Search PubMed⌕ Search

Biomedical subjects

D Elad

Publications and source records attributed to D Elad.

At least 91 records · Page 5Linked to original sources
PubMed1991

Aspergillus clavatus as the probable cause of a lethal mass neurotoxicosis in sheep.

Sprouted barley grains, the waste product of malt extract production, were incriminated as the cause of a lethal (96% mortality) neurotoxic syndrome in sheep fed the grains. Clinical manifestations, comprising tremors, lameness, abnormal gait, paralysis and death indicated a tremorgenic mycotoxicosis. Whilst 50% of the flock died within 17 days, mortality continued over more than 5 months. Pathological findings were limited to neuronal degeneration and necrosis in the midbrain. Germinating grains were shown to be contaminated with growth of Aspergillus clavatus.

Animal Feed↗
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↗
PubMed1991

Shear stress related blood damage along the cusp of a tri-leaflet prosthetic valve.

Blood flowing through a prosthetic heart valve can be damaged by flow-induced shear forces. Fluid dynamics variables and geometric factors play an important role in the evaluation of shear-stress-related blood damage. Central-flow prosthetic valves have been considered as an optimal replacement for mechanical and biological valves. Recently it was shown that shear stress distribution along the surface of a polyurethane cusp reaches values that can damage the blood elements. A mathematical model correlating the effects of shear stresses on blood corpuscles with clinical findings was employed in vitro. The model can be applied to the effects of blood-surface interaction and is of clinical relevance.

Blood Cells↗
PubMed1990

Wall shear stress distribution along the cusp of a tri-leaflet prosthetic valve.

High levels of wall shear stress on the surface of valvular cusps can cause mechanical damage to the blood cells and the cusp surfaces. The shear stresses are also responsible for mechanical failure of prosthetic heart valves. Qualitative measurements of wall shear stress in the vicinity of the leaflets are thus essential for diagnosis of suspected complications and provide important information for the design and fabrication of bioprosthetic heart valves. For this purpose we measured the velocity distribution along the inside wall of the cusps of a tri-leaflet heart valve with a two colour laser Doppler anemometer system. The wall shear stresses on the cusp surface were computed and found to range from 80 to 120 N/m2 during the ejection phase. Wall shear stresses of up to 180 N/m2 were measured in loci of cusp flexure and the accelerated boundary layer. The results of this study show a correlation between the high shear stress loci and the clinically (animal) observed regions of cusp calcification.

Blood Flow Velocity↗
PubMed1990

Neisseria cuniculi in ruminants: epidemiological aspects.

Neisseria cuniculi was isolated, between March 1987 and March 1989, from 38 cases of respiratory disease in small and large ruminants. In all but five cases N. cuniculi was cultured together with other potential respiratory pathogens. A survey was conducted to assess the prevalence of N. cuniculi in the pharyngeal region of Merino and Awassi purebred sheep, Awassi/East-Friesian and Merino/Romanov crossbred sheep and one exotic cross breed (goat/ibex). N. cuniculi was isolated from 80-88% of the animals under 1 month of age. Among older animals, the microorganism was isolated from 20.5% of the pure bred animals and 79.3% of the crossbred ones. This difference was significant (P less than 0.001) by the chi 2 test. The prevalence of N. cuniculi in the second age group coincides with the susceptibility of the breeds to respiratory pathology. This, we believe, is the first report of N. cuniculi involved in multiple cases of respiratory pathology and of a survey assessing the prevalence of this microorganism in small ruminants.

Age Factors↗
PubMed1989

Simulation of airway closure during forced vital capacity.

Airway closure, which disconnects peripheral respiratory units from the trachea, has been observed during expiration to residual volume. It is attributed to dynamic compression that may cause unstable collapse and closure of small airways. During forced vital maneuvers, airway closure is expected to be more significant owing to the maximum expiratory effort. In the present study we have added a simulation of airway closure to the model developed by Elad and associates which simulated flow limitation during forced expiration. Progressive closure is simulated by variation in the number of branches and their cross-sectional areas rather than by change in tube law. The results demonstrate that peripheral airway closure may explain the reduction in maximal flow rate at small lung volumes. It can reproduce either the abrupt fall in maximal expiratory flow-volume curves as observed in dog lungs or the gradual decrease that has been observed in humans.

