Forced Expiratory Flow-volume Curves Research Articles

Die Spirometrie in der ärztlichen Praxis – Teil 1: Die Messung

Spirometry in the Medical Practice - Part 1: Measuring Abstract. Today, every practitioner, as well as every hospital emergency, should be able to perform spirometry. However, the measurement requires solid basic knowledge as well as a certain amount of experience so that consistent and reproducible measurements are possible. Since the measurement depends heavily on the cooperation of the patient, typical errors must be recognised and corrected immediately. A rounded forced expiratory flow volume curve, or a sudden drop of the curve towards zero at the end of exhalation as well as clearly deviating curves or values in the minimum required three measurement manoeuvres are clear hints for an insufficiently forced expiration or an expiration that was stopped too early. Pulmonary function assistants need instructions as to when application of a rapid acting beta agonist with repeated spirometry to detect possible reversibility is necessary. This includes knowing how long therapeutic bronchodilators must be stopped prior to the test.

Raised-Volume Forced Expiratory Flow-Volume Curve in Healthy Taiwanese Infants

The raised-volume rapid thoracoabdominal compression (RVRTC) manoeuvre has been applied to obtain full forced expiratory flow-volume curves in infants. No reference data are available for Asian populations. This study was conducted to establish predictive reference equations for Taiwanese infants. Full-term infants without any chronic disease or major anomaly were enrolled from this cohort study. Full forced expiratory flow-volume curves were acquired using RVRTC manoeuvres through Jaeger’s system. Tidal breath analysis, passive respiratory mechanics, and tidal forced expiratory flow-volume curves were performed and collected at the same measurement. Multiple linear analyses were used to model the variables. We performed 117 tests of RVRTC flow-volume curves in 97 infants. The results revealed that all parameters, except for FEV0.5 /FVC, correlated highly and positively with body length. These parameters correlated significantly with other parameters of passive respiratory mechanics and tidal forced expiratory flow-volume curves. This is the first study to establish equipment-specific reference data of full forced expiration using RVRTC manoeuvres in Asian infants. The results revealed that parameters of RVRTC manoeuvres are moderately related to other parameters of infant lung function. These race-specific reference data can be used to more precisely and efficiently diagnose respiratory diseases in infants of Chinese ethnicity.

Thoracic gas compression during forced expiration in patients with emphysema, interstitial lung disease and obesity

BackgroundDynamic gas compression during forced expiration has an influence on conventional flow-volume spirometry results. The extent of gas compression in different pulmonary disorders remains obscure. Utilizing a flow plethysmograph we determined the difference between thoracic and mouth flows during forced expiration as an indication of thoracic gas compression in subjects with different pulmonary diseases characterized by limitations in pulmonary mechanics.MethodsPatients with emphysema (N = 16), interstitial lung disease (ILD) (N = 15), obesity (N = 15) and healthy controls (N = 16) were included. Compressed expiratory flow-volume curves (at mouth) and corresponding compression-free curves (thoracic) were recorded. Peak flow (PEF) and maximal flows at 75%, 50% and 25% of remaining forced vital capacity (MEF75, MEF50 and MEF25) were derived from both recordings. Their respective difference was assessed as an indicator of gas compression.ResultsIn all groups, significant differences between thoracic and mouth flows were found at MEF50 (p < 0.01). In controls, a significant difference was also measured at MEF75 (p <0.005), in emphysema subjects, at PEF and MEF75 (p < 0.05, p < 0.005) and in obese subjects at MEF75 (p <0.005) and MEF25 (p < 0.01). ILD patients showed the lowest difference between thoracic and mouth flows at MEF75 relative to controls and emphysema patients (p < 0.005, p < 0.001). Obese subjects did not differ from controls, however, the difference between thoracic and mouth flows was significantly higher than in patients with emphysema at MEF50 (p < 0.001) and MEF25 (p < 0.005).ConclusionsAlveolar gas compression distorts the forced expiratory flow volume curve in all studied groups at the middle fraction of forced expiratory flow. Consequently, mouth flows are underestimated and the reduction of flow measured at 75% and 50% of vital capacity is often considerable. However, gas compression profiles in stiff lungs, in patients with decreased elastic recoil in emphysema and in obesity differ; the difference between thoracic and mouth flows in forced expiration was minimal in ILD at the first part of forced expiration and was higher in obesity than in emphysema at the middle and last parts of forced expiration.

