PubMed Health⌕ Search

Biomedical subjects

E Kimmel

Publications and source records attributed to E Kimmel.

At least 19 recordsLinked to original sources
PubMed1995

Lung tissue resistance and hysteretic moduli of lung parenchyma.

Lung tissue resistance (Rti) represents a large and labile component of total pulmonary resistance, but the mechanism is unknown. One hypothesis that has received some support in the literature is that on exposure to contractile agonists airway smooth muscle shortens and then, by the agency of elastic interdependence, induces distortion in surrounding parenchyma. Parenchymal distortion induced in the vicinity of a constricted airway is a pure shear deformation, but currently there are no data available for shear hysteresivity. Guided by a microstructural model, we have assigned stiffness and hysteresivity to microstructural elements and then computed how those properties are expressed at the macroscale in bulk hysteresivities for both shear and volumetric expansion. Hysteresivity for volumetric expansion is shown to be a stiffness-weighted average of hysteresivities of all microstructural components. But as the hysteresivity of microstructural elements increases, that for shear deformation increases to some degree but eventually attains a plateau. Blunted hysteretic response in shear seems to be an intrinsic property of pressure-supported structures, like the lung, that require an inflating pressure to ensure mechanical stability. The analysis indicates that that part of Rti attributable to parenchymal distortion can be at most a small fraction of that attributable to volumetric expansion. These results are purely theoretical in nature, and this suggests that caution is necessary in their interpretation. However, the mechanical basis of the results is sufficiently general to conclude that the hypothesis that parenchymal distortion secondary to bronchoconstriction can account for Rti and its changes seems to be implausible.

Airway Resistance↗
PubMed1993

The steady expiratory pressure-flow relation in a model pulmonary bifurcation.

Experiments were conducted over a range of Reynolds numbers from 50 to 8000 to study the pressure-flow relationship for a single bifurcation in a multi-generation model during steady expiratory flow. Using the energy equation, the measured static pressure drop was decomposed into separate components due to fluid acceleration and viscous energy dissipation. The frictional pressure drop was found to closely approximate that for an equivalent length of curved tube with the same curvature ratio as in the model bifurcation. The sensitivity of these results to changes in airway cross-sectional shape, non-planar configuration, and flow regime (laminar-turbulent) was investigated. In separate experiments using dye visualization and hot-wire anemometry, a transition to turbulent flow was observed at Reynolds numbers between 1000 and 1500. Transition had very little effect on the pressure-flow relation.

Acceleration↗
PubMed1991

Numerical schemes for unsteady fluid flow through collapsible tubes.

The study of fluid flow through compliant tubes is a fluid-structure type problem, in which a dynamic equilibrium is maintained between the fluid and the tube wall. The analogy between this flow and gas dynamics initiated the use of a number of numerical methods which were originally developed to solve compressible flow in rigid ducts. In this study we investigate the solutions obtained by applying the Lax-Wendroff and MacCormack schemes to one-dimensional incompressible flow through a straight collapsible tube. The time-evolving numerical results were compared with exact steady-state solutions. For boundary conditions which were held fixed after a prescribed rise time, the unsteady numerical solution converges to the exact steady-state solution with very good accuracy. The stability and accuracy of all the methods depend on the amount of viscous pressure loss dictated by wall friction. Flows with undamped oscillations cannot, however, be solved with these techniques.

Elasticity↗
PubMed1990

Determination of the toxicity of cyclotriphosphazene hydraulic fluid by 21-day repeated inhalation and dermal exposure.

Cyclotriphosphazene (CTP) ester is one of a series of compounds developed for use as a fire-resistant hydraulic fluid. The most significant routes of industrial exposure to hydraulic fluids are dermal, because of spills or leaks, and aerosol inhalation from pressurized system leaks. This study was designed to evaluate the toxic effects associated with repeated or continuous exposure to CTP by both dermal and inhalation routes. Male and female Fischer 344 (F-344) rats were exposed for 3 weeks to air alone, or to 0.25, 0.50, or 1.00 mg CTP/L. No deaths or signs of toxic stress occurred during the exposure period. A depression in mean body weight gain and increases in numbers of pulmonary alveolar macrophages and renal hyaline droplets were noted in both genders. Male and female New Zealand White (NZW) rabbits were treated dermally for 3 weeks with mineral oil, or 0.25, 0.50, or 1.00 g CTP/kg. No toxic effects were noted in either gender of rabbits.

Administration, Cutaneous↗
PubMed1990

Surface tension and the dodecahedron model for lung elasticity.

Macroscopic elastic moduli governing the incremental deformations of lung parenchyma are calculated on the basis of a model for an individual lung element in the shape of a regular dodecahedron. Elastic stiffness within the element is provided by pin-jointed tension members along the edges of the dodecahedron, surface tension is incorporated into its pentagonal faces, and the influence of transpulmonary pressure is simulated by an externally applied hydrostatic tension. The analysis is based on a variational statement of nonlinear structural mechanics, and the results show how the moduli depend on the effective inflation pressure, the constitutive behavior of the idealized truss members, and the surface-area dependent surface tension. The theory is discussed in the light of available experimental information. A more general analysis is needed to account for the effects of structural as well as surface-tension hysteresis.

