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Background Late and moderate prematurity may have an impact on pulmonary function during childhood. The present study aimed to investigate lung mechanics in school-age children born moderate-to-late preterm (MLPT). Methods Children aged 5-10 years were enrolled in this case-control study. Lung function and bronchodilator response were assessed by impulse oscillometry (IOS) at two hospital-based specialized clinics. A structured questionnaire was employed to assess respiratory morbidities. Results A total of 123 children was divided into two groups: case (MLPT) n = 52 and control (children born at term) n = 71. The results showed no difference between groups in mean baseline IOS variables: R5 0.80 ± 0.20 vs 0.82 ± 0.22 kPa/L/s, p = 0.594, R20 0.54 ± 0.13 vs 0.55 ± 0.13 kPa/L/s, p = 0.732, R5-R20 0.26 ± 0.12 vs 0.27 ± 0.15 kPa/L/s, p = 0.615, X5 -0.29 ± 0.01 vs -0.29 ± 0.1 kPa/L/s, p = 0.990, Fres 21.1 ± 3.3 vs 21.7 ± 3.1 L/s, p = 0.380, and AX 2.7 ± 3.36 vs 2.5 ± 1.31 kPa/L/s, p = 0.626. Bronchodilator response and the occurrence of respiratory morbidities after birth were also similar between groups. Conclusions This study found lung mechanics parameters to be similar in school-age children born MLPT and those born at term, suggesting that pulmonary plasticity continues to occur in children up to school age. Impact Late and moderate prematurity is associated with an increased risk of reduced pulmonary function during childhood. Follow-up reports in adolescents and adults born MLPT are scarce but have indicated pulmonary plasticity with normalization of airway function. Our results show that the lung function in school-age children born MLPT is similar to that of children born at term.

We aimed to evaluate if lung mechanics measured by forced oscillatory technique (FOT) during the first day of life help identify extremely low gestational age newborns (ELGANs) at risk of prolonged mechanical ventilation (MV) and oxygen dependency.Positive end-expiratory pressure (PEEP) was increased 2 cmHTwenty-two newborns (24FOT can be applied bedside in ELGANs, where early changes in lung mechanics with PEEP improve clinical prediction of respiratory outcomes.

Sustained inflation (SI) at birth facilitates establishment of functional residual capacity (FRC) in the preterm lung, but the ideal lung recruitment strategy is unclear. We have compared the effect of SI and a stepwise positive end-expiratory pressure (PEEP; SEP) strategy in a preterm model.127 d gestation lambs received either 20-s SI (n = 9) or 2 cmH2O stepwise PEEP increases to 20 cmH2O every 10 inflations, and then decreases to 6 cmH2O (n = 10). Ventilation continued for 70 min, with surfactant administered at 10 min. Alveolar-arterial oxygen gradient (AaDO2), compliance (C(dyn)), end-expiratory thoracic volume (EEVRIP; respiratory inductive plethysmography), and EEV and C(dyn) in the gravity-dependent and nondependent hemithoraces (electrical impedance tomography) were measured throughout. Early mRNA markers of lung injury were analyzed using quantitative real-time PCR.From 15 min of life, AaDO2 was lower in SEP group (P0.005; two-way ANOVA). SEP resulted in higher and more homogeneous C(dyn) (P0.0001). Mean (SD) EEVRIP at 5 min was 18 (9) ml/kg and 6 (5) ml/kg following SEP and SI, respectively (P = 0.021; Bonferroni posttest); this difference was due to a greater nondependent hemithorax EEV. There was no difference in markers of lung injury.An SEP at birth improved gas exchange, lung mechanics, and EEV, without increasing lung injury, compared to the SI strategy used.

517 Characterisation of Lung Mechanics After Fetal Tracheal Occlusion in Newborn Rabbits with Lung Hypoplasia Induced by Diaphragmatic Hernia (CDH)

36 Characterisation of Lung Mechanics and Inflammation in Heterozygous Abca3 Mice After Exposure to 95% Oxygen or Room Air

Background: The importance of achieving lungrecruitment at birth is well recognised but the optimalstrategy unclear. Aim: To determine the feasibility of measuringregional lung mechanics during three lungrecruitment strategies at birth, and their outcomes, in a preterm lung model. Method: Nine 127d old lambs (mean weight 2.7kg)were studied. During delivery of head and thoraxthe fetus was intubated and electrical impedancetomography (EIT) electrodes applied. Oncedelivered one of three ventilation strategies wasapplied: In all strategies, FIO2 and TTV were adjusted tomaintain SpO2 88-92% and PaCO2 45-55mmHg. Gas exchange, lung mechanics and regional lungvolume/tidal volume (EIT) measured until 70-min life. Results: There was no difference in regional EELVbut at 8-min more uniform aeration occurred withescalating PEEP than Surfactant+SI; mean(SD)anterior:poster hemithorax aeration 0.6(0.4):0.7(1.2)vs 0.7(0.4):0.4(0.3) impedance units. Surfactant+SIand escalating PEEP improved oxygenationcompared to SI+Surfactant (Fig). There were nosustained differences in CrsPaCO2 and VR. Conclusions: Exploring the interaction betweentype of recruitment manoeuvre and adjunctivetherapies birth using methods which may betranslatable to the clinical environment is feasibleand may yield interesting results.