Factors associated with aerobic fitness in adolescents with asthma

In adolescents with asthma, information on factors associated with cardiorespiratory fitness levels is limited. The present study aimed to determine if objectively measured physical activity as well as potential relevant factors such as lung function, asthma exacerbations, use of inhaled corticosteroids or skin fold thickness are associated with direct measurements of peak oxygen uptake (V˙O2peak) in adolescents with asthma. From a nested case-control study at 13-years in the Environment and Childhood Asthma birth cohort study in Oslo, Norway, 86 13-years old adolescents with and 76 without asthma performed maximal running on a treadmill with V˙O2peak measured. The sum of four skin fold thicknesses was recorded, followed by wearing an activity monitor for four consecutive days. Lung function was measured by maximum forced expiratory flow-volume curves and body plethysmography. Asthma exacerbations and use of medication were registered by parental structured interview. Data were analysed using multiple regression analysis. Vigorous physical activity (coefficients with 95% confidence intervals; 1.73 (0.32, 3.14)) and skin fold thickness -0.35 (-0.41, -0.28)) were significantly associated with V˙O2peak in adolescents with asthma. Neither use of inhaled corticosteroids, lung function nor number of asthma exacerbations was associated with V˙O2peak when taking physical activity and skin fold thickness into account. In the adolescents without asthma only skin fold thicknesses was negatively associated with V˙O2peak -3.5 (-4.1, -2.8). V˙O2peak appears to be determined by vigorous physical activity level in Norwegian adolescents with asthma and not by asthma-related factors such as use of inhaled corticosteroids, lung function nor number of asthma exacerbations.

Asthma symptoms in rural living Tanzanian children; prevalence and the relation to aerobic fitness and body fat

To determine the prevalence of asthma symptoms in children from a rural district in North-Tanzania, and their relationship to aerobic fitness and body fat. In Manyara region in Tanzania, children (aged 9-10 years) were randomly selected to participate in the present cross-sectional study. Hundred and seventy two participants completed a video questionnaire showing the symptoms and signs of asthma. Lung function was measured by maximum forced expiratory flow-volume curves. Aerobic fitness was estimated from a standardized indirect maximal cycle ergometer test and sum of three skinfolds reflected body fat. Twenty four per cent reported asthma symptoms last year. Severe wheezing attacks last year were reported in 5% of the participants. Thirty seven per cent of the participants were underweight. Underweight children had significantly lower (P < 0.02) lung function (per cent of predicted). Lower body fat was associated with higher occurrence of asthma symptoms (odds ratio and 95% CI; 0.45 (0.22-0.95; P = 0.04). Aerobic fitness was not associated with asthma symptoms. More than every fifth 9-10 year old child from a rural district in North-Tanzania reported asthma symptoms. Lower body fat was associated with higher occurrence of asthma symptoms, but aerobic fitness was not associated with asthma symptoms.

Advances in the Study of Lung Function in Infants: Forced Expiratory Maneuvers From an Increased Lung Volume

Forced expiratory maneuvers from an increased lung volume in infants date from 1989 and consist of raising the inspiratory volume by applying a specific inflation pressure until a level close to the total lung capacity is reached. The chest and abdomen are then compressed by means of an inflatable jacket in order to obtain a forced expiratory flow-volume curve similar to that obtained for an adult. Forced expiration from an increased lung volume in infants is useful, just as the maneuver is in older patients, for studying airway function, diagnosing obstructive diseases early, and assessing response to treatment. The objective of this review is to provide information on the physiological bases and technical aspects of a lung function test that has proven highly useful for the study of the airways of healthy infants as well as those with respiratory diseases.

