (65%) for 4 years old, and 40 (87%) for 5 years old. The number of acceptable efforts correlated with age (r = 0.29, P < 0.001) but not gender. The mean number of acceptable efforts on the first visit was 2.66 (± 2.54 SD; range 0-10). One hundred twenty subjects (60%) had two acceptable efforts; 102 had FEV0.5 within 10% or 0.1 L and 104 had FVC within 10% or 0.1 L of best effort. The Asthma Health Screening Survey (AHSS) was 78% sensitive when compared to a specialist exam and 86% compared to a self-reported prior diagnosis of asthma.

CONCLUSIONS

Technicians without prior experience were able to obtain acceptable and reproducible spirometry results from the preschool aged children; the number of acceptable efforts correlated significantly with age.

An official American Thoracic Society workshop report: optimal lung function tests for monitoring cystic fibrosis, bronchopulmonary dysplasia, and recurrent wheezing in children less than 6 years of age

Although pulmonary function testing plays a key role in the diagnosis and management of chronic pulmonary conditions in children under 6 years of age, objective physiologic assessment is limited in the clinical care of infants and children less than 6 years old, due to the challenges of measuring lung function in this age range. Ongoing research in lung function testing in infants, toddlers, and preschoolers has resulted in techniques that show promise as safe, feasible, and potentially clinically useful tests. Official American Thoracic Society workshops were convened in 2009 and 2010 to review six lung function tests based on a comprehensive review of the literature (infant raised-volume rapid thoracic compression and plethysmography, preschool spirometry, specific airway resistance, forced oscillation, the interrupter technique, and multiple-breath washout). In these proceedings, the current state of the art for each of these tests is reviewed as it applies to the clinical management of infants and children under 6 years of age with cystic fibrosis, bronchopulmonary dysplasia, and recurrent wheeze, using a standardized format that allows easy comparison between the measures. Although insufficient evidence exists to recommend incorporation of these tests into the routine diagnostic evaluation and clinical monitoring of infants and young children with cystic fibrosis, bronchopulmonary dysplasia, or recurrent wheeze, they may be valuable tools with which to address specific concerns, such as ongoing symptoms or monitoring response to treatment, and as outcome measures in clinical research studies.

Measurement of Interrupter Respiratory Resistance and Spirometry in Preschool Children: Influence of Respiratory Symptoms

Pulmonary function tests play an important role in the diagnosis and management of respiratory diseases in children. The purpose of the study was to evaluate lung function using the interrupter resistance technique (Rint) and spirometry (flow-volume and volume-time) in preschool children and to correlate the findings with respiratory symptoms. We studied 103 children (65 males, 38 females; mean age 5.2±0.7 years; range 3.6–5.8). For each child we collected family history concerning: respiratory diseases, skin prick tests, smoking during maternal pregnancy, history of gestational and neonatal period. All children performed lung function tests (Rint and spirometry) and skin prick test for inhalant and food allergens. Twenty-eight subjects (27.2%) had respiratory symptoms (RS). Expiratory Rint were performed in all subjects and spirometry was carried out on 76 children (73.8%). Spirometric indices were not statistically different between subjects without respiratory symptoms (controls) and RS children except for FEF25–75 expressed as a percentage of the predicted value (RS: 81.5±13.7% vs controls: 94.5±15.8%; p <0.001). Rint mean values were significantly higher in RS children than in controls (RS: 135.6 ±24.8% vs controls: 102.4 ±21.7%; p< 0.0001). We found a statistically negative correlation between Rint and the following Spirometric indices: FEV0.5 (R= −0.696; p < 0.0001), FEV, (R= − 0.728; p < 0.0001) and FEF25–75 (R= −0.681; p < 0.0001). In preschool children with respiratory disease we found significantly higher mean values of Rint and lower FEF25-75 than in the control group and a significant negative relationship between Rint and Spirometric indices.

Feasibility and reproducibility of spirometry and inductance plethysmography in healthy Brazilian preschoolers

RATIONALE

Preschoolers show peculiarities that reinforce the importance of assessing their pulmonary function. However, there are few data on the success rate and between-occasions reproducibility of pulmonary function tests in preschoolers, particularly in the Brazilian population.

OBJECTIVE

To assess the success rate and between-occasions reproducibility of the variables obtained by spirometry and respiratory inductive plethysmography in healthy children aged 4-6 years.

METHODS

Breathing pattern was assessed by plethysmography (tidal volume-V(T), respiratory rate-f, inspiratory duty cycle-Ti/Ttot, mean respiratory flow-V(T)/Ti, displacement of the rib cage-RC and phase relation during the total breath-PhRTB) and spirometry (forced vital capacity-FVC, forced expiratory volume in 0.5 sec-FEV0.5 and forced expiratory volume in first second-FEV1) in 47 healthy children, aged 4-6 years. To evaluate between-occasions reproducibility, 10 children (according to the sample size calculation) were reassessed after 3 weeks. Between-occasions reproducibility was evaluated by paired t-test, considering significant P < 0.05, Intraclass Correlation Coefficient (ICC) and coefficient of variation of method error (CV(ME)).