The passive exhalation flow-volume plots of preterm lambs exhibit curvature. To explain this curvature, we proposed two mathematical models that could predict the measured passive exhalation flow-volume data well. One model takes into account the flow and volume dependence of resistance and compliance. The second model emphasizes the time dependence of lung mechanics and considers the respiratory system viscoelastic properties and the analogy of the lung to two electronic resistor-capacitor circuits connected in parallel. We attempted to determine which of the two models is more valid by analyzing passive exhalation flow-volume data that were obtained while briefly obstructing flow midway through deflation. In 14 preterm lambs (130 d gestation), the flow of exhaled gas increased from 76 ± 35 mL/s when measured just before obstruction to 90 + 30 mL/s when measured immediately after release of the obstruction (p < 0.0001). This finding suggests that a time-dependent phenomenon was taking place during obstruction and is inconsistent with the model based upon the flow and volume dependence of resistance and compliance. We made similar measurements in four near-term (143–146 d gestation) and four full-term lambs (9–12 d of age). Their flow-volume curves were relatively linear, and they showed no increases in flow after removal of the obstruction. The results of this study strongly suggest that time-dependent phenomena caused the curvilin earity in the passive exhalation flow-volume plots of preterm lambs. We suspect that the time-dependent phenomena is associated with the premature lung and with parenchymal lung disease. The models of viscoelastance and of parallel inhomogeneities in the lung are consistent with our observations.

202 Cerebral Haemodynamics and Lung Mechanics in Preterm Infants During Synchronized Intermittent Mandatory Ventilation (SIMV) and Synchronized Intermittent Positive Pressure Ventilation (SIPPV), with and Without Volume Guaranteed (VG)

The Effects of Broncho-Alveolar Lavage (BAL) on Lung Mechanics in Ventilated Newborns Infants

Lung Inflation is Required to Improve Lung Mechanics and Enhance Surfactant Production in Cardiopulmonary By-Pass for Reparation of Atrial and Ventricular Septal Defects

LUNG MECHANICS IN NEWBORN INFANTS WITH SEVERE CONGENITAL DIAPHRAGMATIC HERNIA (CDH) BEFORE AND AFTER SURGICAL REPAIR

Systemic and inhaled dexamethasone treatments have been shown to improve lung mechanics in preterm infants with chronic lung disease. 253 infants were enrolled in a multicenter randomized, placebo-controlled, double-blind clinical trial of early administration of beclomethasone (40μg/kg/day, tapered over 4 weeks) or placebo given by metered dose inhaler and aerochamber® (Mongahan Medical Corp., Inc). These infants were < 33 wks GA and

Lung Mechanics and Inflammatory Response in Meconium Injured Rats following Lung Lavage with Perfluorochemical or KL4 Surfactant † 1757

Lung Mechanics Measurements in Preterm Neonates: Effects of Breathing Pattern and Patient Characteristics 1715

Background: 2 treatment strategies to compare GE and LM in artificial RDS after lavage (paO2 constantly < 13 kPa; lung compliance(Crs< ½ baseline, FiO2=1.0 and VT=5-10 ml/kg). Subjects: 13 newborn piglets (< 2 days: MW. 1708 g). Measurement of Crs. blood gases, systemic and pressure of respiratory system before (baseline), 0 and 60 min after injury and 15, 30, 60 and 120 min. after intervention: Randomized surfactant (n=7: Alveofact 100 mg/kg) or RM 101 (n=6; 2 ml/kg/min initially, reduced to 0.5 ml/kg/min) intratracheal via bypass-tube without disconnecting ventilation.

Aim. To evaluate the effect of iNO on gas exchange, cardiovascular profile and lung mechanics in a model of pulmonary hypertension(PH) induced by tracheal instillation of meconium (eMAS) in newborn lambs.

Background. Increases in lung resistance (RL) due to i.v. histamine bolus are reported to become more pronounced with postnatal maturation (Dreshaj et al; J. Appl. Physiol. 81(4): 1785-1791, 1996). Objective. To determine if postnatal development affects the changes in RL and lung elastance (EL =1/compliance) during constant infusion of histamine. Methods. We continuously measured airway opening pressure (Pao), flow and esophageal pressure (Pes) during 30-minute intravenous infusions of histamine in seven tracheostomized, anesthetized, paralyzed and mechanically ventilated (constant tidal volume) piglets [3 newborn (4-6 days, 2.5-3.0 Kg) and 4 weaned (8 weeks, 12.3-18 Kg)]. Measurements were repeated at two concentrations (0.5 and 5.0 μg/Kg/min). RL and EL were determined by multiple linear regression; i.e., Pao(t)-Pes(t)=RL·flow(t) + EL·volume(t). Results. For both groups, RL and EL increased with histamine in a dose dependent fashion. The increases in EL were comparable regardless of dose. Changes in RL were similar at the lower histamine dose (figure). At the higher dose, the increases in RL were similar during early infusion ( 10 min) in older piglets. Conclusion. Differences in the response to histamine, in older versus newborn piglets, were only evident as a sharper rise in RL during the latter part of the higher dose infusion. Such age dependence of RL is consistent with histamine bolus data. We speculate that this phenomenon may be related to increased central airway involvement in the response as opposed to a predominantly peripheral effect because: 1) the sharp rise in RL did not coincide with a similar increase in EL, and 2) rise in RL only occurs late, when accumulation of histamine may have led to bolus-like conditions. Supported in part by an equipment grant from Novametrix Medical Systems Inc.