Non-invasive forced expiratory flow–volume curves to measure lung function in cats

Forced expiratory flow-volume curves were performed in 15 cats using the non-invasive thoracic compression techniques developed for use in human infants. Cats breathed through a face mask and pneumotachygraph from which flow and volume were obtained. Thoracic compression was applied from an inflatable bag in a non-expandable jacket surrounding the animal. Bag inflation at end inspiration was initiated by a computer pulse to a pressurized chamber. Processed signals from the pneumotachygraph determined maximum-forced expiratory flow at lung volume equivalent to functional residual capacity (FRC), termed V'maxFRC. Different compression pressures were used, and the highest value from a technically satisfactory flow-volume loop was taken as the result. Mean (+/- 95% CI) V'maxFRC was 422 (369-475) ml/s. Compared with infants of similar weight (V'maxFRC approximately 180 ml/s), cats had a much higher V'maxFRC. Tests repeated another day showed a mean (+/-95% CI) percentage difference between paired tests to be 2.8 (-12.6, +18.3)%. Non-invasive forced expiratory flow-volume measurements can be reliably obtained in sedated cats.

SENSITIVITY OF SPIROMETRIC MEASUREMENTS TO DETECT AIRWAY OBSTRUCTION IN INFANTS

Jones MH, Howard J, Davis S, Kisling J, Tepper R. Am J Respir Crit Care Med . 2003;167:1283–1286 To demonstrate the ability of forced expiratory flow (FEF) volume curves from increased lung volumes to discriminate among infants with differing severities of respiratory symptoms and to compare the ability of variables used to quantify the flow volume curves to detect airway obstruction. Infants referred to a pediatric pulmonary clinic were classified into 2 groups. Group 1 patients had previous respiratory symptoms but …

Measurement of Forced Expiratory Flows and Lung Volumes

After completing this article, readers should be able to: 1. Describe the information that measurements of forced expiratory flow can provide in spontaneously breathing and mechanically ventilated infants. 2. Delineate how lung volume can be measured. The measurements of forced expiratory flows and lung volumes are important to the evaluation of patients who have respiratory symptoms. Until recently, measurements have been restricted to adults and children old enough to cooperate with testing maneuvers. Newer techniques have enabled such measurements to be made in infants and led to improved understanding of normal lung and airway growth during infancy and early childhood, when dramatic changes occur. The measurements have had important clinical uses in the evaluation and treatment of infants who have respiratory disease, but their use has been limited because they require specialized equipment and expertise as well as sedation of the infant. In this article, we discuss the techniques required for measurement of forced expiratory flows and lung volumes, their limitations, and applications in clinical practice. Detection of airflow obstruction, by physical examination or by quantitative measurement techniques, is facilitated by increasing expiratory flow rates. Measurement of forced expiratory flows is useful because flow rates are inversely proportional to the fourth power of the radius of the airway and, therefore, are indicative of airway size when flow is limited. Disease states affecting the airways, including asthma, bronchopulmonary dysplasia (BPD), or congenital lesions such as pulmonary hypoplasia or vascular airway compression, are expected to decrease expiratory flow. Infants typically are sedated for testing to maintain relaxed breathing with a face mask placed over the mouth and nose. This sedation often is perceived by parents and physicians as one of the barriers to such testing. (1) However, sedation can be achieved safely using oral chloral hydrate at a dose of 80 to 100 mg/kg. …

Sensitivity of spirometric measurements to detect airway obstruction in infants.

