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At least 73 records · Page 4Linked to original sources
PubMed2000

Respiratory system inertance: investigation in a physical inertance model.

For analysis of respiratory system mechanics the very complex structure of the respiratory system is strongly simplified to a simple resistance-compliance-model. While for most patients this simplification seems sufficient, in patients with pulmonary disease this model is inappropriate. Additionally, to regional inhomogeneity throughout the lung, large volume accelerations due to the strongly decreased respiratory system compliance together with a mass increase of the patients' lungs, i.e. an increased respiratory system inertance Irs, result in a significant inertive pressure contribution. The aim of this study was to develop a physical inertance model, and its description by conventional methods of respiratory monitoring. Its parameters are adjustable within the physiological range, with Irs between 0.06 and 0.2 mbar.s2.l-1. The model proved well with static and dynamic analysis of respiratory system parameters. Using our physical model it is possible to evaluate new methods of respiratory monitoring and to investigate experimentally the interrelationship of respiratory system parameters.

Airway Resistance↗
PubMed1997

Poor performance and field evaluation of the respiratory system.

A thorough examination of the respiratory system is an important part of the work-up for poor performance in horses. This article provides a systematic approach to field evaluation of horses with poor performance due to respiratory system dysfunction. The information is organized to help the reader evaluate pertinent historical and physical examination findings so that a list of differential diagnoses can be generated. Also, pertinent ancillary diagnostic modalities that can help further characterize and localize causes for respiratory dysfunction in horses presented for poor performance are discussed.

Ambulatory Care↗
PubMed1976

[Mathematical simulation of the respiratory system (author's transl)].

The respiratory system is described as a feedback control system. The controller consists of the peripheral chemoreceptors and the central chemosensitive structures, the respiratory centre in the medulla oblongata and the thorax-lung pump which they drive. The controlled system is comprised of three compartments (lung, brain and the remaining tissue) connected by the blood circulation. The controlled values are arterial pH and arterial O2 partial pressure and cerebral extracellular pH. Earlier models have been improved by: (1) the dead space description, (2) the thermodynamic formulation of the CO2 dissociation equation and the simple but accurate O2 dissociation equation of the blood, (3) the alteration of the CO2 dissociation equation for the brain and the remaining tissue to accommodate recent results, (4) the application of the one-receptor-theory of central chemosensitivity, (5) the pH dependence of brain circulation, (6) the bicarbonate exchange between blood and extracellular fluid of the brain and (7) the introduction of variable circulation times. Respiratory and metabolic disturbances of the respiratory system are analyzed. The mathematical formulation of the respiratory system is a differential difference equation system. In the steady state the experimental results are reproduced fairly well. A slight discrepancy is found in the simulation of metabolic acidosis. Apparently we have assumed the sensitivity of the peripheral chemoreceptors to be too large so that the respiratory response is not correctly predicted. In the numerical solution there is an overshoot in the on-transient and a damped oscillation in the off-transient of the alveolar CO2 partial pressure during respiratory acidosis. We have varied the parameters to make deviations small. The best agreement seems to result, if the central threshold is near the normal extracellular pH of the brain. A further deviation from experimental findings is that the cerebral CO2 and H+ concentration, the blood circulation of the brain, the alveolar O2 partial tension and the ventilation show a slight oscillation in the off-transient. Except for these discrepancies the experimental results, especially the stability of the extracellular pH of the brain, are reproduced fairly well. During hypoxia there are deviations form the experimental results if the central residual activity is constant and the central threshold deviates from the normal extracellular pH of the brain. But if the central residual activity is pH dependent and if the central threshold is equal to the normal extracellular pH of the brain, then the time course of VE and the other variables agree fairly well with experimental results. There is also a good correspondence between the theoretical and experimental data during hyperoxia. During metabolic acidosis the time constant of the bicarbonate exchange between blood and extracellular fluid of the brain is important. If a time constant of one minute is assumed, then the predicted and the experimental results correspond sufficiently well.

