Functional transcranial Doppler assessment of cerebral blood flow velocities changes during attention tasks

Background and Purpose:  Aim of our study was to evaluate cerebral hemodynamic changes during performance of attention tasks and to correlate them with reaction time (RT) and percentage of right answers.
Methods:  Mean flow velocity (MFV) in middle cerebral arteries was monitored in 30 subjects by transcranial Doppler during tonic alertness, phasic alertness, focused and divided attention tasks.
Results:  Mean flow velocity increase was significantly higher during divided attention with respect to other tasks ( P  < .001). MFV increase was higher in the right than in the left side ( P  < .001). Asymmetry during attention tasks resulted significantly higher than that observed in tonic alertness condition. RT was increased during focused attention tasks ( P  < .001 vs. both alert tasks), with further increase during divided attention tasks ( P  < .001 vs. focused attention task). RT was inversely related to MFV increase only during tonic alertness ( P  = 0.012 for left side; P  = 0.008 for right side). During the divided attention tasks, an association was found between MFV increase and correct answers ( r  = 0.39, P  = 0.033).
Conclusions:  These data show a relationship between RT, correct answers and changes in blood flow velocity and suggest that this method of cerebral blood flow investigation could be a useful approach during assessment of patients with attention deficit.     

Influence of biological factors on changes in mean cerebral blood flow velocity in normal ageing: a transcranial Doppler study

Analysis of the blood flow velocities in the middle cerebral artery by transcranial Doppler ultrasonography was performed in 158 healthy volunteers (aged 14-70 years; 82 men and 76 women). In a subgroup of 38 men and 21 women the end-tidal [CO₂] was also measured. The influence of biological factors such as age, sex, end-tidal [CO₂], and pulsatility and resistance indices on the mean blood flow velocity in normal ageing was investigated by multiple regression analysis. In both sex groups the measured mean blood flow velocity decreased significantly with age (P values < 0.0003 for women and < 0.0001 for men). Women had significantly higher blood flow velocities than men (P = 0.008) and the age-corrected sex difference of 5.2 cm s^–1 did not significantly depend on age (P = 0.93). The age-related linear decline of the mean blood flow velocity could not be explained by a concomitant decrease of the end-tidal [CO₂]. In a group of subjects older than 50 years, the decrease of the mean blood flow velocity was significantly related to the increase of the pulsatility or resistance index.     

Brain activity and blood flow velocity changes: a transcranial Doppler study

Seventy volunteers with no sign of cerebral vascular disease performed two series of 6 cognitive tasks, 3 of which are assumed to be processed predominantly by the left and 3 by the right hemisphere. During the tasks, blood flow velocity changes in the middle cerebral artery were recorded every 3 seconds by the transcranial Doppler method (TCD). All tasks increased blood flow velocities in both MCAs, but only the "right hemispheric" tasks resulted in a statistically significantly higher increase than the left MCA. The time course of velocity changes reflects the increase in blood flow caused by increased brain metabolism during brain activity. During stimulation of the right and/or left visual field, blood flow velocity changes were recorded in the P2-segment of the corresponding hemisphere. In 76 volunteers, the study was performed. The time course of velocity changes was similar to that in the MCA study. Velocity rose as a result of increasing complexity of the visual stimulus. The velocity changes are similar to blood flow increases reported in the literature and rose by as much 2 to 25%. Assuming that the diameter of the large branches of the circle of Willis does not change during mental activity, blood flow velocity changes reflect blood flow volume changes. With the TCD method the close relationship among brain activity, metabolism, and blood flow can be reliably investigated. The high spatial resolution enables information to be given about the onset of autoregulation.     

Changing cerebral blood flow velocity detected by transcranial Doppler ultrasound during head up tilt in patients with multiple sclerosis

Background and purpose:  Multiple sclerosis (MS) is a chronic inflammatory disease of central nervous system. We aimed to investigate the cerebral blood flow velocity (CBFV) changes in MS by transcranial Doppler.
Methods:  Twenty patients with MS, 20 age-matched healthy controls were included in the study. In both groups, blood flow velocities (BFVs) of middle cerebral arteries (MCAs) were evaluated. The changes of blood pressure, heart rate along with the changes in BFV of MCA were recorded after the patients were raised to upright position.
Results:  In both groups, upon raising the tilt table to the upright position, the mean CBFV values were found to be lower in comparison with the recorded baseline values ( P values <0.05). The decline in the mean CBFV values was more significant in patients with MS ( P  = 0.01).
Conclusion:  Our study showed upon raise of the tilt table, the mean BFVs decreased more in MS patients than control group with a more prominent change in the subgroup of MS patients with expanded disability scale scores ≥2. By use of transcranial Doppler ultrasound, it may be possible to evaluate BFV changes in patients with MS.     