We evaluated the ability of forced expiratory flow volume curves from raised lung volumes to assess airway function among infants with differing severities of respiratory symptoms. Group 1 (n = 33) had previous respiratory symptoms but were currently asymptomatic; group 2 (n = 36) was symptomatic at the time of evaluation. As a control group, we used our previously published sample of 155 healthy infants. Flow volume curves were quantified by FVC, FEF50, FEF75, FEF25-75, FEV0.5, and FEV0.5/FVC, which were expressed as Z scores. All variables except FVC had Z scores that were significantly less than zero and distinguished groups 1 and 2 with progressively lower Z scores. The mean Z scores of the flow variables (FEF50%, FEF75%, and FEF25-75%) were more negative than the Z scores for the timed expired volumes (FEV0.5 or FEV0.5/FVC) for both groups. In general, measures of flow identified a greater number of infants with abnormal lung function than measures of timed volume; FEF50 had the highest performance in detecting abnormal lung function. In summary, forced expiratory maneuvers obtained by the raised volume rapid compression technique can discriminate among groups of infants with differing severity of respiratory symptoms, and measures of forced expiratory flows were better than timed expiratory volume in detecting abnormal airway function.

Maximal and partial expiratory flow rates in a population sample of 10- to 11-yr-old schoolchildren. Effect of volume history and relation to asthma and maternal smoking.

The effect of volume history on forced expiratory flow rates has been reported to differ between patients with asthma and healthy persons, and it has been hypothesized that the peripheral airway inflammation of patients with asthma may underlie this difference. There are no published data, however, on the distribution of such volume history effects or the relation of these effects to airways disease in children. We obtained combined partial and maximal forced expiratory flow-volume curves on 1,834 children, age 10-11 yr, in eight communities in the United States and Canada. The effect of a deep inhalation on forced expiratory flow rates at low lung volumes was quantitated by the ratio of V (30) during a maximal expiratory maneuver (V (30M)) to V (30) during a partial expiratory maneuver (V (30P)). The V (30M)/V (30P) ratio was slightly higher among girls than boys (1.26 versus 1.18, p = 0.0001) indicating that a deep inhalation increased V (30) slightly more among girls than among boys. The V (30M)/V (30P) ratio was related to neither history of asthma nor to maternal smoking. In contrast, most spirometric indices from either the maximal or the partial expiratory flow-volume curve were lower in association with a history of asthma or a report of maternal smoking. The ratio of FEF(25-75)/FVC was particularly consistent as a measurement that discriminated both of these effects in boys and girls. These results suggest that the measurement of volume history effects offers no benefits for epidemiological studies of childhood respiratory disease whereas spirometric indices such as the FEF(25-75)/FVC ratio are quite sensitive to the effects of asthma and environmental tobacco smoke exposure on the airways.

Crying significantly reduces absorption of aerosolised drug in infants

AIMTherapeutic aerosols are routinely used in the management of infant obstructive airways disease. Infants often become distressed during administration. The aim of this study was to determine the influence of...

Expiratory Flow Limitation During Spontaneous Breathing: Comparison of Patients With Restrictive and Obstructive Respiratory Disorders

Comparison of tidal and forced expiratory flow-volume (V-V) curves has inherent technical problems in the characterization of expiratory flow limitation. In addition, patients with neuromuscular disorders may be unable to perform forced expiratory maneuvers because of muscle weakness or poor coordination. A recently developed simple, noninvasive technique that avoids these problems was used to detect expiratory flow limitation at rest in 19 seated patients with restrictive respiratory (13 with musculoskeletal) disorders (RD) and 20 with chronic obstructive airway disease (COAD). A large rehabilitation hospital for the care of patients with chronic musculoskeletal and respiratory disorders. The method consisted of applying negative pressure of about 5 cm H2O at the airway opening during expiration and comparing the ensuing V-V curve to the preceding tidal V-V curve. While nine patients with COAD demonstrated flow limitation, only one patient with RD did so. Patients with expiratory flow limitation exhibited various contours of the control tidal expiratory V-V curve. Thus, inspection of the tidal V-V curve is not a reliable means of detecting expiratory flow limitation. We conclude that expiratory flow limitation during resting breathing is common in patients with COAD but not in patients with RD.

