Normal values for forced oscillatory respiratory resistance in children

Intra-breath changes in respiratory mechanics are sensitive to history of respiratory illness in preschool children: the SEPAGES cohort

BACKGROUND

Intra-breath oscillometry has been proposed as a sensitive means of detecting airway obstruction in young children. We aimed to assess the impact of early life wheezing and lower respiratory tract illness on lung function, using both standard and intra-breath oscillometry in 3 year old children.

METHODS

History of doctor-diagnosed asthma, wheezing, bronchiolitis and bronchitis and hospitalisation for respiratory problems were assessed by questionnaires in 384 population-based children. Association of respiratory history with standard and intra-breath oscillometry parameters, including resistance at 7 Hz (R7), frequency-dependence of resistance (R7 - 19), reactance at 7 Hz (X7), area of the reactance curve (AX), end-inspiratory and end-expiratory R (ReI, ReE) and X (XeI, XeE), and volume-dependence of resistance (ΔR = ReE-ReI) was estimated by linear regression adjusted on confounders.

RESULTS

Among the 320 children who accepted the oscillometry test, 281 (88%) performed 3 technically acceptable and reproducible standard oscillometry measurements and 251 children also performed one intra-breath oscillometry measurement. Asthma was associated with higher ReI, ReE, ΔR and R7 and wheezing was associated with higher ΔR. Bronchiolitis was associated with higher R7 and AX and lower XeI and bronchitis with higher ReI. No statistically significant association was observed for hospitalisation.

CONCLUSIONS

Our findings confirm the good success rate of oscillometry in 3-year-old children and indicate an association between a history of early-life wheezing and lower respiratory tract illness and lower lung function as assessed by both standard and intra-breath oscillometry. Our study supports the relevance of using intra-breath oscillometry parameters as sensitive outcome measures in preschool children in epidemiological cohorts.

Priorities for future research into asthma diagnostic tools: A PAN-EU consensus exercise from the European asthma research innovation partnership (EARIP)

The diagnosis of asthma is currently based on clinical history, physical examination and lung function, and to date, there are no accurate objective tests either to confirm the diagnosis or to discriminate between different types of asthma. This consensus exercise reviews the state of the art in asthma diagnosis to identify opportunities for future investment based on the likelihood of their successful development, potential for widespread adoption and their perceived impact on asthma patients. Using a two-stage e-Delphi process and a summarizing workshop, a group of European asthma experts including health professionals, researchers, people with asthma and industry representatives ranked the potential impact of research investment in each technique or tool for asthma diagnosis and monitoring. After a systematic review of the literature, 21 statements were extracted and were subject of the two-stage Delphi process. Eleven statements were scored 3 or more and were further discussed and ranked in a face-to-face workshop. The three most important diagnostic/predictive tools ranked were as follows: "New biological markers of asthma (eg genomics, proteomics and metabolomics) as a tool for diagnosis and/or monitoring," "Prediction of future asthma in preschool children with reasonable accuracy" and "Tools to measure volatile organic compounds (VOCs) in exhaled breath."

Defining 'healthy' in preschool-aged children for forced oscillation technique reference equations

BACKGROUND AND OBJECTIVE

Selecting 'healthy' preschool-aged children for reference ranges may not be straightforward. Relaxing inclusion criteria for normative data does not affect spirometry z-scores. We therefore investigated the effect of similarly relaxing inclusion criteria in preschoolers on reference ranges for respiratory impedance (Zrs) using a modified forced oscillation technique (FOT).

METHODS

The International Study of Asthma and Allergies in Childhood questionnaire classified 585 children into a healthy and five mutually exclusive groups. Zrs was measured between 4 and 26 Hz and resistance (R) and compliance (C) obtained by model fitting. Prediction models were determined using mixed effect models and z-scores compared between healthy children and the five groups.

RESULTS

Zrs data were obtained for 494 participants (4.30 ± 0.7 years) on 587 occasions. Comparison of the Zrs z-scores between the healthy children and the health groups found significant differences in children with asthma, current wheeze and respiratory symptoms, but not in children born preterm or with early-life wheeze. Adding these two groups to the healthy dataset had no significant effect on the distribution of z-scores and increased the size of the dataset by 22.3%.

CONCLUSION

Our data suggest that preschool-aged children born preterm or with early-life wheeze can be included in FOT reference equations, while those with asthma, current wheeze and respiratory symptoms within 4 weeks of testing should be excluded. This more inclusive approach results in more robust FOT reference ranges.

