Transcranial Doppler Technique Research Articles

Comparison of transcranial doppler ultrasound indices in large and small vessel disease cerebral infarction

Background: Atherosclerotic involvement of large and small cerebral arteries leading to infarction is among the most prevalent subtypes of stroke worldwide. The hemodynamic changes due to these arterial pathologies can be studied non-invasively and in real-time by using transcranial Doppler (TCD) techniques. TCD indices of the studied arteries may guide the clinician in differentiating these two underlying arterial pathologies. Methods: A cross-sectional study of patients with small and large vessel types of cerebral infraction based on the Trial of ORG 10172 in Acute Stroke Treatment (TOAST) stroke classification was undertaken in the inpatient population of neurology service of Razi Hospital, Tabriz, Iran, from October 2018 to October 2019. After clinical diagnosis, all cases underwent TCD studies, brain magnetic resonance imaging (MRI), and brain and cervical four-vessel magnetic resonance angiography (MRA). The results of TCD indices related to major arteries of the circle of Willis were tabulated and compared between large and small vessel subtypes of cerebral infarction. Results: A statistically significant difference between right middle cerebral artery (MCA) pulsatility index (PI), left MCA PI, right internal carotid artery (ICA) PI, end-diastolic velocity (EDV), left ICA PI, left ICA EDV, left anterior cerebral artery (ACA) PI, and right vertebral artery (VA) PI measures of the two groups was seen (P < 0.05). In comparison to the large vessel group, left ACA, right VA, and bilateral MCAs and ICAs in the small-vessel stroke group demonstrated an elevated PI. Conclusion: A significant increase of PI occurs in the majority of intracranial arteries of patients with small vessel stroke. This makes PI a valuable marker for differentiating strokes with different underlying pathophysiologies.

Intraoperative Neurophysiology and Transcranial Doppler for Detection of Cerebral Ischemia and Hyperperfusion During Carotid Endarterectomy

To evaluate and compare efficacy of intraoperative neurophysiological monitoring (IONM) and intraoperative transcranial Doppler (TCD) techniques for identification of hypoperfusion during carotid artery clamp and hyperperfusion after release of occlusion during carotid endarterectomy. This was a retrospective, consecutive case series of 152 patients undergoing carotid endarterectomy between June 2018 and March 2020. Somatosensory evoked potentials, motor evoked potentials, electroencephalogram, and TCD were obtained. Three patient cohorts were observed after clamping the carotid artery: A, in 132 of 152 patients (87%), TCD blood flow velocity decreased by <50% and there were no changes in IONM; B, in 5 of 152 (3%) patients, TCD blood flow rate was reduced 50%-100% with no changes in IONM; C, in 15 patients (10%), blood flow velocity was reduced by 50%-100% and all IONM modalities met warning criteria. With increased blood pressure, IONM and blood flow velocities improved to less than warning criteria in 8 of 15 patients. In 6 of the 7 remaining patients, IONM modalities recovered to baseline immediately after clamps were removed from the carotid artery. The 1 patient with persistent motor evoked potential deterioration experienced postoperative proximal muscle weakness, which recovered 48 hours later. In 22 patients, TCD detected hyperperfusion at the moment of clamp release. TCD blood flow velocity is correlated with motor evoked potential and somatosensory evoked potential amplitude changes after clamping. After declamping, TCD can detect hyperperfusion and help regulate blood pressure to prevent hyperperfusion.

Human ophthalmic artery as a sensor for non-invasive intracranial pressure monitoring: numerical modeling and in vivo pilot study

Intracranial pressure (ICP) monitoring is important in managing neurosurgical, neurological, and ophthalmological patients with open-angle glaucoma. Non-invasive two-depth transcranial Doppler (TCD) technique is used in a novel method for ICP snapshot measurement that has been previously investigated prospectively, and the results showed clinically acceptable accuracy and precision. The aim of this study was to investigate possibility of using the ophthalmic artery (OA) as a pressure sensor for continuous ICP monitoring. First, numerical modeling was done to investigate the possibility, and then a pilot clinical study was conducted to compare two-depth TCD-based non-invasive ICP monitoring data with readings from an invasive Codman ICP microsensor from patients with severe traumatic brain injury. The numerical modeling showed that the systematic error of non-invasive ICP monitoring was < 1.0 mmHg after eliminating the intraorbital and blood pressure gradient. In a clinical study, a total of 1928 paired data points were collected, and the extreme data points of measured differences between invasive and non-invasive ICP were − 3.94 and 4.68 mmHg (95% CI − 2.55 to 2.72). The total mean and SD were 0.086 ± 1.34 mmHg, and the correlation coefficient was 0.94. The results show that the OA can be used as a linear natural pressure sensor and that it could potentially be possible to monitor the ICP for up to 1 h without recalibration.

