Larry O. Reynolds

Diffuse reflectance from a finite blood medium: applications to the modeling of fiber optic catheters.

The scattering and absorption of light by randomly oriented, discretely scattering, red blood cells imbedded in a homogeneous plasma medium can be described by the P1 approximation to the one-speed transport equation, where the cells have the dual role of anisotropic sources for first scattering events and of scattering and absorption sites for subsequent scattering events. Equations for diffuse reflectance defined for a finite size receiver in the plane of a normally incident cylindrical photon beam are derived and compared with experimental data to fundamentally justify the basic sending-receiving characteristics of a fiber optic catheter model. A model of the fiber optic catheter used for the spectrophotometric measurement of oxygen content in blood is developed from the theory and compared with experimental results to further substantiate the theoretical approach.

Application of radiation-grafted hydrogels as blood-contacting biomaterials

Abstract This article reviews the interactions of radiation-grafted hydrogels with blood and its components, both in vitro and in vivo . It has been found that as the hydrogel water content increases for radiation-grafted hydrogels of moderate to high water contents (15–85%) they tend a) to adsorb fewer protein molecules, and to desorb them more readily in vitro , b) to form thrombus but to adhere the thrombi less readily in the in vivo canine ring tests, and c) to cause more rapid formation and greater volumes of platelet microemboli in the ex vivo A-V femoral baboon shunt. At low water contents (below 10%) the grafted HEMA/EMA copolymer “hydrogels” exhibit an unexpected minimum in platelet consumption, which may be related less to the absorbed water in the graft copolymer than to the polymer composition at the surface. These results suggest that special radiation graft copolymer compositions may be selected to fit specific biological needs.

Backscattering of a picosecond pulse from densely distributed scatterers

A theoretical and experimental study of the backscattering characteristics of a picosecond pulse scattered from a dense diffusing medium is presented. The theory uses a diffusion solution to the time-dependent equation of radiative transfer and the formulation of a picosecond range-gating technique. The experimental system consists of a high-power laser range-gating system, based on a picosecond Kerr-effect shutter. The results of experiments carried out on aqueous solutions of latex microspheres agree well with the theoretical calculations, not only in the pulse shape but in the relative magnitudes of the pulse height for different particle sizes and concentrations.

The Importance of Vascular Graft Surface Composition as Demonstrated by a New Gas Discharge Treatment for Small Diameter Grafts

Biomaterial surface chemistry can have an important influence on biologic responses. Vascular graft chemistries may be modified in a number of ways. In this paper we report on a surface treatment using a gas discharge that deposits a thin coating onto the graft surface, significantly changing its surface chemistry, but without measurable change in porosity, compliance, or surface topography. Treatments with tetrafluoroethylene (TFE) gas yield dramatic improvements in both thrombo and emboli resistance of the graft, based on in vitro and ex vivo tests.

Pulmonary microembolism: a cause of lung injury.

Microthrombi found in the pulmonary capillaries in patients dying with post-traumatic pulmonary insufficiency suggests that pulmonary microembolism (PME) may be etiologically important, but a temporal relationship has not been demonstrated. We used a modified Lim-Blaisdell model of PME to cause a severe ischemic soft tissue injury in dogs. The appearance of microaggregates (MA) in the venous circulation was measured using a laser optical scanning technique. The effect of MA on pulmonary physiologic and histologic parameters was measured and compared to control animals. In the ischemic soft tissue injury group, following restoration of local circulation, the platelet count dropped by 72% (P less than 0.00002), the number of MA increased by 800% (P less than 0.00002), the mean pulmonary artery pressure (PA) increased from 15.6 to 32 mm Hg (P less than 0.00002), and electron micrographs of lung obtained at 4 hr after ischemic insult revealed PM with severe lung injury that was consistent with a capillary membrane leak. The control group never demonstrated a significant change in platelets, MA, PA, or histologic lung injury. These findings imply that MA found in the pulmonary microcirculation are temporally related to the development of physiologic and anatomic lung abnormalities.

The Smaller Diameter Vascular Graft — A Biomaterials Challenge

The surface composition of a biomaterial can have an important influence on biologic responses. The surface composition of a synthetic vascular graft may be modified in a number of ways. In this paper we report on a surface treatment using a gas discharge which deposits a thin coating onto the graft surface, significantly changing its surface chemistry, but without measurable change in porosity, compliance or surface topography. Treatments with tetrafluoroethylene (TFE) gas yield dramatic improvements in both thrombo-and emboli-resistance of the graft, based on in vitro measurements and ex vivo tests using a baboon.