Shape and position of the complete dose-response curve for inhaled methacholine in normal subjects.

Plateaus on the inhalation concentration-response curve have been described in normal subjects and patients with mild asthma. To determine the prevalence of plateaus on inhalation concentration-response curves, and the position of the curves in normal subjects, we measured complete dose-response curves for methacholine (1 mg/ml to 256 mg/ml) in 73 nonatopic, nonsmoking, nonasthmatic normal subjects between the ages of 20 and 76 yr. Measurements included FEV1, maximal expiratory flow at 50% and 30% of vital capacity on partial and complete forced expiratory flow-volume curves (Vmax50p, Vmax50c, Vmax30p, Vmax30c) and pulmonary resistance (RL). Plateau responses, EC50 values and slopes were measured. Plateaus were present in 25, 27, 24, 34, 35, and 16 subjects for FEV1, Vmax50c, Vmax30c, Vmax50p, Vmax30p, and RL, respectively. In those who achieved a plateau, the mean maximal decrease in FEV1 (+/- SD) was 21 +/- 8%, in Vmax50c it was 46 +/- 16%, in Vmax50p it was 67 +/- 12%, in Vmax30c it was 58 +/- 21%, and in Vmax30p it was 75 +/- 15%, and the increase in RL was 213 +/- 89%. In summary, the results of this study showed that easily identifiable plateaus develop on the inhalation concentration-response curves of approximately 40% of normal subjects after only moderate decreases in maximum flow and increases in RL. Maximal response at the plateau was greater on partial flow-volume curves and at lower lung volumes (30% versus 50% of VC). Comparison of these data with data from patients at risk for airway hyperresponsiveness will allow definition of the mechanisms leading to airway hyperresponsiveness.

A new technique to generate and assess forced expiration from raised lung volume in infants.

We have developed a new technique that allows assessment of infant lung function over an extended volume range. The lungs are rapidly inflated to a predetermined inflation pressure (PP) using a modified diaphragm pump. Forced expiratory flow-volume (FEFV) curves are then generated from raised lung volumes using an inflatable plastic jacket. We studied 26 normal infants with a median age of 14 mo (range, 3 to 23 mo). FEFV curves were obtained in each infant from end-tidal inspiration and from lung volumes set by a range of PP (15 to 20 cm H2O). Mean (SE) volume above FRC was 107 ml (9 ml), and mean forced expiratory time was 0.73 s (0.05 s) at end-tidal inspiration. Both measurements increased progressively with increases in PP to 251 ml (13 ml) and 1.04 s (0.06 s), respectively, at 20 cm H2O PP (p < 0.0001). Mean intrasubject coefficient of variation was 15.5% (95% confidence interval, 12 to 19%) for maximal flow at FRC, but it was less than 6% (95% CI, 4 to 8%) for forced expiratory volume-time (FEVt) measurements at all levels of PP. Twenty-seven recurrently wheezy infants with a median age of 13 mo (range, 6 to 18 mo) were subsequently studied using a PP of 17.5 cm H2O. Wheezy infants had a lower VmaxFRC [mean (1.39 ml/s/cm) and 95% CI (1.15 to 1.63 ml/s/cm)] than did normal infants (1.78 ml/s/cm; CI, 1.51 to 2.05) (p < 0.05). FEV1 measurements were all lower in wheezy infants than in normals infants: mean FEV0.5, 1.86 ml/cm (CI, 1.73 to 1.98) and 2.31 ml/cm (CI, 2.15 to 2.48), respectively (p < 0.0001); FEV0.75, 2.20 ml/cm (CI, 2.07 to 2.32) and 2.72 ml/cm (CI, 2.52 to 2.91), respectively (p < 0.0001); FEV1.0, 2.42 ml/cm (CI, 2.26 to 2.58) and 2.84 ml/cm (CI, 2.63 to 3.06), respectively (p < 0.005). The Ci values of each FEVt measurement did not overlap between the wheezy and normal groups; however, the CI values of VmaxFRC overlapped markedly. In addition, FEVt parameters showed greater sensitivity in detecting reduced lung function (71 to 89%) than did VmaxFRC parameters (56%). We conclude that (1) FEVt measurements derived from a lung volume set by a standardized pressure are more reproducible than flow measurements in the tidal volume range; (2) FEVt measurements are significantly lower in wheezy infants than in normal infants, show less overlap than flow measurements in the tidal volume range, and therefore are better able to separate the two populations.