The Forced Oscillation Technique in Paediatric Respiratory Practice

The Forced Oscillation Technique (FOT) is a lung function modality based on the application of an external oscillatory signal in order to determine the mechanical response of the respiratory system. The method is in principal noninvasive and requires minimal patient cooperation, which makes it suitable for use in young paediatric patients. The FOT has been successfully applied in various paediatric respiratory disorders, such as asthma, cystic fibrosis, and chronic lung disease of prematurity, in order to assess airway obstruction, bronchodilator response, and airway responsiveness after bronchoprovocation challenge. This technique may be more sensitive than spirometry in identifying disturbances of peripheral airways and assessing the level of asthma control or the effectiveness of therapy at the long term. Further research is required to determine the exact role of the FOT in paediatric lung function testing and to incorporate the method in specific diagnostic and management algorithms.

Forced oscillation technique and childhood asthma

Most infants and preschool children are not able to voluntarily perform the physiological maneuvers required to complete the pulmonary function tests that are used in adults and older children. Recently, commercial devices using forced oscillation technique (FOT) suitable for young children have become available. In devices with FOT, an oscillation pressure wave is generated by a loud speaker, is applied to the respiratory system, usually at the mouth, and the resulting pressure-flow relationship is analyzed in terms of impedance (Zrs). Zrs encompasses both resistance (Rrs) and reactance (Xrs). Rrs is calculated from pressure and flow signals, and is a measure of central and peripheral airway caliber. Xrs is derived from the pressure in the phase with volume and is related to compliance (Crs) and inertance (Irs). These parameters individually indicate the condition of the small and large airways in each patient and indirectly suggest the presence of airway inflammation. It is agreed that the clinical diagnostic capacity of FOT is comparable to that of spirometry. One of the advantages of FOT is that minimal cooperation of the patient is needed and no respiratory maneuvers are required. The use of FOT should be considered in patients in whom spirometry or other pulmonary function tests cannot be performed or in cases where the results of other tests appear to be unreliable. In addition, this approach is effective in assessing bronchial hyperresponsiveness. Considering these qualities, FOT is a useful method to study pulmonary function in preschool children with asthma.

Respiratory impedance and bronchodilator response in healthy Italian preschool children

OBJECTIVE

To define normal values for respiratory resistance (R(rs)) and reactance (X(rs)) and bronchodilator response (BDR) in a population of healthy Italian preschool children using a commercially available forced oscillation device.

METHODS

R(rs) and X(rs) were measured in kindergartens in Viterbo, Italy. Regression analysis was performed taking into account height, weight, age, gender, and reference equations calculated. The coefficient of repeatability (CR) between two tests performed 15 min apart was calculated in a subset of children. BDR was assessed by repeating the measurements 15 min after the administration of 200 µg of inhaled salbutamol and calculated as an absolute change in R(rs) and X(rs) at 8 Hz, as a percent change in baseline, and as a change in Z-score calculated from the reference equations.

RESULTS

Lung function was attempted in 175 healthy children and successful in 163 (81 male, median age 4.8, range 2.9-6.1 years). R(rs) and X(rs) at 6, 8, and 10 Hz were related to height but not other variables. The CR was 1.53 hPa s L(-1) for R(rs8) and 0.91 hPa s L(-1) for X(rs8). The 5th percentile for absolute R(rs8) BDR was -3.16 hPa s L(-1), whereas the 95th percentile for absolute X(rs8) BDR was 2.25 hPa s L(-1). These cut-off values corresponded to a change in the Z-score of -1.88 and 2.48, respectively.

CONCLUSIONS

We have established reference equations for R(rs) and X(rs) in healthy Italian preschool children using forced oscillations. We recommend a change in Z-score of -1.88 for R(rs8) and 2.48 for X(rs8) as cut-off values for a positive BDR.

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.

Reference equations for pulmonary function tests in preschool children: a review

Recent developments in pulmonary function tests (PFTs) in preschool children (2-5 years of age) have meant that objective assessments of respiratory function are now possible for this age group. However, the application and interpretation of these tests may be limited by the relative paucity of appropriate reference equations. This review summarizes available preschool reference equations, identifies the current gaps and limitations in the methodologies and statistics used and proposes future directions for improving reference data. A PubMed search which included the MeSH terms (preschool [2-5years]), (respiratory function test), and (reference value) yielded 214 publications which were screened to identify 34 publications presenting 36 reference equations for seven techniques. There were considerable differences with respect to population characteristics, recruitment strategies, equipment and methodologies and reported parameters both within and between each measurement technique. Despite an increasing number of reference equations for PFT for preschool children, the extent to which these can be generalized to other populations may be limited in some cases by inclusion of relatively few children less than 5 years of age, a lack of details regarding the sample populations and measurement techniques and/or inappropriate statistical analysis. A fresh approach based on large sample sizes, clearly documented population characteristics, equipment and protocols, and more rigorous modern statistical methods both for developing reference equations and interpreting results could enhance clinical application of these tests. This in turn would maximize the tremendous opportunities to detect early lung disease offered by the recent surge in developing suitable tests for preschool children.

