Within- and between-day variability of respiratory impedance,using impulse oscillometry in adolescent asthmatics

The objectives of the present study were to: 1) assess spirometric indices and respiratory impedance with forced oscillation (FO), using impulse oscillometry (IOS) in clinically stable asthmatic children over 3 consecutive days; 2) assess FO reactance (X), using an integrated index and resistance (R) separately during inspiration and expiration; and 3) assess effects on FO of hand support of cheeks vs. no hand support. Our hypotheses were: 1) because of increased sensitivity, IOS manifests day-to-day variability not demonstrable by spirometry; 2) IOS R during expiration exceeds that during inspiration; and 3) hand support of cheeks affects IOS R and X only minimally. We obtained triplicate twice-daily measures of IOS R and X in asthmatic adolescents at summer camp, in a convenience sample of children willing, with parental permission, to undergo repeated testing on consecutive days. Subjects received all medications between 6:30-7:30 AM, and were bronchodilated at time of testing. Subjects underwent IOS tests without hand support of cheeks, followed by tests with both hands supporting cheeks. ANOVA and regression analyses were used to discern technique differences.Significant differences in IOS inspiratory R5, R5 - R15 (frequency dependence of R), and low frequency reactance area (AX) occurred across 3 days, but spirometric indices were unchanged. Inspiratory R at 5 Hz (R5) was significantly smaller than expiratory R5 (P < 0.0001). ANOVA revealed no significant differences between hand and facial muscle cheek support for IOS R and X below 15 Hz, but significant differences occurred above 15 Hz.In conclusion, inspiratory R5, R5 - R15, and AX are sensitive measures for detecting changes in bronchomotor tone in adolescent asthmatic subjects, while expiratory R5 may be influenced by additional factors. Manual support of cheeks does not appear to affect IOS indices of peripheral airway obstruction in adolescent asthmatics. IOS is a practical method for quantifying respiratory mechanics, and its potential role in disease management warrants further study.     

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.     

Airway resistance measured by the interrupter technique: expiration or inspiration, mean or median?

The measurement of airway resistance by the interrupter technique (Rint) needs standardization. Should measurements be made be during the expiratory or inspiratory phase of tidal breathing? In reported studies, the measurement of Rint has been calculated as the median or mean of a small number of values, is there an important difference? Subjects were 2.5-5.0 yrs (median 4.0 yrs) who had previous respiratory symptoms. The Rint in expiration (RintE) and inspiration (RintI) pre and postsalbutamol, the coefficient of variation (CV) of values contributing to measurements, and bronchodilator responsiveness(BDR) in both phases were compared. Measurements using median and mean were compared. RintE was higher than RintI by 4% (p < 0.01). The CV of values making up RintE and RintI, and BDR measured in expiration and inspiration were similar. The median difference between means and medians of values making up measurements was 0.6% (range -6-11%). RintE has been shown to be consistently greater then RintI but the difference in this study is small. It is suggested that one or the other is chosen as the standard. In the present data the mean of a set of values contributing to a measurement was not significantly different from the median. However, the use of the median has been recommended since it is less affected by possible outlying values such as might be included by fully automated equipment.     

Inspiratory-expiratory responses to alternate-breath oscillation of PACO2 and PAO2.

Breath-by-breath respiratory responses of three healthy adults to imposed alternate-breath oscillation of end-tidal PCO2 (between +5 and +15 torr above the eupnoeic level) and/or PO2 (between 80 and 45 torr) were studied at rest and during mild cycle ergometer exercise. There was often alternation in inspiratory and expiratory tidal volumes and mean flows, and in expiratory duration, but not in inspiratory duration. The latency of responses, estimated by cross-correlation, corresponded closely to the lung-ear transport delay (measured by oximetry). There were two general patterns of response: in-phase, with inspiratory responses leading expiratory, and, more often, out-of-phase, with expiratory responses leading inspiratory. These patterns were associated with arrival of the onset of the alternating signal at the ear in inspiration and expiration, respectively. It is concluded that the timing of alternating humoral signals at the carotid bodies in relation to the phase of respiration determines the pattern of inspiratory-expiratory response, and that expiratory events can be independent of the previous inspiration.     

