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.     

Usefulness of the forced oscillation technique in assessing the therapeutic result of tracheobronchial central airway obstruction

Background

Pulmonary function tests (PFTs) comprise the traditional method for detecting central airway obstruction (CAO) and evaluating therapeutic effects, but are effort-dependent. By contrast, the forced oscillation technique (FOT) is performed during tidal breathing in an effort-independent mode and is universally used to assess respiratory function in patients with chronic obstructive pulmonary disease (COPD) and asthma. We used the FOT to measure airway resistance and reactance in patients with CAO before and after interventional bronchoscopy and compared the results to data obtained using PFTs.

Sensitivity of a simplified forced oscillation technique for detection of upper airway obstruction

The sensitivity of a simplified variant of forced oscillation technique (FOT) was studied for assessment of dynamic upper airway obstruction during nasal continuous positive airway pressure (nCPAP) therapy for obstructive sleep apnoea (OSA). The airway impedance P[FOT] was measured by FOT and the oesophageal pressure (P(oes)) was recorded during stable stage II sleep in 11 patients with OSA. The CPAP level was initially set high enough to completely abolish upper airway obstruction. To induce gradually increasing upper airway re-obstruction, the CPAP pressure was then lowered stepwise. Thirty six such manoeuvres were analysed, blind, to define the first inspiration at which upper airway re-obstruction was detectable by analysis of P[FOT](t(FOT)) and by P(oes)(t(oes)), respectively. On seven occasions t(FOT) and t(oes) occurred together, in the remaining 29 cases t(FOT) preceded t(oes) with a mean latency of 6.0+/-7.7 (0-32) breath cycles. In no case did t(oes) preceed t(FOT). FOT is a highly sensitive tool for the assessment of incipient upper airway obstruction during nCPAP therapy.     

Evaluation of a simplified oscillation technique for assessing airway obstruction in sleep apnoea.

The forced oscillation technique (FOT) is a noninvasive method that is useful for assessing airway obstruction and for titrating continuous positive airway pressure (CPAP) in patients with sleep apnoea. The aim was to evaluate the routine applicability of a simplified FOT set-up based on recording pressure and flow at the level of the CPAP device, i.e. obviating the need for connecting the transducers to the nasal mask. A correction to account for the tubing and the exhaust port was applied. This simplified FOT was evaluated on nine patients with moderate or severe sleep apnoea during routine CPAP titration. Patient impedance measured by the simplified FOT ([Z]) was compared with actual patient impedance ([Zrs]) measured simultaneously with a reference FOT based on recording pressure and flow at the nasal mask. An excellent agreement was found between [Z] and [Zrs] over the wide range of airway obstruction explored (4.8-72.1 cmH2O x s x L(-1)): [Z] = [Zrs] x 0.86 + 1.3 cmH2O x s x L(-1) (r = 0.99). Moreover, the simplified and the conventional FOT settings detected the same respiratory events during sleep. These results demonstrate that this simplified FOT is applicable for measuring airway obstruction during routine sleep studies in patients with sleep apnoea.     

Three-dimensional imaging forced oscillation technique to assess position-dependent airway obstruction in relapsing polychondritis: A case report

Relapsing polychondritis (RP) is characterized by recurrent systemic inflammation of the cartilages and is accompanied by central airway collapse. We report a case wherein three-dimensional imaging of respiratory system resistance (Rrs) and respiratory system reactance (Xrs) by using MostGraph (CHEST M.I., Tokyo, Japan), a forced oscillation system, revealed that Rrs and Xrs in the inspiratory and expiratory phases correlated with proximal airway collapse. The degree of difference in Rrs and Xrs between the supine and sitting positions reflected airway collapse more closely than did the pulmonary function test. MostGraph could be a useful tool for assessing airway collapse in RP.     