Respiratory function in healthy young children using forced oscillations

BACKGROUND

Monitoring of respiratory function is important in the diagnosis and management of respiratory disease. The forced oscillation technique requires minimal patient cooperation and is ideal for the determination of respiratory function in young children. This study aimed to develop reference ranges and to document the repeatability in healthy young children using commercially available forced oscillation equipment.

METHODS

The forced oscillation technique, which uses a pseudo-random noise forcing signal between 4 and 48 Hz, was used to measure respiratory function in healthy young children. Repeatability over a 15 min period was also assessed. Regression equations and standardised Z scores were determined for respiratory resistance (Rrs) and reactance (Xrs) at 6, 8 and 10 Hz.

RESULTS

Respiratory function was obtained in 158 healthy children aged two to seven years and between 92 and 127 cm in height. Oscillatory respiratory mechanics exhibited linear relationships with height. Within-test variability for resistance ranged between 6% and 9% and between 17% and 20% for reactance. Resistance and reactance did not change significantly over a 15 min period.

CONCLUSIONS

Reference ranges for respiratory impedance variables in healthy children aged two to seven years are presented. The short-term repeatability of forced oscillatory variables in this age group is reported, allowing appropriate cut-off values for therapeutic interventions to be defined.

Impulse Oscillometry

OBJECTIVES

To generate reference equations in North American children to be used for assessing respiratory function through the forced oscillation (Rfo) technique, and to determine the changes in oscillatory resistance, reactance, and resonant frequency (Fres) in relation to age, body height, and weight.

DESIGN/SETTING

A prospective cross-sectional study performed on healthy children selected according to strict criteria of American Thoracic Society and European Respiratory Society recommendations.

MEASUREMENTS

Triplicate measures were obtained of resistance and reactance at 5, 10, 15, 20, 25, and 35 Hz as well as Fres through the impulse oscillometer (MasterScreen IOS; Jaeger/Toennies; Höchberg, Germany). Two hundred twenty-two white children--normally distributed within the 3- to 10-year age range and 100 to 150 cm in height--were recruited in Montreal, Canada. We used regression analysis to generate multiple predictive equations separately per gender and frequency on age, height, and body weight.

RESULTS

Stepwise multiple regression in both natural and logarithmic forms for height, weight, age, and gender showed that standing height was the only significant predictor for all variables. Minimal variability was noted in each subject among the triplicate measurements (p = 0.68 to 0.96). Coherence was > 0.9 at all oscillating frequencies except 5 Hz (< 0.72), with tendencies to lower values in young children.

CONCLUSIONS

Resistance and Fres decrease by height, but also by age; and reactance increases. As opposed to our past experience with spirometry in compatible age groups, the Rfo technique was well accepted by preschool children.

Measurements of airway mechanics in spontaneously breathing young children

This paper gives an overview of the general principles of airway mechanics and methods to measure lung function in non-sedated, spontaneously breathing young children. Although lower airway obstruction is probably best evaluated using FEV(1), other techniques can be applied when such measurement is impossible, as in young children. These techniques include measurement of resistance using the interrupter or impulse oscillation techniques.

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.

Input respiratory impedance measured by head generator in preschool children

The upper airway wall motion represents a serious problem when measuring the input impedance of the respiratory system (Zrs) by the forced oscillation technique, particularly in young children. To minimize this error, it has been proposed to vary transrespiratory pressure around the head rather than directly at the mouth, using the head generator technique (HGT). The aim of this study was to collect normative data in preschool children in whom the technique may prove most useful. Zrs was measured using HGT and 4-32-Hz pseudorandom noise input in 127 healthy children. Age ranged from 2. 8 to 7.4 years and height (H) from 0.89 to 1.29 m. The fast Fourier transforms of pressure and flow allowed us to calculate respiratory system resistance (Rrs(f)) and reactance (Xrs(f)) at each frequency (f). Resonant frequency (fn), respiratory system inertance (Irs), and compliance (Crs) were derived from the Xrs(f) data. The technique was accepted by more than 95% of the children. A coherence function </=0.95 required us to reject Zrs values in the lower frequency spectrum. These missing data did not allow reliable estimation of fn, Irs, and Crs in 44% of children. Regression equations of Zrs on growth parameters were obtained. H was the only significant predictive variable. The decrease of Rrs with growth was best described by a multiplicative model [e.g., ln (Rrs(20)) = 2. 5301 - 2.3837. ln (H)]. The slope of the regression lines of Xrs on H was dependent on f: positive between 4 and 16 Hz, negative at high frequency (e.g., 32 Hz), and nonsignificant in the intermediate range (e.g., 20 Hz). Irs and fn decreased significantly and Crs increased as H increased. The current study provides reference values for input impedance of the respiratory system in preschool children with upper airway artifacts minimized. HGT should be particularly helpful at or around 20 Hz, where the signal to noise ratio is larger than at lower frequencies but where upper airway artifacts may significantly corrupt measurements with the standard generator.

