Intrasubject variability of pulmonary function testing in healthy children

Relationships between lung function, allergy, and wheezing in urban children

BACKGROUND

Allergic sensitization and low lung function in early childhood are risk factors for subsequent wheezing and asthma. However, it is unclear how allergic sensitization affects lung function over time.

OBJECTIVE

We sought to test whether allergy influences lung function and whether these factors synergistically increase the risk of continued wheezing in childhood.

METHODS

We analyzed longitudinal measurements of lung function (spirometry and impulse oscillometry) and allergic sensitization (aeroallergen skin tests and serum allergen-specific IgE) throughout early childhood in the Urban Environmental and Childhood Asthma study, which included high-risk urban children living in disadvantaged neighborhoods. Intraclass correlation coefficients were calculated to assess lung function stability. Cluster analysis identified low, medium, and high allergy trajectories, which were compared with lung function and wheezing episodes in linear regression models. A variable selection model assessed predictors at age 5 years for continued wheezing through age 12 years.

RESULTS

Lung function adjusted for growth was stable (intraclass correlation coefficient, 0.5-0.7) from age 5 to 12 years and unrelated to allergy trajectory. Lung function and allergic sensitization were associated with wheezing episodes in an additive fashion. In children with asthma, measuring lung function at age 5 years added little to the medical history for predicting future wheezing episodes through age 12 years.

CONCLUSIONS

In high-risk urban children, age-related trajectories of allergic sensitization were not associated with lung function development; however, both indicators were related to continued wheezing. These results underscore the importance of understanding early-life factors that negatively affect lung development and suggest that treating allergic sensitization may not alter lung function development in early to mid-childhood.

Comparison of particles in exhaled air and multiple breath washout for assessment of small airway function in children with cystic fibrosis

BACKGROUND

The introduction of modulator therapy for cystic fibrosis (CF) has led to an increased interest in the detection of small airway disease (SAD) as sensitive marker of treatment response. The particles in exhaled air (PExA) method, which records exhaled particle mass (PEx ng/L) and number (PExNR), detects SAD in adult patients. Our primary aim was to investigate if PExA outcomes in children with CF are different when compared to controls and associated with more severe disease. Secondary aims were to assess feasibility and repeatability of PExA in children with CF and to correlate PExA to multiple breath nitrogen washout (MBNW) as an established marker of SAD.

METHODS

Thirteen healthy children (HC), 17 children with CF with normal lung function (CF-N) (FEV1 z-score ≥ -1.64) and six with airway obstruction (CF-AO) (FEV1 z-score < -1.64) between 8 and 18 years performed MBNW followed by PExA and spirometry. Children with CF repeated the measurements after 3 months.

RESULTS

PEx ng/L and PExNR/L per liter of exhaled breath were similar between the three groups. The lung clearance index (LCI) was significantly higher in both CF-N and CF-AO compared to HC. All participants, except one, were able to perform PExA. Coefficient of variation for PEx ng/l was (median) 0.38, range 0-1.25 and PExNR/l 0.38, 0-1.09. Correlation between LCI and PEx ng/l was low, rs 0.32 (p = .07).

CONCLUSION

PExA is feasible in children. In contrast to LCI, PExA did not differentiate healthy children from children with CF suggesting it to be a less sensitive tool to detect SAD.

Perception of Pulmonary Function in Children with Asthma and Cystic Fibrosis

Background: Under-perception of pulmonary dysfunction may delay appropriate treatment, while over-perception may result in unnecessary treatments. Objectives: To evaluate the ability of patients with asthma or cystic fibrosis and their subspecialty caregivers to assess changes in lung function based on their subjective clinical impressions. Methods: Patients were asked to qualitatively describe how they felt compared to their prior visit (same/better/worse) and to quantitatively estimate their forced expiratory volume in 1 s (FEV₁) after being reminded of their FEV₁ at the prior visit. Providers made similar estimates based on history and physical examination and knowledge of prior FEV₁. After adjusting for relevant clinical covariates, lung function estimates were categorized as accurate (±5% of measured FEV₁), overestimated (>5% above measured), and underestimated (>5% below measured). Results: One hundred nine patients estimated FEV₁ on 179 occasions. Concordance between patient qualitative assessment and FEV₁-based categories was low (κ = 0.08); 44% of patients reported feeling better than the FEV₁-based category showed. Quantitatively, 56% of patient estimates were accurate, 18% were underestimated, and 26% overestimated; accuracy improved with age (odds ratio = 1.16, P = 0.01). Concordance between provider qualitative assessments and FEV₁-based category was moderate (κ = 0.35); about 19% said their patient looked better than the FEV₁-based category showed. Quantitatively, 65% of provider estimates were accurate, 16% were underestimated, and 19% were overestimated; accuracy improved with years of experience. Conclusions: Patients' and providers' perceptions of lung function were low to moderately accurate. Relying on subjective impression may place patients at risk for unnecessary treatments or increased morbidity. These findings highlight the importance of objective lung function assessment.

