Functional Transcranial Doppler Research Articles

Evaluation of the Stability of Blood Flow over Time in the Dominant Hemisphere: A Functional Transcranial Doppler Study

Functional transcranial Doppler (fTCD) has been used for the identification of cerebral hemispheric dominance in various cognitive tasks. In our study, we have used fTCD with the aim to compare blood flow patterns in the hemispheres not only during the task activation periods but also in the post-stimulus phase. Normal volunteers, 25 right and 25 left-handed, were included. Mean flow velocities (FVs) in the bilateral middle cerebral arteries were recorded during the performance of six cognitive tasks and during the intervals between tasks. The lateralization index (LI) was calculated separately for each test (LI1-6), on the basis of the percent change of blood FV from baseline. To estimate flow fluctuations, a novel index, the LI-variability, was also calculated using a formula constituted by the minimum and maximum mean values recorded at specific time intervals during the entire procedure. Laterization indices, LI-3 and LI-4, corresponding to word generation and reading aloud tasks, produced the highest degree of activation. A perfect agreement (Cohen's kappa=1.000, P<0.001) was observed among LI-3, LI-4, and LI-V. The repetition of recordings gave excellent test-retest reliability in 10 randomly selected participants. Our results suggest that the hemisphere that is characterized as dominant by fTCD maintains a more stable flow pattern during the performance of successive cognitive tasks. Although it could not be considered as a clinically useful tool as yet, this observation introduces a novel parameter such as the stability of blood flow over time, which could potentially provide insight in the study of cerebral functions.

Constant Delay in Adapted Cerebral Response to Light Stimulation in Premature Neonates: A Transcranial Doppler Study

Transcranial Doppler has been used previously to determine hemodynamic response to sensorial stimulation in adults but not in the neonatal period. Cerebral blood flow velocity (CBFV) was recorded in both middle cerebral arteries (MCA) and posterior cerebral arteries (PCA) in 100 premature neonates (male 56; female 44; 26 to 36 weeks gestation) from birth to 12 months. Brain development was evaluated on clinical examination. No difference in velocities was noted on prestimulation recordings from birth to 12 months. During light stimulation before six months, the CBFV was reduced (–11 ± 6% in MCA and –13 ± 5% in PCA compared with baseline values). After stimulation, the CBFV was increased (+6.7 ± 3% in MCA and + 10.5 ± 4% in PCA compared with baseline values). This study is in favor of cortex maturation in normal premature neonates at only six months. Consequently, functional transcranial Doppler technique will be helpful for the diagnosis of abnormal maturation timing in neonates with possible developmental retardation. (E-mail: tranquart@med.univ-tours.fr)

Effects of physiological aging and cerebrovascular risk factors on the hemodynamic response to brain activation: A functional transcranial doppler study

Effects of physiological aging and cerebrovascular risk factors on the hemodynamic response to brain activation: A functional transcranial doppler study

Cerebral blood flow in essential hypotension during emotional activation

Variations of blood flow velocity in the left and right middle cerebral arteries (MCA) were measured in 20 hypotensive women and 20 normotensive control subjects during emotional stimulation using functional transcranial Doppler sonography (fTDS). The emotional stimuli were composed of three series (neutral, pleasant, and unpleasant) of 20 pictures from the International Affective Picture System (IAPS). Both groups exhibited greater increases in right than left MCA blood flow during emotional stimulation. However hypotensive subjects showed smaller increases in blood flow than did normotensive controls. Furthermore hypotensives exhibited lower MCA blood flow velocity in both hemispheres at rest than did normotensives. Nevertheless the hypotensive group rated the emotional pictures as more arousing than did the control group. Results suggest a decreased blood flow, in addition to peripheral, in the central nervous system (CNS) of hypotensives, which was associated with normal emotional responses for both valence and hemispherical asymmetry, but also with a general increase of arousal levels. This dissociation might be related to an increase in anterior cerebral arteries (ACA) blood flow and/or to hypotension-mediated baroreceptors' up-regulation to the reticular system.

