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Variability in preterm lamb lung mechanics after intra-amniotic endotoxin is associated with changes in surfactant pool size and morphometry. Am J Physiol Lung Cell Mol Physiol 287: L992-L998, 2004. First published July 9, 2004; doi: 10.1152/ajplung.00158.2004.--Antenatal exposure to intra-amniotic (IA) endotoxin initiates a complex series of events, including an inflammatory cascade, increased surfactant production and alterations to lung structure. Using the low frequency forced oscillation technique as a sensitive tool for measurement of respiratory impedance, we aimed to determine which factors contributed most to measured changes in lung mechanics. Respiratory impedance data obtained from sedated preterm lambs exposed to either IA injection with saline or 20 mg of endotoxin 1, 2, 4, and 15 days before delivery at 125 days gestation were studied, and association with indexes of standard lung morphometry, inflammatory response, and alveolar surfactant-saturated phosphatidylcholine (Sat PC) pool size was demonstrated. Reduction in tissue impedance with increasing interval between exposure and delivery was evident as early as 4 days after IA endotoxin injection, coinciding with resolution of inflammatory reaction, increased alveolar surfactant pools, and contribution of alveolar ducts to the parenchymal fraction, and a later decrease in the tissue component of the parenchymal fraction. Decreases in tissue damping (resistance) were more marked than decreases in tissue elastance. Log alveolar Sat PC accounted for most variability in tissue damping (88.9%) and tissue elastance (73.4%), whereas tissue fraction contributed 2 and 6.4%, respectively. The alveolar Sat PC pool size was the sole factor contributing to change in tissue hysteresivity. No changes were observed in airway resistance. Despite the complex cascade of events initiated by antenatal endotoxin exposure, variability in lung tissue mechanics is associated primarily with changes in alveolar Sat PC pool and lung morphology. fetal organ maturity; lung compliance; oscillometry; respiratory mechanics

Impact of microvascular circulation on peripheral lung stability. Am J Physiol Lung Cell Mol Physiol 287: L879-L889, 2004. First published June 18, 2004; 10.1152/ajplung.00263.2003.--The involvement of pulmonary circulation in the mechanical properties was studied in isolated rat lungs. Pulmonary input impedance (ZL) was measured at a mean transpulmonary pressure ([Ptp.sub.mean]) of 2 cm[H.sub.2]O before and after physiological perfusion with either blood or albumin. In these lungs and in a group of unperfused lungs, ZL was also measured at [Ptp.sub.mean] values between 1 and 8 cm[H.sub.2]O. Airway resistance ([R.sub.aw]) and parenchymal damping (G) and elastance (H) were estimated from ZL. End-expiratory lung volume (EELV) was measured by immersion before and after blood perfusion. The orientation of the elastin fibers relative to the basal membrane was assessed in additional unperfused and blood-perfused lungs. Pressurization of the pulmonary capillaries significantly decreased H by 31.5 [+ or -] 3.7% and 18.7 [+ or -] 2.7% for blood and albumin, respectively. Perfusion had no effect on [R.sub.aw] but markedly altered the [Ptp.sub.mean] dependences of G and H forced oscillations; alveolar wall; elastin; end-expiratory lung volume

Study of isolated dog lungs reveals that the timing and magnitude of pressure application at the airway entrance is crucial for initiating the avalanche process of alveolar recruitment. Pathological conditions including excessive intrabronchial fluid and reduced pulmonary elasticity may cause changes in this process. A model to describe the process reveals that power-law distributions are similar to that of self-organized critical systems.

ABSTRACT: Background and objective: Selecting ‘healthy’ preschool‐aged children for reference ranges may not be straightforward. Relaxing inclusion criteria for normative data does not affect spirometry z‐scores. We therefore investigated the effect of similarly relaxing inclusion criteria in preschoolers on reference ranges for respiratory impedance (Zrs) using a modified forced oscillation technique (FOT). Methods: The International Study of Asthma and Allergies in Childhood questionnaire classified 585 children into a healthy and five mutually exclusive groups. Zrs was measured between 4 and 26 Hz and resistance (R) and compliance (C) obtained by model fitting. Prediction models were determined using mixed effect models and z‐scores compared between healthy children and the five groups. Results: Zrs data were obtained for 494 participants (4.30 ± 0.7 years) on 587 occasions. Comparison of the Zrs z‐scores between the healthy children and the health groups found significant differences in children with asthma, current wheeze and respiratory symptoms, but not in children born preterm or with early‐life wheeze. Adding these two groups to the healthy dataset had no significant effect on the distribution of z‐scores and increased the size of the dataset by 22.3%. Conclusion: Our data suggest that preschool‐aged children born preterm or with early‐life wheeze can be included in FOT reference equations, while those with asthma, current wheeze and respiratory symptoms within 4 weeks of testing should be excluded. This more inclusive approach results in more robust FOT reference ranges. [ABSTRACT FROM AUTHOR]

ABSTRACT Background and objective Mannitol challenge testing is an established tool for clinical asthma diagnosis, and can be performed outside of specialized respiratory laboratories. Despite applicability in both clinical and non-clinical populations, with different pre-test asthma probabilities, differences in diagnostic properties have not been well explored. This study aimed to quantify the diagnostic utility of mannitol challenge testing for asthma in a community cohort and a symptomatic wheezing subset of this cohort. Methods During the 22-year follow-up of the Western Australian Pregnancy (Raine) Cohort, 772 participants (384 males) completed mannitol challenge and skin prick testing and respiratory health questionnaires, of whom 148 reporting wheeze in the past 12 months were included in a wheezing subset. Results Responsiveness to mannitol had low sensitivity (19%) and high specificity (97%) to identify current asthma in the complete cohort, with positive and negative predictive values ( PPV and NPV) of 45% and 92%, respectively. Within the wheezing subset, sensitivity (19%) and specificity (94%) remained similar, but PPV increased to 79%, and NPV decreased to 52%. Conclusion Our findings support previously reported high specificity and good PPV for mannitol challenge testing in symptomatic wheezing populations, and highlight the need for caution when interpreting mannitol test results in non-clinical populations. [ABSTRACT FROM AUTHOR]