Infant Pulmonary Function Testing Research Articles

Comprehensive pulmonary function analysis identifies predominant obstructive phenotype in former premature infants around one year of age.

Preterm infants suffer from significant respiratory morbidity during the first years of life, but the underlying lung pathophysiology is not fully understood. This study aimed to comprehensively characterize the pulmonary functions of preterm infants using full infant pulmonary function testing (iPFT). Between 2008 and 2019, we recruited 150 infants (Mage 10.5 ± 6 months) of them 104 preterm infants (median gestational age [GA] = 34 weeks (28-36), n = 23 with bronchopulmonary disease [BPD]) and 46 controls born at term. We compared full iPFT parameters of preterm infants to a control group of term infants. Subanalysis included a comparison of preterm infants by BPD status and GA. Preterm infants had impaired flow parameters, reduced compliance, and air trapping, compared to term infants. Only 15% (n = 14) of the preterm group had normal iPFT, compared to 69% (n = 31) of the term group. The majority of the impaired iPFT in preterm infants were obstructive and 72% (n = 69) had no response to bronchodilators. Reduced maximal flow at the functional residual capacity point (V'maxFRC) was associated with low birth weight and GA. There were no major differences between preterm infants with or without BPD. Preterm infants in the first year of life, demonstrated a high prevalence of obstructive iPFT unresponsive to bronchodilators. BPD status did not add to the degree of pulmonary impairment. These data reveal an airway-predominant pathology of the modern-era prematurity-associated lung disease. Pulmonary function screening tests at an early age may be of value in determining the presence and severity of lung disease in the preterm population. V'maxFRC may provide a good assessment of pulmonary impairment in preterm infants.

Presurgical pulmonary function tests in the first few days of life in neonates with congenital heart disease, a pilot study.

To compare early pulmonary function tests (PFTs) in neonates with critical congenital heart disease (CHD) compared to a historical reference group. Infants ≥ 37 weeks gestation with critical CHD were studied within the first few days of life, prior to cardiac surgery, and compared to data from a published reference group of healthy term neonates without CHD, studied at the same institution. Passive respiratory resistance (Rrs) and compliance (Crs) were measured with the single breath occlusion technique following specific acceptance criteria. The study was powered for a 30% difference in Rrs. PFTs in 24 infants with CHD were compared to 31 historical reference infants. There was no difference in the Rrs between the groups. The infants with CHD had a significantly decreased Crs (1.02 ± 0.26 mL/cmH2O/kg versus 1.32 ± 0.36; (p < 0.05; mean ± SD)). Further prospective studies are required to quantify early PFTs in infants with CHD of different phenotypes.

Infant Pulmonary Function Tests in Children with Airway Anomalies and Correlation with Bronchoscopy Findings

Infant Pulmonary Function Tests in Children with Airway Anomalies and Correlation with Bronchoscopy Findings

Lung Function Tests in Infants and Children.

Lung function testing is an essential modality of investigation in children as it provides objective evidence of lung disease/health. With advances in technology, various tests are available that can aid in the diagnosis of lung disease, assess the progression and response to therapy and document the lung development and evolving lung diseases in infants. This narrative review discusses lung function tests in infants and children. Currently, lung function tests can be performed in every age group, from neonates to the elderly. Spirometry and peak expiratory flow rate (PEFR) are the most employed tests in children more than six years of age. Spirometry helps diagnose and monitoring of both obstructive and restrictive diseases. There is a need for expertise to perform and interpret spirometry correctly. The forced oscillation technique (FOT) or impulse oscillometry (IOS) is done with tidal volume breathing and is feasible even in preschool children. Their utility is mainly restricted to asthma in children at present. Lung function tests can be performed in neonates, infants and children using infant pulmonary function test (PFT) equipment, although their availability is limited. Diffusion capacity for carbon monoxide (DLCO) is a valuable tool in restrictive lung diseases. Lung volumes can be assessed by body plethysmography and multiple washout technique. The latter can also assess lung clearance index. It is essential to perform and interpret the lung function test results correctly and correlate them with the clinical condition for optimum treatment and outcome.

