Cardiopulmonary exercise testing in adolescence following extremely premature birth.

BACKGROUND: Although extremely premature birth disrupts lung development, adolescent survivors of extreme prematurity show good clinical and physiologic outcomes. Cardiopulmonary limitations may not be clinically evident at rest. Data regarding exercise limitation in adolescents following preterm birth in the postsurfactant era are limited. RESEARCH QUESTION: What are the long-term effects of bronchopulmonary dysplasia (BPD) and extreme prematurity (<29 weeks) on ventilatory response during exercise in adolescents in the postsurfactant era? STUDY DESIGN AND METHODS: We followed a longitudinally recruited cohort of children aged 13-19 years who were born at a gestational age of <29 weeks (study group - SG). We compared the cardiopulmonary exercise testing (CPET) results of those with and without BPD, to their own CPET results from elementary school age (mean 9.09 ± 1.05 years). RESULTS: Thirty-seven children aged 15.73 ± 1.31 years, mean gestational age 26 weeks ( ± 1.19), completed the study. CPET parameters in adolescence were within the normal range for age, including mean V̇O2 peak of 91% predicted. The BPD and non-BPD subgroups had similar results. In the longitudinal analysis of the SG, improvement was observed in adolescence, compared with elementary school age, in breathing reserve (36.37 ± 18.99 vs. 26.58 ± 17.92, p = 0.044), tidal volume as a fraction of vital capacity achieved at maximal load (0.51 ± 0.13 vs. 0.37 ± 0.08, p < 0.001), and respiratory exchange ratio at maximal load (1.18 ± 0.13 vs. 1.11 ± 0.10, p = 0.021). INTERPRETATION: In the current cohort, adolescents born extremely premature have essentially normal ventilatory response during exercise, unrelated to BPD diagnosis. CPET results in this population improve over time.

Infant pulmonary function tests in individuals with Down syndrome.

BACKGROUND AND OBJECTIVE: Down 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. METHODS: An 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. RESULTS: iPFT 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. CONCLUSION: Our 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.

Lung function response to bronchodilator nebulization via hood in wheezy infants: a pilot study.

BACKGROUND: In infants, small volume nebulizers with a face mask are commonly used to facilitate aerosol therapy. However, infants may be disturbed by mask application, causing poor mask-to-face seal and thus reducing the dose delivered. OBJECTIVES: To compare lung function response to bronchodilator nebulization via two delivery devices: hood versus mask. METHODS: We studied 26 recurrently wheezy infants aged 45.8 weeks (95% confidence interval 39.6-52.0). Inhalations of 0.30 mg/kg salbutamol were administered in two alliqots 30 minutes apart using mask and hood in alternating order (M+H or H+M). Response to inhalations was measured by maximal expiratory flows at functional residual capacity (V'maxFRC) at 5 minute intervals after each dose, and area under the V'maxFRC curve (AUC) was documented. RESULTS: A small but significant response to salbutamol was observed following the second inhalation with V'maxFRC, improving by 31.7% (7.2-56.2, P (0.02) and AUC by 425% x min (-154, 1004; P < 0.02). The improvement following salbutamol was similar by both delivery modalities but with a small but significantly better response when H was used after M (P < 0.01). CONCLUSIONS: Nebulized salbutamol induced a variable but positive response in wheezy infants. Salbutamol via hood was as effective as conventional face mask delivery. Since it is simple and patient-friendly, it could replace the face mask method particularly with uncooperative infants.

Palivizumab Following Extremely Premature Birth Does Not Affect Pulmonary Outcomes in Adolescence.