Changes in respiratory mechanics with increasing degrees of airway obstruction in COPD: detection by forced oscillation technique

The Forced Oscillation Technique (FOT) is a method for non-invasively assessing respiratory mechanics during spontaneous breathing, demanding little cooperation. The aim of this study was to test the ability of FOT to describe the changes in respiratory mechanics in progressive COPD. The study was performed in a control group formed by 21 healthy subjects and 79 outpatients with COPD, which were classified by spirometry, according to the degree of airway obstruction, in mild, moderate and severe groups. Resistive impedance data were submitted to linear regression analysis over the 4-16 Hz frequency range, which yielded the total respiratory system resistance extrapolated at 0 Hz (R0), the respiratory system conductance (Grs), mean respiratory resistance (Rm), and the resistance/frequency slope (S). Reactance data were interpreted using the mean values (Xm) over the 4-32 Hz frequency range, the dynamic compliance (Crs,dyn), the dynamic elastance (E(rs,dyn)), and the resonant frequency (fr) data. Considering the control and mild groups, the increase of airway obstruction resulted in a significant increase of R0 (P<0.008), Rm (P<0.001), and a significant reduction in Grs (P<0.002). Reactive parameters, Crs, dyn and Ers,dyn also presented significant modifications. The subsequent increase (mild to moderate) showed a significant raise of R(0) (P<0.007), S (P<0.001), and a reduction in Grs (P<0.015), while significant increases in Xrs (P<0.001), and Ers,dyn (P<0.02), and also a reduction in Crs, dyn (P<0.02) were also observed. In contrast to earlier stages, in the late stage of the airway obstruction increase (moderate to severe obstruction), resistive parameters did not present statistically significant modifications, while significant modifications were observed in Xrs (P<0.02), Crs, dyn (P<0.003) and Ers,dyn (P<0.003). The results of this study demonstrated that the FOT is useful for detecting the respiratory mechanics modifications in COPD patients. The initial phases of airway obstruction in COPD can be described mainly by resistive parameters, while in more advanced phases, reactive parameters seem to be more useful. Since the FOT has the advantage of being a simple method, such a technique may give a significant clinical contribution, representing an alternative and/or complement to the evaluation of respiratory mechanics by means of forced expiration.     

Unsupervised self-testing of airway obstruction by forced oscillation at the patient's home.

As active patient cooperation is not required, the forced oscillation technique (FOT) could be suitable for measuring airway obstruction in routine home applications. Nevertheless, FOT has never been used at the patient's home to date. The aim of this study was to assess the feasibility of FOT and the reproducibility of measured respiratory resistance (Rrs) in routine patient self-testing at home. Altogether, nine asthmatic patients self-measured their Rrs with a portable FOT device and spirometry for 10-14 days, in the morning and evening, and before and after bronchodilator inhalation. During each measurement session, the patients carried out four consecutive FOT measurements. Grubbs' discordancy test for detecting outliers was used to evaluate intermeasure reliability. Only 4.9% of Rrs data reported by patients were rejected as artefacts. The coefficient of variation of Rrs was 7.9 +/- 6.3% (mean +/- SD). When compared with spirometry, the per cent change in Rrs for detecting a positive bronchodilator response showed an 83% sensitivity and 72% specificity. Unsupervised self-measurement of respiratory resistance at the patient's home provided results similar to those obtained by a technician in a lung function lab. Forced oscillation technique could be a useful tool for the routine follow-up of asthmatic patients at home.     

