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Biomedical subjects

S N Vaslef

Publications and source records attributed to S N Vaslef.

9 recordsLinked to original sources
PubMed1997

Multiple impalement with survival.

An unusual case of multiple impalement by chain-link fence posts is presented in which facial, thoracic, and abdominal injuries were sustained following a rollover motor vehicle crash. Torso impalement injuries are briefly reviewed and guidelines for the management of such injuries are described.

Abdominal Injuries↗
PubMed1994

Computer-assisted design of an implantable, intrathoracic artificial lung.

A semiempirical mathematical model of convective oxygen transport is used to design a new, low pressure loss, implantable artificial lung that could be used as a bridge to lung transplantation in patients with advanced respiratory failure. The mass transfer and flow friction relations pertinent to the design of a cross-flow hollow fiber membrane lung are described. The artificial lung is designed to transfer over 200 ml/min of oxygen at blood flow rates up to 5 L/min. A compact design and a blood-side pressure loss of < 15 mm Hg allows the device to be implanted in the left chest without the need for a prosthetic blood pump. Surgical implantation of the artificial lung would require the creation of inflow and outflow anastomoses. Oxygen would be supplied via an external source. Blood properties, operating conditions, and empirically determined mass transfer and flow properties are all specified and input into a computer program that numerically solves the design equations. Computer-generated values for the device frontal area, blood path length, and fiber surface area are thereby obtained. The use of this computer-assisted design minimizes the need for extensive trial-and-error testing of prototype devices. Results from in vitro tests of a prototype implantable lung indicate that the mathematical model we describe is an accurate and useful tool in the design of hollow fiber artificial lungs.

Algorithms↗
PubMedDate not supplied

Development of an intravascular lung assist device.

Intravascular lung assist devices (ILADs) must provide sufficient gas transport without excessive pressure drop. In vitro studies of fiber-bundle devices determined the effect of geometric configuration on gas transfer efficiency, the amount of surface area needed to achieve sufficient gas transport, and the relationship between gas transport and blood-side pressure drop. ILADs with cross-flow fibers transfer at least 10 times more O2 than parallel flow ILADs of the same surface area, and six to eight times more CO2. Some tested devices with 0.4-0.6 m2 of surface area can transfer 100 ml/min of both O2 and CO2. Configurations with high gas transport, however, often require moderate pressure drops.

Animals↗
PubMedDate not supplied

Design and evaluation of a new, low pressure loss, implantable artificial lung.

The authors designed and tested an artificial lung intended for intrathoracic implantation as a bridge to lung transplantation in chronic pulmonary insufficiency or as an alternative in the treatment of advanced acute respiratory failure. The prototype devices are comprised of 380 microns outer diameter polypropylene matted fibers with a blood path length of 3.5 cm, frontal area of 128 cm2, void fraction (porosity) of 0.53, and surface area of approximately 2.2 m2. Blood flow is external and approximately perpendicular to the fiber bundle, which fits in an extruded, flexible polyethylene terephthalate housing. Inflow and outflow anastomoses are made to the pulmonary artery and the left atrium, respectively, thereby avoiding a prosthetic blood pump. Inlet and outlet gas lines exit through the chest wall. Nine in vitro experiments of oxygen (O2) transfer performance by the device, with water, initially were done. Our previously described semiempirical mathematical model of convective O2 transfer in cross-flow, hollow fiber membrane lungs was applied to the results from the water tests to predict the transfer rates at any set of blood conditions. Five in vitro blood tests were conducted using a single-pass technique to evaluate O2 and carbon dioxide (CO2) transfer rates, measure pressure losses, and compare predicted and measured O2 transfer rates. O2 transfer rates of 150-200 ml/min, and CO2 transfer rates exceeding 200 ml/min, could be achieved at blood flow rates as great as 4 l/min. Pressure drops of approximately 10-20 mmHg were observed at blood flow rates of 2-4 l/min. Preliminary results of device implantation in two pigs indicate the feasibility of achieving clinically significant O2 and CO2 transfer rates with a low blood-side pressure loss.

Animals↗
PubMedDate not supplied

Enhanced oxygen delivery induced by perfluorocarbon emulsions in capillary tube oxygenators.

Previous studies showed that a new generation of perfluorocarbon (PFC) emulsions increased tissue PO2 in the cat retina to a degree that could not be explained by the small increase in arterial O2 content seen after the infusion of low doses of 1 g PFC/kg body weight. It seems that increased O2 delivery at the tissue level after PFC infusion is caused by a local effect in the microcirculation. The authors studies this effect in vitro at steady state in a closed loop circuit, consisting of one of two types of capillary tube oxygenators, deoxygenator(s), a reservoir bag filled with anticoagulated bovine blood or saline (control), and a roller pump, to see if the addition of PFC would have an effect on the PO2 difference (delta PO2) across the capillary tube membrane oxygenator at a blood flow rate of 3 l/min. Perfluorocarbon was added in three incremental doses, each giving about 0.7 vol% of PFC. The delta PO2 across the oxygenator was measured before and after each dose. The mean percent increases in delta PO2 in blood for two types of oxygenators were 19.2 +/- 8% (mean +/- SD, n = 6, P = 0.002) and 9.9 +/- 4% (n = 3, P = 0.05), respectively, whereas the mean percent change in delta PO2 in saline was -4.9 +/- 2% (n = 2, P = 0.2). Inlet PO2s to the oxygenator were only minimally increased. The authors conclude that O2 delivery was significantly enhanced after injection of PFC in blood in this capillary tube model. A near wall excess of PFC particles may account for the augmentation of O2 diffusion in this model.

Animals↗
PubMedDate not supplied

Use of a mathematical model to predict oxygen transfer rates in hollow fiber membrane oxygenators.

A semi-empirical theoretical model of oxygen transfer is used to predict the rates of oxygen transfer to blood in hollow fiber membrane oxygenators over a wide range of inlet conditions. The predicted oxygen transfer rates are based on performance of the devices with water, which is more cost effective and easier to handle than blood for in vitro evaluations. Water experiments were conducted at three different flow rates to evaluate oxygen transfer performance in three commercially available membrane oxygenators. Data obtained from these experiments were used in a computer model to predict the rate of oxygen transfer to bovine blood at specified inlet conditions. Blood experiments were conducted at three different flow rates at a wide variety of inlet conditions, including different pH levels, hemoglobin concentrations, and oxyhemoglobin saturations for the three types of oxygenators. The measured and predicted oxygen transfer rates are closely correlated, which suggests that we have an accurate, reliable method for predicting oxygen transfer in hollow fiber membrane lungs.

Animals↗