Interplay of cerebral autoregulation and neurovascular coupling evaluated by functional TCD in different orthostatic conditions

Adequate cerebral blood flow (CBF) is mainly governed by neurovascular coupling (NC) which adapts local CBF to underlying cortical activity,and cerebral autoregulation (CA)that tends to maintain constant CBF despite changes in arterial blood pressure (BP). Since it was suggested that resistance vessels play an important role in both mechanisms, we investigated the irregulative interplay by performing a functional transcranial Doppler(f-TCD) test under different orthostatic conditions. Fifteen healthy volunteers performed a visual reading test stimulation task after stabilized in sitting, supine and upright position on a tilt table. Simultaneously, BP and heart rate (HR) were recorded by a photoplethysmographic method and CBF velocity was measured with TCD in left posterior cerebral artery, and, as a reference, also in right middle cerebral artery. Evoked flow velocity (FV) responses were evaluated by a control system approach for systolic and diastolic data. Parameters studied were baseline FV with eyes closed, stable FV under stimulation (gain), oscillatory feature (natural frequency) and damping (attenuation) of the control system model, rate time, and also systolic and diastolic BP and HR. ANOVA test was used for comparing the values of variables in different postural settings, inferring statistical significance at a p < 0,05 level. Although there was a significant variation on the different orthostatic conditions in systolic (p = 0,027) and diastolic (p = 0,001) BP and HR (p = 0,0001), there was no significant change in the basal or evoked CBF velocities. An intact CA compensates the different orthostatic conditions completely thus allowing an independent regulation of NC according to the metabolic needs of cortical stimulation.

Effects of physiological aging and cerebrovascular risk factors on the hemodynamic response to brain activation: a functional transcranial Doppler study

The influence of the vascular system on the coupling of cerebral blood flow (CBF) to focal brain activation during aging is incompletely understood. Using functional transcranial Doppler sonography and a hypercapnic challenge as a marker of intact cerebral vasoreactivity, we determined CBF velocity (CBFV) changes in response to a language and arithmetic task in a group of 43 healthy young subjects (mean age 32 +/- 8.6 years), 18 healthy old subjects (mean age 64 +/- 9.8 years) and 29 old subjects with risk factors for an atherosclerosis (mean age 69 +/- 8.4 years). Despite a similar performance during the cognitive tasks the CBFV changes were significantly lower in the group of old subjects with vascular risk factors compared with the healthy young and old subjects. Similarly, the CBFV changes during hypercapnia were significantly lower in the group of old subjects with vascular risk factors compared with the healthy young and old subjects. In contrast, both cognitive tasks and hypercapnia produced comparable CBFV changes in the group of healthy young and old subjects. These results suggest that the hemodynamic response to neuronal activation is unaffected by aging alone, whereas the presence of cardiovascular risk factors significantly diminishes the capability of cerebral vessels to react to vasodilating stimuli.

Cerebral lateralisation for facial processing: Gender-related cognitive styles determined using Fourier analysis of mean cerebral blood flow velocity in the middle cerebral arteries

Facial processing was studied in 16 (eight men and eight women) right-handed healthy participants using a new functional transcranial Doppler technique called functional transcranial Doppler spectroscopy (fTCDS). MFV was recorded simultaneously in both right and left middle cerebral arteries in dark condition and during visual processing of object and facial tasks. fTCDS used Fourier analysis of mean flow velocity (MFV) time series to derive spectral density estimates that correlate with expected mental activity. Men were right lateralised for object and facial perception, while women were left lateralised for facial tasks but showed a right tendency or no lateralisation for object perception. For facial perception, men used a category-specific process-mapping system for right cognitive style, but women used same for the left.

