Ellen M. Keough

The contribution of blood flow by the anterior ciliary arteries to the anterior segment in the primate eye

The anterior portion of the eye receives arterial blood from two circulations. One circulation is external to the globe—the anterior ciliary arteries; the other is internal to it—the long posterior ciliary arteries. This study determined the percentage contribution to anterior segment blood flow by anterior ciliary arteries in primates by the reference blood flow method using 15±3 μ103Ru labeled microspheres. Recti muscles were isolated by standard strabismus surgery in both eyes. Next, with one eye serving as a sham-operated control, the fellow eye underwent tenotomy immediately prior to the microsphere injection. The surgical disruption of the external circulation in the experimental eyes significantly reduced (P < 0·01) blood flow to the anterior segment. Anterior segment blood flow values for the tenotomized eyes (0·11±0·03 ml/min/g) were 70–80% less than the control eye values (0·34±0·07 ml/min/g). Therefore, the majority of blood flow to the primate anterior segment is carried by the anterior ciliary arteries.

Aspirin decreases platelet uptake on Dacron vascular grafts in baboons.

The influence of a single dose of aspirin (5.4–7.4 mg/kg) on platelet uptake on 4-mm Dacron interposition grafts was studied in a baboon model using gamma camera scanning for 111-Indium labeled platelets. In vitro assessment of platelet function after aspirin administration revealed that in the baboon, as in the human, aspirin abolished arachidonic acid-induced platelet aggregation, prolonged the lag time between exposure to collagen and aggregation, and decreased plasma thromboxane B1 levels. Aspirin also prolonged the template bleeding time. Scans for 111-Indium labeled platelets revealed that pretreatment with a single dose of aspirin decreased platelet uptake on 4-mm Dacron carotid Interposition grafts. This decrease in platelet uptake was associated with a significant improvement in 2-hour graft patency and with a trend toward improved 2-week patency.

A baboon flow-regulated shunt for the study of small caliber vascular grafts

Synthetic vascular grafts often occlude when used in low-flow high-resistance reconstructions. In order to study the pathophysiology of graft failure a flow-regulated ex vivo shunt was designed for insertion into the baboon femoral artery and vein. Synthetic graft materials (4 mm i.d.) can be placed into the shunt circuit and studied at known rates of flow for uptake of 111In-labeled platelets. Segments of the grafts can be removed from the shunt circuit at specified time intervals for morphologic study with scanning electron microscopy (SEM). In this paper the shunt model is described in detail and early experiments with it are reported. Labeled platelet uptake and SEM studies suggest that flow rate and graft composition influence the deposition of platelets and other blood components on graft surfaces. At high-flow knitted Dacron attracts large numbers of platelets, and becomes covered with a nearly confluent platelet-protein carpet within 1 hr. At low flow platelet uptake and development of the platelet-protein carpet is slower. Polytetrafluoroethylene (PTFE) attracts few platelets at high-flow rates, but at lower-flow rates begins to develop a platelet-protein carpet similar to that seen on knitted Dacron. Flow-related factors influencing platelet deposition are discussed and further experiments to be carried out with this model are described.

Regional ischemia and compensatory vascular dynamics following selective tenotomy in primates

The effect of horizontal (H) and vertical (V) recti tenotomy on blood flow to primate anterior segment was determined using the Reference Blood Flow Method with 15 μm 103Ru labeled microspheres. Tenotomy of the medial and lateral (H) recti resulted in increased blood flow to the whole anterior segment and to the unit iris plus ciliary body with ciliary processes (ICBCP). Blood flow to the medial and inferior quadrants in the H-experimental eyes was significantly higher than in corresponding quadrants of the control. No significant differences were found in the proportion of total ICBCP blood flow received by each quadrant in the control or experimental eye. Tenotomy of the superior and inferior (V) recti in the experimental eye resulted in a decreased blood flow to the whole ICBCP. The medial ICBCP quadrant had a higher blood flow than any of the other quadrants in the V-experimental eye, accounting for approximately 70% of the total ICBCP blood flow. The data suggest that either horizontal or vertical recti tenotomy initiates a compensatory increase in the medial ICBCP quadrant blood flow, possibly via the medial long posterior ciliary artery (mLPCA). A diagrammatic representation of the basal and compensatory vascular dynamics is presented.

Differential organ perfusion in the hypovolemic neonate: A neonatal animal study

Organ blood flow during hypovolemia in a neonatal animal has not previously been measured. Sixteen neonatal piglets were divided into a control group (8) and experimental group (8); the experimentals were bled 20% of their estimated blood volume and after stabilization, 103 Ru microspheres were injected into the left ventricle. The animals were then sacrificed and all organs measured for activity. The reference organ sample method was used. Both cardiac output and blood flows decreased in the hypovolemic state. In order to identify changes in flow different from those caused by a decrease in cardiac output, the perfusion coefficient (V 0 ) was developed. The V 0 is a measure of the change in flow compared to the change in cardiac output. Three flow types were identified using the V 0 . If the V 0 0 >1.10, flow is preferred; and V 0 =0.9–1.10, flow is sustained. All intraabdominal organs had V 0 indicating impaired flow, with the exception of the liver. Portions of the brain had V 0 in the sustained area and other parts had preferred flow as did the left ventricle. The skin and skeletal muscles fell into the impaired flow area. From this study it was apparent that differential organ perfusion occurred in the hypovolemic neonatal piglet. The gastrointestinal tract is sacrificed to preserve cardiac and brain function. The perfusion coefficient (V 0 ) proved to be a valuable tool when comparing changes in flow to various organs in the hypovolemic state.

Comparative ocular blood flow

Abstract 1. 1. Blood flow values for the mammalian anterior uvea were not significantly different among species but was higher than that of the avian anterior uvea. 2. 2. Blood flow to the primate choroid was significantly higher than that of other species. 3. 3. The blood flow ratio which reflects the distribution of total ocular flow was significantly higher in primates than in sheep or geese. 4. 4. The anterior ciliary artery circulation is of major importance to anterior segment blood flow in primates but not in other mammals. 5. 5. Therefore primates are the only suitable models for ischemia following strabismus surgery.