BACKGROUND: Prematurity is a risk factor for impaired lung function. We sought to assess the long-term effect of palivizumab immunization and extreme prematurity (<29 weeks gestation) on respiratory symptoms and pulmonary function in adolescence. RESEARCH QUESTION: What is the long-term effect of palivizumab immunization and extreme prematurity (<29 weeks) on respiratory symptoms and pulmonary function in adolescence? STUDY DESIGN AND METHODS: We examined survivors of extreme prematurity (<29 weeks gestation) at 13 to 18 years of age (study group). Study group babies who were born immediately before palivizumab immunization (nonpalivizumab group [NPG]) were compared with those babies who were born just after implementation (PG) and with a control group. For study group patients, lung function in adolescence was further compared longitudinally with that at primary school age. RESULTS: Sixty-four adolescents aged 15.76 ± 1.52 years were included: 46 in the study group (17 PG and 29 NPG) and 18 in the control group. For the study group, wheezing episodes, inhaler use, and hospitalizations were uncommon. For the study group compared with the control group, FEV1 percent predicted was 82.60% ± 13.54% vs 105.83% ± 13.12% (P < .001), and the lung clearance index was 7.67 ± 1.02 vs 7.46 ± 0.70 (P = .48), respectively. Study group adolescents with bronchopulmonary dysplasia had a higher lung clearance index than did adolescents with no bronchopulmonary dysplasia (7.94 ± 1.11 vs 7.20 ± 0.60; P = .002). PG and NPG adolescents were not significantly different. Comparing the study group in adolescence with primary school age, we found improvement in mean FEV1 percent predicted bronchodilator response (0.37% ± 9.98% vs 5.67% ± 9.87%; P = .036) and mean provocative concentration causing 20% decline in FEV1 (12.16 ± 4.71 mg/mL vs 4.14 ± 4.51 mg/mL, respectively; P < .001). INTERPRETATION: Palivizumab did not provide any discernable long-term protective effect. Nevertheless, adolescent survivors of extreme prematurity showed good clinical and physiologic outcomes, except for mildly raised lung clearance index in patients with bronchopulmonary dysplasia. Airway hyperreactivity detected at primary school age, decreased by adolescence.

Use of the forced oscillation technique to detect bronchodilation in children: experience from the Schneider Children's Medical Center of Israel.

BACKGROUND: The forced oscillation technique is a noninvasive and effort-independent technique that is well suited for lung function measurement in young children. FOT employs small-amplitude pressure oscillations superimposed on normal breathing. Therefore, it has the advantage over conventional lung function techniques in that it does not require patient cooperation for conducting respiratory maneuvers. OBJECTIVES: To test the feasibility of the FOT test in preschool children and to compare the results to the commonly used spirometry before and after the administration of bronchodilator therapy. METHODS: Forty-six children (median age 4.9 years, range 1.8-18.3) attending the pulmonary clinic at Schneider Children's Medical Center tried to perform FOT and routine spirometry. Results were retrospectively analyzed. RESULTS: Of the 46 children 40 succeeded in performing FOT and only 29 succeeded in performing simple spirometry. All but one of the 32 children aged 4 years and above (97%) could perform both tests. Nine of 14 children (64%) aged 4 and less could perform the FOT but only 3 (21%) could perform spirometry. Baseline values of respiratory resistance measured at 6 Hz (R6) negatively correlated with body length (r2 = 0.68, P < 0.005). Twenty-four children performed both tests before and after bronchodilator therapy. A significant concordance was found between the measured responses to bronchodilators by FOT and spirometry (P < 0.01). Only one child had a negative response by FOT but a positive response by spirometry. CONCLUSIONS: The FOT is a simple, non-invasive technique that does not require subject cooperation and thus can be utilized for measuring lung function in children as young as 2 years old. Furthermore, the FOT was shown to reliably measure response to bronchodilator therapy.

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.

Non-invasive measurement of total respiratory compliance and resistance in cats.

We adapted non-invasive techniques developed for human infants to measure total respiratory system compliance (Crs) and resistance (Rrs) in 21 healthy cats. The animals breathed through a face mask attached to a respiratory circuit and measurements were taken of changes in lung volume and airway pressure during brief occlusions of the airway at different lung volumes. The slope of the plot of change in volume against airway pressure yielded the multiple occlusion Crs with a mean (+/-95%CI) value of 6.8 (6.3-7.3) ml/cm H2O. In 12 animals measurements were made by the single breath technique in which occlusion was made early in expiration and on release, a plot of the subsequent relaxed expiratory flow and volume yielded the time constant (taurs), Crs and Rrs with mean (+/-95%CI) values of 0.27 (0.22-0.31) s, 7.0 (6.1-7.8) ml/cm H2O, and 38.7 (33.7-43.6) cm H2O/l/s, respectively. Rrs was significantly correlated inversely with forced expiratory flow at resting lung volume (V'maxFRC).

The Application of Biphasic Extrathoracic Cuirass-Assisted Ventilation in Normal Subjects Wearing Chemical-Biological-Radiological-Nuclear (CBRN) Gas Masks.