A PROTOTYPE COMPUTERIZED SYSTEM FOR MEASUREMENT OF LUNG MECHANICS DURING TOTAL LIQUID VENTILATION. 91

We compared lung mechanics and EMG amplitude and duration of 11 rabbits during IMV and SIMV (Star Sync®), before and during resistive loading. SIMV response time was 50 ±13 msec. We recorded airway flow, pleural pressure, lung volume (jacket plethysmograph) and EMG (needle electrodes In the diaphragm). We computed compliance (C), resistance (R), Inspiratory work (W) and tidal volume (TV) for mechanical breaths.

Studies with animal surfactant preparations have shown dramatic improvements in oxygenation without concomitant changes in dynamic compliance. The present study deals with the effects of a purely synthetic surfactant (E) upon arterial blood gases (ABG) and compliance (Crs)/resistance (Rrs), determined by the recently introduced single breath occlusion technique. Six premature babies with HMD, enrolled in the European OSIRIS trial were studied. Crs/Rrs and ABG were determined 30 min. before and after E administration and repeated at 24 h intervals. Results: Pre- and post values (means) are given for the 1st and 2nd dose. Measurements 3 and 4 are follow-ups. *p

The effect of continuous positive airways pressure /CPAP/ on lung mechanics and lung volumes were studied in 12 healthy neonates using a total body plethysmograph. As expected, TGV rose and the resistance fell. Dynamic compliance was calculated from the tidal volume and oesophageal pressure corrected for variations in mouth pressure. The compliance fell in all the infants. One possible explanation was that the CPAP had caused changes in the pulmonary vascular compartment. In a further 12 babies the effect of CPAP was compared to a continuous negative pressure applied to the infant's trunk. Both systems produced similar changes in resistance and compliance. Half the distending pressure was tranferred to the mediastinal structures. Squeezing the chest with a small positive external pressure led to a rise in dynamic compliance. We are unable to explain the fall in compliance produced by the distending pressure. The transfer of half the distending pressure suggests that the compliance of the functioning chest wall is similar to that of the lung over the pressure range studied.

SURFACTANT TA (FUJIWARA) AND DRY SURFACTANT (MORLEY): EFFECTSON LUNG MECHANICS AND ALVEOLAR SIZE DISTRIBUTION IN PREMATURE RABBITS

In clinical practice, lung compliance is often inferred from pressure and volume readings on the respirator dials. These estimates differ from measured lung compliance (CL) in that both pressure and volume are diminished by gas compression, flexing of the tubing and any leaks. Lung compliance was measured using a pneumotach and esophageal balloon and compared with ΔV/ΔP from the dials of the Bourns respirator. 102 data pairs from 25 prematures with HMD at varying stages of the disease were compared. Infants ranged from 14 hours to 48 days in age. The overall correlation between true and calculated compliance was poor, R=.539. The calculated values from the respirator were neither systematically above or below the actual CL values. The problem was random variation. Sources of error include high peak pressures which cause increased compression in the tubing and low apparent CL, leaks in the tubing or respirator, which cause high apparent CL, and inaccuracies in the respirator dials themselves. These data suggest that inferences about lung mechanics from the respirator readings are inaccurate and can be misleading.

SINGLE-BREATH LUNG MECHANICS DURING NEONATAL MECHANICAL VENTILATION: CLINICAL VALUE OF RESPIRATORY RESISTANCE

The effect of PEEP on lung mechanics and on the work of breathing was studied in 8 preterm lambs delivered by cesarean section at 134 days gestation. Indwelling arterial, venous, and tracheal cannulae were placed before clamping the cord. Assisted mechanical ventilation was performed at a tidal volume of 15/ml/Kg and a rate of 30-40/min at FIO2 of 0.95. Measurements of intraesophageal and tracheal pressures, air flow, tidal volume, and functional residual capacity enabled calculation of dynamic compliance (CL), specific compliance (CS), inspiratory resistance (RI), expiratory resistance (RE), and work of breathing at 0, 3, 6, and 10 cm H2O PEEP. Dynamic compliance and CS decreased by 0.11 ml/cm H2O/Kg and 0.0051 1/cm H2O per cm H2O PEEP respectively for PEEP above 3 cm H2O. Functional residual capacity increased (p

PDA ligation has been suggested in patients with HMD and large left to right shunts to improve lung function even in the absence of heart failure. The presumption is that lung mechanics will benefit, even though measurements have not been made to test this hypothesis.