Infant pulmonary function tests in individuals with Down syndrome

Background and objectiveDown syndrome is associated with significant respiratory morbidity. The available pulmonary function testing data in school aged children and adults with Down show evidence of restrictive lung disease. We aimed to evaluated infant pulmonary function tests (iPFTs) in individuals with Down. MethodsAn observational case-control study evaluating iPFTs results from a registry of patients assessed at the Hadassah Hebrew University Medical Center between 2008 and 2018. iPFTs results in Infants with Down were compared to a spirometry control group of infants with normal expiratory airflows, using the Mann–Whitney U and Fisher's exact tests. ResultsiPFT data from 66 infants (20 Down and 46 control) were evaluated in the study. Most infants with Down showed abnormalities of an obstructive lung disease with mildly increased lung volumes and significantly decreased expiratory flows, mostly unresponsive to bronchodilators. Airflow limitations were most prominent at low lung volumes (median (IQR); maximal expiratory flow at functional residual capacity, V˙max FRC = 48 (26–78) %predicted in Down Vs. V˙max FRC = 100 (93–114) %predicted in controls, p < 0.001). We further observed an alteration in breathing mechanics with significantly decreased respiratory system compliance and increased airway resistance associated with decreased tidal volumes but similar minute ventilation. ConclusionOur study shows that infants with have a fixed airflow obstruction phenotype. These results add comprehensive data to allow better understanding of the lung disease present early in life of infants with Down syndrome. Further studies are required to improve management of respiratory disease in individuals with Down.

Symptomatic preterm infants suffer from lung function deficits, regardless of bronchopulmonary dysplasia.

The long-term respiratory consequences for children with bronchopulmonary dysplasia (BPD) are well known. However, there is little emphasis on monitoring preterm infants without BPD. Few studies have explored the lung function status of infants with the symptoms of chronic lung disease of prematurity (CLD). To evaluate functional lung deficits in preterm infants with CLD, and to assess the perinatal determinants of diminished lung function. In our cross-sectional study, 132 preterm infants with symptomatic CLD underwent infant pulmonary function testing (iPFT) at a median post-term age of 0.9 years. The iPFT included bodypletysmography, compliance measurement, tidal breath analysis, and rapid thoracoabdominal compression. The relationships between the respective z scores of the iPFT parameters and perinatal characteristics, postnatal treatment, and BPD status were investigated. Seventy-threepatients (55.3%) were born before the 28th week of gestation, and 92 (69.7%) met the BPD criteria. Functional deficits were detected in 85.8%. The obstructive ventilatory pattern was more prevalent than restrictive (36.3 vs. 12.4%, p < 0.001). Infants with restriction had lower birth weight (BW) and required a longer duration of oxygenotherapy. In a univariate model, the lung function correlated with the duration of invasive mechanical ventilation, gestational week, and BW. In a general linear model, BPD status was not an additional determinant of the iPFT results. IPFT may reveal significant functional deficits in preterm infants with CLD even without BPD. The current symptoms and perinatal factors may be more important determinants of functional deficits than the BPD status itself.

Bronchodilator responsiveness and dysanapsis in bronchopulmonary dysplasia.

BackgroundThe incidence of bronchopulmonary dysplasia (BPD) following preterm birth is increasing. Bronchodilators are often used to treat patients with BPD with little evidence to guide therapy. The aim of this study was to test the hypothesis that there are infant pulmonary function test (iPFT) parameters that can predict subsequent bronchodilator response in infants with BPD.MethodsSubjects in this study were part of a patient group in which we reported three BPD phenotypes (obstructive, restrictive and mixed) based on iPFT data. From that group, a cohort of 93 patients with iPFT data including bronchodilator response was eligible for this study.ResultsBronchodilator responsiveness was found in 59 people (63%) in the cohort. There were no differences in demographics between the responders and non-responders. There was no difference in forced vital capacity (FVC) between the two groups. Responders had significantly lower forced expiratory volume in 0.5 s (FEV0.5) and FEV0.5/FVC (p<0.005) and greater indices of hyperinflation than did non-responders (p<0.005). Logistic regression modelling found that pre-bronchodilator FEV0.5 and functional residual capacity/total lung capacity were significantly associated with bronchodilator response. The magnitude of response to bronchodilators was negatively correlated (R= −0.49, R2= 0.24, p<0.001) with the FEV0.5. The median dysanapsis ratio in responders (0.08, 95% CI 0.05–0.19) was significantly (p=0.005) smaller than in non-responders (0.18, 95% CI 0.06–0.38).ConclusionThese findings demonstrate that there are pulmonary function test parameters associated with bronchodilator response. Responders had evidence of greater dysanaptic lung growth than non-responders.