Bicarbonates↗
PubMed2004

Elastic properties of the respiratory system in infants with cystic fibrosis.

Respiratory system compliance (Crs) in infants with cystic fibrosis (CF) has been reported as decreased or not different compared with healthy control subjects; however, the reported measurements of Crs were "quasi-static" or by the single-breath occlusion technique, with all measurements limited to tidal lung volume, as well as using inspiratory rather than expiratory pressures. We compared the passive elastic properties of the respiratory system of sleeping infants with CF (n = 10) and healthy control subjects (n = 34) by measuring static deflation pressure--volume (PV) curves from a lung volume at 30 cm H(2)O (V(30)) to FRC. There was no significant difference between the groups for Crs, which was measured as the slope between airway relaxation pressures of 5 and 15 cm H(2)O, the linear portion of the deflation PV curve. In addition, when PV curves were normalized to V(30), there were no differences between the infants with CF and healthy control subjects in the fractional volumes at any airway pressure. The infants with CF had significantly lower forced expiratory flows; however, lower flows did not correlate with fractional volumes measured from the PV curve. Our findings indicate that infants with CF have normal elastic properties of the respiratory system.

Case-Control Studies↗
PubMed1998

Relationship of structure and function of the avian respiratory system to disease susceptibility.

The avian respiratory system exchanges oxygen and carbon dioxide between the gas and the blood utilizing a relatively small, rigid, flow-through lung, and a system of air sacs that act as bellows to move the gas through the lung. Gas movement through the paleopulmonic parabronchi, the main gas exchanging bronchi, in the lung is in the same direction during both inspiration and expiration, i.e., from the mediodorsal secondary bronchi to the medioventral secondary bronchi. During inspiration, acceleration of the gas at the segmentum accelerans of the primary bronchus increases gas velocity so it does not enter the medioventral secondary bronchi. During expiration, airway resistance is increased in he intrapulmonary primary bronchus because of dynamic compression causing gas to enter the mediodorsal secondary bronchi. Reduction in air flow velocity may decrease the efficiency of this aerodynamic valving and thereby decrease the efficiency of gas exchange. The convective gas flow in the avian parabronchus is orientated at a 90 degree angle with respect to the parabronchial blood flow; hence, the cross-current designation of this gas exchanger. With this design, the partial pressure of oxygen in the blood leaving the parabronchus can be higher than that in the gas exiting this structure, giving the avian lung a high gas exchange efficacy. The relationship of the partial pressure of oxygen in the moist inspired gas to that in the blood leaving the lung is dependent on he rate of ventilation. A low ventilation rate may produce a ow oxygen partial pressure in part of the parabronchus, thereby inducing hypoxic vasoconstriction in the pulmonary arterioles supplying this region. Inhaled foreign particles are removed by nasal mucociliary action, by escalator in the trachea, primary bronchi, and secondary bronchi. Small particles that enter parabronchi appear to be phagocytized by the epithelial cells in eh atria and infundibulum. These particles can e transported to interstitial macrophages but the disposition of the particles from this site is unknown. The predominant site of respiratory infections in the caudal air sacs, compared to other parts of the respiratory system, can be explained by the gas flow pathway and the mechanisms present in the parabronchi for particle removal.

Animals↗
PubMed1998

Therapeutic, toxic, and lethal concentrations of 73 drugs affecting respiratory system in human fluids.

BACKGROUND: Drugs affecting the respiratory system are an important group of pharmaceutical specialties in poisoning with relatively high frequency. METHODS: As a continuation of our published studies on the concentrations of drugs of abuse and drugs affecting cardiovascular and hematopoietic systems, we have reviewed the published data to select respiratory drugs on the basis of conservative criteria and our own experience. RESULTS: A compilation of the concentrations of 73 drugs affecting the respiratory system--in whole blood, serum/plasma, and urine, and corresponding to therapeutic, toxic, or lethal concentrations--is given. CONCLUSIONS: The table presented can be helpful in interpretation of the concentrations of this group of medicines encountered in clinical, toxicologic, and forensic cases.

