Specific airway resistance,interrupter resistance,and respiratory impedance in healthy children aged 2–7 years

We report data on respiratory function in healthy children aged 2–7 years in whom we measured respiratory resistance by the interrupter technique (Rint); total respiratory impedance (Zrs), respiratory resistance (Rrs), and reactance (Xrs) by the impulse oscillation technique; and specific airway resistance (sRaw) by a modified procedure method in the whole body plethysmograph. Measurements were attempted in 151 children and were successfully obtained in 121 children with a mean (SD) age of 5.3 (1.5) years; no measurements were possible in 30 children (mean age 3 (0.9) years). The repeatability of measurements was independent of the age of the subjects, and the within-subject coefficient of variation was 11.1%, 8.1%, 10.8%, and 10.2% for sRaw, Rint, Zrs, and Rrs at 5 Hz (Rrs5), respectively. All lung function indices were linearly related to age, height, and weight. A significant negative correlation with age, height, and weight was found for Rint, Zrs, and Rrs5. Xrs5 was positively correlated to age and body size. The mean values of Rint, Rrs5, Xrs5, and Zrs in children younger and older than 5 years were 1.04, 1.38, −0.5, and 1.48 kPa · L⁻¹ · s and 0.9, 1.18, −0.37, and 1.23 kPa · L⁻¹ · s, respectively. sRaw showed no significant correlation with body size or age and the mean sRaw in children younger and older than 5 years was 1.09 and 1.13 kPa · s, respectively. None of the indices of respiratory function differed between boys and girls. Xrs and Rrs exhibited a significant frequency dependence in the range of 5–35 Hz. The techniques applied in this study require minimal cooperation and allow measurement of lung function in 80% of our population of awake young children. Further studies are needed to evaluate the potentials of the presently established reference values for clinical and epidemiological purposes. Pediatr Pulmonol. 1998; 25:322–331. © 1998 Wiley-Liss, Inc.     

Discriminative capacity of bronchodilator response measured with three different lung function techniques in asthmatic and healthy children aged 2 to 5 years

The primary aim of this study was to quantify and compare bronchodilator responsiveness in healthy and asthmatic children aged 2 to 5 yr. The secondary aim of the study was to compare discriminative capacity (i.e., sensitivity, specificity, and predictive values of the reversibility test for the diagnosis of asthma) for each of the lung function tests applied in the study. Specific airway resistance (sRaw) as measured by whole-body plethysmography, respiratory resistance as measured with the interrupter technique (Rint), and respiratory resistance and reactance at 5 Hz (Rrs5, Xrs5, respectively) as measured with the impulse oscillation technique were assessed before and 20 min after inhalation of terbutaline from a pressurized metered-dose inhaler via a metal spacer by 92 children (37 healthy controls and 55 asthmatic subjects). The study of healthy children followed a randomized, double-blind, crossover design, whereas the study of asthmatic children was open. Baseline lung function was significantly decreased in asthmatic children as compared with healthy control subjects as reflected by all techniques used in the study. sRaw, Rint, and Rrs5, but not Xrs5, improved significantly with terbutaline as compared with placebo in healthy control subjects. Lung function improved to a significantly greater extent in asthmatic children than in control subjects as reflected by all methods. sRaw provided the best discriminative power of such a bronchodilator response, with a sensitivity of 66% and specificity of 81% at the cutoff level of a 25% decrease in sRaw after bronchodilator administration. In conclusion, bronchodilator response measured by sRaw allows a separation of asthmatic from healthy young children. This may help define asthma in this clinically difficult-to-manage group of young wheezy children. The sensitivity and specificity of the other methods used in the study were less than those of sRaw.     

Observer variability of lung function measurements in 2-6-yr-old children.