Transcranial Doppler ultrasonic assessment of middle cerebral artery blood flow velocity changes during verbal and visuospatial cognitive tasks

Hemisphere specific changes of blood flow velocity in the right and left middle cerebral artery (MCA) induced by cognitive demands of verbal and nonverbal tasks were examined by means of a newly developed technique of simultaneous bilateral transcranial ultrasonic Doppler sonography (TCD). Thirty-one right-handed healthy volunteers served as subjects. Identical stimulus and response procedures were used with all tasks to avoid possible differential effects of these conditions on blood flow velocity. Compared to the preceding resting phase, the increase in flow velocity induced by each of the verbal tasks (sentence completion, similar or contrasting word meanings, similarities) proved to be significantly higher in the left than in the right MCA. Among the non-verbal visuospatial tasks only the “identical pictures” (perceptual speed) task led to a complementary higher increase in right MCA blood flow velocity. No such asymmetry in blood flow acceleration was observed, however, with the tasks “figure assembly” and “cube comparison” which require visualization and mental rotation of figures. The findings underline the recently emerging uncertainty in neuropsychological research with regard to the functional specialization of the right hemisphere.     

Cerebral blood flow velocity changes during dichotic listening with directed or divided attention: a transcranial Doppler ultrasonography study.

Simultaneous bilateral transcranial Doppler ultrasonography (TCD) monitoring of blood flow velocity (BFV) in the middle cerebral arteries was performed in 28 normal right-handed volunteers during linguistic dichotic listening tasks to investigate the effect of hemispheric specialisation and allocation of attention. A control task that required the repetition of monaurally presented words was followed by three randomised dichotic listening tasks in which the subjects were instructed to direct their attention to the word stimuli of the right ear, the left ear, or to divide their attention between both ears. Behavioural data indicated that the subjects used the required attentional strategies. A significant right ear advantage was not obtained in the divided attention condition due to a ceiling effect. Each task resulted in a significant bilateral increase in BFV. We found no significant lateralisation of BFV change for any of the tasks. We noted marked differences in BFV change between the different conditions that were significant in the right hemisphere, showed a borderline significance in the left hemisphere and appeared to be related with the difficulty of the task. We conclude that the hemodynamic changes caused by attentional strategies or hemispheric specialisation in processing dichotic stimuli over and above the effect of bilateral auditory stimulation, are too subtle to be detected as lateralised changes in BFV. Functional TCD could be used for the evaluation of a task's workload relative to other tasks, and may contribute to elucidate the role of the right hemisphere in attention and arousal.     

Cerebral blood flow during vagus nerve stimulation--a transcranial Doppler study

BACKGROUND AND OBJECTIVES: Vagus nerve stimulation (VNS) is an approved treatment of partial onset seizures and has recently shown antidepressant effects in patients with treatment-resistant depression. This study was conducted to investigate whether acute VNS has an influence on cerebral blood flow (CBF) in humans. METHODS: This investigation was designed as an add-on study. In 10 patients with an implanted stimulator who participated in a multicenter clinical trial to evaluate the efficacy of VNS in depression, CBF was investigated by functional transcranial Doppler at baseline (before the stimulator was turned on for the first time) and during stimulation with three different stimulation intensities in a randomized order. RESULTS: Immediately after every increase of the current, CBF velocity showed a nonsignificant increase. Otherwise, no change of CBF above standard deviation could be registered. CONCLUSION: Acute VNS does not have an influence on CBF velocity in depressive patients.     

