Arteriovenous ECMO for neonatal respiratory support. A study in perigestational lambs.

A study was undertaken to investigate the applicability of the arteriovenous mode of perfusion for partial support of neonatal respiration. Perigestational lambs, delivered by cesarean section, served as the animal model of respiratory distress. Arteriovenous flow was accomplished between a single umbilical artery and vein. A microchannel membrane oxygenator was used to provide partial respiratory support to the newborn lambs. Total systemic flow, pulmonary blood flow, and pulmonary vascular resistance were assessed at various rates of arteriovenous perfusion and correlated with systemic oxygenation. A reduction in right-to-left shunting of blood and pulmonary vascular resistance occurred as arterial oxygenation rose from conditions of hypoxemia to PaO2 values higher than 50 torr. Myocardial performance was not impaired at rates of arteriovenous perfusion below 30 percent of the total systemic flow, as evidenced by normal electrocardiographic tracings, pulmonary capillary wedge pressures, and central venous pressures. Arteriovenous extracorporeal membrane oxgenation (ECMO) may be particularly suitable for use in infants with hypoxia and high pulmonary vascular resistance.

Cardiopulmonary dynamics during arteriovenous perfusion: cardiac output, pulmonary arterial resistance, and right venticular stroke work.

The effects of arteriovenous perfusion on myocardial performance, pulmonary circulatory dynamics, and organ preservation were studied in dogs in order to evaluate the applicability of arteriovenous extracorporeal membrane oxygenation for partial respiratory support. Studies were made on normally oxygenated dogs, on dogs made hypoxic by oxygen deprivation and ventilatory depression, and on dogs with pulmonary injury and moderate pulmonary hypertension induced by injection of oleic acid into the right ventricle. The latter two groups were included to assess the changes that occur in cardiopulmonary dynamics in the presence of hypoxia and pulmonary hypertension. A microchannel membrane oxygenator was employed to provide partial respiratory support to the group of animals with pulmonary injury. The results indicate that no deleterious hemodynamic changes occurred in any of the groups of animals with arteriovenous flow for periods of up to 5 hours at rates corresponding to 20 to 35% of the total cardiac output. Adequate systemic oxygenation was provided by the microchannel oxygenator at these rates of arteriovenous perfusion.

Analysis and comparison of venous air embolism detection methods.

Changes in precordial ultrasonic Doppler patterns in dogs were compared with changes of end-tidal carbon dioxide (EtCO2) and pulmonary arterial pressure (PAP). Possible mechanisms of pulmonary arterial hypertension after air embolism in dogs are discussed. After the injection of air, an immediate change in the Doppler ultrasonic pattern was detected, including a shift of the base line. The duration of change of Doppler patterns varied depending upon the length of time that trapped air remained in the right heart. There was a delay of 15 to 30 seconds before the EtCO2 and PAP responded. In a group of dogs pretreated with 0.3 mg of propranolol per kg, there was a significant decrease in the PAP response due to induced air embolism compared to the control group (P < 0.05). We found that the Doppler ultrasonic device was the most sensitive for detecting venous air embolism at a level as low as 0.05 ml of air per kg compared to 0.25 ml/kg for the PAP and EtCO2 responses.

Experimental determination of wall shear rate in canine carotid arteries perfused in vitro.

The mathematical model of Hung (Tsai and Hung, 1984) is employed to determine the wall shear rate acting on canine carotid arteries perfused in vitro. Model equations for pulsatile flow in a deformable vessel are coupled with experimental data of dynamic pressure drop, flow rate, vessel radius and radial wall motion. Derived quantities, e.g. velocity profiles and wall shear, are obtained for vessels exposed to 'normotensive' hemodynamics, 'hypertension' simulations and perfusions in which the compliance of the vessel wall is deliberately altered. Our results indicate that wall shear varies markedly as a function of the hemodynamic environment. The effects of vessel radius vs flow rate on the development of wall shear are also demonstrated. It is found that convective processes correlate with the magnitude of wall shear in the 'hypertension' simulations. The present findings and complementary published data may explain, at least in part, the variations in vessel wall transport and endothelial cell biology we observe as a function of the hemodynamic environment. For example we have documented that the exposure of canine carotids to 'hypertensive' (vs 'normotensive') hemodynamics is associated with an increased flux of lipoproteins (LDL) into the intima and luminal media. Alternations in wall compliance, on the other hand, profoundly influence endothelial shape, orientation and cytoskeletal array.

Biomechanics of spinal cord injury.

This article summarizes the biomechanical relationship of the spinal column to load stresses with respect to column failure, and the resulting associated central nervous system injury. In addition, it presents pertinent animal research, which has focused onto the development standardized animal spinal cord injury model.

Electromigration of carrier-free radionuclide ions Bismuth complexes in aqueous solutions of oxalic, fumaric and succinic acids.