Forensic Medicine↗
PubMed2000

The mammalian respiratory system and critical windows of exposure for children's health.

The respiratory system is a complex organ system composed of multiple cell types involved in a variety of functions. The development of the respiratory system occurs from embryogenesis to adult life, passing through several distinct stages of maturation and growth. We review embryonic, fetal, and postnatal phases of lung development. We also discuss branching morphogenesis and cellular differentiation of the respiratory system, as well as the postnatal development of xenobiotic metabolizing systems within the lungs. Exposure of the respiratory system to a wide range of chemicals and environmental toxicants during perinatal life has the potential to significantly affect the maturation, growth, and function of this organ system. Although the potential targets for exposure to toxic factors are currently not known, they are likely to affect critical molecular signals expressed during distinct stages of lung development. The effects of exposure to environmental tobacco smoke during critical windows of perinatal growth are provided as an example leading to altered cellular and physiological function of the lungs. An understanding of critical windows of exposure of the respiratory system on children's health requires consideration that lung development is a multistep process and cannot be based on studies in adults.

Adult↗
PubMed1984

Oscillatory mechanics of the respiratory system in ozone-exposed rats.

The respiratory system impedance of tracheostomized cardiorespiratory disease-free Sprague-Dawley rats was measured from 20 to 90 Hz at constant flow amplitudes in 10 rats exposed to 0.64 ppm (UV) ozone for 7 days, and eight rats exposed to the same level of ozone for 20 days. This data was compared with respiratory system impedence spectra of 24 normal rats obtained in the same manner. When compared with control, the real part (effective resistance) was significantly different at several frequencies in the 7-day group (P less than 0.05), and group means were higher at all frequencies. The 20-day group showed no significant differences in effective resistance. The imaginary part (effective reactance) was significantly lower at higher frequencies (f greater than 36) in both exposure groups (P less than 0.05). When the impedance curves for each individual were fit to a lumped six-parameter model, and the parameters were compared, only the peripheral resistance parameter of the 7-day group was significantly different from control (P less than 0.05). We conclude that ozone exposure at this level causes changes in respiratory system impedance, that these changes consist primarily of decreased reactances at higher frequencies, and that at 7 days these changes can be modeled by an increase in peripheral resistance.

Airway Resistance↗
PubMed1991

Clinical examination of the respiratory system.

Aspects of a detailed examination of the respiratory system of the horse with suspected respiratory system disease are described. This review includes discussions of the terminology of signs associated with respiratory system disease; radiographic examination of the upper and lower airways and thorax; nuclear scintigraphy; percutaneous and endoscopic tracheal aspiration; bronchoalveolar lavage; electromyography; blood gas analysis; and pleuroscopy and pleural fluid examination.

Animals↗
PubMed1978

Simulated respiratory system for in vitro evaluation of two inhalation delivery systems using selected steroids.

A simulated respiratory system was developed for the in vitro evaluation of two differently designed oral inhalation delivery systems. The deposition properties of a newly designed delivery system used for triamcinolone acetonide were compared to the more conventional, commercially available adapter utilized for an aerosol containing beclomethasone dipropionate. The simulated respiratory system was constructed so that the delivered dose of active ingredient could be classified into two fractions: the fraction that would be deposited in the oral cavity and throat and the fraction that would reach the desired site of activity in the respiratory tract. Based on this method, the newly designed system delivered more than 95% of the labeled dose to the desired site. The beclomethasone dipropionate aerosol system, which was observed to discharge the active ingredient with a greater intensity, delivered approximately 40% of the labeled dose. The particle-size distribution of the dose dispensed from the newly designed delivery system attached to the triamcinolone acetonide aerosol was determined using an impactor technique. No effort was made to correlate these results with an in vivo response.

Aerosols↗
PubMed2000

Analysis of nonlinear volume-dependent respiratory system mechanics in pediatric patients.