Building Capacity and Assessing Stroke Risk with Transcranial Doppler Ultrasonography in Sub-Saharan Africa: The Reach Experience

Introduction: Transcranial Doppler (TCD) screening data from Uganda, Tanzania, and Nigeria have documented elevated velocities in &amp;gt;20% of children with sickle cell anemia (SCA) not receiving hydroxyurea treatment. Realizing Effectiveness Across Continents with Hydroxyurea (REACH, NCT01966731) has demonstrated the safety, feasibility, and benefits of hydroxyurea for children with SCA living in sub-Saharan Africa, especially when escalated to maximum tolerated dose (MTD). Whether hydroxyurea also confers protection against stroke risk in this setting remains unproven, though hydroxyurea-associated increases in hemoglobin and fetal hemoglobin, plus decreases in TCD arterial flow velocities, should lower the risk of both primary and secondary stroke. The availability of TCD equipment and appropriately trained and certified TCD examiners to perform this non-invasive and inexpensive procedure is an important limitation in low-resource settings. Methods: REACH teams in Angola, Democratic Republic of Congo, Kenya, and Uganda identified two local persons at each site to receive formal TCD training and certification from two experienced and certified super-users, one from Uganda and one from the US. Initial training included hands-on teaching at each site by the Ugandan trainer, followed by didactic teaching and hands-on examinations at a central African location with both trainers and all four REACH teams. Follow-up training included monthly web-based teaching sessions of TCD technique and discussion of centrally reviewed exams. Each local examiner had at least 30 completed examinations reviewed, critiqued, and discussed together with the trainers before becoming formally certified as a REACH TCD examiner. After certification, all REACH participants taking hydroxyurea at a stable dose were eligible for TCD using a standardized protocol with identical Sonara/tek advanced non-imaging TCD ultrasound units with 2MHz probes and version 7 software (Natus, Middleton, WI). Time-averaged maximum velocities (TAMV) were measured in the middle cerebral artery, distal internal carotid artery, and the bifurcation. The highest TAMV was recorded and categorized as normal (&amp;lt;170 cm/sec), conditional (170-199 cm/sec), or abnormal (≥200 cm/sec) and correlated with laboratory and clinical parameters. Results: Between November 2018 and March 2020, a total of 481 children in REACH received TCD screening; the average age was 9.3 ± 2.6 years, on hydroxyurea for 43 ± 8 months at an average dose of 23.5 ± 5.0 mg/kg/day with good response (Hb = 8.4 ± 1.3 g/dL, HbF = 23.9 ± 5.0%). There were 16 (3.3%) inadequate exams, defined as no vessel flow in either hemisphere; 5 inadequate exams were in children with prior stroke at hydroxyurea initiation and 1 with stroke on treatment. Of 465 adequate exams, the overall median TAMV was 128 cm/sec (IQR 25 cm/sec) with 449 normal velocities (96.6% overall, range by site 95.1-99.2%), 16 conditional velocities (3.4% overall, range by site 2.3-4.9%), and no abnormal velocities. In univariate analysis, maximum TAMV was inversely correlated with hemoglobin (r = -0.29, p&amp;lt;0.0001), age (r = -0.23, p&amp;lt;0.0001), and fetal hemoglobin (r = -0.12, p=0.027); and positively correlated with reticulocytes (r = 0.17, p&amp;lt;0.001). No gender difference was noted, but alpha thalassemia trait (2-gene deletion) was associated with significantly lower TCD velocities, while G6PD A- deficiency had no observed effects. Conclusions: Robust TCD screening capability was developed in REACH with detailed training, certification, and oversight of local personnel, most of whom had no prior experience. Compared to untreated children, very few REACH participants had elevated TAMV velocities, confirming that hydroxyurea lowers TCD velocities and reduces stroke risk for children with SCA in sub-Saharan Africa. The observed associations between TAMV and both hemoglobin and fetal hemoglobin document the importance of escalating hydroxyurea to achieve and maintain an optimized dose. In low-resource settings, TCD screening efforts by trained and certified examiners should be aligned with hydroxyurea treatment protocols that feature dose escalation, to provide a feasible and effective stroke prevention program. TCD screening of African children with SCA will allow early identification of stroke risk and optimized hydroxyurea dosing, thereby reducing morbidity and mortality in this vulnerable population. Disclosures Aygun: National Heart, Lung, and Blood Institute: Research Funding; bluebird bio: Membership on an entity's Board of Directors or advisory committees, Research Funding; Patient-Centered Outsomes Research Institute: Research Funding; National Institute of Nursing Research: Research Funding.

