Transcranial Doppler for evaluation of cerebral autoregulation

Abstract

Transcranial Doppler ultrasound (TCD) can measure cerebral blood flow velocity in the main intracranial vessels non-invasively and with high accuracy. Combined with the availability of non-invasive devices for continuous measurement of arterial blood pressure, the relatively low cost, ease-of-use, and excellent temporal resolution of TCD have stimulated the development of new techniques to assess cerebral autoregulation in the laboratory or bedside using a dynamic approach, instead of the more classical 'static' method. Clinical applications have shown consistent results in certain conditions such as severe head injury and carotid artery disease. Studies in syncopal patients revealed a more complex pattern due to aetiological non-homogeneity and methodological limitations mainly due to inadequate sample-size. Different analytical models to quantify autoregulatory performance have also contributed to the diversity of results in the literature. The review concludes with specific recommendations for areas where further validation and research are needed to improve the reliability and usefulness of TCD in clinical practice.

Assessment of cerebral autoregulation: the quandary of quantification

“…Likewise, there has been significant clinical interest in the role that CA impairment might play in the causation, progression, and risk of debilitating disorders such as ischemic stroke (9), intracranial hemorrhage (37), and traumatic brain injury (13,14). However, while a wide variety of techniques have been developed and adopted for CA assessment over the last 20 yr (34), there remains no consensus on which approach can be considered the "gold standard." Consequently, many techniques are presently applied, making it difficult to compare and validate results across studies (32).…”

Cerebral autoregulation in pregnancies complicated by diabetes and overweight

“…Cerebral autoregulation was assessed using a combination of transcranial Doppler (TCD) and continuous noninvasive BP measurement 10 and is expressed as the autoregulation index (ARI), with 0 being absent and 9 perfect cerebral autoregulation. 10 Simultaneous TCD evaluation of both middle cerebral arteries (MCAs) was carried out using two 2 MHz pulsed, range-gated probes (Spencer Technologies, Seattle, WA), held in place using a head frame.…”

“…10 Simultaneous TCD evaluation of both middle cerebral arteries (MCAs) was carried out using two 2 MHz pulsed, range-gated probes (Spencer Technologies, Seattle, WA), held in place using a head frame. If only one MCA could be found, that one side was used in the analysis.…”

“…Cerebral autoregulation was determined from the CBFV responses to spontaneous fluctuations in mean arterial BP as described previously using fast Fourier transform (FFT) and compared to 10 template curves proposed by Tiecks et al and used as described in previous studies 8,10 Cerebral haemodynamic parameters are reported as the average over a 7-min baseline recording.…”

Measuring cerebrovascular autoregulation in preterm infants using near-infrared spectroscopy: an overview of the literature

“…Traditionally, transcranial Doppler (TCD) ultrasound is used to measure cerebral blood flow velocity (CBFV) continuously at the bedside to determine dynamic autoregulation [17,18]. Limitations of this noninvasive technique are the assumption of a constant intracerebral vessel caliber, not taking into account the angle of vessel insonation and difficulties with obtaining long and stable recordings.…”