Assessment of Thrombelastography and Platelet Life Span in Ovines

Abstract

Ovines are a common animal model for the study of cardiovascular devices, where consideration of blood biocompatibility is an essential design criterion. In the ovine model, tools to assess blood biocompatibility are limited and continued investigation to identify and apply additional assays is merited. Toward this end, the thrombelastograph, clinically utilized to assess hemostasis, was employed to characterize normal ovine parameters. In addition, platelet labeling with biotin was evaluated for its potential applicability to quantify ovine platelet life span. Mean ovine thrombelastograph values were reaction-time: 4.9 min, K-time: 2 min, angle: 64.1°, maximum amplitude: 68.6 mm, actual clot strength: 11.9 Kd/sc, and coagulation index: 1.5. Reaction time was significantly shorter and maximum amplitude, actual clot strength, and coagulation index were all significantly higher when compared to normal human thrombelastograph values suggesting some hypercoagulability of sheep blood. Biotinylation and reinfusion of ovine platelets allowed temporal tracking of the labeled platelet cohort with flow cytometry. These data indicated a mean ovine platelet life span of 188 h with a half-life of 84 h. The collection of these parameters for normal ovines demonstrates the applicability of these techniques for subsequent studies where cardiovascular devices may be evaluated, and provides an indication of normal ovine values for comparison purposes.

Treatment of a flunixin meglumine overdose with intravenous administration of lipid emulsion and therapeutic plasma exchange in a Nigerian dwarf buck kid (Capra aegagrus hircus)

“…The pattern of hypercoagulability in this case mirrors previous reports of small ruminants having increased coagulability, measured by thromboelastography, in comparison to humans and other species 22 . In previous work evaluating caprine response to heparin bolus and constant‐rate‐infusion, goats required higher doses than sheep and humans to reach anticoagulation thresholds (ACT >400 seconds) 19 .…”

“…The pattern of hypercoagulability in this case mirrors previous reports of small ruminants having increased coagulability, measured by thromboelastography, in comparison to humans and other species. 22 In previous work evaluating caprine response to heparin bolus and constant-rate-infusion, goats required higher doses than sheep and humans to reach anticoagulation thresholds (ACT >400 seconds). 19 Other anticoagulation strategies such as regional citrate anticoagulation (RCA) limited to the blood in the extracorporeal circuit could have been attempted to overcome the goat's hypercoagulability.…”

Morphological and cytochemical characteristics of Varanus niloticus (Squamata, Varanidae) blood cells

“…Only mammals have exhibited enucleated platelets while reptiles and birds have nucleated thrombocytes, which are arguably functionally less efficient than mammalian platelets (Martin & Wagner, 2019; Schmaier et al, 2011). The platelets of mammals are relatively short‐lived as the life spans range between 10 days in humans and 5 days in mice (Johnson et al, 2018; Lebois & Josefsson, 2016). Taking in our consideration the mean erythrocyte lifespan in reptiles ranges between 600 to 800 days while in humans it is only 120 days, thrombocytes have a longer lifespan of thrombocytes in reptiles (Louis et al, 2020; Olsson et al, 2020).…”

Difference in coagulation systems of large animal species used in cardiovascular research: a systematic review

“…Sheep are frequently used as a preclinical animal model for the assessment of cardiovascular device function and biocompatibility. Adult sheep have hearts that are similar in size to the human heart for evaluation of implantable devices [10]. Apart from its advantageous anatomical dimensions, another feature of the ovine organism is that it allows for the evaluation of tissue calcification and thus the conduction of hemo-and biocompatibility studies [3].…”