Hemodynamic cerebral ischemia during carotid endarterectomy evaluated by intraoperative monitoring and post-operative diffusion-weighted imaging

Objective: We used the result of monitoring to evaluate patients with post-operative neurological deficits attributable to hemodynamic cerebral ischemia owing to cross-clamping of the carotid artery.Methods: We evaluated 131 carotid endarterectomy (CEA) procedures performed on 118 patients, 96 men and 22 women ranging in age from 38 to 82 years (mean: 67.1 years). For monitoring, we used a combination of somatosensory evoked potential (SEP), functional dynamic electroencephalography (EEG), near-infrared spectroscopy (NIRS) and transcranial Doppler (TCD). Patients who awoke with neurological deficits after CEA immediately underwent diffusion-weighted imaging (DWI) and magnetic resonance angiography (MRA).Results: In 30 of the 131 procedures (22.9%), intraoperative monitoring disclosed abnormalities after cross-clamping of the internal carotid artery (ICA). In two of these 30 patients, shunt was not introduced, because of full recovery of monitoring after blood pressure increasing, however, one patient demonstrated transient ischemic attack (TIA). In six of remaining 28 patients who need shunt, transient hemodynamic cerebral ischemia occurred, however, all patients recovered gradually within 18 hours after CEA. No new lesions were detected on post-operative DWI of the seven patients and MRA demonstrated good patency of the carotid artery. The other 101 patients whose intraoperative monitoring after cross-clamping of the ICA did not disclose abnormalities demonstrated no hemodynamic TIA.Conclusion: Hemodynamic ischemia owing to cross-clamping of the ICA is rare in patients treated by CEA. However, in patients manifesting neurological deficits upon awakening from CEA, DWI and MRA should be performed immediately to facilitate their prompt treatment.

Functional transcranial Doppler sonography assessing language function in children: Validation data in neuropediatric patients

Background: There is a demand to establish complemental methods for the assessment of language lateralization in neuropediatric patients. Today's standard methods for the assessment of language lateralization, functional magnetic resonance imaging (fMRI) and the intracarotid brevital procedure (Wada test) cannot be utilized in every case. Their inherent characteristics circumvent the applicability in children with diminished capacity to cooperate. Functional transcranial Doppler sonography (fTCD) offers a tool to assess the language lateralization in a convenient and non-frightening way even in young children. Here, the first findings on a direct validation of the fTCD procedure are presented comparing fTCD with fMRI and the Wada test.

The association between scalp hair-whorl direction, handedness and hemispheric language dominance:: Is there a common genetic basis of lateralization?

The hemispheres of the human brain are functionally asymmetric. The left hemisphere tends to be dominant for language and superior in the control of manual dexterity. The mechanisms underlying these asymmetries are not known. Genetic as well as environmental factors are discussed.Recently, atypical anticlockwise hair-whorl direction has been related to an increased probability for non-right-handedness and atypical hemispheric language dominance. These findings are fascinating and important since hair-whorl direction is a structural marker of lateralization and could provide a readily observable anatomical clue to functional brain lateralization.Based on data on handedness and hair-whorl direction, Amar Klar proposed a genetic model (“random-recessive model”) in that a single gene with two alleles controls both handedness and hair-whorl orientation (Klar, A.J.S., 2003. Human handedness and scalp hair-whorl direction develop from a common genetic mechanism. Genetics 165, 269–276). The present study was designed to further investigate the relationship between scalp hair-whorl direction with handedness and hemispheric language dominance. 1212 subjects were investigated for scalp hair-whorl direction and handedness. Additionally, we determined hemispheric language dominance (as assessed by a word generation task) in a subgroup of 212 subjects using functional transcranial Doppler sonography (fTCD). As for the single attributes – hair-whorl direction, handedness, and language dominance – we reproduced previously published results. However, we found no association between hair-whorl direction and either language dominance or handedness. These results strongly argue against a common genetic basis of handedness or language lateralization with scalp hair-whorl direction. Inspection of hair patterns will not help us to determine language dominance.