Elasticity↗
PubMed1988

Numerical solutions for steady and unsteady flow in a model of the pulmonary airways.

A computational model is presented for unsteady flow through a collapsible tube with variable wall stiffness. The one-dimensional flow equations are solved for inlet, outlet and external conditions that vary with time and for a tube with time-dependent, spatially-distributed local properties. In particular, the effects of nonuniformities and local perturbations in stiffness distribution in the tube are studied. By allowing the flow to evolve in time, asymptotically steady flows are calculated. When simulating a quasi-steady reduction in downstream pressure, the model demonstrates critical transitions, the phenomena of wave-speed limitation and the sites of flow limitation. It also exhibits conditions for which viscous flow limitation occurs. Computations of rapid, unsteady changes of the exit pressure illustrate the phenomena occurring at the onset of a cough, and the generation and propagation of elastic jumps.

Computer Simulation↗
PubMed1987

A cellular model of lung elasticity.

The mechanics of the lung parenchyma is studied using models comprised of line members interconnected to form 3-D cellular structures. The mechanical properties are represented as elastic constants of a continuum. These are determined by perturbing each individual cell from a reference state by an increment in stress which is superimposed upon the uniform stretching forces initially present in the members due to the transpulmonary pressure. A force balance on the distorted structure, together with a force-deformation law for the members, leads to a calculation of the strain increments of the members. Predictions based on the analysis of the 3-D isotropic dodecahedron are in good agreement with experimental values for the Young's, shear, and bulk moduli reported in the literature. The model provides an explanation for the dependence of the elastic moduli on transpulmonary pressure, the geometrical details of the structure, and the stress-strain law of the tissue.

Elasticity↗
PubMed1986

Augmentation of cardiac output and carotid blood flow by chest and abdomen phased compression cardiopulmonary resuscitation.

Phased compression cardiopulmonary resuscitation, whereby the chest and abdomen are compressed sequentially, is a new approach to the classical cardiopulmonary resuscitation technique, which is based on the compression of the chest alone. Six dogs with cardiac arrest were treated by external chest and abdominal compression using a rigid plexiglas suit lined with flexible perithoracic and periabdominal bladders. Fast inflation and deflation of the two independent bladders, together with forced ventilation of the lung, generated phased pressure pulses. The physiological variables monitored throughout the experiment included central venous, left ventricular, and central arterial pressures, carotid blood flow, cardiac output, and acid base balance. The phased compression technique was performed with phased time lags of 0, 150, 300, 400, 600, 700, and 850 ms between the abdominal and thoracic pressure pulses. A random sequence of the different phased compression modes, each lasting for 3-10 minutes, was applied during the prolonged resuscitation procedure that lasted for up to 70 minutes. By starting the abdominal compression 300-400 ms before the thoracic compression the carotid flow index improved by 77% (from 13% with simultaneous compression to 23% with phased compression) and the cardiac output index increased by 65% (from 7.8% with simultaneous compression to 12.5%). The results provide insight into the chest pump concept and the role of intrathoracic and intra-abdominal pressures in generating improved blood circulation during cardiopulmonary resuscitation, and show the advantages of phased compression over chest compression alone and simultaneous chest and abdominal compression.

Animals↗
PubMed1985

Morphologic and physiologic response of lungs to steroid and cigarette smoke: an animal model.

The combined effects of cigarette smoke inhalation and hydrocortisone acetate (HCA) treatment induce prominent abnormalities in lungs of C57BL/6 male mice. These abnormalities include (1) a marked reduction of pulmonary macrophage population which is normally elevated by smoke inhalation, (2) an accumulation of surfactant and flocculent material in alveoli, (3) a decrease in alveolar space surrounded by normal septal tissue, and (4) an increase in hypertrophied alveolar parenchyma. Concomitant with altered lung morphology, lung volume and gas diffusing capacity were significantly compromised in animals subjected to smoke exposure and steroid treatment. It was found that smoke inhalation or HCA administration alone had no ill effects on the animals. The data presented indicate that manifestation of pathologic conditions resembling pulmonary fibrosis and pulmonary alveolar proteinosis is a result of cigarette smoke-drug interaction. The information reported provides a basis for an animal model which might be applicable to assessment of factors related to smoke inhalation and development of pulmonary disorders.

Animals↗
PubMed1985

Intrathoracic and abdominal pressure variations as an efficient method for cardiopulmonary resuscitation: studies in dogs compared with computer model results.

