Specifications for equipment used for infant pulmonary function testing. ERS/ATS Task Force on Standards for Infant Respiratory Function Testing. European Respiratory Society/ American Thoracic Society

Feasibility of repetitive lung function measurements by raised volume rapid thoracoabdominal compression during methacholine challenge in young infants

BACKGROUND

The aim of the study was to evaluate the feasibility of lung function measurements by the raised volume rapid thoracoabdominal compression (RVRTC) technique during bronchial methacholine challenge in young infants.

METHOD

Four hundred two healthy infants were tested at 1 month of age with RVRTC during repeated methacholine challenges with quadrupling doses from 0.037 to 16.674 mumol.

RESULTS

Measurement of baseline lung function was successful in 99% and the provocative dose (PD) was achieved in 79% of infants by forced expiratory volume in 0.5 s (FEV(0.5)). Additionally, the PD was successfully measured in 87% by transcutaneous oxygen pressure. No serious adverse events were observed during testing or after discharge from the clinic. The methacholine dose range was appropriate as PD could be determined in the majority of infants. FEV(0.5) values in 21% of infants dropped > 40% during the test. Short-lasting, self-limiting episodes of hypoxemia of < 80% occurred in 1% of infants and bradycardia < 90 beats/min in 19% of infants. The most common observations by parents were changes in the patterns of sleeping (95%), eating (57%), and behavior (58%) of the infant after hospital discharge. The mean acceptability rating among parents was 8 on a scale from 1 to 10, with 13% rating < or = 5. It took one operator 3 h to complete the test, with the actual lung function testing accounting for half the time.

CONCLUSION

This very comprehensive experience with standardized measurements of lung function by RVRTC during methacholine challenge in young infants in a single center leads us to conclude that the test is feasible and safe to perform in asymptomatic young infants.

The influence of maternal respiratory infections during pregnancy on infant lung function

INTRODUCTION

We studied whether maternal respiratory infections during pregnancy adversely influence lung growth and development of the offspring, resulting in poor early life lung function.

METHODS

Infants were participants of the Wheezing Illnesses Study Leidsche Rijn (WHISTLER). Lung function measurements (single occlusion technique) were performed during natural sleep. Questionnaire data were used to obtain information on maternal respiratory infections during pregnancy. Multivariate analysis was conducted to assess the relationship between maternal respiratory infections during pregnancy and resistance and compliance of the respiratory system, adjusting for potential confounding variables.

RESULTS

Lower values of compliance (Crs) were found in infants of mothers with respiratory infections during pregnancy; Crs fell by 5.5% (P = 0.031). The difference in Crs between infants of mothers with and without respiratory infections during pregnancy remained unchanged and statistically significant after adjusting for potential confounding variables. The more respiratory infections the mother experienced during pregnancy, the lower the value of Crs was in her offspring (P for trend = 0.016). Using Crs corrected for body weight the relationship with maternal infections was non-significant, however still showing a trend.

CONCLUSIONS

The results of this study may indicate that mothers who experience respiratory infections during pregnancy have newborns with lower compliance of the respiratory system.

Deadspace estimation from CO2 versus molar mass measurements in infants

BACKGROUND

Estimation of respiratory deadspace is often based on the CO2 expirogram, however presence of the CO2 sensor increases equipment deadspace, which in turn influences breathing pattern and calculation of lung volume. In addition, it is necessary to correct for the delay between the sensor and flow signals. We propose a new method for estimation of effective deadspace using the molar mass (MM) signal from an ultrasonic flowmeter device, which does not require delay correction. We hypothesize that this estimation is correlated with that calculated from the CO2 signal using the Fowler method.

METHODS

Breath-by-breath CO2, MM and flow measurements were made in a group of 77 term-born healthy infants. Fowler deadspace (Vd,Fowler) was calculated after correcting for the flow-dependent delay in the CO2 signal. Deadspace estimated from the MM signal (Vd,MM) was defined as the volume passing through the flowhead between start of expiration and the 10% rise point in MM.

RESULTS

Correlation (r = 0.456, P < 0.0001) was found between Vd,MM and Vd,Fowler averaged over all measurements, with a mean difference of -1.4% (95% CI -4.1 to 1.3%). Vd,MM ranged from 6.6 to 11.4 ml between subjects, while Vd,Fowler ranged from 5.9 to 12.0 ml. Mean intra-measurement CV over 5-10 breaths was 7.8 +/- 5.6% for Vd,MM and 7.8 +/- 3.7% for Vd,Fowler. Mean intra-subject CV was 6.0 +/- 4.5% for Vd,MM and 8.3 +/- 5.9% for Vd,Fowler. Correcting for the CO2 signal delay resulted in a 12% difference (P = 0.022) in Vd,Fowler. Vd,MM could be obtained more frequently than Vd,Fowler in infants with CLD, with a high variability.

CONCLUSIONS

Use of the MM signal provides a feasible estimate of Fowler deadspace without introducing additional equipment deadspace. The simple calculation without need for delay correction makes individual adjustment for deadspace in FRC measurements possible. This is especially important given the relative large range of deadspace seen in this homogeneous group of infants.

Optimized temperature and deadspace correction improve analysis of multiple breath washout measurements by ultrasonic flowmeter in infants

BACKGROUND

Assessment of lung volume (FRC) and ventilation inhomogeneities with ultrasonic flowmeter and multiple breath washout (MBW) has been used to provide important information about lung disease in infants. Sub-optimal adjustment of the mainstream molar mass (MM) signal for temperature and external deadspace may lead to analysis errors in infants with critically small tidal volume changes during breathing.

METHODS

We measured expiratory temperature in human infants at 5 weeks of age and examined the influence of temperature and deadspace changes on FRC results with computer simulation modeling. A new analysis method with optimized temperature and deadspace settings was then derived, tested for robustness to analysis errors and compared with the previously used analysis methods.

RESULTS

Temperature in the facemask was higher and variations of deadspace volumes larger than previously assumed. Both showed considerable impact upon FRC and LCI results with high variability when obtained with the previously used analysis model. Using the measured temperature we optimized model parameters and tested a newly derived analysis method, which was found to be more robust to variations in deadspace. Comparison between both analysis methods showed systematic differences and a wide scatter.