Use of the forced oscillation technique to assess airway obstruction and reversibility in children

The forced oscillation technique (FOT) is particularly attractive in a pediatric setting as it requires only passive cooperation from the child. We assessed the sensitivity and specificity of this method for detecting airway obstruction and its reversibility in 313 children (3 to 16 yr of age) with asthma or chronic nocturnal cough. Baseline and post-bronchodilator (n = 251) resistance were measured (R(0)) with the FOT. Baseline R(0) was normalized for height and weight [R(0)(SD)]. In children able to perform forced expiratory maneuvers (n = 181), R(0)(SD) was independently correlated with FEV(1) (p < 0.02) and maximal expiratory flow at 50% (MEF(50)) (p < 0.004). The optimal R(0)(SD) cutoff value given by receiver operating characteristic (ROC) curves to discriminate between children with baseline FEV(1) < 80% or >/= 80% of predicted values yielded 84% sensitivity and 73% specificity. Post-bronchodilator changes in R(0)(SD) [DeltaR(0)(SD)] were mostly correlated to changes in MEF(50). The optimal DeltaR(0)(SD) cutoff value to discriminate between children with the presence or absence of significant reversibility in FEV(1) yielded 69% sensitivity and 78% specificity. In children unable to perform forced expiratory maneuvers (n = 132), this DeltaR(0)(SD) cutoff clearly identified a subgroup of young children with high R(0) values at baseline, that returned to normal after bronchodilation. We conclude that FOT measurements allow reliable evaluation of bronchial obstruction and its reversibility in asthmatic children over 3 yr old.

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 x L(-1) x s and 0.9, 1.18, -0.37, and 1.23 kPa x L(-1) x 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 x 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.

Pediatric reference values for respiratory resistance measured by forced oscillation

OBJECTIVES

To determine, in North American children, reference values for respiratory resistance measurements by the forced oscillation (Rfo) technique and to examine whether sitting height, as index of truncal length, is a better determinant of resistance, less influenced by race and gender, than standing height.

DESIGN/SETTING

A prospective cross-sectional study of healthy nonobese children, carefully selected for absence of atopy, exposure to tobacco smoke, and recent upper respiratory tract infection.

MEASUREMENTS

Three measurements of respiratory resistance by forced oscillation were obtained at the fixed frequencies of 8 Hz (Rfo8), 12 Hz (Rfo12), and at 16 Hz (Rfo16) using the Custo Vit R (Custo Med GMBH; Munich, Germany). In cooperative children, routine spirometry (FEV1, FVC, and peak expiratory flow rate [PEFR]) was also performed.

RESULTS

We recruited 217 healthy children aged 3 to 17 years. Reproducible measurements of Rfo8 were obtained for 206 children, Rfo12 for 197 children, and Rfo16 for 209 children. Normal FEV1, FVC, and PEFR values were documented in all 69 subjects who were able to reproducibly cooperate with spirometry. Multiple linear regression identified measurements of either sitting or standing height as the best, and equally strong, determinants of respiratory resistance at all three frequencies. Gender and race were not important factors once either sitting or standing height measurement was considered. Our regression equations at 8 Hz are comparable to published reference values obtained at fixed frequencies of 6, 8, and 10 Hz using other instruments. However, in comparison to our results, prior values tended to underestimate resistance in the shortest children or to overestimate it in the tallest ones. Our regression equation for Rfo12 is similar to the only previously published one, while no reference values at 16 Hz were available for comparison.

CONCLUSIONS

Height is the best predictor for total respiratory resistance at 8, 12, and 16 Hz in children aged > or = 3 years. Use of sitting height does not appear to be a stronger determinant of resistance than standing height.