Intrathoracic pressure variations are currently proposed as the main flow-generation mechanisms in standard and modified cardiopulmonary resuscitation (CPR) techniques. A method of changing pressure within the thorax and abdomen without any degree of heart compression was developed and tested in dogs. Intrathoracic and abdominal pressure waves were induced by cyclic inflation and deflation of the lungs and of perithoracic and periabdominal balloons. Various modes of CPR, depending on the rate of cycling, the use of a periabdominal balloon inflation, and a delay between the abdominal and thoracic pressure waves, were studied during ventricular fibrillation. During artificial systole (high intrathoracic pressure phase), the pressure which developed in the right ventricle (96.7 +/- 20.5 mmHg) was higher than the pressure in the aorta (89.3 +/- 20.5 mmHg, p less than 0.001). In artificial diastole (low intrathoracic pressure phase), the right ventricular pressure (11.7 +/- 2.6 mmHg) was lower than the aortic pressure (17.5 +/- 3.3 mmHg, p less than 0.001). The average flow in the carotid artery was 21.7 +/- 7.8 ml . min-1, which was 18 +/- 6% of the baseline carotid flow before CPR. Three different factors were found to improve the efficiency of CPR: periabdominal balloon inflation simultaneous with the intrathoracic pressure waves; increased frequency of the pressure waves from 60 to 100 cycles per minute; and inflation of the periabdominal balloon 50 to 100 ms before the thoracic balloon. Blood-gas and acid-base balance analysis during CPR revealed well-oxygenated arterial blood with a marked respiratory alkalosis and a slowly developing metabolic acidosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdomen↗
PubMed1985

[Spondyloepiphyseal dysplasia tarda].

The authors report on a case of spondyloepiphyseal dysplasia tarda (SDT). The most important clinical and radiological signs are described and the criteria for differential diagnosis listed. Among the bone dysplasias Maroteaux, Lamy and Bernhard distinguished in 1957 a discrete form which they called spondyloepiphyseal dysplasia tarda. The condition was found in 20 patients from four generations of three families studied. SDT is a rare and little-known abnormality of bone development. There have been very few communications concerning this condition. Furthermore, this very rare condition is not considered often enough in differential diagnosis and the findings are often misinterpreted; this also occurred in earlier examinations of the case reported here. As early as 1937, Volhard et al. saw a clinical picture corresponding to this condition in three brothers, but they did not take the malformation to be an autonomous disease; they merely stated that the clinical picture differed from that of Morquio's disease. Giedeon et al. classified the changes found in their patients as being associated with Morquio-Brailsford dysostosis.

Adult↗
PubMed1983

Pulsatile flow in tapered tubes: a model of blood flow with large disturbances.

Blood flow-through segments of large arteries of man, between adjacent bifurcations, can be modeled as pulsatile flow in tapered converging tubes, of small angle of convergence, up to 2 deg. Assuming linearity, rigid tube and homogeneous Newtonian fluid, the physiological flow field is governed by the Navier-Stokes equation with dominant nonlinear and unsteady terms. Analytical solution of this problem is presented based on an integral method technique. The solution shows that even for small tapering the flow pattern is markedly different from the flow obtained for a uniform tube. The periodic shear stresses at the wall and pressure gradients increase both in their mean value and amplitude with increased distance downstream. These results are highly significant in the process of atherogenesis.

Animals↗
PubMedDate not supplied

Blood gas and acid-base balance during cardiopulmonary resuscitation by intrathoracic and abdominal pressure variations.

The blood gases and acid-base balance in a modified cardiopulmonary resuscitation (CPR) technique, based on intrathoracic and abdominal pressure variations by means of circumferential chest and abdominal balloon inflation, were examined in seven mongrel dogs. CPR proceeded for periods lasting 30 min or more and was monitored by measurements of aortic and right ventricular pressures and carotid blood flow during the compression (artificial systole) and the relaxation phase (artificial diastole). The carotid blood flow was 21.7 +/- 7.8 (mean +/- SD) ml/min, which was 0.18 +/- 0.6 (mean +/- SD) of the baseline mean carotid flow. Arterial blood was well oxygenated throughout the experiments, and low PCO2 levels (5-9 mm Hg) caused an initial severe alkalosis (pH = 7.94). However, a gradual decline in the pH was observed, reaching a value of 7.34 +/- 0.11 in the arterial blood after 30 min of CPR. The venous blood had a very low oxygen content (less than 25.5%) with a low PO2 and a normal PCO2 (43.7 +/- 7.3 mm Hg) throughout the experiment. A gradually developing metabolic acidosis was reflected in the pH values, and an increase in base deficit from 2.25 +/- 5.6 meq/1 prior to CPR to 16.7 +/- 3.2 meq/1 after 30 min of CPR was observed. High arteriovenous differences in oxygen content (greater than 66.4%) and CO2 tension (30.1-41.5 mm Hg) with a slowly developing metabolic acidosis were noted. Thus, CPR by thoracic and abdominal pressure variations is associated with a slowly developing metabolic acidosis which is the result of the combination of hyperventilation and a low perfusion state.

Abdomen↗