The aim of this study was to assess the within-observer and between-observer variability of lung function measurements in children aged 2-6 yrs. Two observers examined 22 asthmatic children independently according to a predefined protocol. Each observer obtained duplicate measurements of respiratory resistance by the interrupter technique (Rint), respiratory resistance (Rrs,5) and reactance (Xrs,5) at 5 Hz by the impulse oscillation technique and the specific airway resistance (sRaw) by whole body plethysmography. The within-subject SD (SDw) was not significantly different in the two observers. The ratio SDw between observers/mean SDw within observers was 0.94, 1.25, 1.35 and 2.86 for Xrs,5, Rrs,5, sRaw and Rint, respectively, indicating greater between-observer variability of the latter. The systematic difference between observers assessed by the difference between observer means (expressed as a percentage of their mean value) was 11, 7, 6 and 2% for Xrs,5, sRaw, Rrs,5 and Rint, respectively. These differences were statistically significant, except that for Rint. In conclusion, specific airway resistance, impulse oscillation technique and respiratory resistance assessed by the interrupter technique measurements in young children are subject to influence by the observer, and the random variability between observers appears to be particularly great for respiratory resistance assessed by the interrupter technique. The authors suggest that the between-observer variability should be investigated when evaluating novel methods for testing lung function.     

Repeatability of methacholine challenges in 2 to 4-year-old children with asthma,using a new technique for quantitative delivery of aerosol

To determine the repeatability of bronchial responsiveness in awake young children, two methacholine challenge tests were performed on separate days in 16 children with stable asthma (mean age, 3¾ years). Methacholine was administered using a new method for quantitative delivery of aerosol that eliminates the effect of dilution of the aerosol by entrainment of air and enables quantitative delivery of aerosol according to body weight. Respiratory function was monitored by measurement of respiratory resistance by the interrupter technique (Rint), respiratory resistance and reactance at 5 Hz (Rrs5, Xrs5) by the impulse oscillation technique, transcutaneous measurements of oxygen (PtcO₂), and specific airway resistance (sRaw). Repeatability was evaluated by determining the provocative dose that caused a defined percentage of change relative to baseline (PD%: Rint PD₃₀, Rrs5 PD₃₀, Xrs5 PD₃₀, PtcO₂ PD₁₀, and sRaw PD₅₀. Repeatability was estimated from the difference between the PD_% obtained at the time of the two tests. Using the numeric value of these differences, the repeatability of Xrs5 PD₈₀, PtcO₂ PD₁₀, and sRaw PD₅₀ was [mean (SD)]: [0.8 (0.5)] [0.5 (0.4)] and [0.7 (0.6)] doubling doses, respectively. Rint PD₃₀ and Rrs5 PD₃₀ proved to be less reproducible: [1.2 (1)] and [1.6 (0.9)] doubling doses, respectively. The new method of aerosol delivery offers a means of standardizing the bronchoconstrictor stimulus, and the results show that estimates of bronchial responsiveness in young children can be obtained reproducibly within one doubling dose of methacholine. Pediatr. Pulmonol. 1997;23:278–286. © 1997 Wiley-Liss, Inc.     

Lung function response to cold air challenge in asthmatic and healthy children of 2-5 years of age

The aim of the study was to assess feasibility, sensitivity, specificity, predictive value, and repeatability of cold, dry air challenge (CACh) as a diagnostic test for asthma in young children 2 to 5 yr of age. Response to a 4-min single-step isocapnic CACh was measured in 38 asthmatics and 29 control subjects. Specific airway resistance (sRaw) by whole body plethysmography was the primary outcome. In addition, lung function was measured as respiratory resistance by the interrupter technique (Rint) and respiratory resistance and reactance at 5 Hz (Rrs5, Xrs5) by the impulse oscillation technique. At baseline, lung function measures differed significantly between asthmatics and healthy control subjects. CACh was readily performed in young children. Response was expressed as change from baseline in numbers of within-subject standard deviation (SDw). Hyperresponsiveness defined as change in lung function of more than 3 SDw was detected by sRaw in 26 of 38 asthmatics versus 2 of 29 control subjects, by Rint in 12 of 38 asthmatics versus 1 of 29 control subjects, by Xrs5 in 9 of 38 asthmatics versus zero of 29 control subjects and by Rrs5 in 7 of 38 asthmatics versus 1 of 29 control subjects. Thus sRaw had the highest sensitivity (68%). Specificity ranged from 93 to 100%. The correlation coefficient between sRaw responses to CACh repeated within 8 wk was 96%. In conclusion, CACh is feasible in young children age 2 to 5 yr. Whole body plethysmography (sRaw) was superior in separating asthmatics from healthy control subjects. Change in sRaw in response to CACh may be used as a diagnostic test for asthma in young children.     