RESULTS

The results showed an 83% success rate for spirometry and a 98% success rate for plethysmography. Regarding reproducibility, there were no significant differences between the variables of any test. Spirometry ICC was above 0.80 and the CV(ME) was lower than 10%. The plethysmography ICC was between 0.61 and 0.95, and the CV(ME) was between 2% and 31%.

CONCLUSIONS

These results suggest a high success rate in performing the pulmonary function tests and good between-occasions reproducibility for spirometry and plethysmography in healthy preschoolers.

Evaluation of interrupter resistance in methacholine challenge testing in children

Bronchial hyperresponsiveness (BHR) is a key feature of asthma and is assessed using bronchial provocation tests. The primary outcome in such tests (a 20% decrease in forced expiratory volume in 1 sec (FEV1)) is difficult to measure in young patients. This study evaluated the sensitivity and specificity of the interrupter resistance (Rint ) technique, which does not require active patient participation, by comparing it to the primary outcome measure. Methacholine challenge tests were performed in children with a history of moderate asthma and BHR. Mean and individual changes in Rint and FEV1 were studied. A receiver operating characteristic (ROC) curve was used to describe sensitivity and specificity of Rint . Seventy-three children (median age: 9.2 years; range: 6.3-13.4 years) participated. There was a significant (P < 0.01) increase in mean Rint with increasing methacholine doses. However, individual changes of Rint showed large fluctuations. There was great overlap in change of Rint between children who did and did not reach the FEV1 endpoint. A ROC curve showed an area under the curve of 0.65. Because of low sensitivity and specificity, the use of Rint to diagnose BHR in individual patients seems limited.

Assessment and validation of bronchodilation using the interrupter technique in preschool children

OBJECTIVE

To determine and validate a cut-off value for bronchodilation using the interrupter resistance (Rint) in preschool children.

PATIENTS AND METHODS

Rint was measured in 60 healthy children (age range 2.7-6.4 years) before and after salbutamol inhalation (200 microg). Four potential methods for assessing BDR were evaluated: percent change from baseline, percent change of predicted values, absolute change in Rint, and change in Z-score. These cut-off values, determined as the fifth percentile of the healthy group, were applied to children referred for the assessment of recurrent wheezing, classified on the basis of acute symptoms and/or abnormal chest examination into symptomatic (n = 60, age range 2.9-6.1 years) and asymptomatic (n = 60, age range 2.5-5.7 years) groups.

RESULTS

The cut-off values for bronchodilation calculated in healthy children were: -32% baseline; -33% predicted; -0.26 kPa L(-1) sec; and -1.25 Z-scores. Assessing BDR in children with a history of wheezing by either a decrease in absolute Rint or a decrease in Z-score gave sensitivity, specificity, negative predictive value, and positive predictive value all >80% for detecting children with current respiratory symptoms.

CONCLUSIONS

Both a decrease in Rint > or =0.26 kPa L(-1) sec and a decrease in Z-score of > or =1.25 are appropriate for assessing BDR in preschool children with a history of recurrent wheezing. As Z-score is a more general solution, we recommend using a change in Z-score to determine BDR in preschool children. Further longitudinal studies will be required to determine the clinical utility of measuring BDR in managing lung disease in such children.

Lung function testing in preschool-aged children with cystic fibrosis in the clinical setting

In cystic fibrosis (CF) lung function testing is a means of monitoring progression of lung disease. The preschool years have often been referred to as the "silent years" due to the previous lack suitable measures of lung function testing in this age group. This review outlines the various techniques of lung function testing in preschool children with CF in the clinical setting. This includes measures requiring tidal breathing including the forced oscillation technique, the interrupter technique, plethysmography, and multiple breath washout, as well as spirometry that requires respiratory maneuvers. We describe the feasibility and variability of different lung function methods used in preschoolers and report measurements made during tidal breathing have greater feasibility, although greater variability compared to spirometry. We also report associations with lung function and markers of CF lung disease. In the preschool age group measurements made during tidal breathing may be more appropriate in the clinic setting than those that require a higher degree of cooperation and specific respiratory maneuvers.maneuvers.

Short-term effect of physiotherapy on variability of the lung clearance index in children with cystic fibrosis