Effects of Respiration on Pulmonary Venous Flow and Its Clinical Applications by Doppler Echocardiography

Objectives: This study was aimed to explore respiratory variations of pulmonary venous flow and its clinical applications and the potential mechanism. Methods: Pulsed-wave Doppler waveforms of right-upper pulmonary vein were recorded with Siemens Sequoia 512 in 20 healthy young subjects. Electrocardiogram and respiratory tracing were recorded simultaneously. The inspiratory and expiratory pulmonary venous peak flow velocities of S - and D - waves and their velocity–time integrals (VTIs) were acquired and averaged for five consecutive respiratory cycles, respectively. The ratios of velocities and the VTIs of S - to D - waves (S/D, VTIs/VTId) during inspiration and expiration were calculated. Results: The velocity and VTI of S - wave did not vary significantly between inspiration and expiration (58.31 cm/sec ± 9.22 cm/sec, 58.96 cm/sec ± 7.79 cm/sec, P = 0.221; 16.29 cm ± 2.59 cm, 16.54 cm ± 2.18 cm, P = 0.090), while the velocity and VTI of D - wave increased significantly from inspiration to expiration (48.23 cm/sec ± 8.32 cm/sec, 51.82 cm/sec ± 8.72 cm/sec, P < 0.0001; 10.84 cm ± 1.65 cm, 11.66 cm ± 1.53 cm, P < 0.0001), resulting in significantly decreased ratios of the velocity and the VTI of S - to D - waves from inspiration to expiration (1.23 ± 0.22, 1.17 ± 0.27, P < 0.0001; 1.53 ± 0.31, 1.43 ± 0.22, P < 0.0001). Conclusions: Respiration has significant influence on pulmonary venous flow, which should be taken into account in evaluating left ventricular diastolic function when adopting pulmonary venous flow waveform, especially in diseased settings. The different anatomical positions of left and right heart relative to the thoracic cavity may account for the respiratory variations of pulmonary venous flow.     

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.     

Applicability of interrupter resistance measurements for evaluation of exercise-induced bronchoconstriction in children

The interrupter technique is a noninvasive method for measuring air-flow resistance during tidal breathing. This method requires minimal cooperation, and is therefore promising for use in uncooperative children. The aim of this study was to evaluate applicability interrupter resistance (Rint) measurements in the assessment of exercise-induced bronchoconstriction (EIB). Fifty children aged 5-12 years with mild to moderate asthma were tested by exercise challenge, consisting of free outdoor running for 6 min at 80-90% of maximal predicted heart rate for age. Rint, forced expiratory volume in 1 sec (FEV1), and peak expiratory flow (PEF) were measured before and 10 min after exercise. EIB was defined as a fall of 10% or more in FEV1 after exercise. The repeatability of Rint was assessed, and its response to exercise challenge was compared with current standardized methods. The mean intermeasurement coefficient of variation was 4.6% (SD, +/- 3.0%), and the repeatability coefficient was 0.056 kPa/l/sec. Eighteen (36%) of the 50 children had EIB after exercise challenge test. The area under the receiver-operating characteristic (ROC) curve was 0.953 (95% confidence interval, 0.853-0.992; P < 0.001), and the optimal Rint cutoff value was 15.2%, producing a sensitivity of 88.9% and a specificity of 96.9%. The positive and negative predictive values were 94.1% and 93.9%, respectively. The kappa value between FEV1 and Rint was 0.83. The repeatability of Rint measurements was good, and the results of exercise challenge tests using Rint measurements have excellent agreement with the current standardized methods to detect EIB. Considering that only minimal comprehension and coordination are needed without forced breathing technique, the Rint measurement can provide a useful alternative for assessment of EIB in children unable to perform reliable spirometry.     