CONCLUSION

Corrected deadspace and more realistic temperature assumptions improved the stability of the analysis of MM measurements obtained by ultrasonic flowmeter in infants. This new analysis method using the only currently available commercial ultrasonic flowmeter in infants may help to improve stability of the analysis and further facilitate assessment of lung volume and ventilation inhomogeneities in infants.

Very prematurely born infants wheezing at follow-up: lung function and risk factors

OBJECTIVES

To determine whether abnormalities of lung volume and/or airway function were associated with wheeze at follow-up in infants born very prematurely and to identify risk factors for wheeze.

DESIGN

Lung function data obtained at 1 year of age were collated from two cohorts of infants recruited into the UKOS and an RSV study, respectively.

SETTING

Infant pulmonary function laboratory.

PATIENTS

111 infants (mean gestational age 26.3 (SD 1.6) weeks).

INTERVENTIONS

Lung function measurements at 1 year of age corrected for gestational age at birth. Diary cards and respiratory questionnaires were completed to document wheeze.

MAIN OUTCOME MEASURES

Functional residual capacity (FRC(pleth) and FRC(He)), airways resistance (R(aw)), FRC(He):FRC(pleth) and tidal breathing parameters (T(PTEF):T(E)).

RESULTS

The 60 infants who wheezed at follow-up had significantly lower mean FRC(He), FRC(He):FRC(pleth) and T(PTEF):T(E), but higher mean R(aw) than the 51 without wheeze. Regression analysis demonstrated that gestational age, length at assessment, family history of atopy and a low FRC(He):FRC(pleth) were significantly associated with wheeze.

CONCLUSIONS

Wheeze at follow-up in very prematurely born infants is associated with gas trapping, suggesting abnormalities of the small airways.

Mucoviscidose : du bon usage des explorations fonctionnelles respiratoires

INTRODUCTION

Neonatal screening for cystic fibrosis (CF) leads to early dedicated specialist care for all patients.

BACKGROUND

Pulmonary function tests (PFT) are mandatory for routine monitoring of CF patients. The aim of this article is to review the current guidelines for PFTs in CF, particularly the type of test, the age and the clinical status of the patient.

VIEWPOINT

The regular use of spirometry is generally accepted. Many other tests are used but their clinical value in the routine follow-up of CF patients remains to be established.

CONCLUSION

Further efforts should be made to evaluate the value of PFTs in CF, particularly in very young children.

[Advances in the study of infant lung function: forced expiratory maneuvers from an increased lung volume]

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

Passive respiratory mechanics measured during natural sleep in healthy term neonates and infants up to 8 weeks of life

The single occlusion technique (SOT) is a simple and noninvasive technique for measurement of passive respiratory mechanics in infants. Reference values based on measurements of a large population of healthy infants performed outside specialized research laboratories are lacking. The aim of this study was to present reference values for passive respiratory mechanics based on a large population of healthy term neonates and infants measured during natural sleep in routine care. As part of the ongoing Wheezing Illnesses Study Leidsche Rijn (WHISTLER), the compliance (C(rs)) and resistance (R(rs)) of the respiratory system were measured in 450 healthy unsedated neonates and infants with a mean age of 4.6 +/- 1.3 weeks. Multivariable regression analysis, with gestational age, age at measurement, body size, sex, and ethnicity as possible predictors, was carried out to estimate prediction equations for mean C(rs) and R(rs) values. Technically acceptable lung function measurements could be performed in 328 (73%) neonates and infants. Median C(rs) was 39.5 (range 14.8-79.1) ml/kPa and median R(rs) was 7.4 (range 3.8-19.5) kPa/L/sec. The following regression equations for C(rs) and R(rs) were obtained: ln C(rs) = 1.677 + 1.3 x 10(-4) x birth weight (g) + 0.030 x birth length (cm) and ln R(rs) = 2.496-3.1 x 10(-6) x birth length(3) (cm(3)) - 0.114 x sex. We provided reference values for passive respiratory mechanics using the SOT in a large population of healthy term neonates and infants measured during natural sleep. These data provide a frame of reference for assessing the normality of SOT measurements performed in routine care.

Noninvasive monitoring of chest wall movement in infants using laser

Traditionally, non-invasive monitoring of tidal volume in infants has been performed using impedance plethysmography analyzed using a one or two compartment model. We developed a new laser system for use in infants, which measures antero-posterior movement of the chest wall during quiet sleep. In 24 unsedated or sedated infants (11 healthy, 13 with respiratory disease), we examined whether the analysis of thoracoabdominal movement based on a three compartment model could more accurately estimate tidal volume in comparison to V(T) measured at the mouth. Using five laser signals, chest wall movements were measured at the right and left, upper and lower ribcage and the abdomen. Within the tidal volume range from 4.6 to 135.7 ml, a three compartment model showed good short term repeatability and the best agreement with tidal volume measured at mouth (r(2) = 0.86) compared to that of a single compartment model (r(2) = 0.62, P < 0.0001) and a two compartment model (r(2) = 0.82, P < 0.01), particularly in the presence of respiratory disease. Three compartment modeling of a 5 laser thoracoabdominal monitoring permits more accurate estimates of tidal volume in infants and potentially of regional differences of chest wall displacement in future studies.

Functional residual capacity measurement by heptafluoropropane in ventilated newborn lungs: in vitro and in vivo validation

OBJECTIVE

Heptafluoropropane is an inert gas commercially used as propellant for inhalers. Since heptafluoropropane can be detected in low concentrations, it could also be used as a tracer gas to measure functional residual capacity and ventilation homogeneity. The aim of the present study was to validate functional residual capacity measurements by heptafluoropropane wash-in/wash-out (0.8%) during mechanical ventilation in small, surfactant-depleted lungs using a newborn piglet model.

DESIGN

Prospective laboratory and animal trial.

SETTING

Animal laboratory in a university setting.

SUBJECTS

Sixteen newborn piglets (age<12 hrs, median weight 1390 g [705-4200 g]) before and after surfactant depletion (Pao2<100 torr in Fio2=1.0) by lung lavage.

INTERVENTIONS

Heptafluoropropane was measured with a new infrared mainstream sensor connected with the flow sensor of the Dräger Babylog 8000. Accuracy and precision of the measurement technique were tested in a mechanical lung model with a volume range from 11 to 35 mL. Reproducibility of the method and its sensitivity to detect changes of functional residual capacity were assessed in vivo by variation of ventilatory variables.