Multiple breath washout (MBW) for measuring the lung clearance index (LCI) has been proposed as a non-invasive tool for detecting early cystic fibrosis (CF) lung disease. The LCI is highly repeatable and reproducible in healthy subjects. In patients with CF, within-test variability is low. However, application of physiotherapy (PT) immediately preceding MBW may affect LCI variability in CF patients and thus interpretation of repeat measurements and treatment effects. Therefore, the aim of the present study was to prospectively assess the short-term effect of PT on LCI in CF patients in order to address the question whether or not standardized timing of PT and MBW has to be considered when introducing MBW into clinical CF management. Twenty-seven out of 32 patients (5.7-15.9 years) with CF successfully performed two technically acceptable MBW tests with the EasyOne Pro, MBW Module (ndd, Switzerland) at intervals of 1(1/2) hr. Sixteen out of 27 received 30 min PT in between, whereas 11/27 did not.Repeatability expressed as intraindividual coefficient of variation (CV) was 6.1% pre-PT and 6.5% post-PT. Mean difference (95% CI) of LCI between the two tests was -0.20 (-0.51; 0.11). Reproducibility (SD) was 4.6% (3.1). Repeatability was 4.2% and 7.1% without intervention. Mean difference (95% CI) of LCI between 1st and 2nd test was 0.07 (-0.22; 0.35). Reproducibility (SD) was 2.6% (2.1).In conclusion, PT does not have a consistent effect on the LCI. Repeatability was slightly poorer than published for healthy subjects possibly reflecting variable mucus plugging, and, thus, variable trapped air in patients with CF. Reproducibility was good and independent on intervention. From our data, we conclude that timing of PT in relation to MBW can be ignored when designing study protocols or when interpreting longitudinal data and treatment effects.

Reproducibility of multiple breath washout indices in the unsedated preterm neonate

Multiple breath inert gas washout (MBW) is gaining popularity for measurements of resting lung volume and ventilation inhomogeneity. Test reproducibility is an important determinant of the clinical applicability of diagnostic tests. The between-test reproducibility of variables derived from MBW tests in newborn infants is unknown. We aimed to determine the within-test repeatability and short-term between-test reproducibility of MBW variables in unsedated preterm infants. We hypothesized that measurements obtained within a 3-day interval in clinically stable preterm infants would be reproducible and suitable for use as an objective clinical outcome measurement. In this cross-sectional observational study, clinically stable hospitalized preterm infants whose parents had given informed consent for MBW studies were tested twice within 72 hr during quiet, unsedated sleep. Functional residual capacity (FRC), lung clearance index (LCI), and the first and second to zeroeth moment ratios (M(1):M(0); M(2):M(0)) were computed from MBW traces obtained using a mainstream ultrasonic flowmeter and 4% sulphur hexafluoride (MBW(SF6)). Within-test repeatability and between-test reproducibility were determined. Within-test repeatability (expressed as a coefficient of variability (C(v))) for differences between two and four replicate measurements on the same test occasion, were 9.3% (FRC), 9.0% (LCI), 7.6% (M(1):M(0)), and 15.6% (M(2):M(0)), respectively. The within-test C(v)'s were not statistically different to the between-tests C(v)'s, which were 7.7% (FRC), 10.3% (LCI), 6.1% (M(1):M(0)), and 13.0% (M(2):M(0)), respectively. Among unsedated preterm infants, between-test reproducibility over a 3-day interval was similar to within-test repeatability. The wide limits of agreement may limit the application of these measures to detect a clinically significant change in condition in small preterm infants.

Lung clearance index: normal values, repeatability, and reproducibility in healthy children and adolescents

There is increasing interest in using the Multiple Breath Washout technique and the lung clearance index (LCI) for detecting early pulmonary changes, for example, in cystic fibrosis lung disease. However, there are still limited data regarding equipment specific reference ranges, repeatability and reproducibility. The aim of this prospective study was to assess within-test repeatability, short term reproducibility and long term reproducibility, and to establish normal values for the LCI in healthy children and adolescents using the sidestream ultrasonic flow sensor (EasyOne Pro, MBW Module, ndd Medical Technologies, Switzerland). Fourty-four volunteers (5.3-20.3 years) were recruited for the 1st test. Twenty-two out of 44 were measured on a 2nd test occasion after an interval of 1 hr (2nd test). Thirty-four out of 44 agreed to come back for a follow up test 6-15 months later (3rd test). Mean LCI (SD) was 6.2 (0.4), 6.3 (0.4), and 6.0 (0.4) at the 1st, 2nd, and 3rd test. The upper limit of normal was 7.0 for all subjects. Within-test repeatability was 5.1%. Short-term reproducibility (1st test vs. 2nd test) was 4.2% with a mean difference of -0.13 (95% CI -0.350; 0.087). Long-term reproducibility (1st test vs. 3rd test) was 5.1%, with a mean difference of 0.017 (95% CI -0.016; 0.348). With this low variability of the LCI for both, within and between tests, our study demonstrates reliability and robustness of equipment, protocol and analysis and the reliability of the MBW technique in general. The present data will help to interpret the effect of therapeutic interventions and interpretation of longitudinal data in patients with pulmonary diseases.