Postinfectious bronchiolitis obliterans in children: lessons from bronchiolitis obliterans after lung transplantation and hematopoietic stem cell transplantation

Postinfectious bronchiolitis obliterans (PIBO) is an irreversible obstructive lung disease characterized by subepithelial inflammation and fibrotic narrowing of the bronchioles after lower respiratory tract infection during childhood, especially early childhood. Although diagnosis of PIBO should be confirmed by histopathology, it is generally based on history and clinical findings. Irreversible airway obstruction is demonstrated by decreased forced expiratory volume in 1 second with an absent bronchodilator response, and by mosaic perfusion, air trapping, and/or bronchiectasis on computed tomography images. However, lung function tests using spirometry are not feasible in young children, and most cases of PIBO develop during early childhood. Further studies focused on obtaining serial measurements of lung function in infants and toddlers with a risk of bronchiolitis obliterans (BO) after lower respiratory tract infection are therefore needed. Although an optimal treatment for PIBO has not been established, corticosteroids have been used to target the inflammatory component. Other treatment modalities for BO after lung transplantation or hematopoietic stem cell transplantation have been studied in clinical trials, and the results can be extrapolated for the treatment of PIBO. Lung transplantation remains the final option for children with PIBO who have progressed to end-stage lung disease.

Bisphenol a exposure and the development of wheeze and lung function in children through age 5 years

IMPORTANCE

Bisphenol A (BPA), a prevalent endocrine-disrupting chemical, has been associated with wheezing in children, but few studies have examined its effect on lung function or wheeze in older children.

OBJECTIVES

To test whether BPA exposure is associated with lung function, with wheeze, and with pattern of wheeze in children during their first 5 years.

DESIGN, SETTING, AND PARTICIPANTS

A birth cohort study, enrolled during early pregnancy in the greater Cincinnati, Ohio, area among 398 mother-infant dyads. We collected maternal urine samples during pregnancy (at 16 and 26 weeks) and child urine samples annually to assess gestational and child BPA exposure.

MAIN OUTCOMES AND MEASURES

We assessed parent-reported wheeze every 6 months for 5 years and measured child forced expiratory volume in the first second of expiration (FEV1) at age 4 and 5 years. We evaluated associations of BPA exposure with respiratory outcomes, including FEV1, child wheeze, and wheeze phenotype.

RESULTS

Urinary BPA concentrations and FEV1 data were available for 208 children and urinary BPA concentrations and parent-reported wheeze data were available for 360 children. The mean maternal urinary BPA concentration ranged from 0.53 to 293.55 µg/g of creatinine. In multivariable analysis, every 10-fold increase in the mean maternal urinary BPA concentration was associated with a 14.2% (95% CI, -24.5% to -3.9%) decrease in the percentage predicted FEV1 at 4 years, but no association was found at 5 years. In multivariable analysis, every 10-fold increase in the mean maternal urinary BPA concentration was marginally associated with a 54.8% increase in the odds of wheezing (adjusted odds ratio, 1.55; 95% CI, 0.91-2.63). While the mean maternal urinary BPA concentration was not associated with wheeze phenotype, a 10-fold increase in the 16-week maternal urinary BPA concentration was associated with a 4.27-fold increase in the odds of persistent wheeze (adjusted odds ratio, 4.27; 95% CI, 1.37-13.30). Child urinary BPA concentrations were not associated with FEV1 or wheeze.

CONCLUSIONS AND RELEVANCE

These results provide evidence suggesting that prenatal but not postnatal exposure to BPA is associated with diminished lung function and the development of persistent wheeze in children.

