Predictive Value of Cerebrovascular Time Constant for Delayed Cerebral Ischemia after Aneurysmal Subarachnoid Hemorrhage.

Time constant of the cerebral arterial bed (tau) is a transcranial Doppler (TCD) based metric that is expected to quantify the transit time of red blood cells from the insonation point to the arteriole-capillary boundary during a cardiac cycle. This study aims to assess the potential of tau as an early predictor of delayed cerebral ischemia (DCI). Consecutive patients (56 +/- 15 years) treated for aneurysmal subarachnoid haemorrhage were included in the study. tau was assessed through a modelling approach that involved simultaneous recordings of arterial blood pressure and cerebral blood flow velocity (CBFV) from TCD's first recordings. 71 patients were included. 17 patients experienced DCI. tau was significantly shorter in patients who later developed DCI: 187 +/- 64 ms vs. 249 +/- 184 ms; p = 0.040 with moderate effect size (rG = 0.24). Logistic regression showed that there was a significant association between increased CBFV, shortened tau, and the development of DCI (chi 2 = 11.54; p = 0.003) with AUC for the model 0.75. Patients who had both shortened tau and increased CBFV were 20 times more likely to develop DCI (OR = 20.4 (2.2-187.7)). Our results suggest that early alterations in tau are associated with DCI after aSAH. The highest performance of the model including both CBFV and tau may suggest the importance of both macrovascular and microvascular changes assessment.