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Biomedical subjects

J D Gaylor

Publications and source records attributed to J D Gaylor.

At least 19 recordsLinked to original sources
PubMed1992

Development of a digital adaptive control system for PO2 regulation in a membrane oxygenator.

Regulation of gas exchange in artificial lungs (oxygenators) during cardiopulmonary bypass is normally achieved by manual control of the gas composition and flow in response to intermittent sampling of the arterial partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2). Manual control often results in abnormal blood gases which have been implicated in patient morbidity as well as influencing perfusion safety. Fine control of PaO2 and PaCO2 may be achieved by a combination of an in-line blood gas monitoring system and a membrane type oxygenator which is automatically regulated. The overall dynamics of the oxygenation process and control system components are complex and have nonlinear, multivariable and time-varying characteristics. Consequently, an adaptive control system approach is necessary. The implementation of a digital self-tuning control regime for PaO2 is described here. The controller is based on an explicit Linear Quadratic Gaussian (LQG) self-tuning control design which is presented using a polynomial equation approach. The controller performance was investigated in in vitro experiments. The self-tuner performed satisfactorily with various sensor/oxygenator combinations for blood flow and temperature load disturbances. In contrast, a nonadaptive (proportional-integral, PI) type of control system was found to be unsuitable.

Carbon Dioxide↗
PubMed1991

An in vitro technique to assess oxygenator potential for respiratory failure therapies.

To assess microporous membrane oxygenators (MMO) for long-term respiratory support, an in vitro test of 4 days duration has been developed. The objective is to screen oxygenators before they undergo expensive animal trials. As a sensitive indicator of performance change, CO2 transfer rates (VCO2) are determined with fresh bovine blood at the start, after 48 hours and after 96 hours of perfusion. Blood is used only for gas exchange evaluation and is replaced with plasma in the intervening periods. Data are obtained at blood flow rates (QB) of 1.0, 1.5 and 2.0 l/min for gas: blood flow ratios (QG:QB) of 2:1 and 5:1. The test has been conducted on Bentley BOS-CM50 oxygenators (n = 10). With heated dry air ventilation there was no significant change in VCO2 with time for all QB and QG:QB combinations. Plasma leakage did not occur into the gas compartment of the MMO. Similar results were obtained with heated humidified air ventilation. The findings are in agreement with existing animal studies of 4-7 days duration.

Animals↗
PubMed1989

Efficient continuous flow washing of red blood cells for exogenous agent loading using a hollow fiber plasma separator.

Red blood cells (RBCs) are naturally occurring and biodegradable and are therefore ideal in vivo exogeneous agent (EA) carriers. Before being loaded with the EAs, the RBCs are washed, a process that normally involves repeated centrifugation with an iso-osmotic solution. Washing the RBCs can be achieved more efficiently and rapidly using a capillary hollow fiber plasma separator until the blood is 99.5% protein free. Here, a separator area of 0.25 m2 was preferentially selected over a 0.5 m2 device because the reduction in RBC washing time associated with the latter was considered insufficient to justify the use of the more costly (0.5 m2) separator. Mathematical modelling of this continuous flow system indicates that washing time is mainly dependent on the volume of blood to be processed and the filtration rate. Using the separator, 300 ml of blood can be washed in less than 15 min.

Buffers↗
PubMed1988

Membrane oxygenators: current developments in design and application.

Cardiopulmonary bypass (CPB) procedures require a blood-gas exchanger (oxygenator) to temporarily replace the respiratory function of the lungs. In the past the majority of CPB procedures have been carried out with bubble oxygenators which effect gas exchange by dispersion of bubbles into the blood. Membrane oxygenators, on the other hand, utilize a hydrophobic gas permeable membrane between the blood and gas phases. Bubble oxygenators are being superseded by membrane types for CPB due to improvements in membrane technology and mass transfer efficiency. These advances are reviewed in this paper and are illustrated by reference to the gas exchange and operating characteristics of a number of clinical oxygenators designed for adult CPB. Membrane oxygenators are also being used for long-term support in the treatment of acute respiratory failure. Operated in a partial bypass circuit, the oxygenator may have to function for several days or weeks. In one particular treatment method, the rate of spontaneous breathing is controlled by the partial or total removal of the metabolic CO2 production by the membrane oxygenator. For this method, known as extracorporeal CO2 removal (ECCO2R), the oxygenator must be optimized for CO2 transfer at low blood flow rates. The suitability of clinical oxygenators for ECCO2R is discussed in terms of gas exchange and functionality over a prolonged operation.

Equipment Design↗
PubMed1987

The preclinical evaluation of the water vapour transmission rate through burn wound dressings.

The control of evaporative water loss, following burn injury, is of major importance to the overall condition of the patient, whether this control is by natural eschar or by a dressing. It is therefore important to preclinically determine the water vapour transmission rate of these dressings, firstly to make comparisons between different materials and secondly to screen prototype materials, under controlled conditions. A preclinical (in vitro) technique is described and the results are given for several commercially available dressings which encompass foam, film and hydrogel material categories.

Bandages↗
PubMed1987

An in vitro assessment of wound dressing conformability.