Infant Pulmonary Function Tests in Individuals with Down Syndrome

Infant Pulmonary Function Tests in Individuals with Down Syndrome

Pulmonary function tests in extremely low gestational age infants at one year of age.

Identifying neonatal and post-discharge exposures among extremely low gestational age newborns (ELGANs) that drive increased pulmonary morbidity and abnormal lung function at 1 year of age proves challenging. The NIH-sponsored Prematurity and Respiratory Outcomes Program (PROP), evaluated infant pulmonary function tests (iPFTs) at 1 year corrected age to determine which demographic and clinical factors are associated with abnormal lung function. iPFTs were performed on a PROP subcohort of 135 participants following Institutional Review Board (IRB)-approved written consent. Demographic data, Neonatal Intensive Care Unit (NICU) clinical care, and post-NICU exposures were analyzed for association with iPFTs. A significant decrease in forced expiratory volume at 0.5 s (FEV0.5 ) and/or forced expiratory flows at 75% of forced vital capacity (FEF75 ), were associated with male sex and African American race. Clinical factors including longer duration of ventilatory support, exposure to systemic steroids, and weight less than the 10th percentile at 36 weeks postmenstrual age were also associated with airflow obstruction, whereas supplemental oxygen requirement and bronchopulmonary dysplasia were not. Additionally, the need for respiratory medications, technology, or hospitalizations during the first year, ascertained by a quarterly survey, were the only post-NICU factors associated with decreased FEV0.5 and FEF75 . Only 7% of infants had reversible airflow obstruction. Neonatal demographic factors, respiratory support in the NICU, and a history of greater post-NICU medical utilization for respiratory disease had the strongest association with lower lung function at 1 year in ELGANs.

Hyperinflation is associated with increased respiratory rate and is a more sensitive measure of cystic fibrosis lung disease during infancy compared to forced expiratory measures.

The goal of this study was to identify clinical features associated with abnormal infant pulmonary function tests (iPFTs), specifically functional residual capacity (FRC), in infants with cystic fibrosis (CF) diagnosed via newborn screen (NBS). We hypothesized that poor nutritional status in the first 6-12 months would be associated with increased FRC at 12-24 months. This study utilized a combination of retrospectively and prospectively collected data from ongoing research studies and iPFTs performed for clinical indications. Demographic and clinical features were obtained from the electronic medical record. Forced expiratory flows and volumes were obtained using the raised volume rapid thoracoabdominal technique (RVRTC) and FRC was measured via plethysmography. A total of 45 CF NBS infants had iPFTs performed between 12 and 24 months. Mean forced vital capacity, forced expiratory volume in 0.5 s, and forced expiratory flows were all within normal limits. In contrast, the mean FRC z-score was 2.18 (95% confidence interval [CI] = 1.48, 2.88) and the mean respiratory rate (RR) z-score was 1.42 (95% CI = 0.95, 1.89). There was no significant association between poor nutritional status and abnormal lung function. However, there was a significant association between higher RR and increased FRC, and a RR cutoff of 36 breaths/min resulted in 92% sensitivity to detect hyperinflation with 32% specificity. These results suggest that FRC is a more sensitive measure of early CF lung disease than RVRTC measurements and that RR may be a simple, noninvasive clinical marker to identify CF NBS infants with hyperinflation.

The Use of Infant Pulmonary Function Tests in the Diagnosis of Neuroendocrine Cell Hyperplasia of Infancy

Infant pulmonary function tests (iPFTs) in subjects with neuroendocrine cell hyperplasia of infancy (NEHI) have demonstrated substantial expiratory airflow obstruction and air trapping. Can indices from iPFTs be used in the diagnosis of NEHI? This is an observational case-control study evaluating iPFT results from a registry of patients assessed at the Hadassah Hebrew University Medical Center between 2008 and 2018. iPFTs results in infants with NEHI were compared to two disease control infant groups (infants evaluated for recurrent wheezing and infants evaluated due to prematurity) and a spirometry control group of infants with normal expiratory airflow, using the Kruskal-Wallis test. Receiver operating characteristic (ROC) curves were used to assess the diagnostic accuracy of iPFT indices. We evaluated iPFT data in 481 infants (15, NEHI; 292, wheezing; 128, premature; and 46, spirometry control group). Infants with NEHI had significantly increased trapped air volumes (median functional residual capacity measured with infant whole-body plethysmography [FRCpleth] was 199%predicted; median ratio of residual volume to total lung capacity was 59%predicted) when compared with results in all evaluated groups of infants (P< .001), including multiple pairwise comparisons. Airflow limitation was demonstrated in infants with NEHI when compared with the infants in the spirometry control group but was similar to the two disease control groups. FRCpleth had the best discriminatory ability for NEHI diagnosis, with an FRCpleth≥ 150%predicted demonstrating a ROC of 0.91 (95%CI, 0.82-1.00), sensitivity of 86.7%(95%CI, 59.5%-98.3%), and specificity of 95.5%(95%CI, 93.2%-97.3%). Findings on iPFTs of markedly increased air trapping, out of proportion to the degree of airflow limitation, are characteristic of infants with NEHI. iPFT results demonstrating an FRCpleth≥ 150%predicted are highly specific for NEHI and may aid in early diagnosis. Further research is required to confirm these findings in a prospective cohort and to understand the pathophysiologic explanation for these findings.

