8. Subject has known allergy to urethane, nylon, or silicone. 9. Myocardial infarction within 60 days prior to enrollment. 10.History of stroke within 60 days prior to enrollment. 11.History of thrombolytic therapy within two weeks of enrollment. 12.Subject has acute or chronic renal disease (e.g., as measured by a serum creatinine of >2.5 mg/dL or >220 umol/L), or on dialysis.