OBJECTIVE: Mobile RTX (MRTX), a portable light-weighted ventilator, provides noninvasive respiratory support using biphasic extrathoracic cuirass-assisted ventilation. Despite the effectiveness of chemical-biological-radiological-nuclear (CBRN) gas masks, they cause respiratory loading as a result of added dead space and resistance. This prospective comparative pilot study was conducted to investigate the safety and efficacy of assisted ventilation provided by MRTX in healthy adult volunteers wearing CBRN gas masks at rest. METHODS: Cardiorespiratory parameters were monitored in 11 healthy adult volunteers breathing spontaneously or with assisted ventilation provided by MRTX, freely or with the mask on. Comparisons were made by single-factor analysis of variance. RESULTS: AV significantly increased minute ventilation (p < 0.001). MRTX increased minute ventilation by 6.4 L/min (mean, 95% confidence interval: 3.1, 9.8; p < 0.005) and by 4.7 L/min (1.8, 7.5; p < 0.01) during spontaneous breathing and with the mask on, respectively. Simultaneously, end-tidal carbon dioxide partial pressure decreased by 3.6 mmHg (2.2, 5.1; p < 0.001) and by 6.5 mmHg (3.8, 9.1; p < 0.001). DISCUSSION: Biphasic extrathoracic cuirass assisted ventilation provided by MRTX is safe and effective in supporting adequate needs at rest even when wearing protective masks. MRTX should be further assessed as a possible adjunct to currently used field ventilation in CBRN scenarios.

Short- and Long-term Pulmonary Outcome of Palivizumab in Children Born Extremely Prematurely.

BACKGROUND: Palivizumab reduces the severity of respiratory syncytial virus infection in premature infants, but whether there is a protective effect beyond the preschool age is unknown. This study sought to assess the short- and long-term effects of palivizumab immunization on respiratory morbidity and pulmonary function at school age in children born extremely prematurely. METHODS: Infants born before 29 weeks' gestation in 2000 to 2003 were assessed at school age by parental questionnaire, hospital chart review, and lung function tests. Children born immediately before the introduction of routine palivizumab prophylaxis were compared with age-matched children who received palivizumab prophylaxis during the first respiratory syncytial virus season. RESULTS: Sixty-three children with a mean age 8.9 years were included: 30 had received palivizumab and 33 had not (control subjects). The groups were similar in terms of gestational age, birth weight, need for mechanical ventilation, and oxygen supplementation. Fifty-three percent of the palivizumab group, compared with 39% of the control group, had bronchopulmonary dysplasia (P = .14). Wheezing occurred in the first 2 years of life in 27% of the palivizumab group and in 70% of control subjects (P = .008); respective hospitalization rates were 33% and 70% (P = .001). At school age, rates of hyperresponsiveness (provocative concentration leading to a 20% fall in FEV1 < 1 mg/mL) were 33% and 48%, respectively (P = .38). Spirometry, lung volumes, diffusion, and exhaled nitric oxide were within normal limits, with no significant differences between groups. CONCLUSION: Palivizumab prophylaxis was associated with reduced wheezing episodes and hospitalizations during the first 2 years of life in children born extremely prematurely. However, it did not affect pulmonary outcome at school age.

Comparison of maximal midexpiratory flow rate and forced expiratory flow at 50% of vital capacity in children.

BACKGROUND: The mid-portion of the maximal expiratory flow-volume (MEFV) curve is often described by values of the mean forced expired flow as lung volume decreases from 75% to 25% of vital capacity (ie, forced expiratory flow, midexpiratory phase [FEF(25-75)]). It is common practice to report also forced expired flow at 50% of vital capacity (FEF(50)). STUDY OBJECTIVE: To investigate whether FEF(50) and FEF(25-75) are highly correlated or whether the difference between them reflects a degree of airways obstruction. Also, we wanted to investigate the correlation between the two in cases of irregularly shaped MEFV curves (ie, "saw-toothing"). DESIGN: Analysis of the correlation between FEF(50) and FEF(25-75) in a single determination. We assessed the relationship between the FEF(50)/FEF(25-75) ratio and the degree of airways obstruction, as reflected by other traditional parameters such as FEV(1), FEV(1)/FVC ratio, and specific airway conductance (SGaw). PATIENTS: There were 1,350 forced expiratory maneuvers performed by children with a broad range of pulmonary abnormalities. RESULTS: FEF(50) correlated with FEF(25-75) as follows: FEF(50) (L/s) = 0.041 + 1.136*FEF(25-75)(L/s); r(2) = 0.956; standard error of the estimate = 0.013; p < 0.0001. The FEF(50)/FEF(25-75) ratio remained stable and did not correlate with FEV(1) (r = 0.12), FEV(1)/FVC ratio (r = 0.11), or SGaw (r = 0.02; difference not significant). The correlation between FEF(25-75) and FEF(50) was similar for both the smooth curve (r = 0.97) and the irregular curve (r = 0.96). CONCLUSIONS: Although not identical, FEF(25-75) and FEF(50) are highly correlated, and the ratio of the two is fairly constant. Therefore, the practice of reporting both of them is unnecessary. We suggest that it is reasonable to prefer FEF(50).