Lung function and short-term outcome in young asthmatic children.

The aims of this study were to investigate lung function in 2-5-yr-old stable asthmatic children consecutively referred from general practitioners and to analyse the outcome on the basis of their requirement for antiasthmatic treatment and symptoms after 1.6-4.5 yrs. Lung function was measured in 110 children with a mean+/-SD age of 3.8+/-1.0 yrs using the interruptor technique (resistance assessed using the interruptor technique (Rint)), whole body plethysmography (specific airway resistance (sRaw) and respiratory resistance (Rrs,5)and reactance at 5 Hz (Xrs,5) using the impulse oscillation technique. Rint, sRaw, Xrs,5 and Rrs,5 were suggestive of impaired lung function in 44%, 14%, 11% and 7.5% of the children, respectively, with a predominance of children aged 2-3 yrs. Sixty-five per cent were treated with inhaled steroids, and 35% were treated only with beta2-agonists as needed; lung function was not significantly different between these two groups. Outcome after 2.9+/-0.7 yrs was not significantly different between children with Rint measurements above and those children with Rint measurements within the reference range at enrolment. Of these children, 58 and 59% were currently on antiasthmatic treatment, and 40% and 49% had current symptoms, respectively. Impairment of lung function may be a common finding in stable young asthmatic children, but apparently this is not a risk factor for persistence of asthmatic symptoms.     

Evaluation of Bronchial Hyperresponsiveness by Monitoring of Transcutaneous Oxygen Tension and Arterial Oxygen Saturation during Methacholine Challenge in Asthmatic Children

Background. Bronchial hyperresponsiveness (BHR) is a key feature of asthma, but the measurement of BHR is hampered by the fact that most tests of airway caliber are difficult to conduct at a young age. Methacholine-induced bronchoconstriction is associated with significant hypoxemia, which can be assessed noninvasively by transcutaneous oxygen pressure (tcPO₂) and pulse oximetry. Evaluating BHR by monitoring tcPO₂ instead of respiratory resistance (Rrs) has been used over a wide age range in childhood.

Objective. To investigate whether there is a consistent relationship between changes in arterial oxygen saturation (SaO₂) and respiratory resistance (Rrs) similar to the relationship between tcPO₂ and Rrs during methacholine challenge in young children and to assess the usefulness of SaO₂ as a parameter for the indirect measurement of BHR.

Method. We performed methacholine inhalation challenge by monitoring SaO₂, tcPO₂ and Rrs in 37 asthmatic children 5 to 7 years of age. Consecutive doses of methacholine were doubled until a 10% decrease in tcPO₂ from the baseline was reached. We recorded the cumulative dose of methacholine (Dmin) at the inflection point of tcPO₂ (Dmin-tcPO₂), SaO₂ (Dmin-SaO₂), and Rrs(Dmin-Rrs).

Results. The mean value of Dmin-Rrs was 4.27 ± 2.02 units, the mean value of Dmin-tcPO₂ was 4.48 ± 2.01 units, and the mean value of Dmin-SaO₂ was 4.57 ± 0.20 units. Inhalation of increasing doses of methacholine raised Rrs curvilinearly and depressed tcPO₂ and SaO₂. There were no significant differences between any of the parameters. There were significant relationships between Dmin-tcPO₂ and Dmin-Rrs (r = 0.914, p < 0.001) and between Dmin-SaO₂ and Dmin-Rrs (r = 0.905, p < 0.001) and a relationship between Dmin-tcPO₂ and Dmin-SaO₂ (r = 0.949, p < 0.001).

Conclusion. We concluded that measurement of SaO₂ and/or tcPO₂ during methacholine inhalation challenge may be used to assess bronchial hyperresponsiveness. This study showed that both SaO₂ and tcPO₂ monitoring are safe, useful, and tolerable for use in children who are too young to cooperate with lung function tests.     

