On the use and misuse of cerebral hemodynamics terminology using transcranial Doppler ultrasound: a call for standardization

Abstract

Cerebral hemodynamics (e.g., cerebral blood flow) can be measured and quantified using many different methods, with Transcranial Doppler ultrasound (TCD) being one of the most commonly utilized approaches. In human physiology, the terminology used to describe metrics of cerebral hemodynamics are inconsistent, and in some instances technically inaccurate; this is especially true when evaluating, reporting, and interpreting measures from TCD. Therefore, this perspectives article presents recommended terminology when reporting cerebral hemodynamic data. We discuss the current use and misuse of the terminology in the context of using TCD to measure and quantify cerebral hemodynamics and present our rationale and consensus on the terminology that we recommend moving forward. For example, one recommendation is to discontinue use of the term "cerebral blood flow velocity" in favor of "cerebral blood velocity" with precise indication of the vessel of interest. We also recommend clarity when differentiating between discrete cerebrovascular regulatory mechanisms, namely cerebral autoregulation, neurovascular coupling, and cerebrovascular reactivity. This will be a useful guide for investigators in the field of cerebral hemodynamics research.

Directional sensitivity of dynamic cerebral autoregulation during spontaneous fluctuations in arterial blood pressure at rest

“…18,43 Limitations of the study The use of transcranial Doppler ultrasound generates concerns about the stability of the insonated artery diameter, in our case the MCA, that could lead to distorted results, due to alterations in the relationship between CBFv and absolute flow. 46 In our case, changes in MCA diameter were unlikely to have occurred within each recording, since measurements were obtained during stable poikilocapnia 21,22,47 and significant changes in MCA diameter were only reported at elevated values of hypercapnia. 48,49 Moreover, the ARI index is only dependent on the temporal pattern of the SRMCAv-MAP, and would not be affected by amplitude changes in MCAv or MAP, unless there were relatively fast changes in MCA diameter, say over 2-10 s, something that has never been demonstrated.…”

Transfer function analysis of dynamic cerebral autoregulation: A CARNet white paper 2022 update

“… 1 , 7 , 26 , 27 Historically, the envelope of the TCD output has been referred to as cerebral blood flow velocity (CBFV) in the wider literature, but there is a growing consensus that using the term ‘flow’ is not appropriate, since the physical quantity that is being measured is the average speed of blood across the insonated vessel diameter, and not absolute flow. 28 For this reason, we recommend the use of CBv as the general abbreviation for cerebral blood velocity. Specifying the artery that was insonated, with the abbreviations MCAv, PCAv, or ACAv, for example, is also highly recommended.…”

“…Specifying the artery that was insonated, with the abbreviations MCAv, PCAv, or ACAv, for example, is also highly recommended. 28 With respect to BP, the majority of dCA studies use arterial volume clamping of a finger artery to obtain continuous non-invasive measurements. Importantly, good agreement exists between non-invasive arterial volume clamping and invasive (intra-arterial catheter) techniques, with the former not known to distort time-varying estimates of dCA.…”

Capturing postural blood pressure dynamics with near-infrared spectroscopy-measured cerebral oxygenation

“…To explore this, cerebral hemodynamic responses to standing can be tracked specifically by transcranial Doppler (TCD), which uses ultrasound to measure cerebral blood velocity (CBv) changes, most often in the middle cerebral artery (MCAv). These measurements reflect changes in CBF, provided that the artery diameter remains stable [22]. Until now, no studies have compared the oxygenation responses measured by long and short NIRS channels to postural BP changes.…”