MEASUREMENTS AND MAIN RESULTS

In vitro the absolute error of functional residual capacity was <1 mL (relative errors<3%) with a coefficient of variation<4%. The coefficient of variation of consecutive in vivo measurements was only slightly higher (<5.1%). Measurement of heptafluoropropane concentrations in blood showed no significant accumulation for repeated functional residual capacity measurements within short time periods. After lung lavage, the functional residual capacity decreased from 20.9 mL/kg to 14.5 mL/kg (p<.05) despite increased ventilatory pressures, and lung clearance index (p<.001) and moment ratios (p<.01) increased significantly due to uneven alveolar ventilation. In healthy lungs, the increase in peak inflation pressure and positive end-expiratory pressure by 3-4 cm H2O had only a moderate effect on functional residual capacity (20.9+/-8.6 vs. 26.0+/-11.9 mL/kg, p=.17) and no effect on ventilatory homogeneity, whereas in surfactant-depleted lungs the functional residual capacity increased from 14.5+/-6.7 mL/kg to 29.9+/-12.6 mL/kg (p<.001) and lung clearance index and moment ratios decreased significantly (p < .01).

CONCLUSIONS

Heptafluoropropane is a suitable tracer gas for precise functional residual capacity measurements tested in vitro and allows for reproducible measurements in ventilated small lungs without any adverse effects on mechanical ventilation. The sensitivity of the method is sufficiently high to demonstrate the effect of changes in ventilatory settings on the functional residual capacity and ventilation homogeneity.

Respiratory function of very prematurely born infants at follow up: influence of sex

OBJECTIVE

To test the hypothesis that male compared with female prematurely born infants would have worse lung function at follow up.

DESIGN

Prospective follow up study.

SETTING

Tertiary neonatal intensive care units

PATIENTS

Seventy six infants, mean (SD) gestational age 26.4 (1.5) weeks, from the United Kingdom oscillation study.

INTERVENTIONS

Lung function measurements at a corrected age of 1 year.

MAIN OUTCOME MEASURES

Airways resistance (Raw) and functional residual capacity (FRC(pleth)) measured by whole body plethysmography, specific conductance (sGaw) calculated from Raw and FRC(pleth), and FRC measured by a helium gas dilution technique (FRC(He)).

RESULTS

The 42 male infants differed significantly from the 34 female infants in having a lower birth weight for gestation, requiring more days of ventilation, and a greater proportion being oxygen dependent at 36 weeks postmenstrual age and discharge. Furthermore, mean Raw and FRC(pleth) were significantly higher and mean sGaw significantly lower. After adjustment for birth and current size differences, the sex differences in FRC(pleth) and sGaw were 15% and 26% respectively and remained significant.

CONCLUSION

Lung function at follow up of prematurely born infants is influenced by sex.

Lung-function tests in neonates and infants with chronic lung disease: tidal breathing and respiratory control

This paper is the fourth in a series of reviews that will summarize available data and critically discuss the potential role of lung-function testing in infants with acute neonatal respiratory disorders and chronic lung disease of infancy. The current paper addresses information derived from tidal breathing measurements within the framework outlined in the introductory paper of this series, with particular reference to how these measurements inform on control of breathing. Infants with acute and chronic respiratory illness demonstrate differences in tidal breathing and its control that are of clinical consequence and can be measured objectively. The increased incidence of significant apnea in preterm infants and infants with chronic lung disease, together with the reportedly increased risk of sudden unexplained death within the latter group, suggests that control of breathing is affected by both maturation and disease. Clinical observations are supported by formal comparison of tidal breathing parameters and control of breathing indices in the research setting.

Lung function tests in neonates and infants with chronic lung disease of infancy: functional residual capacity

This is the second paper in a review series that will summarize available data and discuss the potential role of lung function testing in infants and young children with acute neonatal respiratory disorders and chronic lung disease of infancy. The current paper addresses the expansive subject of measurements of lung volume using plethysmography and gas dilution/washout techniques. Following orientation of the reader to the subject area, we focus our comments on 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. Measurements of lung volume are important both for assessing growth and development of lungs in health and disease, and for interpreting volume-dependent lung function parameters such as respiratory compliance, resistance, forced expiratory flows, and indices of gas-mixing efficiency. Acute neonatal lung disease is characterized by severely reduced functional residual capacity (FRC), with treatments aimed at securing optimal lung recruitment. While FRC may remain reduced in established chronic lung disease of infancy, more commonly it becomes normalized or even elevated due to hyperinflation, with or without gas-trapping, secondary to airway obstruction. Ideally, accurate and reliable bedside measurements of FRC would be feasible from birth, throughout all phases of postnatal care (including assisted ventilation), and during subsequent long-term follow-up. Although lung volume measurements in extremely preterm infants were described in a research environment, resolution of several issues is required before such investigations can be translated into routine clinical monitoring.

Problems in the measurement of functional residual capacity

Accurate assessment of lung volume in infancy is important to determine the impact of disease and the efficacy of therapies. A new generation of infant plethysmographs with lower apparatus deadspace has been produced, but gives lower volume results than those from older traditional plethysmographs. We hypothesized that the new plethysmographs might have greater sensitivity to the adiabatic effect and hence they, rather than the traditional plethysmographs, produced erroneous results. Our aim was to assess the influence of the adiabatic effect on the results of a contemporary plethysmograph, an older traditional plethysmograph and a helium gas dilution system using a lung model. Altering the amount of copper wool within the lung model allowed the influence of the adiabatic effect on the plethysmographic results to be assessed. The measured compared to the actual volumes were significantly lower for the contemporary plethysmograph compared to the traditional plethysmograph (p < 0.001) and to the helium gas dilution system (p < 0.001). Under optimal testing conditions the contemporary plethysmograph under-recorded by 11-13%, whereas the other two systems gave similar results to the actual volumes. As the effect of the adiabatic effect was increased, the discrepancy between the results of the contemporary and the traditional plethysmographs increased. We conclude, the contemporary plethysmograph is more sensitive to adiabatic effects and hence under-records.