Measurement of respiratory system resistance by forced oscillation in normal children: a comparison with spirometric values

In 377 children, the commercially available Siregnost FD-5 was used to measure respiratory system resistance (Rrs) by forced oscillation at 10 Hz. The children were between 3 and 18 years of age and, by a detailed questionnaire and conventional pulmonary function testing in 335, they were shown to be representative of the normal pediatric population. There was a linear relationship between Rrs and height (Rrs = 13.9-0.064 x ht (cm), r = -0.87). Children less than 6 years of age had no trouble with using the forced oscillation technique. The smoking of tobacco in the house, the presence of carpets in the child's bedroom, or an atopic family history, alone or in combination, had no influence on Rrs or on any spirometric measure. Forced oscillation is useful in children too young to be able to cooperate with conventional pulmonary function testing.

Mechanics of the ventilatory system in sedated infants: forced oscillations versus single-breath method

The real--Re(Z)--and imaginary--Im(Z)--parts of the ventilatory system impedance were measured between 6 and 30 Hz in 18 normal infants and in 19 with airway obstruction. The intercept (R0) and slope (S) of the Re(Z)-frequency function, as well as inertance (I) and compliance (C) estimated from Im(Z), were compared with ventilatory system resistance (Rrs) and compliance (Crs) (single-breath method). R0 correlated significantly with Rrs (r = 0.86), although the slope of the regression equation was significantly lower than 1 (P less than 0.01). Negative frequency dependence of Re(Z) was observed in all subjects and a significant correlation was found between S and Rrs (r = -0.80). "Inertance" was negative in 20 subjects and correlated negatively with Rrs (r = -0.61). C correlated with Crs (r = 0.64) and with 1/Rrs (r = 0.85). The ratio of C to Crs (mean +/- SD = 0.168 +/- 0.082) also correlated with 1/Rrs (r = 0.51). The main characteristics of the total impedance/frequency function could be simulated with a model featuring the upper airway wall (Zuaw) in parallel with the ventilatory system (Zrs). It is suggested that the differential change in Zuaw and Zrs with growth accounts for the marked frequency dependence of Re(Z) as well as the inaccurate estimation of both I and C in this population.

A trial of metaproterenol by metered-dose inhaler and two spacers in preschool asthmatics

Because most young children have difficulty in coordination for correct use of metered-dose inhalers (MDI), a trial of two spacer devices attached to MDIs was performed. In 13 children with asthma, aged 2-5 years old, a collapsible bag (Inspir-Ease) and a tube spacer (Aerochamber) were tested in a double-blind crossover trial with metaproterenol (1,300 micrograms). Respiratory resistance was measured by the forced oscillation method. Thirty minutes after metaproterenol administration there was a significant decrease in resistance with both spacers, while no significant change occurred after placebo administration. There was no difference in degree of bronchodilation between the two spacers. It is concluded that metaproterenol can be safely and effectively administered to preschool asthmatics by an MDI with spacer devices.

Pulmonary mechanics in normal infants and young children during first 5 years of life

To characterize lung function in young children we measured lung compliance and pulmonary conductance in 40 normal infants and children ranging in age from the newborn period to 5 years. Inspiratory and expiratory flow was measured by a pneumotachograph, esophageal pressure through a water-filled feeding tube, and functional residual capacity (FRC) by a N2 washout technique. The esophageal pressure change per breath [(mean +/- SD) 7.3 +/- 1.4 cm H2O] and specific compliance (75 +/- 13 ml/cm H2O/L-FRC) did not change with growth. Specific conductance was high (0.60 L/s/cm H2O/L-FRC) in preterm infants, decreasing rapidly with initial growth but minimally beyond 10 kg of body weight, and stabilizing at 0.10 L/s/cm H2O/L-FRC. During the age period studied, compliance increased approximately x 25 whereas conductance only rose five-fold. The changes in compliance and conductance were well correlated to FRC, body weight, and length. These findings suggest that in the last trimester of pregnancy the airways are already well developed and postnatal lung growth occurs mainly by formation of new alveoli, leading to a proportional increase in FRC and lung compliance. Postnatally, conductance increases much more slowly than FRC, resulting in a rapid drop in specific conductance.

Normal values for forced oscillation parameters in small children

A commercially available forced oscillation unit was used to perform pulmonary function testing in 90 healthy children, aged 4 to 7 years. Normal values for resistance and reactance of the respiratory system, resonant frequency, and frequency dependence are reported. The implications of each of the forced oscillation parameters, and their potential usefulness as objective measures of pulmonary function in young children, are discussed.