alpha-Actin: disposition, quantities, and estimated effects on lung recoil and compliance.
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We have investigated the basis and implications of pneumoconstriction by measuring disposition and quantities of alpha-smooth muscle actin in rat and guinea pig lungs and modeling its effects on lung recoil and compliance. A robust marker of contractility, alpha-smooth muscle actin appears in smooth muscle or myofibroblast-like cells in pleura, airways, blood vessels, and alveolar ductal tissues. In each site, we measured its transected area by immunofluorescent staining and frequency-modulated scanning confocal microscopy. We incorporated these data in a model of the parenchyma consisting of an extensive elastic network with embedded contractile structures. We conclude that contraction at any one of these sites alone can decrease parenchymal compliance by 20-30% during tidal breathing. This is due mostly to the stiffness of activated contractile elements undergoing passive cycling; constant muscle tension would have little effect. The magnitude of the effect corresponds with known responses of the lung to hypocapnia, consistent with a homeostatic function in which gas exchange is defended by redistributing ventilation away from overventilated units. (+info)
Pulmonary function changes in normal rats induced by antibody against rat IgE.
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Changes in pulmonary function, as measured by airway conductance and dynamic compliance, in normal rats have been provoked by the administration of a rabbit antisera prepared against rat IgE myeloma protein. The response is specific in that neither anti-IgG nor normal rabbit serum induced pulmonary changes. Pre-treatment with disodium cromoglycate inhibits the bronchospasm in a dose related manner. In addition, drug protection can be demonstrated with as long 1 hr pre-dosing. (+info)
Pulmonary mechanics and diffusion after 'shock lung'.
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Pulmonary function studies performed in seven patients who had recovered from 'shock lung' showed a highly significant decrease of diffusing properties of the lung, a slight loss of lung recoil pressure, and a borderline increase of residual volume with normal vital capacity and total lung capacity. Pulmonary compliance was normal. The interpretation of these findings is discussed. (+info)
Monitoring of nonlinear respiratory elastance using a multiple linear regression analysis.
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The elastic pressure/volume (P/V) curve obtained by the multiple linear regression (MLR) technique using a new model, was compared with the quasi-static P/V points obtained by the rapid airway occlusion technique. Seven infants were studied during mechanical ventilation using a pressure controlled mode. The resistive pressure was subtracted from airway opening pressure, thus determining the elastance related pressure, which was then plotted against the volume to make an MLR-elastance curve. Quasi-static P/V curves of the rapid occlusion technique were constructed by plotting the different inspiratory and expiratory volumes against the corresponding values of the quasi-static airway pressure. The calculated MLR-elastance curves closely fit the experimental quasi-static P/V points obtained by the occlusion technique. There were, however, some discrepancies due to the viscoelastic behaviour of the respiratory system. Although slightly altered by these discrepancies, the multiple linear regression-elastance curves did fit the observed quasi-static pressure/volume characteristics for use in clinical practice. The multiple linear regression technique may prove to be clinically useful by continuous monitoring of respiratory system mechanics during mechanical ventilation. (+info)
Reference values of interrupter respiratory resistance in healthy preschool white children.
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BACKGROUND: Interrupter respiratory resistance (Rint) is reported to be useful in evaluating lung function in poorly collaborating patients. However, no reference values are available from large samples of preschool children using the standard interrupter method. The aim of this study was to define reference Rint values in a population of healthy preschool children. METHODS: Rint was assessed without supporting the cheeks in children with no history of wheeze from six kindergartens. To evaluate the effects of upper airway compliance on Rint in healthy children, an additional group of preschool children with either no history of wheeze or no respiratory symptoms at the time of testing underwent Rint measurements in our lung function laboratory with and without supporting the cheeks. Short term (about 1 minute apart) and long term (mean 2.5 months apart) repeatability of Rint measurements (2 SDs of the mean paired difference between measurements) was also assessed in children referred for cough or wheeze. RESULTS: A total of 284 healthy white children (age range 3.0-6.4 years) were evaluated. Mean inspiratory and expiratory Rint (RintI and RintE) did not differ significantly in boys and girls. Age, height, and weight showed a significant inverse correlation with both RintI and RintE in the univariate analysis with linear regression. Multiple regression with age, height, and weight as the independent variables showed that all three variables were significantly and independently correlated with RintI, whereas only height was significantly and independently correlated with RintE. Supporting the cheeks had no significant effect on RintI (n=29, median 0.673 v 0.660 kPa/l.s, p=0.098) or RintE (n=39, median 0.702 v 0.713 kPa/l.s, p=0.126). Short term repeatability was 0.202 kPa/l.s for RintI (n=50) and 0.242 kPa/l.s for RintE (n=69). Long term repeatability was 0.208 kPa/l.s for RintE (n=26). CONCLUSIONS: We have reported reference Rint values in preschool white children and have demonstrated the usefulness of this technique in assessing lung function in this age group. (+info)
Comparison of lung protection strategies using conventional and high-frequency oscillatory ventilation.
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This study compared pathophysiological and biochemical indexes of acute lung injury in a saline-lavaged rabbit model with different ventilatory strategies: a control group consisting of moderate tidal volume (V(T)) (10-12 ml/kg) and low positive end-expiratory pressure (PEEP) (4-5 cmH(2)O); and three protective groups: 1) low V(T) (5-6 ml/kg) high PEEP, 2-3 cmH(2)O greater than the lower inflection point; 2) low V(T) (5-6 ml/kg), high PEEP (8-10 cmH(2)O); and 3) high-frequency oscillatory ventilation (HFOV). The strategy using PEEP > inflection point resulted in hypotension and barotrauma. HFOV attenuated the decrease in pulmonary compliance, the lung inflammation assessed by polymorphonuclear leukocyte infiltration and tumor necrosis factor-alpha concentration in the alveolar space, and pathological changes of the small airways and alveoli. Conventional mechanical ventilation using lung protection strategies (low V(T) high PEEP) only attenuated the decrease in oxygenation and pulmonary compliance. Therefore, HFOV may be a preferable option as a lung protection strategy. (+info)
Why are infants prone to wheeze? Physiological aspects of wheezing disorders in infants.
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Wheezing in infants is common and increasing in prevalence. Infants are particularly prone to wheezing due to developmental differences in airway mechanics compared to adults. These effects are enhanced in the presence of airway inflammation. Wheezing in infants is related to flow limitation which is a function of airway calibre and airway wall compliance. This review discusses the factors contributing to flow limitation and hence, wheezing. It tries to make the link between risk factors influencing airway structure, and thus function, with particular emphasis on the special physiological peculiarities of infants and lung growth. While in adults inflammation and remodelling alone may explain structural and functional changes in wheezing disorders, this reviews proposes a model emphasising that in infants inflammation, remodelling and airway development have to be considered as a continuously interacting system. (+info)
Is pulmonary resistance constant, within the range of tidal volume ventilation, in patients with ARDS?
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When managing patients with acute respiratory distress syndrome (ARDS), respiratory system compliance is usually considered first and changes in resistance, although recognized, are neglected. Resistance can change considerably between minimum and maximum lung volume, but is generally assumed to be constant in the tidal volume range (V(T)). We measured resistance during tidal ventilation in 16 patients with ARDS or acute lung injury by the slice method and multiple linear regression analysis. Resistance was constant within V(T) in only six of 16 patients. In the remaining patients, resistance decreased, increased or showed complex changes. We conclude that resistance within V(T) varies considerably from patient to patient and that constant resistance within V(T) is not always likely. (+info)