Pulmonary function testing in children and infants

Pulmonary function testing is performed in children and infants with the aim of documenting lung development with age and making diagnoses of lung diseases. In children and infants with an established lung disease, pulmonary function is tested to assess the disease progression and the efficacy of therapy. It is difficult to carry out the measurements in this age group without disturbances, so obtaining results of good quality and reproducibility is challenging. Young children are often uncooperative during the examinations. This is partly related to their young age but also due to the long testing duration and the unpopular equipment. We address a variety of examination techniques for lung function assessment in children and infants in this review. We describe the measuring principles, examination procedures, clinical findings and their interpretation, as well as advantages and limitations of these methods. The comparability between devices and centres as well as the availability of reference values are still considered a challenge in many of these techniques. In recent years, new technologies have emerged allowing the assessment of lung function not only on the global level but also on the regional level. This opens new possibilities for detecting regional lung function heterogeneity that might lead to a better understanding of respiratory pathophysiology in children.

Spirometry in 5-year-olds--validation of current guidelines and the relation with asthma

INTRODUCTION

Spirometry is more frequently measured in younger children. Our primary aim was to validate 2005 ATS-ERS Task Force standards for spirometry in adults and older children among a population of 5-year-old children. Our secondary aim was to relate spirometry to asthma symptoms.

METHODS

Children were participants in a longitudinal cohort study where asthma symptoms and spirometry were assessed.

RESULTS

Of the 827 children assessed, spirometry was obtained in 638 (85 with wheeze). A back-extrapolated volume/FVC ratio of <5% was achieved in 99% of children, the best two FVC were < or =150 ml of each other in 89% and three efforts were obtained within six attempts in 88%. The best two FVC were within 10% of each other in 82% of children. Only 13% achieved a forced expiratory time (FET) of > or =3 sec, whereas 80% had an FET of > or =1 sec. All criteria (including FET > or =1 s and FVC < or =10%) were met in 400 (65%) of the 638 children. Most spirometric indices were reduced in association with current wheeze and a history of asthma; children with current wheeze had a mean reduction of 0.65 FEV(1) z score compared to healthy children, P < 0.001. An FEV(1) z score of -1.0 had 82% sensitivity but only 50% specificity for current wheeze, the corresponding numbers for an FEF(50) z score of -1.0 being 79% and 71%.

CONCLUSIONS

The standards for spirometry are mostly achieved in this age group but are not necessarily valid and require revision. Reliable spirometry is feasible in 5-year-old children where reduced measurements are associated with asthma symptoms and in whom FEF(50) appears to be the most discriminatory variable.

Lung function tests in neonates and infants with chronic lung disease: forced expiratory maneuvers

This fourth paper in a review series on the role of lung function testing in infants and young children with acute neonatal disorders and chronic lung disease of infancy (CLDI) addresses measurements of forced expiration using rapid thoraco-abdominal compression (RTC) techniques and the forced deflation technique. Following orientation of the reader to the subject area, we focus our comments on the areas of inquiry proposed in the introductory paper to this series. The quality of the published literature is reviewed critically, and recommendations are provided to guide future investigation in this field. All studies on infants and young children with CLDI using forced expiratory or deflation maneuvers demonstrated that forced flows at low lung volume remain persistently low through the first 3 years of life. Measurement of maximal flow at functional residual capacity (V'maxFRC) is the most commonly used method for assessing airway function in infants, but is highly dependent on lung volume and airway tone. Recent studies suggested that the raised volume RTC technique, which assesses lung function over an extended volume range as in older children, may be a more sensitive means of discriminating changes in airway function in infants with respiratory disease. The forced deflation technique allows investigation of pulmonary function during the early development of CLDI in intubated subjects, but its invasive nature precludes its use in the routine setting. For all techniques, there is an urgent need to establish suitable reference data and evaluate within- and between-occasion repeatability, prior to establishing the clinical usefulness of these techniques in assessing baseline airway function and/or response to interventions in subjects with CLDI.