Clinical, functional, and computed tomography findings in a cohort of patients with neuroendocrine cell hyperplasia of infancy.

Neuroendocrine cell hyperplasia of infancy (NEHI) is one of the most common interstitial lung diseases in children. Both the etiology and pathophysiological mechanisms of the disease are still unknown. Prognosis is usually favorable; however, there are significant morbidities during the early years of life. To describe the clinical course, infant pulmonary function tests and computed tomography (CT) findings in a cohort of patients with NEHI in Argentina. This is a observational multicenter cohort study of children diagnosed with NEHI between 2011 and 2020. Twenty patients participated in this study. The median age of onset of symptoms was 3 months and the median age at diagnosis was 6 months. The most common clinical presentation was tachypnea, retractions and hypoxemia. The chest CT findings showed central ground glass opacities and air trapping. Infant pulmonary function tests revealed an obstructive pattern in 75% of the cases (10/12). Most patients (75%) required home oxygen therapy for 17 months (interquartile range 12-25). In 85% of them, tachypnea and hypoxemia spontaneously resolved between the second and third years of life. In this cohort, the first symptoms appeared during the early months of life. The typical clinical, CT, and functional findings allowed the diagnosis without the need of a lung biopsy. Although most patients required home oxygen therapy, they showed a favorable evolution.

Antenatal corticosteriods decrease forced vital capacity in infants born fullterm.

Antenatal corticosteroids (ACS) administration to pregnant women for threatened preterm labor is standard obstetric care to reduce neonatal respiratory distress syndrome and the associated respiratory morbidity. While ACS stimulates surfactant production in the fetal lung, the effects of ACS upon the subsequent growth and development of the lung are unclear. Follow-up studies outside of the neonatal period have been primarily limited to spirometry, and most subjects evaluated were born prematurely. To our knowledge, no study has assessed both airway and parenchymal function in infants or adults following ACS exposure. We hypothesized that ACS impairs lung growth and performed infant pulmonary function testing, which included spirometry, alveolar volume (VA ) and lung diffusion (DL ). As a pilot study, we limited our assessment to infants whose mothers received ACS for threatened preterm labor, but then proceeded to full term delivery. This approach evaluated a more homogenous population and eliminated the confounding effects of preterm birth. We evaluated 36 full-term infants between 4 to 12 months of age; 17 infants had ACS exposure and 19 infants had no ACS exposure. Infants exposed to ACS had a significantly lower forced vital capacity compared with non-ACS exposed infants (250 vs 313 mL; P = .0075). FEV0.5 tended to be lower for the ACS exposed group (205 vs 237 mL; P = .075). VA and DL did not differ between the two groups. These findings suggest that ACS may impair subsequent growth of the lung parenchyma.

Therapy at 30 days of life predicts lung function at 6 to 12 months in infants with congenital diaphragmatic hernia.