Evaluation of airway responsiveness using colored three-dimensional analyses of a new forced oscillation technique in controlled asthmatic and nonasthmatic children

BackgroundBronchodilator response (BDR) is routinely used in asthma management. A new forced oscillation technique (FOT) is able to quickly measure respiratory system resistance (Rrs) and reactance (Xrs) at each tidal breath phase. The present study evaluated bronchial changes by using the new FOT.MethodsRespiratory resistance and reactance were measured using FOT in 132 children (age, 10.86±4.78 years; M:F=88:44), including asthmatic (n=98) and nonasthmatic children (n=34), pre- and post-bronchodilator inhalation in an asymptomatic state. Whole-breath or within-breath changes in Rrs and Xrs were measured and compared pre- and post-bronchodilator inhalation and between each group. All patients performed spirometry and forced expiratory nitric oxide pre- and post-bronchodilator inhalation.ResultsSpirometric parameters showed significant positive changes at V₅₀ and V₂₅ in both groups; however, these changes were not significantly different between the groups. eNO was significantly higher in the asthmatic group than in the nonasthmatic group; however, there was no significant change pre- and post-inhalation in either group. Rrs in the asthma group was significantly higher in the expiratory phase than in the inspiratory phase. Rrs and Xrs before and after bronchodilator inhalation were significantly different in the asthma group alone, except for the expiratory–inspiratory phase of each of these parameters. Changes in Rrs and Xrs at 5 Hz (R5 and X5) in a whole-breath and the inspiratory phase were significantly different between the groups.ConclusionsChanges in X5 and R5 reflect bronchial reversibility. The new FOT is useful for asthmatic children.     

Exercise-induced changes in respiratory impedance in young wheezy children and nonatopic controls

Exercise-induced bronchoconstriction (EIB) is a specific sign of active asthma, but its assessment in young children may be difficult with lung function techniques requiring active cooperation. The aim of the study was to assess the normal pattern of exercise-induced responses of respiratory impedance by using impulse oscillometry (IOS), and to investigate how these responses discriminate wheezy children from control subjects. IOS measurements were performed in a consecutive sample of wheezy children aged 3-7 years (n = 130) and in an aged matched control group of nonatopic children without respiratory symptoms (n = 79) before and after a free running test. After exercise, wheezy children showed significantly larger responses in respiratory resistance (Rrs5), reactance (Xrs5), and the resonance frequency (Fr) than the control subjects. In the control group, the upper 95% confidence limit of the maximal change was 32.5% for Rrs5, 85.7% for Xrs5, and 53.1% for Fr. By using analysis of receiver operating characteristics, the change in Rrs5 distinguished the wheezy children from the control subjects more effectively than change in Xrs5 or Fr. In wheezy children, the response was significantly effected by the outdoor temperature and exercise intensity in terms of maximum heart rate. In conclusion, an increase of 35% in Rrs5 after a free running test can be regarded as an abnormal response. Wheezy children show an enhanced airway response, which is clearly distinguishable from the control subjects. IOS is a feasible method to detect EIB in young children.     

Evaluation of impulse oscillation system: comparison with forced oscillation technique and body plethysmography.

The impulse oscillation system (IOS) has been developed recently to measure respiratory system resistance (Rrs) and reactance (Xrs) at different frequencies up to > or = 25 Hz. IOS has, however, not been validated against established techniques. This study compared IOS with the classical pseudorandom noise forced oscillation technique (FOT) and body plethysmographic airway resistance (Raw) in 49 subjects with a variety of lung disorders and a wide range of Raw (0.10-1.28 kPa x L(-1) x s). Rrs,IOS was slightly greater than Rrs,FOT, especially at lower frequencies, with a mean +/- SD difference at 5-6 Hz of 0.14 +/- 0.09 kPa x L(-1) x s. Comparisons with the wave-tube technique applied on two analogues indicated an overestimation by IOS. Xrs,IOS and Xrs,FOT were very similar, with a slightly higher resonant frequency with IOS than with FOT (mean difference +/- SD 1.35 +/- 3.40 Hz). Raw was only moderately correlated with Rrn,FOT and Rrs-IOS; although the mean differences were small (0.04 +/- 0.14 kPa x L(-1)s for Rrs6,FOT and -0.10 +/- 0.14 kPa x L(-1) x s for Rrs5,IOS), IOS and FOT markedly underestimated high resistance values. In conclusion, the impulse oscillation system yields respiratory system resistance and reactance values similar, but not identical to those provided by the forced oscillation technique.     

