Table 1.

Physiological or pathological factors that contribute to Transcranial Doppler Ultrasound (TCD) flow velocity or waveform alterations

TCD findings are dependent on cerebral perfusion pressure (CPP) and inversely proportional to the cerebrovascular resistance (CVR) [15–21]

ǂTo cause low flow, vasospasm would need to result in > 80% vessel lumen diameter reduction

^*If associated with waveform characteristics such as systolic spikes and absent or reversed diastolic flow

¥It is unknown if PRES represents vasodilation or vasoconstriction in the posterior circulation