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

^aLindegaard Ratio (LR) = (Mean flow velocity in the middle cerebral artery/ mean flow velocity in the extra-cranial carotid artery)

^bPulsatility Index (PI) = (Systolic flow velocity-Diastolic flow velocity/Mean flow velocity)