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

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

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.     

Low-dose, dynamic, expiratory thin-section CT of the lungs using a spiral CT scanner

Seventeen patients with lung transplants were evaluated with inspiratory, postexpiratory, and low-dose, dynamic expiratory thin-section computed tomography (CT). Region of interest measurements were performed on inspiration and expiration images with both techniques, and mean lung attenuation changes between inspiration and expiration images were calculated and compared. Dynamic expiratory thin-section CT resulted in a significantly greater increase in lung attenuation than postexpiratory thin-section CT. Dynamic expiratory thin-section CT may prove useful in the evaluation of patients with lung diseases characterized by air flow obstruction with little increase in patient radiation dose.     

The effect of low density gas breathing on vesicular lung sounds

Turbulent airflow (largely gas density dependent) in larger airways is believed by many lung sound researchers to be the mechanism responsible for the generation of vesicular lung sounds. To test the validity of this concept, we measured the amplitude of lung and tracheal sounds of 6 subjects alternately breathing air and a low density gas mixture (80% helium, 20% oxygen: He-O2). Lung sounds were recorded from 3 chest wall sites: Anterior right upper lobe (RUL), posterior and posterolateral right lower lobe (RLL), and a site over the proximal trachea below the larynx. The subjects rebreathed into an electronic spirometer filled with the test gas, and achieved a peak inspiratory and expiratory airflow of 2-2.5 L/sec. Lung sound amplitude was determined by an automated, flow-corrected measurement procedure. The mean decrease in sound amplitude when breathing He-O2 compared to air was: trachea, inspiration 44%; trachea, expiration 45%; RUL, inspiration 13%; RUL, expiration 25%; RLL, inspiration 15% (expiration at the RLL was too quiet to record). Cross-correlation and frequency analyses of the sounds recorded at the two RLL sites on both test gases revealed no consistent change in frequency or time relationships, indicating absence of effect of gas density on sound transmission between the sound generating airways and chest wall. These data suggest that the mechanism of production of the inspiratory vesicular lung sound is not simply turbulent airflow but some other relatively gas density independent mechanism. The tracheal and expiratory lung sounds do appear to be produced by a more density dependent turbulent mechanism.     

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

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

The effect of the respiratory cycle on liver stiffness values as measured by transient elastography

The findings of several studies suggest that liver stiffness values can be affected by the degree of intrahepatic congestion respiration influence intrahepatic blood volume and may affect liver stiffness. We evaluated the influence of respiration on liver stiffness. Transient elastography (TE) was performed at the end of inspiration and at the end of expiration in patients with chronic liver disease. The median values obtained during the inspiration set and during the expiration set were defined as inspiratory and expiratory liver stiffness, respectively. A total of 123 patients with chronic liver disease were enrolled (mean age 49years; 64.2% men). Liver cirrhosis coexisted in 29 patients (23.6%). Expiratory liver stiffness was significantly higher than inspiratory liver stiffness (8.7 vs 7.9kPa, P=0.001), while the expiratory interquartile range/median ratio (IQR ratio) did not differ from the inspiratory IQR ratio. Expiratory liver stiffness was significantly higher than inspiratory liver stiffness in 49 (39.8%) patients (HE group), expiratory liver stiffness was significantly lower than inspiratory stiffness in 15 (12.2%) patients, and there was no difference in 59 (48.0%) patients. Liver cirrhosis was more frequent in those who had a lower liver stiffness reading in expiration, and only the absence of liver cirrhosis was significantly associated with a higher reading in expiration in multivariate analysis. In conclusion, liver stiffness was significantly elevated during expiration especially in patients without liver cirrhosis. The effect of respiration should be kept in mind during TE readings.     

