A portable device based on the interrupter technique for measuring airway resistance in preschool children.

The interrupter technique for measuring airway resistance is a noninvasive method reported to require minimal subject cooperation. Therefore it has a good potential for use in young children who are not able to cooperate with conventional lung function tests. The interrupter method is based on transient interruption of airflow at the mouth for a brief period during which alveolar pressure equilibrates with mouth pressure. In order to investigate the compliance rate with the interrupter technique in preschool children and to look for associated baseline measures of RINT we performed a study in 214 children of ages from 3 months to 5 years. There was a significant inverse correlation between baserint and age (r = -0.672, p<0.001), and standing height (r = -0.692, p<0.001) in children with recurrent wheezing. However, this was not seen in healthy children. We concluded that the portable interrupter device is very useful in preschool children. The measurements showed that the age and standing height are inversely proportional to the baseline RINT values measured. We reported that these differences would be more apparent in children with a history of recurrent wheezing.     

Evaluation of the interrupter technique for measuring change in airway resistance in 5-year-old asthmatic children

The interrupter technique is a noninvasive method for measuring airway resistance during quiet breathing which requires minimal subject cooperation. It, therefore, has enormous potential for use in young children unable to cooperate with conventional lung function tests. We evaluated the interrupter technique during bronchial challenge with methacholine administered by the tidal breathing method in 10 5-year-old asthmatic children. The mouth pressure/time [P_mo(t)] curve obtained following brief airflow interruption during the expiratory phase of quiet breathing was analyzed to determine the interrupter resistance R,_int using four different methods: R_intC, a smooth curve fit with back-extrapolation; R_intEO, calculated from the pressure change after the postinterruption oscillations had decayed (end-oscillation); R_intL two-point linear fit with back-extrapolation; and R_intEL, calculated from the pressure change at the end of the period of interruption. The four R_int methods were compared for repeatability and sensitivity with the direct measurement of resistance by the forced oscillation technique (R_rs) and with an independent method of measuring the response to challenge, utilizing the change in transcutaneous oxygen tension (P_tcO2). The sensitivity of the methods was defined by a sensitivity index (SI), the change after challenge expressed in multiples of the baseline standard deviation. The P_tCo2 method had the lowest variability and was by far the most sensitive method (geometric mean SI 18.9), at least 1 doubling concentration more sensitive than the other techniques in every subject (P < 0.05). R_intL was more sensitive than the other interrupter methods (geometric mean SI: R_intL 4.2; R_intC 1.O; R_intEO 2.7; R_intEL 3.1; P < 0.05) and similar in sensitivity to R_rs (geometric mean SI 4.6) in 7 out of 10 children in which this could be measured. We conclude that the interrupter method provides a simpler method than the oscillation technique for assessing airway obstruction in this age group. Pediatr Pulmonol. 1995; 20:387–395 . © 1995 Wiley-Liss, Inc.     

Measurement of airway resistance by an interrupter technique in anesthetized dogs during methacholine induced bronchoconstriction

Airway resistance was measured by an interrupter technique in anesthetized and paralyzed dogs. Bronchoconstriction was then induced by the inhalation of methacholine hydrochloride at a concentration of 25 or 50 mg . ml-1 for ten minutes. Airway resistance was measured again immediately after the inhalation of methacholine and 50 minutes later. Under normal conditions, airway resistance increased with a linear relationship to the expiratory airflow as expressed by a function of Y = K1 + K2X. K1 and K2 were calculated by a least square method. As a result, K1 increased markedly immediately after the inhalation of methacholine and returned to the control level thereafter. However, it was still higher than the control 50 minutes later. On the other hand, no statistically significant changes were observed because the changes in K2 were variable. In some cases, K2 increased, while in others it was unchanged. K2 decreased in more cases, however, and a negative value was often seen. This inverse correlation between flow and resistance was supposed to reflect the occurrence of small airway obstructions during the end expiratory phase. Therefore, it was considered that this method is capable of detecting small airway abnormalities which could not be detected by %FEV1.0.     

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.     

