Orthostatic Challenge-Induced Coagulation Activation in Young and Older Persons

Abstract

The incidence of thrombosis increases with aging. We investigated the coagulatory/haemostatic system across the ages and tested the hypothesis that older persons have a hypercoagulable state compared to younger persons at rest, and that standing up (orthostasis) leads to greater changes in coagulation in older persons. In total, 22 older and 20 young participants performed a 6 min sit-to-stand test (orthostatic challenge). Blood was collected prior to and at the end of standing and haemostatic profiling was performed via thrombelastometry (TEM), calibrated automated thrombogram (CAT) and standard coagulation assays. At baseline, three CAT-derived values indicated enhanced capability to generate thrombin in older participants. However, other measured parameters did not suggest a hypercoagulable state in older participants: prolonged TEM-derived coagulation times (295 vs. 209 s, medians, p = 0.0025) and prothrombin times (103 vs. 114%, medians, p = 0.0087), as well as lower TF levels (440 vs. 672 pg/mL, medians, p = 0.0245) and higher t-PA levels (7.3 vs. 3.8 ng/mL, medians, p = 0.0002), indicative of enhanced fibrinolytic capability, were seen. Younger participants were more sensitive to the orthostatic challenge: CAT-derived endogenous thrombin potentials (ETPs) were only increased in the young (1337 to 1350 nM.min, medians, p = 0.0264) and shortening of PTs was significantly higher in the young vs. older participants (p = 0.0242). Our data suggest that the increased thrombosis propensity in older persons is not primarily attributable to a hyperactive coagulation cascade but may be due to other pathologies associated with aging.

Keywords

• aging
• clot formation
• orthostatic challenge
• thrombin generation
• thrombelastometry
• thrombosis