Airway Resistance↗
PubMed1989

Isolation of Neisseria cuniculi from a case of ovine pneumonia.

Neisseria cuniculi was isolated in pure culture from the lungs of a 2-month-old pneumonic lamb. Mouse LD50, evaluated by intraperitoneal and pulmonary inoculation of the microorganism, was 2 X 10(7) colony-forming units in both cases. The role of the organism in pathogenesis of the disease could not be determined. This organism has not previously been reported in sheep.

Animals↗
PubMed1989

In-vitro evaluation of a valveless cardiac-assist pump.

Diseases of the cardiovascular system are a major health-care problem. Nearly 50% of all deaths are due to cardiovascular disease. A number of cardiovascular patients experience heart failure, mostly of the left ventricle, and require some form of mechanical support. Cardiac-assist devices are used widely in the treatment of patients with damaged heart muscle. Cardiac-assist devices have been introduced recently to maintain circulation in heart failure patients, until a suitable heart transplant donor is found. Earlier types of left ventricular assist devices were the copulsation and the counterpulsation pumps, which increased the efficiency of the vascular system and decreased the workload on the failed heart. In this study, the authors investigated the performance of a valveless cardiac assist device that can be operated in copulsation, counterpulsation, or any intermediate mode with the left ventricle. The device has only one connection to the ascending aorta, no valves, and a common inlet/outlet. The authors measured the hemodynamic parameters in all modes and have suggested an optimal mode of operation in a left ventricular heart failure mode.

Heart Diseases↗
PubMed1989

Parametric evaluation of forced expiration using a numerical model.

Numerical calculations were performed to study the influence of several physiologic parameters on a forced expiration. It was found that the axial distribution of airway compliance produced profound changes in the detailed flow pattern, as characterized by the axial distributions of speed index and area ratio, but had little effect on the flow-volume curve. Similar results were obtained when the expression for frictional losses was changed to reflect new experimental results. In contrast, changes in airway size and geometry altered both the detailed flow pattern and the mean expiratory flow rate. The shape of the flow-volume curve remained unchanged.

Forced Expiratory Flow Rates↗
PubMed1988

A model for the nonlinear elastic response of large arteries.

The nonlinear elastic response of large arteries subjected to finite deformations due to action of biaxial principal stresses, is described by simple constitutive equations. Generalized measures of strain and stress are introduced to account for material nonlinearity. This also ensures the existence of a strain energy density function. The orthotropic elastic response is described via quasi-linear relations between strains and stresses. One nonlinear parameter which defines the measures of strain and stress, and three elastic moduli are assumed to be constants. The lateral strain parameters (equivalent to Poisson's ratios in infinitesimal deformations) are deformation dependent. This dependence is defined by empirical relations developed via the incompressibility condition, and by the introduction of a fifth material parameter. The resulting constitutive model compares well with biaxial experimental data of canine carotid arteries.

Animals↗
PubMed1988

Mathematical simulation of forced expiration.

Flow limitation during forced expiration is simulated by a mathematical model. This model draws on the pressure-area law obtained in the accompanying paper, and the methods of analysis for one-dimensional flow in collapsible tubes developed by Shapiro (Trans. ASME J. Biomech. Eng. 99: 126-147, 1977). These methods represent an improvement over previous models in that 1) the effects of changing lung volume and of parenchymal-bronchial interdependence are simulated; 2) a more realistic representation of collapsed airways is employed; 3) a solution is obtained mouthward of the flow-limiting site by allowing for a smooth transition from sub- to supercritical flow speeds, then matching mouth pressure by imposing an elastic jump (an abrupt transition from super- to subcritical flow speeds) at the appropriate location; and 4) the effects of levels of effort (or vacuum pressure) in excess of those required to produce incipient flow limitation are examined, including the effects of potential physiological limitation.