Feasibility and variability of neonatal and infant lung function measurement using the single occlusion technique

INTRODUCTION

For possible use as a predictor of wheezing illnesses in routine care, we evaluated the feasibility and variability of measurement of passive respiratory mechanics in a large, open population of healthy neonates and infants.

METHODS

As part of the ongoing Wheezing Illnesses Study Leidsche Rijn, respiratory compliance (Crs), respiratory resistance (Rrs), and time constant (taurs) were measured during natural sleep in 450 healthy term neonates and infants using the single-occlusion technique (SOT). Interobserver and intraobserver variability of data sampling and the subsequent selection and analysis of occlusions as well as intra-measurement variability were examined.

RESULTS

Technically acceptable lung function measurements could be performed in 328 infants (73%). Low intraobserver and interobserver variability was found for both data sampling (intraclass correlation coefficient [ICC] > or = 0.87) and for selection and analysis of occlusions (ICC > or = 0.99). Intra-measurement variability was low, with a mean intra-measurement coefficients of variation for Crs, Rrs, and taurs of 8.5%, 10.4%, and 15.4%, respectively. Averaging three or more occlusions resulted in stable values of Crs, Rrs, and taurs.

CONCLUSION

Results of this study indicate that feasibility and variability of lung function testing using the SOT is acceptable for use in large populations of healthy neonates and infants in routine care.

Effect of sighs on breathing memory and dynamics in healthy infants

Deep inspirations (sighs) play a significant role in altering lung mechanical and airway wall function; however, their role in respiratory control remains unclear. We examined whether sighs act via a resetting mechanism to improve control of the respiratory regulatory system. Effects of sighs on system variability, short- and long-range memory, and stability were assessed in 25 healthy full-term infants at 1 mo of age [mean 36 (range 28–57) days] during quiet sleep. Variability was examined using moving-window coefficient of variation, short-range memory using autocorrelation function, and long-range memory using detrended fluctuation analysis. Stability was examined by studying the behavior of the attractor with use of phase-space plots. Variability of tidal volume (Vt) and minute ventilation (V̇e) increased during the initial 15 breaths after a sigh. Short-range memory of Vt decreased during the 50 breaths preceding a sigh, becoming uncorrelated (random) during the 10-breath presigh window. Short-range memory increased after a sigh for the entire 50 breaths compared with the randomized data set and for 20 breaths compared with the presigh window. Similar, but shorter duration, changes were noted in V̇e. No change in long-range memory was seen after a sigh. Coefficient of variation and range of points located within a defined attractor segment increased after a sigh. Thus control of breathing in healthy infants shows long-range stability and improvement in short-range memory and variability after a sigh. These results add new evidence that the role of sighs is not purely mechanical.

Respiratory physiotherapy vs. suction: the effects on respiratory function in ventilated infants and children

OBJECTIVE

To assess and compare the effects of physiotherapy and suction on expired tidal volume (V(TE)), respiratory compliance (C(rs)), resistance (R(rs)) and arterial blood gases.

DESIGN

Randomised cross-over study comparing outcomes after both treatments on the same day.

SETTING

Intensive tertiary care units, Great Ormond Street Hospital, London.

PATIENTS

One hundred children on full ventilatory support requiring physiotherapy. Paired measurements were obtained in 90 participants, and 7 others were excluded because of tracheal tube leak.

INTERVENTIONS

Respiratory physiotherapy and suction.

MEASUREMENTS AND RESULTS

Physiotherapy lasted longer and required more saline and catheters per treatment. There were no significant group changes in V(TE) or C(rs) after either treatment, but a tendency for R(rs )to fall following physiotherapy which reached significance in patients on volume-preset ventilation. There were also small but statistically significant reductions in HCO(3)(-), base excess and SaO(2) after physiotherapy. V(TE) and C(rs) increased and R(rs) decreased in excess of their 95% limits of agreement for normal variability in approximately twice as many subjects following physiotherapy than suction, these differences being significant for V(TE) and approaching significance for C(rs) and R(rs).

CONCLUSIONS

Physiotherapy appeared to have an advantage in reducing R(rs )in some patients, but also produced changes in derived blood gas parameters. Within individuals, physiotherapy treatments were also more likely to produce improvements in V(TE), C(rs) and R(rs) than suction. Further research should identify sensitive patient selection criteria and assess longer-term effects of such treatments.

The effect of parental smoking on lung function and development during infancy

While the adverse effects of parental smoking on respiratory health during childhood are well recognized, its potential impact on early lung development is less clear. This review summarizes current evidence on the effect of parental smoking on lung function during infancy. It is difficult to separate the effects of pre- and postnatal exposure, since the majority of mothers who smoke in pregnancy (currently around 30% worldwide) continue to do so thereafter. Nevertheless, measurements undertaken prior to any postnatal exposure have consistently demonstrated significant changes in tidal flow patterns in infants whose mothers smoked in pregnancy. While there is, as yet, no convincing evidence from studies in human infants that smoking during pregnancy is associated with increased airway responsiveness at birth, many studies have demonstrated a reduction in forced expiratory flows (on average by 20%) in infants exposed to parental smoking. While maternal smoking during pregnancy remains the most significant source of such exposure and is likely to be responsible for diminished airway function in early life, continuing postnatal tobacco smoke exposure will increase the risk of respiratory infections, the combination of both being responsible for the two- to fourfold increased risk of wheezing illnesses observed during the first year of life in infants whose parents smoke. These findings emphasize the need to keep infants in a smoke-free environment both before and after birth, not least because of growing awareness that airway function in later life is largely determined by that during foetal development and early infancy.

Maternal atopic disease modifies effects of prenatal risk factors on exhaled nitric oxide in infants

In a prospective healthy birth cohort, we determined whether levels of exhaled nitric oxide (eNO) in healthy unselected infants at the age of 1 month were associated with maternal atopic disease and prenatal and early postnatal environmental exposures. Tidal eNO was measured in 98 healthy, unsedated infants (35 from mothers with atopy) (mean age +/- SD, 36.0 +/- 6.2 days) and was compared with histories taken in standardized interviews. eNO was higher in males compared with females (17.7 vs. 14.6 ppb, p = 0.042) and infants exposed to postnatal maternal smoking (+4.4 ppb, p = 0.027), adjusting for weight and tidal breathing parameters. Prenatal tobacco exposure was associated with higher eNO (+12.0 ppb, p = 0.01) in infants of mothers with asthma and lower eNO (-5.7 ppb) in infants of mothers without asthma (p for interaction < 0.0001). Coffee consumption in pregnancy decreased eNO (-6.0 ppb, p = 0.008) only in children of mothers with atopy (p for interaction = 0.015). Paternal atopy had no influence. In the early phase of immunologic development, before the onset of infections and allergic disease, the effect of prenatal or early postnatal environmental factors on eNO was modified by the presence of maternal atopic disease. This underlines the complex interaction of maternal and environmental factors in the development of airway disease.

