Reaction of blood with artificial surfaces of hemodialyzers. Studies of human blood with platelet defects or coagulation factor deficiencies.

Heparinized human blood was exposed to the dialysis membranes of commercially available pediatric size hemodialyzers in an in vitro flow circuit. Bloods from normal subjects and from patients with various blood coagulation and platelet function deficiencies were tested in this model system. In most cases, there was a heavy linear deposit of leukocytes on the dialysis membrane overlying support structures. In other areas, the cellular deposit was less uniform and consisted of single platelets, platelet aggregates, leukocytes, and occasional fibrocellular microthrombi. The number of adherent platelets was smaller in tests with blood from patients with congenital afibrinogenemia, factor XII deficiency, severe von Willebrand's disease, and thrombasthenia then in tests with blood from normal subjects or hemophilic patients. Hence, fibrinogen, factor XII, the von Willebrand factor, and a normal platelet plasma membrane appear necessary for adhesion of platelets to dialysis membranes.

A nonhuman primate vascular shunt model for thrombus generation.

A nonhuman primate model for thrombus generation was developed. Three different types of test devices constructed of polystyrene or polyethylene-Silastic were exposed to flowing blood in arterioarterial or arteriovenous vascular shunts in rhesus monkeys. The test device design included a simple tube, a vortical flow device, and a turbulent flow device. The amount of thrombus deposited within each individual test device after a 15-minute exposure to blood flowing through the shunt was determined gravimetrically. These studies indicate that a test device designed to include an area of vortical flow generated the greatest amount of thrombus. Test devices fabricated from polystyrene consistently generated larger thrombus deposits than did similar test devices fabricated from polyethylene-Silastic. Arteriovenous shunts proved superior to arterioarterial shunts in that flow was predictable in the former and unpredictable in the latter; venovenous shunts thrombosed quickly. Hematologic studies indicated a progressive fall in platelet count during the 4-hour test interval in all animals, whereas in only a few animals were there a shortening of partial thromboplastin time values, a fall in fibrinogen levels, and the appearance of fibrin degradation products. An optimal model for thrombus generation appears to include vortical flow test devices fabricated of polystyrene exposed to flowing blood in an arteriovenous shunt.

Effects of antithrombotic agents evaluated in a nonhuman primate vascular shunt model.

The effects of aspirin, cyproheptadine, dextran, dipyridamole, and sulfinpyrazone on thrombus deposition were determined. These antithrombotic agents were evaluated in a nonhuman primate model for thrombus generation that employed test devices exposed to blood in an arteriovenous shunt. Thrombus deposition on test devices was quantitated gravimetrically. Of the antithrombotic agents tested, cyproheptadine was found to be the most effective, and aspirin, dextran, and dipyridamole were each somewhat less effective. Sulfinpyrazone had only a slight antithrombotic effect. Ultrastructual studies of thrombus deposited in test devices showed that the various antithrombotic agents tested did not prevent completely the formation of fibrin, aggregation of platelets, or adhesion and spreading of platelets and leukocytes. This model for thrombus generation is felt to be a more efficient means for evaluating antithrombotic agents than previously described nonhuman primate models.

Dynamics of thrombus formation on an artificial surface in vivo. Effects of antithrombotic agents.

A nonhuman primate model for in vivo evaluation of antithrombotic agents is described. In this model, the formation of a thrombus on a segment of Silastic tubing placed in the vena cava of a rhesus monkey is utilized to evaluate the effectiveness of antithrombotic agents. Thrombus formation in this model was found to occur rapidly, but this initial deposit quickly was followed by a reduction in thrombus weight. Eventually, after 2 hours of implantation of the test device, thrombus weight again increased and reached an apparent plateau. Three different antithrombotic agents were evaluated with this model. Warfarin therapy was found to decrease the thrombus weight in approximate proportion to its effect on the prothrombin time. Aspirin and dextran each produced a decrease in thrombus weight in 2 of 3 animals tested. Individual differences in response to thrombotic agents are apparent, but despite this, the model appears to offer advantages for in vivo evaluation of antithrombotic agents.

Blood components deposited on used and reused dialysis membranes.

Hemodialysis cartridges used once and reused once or twice were examined by scanning and transmission electron microscopy. Blood deposits consisting of leukocytes, platelets, and amorphous material covered 15 to 25% of the dialysis membrane surface of cartridges used once. This deposit increased somewhat with cartridge reuse but did not appear to impair the dialysis efficiency of membranes significantly. Leukocytes formed a major part of the blood deposit and spreading of these cells upon dialysis membranes was marked. Single and aggregated platelets were adherent to the dialysis membranes, to leukocytes, and to amorphous debris. Few erythrocytes were present, and fibrin was not identified. There was little evidence for build up or layering of the blood deposit with cartridge reuse. The procedures for dialysis cartridge rinsing used in these studies appear to be highly efficient in removal of adherent blood components.

Reactivity of blood with biomaterials in vitro: evaluation of some in vitro test systems for estimation of the blood compatibility of biomaterials.

Several different in vitro tests designed to estimate the degree of compatibility of blood with biomaterials have been examined to determine possible effects of donor or donor-material interaction. Statistical evaluation of data was performed, and adequate data were collected with each different test system to render such evaluation meaningful. Isolated examples of donor and donor-material interaction were detected, but these proved to be minor or insignificant in each case. Data are presented for each of the in vitro test systems examined to indicate the number of replicate determinations required for observed differences to be significant at the 5% level.

Some interactions of blood with tubular biomaterials.

Native human blood was exposed to polyethylene, poly(vinyl chloride), and Silastic tubing for varying time intervals, following which the relative degree of activation of the intrinsic coagulation system and alterations in cell counts were determined. The effects of pre-exposure of Silastic to purified albumin, high-density lipoprotein, or protein polysaccharide upon subsequent reactivity of blood with these surfaces was determined. In addition, the effects of aspirin, dextran, heparin, and Warfarin on reactivity of blood with Silastic were determined. In each case, changes in coagulation and cell counts were correlated with ultrastructural features of test surfaces following their exposure to blood. Pre-exposure of Silastic to purified proteins had relatively little effect upon subsequent reactivity with blood, while the presence of antithrombotic agents produced numerous changes.

Experimental interactions of components of hemodialysis units with human blood.

An in vitro model test system for estimation of the blood compatibility of hemodialysis membranes and tubing is described. The model test system consists of a modified hemodialysis unit and blood pump through which fresh citrated human blood is circulated. The effects of the use of different pump and tubing types upon hematologic and blood coagulation parameters are described. Preexposure of test surfaces to albumin appeared to enhance blood compatibility characteristics of the model test system, whereas preexposure to a high density lipoprotein preparation or a proteinpolysaccharide preparation was without appreciable benefit. Use of blood from subjects receiving aspirin resulted in enhanced blood compatibility in the test system as did use of heparin. Use of Warfarin or dextran did not appear to enhance blood compatibility of test surfaces under the conditions of this test system. Dialysis membranes and tubing which formed parts of the test system were examined by scanning and transmission electron microscopy in control tests and in tests for effects of proteins and antithrombotic agents.