The forced oscillation technique in children with respiratory disease

The single-frequency forced oscillation technique was used to estimate the total respiratory impedance, resistance, and reactance at 2, 4, and 12 Hz of children who had cricoid stenosis (CS; n = 11), provoked bronchoconstriction (PB; n = 6), or cystic fibrosis (CF; n = 13). The selection criteria for patients who had CS and CF were abnormal forced expiratory volume in 1 sec (FEV!) and/or maximal expiratory flow at 50% vital capacity (Vmax 50%). Sixteen of the 17 patients who had CS or PB were found to have resistance (Rrs) values outside the normal range at 4 Hz; at 2 Hz, 14 were found to have abnormal values and, at 12 Hz, only 9. The reactance in the CS and PB groups was somewhat less discriminative than Rrs at all frequencies. Of the 13 patients who had CF, only 4 had abnormal Rrs values; in this clinical condition, the reactance at 2 Hz was the most discriminative variable, being abnormal in 6 of the 13 patients. Irrespective of the clinical group, the Rrs was, in absolute terms, highest at 2 Hz, and it decreased with increasing frequency. This pattern of negative frequency dependence was, however, not obviously specific for any of the tested clinical conditions and offered no information in addition to a single low-frequency determination.     

Detection of changes in respiratory mechanics due to increasing degrees of airway obstruction in asthma by the forced oscillation technique

Forced expiratory airflows and volumes are often used to assess the airway obstruction in asthmatics. However, forced maneuvers may change bronchial tone and modify airway patency. The aim of this study was to determine whether the Forced Oscillation Technique (FOT), which does not require forced manoeuvres, may be useful to describe the changes in respiratory mechanics in progressive asthma. This study involved 25 healthy and 84 asthmatics, including patients with normal spirometric exam (NE), mild moderate and severe obstruction. Resistive data were interpreted using the respiratory system resistance extrapolated at 0 Hz (R0), the mean respiratory resistance (Rm), and the resistance/frequency slope (S). Reactance data were interpreted by its mean values (Xm), the dynamic compliance (Crs,dyn), and resonant frequency (fr). Receiver operating characteristics curves were used to determine the sensitivity (Se) and specificity (Sp) of FOT parameters in identifying asthma. There were not statistically significant differences between the control and NE groups. Comparing the control and mild groups, significant increases of R0 (P<0.0007), Rm (P<0.003), and S (P<0.003) were observed. In reactive parameters, a significant reduction in Crs,dyn (P<0.04) was observed, while Xm and fr presented significant increases (P<0.0007 and P<0.006, respectively). Comparison between mild and moderate groups showed non-significant modifications in all of the parameters, except for Xm (P<0.02). In the late stages (moderate to severe obstruction), all of the resistive parameters, as well as the reactive ones Xm (P<0.007) and Crs,dyn (P<0.03), presented statistically significant modifications. Among the studied parameters, the effects of airway obstruction in asthma seem to be well described by R0, Rm, S and Xm, which were in close agreement with physiological fundamentals. The best parameters for detecting asthma were R0 (Se=81%, Sp=76%), S (Se=78%, Sp=72%) and Xm (Se=81%, Sp=80%). In conclusion, the results of this study suggest that the FOT can be proposed as an alternative method for the assessment of the respiratory mechanics in asthmatic patients, representing a promising solution to the problem of effort dependence.     

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.     

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.     

An isoflow-volume technique for assessing airway dynamics in children and adults

BACKGROUND: We propose a new approach to the measurement of small airway function as an alternative to recordings of maximal expiratory flow-volume (MEFV) curves. OBJECTIVES: A newly developed technique to record isoflow-volume (IFV) curves to be tested against maximal respiratory flow curves. METHODS: An isoflow whistle (IFW; Iflopen) measures the length of a constant expiration after full inspiration. The note of the whistle enables a subject to generate an even expiration, and the isoflow maintenance times at 1 l x s(-1) (IFMT1) and 2 l x s(-1) (IFMT2) are recorded. The accuracy and reproducibility of the IFV technique were evaluated in 17 healthy adults (age 17-55 years) and in 14 asthmatic children (age 6-14 years). Comparisons with standard lung function parameters, such as forced expiratory volume in 1 s (FEV1), maximal expiratory flow at 50% (MEF50) and 25% (MEF25) vital capacity and peak expiratory flow (PEF), obtained with a Wright Peakflow Meter were undertaken in 102 healthy (aged 8-14 years) and 101 asthmatic children (aged 6-17 years). A bronchial challenge test was performed in 13 asthmatic children. RESULTS: The expired volume measured by the IFW showed an acceptable agreement with that of a pneumotachograph (mean error of 4.32% for IFMT1 and 5.93% for IFMT2). In healthy and in asthmatic children, the correlations between FEV1 and IFMT1 or IFMT2 (r = 0.92 and 0.94, respectively) were found to be greater than that between FEV1 and PEF (r = 0.68). During bronchial challenge tests in 13 asthmatic children, the FEV1 decreased to 69% of baseline and IFMT1 to 58% of baseline. CONCLUSIONS: The IFV technique accurately measured airway obstruction and closely followed changes in standard parameters of the MEFV curve.     