Transcranial Doppler sonography for detecting stenosis or occlusion of intracranial arteries in people with acute ischaemic stroke.

An occlusion or stenosis of intracranial large arteries can be detected in the acute phase of ischaemic stroke in about 42% of patients. The approved therapies for acute ischaemic stroke are thrombolysis with intravenous recombinant tissue plasminogen activator (rt-PA), and mechanical thrombectomy; both aim to recanalise an occluded intracranial artery. The reference standard for the diagnosis of intracranial stenosis and occlusion is intra-arterial angiography (IA) and, recently, computed tomography angiography (CTA) and magnetic resonance angiography (MRA), or contrast-enhanced MRA. Transcranial Doppler (TCD) and transcranial colour Doppler (TCCD) are useful, rapid, noninvasive tools for the assessment of intracranial large arteries pathology. Due to the current lack of consensus regarding the use of TCD and TCCD in clinical practice, we systematically reviewed the literature for studies assessing the diagnostic accuracy of these techniques compared with intra-arterial IA, CTA, and MRA for the detection of intracranial stenosis and occlusion in people presenting with symptoms of ischaemic stroke. To assess the diagnostic accuracy of TCD and TCCD for detecting stenosis and occlusion of intracranial large arteries in people with acute ischaemic stroke. We limited our searches from January 1982 onwards as the transcranial Doppler technique was only introduced into clinical practice in the 1980s. We searched MEDLINE (Ovid) (from 1982 to 2018); Embase (Ovid) (from 1982 to 2018); Database of Abstracts of Reviews of Effects (DARE); and Health Technology Assessment Database (HTA) (from 1982 to 2018). Moreover, we perused the reference lists of all retrieved articles and of previously published relevant review articles, handsearched relevant conference proceedings, searched relevant websites, and contacted experts in the field. We included all studies comparing TCD or TCCD (index tests) with IA, CTA, MRA, or contrast-enhanced MRA (reference standards) in people with acute ischaemic stroke, where all participants underwent both the index test and the reference standard within 24 hours of symptom onset. We included prospective cohort studies and randomised studies of test comparisons. We also considered retrospective studies eligible for inclusion where the original population sample was recruited prospectively but the results were analysed retrospectively. At least two review authors independently screened the titles and abstracts identified by the search strategies, applied the inclusion criteria, extracted data, assessed methodological quality (using QUADAS-2), and investigated heterogeneity. We contacted study authors for missing data. A comprehensive search of major relevant electronic databases (MEDLINE and Embase) from 1982 to 13 March 2018 yielded 13,534 articles, of which nine were deemed eligible for inclusion. The studies included a total of 493 participants. The mean age of included participants was 64.2 years (range 55.8 to 69.9 years). The proportion of men and women was similar across studies. Six studies recruited participants in Europe, one in south America, one in China, and one in Egypt. Risk of bias was high for participant selection but low for flow, timing, index and reference standard. The summary sensitivity and specificity estimates for TCD and TCCD were 95% (95% CI = 0.83 to 0.99) and 95% (95% CI = 0.90 to 0.98), respectively. Considering a prevalence of stenosis or occlusion of 42% (as reported in the literature), for every 1000 people who receive a TCD or TCCD test, stenosis or occlusion will be missed in 21 people (95% CI = 4 to 71) and 29 (95% CI = 12 to 58) will be wrongly diagnosed as harbouring an intracranial occlusion. However, there was substantial heterogeneity between studies, which was no longer evident when only occlusion of the MCA was considered, or when the analysis was limited to participants investigated within six hours. The performance of either TCD or TCCD in ruling in and ruling out a MCA occlusion was good. Limitations of this review were the small number of identified studies and the lack of data on the use of ultrasound contrast medium. This review provides evidence that TCD or TCCD, administered by professionals with adequate experience and skills, can provide useful diagnostic information for detecting stenosis or occlusion of intracranial vessels in people with acute ischaemic stroke, or guide the request for more invasive vascular neuroimaging, especially where CT or MR-based vascular imaging are not immediately available. More studies are needed to confirm or refute the results of this review in a larger sample of stroke patients, to verify the role of contrast medium and to evaluate the clinical advantage of the use of ultrasound.