Effects of respiratory timing and cheek support on resistance measurements, before and after bronchodilation in asthmatic children using the interrupter technique

The interrupter technique (Rint) is a noninvasive method for assessing respiratory resistance. The aims of this study were to assess whether upper airway support affects the measurement of Rint, if inspiratory or expiratory Rint were most reproducible, and which method of assessing Rint correlated best with spirometry results and was the most sensitive for identifying bronchodilator response. Twenty-four asthmatic children with a mean age of 10.3 years (range, 7-16 years) were included in the study. Rint measurements were obtained in inspiration and expiration with cheeks supported and unsupported. Spirometry was then performed. Rint and spirometry measurements were repeated after the inhalation of 600 mcg of salbutamol. The mean Rint supported inspiratory (0.708 KPa/l/sec) and expiratory (0.729 KPa/l/sec) values were significantly higher than the unsupported values (inspiratory, 0.622 KPa/l/sec; expiratory, 0.584 KPa/l/sec), P < 0.05 and P < 0.001, respectively. The reproducibility of Rint was not different whether cheeks were supported or not, or whether the measurements were carried out during inspiration or expiration. Cheek support improved the correlation with all the lung function results, both in inspiratory and expiratory measurements. The best correlations, however, were found for the inspiratory supported Rint results. The most sensitive method to ascertain bronchodilator response (BD) was the inspiratory supported Rint measurement, as 83.3% of children were identified as having a positive response to bronchodilator therapy as defined by a reduction of twice the coefficient of variation of the measurement. In conclusion, cheek support increases Rint but does not impact on reproducibility, though it improves the correlation with spirometric indices. Rint with cheek support on inspiration correlates best with spirometric indices and appears to be the most sensitive measure of response to bronchodilators.     

The interrupter technique to assess airway responsiveness in children with cystic fibrosis

The aim of this study was to assess the validity of the interrupter technique (Rint) in measuring airway responsiveness in children with cystic fibrosis. Fifty children (aged 6-16 years) with cystic fibrosis performed six Rint measurements followed by three acceptable forced expiratory maneuvers. Each child then inhaled 5 mg of nebulized salbutamol by facemask. After 20 min the Rint and forced expiratory measurements were repeated. In the population as a whole a moderate but significant correlation between inverse Rint and FEV1 values was observed, both before and after inhaled bronchodilator (r=0.71 and 0.72, respectively, P < 0.001). However, when changes in Rint and FEV1 readings following inhaled bronchodilator were examined, no relationship was seen. Indeed, the two methods identified completely different subsets of children as being bronchodilator responsive. These results indicate that although a relationship exists between Rint and FEV1 in the whole population, this is not the case in individual children. Rint and FEV1 reflect different aspects of lung function. It is not appropriate to use Rint as a simple alternative for FEV1 in children with cystic fibrosis when assessing airway responsiveness.     

The opening interrupter technique for respiratory resistance measurements in children

Background and objective: The interrupter resistance (Rint) can be calculated from various estimates of alveolar pressure based on mouth pressure during occlusion. We compared Rint, as measured by the opening interrupter technique (Rint1), and the linear back‐extrapolation method (Rint2), with the ‘gold standard’ airway resistance measured by plethysmography (Raw). Methods: The study included 32 asthmatic children and 11 children with cystic fibrosis, aged 5 to 18 years, who were categorized into non‐obstructed (NObs) (n = 27) and obstructed (Obs) (n = 16) groups. Spirometry and the three different resistance measurements were performed on all children. Rint1 and Raw were assessed after a bronchodilator (BD) test in 16 and nine children, respectively, in the Obs group. Results: Raw (0.48 ± 0.20 kPa.s/L) was lower than Rint1 (1.04 ± 0.34 kPa.s/L) and Rint2 (0.63 ± 0.18 kPa.s/L) (P < 0.001). Raw, but neither Rint1 nor Rint2, was significantly higher in the Obs group than in the NObs group (0.57 ± 0.23 vs 0.42 ± 0.16 kPa.s/L, P < 0.05). The differences Rint1‐Raw and Rint2‐Raw were correlated with FEV₁/VC (P < 0.01 and P < 0.001), and Rint1‐Raw was correlated with height (P < 0.001). After BD significant changes in Rint1 and Raw were observed in 5/9 and 7/9 children, respectively. Conclusions: Rint2, as well as Rint1, may be underestimated in the most Obs children and may therefore fail to detect severe obstruction. Rint1 is likely to include a non‐negligible contribution from the tissue component, especially in the youngest children. Although not different between Obs and NObs children at baseline, Rint1 did detect bronchodilation in some Obs children.     