Progressive decline in plethysmographic lung volumes in infants: physiology or technology?

During the last 30 years, there has been an unexplained trend toward declining values for plethysmographic assessments of lung volume at functional residual capacity (FRC) in infants. The aim of this study was to compare data collected from healthy infants using contemporary equipment with published reference data and to explore reasons for discrepancies. Lung volumes were measured in 32 healthy infants (age, 4-93 weeks; weight, 3.9-12.4 kg) using a new, commercially available infant plethysmograph. Mean (SD) FRC was 19.6 (3.4) ml/kg (within subject coefficient of variation 3.4 [2.3%]), which was on average 7.0 [3.5] ml/kg and 2.3 [1.2] SD (Z) scores lower than the recently collated reference data from an American Thoracic Society task force. A total of 66% of these healthy infants had a FRC that was below the predicted normal range. Comparison of equipment, software, and protocols with those from previous reports revealed the importance of minimization of dead space and of adequate subtraction of all compressible occluded volume when calculating FRC in infants. These findings emphasize the need to establish reference data for lung function tests in infants that are appropriate for the equipment and protocols in current use.

Assessment of the single-occlusion technique for measurements of respiratory mechanics and respiratory drive in healthy term neonates using a commercially available computerized pulmonary function testing system

In this study, a critical assessment of the single-occlusion technique as a means of measuring passive respiratory mechanics and respiratory drive (P0.1) was performed in nonintubated spontaneously breathing healthy term neonates using commercially available computerized equipment (PEDS system). In general, we found that quality parameters only partially conformed to the international established standards for measuring passive respiratory mechanics. There was a failure rate of technically acceptable occlusions of about 50% for respiratory mechanics measurements and 20% for P0.1 measurements. Intersubject variability of the data was between 10 and 40%. After studying different lengths of occlusion times (Tocc; 0.2, 0.3, 0.4 and 0.5 s), it was found that acceptable occlusions for passive respiratory mechanics were obtained only if the expiratory Tocc exceeded 0.2 s. Increasing the Tocc had no effect on the absolute values of respiratory mechanics but showed a significant trend towards more technically acceptable occlusions. We speculate that a Tocc of at least 0.4 s may be a prerequisite for obtaining reliable results for respiratory mechanics in healthy term neonates.

In vitro validation of an ultrasonic flowmeter in order to measure the functional residual capacity in newborns

Ultrasonic transit-time airflow meters (UFM) allow simultaneous measurements of volume flow V'(t) and molar mass MM(t) of the breathing gas in the mainstream. Consequently, by using a suitable tracer gas the functional residual capacity (FRC) of the lungs can be measured by a gas wash-in/wash-out technique. The aim of this study was to investigate the in vitro accuracy of a multiple-breath wash-in/wash-out technique for FRC measurements using 4% sulphur hexafluoride (SF6) in air. V'(t) and MM(t) were measured with a Spiroson SCIENTIFIC flowmeter (ECO Medics, CH) with 1.3 ml dead space. Linearity of airflow and MM were tested using different tidal volumes (V(T)) and breathing gases with different O2 and SF6 concentrations. To determine the accuracy of FRC measurements SF6 wash-in and wash-out curves from four mechanical lung models (FRC of 22, 53, 102 and 153 ml) were evaluated by the Spiroson. For each model five measurements were performed with a physiological V(T)/FRC ratio of 0.3 and constant respiratory rate of 30 min(-1). The error of measured V(T) (range 4-60 ml) was <2.5%. There was a strong correlation between the measured and calculated MM of different breathing gases (r = 0.989), and the measuring accuracy was better than 1%. The measured FRC of the four models were 20.3, 49.7, 104.3 and 153.4 ml with a coefficient of variation of 16.5%, 4.5%, 4.9% and 3%. Accordingly, for FRC <100 ml the in vitro accuracy was better than 8% and for FRC >100 ml better than 2.5%. The determination of FRC by MM measurements using the UFM is a simple and cost-effective alternative to conventionally used gas analysers with an acceptable accuracy for many clinical purposes.

Correction factors for oxygen and flow-rate effects on neonatal Fleisch and Lilly pneumotachometers

OBJECTIVE

To assess the effects of different oxygen concentrations and flow rates on the measurement errors of neonatal pneumotachometers in heated and unheated situations and to develop correction factors to correct for these effects.

DESIGN

Prospective laboratory study.

SETTING

Outpatient clinic with equipment in a standardized setting.

SUBJECTS

Neonatal pneumotachometers.

INTERVENTIONS

In standardized conditions, the tested pneumotachometer was calibrated at a flow rate of 3 L/min with 60% oxygen and was set in series with a closed spirometer system being used as a reference. Different air-flow levels (1-9 L/min) and oxygen concentrations (21-100%) were infused into the closed system with the pneumotachometer and spirometer.

MEASUREMENTS AND MAIN RESULTS

The pneumotachometers were significantly affected by changing oxygen concentrations (p < .01) and increasing flow rates (p < .01), increasing the actually measured flow rate. Correction factors, developed by multiple regression analysis, significantly reduced the overall maximum errors of the pneumotachometers from -1.1 to 0.6 L/min to -0.5 to 0.4 L/min.

CONCLUSIONS

The effects of changes in oxygen concentrations and flow rates on neonatal pneumotachometers could be considerably decreased by the use of correction factors such as were calculated in this study. This will preclude frequent calibration procedures with actual flow and oxygen levels during changes in experimental settings.

Accuracy of displayed values of tidal volume in the pediatric intensive care unit

OBJECTIVES

To assess the accuracy of the expired tidal volumes (VT(E)) displayed by one of the most frequently used ventilators that measures exhaled volume at the expiratory valve.