Compromised cerebrovascular modulation in chronic anxiety: evidence from cerebral blood flow velocity measured by transcranial Doppler sonography

Objective Cerebral autoregulation(CA) is the mechanism by which constant cerebral blood flow is maintained despite changes in cerebral perfusion pressure.CA can be evaluated by dynamic monitoring of cerebral blood flow velocity(CBFV) with transcranial Doppler sonography(TCD).The present study aimed to explore CA in chronic anxiety.Methods Subjects with Hamilton anxiety scale scores≥14 were enrolled and the dynamic changes of CBFV in response to an orthostatic challenge were investigated using TCD.Results In both the anxious and the healthy subjects,the mean CBFV was significantly lower in the upright position than when supine.However,the CBFV changes from supine to upright differed between the anxious and the healthy groups.Anxious subjects showed more pronounced decreases in CBFV with abrupt standing.Conclusion Our results indicate that cerebrovascular modulation is compromised in chronic anxiety;anxious subjects have some insufficiency in maintaining cerebral perfusion after postural change.Given the fact that anxiety and impaired CA are associated with cardiovascular disease,early ascertainment of compromised cerebrovascular modulation using TCD might suggest interventional therapies in the anxious population, and improve the primary prevention of cardiovascular disease.     

Cerebral blood flow velocity measurements by transcranial Doppler during postural changes and walking in idiopathic orthostatic hypotension]

Transcranial Doppler (TCD) was utilized to estimate the cerebral blood flow velocity during postural changes or walking in two patients with idiopathic orthostatic hypotension (IOH). The probe of TCD was attached tightly to the temporal skull with a headband to measure the flow velocity of middle cerebral artery (MCA). The patients' postures were altered passively by a tilting table or actively by standing up or walking with their own feet. The TCD study clearly demonstrated a complete loss of autoregulation in Case 2 and an incomplete impairment of autoregulation in Case 1. In both patients, the blood pressure dropped markedly at a standing position, and MCA flow velocity decreased accordingly resulting in manifestation of dizziness. In Case 1, the blood pressure was elevated during walking, and MCA flow velocity increased leading to the improvement of ischemic symptoms. In Case 2, the TCD study was repeated after administration of fluorohydrocortisone, a mineralocorticoid agent, which ameliorated clinical symptoms. The results, however, indicated no improvement of autoregulatory response. The amelioration of symptoms was attributable to the elevation of blood pressure levels. Our study indicates the capability of TCD to estimate cerebral blood flow alteration during postural changes or walking. The TCD appears to be useful for evaluating the autoregulatory response and effectiveness of therapy in patients with orthostatism, like IOH.     

Acute effects of smoking on human cerebral blood flow: a transcranial Doppler ultrasonography study.

Middle cerebral artery (MCA) flow velocity was continuously monitored during smoking in an observational study (n = 14) using transcranial Doppler (TCD) ultrasonography. Cerebral autoregulatory vasodilator capacitance under inspired CO2 challenge was also measured before smoking and at peak smoking effect. Several puffs on a single lighted cigarette over a period of five minutes acutely increased MCA mean flow velocity in every subject (group mean increase: 19%, individual increases ranged 2-64%) with a response onset and offset detectable within several seconds of beginning and ending smoking. The mechanism for the increase in MCA flow velocities appeared to be independent of the CO2 autoregulatory mechanism. Gender subgroup analysis showed smoking acutely suppressed the CO2 vasodilator capacitance by 56% in men but only by 5% in women (p = 0.05). The magnitude of the acute smoking-induced increases in MCA flow velocities appeared to be independent of the estimated cigarette yields for nicotine, carbon monoxide, and "tar." Smoking in healthy subjects acutely increased MCA mean flow velocity, which may reflect a global increase in cerebral blood flow via complex influences on the cerebral autoregulation.     

Cerebral blood velocity in subarachnoid haemorrhage: a transcranial Doppler study.

A study examining the utility of transcranial Doppler ultrasound for the determination of cerebral vasospasm following subarachnoid haemorrhage is reported. A control group of 21 patients and a second group of 20 patients suffering from subarachnoid haemorrhage or aneurysm and a group of 26 with other intracranial pathologies were studied. The Doppler flow velocity (DFV) was significantly higher when vasospasm was present. If it was higher than 100 cm/s, the patients were found to have vasospasm in 80% of cases. If Doppler flow velocity was below 100, less than 10% had spasm. Doppler flow velocity was not found to increase following craniotomy in patients not suffering from subarachnoid haemorrhage. In subarachnoid haemorrhage patients there was a trend to increased Doppler flow velocity especially in patients who developed neurological deficit. Doppler flow velocity and Initial Slope Index by xenon clearance (ISI) were not found to correlate with clinical grade. The ISI/DFV quotient (which can be shown mathematically to be related to vessel diameter) was found to correlate well with clinical grade. In this largely post-operative group, absolute levels, or rate of change of Doppler flow velocity could not be shown to be related to the onset or existence of neurological deficit.     