Evaluation of the interrupter technique for the use of assessing airway obstruction in children

The purpose of this study was to determine if the interrupter technique, a noninvasive method for measuring airflow resistance, could be used to assess airway obstruction in children. In 107 children (74 with asthma, 12 with cystic fibrosis, and 21 without lung disease) conductance (mostly of airways) measured with the interrupter technique (G_int) was correlated with both forced expiratory volume in 1 second (FEV₁) and the forced expired flow rate between 25% and 75% of vital capacity (FEF_25–75. In addition, 17 children with significant airway obstruction due to asthma also had airway resistance measured by body plethysmography (R_aw) before and after treatment. Resistance and conductance measurements made with the interrupter technique were subdivided into inspiratory (R_int-insp, G_int-insp) and expiratory (R_int-exp G_int-exp) values. In the 107 children, a high degree of linear correlation was found between G_int-exsp and FEV₁ for G_int-insp, r = 0.77 (P < 0.001), and for r = 0.76 (P < 0.001). There was also good linear correlation between Gin, and FEF_25–75 for r = 0.70 (P < 0.001), and for G_int-insp, r = 0.67 (P < 0.001). In the 17 asthmatic children who were tested before and after treatment of their airway obstruction, R_int correlated highly with R_aw; for R_int-exp, r = 0.91 (P < 0.001), and for R_int-insp, r = 0.83 (P < 0.001). The pre- to posttreatment changes in R, and R_aw were similar. We conclude that the interrupter technique can be used to assess changes in airway obstruction, but normal values must be established and further investigation is required before the complete extent of its clinical utility will be known. Pediatr Pulmonol. 1994; 17:211–217. © 1994 Wiley-Liss, Inc.     

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.     

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.     

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.     

Measurements of respiratory system resistance by the interrupter technique in healthy and asthmatic children

We studied respiratory system resistance by the interrupter technique (R_int) in healthy and asthmatic children, paying special attention to the effect of cheek compliance and the effects of supporting the cheeks, the influence of lung volume at which interruption was performed, the effect of direction of flow before occlusion (inspiration vs. expiration), and short-term reproducibility of this method. One hundred and thirty-two children (36 controls and 96 asthmatics) were included in the study (mean, 9.0 ± SD 3.6 years). R_int was calculated from the ratio of the alveolar pressure (estimated from mouth pressure during occlusion) to the flow prior to interruption. We observed that (1) underestimation of airway resistance due to upper airway compliance can be minimized by supporting the cheeks; R_int was significantly lower when measured without supporting the cheeks than with support of the cheeks in controls (3.9 ± 0.9 vs. 4.7 ± 1.2 cmH₂O · L⁻¹ · s, respectively) and asthmatics (5.2 ± 1.6 vs 6.9 7 plusmn; 2.0 cmH₂O · L⁻¹ · s); the quantitative differences of R_int with and without cheek support was larger in small children and in the most obstructed children; (2) performing occlusion at mid-tidal volume accurately reflected the respiratory system resistance of the whole respiratory cycle since we observed no difference in R_int when performing occlusion at different volumes during quiet respiration or at the middle of tidal volume; (3) R_int measured during expiration was higher than R_int obtained during inspiration in controls and in asthmatics; moreover, the effect of direction of flow before occlusion was greater in the small children; (4) R_int was closely correlated to height in controls (r = −0.82; P < 0.001); and (5) short-term reproducibility (at 15 min intervals) was satisfactory in controls and asthmatics (coefficients of variation were 9% and 7%, respectively). Pediatr. Pulmonol. 1997;24:78–85. © 1997 Wiley-Liss, Inc.     

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. Pediatr Pulmonol. 2009; 44:1168–1173. © 2009 Wiley‐Liss, Inc.     

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.     

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.     

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 (R_int) 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 R_int and FEV₁ were studied. A receiver operating characteristic (ROC) curve was used to describe sensitivity and specificity of R_int. 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 R_int with increasing methacholine doses. However, individual changes of R_int showed large fluctuations. There was great overlap in change of R_int 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 R_int to diagnose BHR in individual patients seems limited. Pediatr Pulmonol. 2011; 46:266–271. © 2011 Wiley‐Liss, Inc.     