An in vitro assessment technique has been developed to determine the conformability of wound dressings. The technique employed is based on an inflation technique which provides a measurement of the minimum radius of curvature which a specific dressing will adopt under pressure. A pressure of 40 mmHg was chosen as this had been shown to be the maximum tolerable pressure before the occurrence of tissue breakdown. This radius is then matched to the natural radii of the body surfaces and an assessment of conformability can be made. A series of commercially available dressings have been assessed with respect to their conformability, and to the enhancement of their conformability due to viscoelastic creep behaviour.

Bandages↗
PubMed1987

Evaluation of gaseous transmission (O2 and CO2) through burn wound dressings.

The rates of transmission of oxygen and carbon dioxide through various burn wound dressing materials were determined. The British Standard Vacuum technique was used to determine the Gas Transmission Rate (GTR) of hydrophobic dressings. A Gas to Liquid technique was used to determine the GTR of hydrophilic (water containing) dressings. All the materials tested showed greater GTR values for carbon dioxide than for oxygen. The role of the transmission characteristics of the dressings to influence the wound healing environment is discussed.

Bandages↗
PubMed1987

Burn wound dressings--a review.

Man has dressed wounds since life began many millions of years ago. Since this time many materials have been devised for the intention of dressing wounds. This review indicates the vast range presently available, providing a starting point for those seeking information on this subject.

Bandages↗
PubMed1987

The in vitro gaseous transmission of wound dressings.

The permeation properties of dressings to gases are important to the healing processes. It is necessary that dressings are permeable to water vapour, oxygen and carbon dioxide. A series of commercially available dressings have been assessed in vitro in respect of their permeability characteristics to these gases.

Bandages↗
PubMed1986

The physical effects of an adhesive dressing top layer on burn wound dressings.

Three hydrogels were assessed in respect of water-vapour transmission and conformability. These materials were tested alone and as part of a bilaminate dressing which incorporates an adhesive top layer. The adhesive layer used in this study was a compliant adhesive bandage, marketed under the name Mefix. It was observed that this layer reduced the normally high water-vapour transmission rates of the hydrogels to much lower, clinically more acceptable, levels. Mechanically, the Mefix layer protects the underlying hydrogel, prevents tearing and puncturing but decreases conformability by elastic restraint.

Acrylamides↗
PubMed1986

Preclinical assessment of burn wound dressings.

Preclinical assessment procedures for wound dressings have been established taking into account the important parameters of tensile mechanical properties, conformability to body surfaces, water-vapour transmission and gas permeability. A new test has been specifically developed to assess dressing conformability, while the other parameters were assessed using established techniques. The procedures aid clinicians by providing a screen reducing the number proceeding to full expensive clinical trials. They are also of assistance to manufacturers in their bid to optimize the characteristics of dressings and evaluate candidate materials.

Bandages↗
PubMed1986

Repeated membrane plasma separation with on-line sorbent treatment of plasma in the conscious rat.

Repeated membrane plasma separation with on-line sorbent treatment of plasma was performed in unrestrained and conscious rats, thus avoiding the possible effects of repeated stress and exposure to anesthetic agents. The procedure was well tolerated, even after four consecutive perfusions. Blood flow was 0.7 ml/min, with a transmembrane pressure of 18.6 mm Hg and plasma filtration rate of 0.21 ml/min. This allowed 12 ml of plasma (greater than 1 plasma volume) to be treated within 1 h. Levels of albumin, immunoglobulin G, and C3 remained constant during each perfusion and were not significantly different from those of animals subjected to control procedures. Results obtained from filtrate were comparable at 15 and 60 min with values obtained from whole blood, with sieving coefficients of approximately 1. Leukocyte, erythrocyte, and thrombocyte counts remained unchanged during each plasma perfusion. A progressive rise in leukocyte counts occurred following successive perfusions, but this was true also of animals subjected to control procedures.

Animals↗
PubMed1985

Principles of burn dressings.

Throughout history burn wounds have been treated by covering with dressings of many different materials. The successful application of a burn dressing remains an objective for biomaterial development. This paper examines how the burn wound differs from other skin injuries, the requirements of the ideal burn wound dressing, and reviews the type of dressings available. The dressings in common use in the treatment of burns are compared with the 'ideal' dressing, in so far as it can be defined.

Bandages↗
PubMed1985

Non-pressure treatment of hypertrophic scars.

A silicone gel (Dow Corning X7-9119) has been successfully used in the management of hypertrophic scars. The gel softens and reduces scars in a shorter time period than pressure therapy. Relevant properties of the material and its mode of action have been investigated. The mode of action is unknown, but it is not due to pressure, temperature, oxygen tension or occlusion.

Adolescent↗
PubMed1976

Banked blood microfiltration. I. Microfilter composed of five polyurethane foam layers with graded pore size.

Aggregates of amorphous material which develop with storage of banked blood may be a source of pulmonary microembolism in patients having massive transfusions. In order to remove such debris, blood microfilters have been developed and are in routine clinical use. This paper describes the evaluation of one such filter, the Bentley PF 127 model B, which is composed of five layers of polyurethane foam. The time of filtration as a function of the pressure applied, the number of particles removed, the observed changes in blood cells, and the results of scanning electron microscopy of the filter after filtration of human banked blood, are reported.

Blood Banks↗