Pulmonary function tests leading to the diagnosis of vascular ring in an infant.

A 5-month-old baby was referred to our pulmonary clinic because of chronic cough and wheeze, unresponsive to antiasthmatic treatment. Examination in the Infant Pulmonary Function Laboratory suggested an upper airway obstruction. An aberrant right subclavian artery was subsequently confirmed by a barium swallow, flexible bronchoscopy, and an angiographic reconstructed chest CT study. Due to modest symptoms a conservative medical approach was taken. At follow-up 1 year later, the patient had fewer respiratory and gastrointestinal symptoms.

Exhaled nitric oxide is age-dependent in asthma.

We determined whether the exhaled nitric oxide (eNO) level in asthmatics is age-dependent. Eighty-seven asthmatic patients aged 2-41 years were studied. Hyperreactivity to adenosine 5'-monophosphate (AMP) was used to confirm asthma (

Application of a cuirass and institution of biphasic extra-thoracic ventilation by gear-protected physicians.

OBJECTIVES: To evaluate the speed by which cuirass application, followed by biphasic extra-thoracic ventilation, can be instituted by full anti-chemical protective gear-wearing physicians. MATERIALS AND METHODS: Ten physicians of variable subspecialties applied a cuirass on an adult volunteer and instituted biphasic extra-thoracic ventilation, using the RTX respirator (Medivent, London, UK). Endotracheal (ET) intubation and manual ventilation of a mannequin and its ventilation was comparatively assessed. Performances were conducted in a prospective, crossover, randomized manner. Times to successful applications as well as failure rates were recorded. RESULTS: Cuirass application was performed more rapidly (102 +/- 9 s, 177 +/- 31 s, respectively, P <.01) and with a slightly lower failure rate than ET intubation. CONCLUSIONS: Physicians wearing full anti-chemical protective gear applied the cuirass and instituted biphasic extra-thoracic ventilation faster than ET intubation and manual positive pressure ventilation. Extra-thoracic ventilation should be further evaluated as an option for emergent respiratory support during toxic mass casualty events.

Automated, real-time calibration of the respiratory inductance plethysmograph and its application in newborn infants.

Respiratory inductive plethysmography (RIP) is widely used in infants, children and adults. The technique is well accepted as it provides important qualitative information on the pattern of breathing, although its ability to record volume accurately was questioned due to calibration uncertainties. Existing calibration methods require two-position calibration, or patient cooperation in performing various breathing manoeuvres, or prolonged calibration paradigms. The disadvantages from calibration difficulties are even more pronounced in infants. We present a computer system that is capable of performing a single-posture, real-time RIP calibration during natural breathing and is suitable for use in newborns. The calibration algorithm is based on interactive, point-by-point calculations of maximal correlation between airflow at the mouth, Vao, and summed differentiated RIP signals. The quantities are calculated interactively at every sample point, and the process continues until stable results are reached and convergence criteria met. A graphic user interface was developed to assist in the rapid implementation and ease of use. Validation schemes were evaluated in 33 newborn infants against actual Vao. Calibration factors were obtained within 21 +/- 11 s with a mean correlation coefficient of 0.97 +/- 0.03. All RIP-derived values were similar to actual airflow signals, with error values ranging from 0.4 +/- 3.0% for respiratory rate to 1.8 +/- 7.3% for tidal volume. Calibration was found to be stable and reliable for up to 3.5 h and in changing sleep states. It is concluded that the new single-posture real-time RIP calibration system is safe and simple to use, and also quick, accurate and stable. The system was found to be suitable for use in newborns during natural breathing while asleep.

Evaluation of head-out constant volume body plethysmography for measurement of specific airway resistance in conscious, sedated sheep.

