Arthur M. Brant

Biomechanics of the arterial wall under simulated flow conditions

A perfusion apparatus is employed to reproduce quantifiable pulsatile hemodynamics within freshly excised canine carotid arteries. From measurements of pulsatile intraluminal and transmural pressure and the dynamic radial motion of the vessel wall, calculations are made of the vascular incremental modulus of elasticity and hoop, axial, and radial wall stresses. The results of this investigation suggest that an increase in transmural pressure from 120/80 to 240/120 mmHg produces a marked elevation in incremental modulus and arterial wall stress. These parameters are reduced when transmural pressure is lowered while maintaining intraluminal pressure at physiologic values.

Effect of variations in pressure and flow on the geometry of isolated canine carotid arteries

A study is described in which the effects of hemodynamics on arterial geometry are investigated in vitro. A novel perfusion apparatus is employed to deliver pulsatile flow through excised canine carotid arteries under carefully controlled conditions. Data of perfused vessel diameter and arterial wall thickness are derived from the radial displacement of the pulsating vessel as measured using a scanning laser micrometer whose accuracy is determined to be 0.0125 mm (0.0005 in). The results of 30 perfusion experiments suggest that the hemodynamic variables of transmural pressure, pulse pressure and flow rate influence vessel size and radial strain. The physiologic implications of these findings are discussed.

Characterization in vitro of the biomechanical properties of anastomosed host artery-graft combinations

An in vitro investigation is described in which the biomechanical properties of several host artery-graft combinations are characterized under realistic hemodynamic environments. Canine carotid arteries served as the host vessel and were anastomosed to one of the following graft materials: 4 mm I.D. thin-walled expanded polytetrafluoroethylene (e-PTFE), 6 mm I.D. thin-walled e-PTFE, modified human umbilical vein, autogenous foreleg vein, and carotid artery. A novel feature of the experimental design is the use of a pulsatile perfusion apparatus that simulates realistic normotensive or hypertensive hemodynamics, including pulse rate, perfusion pressure, and flow rate. Measurements of dynamic transmural pressure and vessel radial motion (determined with a helium-neon laser micrometer) were obtained during pulsatile perfusion. From these data calculation of the mismatch in diameter and elasticity modulus between the host carotid artery and various graft materials is made. The longitudinal propagation of the non-uniform radial displacement associated with the construction of the anastomotic junction is also calculated and presented. The present methodology is directly applicable to testing of other vascular substitutes and provides repeatable and reliable biomechanical data.

Chronic retinal detachment with secondary retinal macrocyst and peripheral neovascularization.

Purpose: To report the association of a retinal macrocyst with peripheral retinal neovascularization that occurred secondary to a chronic, subclinical rhegmatogenous retinal detachment and to illustrate the utility of wide-field fundus photography. Methods: Case Report Results: A 37 year-old male was diagnosed with chronic retinal detachment on routine eye examination. Further evaluation revealed intraretinal hemorrhages and a retinal macrocyst. Diagnosis was confirmed with wide-field fundus photography and fluorescein angiography. Surgery was recommended to repair the retinal detachment, to allow spontaneous resolution of the macrocyst. Conclusion: Chronic, subclinical retinal detachments may rarely be associated with retinal macrocysts and retinal neovascularization. This altered retinal morphology can be delineated on wide-field fundus imaging, which aids in diagnosis and management.

Experimental determination and mathematical model of the transient incorporation of cholesterol in the arterial wall

Experimental data of the radial incorporation of labeled cholesterol [14C-4] into the artery wall is regressed against a mathematical model that predicts macromolecular transport in this biological system. Data is obtained using excised canine carotid arteries that are perfusedin vitro under pulsatile hemodynamic conditions for 2 hr. Vessels are exposed to either normotensive hemodynamics, hypertensive hemodynamics, or simulations in which the rate of flow or vessel compliance is deliberately altered. Several arteries are studied under normotensive conditions following balloon catheter deendothelialization. Transmural concentration profiles of [14C-4] activity are determined by microcryotomy of longitudinal sections of perfused vessels. Nonlinear Marquardt regression on 12 experimental cases yields parameter estimates of effective diffusivity,D and solute filtration velocity,V. Results of this experimental investigation support our hypothesis that hemodynamics and the endothelial lining influence wall flux in intact vessels. Exposure to altered (vs normotensive) hemodynamics is associated with increased incorporation of labeled cholesterol. A similar observation is made for deendothelialized vessels (e.g. a greater accumulation of label and a rise in convective flux). Based upon our companion measurements of vessel wall forces and endothelial cellular morphology accompanying hemodynamic simulations, we suggest that hemodynamically induced alterations to endothelial structures lead to the increased permeability, convection and incorporation that we observe in this work.