Measurement and repeatability of interrupter resistance in unsedated newborn infants

Interrupter resistance (R(int)) is a useful measure of airway caliber in young children, but has not been well characterized in infants-in whom there are concerns about the accurate measurement of driving pressure. This study aimed to assess the feasibility and repeatability of measuring R(int) in unsedated newborn infants, and to explore alternative algorithms for calculating driving pressure. R(int) measurement was attempted in 28 healthy term newborn infants during natural sleep using the MicroRint device. Paired R(int) measurements were achieved in 24 infants, but after screening of waveforms only 15 infants had at least 5 technically acceptable waveforms on both measurements. R(int) values obtained were comparable with reported values for airflow resistance in newborns using other methods. However, the repeatability coefficient (CR) was much higher than reported values in preschool children using standard back-extrapolation algorithms, with CR 2.47 KPa L(-1) sec (unscreened) and 2.93 KPa L(-1) sec (screened). Other algorithms gave only marginally better repeatability, with all CR values over 50% of the mean R(int) value. Using current commercially available equipment, R(int) is too poorly repeatable to be a reliable measurement of airflow resistance in newborn infants. Lower deadspace equipment is needed, but anatomical and physiological factors in the infant are also important.

Effects of the menstrual cycle on expiratory resistance during whole body exercise in females

Our objective was to determine if the menstrual cycle affected expiratory resistance developed during progressive incremental exercise in females. Eleven females (age = 19.7 ± 1.1 yr., body mass = 58.9 ± 8.8 Kg, height = 1.65 ± 0.3 m) gave consent to participate in the study. Participants were studied during the follicular (day 7 ± 2 days following onset of menses) and luteal (day 21 ± 2 days following onset of menses) phases of their menstrual cycle. The expiratory resistance was significantly higher during the follicular phase at maximal workload versus the luteal phase (1.0 ± 0.06 cm H2O/L/sec vs. 0.9 ± 0.07 cm H2O/L/sec.: p¼ 0.05). No other differences were found in expiratory resistance, oxygen uptake or maximal heart rate during exercise. Results showed that the increase in expiratory resistance during the follicular phase of the menstrual cycle may be contributing to the changes in the pulmonary system of females as reported by other authors. Key pointsDuring maximal exercise there was a significantly larger expiratory resistance during the follicular phase versus luteal phase of the female subjects menstrual cycle.Fluctuation in hormones (especially progesterone and/ or oestrogen) may contribute to changes in expiratory resistance.The increased expiratory resistance may be a contributing factor to the increased occurrence of expiratory flow limitation in female subjects.

Can bronchodilator response predict bronchial response to methacholine in preschool coughers?

The aim of the present study was to determine the relationship between bronchodilator response, assessed by interrupter resistance (Rint), and bronchial reactivity in preschool children with chronic cough. Thirty-eight children coughers (median age 5.0 years, range 2.8-6.4) were tested. Bronchodilator response was recorded within 4 months before methacholine challenge. Response to the latter was assessed using transcutaneous partial pressure of oxygen and Rint. Children were considered responders if a 20% fall in transcutaneous partial pressure of oxygen occurred during the bronchial challenge. Bronchodilator response was not different between responders (n = 24) and nonresponders (n = 14) [median (range) -0.11 (-0.44-0.09) vs. -0.08 (-0.21-0.10) kPa L(-1) sec; respectively]. However, none of the nonresponders had a bronchodilator response larger than -0.21 kPa L(-1) sec, this cutoff had a 100% positive and a 44% negative predictive value to predict a positive methacholine challenge. The relationship between bronchodilator response and bronchial methacholine responsiveness reached the limit of significance (P = 0.048). Furthermore, the magnitude of the bronchodilator response was correlated to the level of methacholine-induced level of bronchoconstriction (P = 0.01), and to the postchallenge bronchodilation (P = 0.04), all values expressed as % predicted. Moreover, the postbronchodilator Rint value obtained with preceding methacholine challenge was lower than the postbronchodilator value without preceding methacholine challenge in 71.4% (10/14) of the nonresponders and in only 33.3% (8/24) of the responders. Conclusions in preschool coughers bronchodilator response, assessed by the interrupter technique, was correlated to the bronchial responsiveness to methacholine. Non responders had a bronchodilator response not larger than -0.21 kPa L(-1) sec.

Effect of bacterial filter on measurement of interrupter resistance in preschool and school-aged children

BACKGROUND

The interrupter technique is increasingly used in preschool children to assess airway resistance (Rint). Use of a bacterial filter is essential for prevention of cross-infection in a clinical setting. It is not known how large an effect this extra resistance and compliance exert upon interrupter measurements, especially on obstructive airways and in smaller children. We aim to determine the contribution of the filter to Rint, in a sample of children attending lung function testing at an asthma clinic.

METHODS

Interrupter measurements were performed according to ATS/ERS guidelines during quiet normal breathing at an expiratory flow trigger of 200 ml s(-1), with the child seated upright with cheeks supported and wearing a nose clip. A minimum of 10 interrupter measurements was made with and without a bacterial filter. Spirometric and plethysmographic tests were also performed.

RESULTS

A small but significant difference (0.12 (95% CI 0.06-0.17) kPa s L(-1), P = 0.0002) with 2x SD of 0.34 kPa s L(-1) was observed between Rint with and without filter in 39 children, with a large spread. This difference was not dependent on Rint magnitude, age or height, nor on lung function parameters (effective resistance, forced expiratory volume in 1 sec, and maximal expiratory flow at 50% of expired vital capacity).