OBJECTIVE: To evaluate the use of a modified whole body plethysmograph in awake sheep. ANIMALS: 10 healthy adult sheep. PROCEDURE: Concurrent measurements of specific airway resistance (sR(aw)) and pulmonary resistance (R(L)) were obtained using a novel noninvasive head-out constant-volume plethysmograph and esophageal balloon-pneumotachography, respectively. All data were collected before and after external resistive loading with 1 and 5.6 cm H2O/L/s. Functional residual capacity (FRC) was measured by helium dilution for computation of airway resistance (R(aw)) preloading (R(aw) = sR(aw)/FRC). RESULTS: The sR(aw) and R(L) were closely correlated in 10 adult sheep. Additionally, sR(aw), and R(L) accurately reflected the magnitude of added resistance. The mean FRC was 52 mL/kg and used to calculate R(aw). At baseline, the values for R(aw) were significantly correlated with sR(aw) and R(L). CONCLUSIONS AND CLINICAL RELEVANCE: Precise measurements of sR(aw) and R(aw) at baseline and sR(aw) after external resistive loading were obtained by use of this novel noninvasive plethysmographic technology. This method should have application to veterinary patients or animals used in research in which noninvasive rapid or serial measurements of sR(aw) in the conscious state are required.

Encouraging pulmonary outcome for surviving, neurologically intact, extremely premature infants in the postsurfactant era.

OBJECTIVE: The aim of this study was to determine the long-term pulmonary outcome of extreme prematurity at a single tertiary-care center from 1997 to 2001 in the postsurfactant era. METHODS: We assessed symptoms, exhaled nitric oxide, spirometry, methacholine challenge (provocative concentration of methacholine required to decrease FEV1 by 20% [PC(20)]), lung volumes, diffusion, and cardiopulmonary exercise tolerance. RESULTS: Of 279 infants born, 192 survived to discharge, and 79 of these developed bronchopulmonary dysplasia (BPD) (65 mild, 12 moderate, two severe). We studied a subgroup of 53 neurologically intact preterm subjects aged 10 ± 1.5 years (28 with BPD [born, 26.2 ± 1.4 weeks; birth weight, 821 ± 164 g] and 25 without BPD [born, 27.2 ± 1 weeks; birth weight, 1,050 ± 181 g]) and compared them with 23 term control subjects. Of the BPD cases, 21 were mild, seven were moderate, and none was severe; 77.4% of subjects received antenatal steroids, and 83% received postnatal surfactant. Sixty percent of the preterm subjects wheezed at age < 2 years compared with 13% of the control subjects (P < .001), but only 13% wheezed in the past year compared with 0% of control subjects (not significant). For preterm and control subjects, respectively (mean ± SD), FEV1 % predicted was 85% ± 10% and 94% ± 10% (P < .001), with limited reversibility; residual volume/total lung capacity was 29.3% ± 5.5% and 25% ± 8% (P < .05); diffusing capacity/alveolar volume was 89.6% ± 9.2% and 97% ± 10% (P < .005); and PC(20) was 6.5 ± 5.8 mg/mL and 11.7 ± 5.5 mg/mL (P < .001). PC(20) was < 4 mg/mL in 49% of preterm subjects despite normal exhaled nitric oxide. Most measurements were similar in premature subjects with and without BPD. Peak oxygen consumption and breathing reserve were normal, but % predicted maximal load (measured in Watts) was 69% ± 15% for subjects with BPD compared with 88% ± 23% for subjects without and 86% ± 20% for control subjects (P < .01). CONCLUSIONS: Pulmonary outcome was encouraging at mid-childhood for neurologically intact survivors in the postsurfactant era. Despite mechanical ventilation and oxygen therapy, most had no or mild BPD. Changes found probably reflect the hypoplastic lungs of prematurity.

Aeration properties of a new sleeping surface for infants.