Airway Obstruction↗
PubMed1988

Tube law for the intrapulmonary airway.

A semiempirical model of a pressure-area relationship for the bronchial airways is developed. It is described by a single similarity law consistent in form with the nonlinear elastic behavior of biological tissue. The tethering effect of the parenchyma is lumped into the wall properties of the bronchi and is included in an effective wall stiffness. The model, which is fitted to the experimental data of Takishima and his associates (J. Appl. Physiol. 38: 875-881, 1975), is lung-volume dependent and is therefore suitable for the analyses of airflow at different lung volumes, especially for modeling of forced expiration.

Airway Resistance↗
PubMed1987

Choking phenomena in a lung-like model.

A simple, continuous, one-dimensional model for the geometry and structure of the bronchial airways is used for the analysis of fluid flow patterns which have been observed in forced expiration maneuvers. Various phenomena within the conducting system associated with flow limitation are investigated: the conditions in which a "choke" (flow limitation) can occur in a compliant system; theoretical flows that are physically impossible; the possibility of having elastic jumps downstream of the choke point; perturbations in the physical parameters of the conducting system.

Airway Obstruction↗
PubMed1986

Inflation waves induced by axial acceleration of the aorta.

The phenomenon of high-amplitude inflation waves resulting from a sharp axial acceleration of the aorta, as may occur in road accidents, is investigated theoretically. The aorta is modeled as an axisymmetric tapered membranic shell (tube) made of an incompressible, nonlinear viscoelastic material with cylindrical orthotropy. It is filled with an inviscid, incompressible fluid whose flow is considered as quasi-one dimensional along the tube axis. The equations of motion of the tube and of the fluid are solved numerically, by using a two-step explicit scheme, for several axial acceleration profiles. The solutions shows that an inflation wave is generated and it propagates in opposite direction to that of the acceleration. The wall stresses, deformations and their time derivatives as well as fluid velocity and pressure are determined along the tube at different time intervals. Peak axial and circumferential stresses are high, with the latter far exceeding the former. These stresses may cause rupture of the aorta.

Acceleration↗
PubMed1985

Clinical pharmacology of apramycin in calves.

The minimal inhibitory concentrations (MIC) of apramycin, a unique aminocyclitol antibiotic, were compared with the MIC of dihydrostreptomycin and neomycin for 323 Salmonella, 178 Escherichia coli and twenty-six Pasteurella multocida isolates recovered from newborn calves. Apramycin exhibited better in vitro anti-bacterial activity than dihydrostreptomycin and neomycin; isolates of Salmonella group B and E. coli resistant to the latter were sensitive to apramycin. The two-compartment open model was appropriate for the analysis of serum apramycin concentrations measured after intravenous (i.v.) administration. The distribution half-life (t 1/2 alpha) of the drug was 28 min, the elimination half-life (t 1/2 beta) was 4.4 h, and the apparent volume of distribution (V1) and the distribution volume at steady state (Vdss) were 0.34 and 0.71 l/kg, respectively. The drug was quickly and completely absorbed after intramuscular (i.m.) injection; peak serum drug concentrations were directly related to the dose administered, they were obtained 1-2 h after treatment and the i.m. t 1/2 beta was 5 h. There was no evidence of drug accumulation in the serum after three daily i.m. injections at 20 mg/kg. More than 95% of the i.v. and i.m. doses were recovered in the urine within 96 h post-treatment but the cumulative percentage of drug recovery in the urine after oral treatment was 11%. The durations of free drug concentrations in the tissues after i.v. and i.m. injection were estimated from the serum drug level data, percent of serum protein binding, Vdss, t 1/2 beta, and the MIC. Computations showed that apramycin should be administered i.m. at 20 mg/kg every 24 h in order to maintain in tissues potentially effective drug concentrations sufficient to inhibit 50% of the Salmonella, E. coli, and P. multocida isolates, and at 12-h intervals to inhibit 90% of the isolates.

Animals↗