CONCLUSIONS

A bacterial filter causes a small difference but is not clinically significant, with a wide spread comparable to the variability of the technique and recommended cut-offs for assessing repeatability and bronchodilation. Age, height or severity of obstruction need not be corrected for in general.

Methacholine challenge in pre-school children--which outcome measure?

The aim of our study was to evaluate the utility of interrupter resistance (R(int)), transcutaneous oximetry and auscultation as outcome measures for a recently suggested tripling-dose methacholine (Mch) challenge in pre-school children. We studied 57 children aged 3-6 years. R(int) was measured at baseline and after each Mch dose. Oxygen saturation (SaO(2)) and transcutaneous oxygen pressure (tcpO(2)) were monitored during the challenge. Mch concentrations of 0.22, 0.66, 2.0, 6.0 and 18.0 mg/ml were nebulised during tidal breathing. The challenge was terminated if there was wheeze, SaO(2) below 91% or persistent cough; this final Mch dose was considered as PCW. Nine healthy children, 17 with cough and 25 with wheeze performed the study up to the point of PCW or all five Mch inhalations. If a change of 20% of predicted R(int) or termination by wheeze, desaturation or cough is taken as a completed test, then 39 out of 51 children (78%) had adequate R(int) measurements on each occasions from start to completion. The success rate for tcpO(2) measurements was similar: 38 out of 51 (76%) had complete tcpO(2) data until a 15% fall of tcpO(2) or clinical endpoint was reached. Using the above-mentioned cut-off levels significant change in R(int) or tcpO(2) preceded PCW in most of the cases. Both R(int) and tcpO(2) measurements may allow detection of bronchial hyper-responsiveness at lower Mch doses and also provide a less subjective measure, but will not be feasible in all children.

Interrupter resistance short-term repeatability and bronchodilator response in preschool children

Interrupter resistance (Rint) technique can be easily and successfully performed in preschool children. The establishment of Rint short-term repeatability is essential to interpret any Rint change after a pharmacological intervention.

AIMS OF THE STUDY

In preschool children with asthma or chronic cough: (1) to assess two indices of short-term repeatability: (a) intra-measurement and (b) within-occasion between-test repeatability; (2) to study the relationship between short-term repeatability and bronchodilator response (BDR).

RESULTS

Rint intra-measurement repeatability assessed by the coefficient of variation was similar at baseline and after bronchodilator in asthmatics and in coughers (median 10% and 12%, respectively). There was no significant difference between asthmatics and coughers for both coefficient of repeatability (CR) (0.25 kPa L(-1)s and 32% of predicted vs 0.16 kPa L(-1) s and 21% of predicted, respectively) and BDR (median -14.7% vs -21.1% of predicted, respectively). However, in 20% of the study children, baseline variability of Rint modified the significance of the BDR.

CONCLUSION

In the present study, Rint short-term repeatability was similar to that of previous studies. Similar Rint repeatability in coughers and in asthmatic children favored the use of asthmatic CR for both populations, and a -35% cut-off as a positive BDR. In 20% of study children, baseline Rint variability could influence the significance of the BDR. In order to improve assessment of BDR using Rint, further studies are needed (1) to compare the variability of Rint to other resistance measurement techniques and (2) to define the best method for Rint calculation and for expression of BDR.

Endpoints for clinical trials in young children with cystic fibrosis

The availability of sensitive, reproducible, and feasible outcome measures for quantifying lung disease in children with cystic fibrosis (CF) younger than 6 years is critical to the conduct of clinical trials in this important population. Historically, identifying and quantifying the presence of lung disease in very young children with CF was hampered by a lack of reproducible measures of lung function or lung pathology. Over the past 10 years, significant progress has led to physiologic, anatomic, and bronchoscopic measures that may serve as endpoints for future intervention trials. These endpoints include infant and preschool lung function testing, computed tomography of the chest, and bronchoalveolar lavage markers of inflammation and infection. Much progress has occurred in standardizing lung function testing, which is essential for multicenter collaboration. Pulmonary exacerbation has the potential to serve as a clinical endpoint; however, there is currently no standardized definition in children with CF younger than 6 years. Further development of these outcomes measures will enable clinical trials in the youngest CF population with the objective of improving long-term prognosis.

Inhaled corticosteroids for recurrent respiratory symptoms in preschool children in general practice: randomized controlled trial

BACKGROUND

Therapy with inhaled corticosteroids (ICS) is beneficial in patients with asthma. However, in preschool children with symptoms like cough, wheeze, or shortness of breath diagnosing asthma is difficult. Therefore, the role of ICS in the management of preschool children with recurrent respiratory symptoms is unclear. We assessed the effectiveness of ICS in preschool children with recurrent respiratory symptoms in general practice.