Cerebral blood flow velocity in untreated panic disorder patients: a transcranial Doppler ultrasonography study.

BACKGROUND: The aim of this study was to compare resting cerebral blood flow velocity values of unmedicated patients in the acute phase of panic disorder with resting values of healthy control subjects. METHODS: Nineteen unmedicated panic disorder patients were assessed for degree of anxiety using the Hamilton Anxiety Scale. The patients and 20 healthy age-matched control subjects were then insonated at rest using transcranial Doppler ultrasonography (TCD). For TCD, the anterior, the middle, and the posterior cerebral arteries were insonated bilaterally in all patients. RESULTS: Compared with healthy age-matched control subjects, acute unmedicated panic disorder patients showed a significant increase in cerebral blood flow velocity, bilaterally in the middle and the anterior cerebral artery, and unilaterally in the left posterior cerebral artery. Cerebral blood flow velocity in the right middle cerebral artery correlated positively to the item "Fear" on the Hamilton Anxiety Scale, whereas pulsatility index in the posterior cerebral artery bilaterally and in the left middle cerebral artery correlated negatively to the item "Mood." CONCLUSIONS: Transcranial Doppler ultrasonography agrees well with validated psychometric methods. If follow-up studies confirm our findings, TCD could allow an objective assessment of the mental state of panic disorder patients and reliably discriminate panic disorder patients from normal control subjects.     

Cerebral blood flow velocity and perfusion in purulent meningitis: a comparative TCD and 99MTC-HMPAO-SPECT study

In 15 patients (median age 33 years; range 17–74 years) suffering from acute pneumococcal (10 cases) and meningococcal (five cases) meningitis, cerebral blood flow velocity (CBFV) was measured in the M₁– segment of the middle cerebral artery (MCA) by transcranial Doppler sonography, and cerebral perfusion changes were evaluated by ^99m-Tchexamethylpropylene amine oxime single photon emission computed tomography (HMPAO SPECT). The objective of the study was to test whether increased CBFV during the acute phase of purulent meningitis reflects hyperemia, and to evaluate focal perfusion abnormalities and their correlation to CBFV changes.
In eight patients with marked side-differences in CBFVs during the acute phase of the disease SPECT scans were normal in five. In three patients unilateral perfusion defects correlated with the side of higher CBFV. In seven patients presenting with symmetrically elevated CBFV, SPECT scans were normal in four and revealed focal abnormalities in the remaining three. Follow up SPECT scans were normal in 14/15 patients.
The results of our study suggest that elevated CBFV in acute bacterial meningitis does not reflect cerebral hyperemia. Focal cerebral perfusion defects occur independently from functional alterations in the cerebral macrovasculature. A causative pathophysiologic relationship of high CBFV and focal perfusion defects cannot be drawn from these data.     

Rhythmic oscillations with a wavelength of 0.5–2 min in transcranial Doppler recordings

We have studied intracranial pressure (ICP) B-waves and their association with rhythmic changes in blood flow velocity (B-wave equivalents) by transcranial Doppler sonography (TCD) monitoring. In overnight TCD recordings in 10 normal young adults, these rhythmic changes in blood flow velocity were higher and more frequent during REM sleep and sleep stage 1 than during other sleep stages. B-wave equivalents also had a longer wavelength during REM sleep. Their relative frequency in these normal subjects over one night ranged from 35 to 73%. Peripheral resistance (assessed by the Pourcelot index) was lower and heart rate was higher at the peak of these oscillations. These results support the hypothesis that ICP B-waves are caused by vasodilation. A non-linear relationship between ICP and blood flow velocity was found during B-waves in 9 of 11 patients with suspected NPH. Our results throw doubt on the suggestion that a relative frequency of less than 80% B-wave activity can be a valid indicator for shunt responsiveness in patients with suspected normal pressure hydrocephalus (NPH). ICP recordings in suspected NPH should be accompanied by polysomnography to avoid misleading results due to variability of B-wave appearance dependant on sleep pattern.     

Microvascular and transcranial Doppler sonographic evaluation of cerebral aneurysm flow pattern

Abstract

Ninety percent of cerebral aneurysms were diagnosed after their first rupture with consecutive subarachnoid haemorrhage. In order to detect the aneurysms before rupture investigation by transcranial Doppler sonography was used on the basis of intra-operative evaluation of the normal aneurysmal flow pattern. In 34 patients the directly registered aneurysmal flow pattern was characterized by mean velocities slower than in parent arteries, by low diastolic flow velocities and by additional peaks superimposed on the normal pulse curve. The transcranial investigation with a large sample volume which includes aneurysm and parent artery was not able to distinguish this aneurysmal flow pattern from the normal one. Only in large to giant aneurysms a pathological flow pattern could be recorded transcranially.     

