The effect of temperature and shear rate on platelet aggregation

Haemodynamic considerations in the design of a skeletal muscle ventricle

Skeletal muscle ventricles (SMVs) configured to operate as diastolic counterpulsators show promise as cardiac assist devices. In four pigs, SMVs were connected to the aorta by a single-limbed conduit and activated during every third cardiac diastole. During the assisted beats, mean diastolic aortic pressure increased by 30.3 +/- 2.2%, peak diastolic aortic pressure increased by 38.5 +/- 2.7%, the endocardial viability ratio increased by 42.3 +/- 3.4%, and mean left anterior descending coronary artery flow increased by 61.6 +/- 4.5%. Although there are major advantages to making the connection to the aorta by a single-limb conduit, the lack of separation between inlet and outlet means that such devices must be designed carefully to avoid thrombogenesis under chronic conditions. Design rules were developed for this configuration, based on earlier in vitro studies. They addressed the problem of stasis by promoting the development of a propagating vortex that travels the length of the ventricle and ensured proper exchange of blood with the circulation by limiting the volume of the connecting conduit. An SMV compatible with these rules was connected in a pig. At elective termination 1 week later, activation of the SMV increased peak diastolic pressure by 20.1% and reduced left-ventricular stroke work in the post-assisted beat by 10.1%. The SMV was free from thrombus.

Hypothermia-induced platelet aggregation in heparinized flowing human blood: identification of a high responder subpopulation

Cold-induced platelet aggregation (CIPA) in PRP has previously been documented in connection with platelet preservation (4-15 degrees C). This report describes hypothermia-induced platelet aggregation (HIPA) in whole blood and at temperatures used in open-heart surgery (24-32 degrees C). HIPA (specifically, the formation of occlusive aggregates) was studied in human whole blood. Fresh heparinized (1.5 U/ml) human blood was cooled and maintained at target temperatures (15, 20, 24, 28, 32, or 37 degrees C) as it flowed (1 ml/min) through 75-cm long 1/32 inches internal diameter polymer conduit. The formation of aggregates in the tubing was verified using optical video microscopy and was quantified by a light-scattering method and a constant-pressure filtration method. Donors were tested at least twice at each target temperature and were classified into three separate response regimes (Low, Medium, and High) on the basis of the number of aggregates and the duration of their appearance. The screening of 121 donors (average age 22.3 +/- 4.3 years) for HIPA at 24 degrees C (the temperature of maximum response) indicated 14% High Responders, 18% Medium Responders, and 68% Low Responders. HIPA was inhibited by EDTA, citrate, PGE1, and Tirofiban, but not by aspirin, and it was enhanced by elevated heparin levels. HIPA was consistently noted in the blood of a subpopulation of donors, and the associated platelet aggregates in the blood of High Responders were rigid and occlusive. It is postulated that such aggregates may contribute to cognitive dysfunction noted in patients undergoing hypothermic open-heart surgery, and that postulus is being investigated.