Assessment of lung volumes in children and adolescents: comparison of two plethysmographic techniques

Thoracic gas volume (Vtg) can be measured with body plethysmography by either repetitive panting or one single inspiratory effort against a shutter occluding the airways. The panting technique is preferred, but may be demanding. We aimed to assess the precision of these two methods and the degree of agreement between them. Vtg and functional residual capacity (FRC) were measured in 155 subjects with a standard, commercially available plethysmograph, acting as a variable-pressure, constant-volume device when Vtg is determined. Total lung capacity (TLC) and residual lung volume (RV) were calculated subsequent to a full vital capacity manoeuvre. For non-asthmatic healthy subjects, the standard deviations (SD) of the differences between two replicate measurements of FRC, TLC and RV were respectively 0.16, 0.13 and 0.14 litres with the panting technique, and 0.18, 0.18 and 0.23 litres with the single inspiratory effort technique. In percentage of the respective lung volumes, the corresponding 1.96 SDs were 20%, 8% and 40% with the panting technique and 23%, 12% and 67% with the single inspiratory effort technique. Between the two techniques, 95% limits of agreement were 21% for FRC, 11% for TLC and 58% for RV. The variability of Vtg and FRC accounted for most of the variability of TLC and RV. In conclusion, the panting and the single inspiratory effort technique produced results that were comparable in magnitude, however with a better precision with the panting technique. The single inspiratory effort technique can be used as an alternative if the panting technique fails.

Exploring the relationship between forced maximal flow at functional residual capacity and parameters of forced expiration from raised lung volume in healthy infants

The raised volume rapid thoraco-abdominal compression technique (RVRTC) is being increasingly used to assess airway function in infants, but as yet no consensus exists regarding the equipment, methods, or analysis of recorded data. The aim of this study was to explore the relationship between maximal flow at functional residual capacity (V'(maxFRC)) and parameters derived from raised lung volumes, and to address analytical aspects of the latter technique in an attempt to assist with future standardization initiatives. Forced vital capacity (FVC) from lung volume raised to 3 kPa, timed forced expiratory volumes (FEV(t)), and forced expiratory flow parameters at different percentages of expired FVC (FEF(%)) were measured in 98 healthy infants (1-69 weeks of age). V'(maxFRC) using the tidal rapid thoraco-abdominal compression (RTC) technique was also measured. The within-subject relationships and within-subject variability of the various parameters were assessed. Duration of forced expiration was < 0.5 sec in 5 infants, meaning that FEV(0.3) and FEV(0.4) were the only timed volume parameters that could be calculated in all infants during the first months of life, and even when it could be calculated, FEV(0.5) approached FVC in many of these infants. It is recommended that FEV(0.4) be routinely reported in infants less than 3 months of age. Contrary to previous reports, within subject variability of V'(maxFRC) was less than that of FEF(75) (mean CV = 6.3% and 8.9%, respectively).A more standardized protocol when analyzing data from the RVRTC would facilitate comparisons of results between centers in the future.

Children with difficult asthma: a practical approach

Many open studies investigating the effects of innovative treatments for steroid-dependent asthma demonstrate some benefit. This is also true of the majority of placebo arms in placebo-controlled trials. This suggests that children with difficult asthma benefit from the high level of input that is typically provided in clinical trials, with or without additional medication. Such intensive management of patients, with the emphasis on establishing the diagnosis, improving adherence, and identifying provoking factors, is the key to optimizing asthma control for these children. For patients with genuinely severe asthma, despite high doses of conventional treatment, a greater understanding of the pathological basis of persistent symptoms is needed. Identification of different pathological subtypes of severe asthma should allow for more rational prescribing of asthma therapy, as well as the design of further trials of potential steroid-sparing treatments.

Determinants of reproducibility of lung function tests in children aged 7 to 10 years

Lung function (LF) tests are part of many investigations in childhood lung disease. However, individual reproducibility of LF will confound between-subject differences. At the same time, increased LF variability has been linked to respiratory disease. In a sample of 598 children, two LF tests, separated by a 5-min interval, were recorded, and reliability (Rel) of forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), and maximal expiratory flow at 50% of FVC (MEF50) was determined. Rel was also assessed in children trained and untrained in the performance of LF. To investigate determinants of reproducibility for FEV1, the absolute difference between two repeated tests was calculated. Whenever this difference was > 120 ml, a child was considered to demonstrate excessive variability (poor reproducibility) in FEV1. For volume parameters coefficients of reliability (Crel) were found to be better than for MEF50 (FEV1: 0.96; FVC: 0.94, MEF50: 0.91). In untrained children Crel for FEV1 was only 0.91, but it was increased in subsequent visits (0.98, 0.97, and 0.97 at the second, third, and fourth tests, respectively). Excessive variability in FEV1 was observed in 10% of children and was related to the presence of wheeze [odds ratio (OR) 6.31; 95% confidence interval (CI) 1.78-22.4), shortness of breath (OR 3.14; 95% CI 1.00-9.93), a diagnosis of asthma (OR 6.25; 95% CI 1.76-22.1), and bronchial hyperresponsiveness (OR 4.30; 95% CI 2.07-8.94). We conclude that increased variability of LF is likely to be present in young children not accustomed to the testing procedure and in children with respiratory symptoms. Therefore, before guidelines for LF testing are applied, children should be trained to perform the tests and we should be cautious in the interpretation of test results in children who present with symptoms.

