Physiological Mechanisms and Significance of Intracranial B Waves.

Objective: Recently published studies have described slow spontaneous cerebral blood flow (CBF) and cerebrospinal fluid (CSF) oscillations measured by magnetic resonance imaging (MRI) as potential drivers of brain glymphatic flow, with a similar frequency as intracranial B-waves. Aiming to establish the relationship between these waveforms, we performed additional analysis of frequency and waveform parameters, of our previously published transcranial Doppler (TCD) and intracranial pressure (ICP) recordings of intracranial B waves, to compare to published MRI frequency measurements of CBF and CSF slow oscillations.

Patients And Methods: We analyzed digital recordings of B waves in 29 patients with head injury, including middle cerebral artery (MCA) flow velocity (FV), ICP, end tidal CO, and arterial blood pressure (ABP).

Intraplaque hemorrhage, fibrous cap status, and microembolic signals in symptomatic patients with mild to moderate carotid artery stenosis: the Plaque at RISK study.

Background And Purpose: In patients with mild to moderate symptomatic carotid artery stenosis, intraplaque hemorrhage (IPH) and a thin/ruptured fibrous cap (FC) as evaluated with MRI, and the presence of microembolic signals (MESs) as detected with transcranial Doppler, are associated with an increased risk of a (recurrent) stroke. The objective of the present study is to determine whether the prevalence of MES differs in patients with and without IPH and thin/ruptured FC, and patients with only a thin/ruptured FC without IPH.

Methods: In this multicenter, diagnostic cohort study, patients with recent transient ischemic attack or minor stroke in the carotid territory and an ipsilateral mild to moderate carotid artery plaque were included.

Time course for autoregulation recovery following severe traumatic brain injury.

Object: The aim of the present study was to evaluate the time course for cerebral autoregulation (AR) recovery following severe traumatic brain injury (TBI).

Methods: Thirty-six patients (27 males and 9 females, mean +/- SEM age 33 +/- 15.1 years) with severe TBI underwent serial dynamic AR studies with leg cuff deflation as a stimulus, until recovery of the AR responses was measured.

Asymmetric dynamic cerebral autoregulatory response to cyclic stimuli.

Background And Purpose: Dynamic cerebral autoregulation has been shown to be fast and effective, but it is not well known if the mechanism is symmetric, that is to say, it acts with equal compensatory action to upward as compared with downward abrupt changes in arterial blood pressure (ABP).

Methods: Fourteen patients with head injuries and 10 normal subjects had bilateral transcranial Doppler and continuous ABP recording. Cyclic ABP stimuli were generated by large thigh cuffs, which were rapidly inflated above systolic pressure for 15 seconds alternating with 15 seconds of deflation.

Cerebral autoregulation and vasomotor reactivity.

Various aspects of the cerebral blood-flow regulation can be assessed by transcranial Doppler (TCD). This chapter describes and discusses the approaches that have been reported in the literature. The steady-state characteristics of the cerebral autoregulation can be determined by changing the blood pressure level, and calculating the response of the vasomotors.

Ambulatory transcranial Doppler cerebral embolic signal detection in symptomatic and asymptomatic carotid stenosis.

Background And Purpose: Transcranial Doppler (TCD) ultrasound can detect asymptomatic emboli in carotid stenosis. Current systems are nonportable and can only record for short durations. A novel ambulatory TCD system allows prolonged recording.

Long-term ambulatory monitoring for cerebral emboli using transcranial Doppler ultrasound.

Background And Purpose: Transcranial Doppler (TCD) monitoring for asymptomatic cerebral emboli is currently limited to short recordings by equipment size, restricting its clinical usefulness. We have developed a first ambulatory TCD system, evaluated it in at-risk patient groups, and used it to study the pattern of embolization in patients with symptomatic carotid stenosis.

Methods: The system comprises an 18x11.

Dynamic pressure--flow velocity relationships in the human cerebral circulation.

Background And Purpose: The pressure-flow velocity relationship in the cerebral circulation is characterized by the critical closing pressure (CCP), which is the pressure at which flow ceases, and the linear slope of a plot between pressure and flow velocity. It has been suggested, but not validated, that CCP can be determined from arterial blood pressure (ABP) and transcranial Doppler (TCD) recordings during the cardiac cycle. We studied a group of patients in whom ventricular fibrillation (VF) was induced.

Cerebral blood flow and dynamic cerebral autoregulation during ethanol intoxication and hypercapnia.

More than one-third of patients diagnosed with head injury are intoxicated with ethanol. Most clinical and animal studies have shown alcohol to have a deleterious impact in the setting of cerebrovascular trauma; however, there are also data showing neuroprotective effects in low ethanol doses. Human studies using imaging modalities suggest that small doses of alcohol produce cerebral vasodilatation and higher doses cerebral vasoconstriction.

Autoregulatory response and CO2 reactivity of the basilar artery.

Background And Purpose: Transcranial Doppler has been extensively used to measure cerebrovascular control mechanisms, including autoregulation in humans and in patients with cerebrovascular diseases. There have been sufficient reports on the measurement of normal autoregulatory response (AR) and CO2 reactivity (CR) of the middle cerebral artery (MCA) but few reports of these indices for the basilar artery (BA). We measured AR and CR in the BA in healthy volunteers to determine normal values and compared them with simultaneous measurements made in the MCA.

Transcranial Doppler assessment of cerebral vasospasm.

This review summarizes the use of transcranial Doppler (TCD) for assessment of cerebral vasospasm. The basic hemodynamic principles are presented, and used as a basis for discussing findings and interpretation methods. The need for additional information and measurements to correctly interpret TCD velocities is analyzed, and the use of a special extracranial Doppler technique is recommended.