Assessment of emphysema in COPD: a functional and radiologic study

OBJECTIVES: A combination of functional measurements reflecting a decrease in maximum flow, a degree of lung hyperinflation, the relationship between maximum inspiratory and expiratory flows, bronchodilator response, and diffusing capacity of the lung for carbon monoxide (DLCO) was used to quantify the extent of emphysema, as assessed by high-resolution CT (HRCT) scanning. DESIGN: Forced inspiratory and expiratory spirometry, lung volumes, reversibility test, and single-breath diffusing capacity were assessed before and after inhaling albuterol, 200 microg. Relationships between lung function variables and emphysema extent, as determined by HRCT scanning, were tested by univariate and multivariate analyses. SUBJECTS: Thirty-nine COPD outpatients with moderate-to-severe obstruction. MEASUREMENTS AND RESULTS: Emphysema extent, as assessed by HRCT scanning, ranged from 18 to 70%. All of the lung function parameters that were studied, except for the change in FEV1 percent predicted after salbutamol inhalation, correlated significantly with the extent of emphysema (r2 range, 0.19 to 0.44). Functional residual capacity, forced expiratory flow at 50% of FVC/forced inspiratory flow at 50% of FVC, DLCO/alveolar volume ratio, and bronchodilator-induced change in FEV1/FVC ratio were the only variables retained by stepwise multiple regression analysis. The multiple regression model explained 71% of the variability of emphysema extent measured by HRCT scanning. CONCLUSIONS: The combination of lung function measurements reflecting lung hyperinflation, bronchial collapsibility, lung diffusing capacity, and bronchodilator response provides a good estimate of the extent of emphysema, as evaluated by HRCT scanning. These data suggest that pulmonary function tests are useful in assessing and monitoring parenchymal damage in COPD patients.     

Pitfalls in spirometry: Clinical relevance

Spirometry is one of the functional tests most used in respiratory medicine to assess lung function in health and disease conditions.Its success is grounded on solid principles of lung mechanics that state that maximal flow on expiration is limited by the physical properties of airways and lung parenchyma.In contrast,on inspiration,flow depends on the force generated by the inspiratory muscles.Reduced expiratory forced flow and volumes usually reflect a deviation from health conditions.Yet due to a complex interplay of different obstructive and restrictive lung diseases within the multiple structural dimensions of the respiratory system,flows and volumes do not always perfectly reflect the impact of the disease on lung function.The present review is intended to shed light on a series of artefacts and biological phenomena that may confound the clinical interpretation of the main spirometric measurements.Among them is thoracic gas compression volume,the volume and time history of the inspiratory manoeuvre that precedes the forced expiration,the effects of heterogeneous distribution of the disease across the respiratory system,and the changes in lung elastic recoil.     

Expiratory airflow patterns and gas exchange in the newborn infant: results of model simulations

A mathematical model simulating the newborn human infant's respiratory system was used to study the effects on gas exchange of varying expiratory airflow pattern and end expiratory lung volume (FRC). Inspiratory flow was modelled as a square wave and was constant for all simulations as were inspiratory and expiratory times. Expiratory airflow was also modelled as a square wave and was varied between 21 and 75 ml/sec with FRC held constant at either 30.2 or 21.2 ml/kg for each simulation. At a given FRC, expiratory airflow pattern had only a trivial effect on blood gases in the steady state. Comparing the extreme cases, fast expiration (75 ml/sec) at low FRC (21.1 ml/kg) with slow expiration (21 ml/sec) at high FRC (30.2 ml/kg), arterial PO2 was 3.8 mm Hg higher and arterial PCO2 1.0 mm Hg lower under the latter conditions. However, when short apneas were imposed, blood gases deteriorated less precipitously following the slow expiration at high FRC. We conclude that expiratory airflow retardation and the resultant elevation in end expiratory lung volume do not greatly enhance gas exchange in the healthy full term infant. However, mechanisms which slow expiratory airflow do provide a buffer for gas exchange during the short apneas often observed in infants.     