METHODS

In this multicenter, randomized, double blind, placebo controlled trial, 96 children aged 1-5 years consulting their general practitioners for recurrent respiratory symptoms and in whom treatment with ICS was considered by the general practitioner were randomly allocated to receive ICS (fluticasone propionate 200 mcg/day by metered dose inhaler/spacer combination) or placebo for 6 months. Outcome assessments were carried out 1, 3, and 6 months after randomization. The primary outcome measure was the symptom score (cough, shortness of breath and wheeze during day and night) as measured by a symptom diary card. Secondary endpoints were symptom-free days, use of rescue medication, adverse events, and lung function variables as measured by the interrupter technique and forced oscillation technique.

RESULTS

During the 6 months treatment period, symptoms improved in both groups, with no differences between ICS and placebo. In addition, none of the secondary outcome parameters showed differences between both treatment groups.

CONCLUSION

ICS treatment has no beneficial effect in preschool children with recurrent respiratory symptoms in general practice. We therefore recommend a watchful waiting policy with only symptomatic treatment in these children. General practitioners and pediatricians should be aware of the high probability of overtreatment when prescribing ICS in these children.

Clinical implications of pulmonary function testing in preschool children

There is increasing recognition of the need for objective physiological measurements of lung function during the preschool years in order to identify and treat early lung disease before irreversible structural changes occur; monitor disease progression and efficacy of therapeutic interventions and distinguish the various wheezing phenotypes that occur in this age group, all of which require different management strategies. While preschool pulmonary function tests are undoubtedly excellent research tools , their role in the clinical management of the individual young child remains more controversial. In particular, further work is required to establish information on the within-subject, between occasion variability and the relative sensitivity and specificity of each technique, as well as developing more appropriate prediction equations for this age group, before they can be used confidently in the clinical management of individual child. This review examines the various challenges facing paediatricians who are responsible for children with respiratory diseases such as asthma, wheezing, cystic fibrosis and chronic lung disease following preterm delivery and summarises recent recommendations from an ATS/ERS Task Force.

Should we use criteria or eyeballing to reject post-interruption tracings?

During the analysis of interrupter resistance (R(int))-measurements, most authors reject post-interruption tracings based on the shape of the pressure-time and flow-time curves. However, objective criteria for rejection are lacking. We aimed to formulate explicit rejection criteria that correspond to eyeballing the curve pattern (daily practice), in order to simplify the analysis. Inter-observer agreement within and between both methods was studied. Results obtained with the developed rejection criteria were compared to those of current practice (eyeballing) using 54 measurements (807 interruptions) of children with severe neurological impairment. Inter-observer agreement on rejection was similar using the criteria or eyeballing (85.6% vs. 82.8%). Using the criteria, more individual interruptions were rejected (43.4% vs. 29.8% using eyeballing), while discarding total measurements (<5 remaining interruptions) was similar (9.2% vs. 7.4% using eyeballing). Results using only the criteria for pressure-time curves were comparable to eyeballing. Outcome values were comparable between any of the used rejection methods and not rejecting at all. In this first detailed study on rejection of post-interruption tracings, explicit rejection criteria were developed. None of the rejection methods influenced the outcome value relevantly. However, rejection criteria can contribute to the standardization of the R(int) technique and simplify decision-making in daily practice.

Spirometry in the diagnosis of asthma in children

PURPOSE OF REVIEW

To review the diagnostic accuracy of lung function measurements made using spirometry for childhood asthma, recent guidelines for the measurement and interpretation of spirometric lung function tests and recent developments for diagnosing asthma.

RECENT FINDINGS

Measurements of lung function and bronchial lability made using spirometry may not perform any better than other tests such as skin prick testing, or measurements of exhaled nitric oxide for diagnosing asthma. New guidelines are available.

SUMMARY

Spirometry is a simple, robust and widely available tool for investigating lung function. There are published guidelines for making measurements and their interpretation. The place of spirometry in the diagnosis of asthma, however, needs clarification. The diagnostic profiles of measurements of bronchodilator responsiveness and bronchial hyperreactivity made using spirometry, although reasonable, are not perfect. In schoolchildren, they are no better than knowledge of aeroallergen sensitization when considering a diagnosis of asthma.

Plethysmograph and interrupter resistance measurements in prematurely born young children

BACKGROUND

Airways obstruction in premature infants is often assessed by plethysmography, which requires sedation. The interrupter (Rint) technique does not require sedation, but has rarely been examined in children under 2 years of age.

OBJECTIVE

To compare Rint results with plethysmographic measurements of airway resistance (Raw) in prematurely born, young children.

DESIGN

Prospective study.

SETTING

Infant and Paediatric Lung Function Laboratories.

PATIENTS

Thirty children with a median gestational age of 25-29 weeks and median postnatal age of 13 months.

INTERVENTIONS AND MAIN OUTCOME MEASURES

The infants were sedated, airway resistance was measured by total body plethysmography (Raw), and Rint measurements were made using a MicroRint device. Further Raw and Rint measurements were made after salbutamol administration if the children remained asleep.

RESULTS

Baseline measurements of Raw and Rint were obtained from 30 and 26 respectively of the children. Mean baseline Rint values were higher than mean baseline Raw results (3.45 v 2.84 kPa/l/s, p = 0.006). Limits of agreement for the mean difference between Rint and Raw were -1.52 to 2.74 kPa/l/s. Ten infants received salbutamol, after which the mean Rint result was 3.6 kPa/l/s and mean Raw was 3.1 kPa/l/s (limits of agreement -0.28 to 1.44 kPa/l/s).