The overall ion mobilities u of carrier-free radiobismuth have been measured in aqueous solutions of some dicarboxylic acids (H(2)L)-xalic, fumaric and succinic-by means of a new version of the electromigration method in electrolytes consisting of HClO(4)/H(2)L, 0.20m H(+), mu = 0.20m; Na(H)ClO(4)/H(2)L, 0.05m H(+), mu = 0.20m; Na(H)ClO(4)/H(2)L, 0.05m H(+), mu = 0.25m; at 298.15 K. Mathematical processing of the experimental functions u = f([L(2-)]) allowed calculation of the mean individual stability constants K(n) and ion mobilities u degrees of the complex ions [BiL(n)](3-2n), n = 1, 2: [Bi(C(2)O(4))](+), log K(1) = 7.65 (8), u degrees = +2.26 (5) x 10(-4) cm(2). sec(-1).V(-1); [Bi(C(2)O(4))(2)](-), log K(2) = 4.81 (2), u degrees = -1.63 (64) x 10(-4) cm(2).sec(-1).V(-1); [Bi(C(4)O(4)H(2))](+), log K(1) = 6.90 (20); [Bi(C(4)O(4)H(4))](+), log K(1) = 8.76 (48).

Management of a giant middle cerebral artery fusiform serpentine aneurysm with distal clip application and retrograde thrombosis: case report and review of the literature.

Giant fusiform aneurysms are rare vascular anomalies that due to their size are often difficult to manage. We describe one such aneurysm that was managed with a superficial temporal to middle cerebral artery bypass followed by the application of a single clip just distal to the vascular dilation. Follow-up angiography has shown aneurysm obliteration by the process of retrograde thrombosis.

Mechanical and neurological response of cat spinal cord under static loading.

The force/deformation relationship of the exposed spinal cord of cats was studied when the force was gradually applied posteriorly at T10. A linear elastic behavior was identified for deformation less than 0.5 mm, but it was not observed when the static force was no longer supported by the dural sheath. Nonlinear force/deformation, along with a strong hysteresis during a cycle of compression and decompression. The mechanical behavior remained practically the same in a repeated loading if the deformation was less than 2 mm. The motor function of cats did not recover after the cord had been compressed to 4 mm. The associated static force was about 15% of the dynamic force producing the same deformation.

Biomechanical responses to open experimental spinal cord injury.

This study evaluates the dynamic biomechanical responses of the cat spinal cord during experimental impact injury. Temporal deformations of the laminectomized spinal cord were recorded by a high speed camera (1500-3000 frames/sec). The cinematograph revealed large deformations, the cord being compressed to half its posterior-anterior diameter 7 msec after the onset of the impact. Peak impact force produced by a 20 gm mass falling from 15 cm height (300 GCF) averaged about 1.2 pounds, and the corresponding stress acting on the dural surface reached 42 pounds per square inch (or 2200 mm Hg). Both positive and negative pressure waves were found to be propagated in the cerebrospinal fluid.

Stress-strain relationship and neurological sequelae of uniaxial elongation of the spinal cord of cats.

An in vivo experimental method was developed to measure the mechanical or rheological properties of the spinal cord of anesthetized cats. This novel approach resulted in measurements of the tensile force in the cord and the modulus of the spinal cord tissue under longitudinal elongation. Both sensory and motor function of the cats recovered within a week after a spinal cord segment had been stretched by a 50% elongation.

The standardization of experimental impact injury to the spinal cord.

The biomechanical criteria for standardization of experimental impact injury to the spinal cord are derived. The theory is verified experimentally using cats. The undesirable effect due to heavy impounders is discussed. A falling mass of 20 gm and a small impounder 5 mm in diameter with a mass of 0.1 gm are recommended, leaving the momentum of the falling body to be controlled for different degrees of trauma.

Arteriovenous perfusion with the pulmonary assist membrane oxygenator.

The feasibility of employing a recently developed pulmonary assist membrane oxygenator for partial respiratory support in arteriovenous perfusion was studied using small mongrel dogs rendered hypoxic by oxygen depression. The unit is employed along with the conventional ventilation techniques (such as CPAP and PEEP) when the latter alone cannot maintain adequate gas exchange in the lung. The results indicate that poorly oxygenated arterial blood can be upgraded to life-sustaining levels when the bypass flow rate through the oxygenator is in the range of 18-33% of the total cardiac output. No cardiovascular derangements were noted at these arteriovenous flow rates for perfusion periods of four to six hours. The present results demonstrate the feasibility of providing partial support to pulmonary function using the pulmonary assist membrane oxygenator.

Fluid-dynamics modelling of the human left ventricle with dynamic mesh for normal and myocardial infarction: preliminary study.

Pulsating blood flow patterns in the left ventricular (LV) were computed for three normal subjects and three patients after myocardial infarction (MI). Cardiac magnetic resonance (MR) images were obtained, segmented and transformed into 25 frames of LV for a computational fluid dynamics (CFD) study. Multi-block structure meshes were generated for 25 frames and 75 intermediate grids. The complete LV cycle was modelled by using ANSYS-CFX 12. The flow patterns and pressure drops in the LV chamber of this study provided some useful information on intra-LV flow patterns with heart diseases.

Biomechanical and neurological response of the spinal cord of a puppy to uniaxial tension.

An in-vivo experimental method was developed to measure the stress-strain relationship of a spinal cord segment of anesthetized puppies. A pseudo Young's modulus was defined for the linear region followed by a nonlinear rheological behavior of finite strain. Both the sensory response and motor function of the puppies were fully recovered within the 5 days after the spinal cord segment in the first lumbar region was elongated once by 50 percent or less. The usefulness of the in-vivo experiments was further elaborated by demonstrating the large artifacts that could be associated in an in-vitro experiment.