Measurement of airway resistance using the interrupter technique in preschool children in the ambulatory setting.

This study describes the feasibility, repeatability, and interrater reliability of the measurement of airway resistance by the interrupter technique (Rint) in children 2-5 yrs of age, and examines whether reversibility to bronchodilator can be demonstrated in wheezy children. The mean of six Rint values was taken as a measurement. If subjects could complete one measurement and then a second 15 min after bronchodilator, baseline testing and reversibility testing were considered feasible. To measure repeatability, two measurements 30 s apart and measurements before and 15 min after placebo bronchodilator were compared. Measurements by two testers were compared for interrater reliability. Change in Rint in wheezy children was measured after bronchodilator. Fifty-six per cent of 2-3-yr-olds (n=79), 81% of 3-4-yr-olds (n=104) and 95% of 4-5-yr-olds (n=88) completed baseline testing, and 53%, 71% and 91% completed reversibility testing. Baseline measurements were 0.47-2.56 kPa x L(-1) x s. Repeatabilities (2 SD of the mean differences between measurements) at 30 s in the three age bands were 0.21, 0.17 and 0.15 kPa x L(-1) x s and 0.19 kPa x L(-1) x s after placebo. Using 0.21 kPa x L(-1) x s as the threshold for reversibility, reversibility was demonstrated in most wheezy children. Interrater reliability was 0.15 kPa x L(-1) x s. Preschool children can undertake measurements of airway resistance by the interrupter technique in ambulatory settings and reversibility to bronchodilator in wheezy children can be demonstrated. This technique promises to be a useful clinical and research tool.     

Comparison of resistance measured by the interrupter technique and by passive mechanics in sedated infants.

Airways resistance measured by the interrupter technique (Rint) requires little patient cooperation and has been successfully used in young children, but little studied in infants. The authors aimed to evaluate the measurement of Rint in infants, using a commercially available device (the MicroRint), by comparing it with an established technique to measure respiratory resistance: the single breath occlusion technique (SBT); and a measure of airflow obstruction during forced expiration. Infants <18 months old with a history of wheeze, sedated with triclofos for pulmonary function testing, had measurements taken and compared to Rint (using the MicroRint), respiratory system resistance (Rrs) by SBT, and to maximal flow at functional residual capacity (V'maxFRC). Paired data from 25 of 37 infants studied was obtained. There was a significant difference between Rint (mean 2.94+/-0.68) and Rrs (4.02+/-0.87), but the two measures were strongly correlated (r=0.7). Rint was negatively correlated with V'maxFRC (r=-0.63). Smaller infants failed to trigger the MicroRint. Interrupter resistance values in infants are significantly lower than values of respiratory system resistance obtained by passive mechanics. However, there is a strong correlation between the two measurements, as well as between resistance measured using the interrupter technique and maximal flow at functional residual capacity, which indicates that resistance measured using the interrupter technique may be a useful marker of airway obstruction in infants. There remain a number of theoretical and technical problems which require further exploration.     