CONCLUSION

The poor agreement between Rint and Raw results suggests that Rint measurements cannot substitute for plethysmographic measurements in sedated prematurely born infants.

Airway resistance measurements in pre-school children with asthmatic symptoms: the interrupter technique

Measuring airway resistance in pre-school children with the interrupter technique has proven to be feasible and reliable in daily clinical practice and research settings. Whether it contributes to diagnosing asthma in pre-school children still remains uncertain. From the results of previous studies a need for standardisation of the technique has emerged. In this overview we will elaborate on research concerning the position of the interrupter technique in the difficult process of diagnosing asthma in pre-school children.

Lung function tests in neonates and infants with chronic lung disease of infancy: functional residual capacity

This is the second paper in a review series that will summarize available data and discuss the potential role of lung function testing in infants and young children with acute neonatal respiratory disorders and chronic lung disease of infancy. The current paper addresses the expansive subject of measurements of lung volume using plethysmography and gas dilution/washout techniques. Following orientation of the reader to the subject area, we focus our comments on areas of inquiry proposed in the introductory paper to this series. The quality of the published literature is reviewed critically, and recommendations are provided to guide future investigation in this field. Measurements of lung volume are important both for assessing growth and development of lungs in health and disease, and for interpreting volume-dependent lung function parameters such as respiratory compliance, resistance, forced expiratory flows, and indices of gas-mixing efficiency. Acute neonatal lung disease is characterized by severely reduced functional residual capacity (FRC), with treatments aimed at securing optimal lung recruitment. While FRC may remain reduced in established chronic lung disease of infancy, more commonly it becomes normalized or even elevated due to hyperinflation, with or without gas-trapping, secondary to airway obstruction. Ideally, accurate and reliable bedside measurements of FRC would be feasible from birth, throughout all phases of postnatal care (including assisted ventilation), and during subsequent long-term follow-up. Although lung volume measurements in extremely preterm infants were described in a research environment, resolution of several issues is required before such investigations can be translated into routine clinical monitoring.

Inhaled corticosteroids for non-specific chronic cough in children

BACKGROUND

Cough in isolation of other clinical features is known as non-specific cough, which has been defined as non-productive cough in the absence of identifiable respiratory disease or any known aetiology. In children with non-specific cough the possibility of asthma being the underlying disorder is often raised (so called cough variant asthma). The proponents of cough variant asthma suggest a therapeutic trial of medications usually used to treat asthma.

OBJECTIVES

To determine the efficacy of inhaled corticosteroids in non-specific cough in children over the age of two years.

SEARCH STRATEGY

Searches were conducted on Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and EMBASE. Searches were current as of March 2004.

SELECTION CRITERIA

All randomised (randomised and quasi-randomised) controlled clinical trials in which an inhaled corticosteroid (beclomethasone (BDP), fluticasone (FP), triamcinalone (TAA) or any other corticosteroid) were given for cough in children over two years of age were included. Two review authors independently assessed articles for inclusion and methodological quality.

DATA COLLECTION AND ANALYSIS

Data from trials was extracted by both review authors and entered into the Cochrane Collaboration software program RevMan Analyses 1.0.2.

MAIN RESULTS

Two trials met the inclusion criteria (123 participants). One compared inhaled beclomethasone dipropionate (400 micrograms per day) with placebo and the other compared fluticasone propionate (2 mg per day for 3 days followed by 1 mg per day for 11 days) with placebo. Both studies used metered dose inhalers via a spacer. With the lower dose of inhaled corticosteroid there was no significant difference between the beclomethasone and placebo groups. With the higher dose there was a significant improvement in nocturnal cough frequency after two weeks in children presenting with persistent nocturnal cough. However, a significant but smaller improvement was also seen with placebo.

AUTHORS' CONCLUSIONS

In one study beclomethasone dipropionate (400 micrograms per day) was no different from placebo in reducing the frequency of cough measured objectively or scored subjectively. There might be a small improvement with very high-dose inhaled corticosteroid but the clinical impact of this is unlikely to beneficial.

Assessing respiratory function in young children: Developmental considerations

The purpose of this review is to provide practitioners and clinical investigators with an update on methods of assessing respiratory function in young children. The importance of this topic is presented in light of the natural history of asthma, as well as maturational changes that occur early in life in terms of airway development. Models of disease are cited to support the concept that injury of the mammalian airway early in postnatal life might have far-reaching consequences in terms of control of airway caliber and responsiveness. The methods currently available to measure respiratory function in our younger patients are outlined. The ability of children to perform the maneuvers necessary for this testing is considered as a function of age. Areas in which research and development are needed are highlighted.

