Table 2 Definitions used to categorize participants into Transcranial Doppler Ultrasound phenotypes

Normal Flow

 (1) Systolic, diastolic, and mean flow velocity in the middle cerebral artery ± 2 standard deviations (SD) from the age normal value

Hyperaemia

 (1) Systolic, diastolic, and mean flow velocity in the middle cerebral artery ≥ 2 SD above the age normal value AND

 (2) Lindegaard ratio (LR)^a < 3

Low flow

 (1) Systolic, diastolic, and mean flow velocity in the middle cerebral artery ≤ 2 SD below the age normal value AND

 (2) Pulsatility index (PI)^b < 1.2

Microvascular obstruction/alteration

 (1) Systolic flow velocity in middle cerebral artery within 2 SD of the age normal value AND

 (2) Diastolic flow velocity in middle cerebral artery ≤ 2 SD below the age normal value AND

 (3) PI ≥ 1.2

Vasospasm

 (1) Mean flow velocity in the middle cerebral artery ≥ 2 SD above the age normal value AND

 (2) LR ≥ 3

Isolated posterior high flow

 (1) Mean flow velocity in the basilar artery ≥ 2 SD above the age normal value AND

 (2) Mean flow velocity in both middle cerebral arteries within 2 SD of the age normal value

Terminal intracranial hypertension

 (1) Systolic flow velocity in the middle cerebral artery ≤ 2 SD below the age normal value WITH associated systolic spikes on waveform analysis AND

 (2) Absence of or reversal of diastolic flow