BACKGROUND: Prone sleeping position, use of soft mattresses and head covering by bedclothes are known risk factors for sudden infant death syndrome (SIDS). Rebreathing carbon dioxide (CO(2) ) may be a possible mechanism or a confounding factor of SIDS. OBJECTIVE: To compare the aeration properties of a new concept of infant sleeping surface (Net) to three commercial mattresses advertised to improve aeration and to two standard infant mattresses. DESIGN: Two experiments were performed: (I) A container (head box), filled with 7% CO(2) mixture, was opened to the mattress to allow gas mixture to passively diffuse outside and equilibrate with the surrounding room air. (II) Simulation of normal breathing of an infant, using a unidirectional reciprocal syringe, to determine CO(2) accumulation within the head box. METHODS: CO(2) concentrations in the head box were continuously measured until CO(2) levels fell below 1% or for 5 min (experiment I), or until CO(2) accumulation levels plateaued or for 6 min (experiment II). RESULTS: The Net had a significantly faster rate of CO(2) elimination (88.5 ± 4.6 and 91.9 ± 0.9 sec, Net alone and when covered with a sheet, respectively) compared to 238.3 ± 14.2 sec to 387.8 ± 7.9 sec for the other mattresses (P < 0.001). Only the Net was able to prevent CO(2) accumulation with maximal CO(2) levels (0.56 ± 0.03% and 1.16 ± 0.05%; Net alone and when covered with a sheet, respectively) significantly lower than the range of 4.6-6.3% for the other mattresses (P < 0.001). CONCLUSIONS: The new sleeping surface exhibited significantly better aeration properties in dispersing CO(2) and in preventing its accumulation.

Relation between partial and raised volume forced expiratory flows in sick infants.

RATIONALE: The maximal expiratory flow-volume (MEFV) and the partial expiratory flow-volume (PEFV) maneuvers are interchangeably performed when testing infant lung function. In recent years, the MEFV has gained popularity over the PEFV as it offers the investigator various forced expiratory flow and volume variables in addition to the sole, maximal flow at functional residual capacity (Vmax FRC) available from the PEFV maneuver. Both types of measure are considered to provide information on airway function. OBJECTIVES: To compare Vmax FRC values by PEFV to flows at low lung volumes by MEFV in infants suffering from a variety of illnesses. METHODS: Retrospective analysis of records of 175 infants attending a tertiary out-patient clinic (age range 2-234 weeks). Comparisons between parameters derived from the PEFV and MEFV curves were made by linear regression and by Bland-Altman plots. MEASUREMENTS AND MAIN RESULTS: Vmax FRC highly correlated with forced expiratory flows at 85% of forced vital capacity (FEF85; r = 0.87, P < 0.0001) with a mean bias of 20 ml/sec, and at 75% (FEF75; r = 0.83, P < 0.0001) with a greater mean bias of -72 ml/sec, but less with forced expired volume in 0.5 sec (FEV0.5; r = 0.66, P < 0.0001) showing a much wider scatter especially in infants with more severe obstruction. Same agreement between Vmax FRC and FEF85 or FEF75 was seen when presented as z-scores (r = 0.77 and 0.76; respectively). CONCLUSIONS: Regardless of the maneuver performed, PEFV or MEFV, Vmax FRC and FEF85, and FEF75 show high agreement in sick infants. As they both describe small airways function, both maneuvers may be interchangeable.

Maximal flow at functional residual capacity in healthy children from birth to 7 years, and beyond.

BACKGROUND: Reference values for maximal expiratory flows throughout childhood have been developed for each age group, but it remains a challenge to find a single outcome measure that can be tracked from birth to childhood. We believe that maximal flow at functional residual capacity (FRC) (VmaxFRC) may be a good candidate. The aim of this article was to explore the possible use of VmaxFRC as a continuous measure in healthy infants and children of preschool age. METHODS: Original spirometric data from healthy infants and preschool children in previously published studies from four centers around the world were reanalyzed (N = 242; ages 0-7 years). In preschool children, VmaxFRC was extracted by reanalysis of available records. Multiple regression analysis was applied to find the best correlation between VmaxFRC and height, weight, and/or age. VmaxFRC values were also compared with previously published data from healthy populations of similar ages. RESULTS: VmaxFRC highly correlated with height from infancy to childhood: Ln{VmaxFRC [L/s]} = -11.99 + (2.561 × Ln{Length[cm]}), where Ln is natural logarithm; r = 0.90; SE = 0.355; P < .0001. Adding weight but not age improved the correlation slightly (r = 0.91). VmaxFRC values were not affected by sex, maneuver modality (passive or voluntary), body posture, or degree of sedation. We found very good agreement between our calculated VmaxFRC values and the extrapolated VmaxFRC values from reference data of similar and older populations. CONCLUSIONS: VmaxFRC can be easily extracted from spirometry and can potentially serve as a continuous spirometric parameter for describing maximal flow at low lung volumes. Further studies are needed to confirm VmaxFRC values in a wider age range in health and disease.