DESIGN

Prospective study.

SETTING

The intensive care units of a pediatric tertiary referral center in London, UK.

PATIENTS

A total of 56 intubated children aged between 3 wks and 16.6 yrs who were clinically stable and ventilated with a Servo 300 ventilator.

INTERVENTIONS

The CO2SMO Plus respiratory monitor, which measures flow at the airway opening, was validated using calibrated syringes and appropriate tracheal tubes and connections. Simultaneous in vivo recordings of VT(E) from the Servo 300 and CO2SMO Plus were compared before (displayed Servo VT(E)) and after (effective Servo VT(E)) compensating for ventilator circuit compliance.

MEASUREMENTS AND MAIN RESULTS

The in vitro accuracy of the CO2SMO Plus was within +/-5% over a wide range of volumes and measurement conditions. The displayed Servo 300 VT(E) overestimated the true VT(E) by between 2% and 91%. The magnitude of error varied within and between children, according to pressure change (peak inspiratory pressure minus positive end-expiratory pressure), VT(E), and circuit size. Mean (sd) error was 32% (20%) in 40 children with displayed Servo VT(E) of <160 mL and 18% (6%) in 16 subjects with displayed Servo VT(E) of >/=160 mL. After correcting for gas compression, effective VT(E) from the Servo 300 underestimated the true VT(E) by up to 64% in the smallest infants but continued to overestimate by as much as 29% in older children.

CONCLUSIONS

The accuracy of tidal volume values is crucially dependent on the site of measurement. Unless measured at the airway opening, displayed values are an inconsistent and misleading indicator of the true volumes delivered.

Monitoring early inflammation in CF. Infant pulmonary function testing

Infant pulmonary function tests (iPFTs) have primarily been used as research tools to further define physiologic pulmonary abnormalities in infants and young children with cystic fibrosis (CF). Methodologies used to measure pulmonary function in infants are described, with particular relevance to CF. A comprehensive review of studies and findings in CF infants using iPFTs is presented. Further goals in improving methodologies and in defining pulmonary disease in CF are presented.

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.

Correlation properties of tidal volume and end-tidal O2 and CO2 concentrations in healthy infants

We investigated whether breath-to-breath fluctuations in tidal volume (VT) and end-tidal O2 and CO2 exhibit long-range correlations and whether parameters describing the correlations can be used as noninvasive descriptors of control of breathing. We measured VT and end-tidal O2 and CO2 over n = 352 +/- 104 breaths in 26 term, healthy, unsedated infants (mean age +/- SD: 36 +/- 6 days) and calculated the detrended fluctuation function [F(n)]. The F(n) of the breath-to-breath time series of VT, O2, and CO2 revealed a linear increase with a breath number on log-log plots with a slope that was significantly different from 0.5 (random) and thus consistent with scale-invariant behavior. Long-range correlations were stronger for O2 than for VT and CO2. The F(n) of many individual signals exhibited a crossover behavior indicating that control mechanisms regulating fluctuations of VT, O2, and CO2 may be different on different time scales. Thus breathing has a memory up to at least 400 breaths that can be characterized by the simple indicator alpha.

Sex-specific prediction equations for Vmax(FRC) in infancy: a multicenter collaborative study

Measurements of maximal flow at functional residual capacity (Vmax(FRC)) from partial forced expiratory maneuvers remain the most popular method for assessing small airway function in infants and young children. However, the lack of appropriate reference data that are both applicable outside the centers that developed them and reflect the normal variability between healthy subjects has limited interpretation of Vmax(FRC) results in both clinical practice and research. To address this problem, we collated Vmax(FRC) data from 459 healthy infants (226 boys) tested on 654 occasions during the first 20 months of life from three collaborating centers. Multiple linear regression analysis indicated that sex, age, and length were important predictors of Vmax (FRC), which was, on average, 20% higher in girls than in boys during the first 9 months of life. (Vmax(FRC))0.5 (ml x second(-1)) = 4.22 + 0.00210 x length2 (cm) for boys (RSD = 3.01; R2 = 0.48), and -1.23 + 0.242 x length for girls (RSD = 2.72; R2 = 0.49). Alternative models incorporating both age and length z scores are also described. Failure to use sex-specific prediction equations for Vmax(FRC) may preclude detection of clinically significant changes in girls and lead to false reports of diminished airway function in boys. Appropriate use of z scores, which indicate a "normal" range (z scores of 0 +/- 2) for Vmax(FRC), during infancy should also improve interpretation of both clinical and research studies.

Tidal exhaled nitric oxide in healthy, unsedated newborn infants with prenatal tobacco exposure

Tidal fractional exhaled nitric oxide (FE(NO)) changes were investigated in healthy, unsedated infants with or without prenatal tobacco exposure. Tidal flow (V), FE(NO), and CO(2) were measured in 20 healthy, unsedated infants [age: 25-58 days, length: 56.5 +/- 2.5 (SE) cm]. NO output (VNO) was calculated (VNO = FE(NO) x V). Two approaches were used to investigate within-breath changes of FE(NO) and VNO. First, we identified phases II and III from the expiratory capnogram. Second, we divided expiration into time-based quartiles. Tidal FE(NO) (range: 14.5 +/- 1.6 to 17.6 +/- 2.1 parts/billion: quartile 4 and phase II, respectively) was not different between portions and exhibited significant negative V dependence. VNO was significantly dependent on the expiratory portion, with quartile 4 being significantly lower than the remaining expiratory portions. Infants exposed to prenatal cigarette smoke (n = 7) exhibited significantly lower FE(NO) and VNO compared with nonexposed (n = 13) infants. We conclude that tidal FE(NO) is V dependent and that VNO may be a more suitable outcome parameter in variable V conditions. Prenatal tobacco exposure resulted in a decreased FE(NO) and VNO in infants.