Cerebral lateralization of praxis in right- and left-handedness: same pattern, different strength

We aimed to investigate the effect of hand effector and handedness on the cerebral lateralization of pantomiming learned movements. Fourteen right-handed and 14 left-handed volunteers performed unimanual and bimanual tool-use pantomimes with their dominant or nondominant hand during fMRI. A left hemispheric lateralization was observed in the right- and left-handed group regardless of which hand(s) performed the task. Asymmetry was most marked in the dorsolateral prefrontal cortex (DLPFC), premotor cortex (PMC), and superior and inferior parietal lobules (SPL and IPL). Unimanual pantomimes did not reveal any significant differences in asymmetric cerebral activation patterns between left- and right-handers. Bimanual pantomimes showed increased left premotor and posterior parietal activation in left- and right-handers. Lateralization indices (LI) of the 10% most active voxels in DLPFC, PMC, SPL, and IPL were calculated for each individual in a contrast that compared all tool versus all control conditions. Left-handers showed a significantly reduced overall LI compared with right-handers. This was mainly due to diminished asymmetry in the IPL and SPL. We conclude that the recollection and pantomiming of learned gestures recruits a similar left lateralized activation pattern in right and left-handed individuals. Handedness only influences the strength (not the side) of the lateralization, with left-handers showing a reduced degree of asymmetry that is most readily observed over the posterior parietal region. Together with similar findings in language and visual processing, these results point to a lesser hemispheric specialization in left-handers that may be considered in the cost/benefit assessment to explain the disproportionate handedness polymorphism in humans.     

Cerebral blood flow velocity changes after ventricular taps and ventriculoperitoneal shunting

Transcranial Doppler ultrasonography (TCD) was performed on 14 patients with hydrocephalus (age range 1 day to 12 years old) before and after ventriculoperitoneal shunting. TCD was also perfomed with simultaneous intracranial pressure (ICP) measurements during ventricular taps through a reservoir in 7 patients. Measurements of the resistance index (RI)=(S-D)/S, peak systolic (S), enddiastolic (D) and time-averaged mean flow velocities were made. After ventricular taps and ventriculoperitoneal shunting there was a significant decrease in RI in all patients. This was due to a greater increase in D compared to S, which suggests a decreased distal cerebrovascular resistance. There was a significant correlation between RI and ICP in the older infants and children and in individual neonates. Successful cerebrospinal fluid diversion reduces ICP and cerebrovascular resistance, thus improving cerebral perfusion. The RI is a reliable index for serial monitoring of cerebrohaemodynamic change in patients with hydrocephalus.     

Lateralization of cerebral blood flow velocity changes during cognitive tasks. A simultaneous bilateral transcranial Doppler study.

BACKGROUND AND PURPOSE: Transcranial Doppler ultrasonography (TCD) permits the assessment of cognitively induced cerebral blood flow velocity (BFV) changes. We sought to investigate the lateralization of BFV acceleration induced by a variety of cognitive tasks and to determine the influence of age, gender, IQ, and quality of the performance on the relative BFV changes. METHODS: Simultaneous bilateral TCD monitoring of BFV in the middle cerebral arteries (MCAs) was performed in 90 normal right-handed volunteers during 13 verbal and visuospatial tasks and their preceding rest periods. RESULTS: All tasks induced a significant bilateral BFV increase in the MCAs compared with the preceding rest periods. Five verbal tasks showed a significant left-hemispheric BFV acceleration. Linguistic tasks that required active or creative processing of the verbal stimuli, such as sentence construction or word fluency, elicited the most asymmetric response. Five visuospatial tasks revealed a significant right-hemispheric BFV shift. Paradigms that combined visuospatial attention and visuomotor manipulation showed the most lateralized acceleration. Older volunteers (aged >50 years) showed higher relative BFV changes, but lateralization was not influenced by age. Gender, IQ, and performance quality did not reveal significant effects on BFV change. CONCLUSIONS: Bilateral TCD is a noninvasive technique that has the potential to connect the particular change in flow pattern of the MCA distribution with selective cognitive activity and thus offers specific functional information of scientific and clinical value.