Veränderte Hirnperfusion während einer Planungsaufgabe bei Patienten mit Schizophrenie: eine funktionelle transkranielle Dopplersonographie-Studie

There is evidence that executive functions are impaired in schizophrenia. Planning may be considered as one form of such complex functions, and deficits in planning abilities have been described in this disorder. Despite the importance of planning impairments in schizophrenia, there have been, to the best of our knowledge, no studies that examined brain perfusion during separate phases of a planning task. This distinction is important, because planning and execution of a plan in normals provoke distinct perfusion changes in the basal cerebral arteries. This functional transcranial Doppler sonography (fTCD) study compared the impact of a planning paradigm on cerebral blood flow velocity (CBFV) of the middle (MCA) and anterior (ACA) cerebral arteries in 14 patients with chronic schizophrenia and 20 healthy volunteers with similar sociodemographic variables. We assessed performance and CBFV during mental planning and movement execution. The main results were: (1) patients were unimpaired in planning times, but they showed longer movement execution times (p <0.01); (2) during mental planning, CBFV in the MCA increased less in patients as compared to healthy volunteers (p <0.005). In conclusion we found evidence of lower CBFV in the MCA during mental planning in chronic schizophrenia, which may suggest that neuronal activation in fronto-lateral cortical regions is impaired in this disease.

Statins and Cerebral Vasomotor Reactivity

See related article, pages 2540-2545. Animal models have shown that cholesterol-lowering therapy with 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (commonly called statins) may augment absolute cerebral blood flow (CBF) by enhancing nitric oxide synthase (eNOS).1 Statins upregulate type III endothelial eNOS in thrombocytes, decrease platelet activation, and protect from cerebral ischemia in normocholesterolemic mice.2 Statins may also provide additional beneficial effects by upregulating endogenous tissue plasminogen activator and enhancing clot lysis in a mouse model of embolic focal ischemia.3 Statins given 24 hours after experimental ischemia can enhance CBF, angiogenesis, neurogenesis and sinaptogenesis.4 How can these findings be applied in the clinical setting? A meta-analysis of published clinical trials showed that low-density lipoprotein–lowering with statins may decrease the risk of stroke in diabetic or hypertensive patients with normal low-density lipoprotein cholesterol at baseline, and in patients with coronary artery disease, with respectively 48%, 27% and 25% reduction in stroke incidence.5 Does any relationship exist among statins and cerebral vasomotor reactivity? Functional transcranial Doppler (TCD) ultrasonography permits the assessment of cognitively induced CBF velocity changes6 and the evaluation of cerebral vasomotor reactivity.7 TCD can be used to reliably evaluate age-related changes in the physiological response of the human cerebral circulation. A diminished nitric oxide–mediated cerebral vasomotor response may exist in aging subjects and in patients with vascular risk factors.8 Because there are no reliable markers for the functional status of the cerebral small vessels in elderly patients at risk of stroke, TCD studies may be useful. Although some parameters …

Language dominance in mesial temporal lobe epilepsy: A functional transcranial Doppler sonography study of brain plasticity

Functional transcranial Doppler sonography was used to study hemispheric language dominance (HLD) in 24 right-handed patients with left temporal lobe epilepsy (TLE) and a structural lesion in the left temporal lobe and in 69 healthy controls. Twenty-five percent of the patients and 4% of controls showed atypical (right or bilateral) HLD. Degree of HLD was not correlated with age, Full Scale IQ, Verbal IQ, spike frequency, seizure frequency, age at seizure onset, or duration of TLE. Atypical HLD appears to be lesion-induced, independent of epilepsy characteristics.