Assessment of airway function in young children with asthma: comparison of spirometry, interrupter technique, and tidal flow by inductance plethsmography

The assessment of airway function in young children requires adaptation of techniques designed for adults and/or application of techniques that do not require complex respiratory maneuvers. We sought to assess two methods of measuring airway function: time to peak expiratory flows as a ratio of expiratory time (T(PTEF)/T(E)), derived from respiratory inductance plethysmography, and total respiratory resistance by the interrupter technique (Rint), both obtained during quiet tidal breathing. Both techniques were referenced to FEV1 and flow at 50% expired volume (FEF50) from conventional spirometry in 30 children aged 4-8 years (median age, 6.9; range, 4.5-8.5 years) with a physician diagnosis of asthma and who were able to perform FEV1 with a repeatability of at least 8%. T(PTEF)/T(E) and Rint were performed in random order followed by spirometry, in order to reduce the possible effects of pulmonary stretch on tidal breathing measures. Coefficients of variation (CV) and mean absolute change/baseline standard deviation were derived for each measurement. Baseline FEV1 did not correlate significantly with T(PTEF)/T(E) (r = 0.025), but did correlate with Rint (r = 0.737, P < 0.001); respective relationships for change after bronchodilator were r = 0.09 (ns) and r = 0.64 (P < 0.001). FEF50 also correlated significantly with Rint (R = 0.769, P < 0.001) but not with T(PTEF)/T(E). FEV1 and FEF50 both increased postbronchodilator, with respective mean changes of 11.4% and 28% (P < 0.001), while Rint decreased by 24.3% (P < 0.001). No significant changes were noted for T(PTEF)/T(E). T(PTEF)/T(E) derived from inductance plethysmography does not detect mild airway obstruction or modest changes in airway caliber following bronchodilator in young children with asthma. The interrupter technique may have a role in assessing baseline airway function and response to therapy in children unable to perform reliable spirometry, and/or when the investigator wishes to avoid the possible influence of forced maneuvers on airway tone.     

Measurements of resistance by the interrupter technique and of transcutaneous partial pressure of oxygen in young children during methacholine challenge

Measurement of bronchial airway responsiveness requires noninvasive techniques in young children. The study was designed to examine the changes in resistance as measured using the interrupter technique (Rint) at the dose of methacholine (M) that induced a fall in transcutaneous partial pressure in O2 (P(tc)O2) > or = 20% (PD(20)P(tc)O2) in young children. Rint was calculated using the linear back-extrapolation method (Rint(L)) and the end-interrupter method (Rint(EI)). Twenty-two children (mean age, 5.2 +/- 1.1 years; range, 3.4 - 7.1 years) with nonspecific respiratory symptoms (mainly chronic cough, n = 17) were tested. P(tc)O2, Rint(L), and Rint(EI) were measured before the test, after saline challenge (baseline (B)), after each dose of M delivered by a dosimeter, and after bronchodilator (BD) inhalation. P(tc)O2 decreased significantly during M challenge, from 85 +/- 6 mmHg (B) to 62 +/- 9 mmHg (P < 0.05), and increased after BD inhalation, to 82 +/- 8 mmHg. Rint(L) and Rint(EI) increased significantly during M challenge, from 0.94 +/- 0.2 KPa/L/s and 1.11 +/- 0.19 KPa/L/s (B) to 1.27 +/- 0.35 KPa/L/s and 1.47 +/- 0.37 KPa/L/s, respectively (P < 0.05), and decreased after BD inhalation to 0.80 +/- 0.17 KPa/L/s and 0.95 +/- 0.18 KPa/L/s, respectively. Nineteen of 22 children reached the PD(20)P(tc)O2 at a dose of M ranging from 50-400 microg. At the PD(20)P(tc)O2, significant changes in Rint(L) and Rint(EI) (sensitivity index (SI) > or = 2) were found in 79% and 63% of children, respectively. We conclude that: 1) M challenge using P(tc)O2 is safe in young children; and 2) our findings are not in favor of the use of Rint as the only indicator of bronchial reaction in young children during M challenge.     

Airway resistance and atopy in preschool children with wheeze and cough.