Perspective: Variation in Guideline Implementation and Adherence Regarding Severe Traumatic Brain Injury Treatment: A CENTER-TBI Survey Study in Europe

Since 1990, the so-called “Brain Decade” was an exciting and promising period for the comprehension and tentative of treatment of the head trauma in order to improve the outcome of those devastating pathology.After several research and pre-clinical and clinical results a lot of protocols started with the concepts of brain autoregulation, brain perfusion, and neural rescue. Brain monitoring, also with the multimodal approach, transcranial Doppler, hypothermia, and neurosurgical techniques for brain decompression were also again updated.In 1992, the Lund protocol (LP) was the first guide published in Europe, for treatment of severe traumatic brain injury (s-TBi) (Grande, 2017). It was a theoretical approach in the field of brain pathophysiology. The main idea was on the way of cerebral perfusion pressure, fluid therapy, ventilation, sedation, nutrition, the use of vasopressors, and osmotherapy. The treatment is standardized, strictly applied with less need for individualization of the patient. Alternative European guidelines were published a few years later and were mainly based on meta-analytic approaches from clinical outcome studies. When introduced, they differed extensively from the LP. We still lack any large randomized outcome study comparing the European guidelines with other guidelines including the LP. From our point of view, there is poor evidence in favor of any of the guidelines used today. Despite the LP has not been changed since its introduction some components of the alternative guidelines have been proposed. As part of the “lucky Generation” of Neuroscientists, witnesses of the brain care evolution changing paradigms and evidence-based medicine era, in this chapter, we analyze and discuss the contents, results, and adherence of the current European protocols for head trauma.

Effects of Mild Orthostatic Stimulation on Cerebral Pulsatile Hemodynamics.

The augmented cerebral hemodynamic pulsatility could lead to the elevated risk of cerebrovascular disease. To determine the impact of an acute orthostatic challenge on a pulsatile component of cerebral hemodynamics, mild lower body negative pressure (LBNP, -30 mmHg) was applied to 29 men. Middle cerebral artery blood flow velocity (MCAv) was measured by transcranial Doppler technique. Stroke volume (SV) was estimated by the Modelflow method with adjustment by the Doppler ultrasound-measured SV at rest. SV, peak and pulsatile MCAv, and pulsatility index were significantly lower during the LBNP stimulation than those at the baseline (e.g., supine resting) (P < 0.05 for all), whereas mean arterial pressure and mean MCAv remained unchanged. The change in SV with the LBNP stimulation significantly correlated with corresponding changes in peak and pulsatile MCAv (r = 0.617, P < 0.001; r = 0.413, P = 0.026, respectively). These results suggest that pulsatile components of cerebrovascular hemodynamics are dampened during the transient period of orthostatic challenge (as simulated using LBNP) when compared to supine rest, and which is partly due to the modified SV.

Extracranial arterial wall volume is increased and shows relationships with vascular MRI measures in idiopathic Parkinson’s disease

ObjectiveIdiopathic Parkinson’s disease (IPD) is the second most common neurodegenerative disorder, often complicated by dementia. Cardiovascular risk factors and spontaneous cerebral emboli (SCE) are strongly associated with Alzheimer’s (AD) and vascular dementia (VaD). We measured SCE in the middle cerebral artery and arterial wall volume in the extracranial arteries in patients with IPD and controls, and explored the relationships with structural and physiological MRI brain neurovascular measures. Patients and MethodsArterial wall volume over 2cm of the axillary and internal carotid arteries (ICA) bilaterally was measured by 3-D tomographic ultrasound in 15 IPD patients and 16 age/gender matched controls. SCE were counted by Transcranial Doppler (TCD) using international consensus criteria. Venous to arterial circulation shunting (v-aCS), usually through a patent foramen ovale (PFO), was measured using a TCD technique with intravenous microbubble contrast. Structural and physiological MRI brain neurovascular measures, acquired separately, comprised white matter lesion volume (WMLV), cerebral blood flow (CBF) and arterial arrival time (AAT). ResultsMean (95% CI) axillary and ICA wall volume was higher in IPD patients at 523 mm3 (446, 600) and 455 mm3 (374, 536) respectively compared with 412 mm3 (342, 483) and 408 mm3 (362, 454) in controls being significant for the axillary artery (p = 0.04).Cerebral WMLV was related to mean arterial wall volume for both axillary (r = 0.555, p = 0.009) and ICA (r = 0.559, p = 0.026) in all participants.SCE were detected in four IPD patients and three controls (p = 1.00). Two IPD patients and three controls were positive for a v-aCS equivalent to PFO (p = 0.477). ConclusionAlthough frequent in AD and VaD, neither SCE nor v-aCS were associated with IPD. This is the first study to demonstrate arterial wall volume is increased in IPD and relates to WMLV.