Flow dependence and repeatability of interrupter resistance in lower airways and nose

The interrupter technique, the simplest method for measuring airflow resistance (R(int)) is particularly valuable under field conditions. We investigate whether during tidal breathing, variations in the flow at which interruption occurs contribute to variability of results. Using a portable device with mouthpiece, sets of 10 measurements of R(int) (R(int,mo)) were made in inspiration and expiration at 0.05 l s(-1) intervals from 0.1 up to 0.9 l s(-1) flow in 22 normal adults, 11 children (5-9 years) and 12 COPD patients. R(int) was also measured via nasal-mask in normal adults (R(int,na)). Intra-subject coefficient of variation was obtained at each flow and flow-dependence of R(int) was assessed. In normal subjects, R(int)-flow relationships were consistent, with a narrow range of absolute values. R(int,na), but not R(int,mo), rose with increasing flow, especially >0.4 l s(-1). Repeatability was poor at flows <0.3 l s(-1) but improved with increasing flow and was better in inspiration than expiration. In children, repeatability was better than in adults and R(int,mo) was not flow dependent at < or =0.4 l s(-1). By contrast, in COPD patients repeatability was less good and R(int,mo) increased with increasing flows. R(int,mo) and R(int,na) should be measured at fixed inspiratory flows. The best signal-to-noise ratios were obtained at 0.4 l s(-1) for R(int) in normal adults and COPD patients and at 0.3 l s(-1) in children.

Difficult asthma in the pre-school child

The most important aspect of dealing with a pre-school child suspected of having difficult asthma, is to ensure that the diagnosis is correct, in order to avoid the inappropriate use of therapies such as inhaled corticosteroids. After exclusion of other diagnoses, if a pre-school child is thought to have asthma, difficult or otherwise, the corollary is, what sort of asthma? Is it a syndrome with airway inflammation susceptible to treatment, or one in which there is no inflammation and time alone will result in resolution of symptoms? Probably the most common mistake in this age group is to fail to recognise the latter and institute ever more aggressive and useless therapies. An approach to excluding other diagnoses, appropriate investigations to elicit the presence of airway inflammation and suggestions for subsequent management have been detailed in this review.

Airway resistance by the interrupter technique: which algorithm for measuring pressure?

Airway resistance using the interrupter technique (Rint) can be measured using commercial devices which employ different algorithms for estimating pressure change. We aim to describe differences in Rint due to algorithm. We compared Rint and change in Rint after bronchodilator, using four algorithms to estimate pressure change following interruption: 1) two-point back-extrapolation to interruption from points 70 msec and 30 msec from interruption, and similarly 2) to 15 msec from interruption, 3) at two-thirds from interruption, and 4) near end-interruption. Flow was measured immediately before interruption. Our subjects were 39 asymptomatic children 2-5 years old with previous intermittent wheeze. Rint differed significantly with algorithm. Geometric mean Rint (95% confidence interval (CI)) for algorithms 1-4 were 1.21 kPa x l(-1) x sec (1.18-1.24 kPa x l(-1) x sec), 1.31 kPa x l(-1) x sec (1.28-1.34 kPa x l(-1) x sec), 1.57 kPa x l(-1) x sec (1.54-1.61 kPa x l(-1) x sec) and 1.71 kPa x l(-1) x sec (1.67-1.75 kPa x l(-1) x sec), respectively. Measurement of change in R(int) following bronchodilator (BDR) did not differ on average with algorithm. Geometric means (95% CI) for BDR measurements for algorithms 1-4 were 29.9% (26.0-34.0%), 30.4% (26.4-34.5%), 32.9% (28.8-37.1%), and 31.7% (27.6-35.8%), respectively. However, measurement of change in individuals could differ by up to 40%, depending on algorithm. In conclusion, there are significant differences in Rint, depending on algorithm used to estimate pressure change. Measurement of change in Rint is unaffected on average, although in individuals there could be significant differences. Each laboratory should state its method and use the same algorithm for longitudinal and group data.

Interrupter resistance and wheezing phenotypes at 4 years of age

It is difficult to distinguish young children with respiratory symptoms who will develop asthma from those with transient symptoms only. Measurement of interrupter resistance may help to identify children at high risk of asthma. The aim of this study is to compare interrupter resistance in 4-year-old children with different wheezing phenotypes. All children participated in the Prevention and Incidence of Asthma and Mite Allergy cohort, a prospective birth cohort of more than 4,000 children. At 4 years of age, data on interrupter resistance plus wheezing phenotype were available for 838 children. Mean interrupter resistance values (95% confidence interval) were 0.95 (0.93, 0.97), 0.95 (0.92, 0.98), 0.96 (0.87, 1.05), and 1.08 (1.02, 1.14) kPa.L(-1).second for never (n = 482), early transient (n = 236), late-onset (n = 22), and persistent (n = 98) wheezing phenotypes, respectively. Additional analyses were performed for children with atopic and nonatopic mothers separately. Both in children with atopic and nonatopic mothers, children with persistent wheeze had significantly higher interrupter resistance values than children with never and early wheeze. In conclusion, mean interrupter resistance values were higher in children with persistent wheeze as compared with children with never and early transient wheezing phenotypes.