Congenital diaphragmatic hernia (CDH) is associated with variable degrees of lung hypoplasia. Pulmonary support at 30 days postnatal age was found to be the strongest predictor of inpatient mortality and morbidity among CDH infants and was also associated with higher pulmonary morbidity at 1 and 5 years. It is not known, however, if there is a relationship between the need for medical therapy at 30 days of life andsubsequent abnormalities in lung function as reflected in infant pulmonary function test (iPFT) measurements. We hypothesized that CDH infants who require more intensive therapy at 30 days would have more abnormal iPFT values at the time of their first infant pulmonary function study, reflecting the more severe spectrum of lung hypoplasia. A single-institution chart review of all CDH survivors who were enrolled in a Pulmonary Hypoplasia Program (PHP) through July 2019, and treated from 2002 to 2019 was performed. All infants were divided into groups based on their need for noninvasive (supplemental oxygen, high flow therapy, noninvasive mechanical ventilation) or invasive (mechanical ventilation, extracorporeal membrane oxygenation) respiratory assistance, bronchodilators, diuretic use, and pulmonary hypertension (PH) therapy (inhaled and/or systemic drugs) at 30 days. Descriptive and statistical analyses were performed between groups comparing subsequent lung function measurements. A total of 382 infants (median gestational age [GA] 38.4 [interquartile range (IQR) = 37.1-39] weeks, 41.8% female, 70.9% Caucasian) with CDH were enrolled in the PHP through July 2019, and 118 infants underwent iPFT. The median age of the first iPFT was 6.6 (IQR = 5.3-11.7) months. Those requiring any pulmonary support at 30 days had a higher functional residual capacity (FRC) (z) (P = .03), residual volume (RV) (z) (P = .008), ratio of RV to total lung capacity (RV/TLC) (z) (P = .0001), and ratio of FRC to TLC (FRC/TLC) (z) (P = .001); a lower forced expiratory volume at 0.5 seconds (FEV0.5) (z) (P = .03) and a lower respiratory system compliance (Crs) (P = .01) than those who did not require any support. Similarly, those requiring diuretics and/or PH therapy at 30 days had higher fractional lung volumes, lower forced expiratory flows and Crs than infants who did not require such support (P < .05). Infants requiring any pulmonary support, diuretics and/or PH therapy at 30 postnatal days have lower forced expiratory flows and higher fractional lung volumes, suggesting a greater degree of lung hypoplasia. Our study suggests that the continued need for PH, diuretic or pulmonary support therapy at 30 days can be used as additional risk-stratification measurements for evaluation of infants with CDH.

Effect of acute respiratory infections in infancy on pulmonary function test at 3 years of age: a prospective birth cohort study

IntroductionAcute respiratory infections (ARIs) in infancy may have a long-term impact on the developing respiratory system. We planned a prospective cohort study to determine the impact of ARI during infancy...

Normative Data of Infant Pulmonary Function Testing: A Prospective Birth Cohort Study from India

To develop a normal reference range of Infant pulmonary function test (IPFT) indices for Indian children. Prospective birth cohort study. Division of Pediatric Pulmonology of a tertiary-care institute in India from August 2012 to March 2017. All neonates born at the institute during the study period were screened for eligibility. IPFT at baseline and every 6-month until 36-months of age. Tidal breathing flow-volume loop (TBFVL), Rapid thoracoabdominal compression (RTC), and Raised volume RTC (RVRTC) indices at baseline and follow-up. 310 newborns were enrolled in the cohort; 281 of them (169 male) had completed 36-months of follow-up at the end of the study period. There was no influence of gender on the baseline IPFT indices. Tidal volume per unit body weight (VT/kg) significantly increased from baseline to 36 months of age (P<0.001) while the peak ratio (tPTEF/tE) initially decreased in first 18-months of age (P<0.001), after that returned to the baseline value by 36 months of age. RTC indices did not change significantly from baseline values. In RVRTC, the ratio of forced expiratory volume in 0.5s to forced vital capacity (FEV0.5/FVC) was significantly decreased from baseline to 36 months of age (P=0.002). Normal values for various IPFT indices for TBFVL, RTC, and RVRTC from neonates to the age of 36-month are provided. These data may be used as normative data for healthy neonates and children of Indian origin.

Infant Pulmonary Function Testing: An Upcoming Modality for Evaluation of Respiratory Disorders

Infant Pulmonary Function Testing: An Upcoming Modality for Evaluation of Respiratory Disorders