Abstract 21400: Morphological Analysis of Transcranial Doppler Waveforms for Large Vessel Occlusion Diagnosis

Introduction: Underlying cardiac conditions such as atrial fibrillation (AF) and cardiac procedures such as transcatheter aortic valve replacement (TAVR) and coronary artery bypass grafting (CABG) have been shown to lead to large vessel occlusions (LVO) causing significant mortality and morbidity and improved pre, peri, post procedural methods for diagnosis are needed. Transcranial Doppler (TCD) is a rapid, inexpensive and portable tool for assessment of cerebral blood flow velocity (CBFV) that is used clinically and has been shown to have potential as a diagnostic aid for LVO. The utilization of the morphological information from the TCD waveform has shown to provide additional diagnostic capabilities in many neurological conditions and may improve LVO detection over traditional TCD metrics of mean velocity and pulsatility index. However, traditional TCD techniques suffer from a number of limitations including operator skill level and variability due to depth and location selection. Hypothesis: The morphology of CBFV waveforms measured with TCD enables detection of LVO while relaxing the need for exact insonation depth relative to occlusion location. Methods: Bilateral TCD scans of 17 pts (66.8 ± 15.2 yrs) with confirmed MCA occlusion were performed immediately following CT/CTA. TCD was also performed on 28 healthy out of hospital controls (55.3 ± 9.5 yrs). Waveform morphology was compared between the two groups. Results: Morphological analysis wherein MCA data for each subject was randomly sampled across depths showed median AUC of 96.3% for LVO detection, with median SEN of 88.9% and SPE of 96.3%. Fig. 1 shows an example of TCD waveforms for control and LVO subjects with similar traditional TCD metrics, but different subtle morphological profiles. Conclusion: Morphological analysis demonstrated high diagnostic accuracy additionally without the need for optimal depth selection, which may reduce the requirement of a trained sonographer.

Role Of Neurosonology In Management Of Stroke

Stroke is one of the most commonly occurring brain diseases and, in spite of its often homogeneous clinical appearance, its causes vary considerably. The implementation of a tailored and targeted therapy in each individual case requires rapid etiological classifi cation and a qualifi ed evaluation of the vascular status. Knowledge of normal vascular anatomy, variants, and anomalies are essential for proper clinical assessment.In clinical neurology, ultrasound became available in the early 1970s. The neurovascular focus developed in the 1980s with the use of extracranial color-coded duplex sonography (ECCS) and transcranial Doppler (TCD) techniques. The development of transcranial color- coded duplex sonography (TCCS) in the early 1990s was an important advance, as TCCS’s diagnostic sensitivity exceeded that of TCD. B-mode and color-mode images generated using TCCS greatly facilitated vessel identifi cation by off ering additional spatial information about vessel courses in relation to bone, parenchymal structures, and ventricles.In the mid-1990s, routine vascular diagnostic procedures was shifted away from TCD to TCCS. The combination of extra- and intracranial duplex ultrasound permits an almost comprehensive assessment of all brain- supplying vessels with a single bedside device. TCD remains the primary method for functional assessments such as right–left shunt diagnosis, assessment of cerebrovascular reactivity, autoregulation, and bilateral continuous monitoring for spontaneous microemboli.What is the best diagnostic approach for patients with acute and chronic brain ischemia? Several angiologic methods are now available for the treatment of stroke patients: DSA, MRA, CTA, and ultrasound. Each technique may yield information that is partly competing and partly complementary regarding vessel anatomy, vessel wall properties, and circulation physiology. Stroke physicians should be aware of the strengths and weaknesses of each of the available methods.

Does Coronary Angiography and Percutaneous Coronary Intervention Affect Cognitive Function?