New techniques and developments in physiologic imaging of airways

Recently, noninvasive imaging methods for assessing regional and individual airway responsiveness have been developed in animal models and applied to humans with obstructive lung disease. This article examines the technique of high-resolution CT scan and MR imaging and their applications to the imaging of airways.

Diagnostic role of residual volume in paediatric patients with chronic symptoms of the lower airways

In bronchial asthma, measurement of absolute lung volumes may reveal lung dysfunction more readily than forced expiratory spirometry. Sixty-one children (aged 4-16 years) with mild to moderate bronchial asthma and 35 children (aged 7-16 years) with other symptoms of the lower airways (OSLA) were studied, and the plethysmographic results were compared with data obtained from 36 healthy volunteers aged 6-16 years. In the first test session, repeatability of forced expiratory volume in one second (FEV1), forced vital capacity (FVC), residual volume (RV), functional residual capacity (FRC) and total lung capacity (TLC) were good. Control subjects were also tested the next day, and intra-subject variability of repeat pulmonary function testing was in the normal range. The FEV1/FVC ratio was significantly higher in control subjects than in patients with asthma or OSLA, but only the decrease in RV after bronchodilator challenge separated patients with asthma from patients with OSLA. Changes in FEV1 and RV after bronchodilator challenge had a significant, although low, inverse correlation. An increase of > or = 5% in FEV1 had a positive predictive value of 44% and a negative predictive value of 68% for the clinical diagnosis of bronchial asthma; for a decrease of > or = 24% in RV, the figures were 86% and 71% respectively. The support of baseline absolute lung volumes on clinical decision-making is not necessarily great. Bronchodilator response, particularly in RV, is more pertinent and may enhance the detection of reversible lung dysfunction.

Effects of pseudomonas aeruginosa colonization on lung function and anthropometric variables in children with cystic fibrosis

The aim of this study was to evaluate how lung function and growth changed over time in children with cystic fibrosis (CF) colonized with pseudomonas aeruginosa (Pa) compared with those free of the organism. A total of 192 children attended our cystic fibrosis clinic between 1982 and 1992. Sixty-two of these had three or more annual assessments for lung function, and 117 had three or more annual assessments for height and weight. When lung function was expressed as a standard deviation score (SDS), forced expiratory volume in 1 second (FEV1) and forced expiratory flow at 25% of vital capacity (FEF25) decreased significantly more with respect to height in colonized compared with noncolonized children: FEV1, -0.052 verses -0.015 SDS/cm (P < 0.05); FEF25, -0.060 verses -0.007 SDS/cm (P < 0.05); forced vital capacity (FVC), -0.034 versus -0.012 (NS). In actual values those patients colonized with Pa increased their FEV1 by 16.4 versus 31.6 mL/cm (P < 0.01); FVC by 28.8 versus 41.4 mL/cm, P < 0.01; and FEF25 by -0.001 versus 0.015 L/s/cm, P < 0.01. In terms of height, colonized children grew at 5.63 versus 6.96 cm/yr, P < 0.001, and height SDS decreased in colonized compared with noncolonized children at -0.031 verses 0.08 SDS/yr, P < 0.05. Clinically, most children with CF, with or without Pa, grew within +/- 1 SD of the norm for weight and height. However, in terms of lung function despite optimum pulmonary management colonized children deteriorated significantly faster.