OBJECTIVE: Analysis of dynamic respiratory system mechanics is generally based on a resistance-compliance model in which nonlinearities of the respiratory mechanics indices are not considered. The recently developed SLICE method analyzing consecutive volume slices of the tidal volume was used for determination of non-linear volume-dependent respiratory system mechanics. Volume-dependent compliance C(Slice) and resistance R(Slice) were compared with C(MLR) and R(MLR) obtained by standard multiple linear regression analysis (MLR). DESIGN: Prospective observational study. SETTING: Pediatric intensive care unit in a university hospital. PATIENTS: Fifteen pediatric patients, aged 24 days to 9.6 yrs, weighing 3-67.5 kg. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: With respect to their pulmonary status, the patients were grouped into three clinical groups: patients with no lung diseases, patients with restrictive lung diseases, and patients with obstructive lung diseases. All patients were mechanically ventilated via a cuffed endotracheal tube in the pressure-controlled mode. Flow and airway pressure were measured at the proximal end of the tube and tracheal pressure was continuously calculated. Respiratory mechanics were determined either with the SLICE method or, as reference, by using standard MLR. In most patients, the pressure-volume relationship was nonlinear, particularly in patients with restrictive and obstructive lung diseases. In the presence of considerable nonlinearity, the volume-dependent respiratory mechanics indices obtained by the SLICE method showed better agreement between recalculated and original pressure-volume loops compared with the MLR results. Furthermore, signs of overdistension of the patient's lung became obvious when using the SLICE method, whereas they were undetected by MLR. CONCLUSIONS: The SLICE method is well suited for the analysis of nonlinear volume-dependent respiratory system mechanics in pediatric patients. The SLICE method may be used as a first step toward an adaptation of ventilator settings with respect to the actual mechanical status of the patient's respiratory system, and, to prevent pulmonary overdistension.

Journal Article↗
PubMedDate not supplied

The total compliance of the respiratory system during the first year of life.

Respiratory system compliance (Crs) was measured in 34 spontaneously breathing infants during the first year of life. An occlusion technique was used whereby several expiratory occlusions were performed at different lung volumes within the tidal range. The airway opening pressure generated during a plateau after occlusion was related to the volume included above the end-tidal level by a regression equation. The slope of this equation represented the compliance of the infant's respiratory system; the intercept was significantly different for preterm (-0.5 ml) and post-term (-5.5 ml) infants and may represent the difference between end-expiratory lung volume during tidal breathing and the relaxed functional residual capacity. The values for respiratory system compliance were similar to those previously reported for infants during muscle relaxation. As a function of body length, Crs = 1.58 X length3.13 X 10(-4) ml . kPa-1. The technique described is simple to apply and is independent of oesophageal pressure measurements.

Body Height↗
PubMed1991

Birthweight, early passive respiratory system mechanics, and ventilator requirements as predictors of outcome in premature infants with respiratory failure.

Early respiratory mechanics have been reported to predict outcome in newborns with respiratory failure. However, it remains unknown whether measurements of pulmonary function add significantly to the predictive value of more readily available variables The present study was designed to answer this question. Passive respiratory system mechanics were measured by an airway occlusion technique in 104 ventilator-dependent premature infants between 6 and 48 hours of life and corrected for infant size. A ventilation index [FiO2 x mean airway pressure (MAP)] was calculated at the time of pulmonary function testing. Poor outcome was defined as death from respiratory failure or need for supplemental oxygen at 28 days. Stepwise logistic function regression examined whether ventilation index and respiratory mechanics added predictive power over and above birthweight. Five infants died, and 45 patients required supplemental oxygen at 28 days. Birthweight was a strong predictor and would have entered the logistic model first in any case. Ventilation index added significantly to the predictive model (P = 0.038). Respiratory system conductance (P = 0.15) and compliance (P = 0.93) entered on the third and last step, respectively. We conclude that in premature infants with respiratory failure, birthweight is a strong predictor of outcome. Early ventilator requirements but not respiratory system mechanics, add significantly to this predictive model.

Birth Weight↗