291 RESPIRATORY MECHANICHS IN INFANTS WITH ACUTE BRONCHIOLITIS

Objective: to determine alterations in pulmonary function tests in infants in acute phase of bronchiolitis. Subjects and methods: Partial forced expiratory flow-volume curves obtained by an inflatable jacket and end-inspiratory single occlusion test were used to determine maximal flow at Functional Residual Capacity (VmaxFRC) and total respiratory system compliance and resistance (Crs, Rrs) in 54 previously healthy infants in acute phase of bronchiolitis and in 44 healthy control infants aged 1-12 months. PEDS and PUFF systems (Medical Associates, Hatfield, Pa, USA) were used for these measurements. Results: see table. Table: age (yr); Length (cm); VmaxFRC (mL/s). (mL/cmH2O). Rrs (cmH2O/Ls). % Predicted by Tepper et al. Am Rev Respir Dis 1986;134:513-9. Mean (standard deviation). Comparision by t test for independent samples. NS: no significative. Conclusion: Important decrease in VmaxRFC and compliance with no significant increase in resistance characterizes acute phase of bronchiolitis.

Gender related differences in airway tone in children

The effects of gender, volume history, and inhaled atropine and isoproterenol on lung mechanics were assessed in 16 normal boys and 14 normal girls using lung volumes, flow-volume curves, and oscillatory resistances. Flows were measured from full and partial forced expiratory flow-volume curves. Six girls and 6 boys were studied before and after inhaled atropine, and 10 boys and 8 girls before and after inhaled isoproterenol. Girls demonstrated a significant increase in flows on full and partial curves with a deep inspiration [Vmax-partial 0.73 +/- 0.34 (SD) to Vmax-full 0.80 +/- 0.37 and 0.83 +/- 0.20 to 1.06 +/- 0.29 TLC/s in each group] and following inhalation of isoproterenol on the partial curves only (0.73 +/- 0.34 to 0.93 +/- 0.40 TLC/s). Boys showed a small but significant increase in Vmax with isoproterenol on full curves but not on partial curves. Following atropine, boys demonstrated a significant increase in Vmax on partial flow-volume curves (0.78 +/- 0.28 to 1.00 +/- 0.35 TLC/s) and a significant decrease in specific respiratory resistance (7.6 +/- 2.7 to 5.1 +/- 0.9 cmH2O/s), whereas girls had no such changes. These data suggest that boys have greater resting airway tone than girls and that this tone is less responsive to deep inspiration and isoproterenol independently, although a combination of isoproterenol and a deep inspiration will produce increased flows in boys. Atropine reduces airway tone predominantly in boys, suggesting that the increased resting airway tone in boys is partially mediated via the vagus nerve.

Assessment of forced expiratory volume-time parameters in detecting histamine-induced bronchoconstriction in wheezy infants.