Applications of transcranial Doppler in the ICU: a review

Transcranial Doppler (TCD) ultrasonography is a technique that uses a hand-held Doppler transducer (placed on the surface of the cranial skin) to measure the velocity and pulsatility of blood flow within the intracranial and the extracranial arteries. This review critically evaluates the evidence for the use of TCD in the critical care population. TCD has been frequently employed for the clinical evaluation of cerebral vasospasm following subarachnoid haemorrhage (SAH). To a lesser degree, TCD has also been used to evaluate cerebral autoregulatory capacity, monitor cerebral circulation during cardiopulmonary bypass and carotid endarterectomies and to diagnose brain death. Technological advances such as M mode, colour Doppler and three-dimensional power Doppler ultrasonography have extended the scope of TCD to include other non-critical care applications including assessment of cerebral emboli, functional TCD and the management of sickle cell disease. Despite publications suggesting concordance between TCD velocity measurements and cerebral blood flow there are few randomized controlled studies demonstrating an improved outcome with the use of TCD monitoring in neurocritical care. Newer developments in this technology include venous Doppler, functional Doppler and use of ultrasound contrast agents.

Cerebrovascular autoregulation as a neuroimaging tool.

Functional transcranial Doppler (fTCD) sonography provides a high temporal resolution measure of blood flow and has over the years proved to be a valuable tool in the clinical evaluation of patients with cerebrovascular disorders. More recently, due to advances in physics and computing, it has become possible to derive indices of cerebrovascular autoregulation (CA) as well as cerebrovascular pressure reactivity (CR), using non-invasive techniques. These indices provide a dynamic representation of the brain's regulatory blood flow mechanisms not only in pathological states but also in health. However, whilst the temporal resolution of these regulatory indices is very good, spatially, the localization of brain regions remains very poor, thus limiting its brain mapping capacity. Functional MRI, on the contrary, is a brain-imaging technique that operates on similar blood flow principles; however, unlike fTCD, it provides high spatial resolution. Because both fTCD and fMRI determine blood flow-dependant imaging parameters, the coupling of fTCD with fMRI may provide greater insight into brain function by virtue of the combined enhanced temporal and spatial resolution that each technique affords. This review summarizes the fTCD technique with particular emphasis on the CA and CR indices and their relationship in traumatic brain injury as well as in health.

Effects of physiological aging and cerebrovascular risk factors on the hemodynamic response to brain activation: A functional transcranial Doppler study

Effects of physiological aging and cerebrovascular risk factors on the hemodynamic response to brain activation: A functional transcranial Doppler study

Comparison between visual half-field performance and cerebral blood flow changes as indicators of language dominance

The determination of hemispheric language dominance (HLD) can be accomplished in two ways. One approach relies on hemispheric differences in cerebral blood flow velocity (CBFV) changes during language activity, while the other approach makes use of performance differences between the left and right visual field when verbal stimuli are presented in a tachistoscopic visual field paradigm. Since both methodologically different approaches claim to assess functional HLD, it seems plausible to expect that the respective laterality indices (LI) would correspond. To test this expectation we measured language lateralisation in 58 healthy right-handed, left-handed, and ambidextrous subjects with both approaches. CBFV changes were recorded with functional transcranial Doppler sonography (fTCD). We applied a lexical decision task with bilateral visual field presentation of abstract nouns and, in addition, a task of mental word generation. In the lexical decision task, a highly significant right visual field advantage was observed for number of correct responses and reaction times, while at the same time and contrary to expectation the increase of CBFV was significantly higher in the right than left hemisphere. During mental word generation, the acceleration of CBF was significantly higher in the left hemisphere. A comparison between individual LI derived from CBF measurement during mental word generation and from visual field performances in the lexical decision task showed a moderate correspondence in classifying the subjects' HLD. However, the correlation between the corresponding individual LI was surprisingly low and not significant. The results are discussed with regard to the issue of a limited reliability of behavioural LI on the one hand and the possibility of a fundamental difference between the behavioural and the physiological indicators of laterality on the other hand.

