Transcranial Doppler Pulsatility Index: What it is and What it Isn’t
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Transcranial Doppler (TCD) pulsatility index (PI) has traditionally been interpreted as a descriptor of distal cerebrovascular resistance (CVR). We sought to evaluate the relationship between PI and CVR in situations, where CVR increases (mild hypocapnia) and decreases (plateau waves of intracranial pressure—ICP).
Recordings from patients with head-injury undergoing monitoring of arterial blood pressure (ABP), ICP, cerebral perfusion pressure (CPP), and TCD assessed cerebral blood flow velocities (FV) were analyzed. The Gosling pulsatility index (PI) was compared between baseline and ICP plateau waves (n = 20 patients) or short term (30–60 min) hypocapnia (n = 31). In addition, a modeling study was conducted with the “spectral” PI (calculated using fundamental harmonic of FV) resulting in a theoretical formula expressing the dependence of PI on balance of cerebrovascular impedances.
PI increased significantly (p < 0.001) while CVR decreased (p < 0.001) during plateau waves. During hypocapnia PI and CVR increased (p < 0.001). The modeling formula explained more than 65% of the variability of Gosling PI and 90% of the variability of the “spectral” PI (R = 0.81 and R = 0.95, respectively).
TCD pulsatility index can be easily and quickly assessed but is usually misinterpreted as a descriptor of CVR. The mathematical model presents a complex relationship between PI and multiple haemodynamic variables.
KeywordsCerebral hemodynamics Plateau waves Transcranial doppler Traumatic brain injury
This study was supported by the National Institute of Health Research, Biomedical Research Centre (Neuroscience Theme), the Medical Research Council (Grants G0600986 and G9439390), and NIHR Senior Investigator Awards (JDP); the Hospital Clinic Grant, Barcelona, Spain (NR) and also by the Swiss National Science Foundation (PBBSP3-125550 to CZ), Bern, Switzerland.
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- 18.Brain Trauma F, American Association of Neurological Surgeon, Congress of Neurological Surgeons, et al. Guidelines for the management of severe traumatic brain injury. XIV. Hyperventilation. J Neurotrauma 2007; 24 Suppl 1:S87–S90.Google Scholar