Measurement of maximal inspiratory pressure in ventilated children

Maximal inspiratory pressure (PIMAX), the maximum negative pressure generated during temporary occlusion of the airway, is commonly used to measure inspiratory muscle strength in mechanically ventilated infants and children. There are, however, no guidelines as to how the PIMAX measurement should be made. We compared the maximum inspiratory pressure generated during airway occlusion (PIMAX(OCC)) to that when a unidirectional valve (PIMAX(UNI)), which allowed expiration, but not inspiration was used. Twenty-two mechanically ventilated children (mean (SD) age 4.8 (4.5) years) were studied. Three sets of end expiratory occlusions were performed for each method in random order. The expired volume during PIMAX(UNI) was assessed and related to the functional residual capacity (FRC) measured using a helium dilution technique.The mean (SD) PIMAX(UNI) (45.5 (15.2) cmH(2)O) was significantly greater than mean (SD) PIMAX(OCC) (30.9 (9.0) cmH(2)O) (P < 0.0001). The mean (SD) expired volume during PIMAX(UNI), was 98 ml (62.3), a mean reduction in FRC of 33.1% (SD 13.9). There were no significant differences between techniques in the baseline respiratory drive, the number of efforts required and the time to reach PIMAX. Regardless of technique, PIMAX was reached in 10 inspiratory efforts or 15 sec of airway occlusion.A unidirectional valve allowing expiration, but not inspiration yields greater PIMAX values in children. Occlusions should be maintained for 12 sec or eight breaths (99% CI of mean).     

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.     

Chest surface mapping of lung sounds during methacholine challenge

Wheeze as an indicator of airway obstruction during bronchoprovocation lacks sensitivity. We therefore studied whether induced airway narrowing is revealed by changes in normal (vesicular) lung sounds. Fifteen subjects with asthma and nine healthy controls, aged 8–16 years, performed a standardized methacholine challenge. Respiratory sounds were recorded with eight contact sensors, placed posteriorly over the right and left superior and basal lower lobes, and anteriorly over both upper lobes, the right middle lobe, and the trachea. Average spectra of normal inspiratory and expiratory sounds, excluding wheeze, were characterized in 12 asthmatics and 9 controls at flows of 1 ± 0.2 L/sec. Airway narrowing was accompanied by significant changes in lung sounds, but not in tracheal sounds. Lung sounds showed a decrease in power at low frequencies during inspiration and an increase in power at high frequencies during expiration. These changes already occurred at a decrease in forced expiratory volume in 1 sec of less than 10% from baseline and were fully reversed after inhalation of salbutamol. Thus, lung sounds were sensitive to changes in airway caliber, but were not specific indicators of bronchial hyperresponsiveness. Pediatr Pulmonol. 1997; 23:21–30. © 1997 Wiley-Liss, Inc     

Bronchodilator responsiveness testing using raised volume forced expiration in recurrently wheezing infants

We hypothesized that a new test of infant lung function, less affected by shifts in lung volume, might better detect bronchodilator effects. Using the raised volume forced expiration technique (RVFET), the effect of a bronchodilator on lung function was studied in 22 infants with a history of recurrent wheeze and five healthy infants. Forced expiratory volume in 0.75 s (FEV_0.75), forced expiratory vital capacity (FVC), and forced expiratory flow at 75% of FVC (FEF_75%) were measured by forcing expiration, using an inflatable jacket from a lung volume set by an inspiratory pressure of 20 cm H₂O. A minimum of five measurements were made at baseline and following the administration of 500 μg of salbutamol from a metered dose inhaler via a small volume metal spacer. Changes in lung function in the group of 25 infants who received salbutamol were compared to seven infants who received placebo aerosol. No significant changes occurred in measures of lung function following salbutamol administration when compared to baseline or placebo despite a significant increase in heart rate. A shift in lung volume is unlikely the reason why infants do not demonstrate a change in forced expiration following bronchodilator administration. Pediatr Pulmonol. 1998; 26:35–41. © 1998 Wiley-Liss, Inc.