Association Between Peripheral Eosinophil Counts and Infant Lung Function

&#x0D; Background and Hypothesis: Some children with allergic asthma have peripheral eosinophilia early in life, suggesting that physiological changes in the lung begin during infancy. While this association has been established, studies have not examined if a link exists between eosinophilia and physiological airway measurements during the first year of life. It is hypothesized that systemic eosinophilia during the first year of life is associated with lower infant pulmonary function measurements.&#x0D; Experimental Design or Project Methods: A birth cohort study investigating the development of the upper airway microbiota over the first year of life was utilized for this study. Systemic absolute eosinophil counts were examined to determine if eosinophilia is associated with decreased infant pulmonary function test (iPFT)values. Blood and iPFT data were collected at 3 and 12 months.&#x0D; Results: 28 participants had blood samples collected. 15 samples were taken at 3 months and 13 at one year. 16 subjects were male, with a majority identifying as African American (14). The average height and weight were 68.0 cm and 8.6 kg. The median absolute eosinophil count was 0.2010^3/uL. Infant iPFT data included tidal volume, respiratory rate, expiration time, tPTEF/tE, resistance, and compliance. No significant correlations were identified between eosinophil counts and iPFT data. This held true when all time points were combined and when examining each visit separately. The strongest correlation coefficient was -0.36 between absolute eosinophil count and FEV0.5. The estimated number of samples needed to power a study examining the association between FEV0.5 and eosinophil counts is 80 samples.&#x0D; Conclusion and Potential Impact: Based on preliminary results, there are not enough samples to achieve significant correlations supporting the original hypothesis. The next step is to analyze more blood from current study participants. It is also planned to examine the association between the airway microbiome and eosinophilia to determine if early allergic markers in the blood may results from airway dysbiosis.

Pulmonary Function Testing in Pediatric Pneumonia Patients With Wheezing Younger Than 3 Years of Age.

Background. Wheezing symptoms are one of the risk factors in young pneumonia patients that often leads to asthma development. Infant pulmonary function test (iPFT) is potentially a useful tool to help identify and manage these high-risk pneumonia patients. Methods. To examine whether patients with wheezing symptoms are more likely to have poorer pulmonary function and treatment outcomes, and also to explore the clinical benefit of iPFT in young pneumonia patients, we conducted a retrospective analysis of 1005 pneumonia inpatients <3 years of age who had undergone iPFT testing in 2016 at Liuzhou Maternity and Child Healthcare Hospital in Guang-Xi, China. Results. We identified from the hospital database 505 pneumonia patients who presented with wheezing and 500 without wheezing. Univariate analysis showed that wheezing symptoms, viral infection, age <1 year, female gender, and prematurity were significantly associated with poorer iPFT results. After adjusting for confounders, patients with wheezing showed significantly poorer pulmonary function. Patients with wheezing had longer length of stay (7.9 ± 3.9 days vs 6.5 ± 2.6 days; P < .001) and lower percent with no residual clinical symptoms at discharge (58% vs 98%; P < .001) when compared with those of non-wheezing patients. In addition, 81% of patients with viral infection as compared with 43% of patients with nonviral infection presented with wheezing symptoms (P < .001). Conclusion. Wheezing symptoms were associated with poorer iPFT measures and treatment outcomes for pneumonia inpatients <3 years of age. Patients with wheezing had poorer treatment outcomes. iPFT can be useful in assessing and monitoring young patients with high risk of developing asthma or chronic lung disease later in life.

Reference equations for the interpretation of forced expiratory and plethysmographic measurements in infants.

Pulmonary function testing is commonly performed for diagnosis and clinical management of respiratory diseases. It is important to use appropriate reference equations from healthy subjects for interpretation of data from infants with lung disease. This study aimed to determine if published reference equations were similar to forced flow measures and plethysmographic infant pulmonary function testing data collected in the Canadian Healthy Infant Longitudinal Development (CHILD) Study. Reference equations for five pulmonary function variables (FEV0.5 , FVC, FEF25-75 , FEV0.5 /FVC ratio and plethysmography (FRCpleth )) were developed using data from the nSpire system. New reference equations developed using healthy data from the CHILD Study were compared to previously published reference equations for forced flow and plethysmographic measures. The current analysis included 131 infants (on 181 test occasions) with forced flow measures and 161 infants (on 246 test occasions) with plethysmography measures, aged 3-24 months. Age and length were major determinants of both forced flow and plethysmography measures. In addition, ethnicity (Caucasian vs non-Caucasian) was significantly associated with FEV0.5 /FVC and FEF25-75 measures. We found that the published reference equations based on custom-built equipment or commercially available systems provided poor fit to our current pulmonary function testing data, resulting in placing a large proportion of our healthy population outside the normal ranges. Our current data support the need for population and device specific reference data for infant pulmonary function studies. By deriving new equipment-specific reference equations for our healthy population, we provide normative data to other centers utilizing this equipment.