The extent to which the measurement of airways resistance by the interrupter technique (Rint) distinguishes preschool children with previous wheeze from those with no respiratory symptoms and helps to classify subjects with persistent cough, was investigated. Rint was measured before and after salbutamol treatment in 82 children with recurrent wheeze, 58 with isolated cough and 48 with no symptoms (control subjects). Their mean age (range) was 3.7 yrs (2-<5 yrs). Median baseline Rint was higher (p<0.0001) in wheezers than in either coughers or control subjects (1.16, 0.94 and 0.88 kPa x L(-1) x s(-1) respectively); coughers did not differ significantly from control subjects (p=0.14). The median ratios of baseline to post-salbutamol measurements (bronchodilator response (BDR)) in the groups differed significantly (1.40, 1.27 and 1.07, p< or =0.01 for all), suggesting that coughers occupy an intermediate position. A BDR ratio of >1.22 had a specificity and sensitivity for wheeze of 80% and 76% respectively. Twenty-eight coughers had a BDR ratio >1.22. Wheezers' immunoglobulin E was inversely related to baseline Rint. It is concluded that measurements of airway resistance by the interrupter technique are useful for classifying preschool children with respiratory symptoms and could be used to monitor the effect of interventions. The relation between atopy and airways resistance suggests that they have separate roles in preschool wheezing. Coughers with a high bronchodilator response could represent "cough-variant" asthma in children who have baseline airway resistance by the interrupter technique measurements similar to control subjects. Whether these children develop classical asthma will only be known at follow-up later in childhood.     

Respiratory impedance and response to salbutamol in healthy Vietnamese children

A high incidence of childhood asthma has been reported in Ha Noi, Viet Nam, indicating a need to document lung function in these children. The degree of airway obstruction and reversibility may be evaluated from the forced oscillation assessment of respiratory resistance to reactance (Rrs, Xrs). Appropriate controls are necessary for a proper interpretation of patients. The aim of the study was to provide reference values on Rrs and Xrs and response to salbutamol in healthy Vietnamese children. One hundred seventy-five children aged 6-11 year recruited from one public school in Ha Noi were studied. Measurements were obtained at baseline and after 200 microg inhaled salbutamol. Significant correlations were disclosed between Rrs or Xrs and standing height (P < 0.0001). Salbutamol significantly decreased Rrs (from 7.1 +/- 1.9 hPa.sec/L to 6.2 +/- 1.8 hPa sec/L, P < 0.0001) and increased Xrs (from -1.22 +/- 0.64 to -0.91 +/- 0.61 hPa.sec/L, P < 0.0001). Rrs response to salbutamol lower limit of 95% confidence interval was -38% from baseline Rrs and, Xrs upper limit was +16% from baseline impedance. It is concluded that reference values for respiratory impedance (Zrs) and thresholds for clinically relevant response to bronchodilator are provided in primary school Vietnamese children. A smaller slope for the observed Rrs-body height relationship is suggested with reference to relevant studies in healthy Caucasians.     

Comparison of the forced oscillation technique and the interrupter technique for assessing airway obstruction and its reversibility in children

The forced oscillation technique (FOT) and interrupter technique are particularly attractive for pediatric use as they require only passive cooperation from the patient. We compared the sensitivity and specificity of these methods for detecting airway obstruction and its reversibility in 118 children (3-16 yr) with asthma or chronic nocturnal cough. FOT (R(0) and R(16)) and interruption (Rint) parameters were measured at baseline and after bronchodilator inhalation (n = 94). Rint was significantly lower than R(0), especially in children with high baseline values. Baseline parameters were normalized for height and weight [R(SD)]. In children able to perform forced expiratory maneuvers (n = 93), the best discrimination between those with baseline FEV(1) < 80% or > or = 80% of predicted values was obtained with R(0)(SD). At a specificity of 80%, R(0)(SD) yielded 66% sensitivity, whereas Rint(SD) yielded only 33% sensitivity. Similarly, postbronchodilator changes in R(0)(SD) [DeltaR(0)(SD)] yielded the best discrimination between children with and without significant reversibility in FEV(1). At a specificity of 80%, DeltaR(0)(SD) yielded 67% sensitivity and DeltaRint(SD) yielded 58% sensitivity. In children unable to perform forced expiratory maneuvers (n = 25), FOT, contrary to the interrupter technique, clearly identified a subgroup of young children with high resistance values at baseline, which returned to normal after bronchodilation. We conclude that, in asthmatic children over 3 yr old, FOT measurements provide a more reliable evaluation of bronchial obstruction and its reversibility compared with the interrupter technique, especially in young children with high baseline values.