Lung compliance, lung volume and transfer factor for carbon monoxide in anaesthetised sheep: normal values and reproducibility of measurements

Measurements of quasistatic compliance (Cqst), effective alveolar volume (VA,eff) and single-breath transfer factor for carbon monoxide (TL,CO, 'sb') were completed in 16 normal, anaesthetised, adult Texel ewes. Regression equations were computed for these variables as a function of bodyweight and the optimal equations selected. The 95 per cent prediction intervals for the equations were calculated such that normal lung function in similar sheep could be accurately predicted. The long term reproducibility of these measurements was assessed in nine sheep, measured at monthly intervals over a period of five months. Although measurements made in individual sheep were often highly variable, the variation between repeated measurements on the separate days for the group was insignificant.

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.

The effect of age on bronchodilator responsiveness

The relationship between age and bronchodilator responsiveness (BDR) in children has not been studied using objective parameters. The aim of this study was to seek such a relationship in young asthmatic children using dose-response curves (DRC). Fourteen asthmatic subjects (age 3-9 years) with a forced expiratory volume in 1 sec (FEV1) less than 80% predicted were studied after being trained to use a spirometer reliably. Each subject completed a DRC by inhaling 5 doses of salbutamol (albuterol) at 15 min intervals until a cumulative total of 6.84 mg of salbutamol had been administered. FEV1, forced vital capacity (FVC), and forced expiratory flow at mid vital capacity (FEF25-75) were measured before and after each nebulization. In addition, arterial oxygen saturation (SaO2) and heart rate (HR) were measured in some of the subjects. All lung function parameters, SaO2 and HR increased significantly between baseline and completion of the DRC. A significant age effect on BDR was detected in FEV1 and FVC, with older children showing a greater response than young ones. The response had plateaued after the maximum dose in the younger but not in the older children. These findings suggest that the level of response to a bronchodilator increases significantly with increasing age in young asthmatics.

Variability of pulmonary function tests in cystic fibrosis

The aim of this study was to define the within-subject variability for tests of respiratory function in patients with cystic fibrosis (CF) within the day, from day to day and from week to week. Twenty-eight patients with CF (aged 9-19 years) and 23 healthy height matched controls (aged 9-18 years) had measurements made of spirometry, lung volumes, maximal flows at three lung volumes and maximal inspiratory and expiratory pressures at the mouth. Testings were done on nine occasions, three times within a day, on consecutive days at one week intervals. Each individual's variability was summarized both as the within-subject coefficient of variation (WCV) and within-subject standard deviation (WSD). Means of WSD and median WCV are reported for both the patients with CF and normal subjects. The within-subject variability of VC, FEV1, TLC, RV, and RV/TLC was more appropriately assessed by the use of WSD rather than WCV. The WSDs in the CF group were significantly more variable (P less than 0.005) than in the normals for VC and FEV1. WCV best summarized within-subject variation for FEF25-75, FRC, V25, V50max and V75max for which the CF subjects were significantly more variable (P less than 0.005). Individuals' variability was very consistent, therefore assessment of significant change could be made more accurately by predetermining the variability of that individual, rather than using group data. We stress the importance to consider increased variability from day to day and week to week in the interpretation of change in lung function in patients with CF, and provide reference values for accurate interpretation of serial pulmonary function test results.

Pulmonary function and respiratory morbidity in school-age children born prematurely and ventilated for neonatal respiratory insufficiency

We examined 72 children aged 6-9 years to assess the effects of prematurity and ventilator treatment on subsequent lung function and respiratory morbidity. The preterm study group (n = 42) was divided into children with a history of bronchopulmonary dysplasia (BPD) (n = 10), children who had had neonatal respiratory treatment but no BPD (n = 19), and children without severe neonatal respiratory problems (n = 13). The BPD children as a group had markedly lower specific airway conductance and larger residual volume than did the full-term control group, but there were no significant differences in spirometric measurements. The BPD group also had higher respiratory morbidity requiring hospitalizations, particularly during the first 2 years of life, than did the children in the other study groups. Therefore, BPD may improve but does not disappear as age increases. Non-BPD children who had had ventilator treatment as neonates recovered well and suffered no severe respiratory problems after infancy. Pulmonary function parameters in prematurely born children without neonatal ventilator treatment did not differ from those in the full-term control group. Thus, neonatal lung disease seems to be a more important determinant of abnormal pulmonary function at a later age than is prematurity alone.

