Endothelial cell--seeded four-millimeter Dacron vascular grafts: effects of blood flow manipulation through the grafts.

The objective of this study was to compare the surface thrombogenicities of endothelial cell-seeded small-diameter vascular grafts with those of nonseeded contralateral grafts under conditions of acute controlled low blood flows through the grafts in a canine carotid artery model. Autologous venous endothelial cells seeded in the preclots onto 6 cm sections of 4 mm (internal diameter) double-velour Dacron grafts covered 15% and 80% of graft luminal surfaces at 3 and 5 weeks postsurgically, respectively. Contralateral nonseeded control graft lumina had pannus ingrowth of endothelium across the anastomoses only. There were significant differences in initial carotid graft blood flow rates between seeded and control grafts at both 3 and 5 weeks postsurgically. When blood flow was reduced to 30% of the initial flow levels for 4 hours through these grafts, endothelial cell-seeded grafts maintained patencies and mean blood flow returned to 63.3% and 93% of initial flow levels at 3 and 5 weeks postsurgically, respectively. Few thrombi accumulated. In contrast, thrombi accumulated on nonseeded graft lumina during restricted blood flow. Some nonseeded grafts occluded during low flows, and the ratios of final flow to initial flow were only 28% at 3 weeks and 20% at 5 weeks in these nonseeded grafts. These data demonstrate the efficacy of seeding autologous endothelial cells on small-diameter grafts in this canine model. If technically successful, endothelial cell seeding may provide a protocol for enhancement of the long-term implantation success of small-diameter vascular grafts used for human vascular repair and replacements.

Controlled flow studies in 4 mm endothelialized dacron grafts.

Endothelial cell seeding of 4 mm ID double velour dacron vascular grafts promoted luminal endothelial cell surfacing and improved small-diameter graft performance as evidenced by the following: Flow rates through endothelial cell seeded grafts were higher than through nonseeded control grafts. With increasing postsurgical time the flow rates through seeded grafts increased as a consequence of greater luminal endothelial cell coverage. During low flow conditions endothelial cell seeded grafts retained thrombus-free surface characteristics whereas thrombus accumulated during low flow in nonseeded grafts. Some nonseeded grafts occluded during low flow. The ability of seeded grafts to retain thrombus-free surfaces during low flow increased with increasing postoperative time as a consequence of greater luminal endothelial cell coverage. Endothelial cell seeding is an efficacious approach to maintaining graft patency during conditions of reduced blood flow.

An analogue echogram range gate tracker for clinical echocardiography.

The fundamental purpose of this paper is to present the results of a feasibility study for an on-line, real-time automatic range gate tracker (ARGT) for clinical echocardiography, specifically for the purpose of determining cardiac output noninvasively and in real time. The basic ARGT design represents an implementation of specific algorithms and a system controller that permit user interaction and interpretation of clinical echocardiograms. In its analytical mode, the ARGT automatically tracks cardiac echoes as visually perceived and selected by the user. While tracking specific cardiac echoes, the ARGT converts the complex ultrasonic echogram into a pair of meaningful analogue signals (corresponding to the motion of the anterior and posterior left ventricular walls) from which dimensional information corresponding to dynamic geometric changes of the heart are derived. From the information, the cardiac output is computed in real time.

The role of coronary adrenergic receptors in the response to nitroglycerine and the regulation of large and small vessel resistance.

The role of coronary adrenergic receptors in response to nitroglycerine and in the regulation of large and small coronary vascular resistance was evaluated in two separate studies involving fifteen anesthetized mongrel dog preparations, before and after alpha- and beta-adrenergic blockade, respectively. Coronary blood flow (CBF) was measured through the left anterior descending (LAD) coronary artery by a non-cannulating electromagnetic flow probe. Pressure catheters were inserted into the arch of the aorta and into a distal apical branch of the LAD coronary artery to measure, respectively, aortic pressure (coronary perfusion pressure (PA), peripheral coronary pressure )PC), and coronary artery pressure gradient (PG = PA -PC). End-diastolic resistances to flow were computed as: (a) large coronary end-diastolic resistance (RL = PG/CBF), and (B) small coronary end-diastolic resistance (RS = PC/CBF). Nitroglycerine (NG) alone increased RL to approximately 180--220% of control and reduced RS to about 60% of control, respectively. Following pharmacologic blockade with propranolol (PRO), NG increased RL to about 180% of control and reduced RS to about 60% of control. Following alpha blockade with phenoxybenzamine (PBZ), NG decreased RL to about 78% of control and decreased RS to about 56% of control. It is concluded that while the overall effect of NG on the coronary vascular resistance is one of vasodilation, RL appears to be increased transiently and RS transiently decreased. Alpha adrenergic blockade appears to abolish this response. The increase in RL in response to NG appears to be associated with the systemic hypotensive effect in response to NG. It is proposed that the observed increase in RL is produced by the increase in cardiac sympathetic nerve activity which is initiated by the systemic hypotensive effect of NG.

Computer-assisted method for multi-exponential curve fitting for determining cerebral blood flow.

A computer program has been developed for use in determining cerebral blood flow using an inert radioactive gas. The basic algorithm involves the determination of multiple exponential coefficients from the complex concentration-time function. The exponential coefficients are determined by 'peeling' away slower exponentials complex function one at a time. The procedure involves the use of a small laboratory computer in the interactive graphics mode. The method is currently in use analyzing data in a cerebral vascular research laboratory.

Large vessel impedance in peripheral atherosclerosis.

Recent studies based on an animal model of arterial stenosis have shown that large vessel impedance (ZL), determined from the high-frequency vascular hydraulic impedance of a stenotic femoral arterial bed, is linearly related to the large vessel stenotic resistance, and somewhat independent of distal (small vessel) arteriolar resistance. To determine the applicability of these findings on human subjects with stenotic atherosclerotic lesions, ZL was determined in the femoral arteries of 17 patients (at the time of reconstructive operations) with no (N), mild (AS), and severe (occlusive) atherosclerotic (ASO) disease, and in a group of patients before and after femoral-to-popliteal bypass procedures (FEM-POP). Data were collected under steady-state conditions (SS) and during peak flow after a 30 mg bolus intra-arterial administration of papaverine hydrochloride (PAPAV). The ZL was found to be significantly greater (P less than 0.05) for the ASO group than for the N group at SS and after PAPAV administration. There was no significant difference in ZL between the SS and PAPAV conditions for all groups. The ZL decreased significantly (P less than 0.01) from the pre- to post-bypass conditions (with and without the stenosis), at steady-state and after papaverine hydrochloride administration. Large vessel impedance appears to provide a reliable index of the severity of a large vessel atherosclerotic stenosis, and is indpendent of small vessel resistance in humans. These findings are consistent with those of previous experimental animal studies.