Cerebral microemboli are frequently observed during coronary angiography (CA) and percutaneous coronary intervention (PCI), and their numbers have been related to the vascular access site used. Although cerebral microemboli can cause silent cerebral lesions, their clinical impact is debated. To study this, 93 patients referred for CA or PCI underwent serial cognitive testing using the Montreal Cognitive Assessment (MoCA) test to detect postprocedural cognitive impairment. Patients were randomized to radial or femoral access. In a subgroup of 35 patients, the number of cerebral microemboli was monitored with transcranial Doppler technique. We found the median precatheterization result of the MoCA test to be 27, and it did not change significantly 4 and 31days, respectively, after the procedure. There was no significant correlation between the number of cerebral microemboli and the difference between preprocedural and postprocedural MoCA tests. The test results did not differ between vascular access sites. One-third of the patients had a precatheterization median MoCA test result <26 corresponding to mild cognitive impairment. In conclusion, using the MoCA test, we could not detect any cognitive impairment after CA or PCI, and no significant correlations were found between the results of the MoCA test and cerebral microemboli or vascular access site, respectively. In patients with suspected coronary heart disease, mild cognitive impairment was common.

Dynamic cerebral autoregulation following acute ischaemic stroke: Comparison of transcranial Doppler and magnetic resonance imaging techniques

Novel MRI-based dynamic cerebral autoregulation (dCA) assessment enables the estimation of both global and spatially discriminated autoregulation index values. Before exploring this technique for the evaluation of focal dCA in acute ischaemic stroke (AIS) patients, it is necessary to compare global dCA estimates made using both TCD and MRI. Both techniques were used to study 11 AIS patients within 48 h of symptom onset, and nine healthy controls. dCA was assessed by the rate of return of CBFV (Rturn) following a sudden drop induced by the thigh cuff manoeuvre. No significant between-hemisphere differences were seen in controls using either the TCD or MRI technique. Inter-hemisphere averaged Rturn values were not different between TCD (1.89 ± 0.67%/s) and MRI (2.07 ± 0.60%/s) either. In patients, there were no differences between the affected and unaffected hemispheres whether assessed by TCD (Rturn 0.67 ± 0.72 vs. 0.98 ± 1.09%/s) or MRI (0.55 ± 1.51 vs. 1.63 ± 0.63%/s). Rturn for both TCD and MRI was impaired in AIS patients compared to controls in both unaffected and affected hemispheres (ANOVA, p = 0.00005). These findings pave the way for wider use of MRI for dCA assessment in health and disease.

Young Patients With Diabetes Have Decreased Cerebrovascular Reactivity Under Hypercapneic Conditions

ObjectiveAdult diabetic patients have an abnormal cerebrovascular response to hypercapnia, but there are few studies focused on diabetes mellitus type 1 and cerebral blood flow in pediatric or adolescent patients. We hypothesize that young patients with diabetes exhibit a different response to hypercapnia than normal control counterparts. MethodsUsing transcranial Doppler techniques, we compared young diabetic patients with healthy controls by measuring cerebral blood velocity before and during carbon dioxide challenge. ResultsSubjects with diabetes had decreased cerebral blood velocity reactivity when compared with the control group (P = 0.005). ConclusionOur results suggest cerebrovascular dysfunction in diabetic patients beginning at an early age. The possibility of long-term implications for cerebrovascular disease demonstrates the need for further studies in the pediatric and adolescent diabetic population to better understand this prevalent condition.

High-tech acupuncture made in Austria — cerebral circulation

It is little known that Austria has tradition in research in Chinese integrative medicine, especially traditional Chinese medicine. For more than 15 years, the research concerning high-tech acupuncture has been playing an important role at the Medical University of Graz, Austria. Within this review article, a short summary concerning high-tech acupuncture and cerebral circulation, and transcranial Doppler (TCD) sonography is presented. TCD has been extensively used in various basic and clinical situations, and in the last decade has established its role also as a tool of investigating the effects of various acupuncture methods. Based on the Doppler principle, it uses ultrasound waves to insonate the blood vessels supplying the brain and to obtain stimulation-induced changes of hemodynamic information. The purpose of this review is to present the basic concepts of TCD technique in relation to acupuncture research, and the specific effects on cerebral hemodynamics caused by acupuncture stimulation.

