Original Articles

Neurocritical Care

, Volume 17, Issue 1, pp 58-66

First online:

Transcranial Doppler Pulsatility Index: What it is and What it Isn’t

  • Nicolás de RivaAffiliated withDivision of Neurosurgery, Department of Clinical Neurosciences, Addenbrooke’s Hospital, University of CambridgeDepartment of Anesthesiology, Hospital Clinic, Universitat de Barcelona
  • , Karol P. BudohoskiAffiliated withDivision of Neurosurgery, Department of Clinical Neurosciences, Addenbrooke’s Hospital, University of Cambridge
  • , Peter SmielewskiAffiliated withDivision of Neurosurgery, Department of Clinical Neurosciences, Addenbrooke’s Hospital, University of Cambridge
  • , Magdalena KasprowiczAffiliated withDivision of Neurosurgery, Department of Clinical Neurosciences, Addenbrooke’s Hospital, University of CambridgeInstitute of Biomedical Engineering and Instrumentation, Wroclaw University of Technology
  • , Christian ZweifelAffiliated withDivision of Neurosurgery, Department of Clinical Neurosciences, Addenbrooke’s Hospital, University of CambridgeDepartment of Neurosurgery, University Hospital of Basel
  • , Luzius A. SteinerAffiliated withDivision of Neurosurgery, Department of Clinical Neurosciences, Addenbrooke’s Hospital, University of CambridgeDepartment of Anaesthesia, Lausanne University Hospital
  • , Matthias ReinhardAffiliated withDivision of Neurosurgery, Department of Clinical Neurosciences, Addenbrooke’s Hospital, University of CambridgeDepartment of Neurology, University of Freiburg
  • , Neus FábregasAffiliated withDepartment of Anesthesiology, Hospital Clinic, Universitat de Barcelona
  • , John D. PickardAffiliated withDivision of Neurosurgery, Department of Clinical Neurosciences, Addenbrooke’s Hospital, University of Cambridge
    • , Marek CzosnykaAffiliated withDivision of Neurosurgery, Department of Clinical Neurosciences, Addenbrooke’s Hospital, University of CambridgeInstitute of Electronic Systems, Warsaw University of Technology Email author 

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Abstract

Background

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).

Methods

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.

Results

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).

Conclusion

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.

Keywords

Cerebral hemodynamics Plateau waves Transcranial doppler Traumatic brain injury