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.     

Lung hyperinflation and its reversibility in patients with airway obstruction of varying severity

The natural history of lung hyperinflation in patients with airway obstruction is unknown. In particular, little information exists about the extent of air trapping and its reversibility to bronchodilator therapy in those with mild airway obstruction. We completed a retrospective analysis of data from individuals with airway obstruction who attended our pulmonary function laboratory and had plethysmographic lung volume measurements pre- and post-bronchodilator (salbutamol). COPD was likely the predominant diagnosis but patients with asthma may have been included. We studied 2,265 subjects (61% male), age 65 ± 9 years (mean ± SD) with a post-bronchodilator FEV(1)/FVC <0.70. We examined relationships between indices of airway obstruction and lung hyperinflation, and measured responses to bronchodilation across subgroups stratified by GOLD criteria. In GOLD stage I, vital capacity (VC) and inspiratory capacity (IC) were in the normal range; pre-bronchodilator residual volume (RV), functional residual capacity (FRC) and specific airway resistance were increased to 135%, 119% and 250% of predicted, respectively. For the group as a whole, RV and FRC increased exponentially as FEV(1) decreased, while VC and IC decreased linearly. Regardless of baseline FEV(1), the most consistent improvement following bronchodilation was RV reduction, in terms of magnitude and responder rate. In conclusion, increases (above normal) in airway resistance and plethysmographic lung volumes were found in those with only minor airway obstruction. Indices of lung hyperinflation increased exponentially as airway obstruction worsened. Those with the greatest resting lung hyperinflation showed the largest bronchodilator-induced volume deflation effects. Reduced air trapping was the predominant response to acute bronchodilation across severity subgroups.     

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.     

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.     

An auto-continuous positive airway pressure device controlled exclusively by the forced oscillation technique.

The forced oscillation technique (FOT) has been demonstrated to be a very sensitive tool for the assessment of upper airway obstruction during nasal continuous positive airway pressure (CPAP) therapy for obstructive sleep apnoea (OSA). The present study was designed to evaluate the therapeutic efficacy of a novel auto-CPAP device based exclusively on the FOT. Following manual CPAP titration, 18 patients with OSA (mean apnoea/hypopnoea index (AHI) 48.0+/-28.1) were allocated to conventional CPAP and auto-CPAP treatment under polysomnographic control in randomized order. The patients were asked to assess their subjective daytime sleepiness using the Epworth Sleepiness Scale (ESS). The mean AHI during auto-CPAP treatment was 3.4+/-3.4 and was comparable with that obtained during conventional CPAP treatment (4.2+/-3.6). The analysis of sleep architecture, the arousal index (6.6+/-2.1 versus 7.3+/-4.4) or the ESS (5.6+/-1.8 versus 7.3+/-4.4) did not reveal any significant differences. However, the mean CPAP pressure during auto-CPAP treatment (0.84+/-0.26 kPa) and in particular the pressure applied in the lateral body position (0.74+/-0.35 kPa), was significantly lower than that employed in conventional CPAP treatment (0.93+/-0.16 kPa, both comparisons: p<0.05). The auto-continuous positive airway pressure device proved equally as effective as conventional continuous positive airway pressure. However, the mean treatment pressure was significantly reduced, especially when patients were sleeping in the lateral position.