Methodological Aspects of Functional Transcranial Doppler Sonography and Recommendations for Simultaneous EEG Recording

The neurovascular coupling describes a vasoregulative principle of the brain that adapts local cerebral blood flow in accordance with the underlying neuronal activity. It is the basis of modern indirect brain imaging techniques. Because of its wide availability and high tolerability the functional transcranial Doppler has been often used to assess brain function in clinical conditions. In the present paper we will give an overview of the current understanding of the coupling, explain basic principles of the Doppler technique and summarize relevant findings of functional Doppler tests in the different vascular territories of the brain. Finally, the concept of a combined functional electroencephalogram and transcranial Doppler technique will be outlined, which allows simultaneous investigation of the neuronal and vascular responses of neurovascular coupling.

Prevalence of transcranial Doppler abnormalities in Nigerian children with sickle cell disease

Transcranial Doppler (TCD) ultrasonography helps to identify children with sickle cell disease (SCD) who are at an increased risk of stroke,making primary stroke prevention a reality. A cross-sectional study of145 Nigerian children aged ≥3 years with SCD was carried out to describe the pattern of cerebral blood flow (CBF) abnormalities. The mean time-averaged mean velocity (TAMV) was 152 ±27.0 cm/sec and122 ±22.0 cm/sec in Hb SS and Hb S1C group, respectively. Abnormal velocities were recorded in six (4.7%) of the Hb SS patients and none of the Hb S1C while conditional risk (CR) velocities were recorded in 19.7% of Hb SS (low conditional 11.0%, high conditional 8.7%) and low conditional in 5.6% of Hb S1C cases. Cerebral flow velocities showed a negative correlation with age and hematocrit. Compared with African-American children, Nigerian children with Hb SS disease have a considerably higher prevalence of CR velocities.

Neurosonology of emboli detection and monitoring

Cerebral embolism is the leading cause of ischemic stroke. Detection of microembolic signals [MES] in cerebral circulation is uniquely attained by several transcranial Doppler techniques, and can not be obtained with any other available imaging modality. Albeit no uniform picture has emerged from the studies, presence and amount of MES can identify a high-risk status in the setting of potential arterial or cardiac sources of cerebral embolism. Real-time MES monitoring during vascular procedures with high cerebral embolism risk seems also promising. The potential of MES detection in improvement of patient care is usually acknowledged, even though several aspects remain yet to be scientifically established. We herein review theory, technique and clinical potential of the neurosonological emboli detection, and try to add to understanding of the journal readership about the recent development on this subject.

Transcranial Doppler microembolic signals and serum marker evidence of brain injury during transcatheter aortic valve implantation

Recent studies have shown that transcatheter aortic valve implantation (TAVI) is associated with new foci of restricted diffusion on cerebral magnetic resonance imaging suggestive of cerebral microembolism. The aim of the present investigation was to quantify the cerebral embolic load and to evaluate during which phase of the TAVI procedure microembolism occurs. We also evaluated the association between the cerebral embolic load and post-procedural release of S100B, a serological marker of cerebral injury. In 21 patients, we described the extent and intra-procedural distribution of microemboli during the TAVI procedure using the transcranial Doppler technique. S100B, a marker of astroglial injury, was measured for 24 h after the procedure, and the area under the curve (AUC(24h) ) relating S100B to time was calculated. During the TAVI procedure, a mean of 282 ± 169 emboli was detected, 37% occurred during manipulation of the aortic arch/root/valve by guide wires and catheters, 22% occurred immediately after balloon dilatation of the native valve and 41% occurred during frame expansion of the valve prosthesis. S100B increased in all patients with a peak at 1 h after the procedure and returned to baseline after 4 h. There was a positive correlation between the total amount of cerebral microemboli and the AUC(24h) for S100B (r = 0.68, P < 0.001). None of the patients developed neurological impairment. TAVI is associated with a substantial amount of cerebral microemboli. The microembolic load correlates to the degree of post-procedural release of a marker of cerebral injury.