Interrupter resistance in preschool children: measurement characteristics and reference values

There is a need for quick, reliable, and noninvasive lung function tests to assess airway obstruction in preschool children both for pediatric pulmonary care as well as for research purposes. We studied feasibility, reproducibility, and validity of measurements of the respiratory system using the interrupter technique (interrupter resistance [Rint]) and obtained reference values in children from a general population, 2 to 7 yr of age. Accuracy was studied by comparisons of Rint with plethysmographic airway resistance (Raw) in 20 patients (7 to 14 yr) with mild to severe chronic airways obstruction and was satisfactory in patients with FEV(1) > 60% predicted. The technique proved sensitive enough to detect changes in airway caliber within a small group of 12 children who developed mild respiratory tract infections. Among children from a general population, subgroups with mild respiratory symptoms or mild respiratory disease had higher mean Rint values. Airway obstruction was better detected using expiratory rather than inspiratory interruptions, both programmed at peak tidal ventilatory flow. Reproducibility within subjects was satisfactory (intraclass correlation 0.82 and 0.79). The same applied to interobserver agreement (intraclass correlation 0.98). The interrupter technique proves to be a reliable and practical test of airway function, suitable for clinical and epidemiologic studies in preschool children.

The infant lung function model: a mechanical analogue to test infant lung function equipment

To facilitate international multicentre studies and quality control of infant pulmonary function measurements, the European Respiratory Society-American Thoracic Society (ERS-ATS) working group for infant lung function testing aims to develop specifications for standardized infant lung function equipment and software. However, a standardized test device is also needed to test whether existing infant lung function equipment is able to meet these requirements. The authors have built a "mechanical model baby" consisting of a linear pump which can reproduce prerecorded tidal flow waveforms with a precision of 0.5% (full stroke), enabling the simulation of tidal and forced flow patterns. This linear pump can be connected to a series of copper lung volumes (range 50-300 mL) with known time constants, so that lung volumes can be reproduced with a precision of +/-1% at frequencies 10-120bpm. Five airflow resistors were built using sinter material. When assessed using flows 0-300 mL.s(-1) all resistors showed a quasilinear pressure/ flow relationship, with slopes 1.0-5.6 kPa.L(-1).s. These resistances could be reproduced with a precision of +/-2.5%. The infant lung model can also be used to assess frequency responses of infant lung function equipment, since the pump is capable of delivering low amplitude volumes up to 20 Hz in a pseudorandom noise manner. In summary, based on error estimations, this infant lung model is able to test whether or not infant lung function equipment meets the requirements suggested by the European Respiratory Society-American Thoracic Society standardization group, that is: flow measurements within +/-2.5%, volume and resistance measurements within +/-5%, frequency response: magnitude attenuation <+/-10% and phase shift <+/-3 degrees at 10 Hz.

Assessment of an infant whole-body plethysmograph using an infant lung function model

In order to facilitate international multicentre studies and improve the quality control of infant pulmonary function measurements, the European Respiratory Society-American Thoracic Society Task Force for infant lung function testing has recently developed specifications for standardized infant lung function equipment and software. A mechanical infant lung model analogue has been developed to assess whether infant lung function equipment is able to meet these requirements. However, the practical testing of infant lung function equipment using such models is highly complex because of the need to use very small pressure and flow changes, and the numerous potentially confounding factors associated with both the design of the device and the testing procedure. The aim of this study was to determine whether the infant lung model is capable of assessing the overall function of an whole-body infant- plethysmograph, using the only infant plethysmograph that was commercially available at the time as an example. The mechanical characteristics of the model such as vibrations or noise did not disturb the delicate plethysmographic measurements and thereby allowed a reliable assessment of the system. A series of tests revealed that the plethysmograph was able to measure airway resistance 1-3.5 kPa.L(-1).s with an accuracy of +/-2.5% and lung volumes 75-300 mL with an accuracy of +/-2.5% under in vitro conditions. To conclude, the infant lung model is a useful means of assessing the overall in vitro performance of infant whole-body plethysmographs, but thermal, mechanical and frequency response characteristics of such a device must be taken into account when interpreting the results of such assessments.

The bias flow nitrogen washout technique for measuring the functional residual capacity in infants. ERS/ATS Task Force on Standards for Infant Respiratory Function Testing

The functional residual capacity (FRC) is the most commonly measured static lung volume in infants. It is important for interpreting volume-dependent pulmonary mechanics, e.g. airway resistance, and defining normal lung growth. The bias flow nitrogen washout technique is widely used for measuring FRC because the dead space and circuit resistance are low, making it suitable for small or sick infants. Moreover, data acquisition and calculation are easily programmed for a personal computer. The aim of this paper is to provide recommendations pertaining to equipment requirements, study procedures and reporting of data for functional residual capacity measurements. While measuring the functional residual capacity is regarded as physiologically and clinically important, the accuracy of the measurement is undoubtedly equally important. Hence, the paper also emphasizes factors influencing the accuracy of functional residual capacity measurements independent of equipment requirements. These recommendations represent the "State of the Art" in 2000.

Assessment of passive respiratory mechanics in infants: double versus single occlusion?

The single breath or occlusion technique (SOT) is widely used to assess passive respiratory mechanics in infants, but depends on various underlying assumptions. Recently, it has been proposed that such measurements could be internally validated by performing two brief airway occlusions during the same expiration. The aim of this study was to evaluate the use of the double occlusion technique (DOT) using a new commercially available program (Jaeger MasterScreen BabyBody Erich Jaeger GmbH, Würzburg, Germany). Paired measurements of respiratory system compliance (Crs) and resistance (Rrs) using both SOT and DOT were obtained in 18 healthy sedated infants (age range 4-41 weeks, weight 2.7-9.9 kg). There was close agreement between both methods of assessing Crs in all infants, the mean within-subject difference (95% confidence interval (CI)) for DOT-SOT being -0.06 (-0.55- +0.42) mL x kPa(-1) x kg(-1). By contrast, estimates of Rrs,DO were on average 20% lower than those for Rrs,SO, (mean within-subject difference (95% CI) being -0.67 (-1.04- -0.31) kPa x L(-1) x s; p<0.01). The relatively lower values obtained for Rrs,DO may reflect the higher mean lung volume at which it was calculated. Further work is required to investigate the clinical and epidemiological relevance of this new approach, and whether there are any advantages of using both techniques when assessing passive mechanics in infants.

Deadspace free ventilatory measurements in newborns during mechanical ventilation

OBJECTIVE

To improve the accuracy of ventilatory measurements in ventilated newborns by means of a numerical correction when a deadspace free differential measuring method using two pneumotachographs (PNTs) is applied and to investigate the clinical usefulness of this correction procedure.

DESIGN

In vitro study and prospective animal study.