The effect of methylprednisolone treatment on cerebral reactivity in patients with multiple sclerosis

We assessed the effect of intravenous high-dose methylprednisolone (IVMP) on cerebral reactivity in multiple sclerosis (MS) patients during exacerbations by means of functional transcranial Doppler imaging. Forty-eight clinically defined MS patients were evaluated with visual evoked potentials (VEP) and functional transcranial Doppler sonography (TCD) of both posterior cerebral arteries before and after 5 days of 1000 mg IVMP. After treatment, mean Expanded Disability Status Scale score, mean blood flow velocities and mean blood flow velocities at rest and at stimulation, significantly decreased ( p < 0.0001, for each). The change in cerebral blood flow velocity ratio (CBFv) with visual stimulation after treatment increased slightly ( p = 0.20). All TCD parameters were not significantly correlated with VEP changes. In conclusion, we observed significant changes in CBFv with a non-significant increase in vascular reactivity after treatment with IVMP in exacerbations of MS. Case-control studies are necessary to draw conclusions regarding the beneficial effects of IVMP treatment.

Sildenafil Improves Dynamic Vascular Function in the Brain: Studies in Patients with Pulmonary Hypertension

Background: Prostaglandins and nitric oxide play a pivotal role in the regulation of macro- and microcirculatory blood flow distribution. Interference with both mediator systems have been implicated in cerebrovascular dysfunction. Inhaled iloprost (long-acting prostacyclin analogue) and the phosphodiesterase-5 inhibitor sildenafil have recently shown efficacy in the treatment of chronic pulmonary hypertension. We investigated the impact of these agents on cerebral microcirculatory regulation in patients suffering from this disease. Methods: In 11 patients suffering from severe pulmonary hypertension, a functional transcranial Doppler test utilizing a visual stimulation paradigm was undertaken to measure the evoked flow velocity in the posterior cerebral artery. Measurements were performed in parallel to right heart catheterization and pharmacological testing of the pulmonary vasoreactivity. After assessment of baseline measurements, inhaled iloprost and oral sildenafil were given consecutively for testing of cerebral and pulmonary vascular function. The data gained from the Doppler measurements were compared to data from 22 healthy volunteers. Results: Both substances provoked a significant reduction of pulmonary arterial pressure and vascular resistance, accompanied by minor changes in systemic vascular resistance. In contrast to these superimposable hemodynamic profiles opposite effects were observed regarding cerebral vascular tone: cerebral microvascular reactivity, as assessed by attenuation and time rate parameters, was significantly improved by sildenafil, but slightly worsened by iloprost. Conclusions: Sildenafil has beneficial effects on cerebral vascular reactivity indicative of an improvement in neurovascular coupling in patients with pulmonary hypertension. These results warrant further investigations of the influence of sildenafil on dynamic vascular function in the brain independent of the underlying disease.

Cerebral blood flow velocity changes during meaningful and meaningless gestures – a functional transcranial Doppler study

The aim of the study was to use functional transcranial Doppler to investigate the possibility of revealing different activation patterns during healthy subjects' performance of meaningful and meaningless actions. Mean flow velocity (MFV) changes were recorded in middle cerebral arteries (MCAs) of 26 normal subjects during a rest phase and during performance of meaningful and meaningless actions. The meaningful task consisted of pouring sugar into a cup with a teaspoon. The meaningless action was an arm movement similar to that necessary for pouring sugar in a cup but without any tool and thus without a goal. Performing actions with or without meaning was associated with different patterns of MFV changes, as documented by the triple interaction condition x performing arm x side of recording [F(1, 25)=10.977; P=0.003]. During the meaningful action, MFV in MCAs increased significantly more than during the meaningless action. During the meaningless action, the MFV increase was significantly higher in the contralateral than in the ipsilateral MCA to the arm performing the task and the meaningful action determined a bilateral MFV increase only when the task was performed with the left arm. When the same task was performed with the right arm, the MFV increase was significantly higher in the contralateral than in the ipsilateral MCA. These findings suggest that the content of an action can influence MFV changes and further confirm the usefulness of transcranial Doppler in neuropsychological investigation.