Applicability of interrupter resistance measurements using the MicroRint in daily practice

This study was performed to evaluate the applicability of a simple device (MicroRint) for measuring airway resistance, to derive normal values and to compare values with maximal expiratory flow volume (MEFV) parameters in asthmatic and healthy children. Repetitive R(int) measurements were performed in 125 healthy children and 107 asthmatic children (age range 0.8-16.8 years). In 42 asthmatic patients R(int) and MEFV values were compared and in 29 asthmatic children bronchodilation testing was performed. Successful R(int) measurements were possible in 91% of the children. The mean coefficient of variation of repeated measurements was 7.1 (+/-6.1)%. R(int) values of healthy children showed a significant curvilinear correlation with age (r=-0.80, P < 0.001) and height (r=-0.81, P < 0.001). In asthmatic and healthy children R(int) values were comparable. A significant inverse correlation was found between R(int) and MEFV values (for FEV1 and R(int) r=-0.80, P < 0.001). After bronchodilation there was a significant increase in FEV1 and decrease in R(int), but changes between the two parameters did not correlate. In conclusion, the interrupter technique is feasible and repeatable in children and has a significant correlation with other parameters of airway caliber. Baseline values do not discriminate healthy from asthmatic children.     

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.     

Baseline and post-bronchodilator interrupter resistance and spirometry in asthmatic children

In children unable to perform reliable spirometry, the interrupter resistance (R_int) technique for assessing respiratory resistance is easy to perform. However, few data are available on the possibility to use R_int as a surrogate for spirometry. We aimed at comparing R_int and spirometry at baseline and after bronchodilator administration in a large population of asthmatic children. We collected retrospectively R_int and spirometry results measured in 695 children [median age 7.8 (range 4.8–13.9) years] referred to our lab for routine assessment of asthma disease. Correlations between R_int and spirometry were studied using data expressed as z‐scores. Receiver operator characteristic curves for the baseline R_int value (z‐score) and the bronchodilator effect (percentage predicted value and z‐score) were generated to assess diagnostic performance. At baseline, the relationship between raw values of R_int and FEV₁ was not linear. Despite a highly significant inverse correlation between R_int and all of the spirometry indices (FEV₁, FVC, FEV₁/FVC, FEF_25–75%; P < 0.0001), R_int could detect baseline obstruction (FEV₁ z‐score ≤ ?2) with only 42% sensitivity and 95% specificity. Post‐bronchodilator changes in R_int and FEV₁ were inversely correlated (rhô = ?0.50, P < 0.0001), and R_int (≥35% predicted value decrease) detected FEV₁ reversibility (>12% baseline increase) with 70% sensitivity and 69% specificity (AUC = 0.79). R_int measurements fitted a one‐compartment model that explained the relationship between flows and airway resistance. We found that R_int had poor sensitivity to detect baseline obstruction, but fairly good sensitivity and specificity to detect reversibility. However, in order to implement asthma guidelines for children unable to produce reliable spirometry, bronchodilator response measured by R_int should be systematically studied and further assessed in conjunction with clinical outcomes. Pediatr Pulmonol. 2012. 47:987–993. © 2012 Wiley Periodicals, Inc.     

Pre/postbronchodilator interrupter resistance values in healthy young children

The interrupter technique estimates flow resistance. It entails occlusion of the airways during tidal breathing while flow and mouth pressure are recorded. This noninvasive technique is easy to use in young children. The aim of the present study was to measure inspiratory and expiratory interrupter resistance (Rint(insp), Rint(exp)) before and after bronchodilator administration in young healthy white children. We designed a multicenter study using a standardized procedure for Rint measurements. Centers in five French cities studied 91 children (48 boys and 43 girls; height, 92 to 129 cm; mean age 5.3 +/- 1.4 years). Mean values were not significantly different for Rint(insp) and Rint(exp) (0.78 +/- 0.21 versus 0.78 +/- 0.20 KPa x L(-1) x second). However, the difference between Rint(insp) and Rint(exp) decreased significantly with age and being positive before 5 years and negative later on (p < 0.02). Rint(insp) and Rint(exp) decreased significantly with height (Rint(insp) [KPa x L(-1) x second] = 2.289 - 1.37. 10(-2) x H [cm], Rint(exp) [KPa. L(-1) x second] = 2.021 - 1.12.10(-2) x H [cm]; p < 0.001). Bronchodilator (salbutamol) administration significantly decreased Rint(insp) and Rint(exp) (p < 0.001). Bronchodilator-induced changes (% of predicted values) in mean Rint(insp) and mean Rint(exp) were -15% (95% confidence interval, -46 to +15%) and -12% (95% confidence interval, -46 to +22%), respectively. Sex did not affect pre- or postbronchodilator values. Data from the present study may prove useful for testing lung function in young children with respiratory disorders who failed to cooperate with forced expiratory maneuvers.