SETTING

Research laboratory of the Clinic of Neonatology and the Animal Research Laboratory, Charité Hospital Berlin.

SUBJECTS

Ten newborn piglets, weighing 610-1340 g (median, 930 g), age <12 hrs.

INTERVENTIONS

The accuracy of both the deadspace free method and the endotracheal flow measurements (conventional method) was investigated using mechanical lung models. A correction procedure for the deadspace free method was developed considering signal delay time and tube compliance between both PNTs. This method was applied to the piglets measured during partial liquid ventilation (PLV). Measurements were done before and after lung lavage and during 30 and 120 mins of PLV (30 mL/kg body weight perfluorocarbon).

MEASUREMENTS AND MAIN RESULTS

In vitro measurements showed volume differences between both methods of 8%, 12%, 16%, and 17%, respectively, depending on the distance between the PNTs of 10, 60, 120, and 180 cm. After applying the correction algorithm, the differences decreased to 3%, 0%, -2%, and -8%, respectively. The piglets were measured with 120-cm tube length between the PNTs. The correction algorithm reduced the measured tidal volume before lavage by 7%, after lavage by 14%, 30-min PLV by 12%, and 120-min PLV by 10%, corresponding to the changes in respiratory compliance of 1.2, 0.6, 1.0, and 1.1 mL/cm H2O.

CONCLUSIONS

The deadspace free method can be advantageously used for continuous measurements in newborns despite much higher technical expense. The correcting procedure improved the accuracy of the volume measurement remarkably, especially for lower respiratory compliance.

Plethysmographic measurements of lung volume and airway resistance. ERS/ATS Task Force on Standards for Infant Respiratory Function Testing. European Respiratory Society/ American Thoracic Society

Functional residual capacity (FRC) is the only static lung volume that can be measured routinely in infants. It is important for interpreting volume-dependent pulmonary mechanics such as airway resistance or forced expiratory flows, and for defining normal lung growth. Despite requiring complex equipment, the plethysmographic method for measuring FRC is very simple to apply and, unlike the gas dilution techniques, enables repeat measures of lung volume to be obtained within a few minutes. This method has the further advantage that with suitable adaptations to the equipment, simultaneous measurements of airway resistance can also be obtained. The aim of this paper is to provide recommendations pertaining to equipment requirements, study procedures and reporting of data for plethysmographic measurements in infants. Implementation of these recommendations should help to ensure that such measurements are as accurate as possible and that meaningful comparisons can be made between data collected in different centres or with different equipment. These guidelines cover numerous aspects including terminology and definitions, equipment, data acquisition and analysis and reporting of results and also highlight areas where further research is needed before consensus can be reached.

In vitro assessment of equipment and software to assess tidal breathing parameters in infants

The aim of this in vitro study was to compare the measurement accuracy of two currently available devices for measuring tidal breathing in infants. A mechanical model pump was used to generate flow profiles which simulated those observed in infants. A range of flows was applied simultaneously to two different devices, namely the commercially available SensorMedics 2600 (SM 2600) and more recently developed, custom-made equipment based on the flow-through technique (FTT). Automatically derived values from both devices were compared with one another and with manual calculations of printouts of the same breaths. There were no differences in the raw flow signal obtained from the two devices, nor between values calculated automatically or manually from the FTT. Similarly, the deviations between the FTT and SM 2600 were <3% for tidal volume, respiratory frequency and minute ventilation. However, when comparing either with manually calculated values or those derived automatically from the FTT, there was a systematic and highly significant underestimation of shape-dependent parameters, such as the time to peak tidal expiratory flow as a proportion of tidal expiratory time (tPTEF/tE), derived by the SM 2600. The lower the applied flow, the higher the observed deviations, the underestimation being up to 60% when flows simulating those observed in preterm neonates were applied. These errors appear to result from differences in signal processing such as the algorithms used for breath detection and can only be detected if appropriate nonsinusoidal flow profiles representing those seen in infants are used to evaluate equipment.

Effect of apparatus dead space on breathing parameters in newborns: "flow-through" versus conventional techniques

Commercial devices for tidal breathing measurements in newborns allow only short-term measurements, due to the high apparatus dead space of the face mask and pneumotachometer. The flow-through technique (FTT) minimizes the dead space by a background flow, thereby allowing long-term measurements. The aim of this study was to investigate the comparability of tidal breathing parameters using both techniques. Paired measurements of tidal breathing were performed in 86 sleeping infants (median (range) body weight 2.8 kg (1.9-5.3 kg), age 65 days (3-150 days)), using the FTT and SensorMedics 2600 (SM 2600). There was a significant bias (p <0.001) in all tidal breathing parameters. Compared with the FTT, increases (95% confidence interval (CI)) in tidal volume (VT), respiratory frequency (fR), and minute ventilation (V'E) were 0.74 (0.5-1.0) mL.kg(-1), 9.0 (6.9-11.2).min(-1) and 92 (74-109) mL.min(-1).kg(-1) when measured with the SM 2600, representing average increases of 13, 17 and 30%, respectively, in response to the added dead space. By contrast, time to peak tidal expiratory flow as a proportion of expiratory time (tPTEF/tE) was changed by -0.09 (-0.11-0.08). The mean (95% CI) change in tPTEF/tE of -54 (-62-45)%, when measured in infants by the SM 2600, was remarkably similar to that observed during in vitro validation studies (-59 (-73-44)%), suggesting that the discrepancies in timing parameters may be largely attributable to differences in signal processing. In conclusion, differences in measurement technique and precision of the devices used can result in significant differences in tidal breathing parameters. This may impede the comparison of results within and between infants and the clinical interpretation of tidal breathing measurements in newborns.

Passive respiratory mechanics: the occlusion techniques

The aim of this position paper is to define quality control and acceptance criteria for measuring passive respiratory mechanics in infants using the occlusion techniques to ensure that valid results are obtained. These guidelines cover numerous aspects including: 1) terminology and definitions; 2) equipment; 3) data acquisition; 4) data handling and analysis; 5) reporting of results. Adherence to these guidelines should ensure that measurement of passive respiratory mechanics in infants in different lung function laboratories could be performed with an acceptable degree of safety, precision, and reproducibility. This will facilitate multi-centre collection of data and performance of clinical investigations.