Repeatability of ventilatory function measurements in a population survey of 7 year old children

The within subject variability of forced vital capacity (FVC), forced expiratory volumes in one second (FEV1) and half a second (FEV0.5), peak expiratory flow (PEF), and flow rates at 25-75%, 75-85%, 25%, 50%, and 75% of expired FVC were assessed among 7 year old children from the general population. Within occasion variability in 232 children was lowest for FVC (coefficient of variation (CV) 5%) and FEV1 (CV 4%), and greatest for end expiratory flow rates. The precision of measurement for FEV1 supports its use for bronchial provocation tests, particularly those using a graded challenge. In this context the value of PEF (CV 7%) and mid expiratory flow rates (CV 11%) is limited by their poorer repeatability. Between occasion variability was assessed in 171 children tested at an interval of one to four weeks. The difference between the variances between occasions and within occasions was attributed to biological variation; this accounted for a substantial component of the between occasion variance in all indices, particularly FEV1 (73%) and PEF (66%). Together, within subject variability, sex, and height accounted for about half of the measured variance between subjects for all indices except FVC (68%). These results have implications for epidemiological studies.

Relation of armspan to height and the prediction of lung function

Height and armspan were measured in healthy 8-18 year old boys and girls to assess the appropriate correction factor to be applied when height cannot be measured easily. No correction factor was found necessary, height being directly estimated from armspan.

Reproducibility of pulmonary mechanics measurements in dairy cattle

The reproducibility of pulmonary mechanics measurements in dairy cattle was examined using two study designs. In design A measurements were made with six cows on two days, and in design B measurements were made with four cows on six days. The mean coefficients of variation for within-day measurements for individuals ranged from 9.2 to 25.9% indicating considerable within-day variability. In design A there were no significant differences between days (P less than 0.05) for any measured variable for the group, but there were often significant differences between the two days for individuals. In design B there were significant cow-day interactions for all variables, again indicating significant differences between days for individuals. There were significant differences between days for the group for respiratory rate, and duration of inspiration and expiration. Both the interactions and differences between days appeared to be random. The high variability and limited reproducibility of pulmonary mechanics measurements, particularly in individual animals, indicate the need for caution in the interpretation of pulmonary mechanics measurements in dairy cattle.

Relationship between maldistribution of ventilation and airways obstruction in children with asthma

This study was designed to explore the relationship between ventilation non-uniformity, as assessed by moment analysis of nitrogen washout, and airways obstruction, as assessed by spirometry, in children with asthma. Moment ratios derived from the multibreath washout curves in asthmatics were significantly higher than those obtained from healthy controls (P less than 0.001). Among patients with asthma, moment ratios showed a high degree of negative correlations with spirometric variables expressed as percent of predicted, i.e., increasing airways obstruction was associated with increasing ventilation non-uniformity. When the subjects were tested on multiple occasions during one test day the results demonstrated a strong quantitative relationship within subjects between spontaneous changes in moment ratios and spirometric variables (P less than 0.001), with the slope of the regressions showing a trend to vary from one patient to another. Chi squared analysis showed that significant changes in FEV1 were paralleled by corresponding significant changes in moment ratios with a sensitivity of approximately 81% and a specificity of 82%. Additionally, changes in FEV1 induced by an inhaled bronchodilator were associated with concomitant changes in moment ratios. We conclude that: (1) the majority of children with asthma have some degree of ventilation non-uniformity which is correlated with their degree of airways obstruction, and (2) spontaneous changes in airways obstruction in such subjects are paralleled by changes in ventilation non-uniformity.

Computerized single-breath nitrogen washout in children: variability and reproducibility

The variability, short-term (1 hour) and long-term (2 weeks) reproducibility of the variables derived from the single-breath N2 test were evaluated in a group of 56 healthy children aged 10 to 16 years with a computerized system. The variability was low for vital capacity and total lung capacity (coefficient of variation less than 3%), moderate for residual volume and phase III N2 slope (9 and 13%) and very high for closing volume (more than 50%). A closing volume could not be identified by the computer algorithm in 18.3% of the trials. The reproducibility of the variables was satisfactory both at 1 hour and at 2 weeks, with the exception of the closing volume, whose increase at 2 weeks seemed to be due to methodological factors. We conclude that reliable results of static lung volumes and phase III N2 slope, but not of closing volume, may be obtained in children by a computerized system in epidemiological studies.