The brain at work

Our understanding of the cerebral blood flow (CBF) response to exercise has evolved dramatically over some 20 years in parallel with the advent of new methods to measure brain perfusion in humans. Previously, the Kety–Schmidt method was the only method available for evaluation of CBF in humans. The outflow from the brain through the internal jugular vein was taken to represent CBF and no change was found during exercise, probably because the spinal veins become more important when humans are upright as is the case for most exercise studies (Ide & Secher, 2000). As a consequence, it was often considered that exercise was the exception for which cerebral ‘activation’ (and maybe thinking?) was not required. Yet, with the introduction of methods that evaluate brain tissue flow (133Xenon-clearance) or inflow to the brain through the common or, ideally the internal carotic artery, an ∼20% increase in CBF during mild- to moderate-intensity dynamic exercise was observed. The CBF then levels out or maybe decreases when exercise becomes intense, with the decrease in the arterial carbon dioxide tension accompanying the exponential increase in ventilation. Thus CBF, and indeed cerebral oxygenation responses during incremental exercise, were hypothesised to follow an inverted U-shaped curve. The vast majority of human studies have applied a transcranial Doppler (TCD) approach to evaluate changes in CBF during exercise. Although this approach has the advantage that it can be used during high-intensity dynamic exercise of a large muscle mass, when using the TCD technique one must assume that the diameter of the isonated artery does not change. This assumption has become universally accepted although TCD was introduced by R. Aaslid (1984) to detect vasospasm after neurosurgical procedures. In support of the supposition that the diameter of the isonated artery at the base of the brain (often the middle cerebral artery (MCA)) remains constant during exercise, an inverted U-shape response to incremental exercise is detected with the TCD, and the magnitude of the increase in mean flow velocity is similar to that determined by other estimates of CBF (∼20%). In contrast, the diameter of the MCA increases in response to hypoxia (Wilson et al. 2011) and constricts in response to the administration of the α1-adrenergic receptor agonist phenylephrine (Ogoh et al. 2011), indicating that there is a need for new ambulatory methods for the evaluation of CBF. In a recent issue of The Journal of Physiology, Vogiatzis et al. (2011) introduced a new method using near-infrared spectroscopy to detect CBF (in the frontal lobe) during progressive exercise after bolus injection of idocyanine green, with and without hypoxia, in trained cyclists. It is comforting that the inverted U-shape CBF response to incremental exercise is confirmed by this initiative, and that the validity of the method is supported by an increase in CBF during hypoxia. Yet, as mentioned by the authors, the determined CBF is unreasonably low (23 ml min−1 100 g−1) compared to a normal value of ∼50 ml min−1 100 g−1 and the increase with CBF during exercise is twice as large as normally found. Near-infrared light has to pass through the skin and the scalp to reach the frontal lobe and the authors consider that the low skin (and scalp) blood flow could influence the result. Accordingly, it would be of value if this method for determination of CBF were repeated during exercise after skin blood flow is eliminated, e.g. by cooling the skin or after the administration of phenylephrine (Ogoh et al. 2011). The TCD technique has been invaluable for the development in understanding the brain at work both under normoxic and hypoxic conditions; however, it is problematic that the TCD evaluation of CBF is expressed as a velocity. Such a limitation may be surmounted by using near-infrared spectroscopy to determine CBF during exercise (Vogiatzis et al. 2011), although the extent of the influence of skin blood flow must be established. Similarly, flow in basal cerebral arteries may be evaluated by duplex ultrasound (Wilson et al. 2011) as it is established for peripheral arteries. Accordingly, we now have two additional methods available to take the evaluation of CBF during hypoxic exercise to new heights and the study by Vogiatzis et al. (2011) provides support to the notion that exercise in hypoxia is limited by cerebral oxygen supply and brain oxygenation.

Gender-related differences in physiologic color space: a functional transcranial Doppler (f TCD) study

Simultaneous color contrast and color constancy are memory processes associated with color vision, however, the gender-related differences of 'physiologic color space' remains unknown. Color processing was studied in 16 (8 men and 8 women) right-handed healthy subjects using functional transcranial Doppler (fTCD) technique. Mean flow velocity (MFV) was recorded in both right (RMCA) and left (LMCA) middle cerebral arteries in dark and white light conditions, and during color (blue and yellow) stimulations. The data was plotted in a 3D quadratic curve fit to derive a 'physiologic color space' showing the effects of luminance and chromatic contrasts. In men, wavelength-differencing of opponent pairs (yellow-blue) was adjudged by changes in the RMCA MFV for Yellow plotted on the Y-axis, and the RMCA MFV for Blue plotted on the X-axis. In women, frequency-differencing for opponent pairs (blue-yellow) was adjudged by changes in the LMCA MFV for Yellow plotted on the Y-axis, and the LMCA MFV for Blue plotted on the X-axis. The luminance effect on the LMCA MFV in response to white light with the highest luminous flux, was plotted on the (Z - axis), in both men and women. The 3D-color space for women was a mirror-image of that for men, and showed enhanced color constancy. The exponential function model was applied to the data in men, while the logarithmic function model was applied to the data in women. Color space determination may be useful in the study of color memory, adaptive neuroplasticity, cognitive impairment in stroke and neurodegenerative diseases.