A new technique recently introduced allows the measurement of infant lung function from lung volumes raised by a pump prior to generation of forced expiratory flow-volume (FEFV) curves. Forced expiratory volume-time (FEV1) parameters rather than traditional flow parameters are used. The aim of this study was to assess the usefulness of FEV1 parameters in detecting airway responsiveness to histamine in recurrently wheezy infants. Ten infants (age 7-18 months) sedated with 80 mg/kg chloral hydrate underwent a histamine inhalation challenge. Throughout the challenge FEFV curves were generated from end-tidal inspiration. Raised FEFV curves, from a lung volume preset by 15 cmH2O inflation pressure, were gathered at baseline and after the final concentration of histamine. The mean fall from baseline was 47% in maximal flow at functional residual capacity (VmaxFRC) (P < 0.0005), 15.5% in FEV0.5 (P < 0.0001), 13.5% in FEV0.75 (P < 0.005), and 11.0% in FEV1.0 (P = 0.057), after the final concentration of histamine delivered. Tidal volume and inspiratory volume reached above FRC between pre- and posthistamine did not change. Mean oxygen saturation fell significantly from 97 to 93%. We conclude that FEV1 parameters adequately detect reduced lung function during histamine-induced bronchoconstriction and appear suitable for histamine challenge testing in infants.

Bronchial responsiveness and lung function in infants with lower respiratory tract illness over the first six months of life.

The aim of this study was to determine whether increased bronchial responsiveness to histamine is associated with lower respiratory tract illness (one or more episodes of wheeze or cough, or both) in infancy. Fifty four normal newborn infants who had at least one atopic parent were recruited. At a median age of 6.5 months, 45 infants, 23 with a history of lower respiratory tract illness, and 22 without, underwent pulmonary function testing during a symptom free period. The maximum flow at functional residual capacity (VmaxFRC) was calculated from partial forced expiratory flow volume curves using the squeeze technique. Bronchial responsiveness to increasing doses of histamine was assessed by determining the provoking concentration which caused a 30% decrease in VmaxFRC (PC30). The length adjusted VmaxFRC was lower for symptomatic infants before the challenge (median 125 ml/s; 95% confidence intervals (CI) 85 to 164 ml/s) compared with control infants (median 215 ml/s; 95% CI 159 to 298 ml/s). There was no significant difference in PC30 between symptomatic infants (median 10.3 g/l; 95% CI 2.8 to 23.8 g/l) and control infants (median 16.5 g/l; 95% CI 2.4 to 27.9 g/l). Bronchial responsiveness to histamine can be shown in most infants early in life and is independent of lower respiratory tract symptoms including wheezing.

Partial forced expiratory flow-volume curves in young children during ketamine anesthesia.

Maximal flows at functional residual capacity (VmaxFRC) from partial forced expiratory flow-volume (PEFV) curves were obtained in 14 normal preschool children (8 boys, 6 girls) of average age 44 mo, under general anesthesia before elective surgery. PEFV curves were generated from end inspiration by rapid compression of the chest wall with an inflatable jacket. VmaxFRC, expressed in milliliter per second, correlated linearly with height, weight, age, and FRC in milliliter and milliliters per kilogram. The best correlation of VmaxFRC (ml/s) was to height to the power of 2.47, which agrees with the results predicted by wave-speed theory. Mean FRC-corrected VmaxFRC was 2.42 +/- 0.50 (SD) FRC's/s with no significant difference between boys (2.35 FRC's/s) and girls (2.51 FRC's/s). There was no correlation between lung-size corrected VmaxFRC and height, weight, or age, but it tended to decrease with increasing FRC. The intersubject variability for VmaxFRC was reduced by normalizing for FRC, and was significantly better than that reported for awake children. This can be attributed to the greater control over volume history and more reliable maximal flow generation during anesthesia. The intrasubject coefficient of variation (CV) for VmaxFRC was 12.2%, and the intersubject CV was 20.0%. The difference may represent the variability due to dysanapsis. It is concluded that dysanapsis is not a prominent factor in children of this age group. In addition, the similarity of the regression equation for VmaxFRC vs. height to that of FRC vs. height supports the concept of equidimensional growth of the airways and lung parenchyma.