Bilateral Blood Flow Velocity Research Articles

Experimental carotid baroreceptor stimulation reduces blood flow velocities in the anterior and middle cerebral arteries of healthy individuals

This study investigated effects of experimental baroreceptor stimulation on bilateral blood flow velocities in the anterior and middle cerebral arteries (ACA and MCA) using functional transcranial Doppler sonography. Carotid baroreceptors were stimulated by neck suction in 33 healthy participants. Therefore, negative pressure (− 50 mmHg) was applied; neck pressure (+ 10 mmHg) was used as a control condition. Heart rate (HR) and blood pressure (BP) were also continuously recorded. Neck suction led to reductions in bilateral ACA and MCA blood flow velocities, which accompanied the expected HR and BP decreases; HR and BP decreases correlated positively with the ACA flow velocity decline. The observations suggest reduction of blood flow in the perfusion territories of the ACA and MCA during baroreceptor stimulation. Baroreceptor-related HR and BP decreases may contribute to the cerebral blood flow decline. The findings underline the interaction between peripheral and cerebral hemodynamic regulation in autoregulatory control of cerebral perfusion.

Cerebral blood flow modulations during antisaccade preparation in chronic hypotension.

In addition to symptoms including fatigue, dizziness, reduced drive, or mood disturbance, individuals with chronic low blood pressure (hypotension) frequently report cognitive complaints. While attentional deficits have been empirically confirmed, it is still unknown whether the impairments also encompass executive functions. This study investigated cerebral blood flow modulations in hypotension during a precued antisaccade/prosaccade task requiring the executive function of proactive inhibition in addition to preparatory attention. Using functional transcranial Doppler sonography, bilateral blood flow velocities in the middle cerebral arteries (MCA) were recorded in 39 hypotensive and 40 normotensive participants. In the task, a stimulus appeared left or right of a fixation point 5s after a cuing stimulus; subjects had to move their gaze to the mirror image position of the stimulus (antisaccade) or toward it (prosaccade control condition). Video-based eye tracking was used for ocular recording. A right dominant MCA blood flow increase arose during task preparation, which was smaller in hypotensive than normotensive participants. In addition, hypotensive participants exhibited lower peak velocity of the saccadic response. The extent of the reductions in blood flow and task performance in hypotension did not differ between antisaccade and prosaccade conditions. The smaller MCA flow increase may reflect reduced activity in the dorsolateral prefrontal and inferior parietal cortices during proactive inhibition and preparatory attention in hypotension. Given that group differences in blood flow and performance arose independent of task complexity and executive function load, hypotension may be characterized by basic attentional impairments rather than particular executive function deficits.

Cerebral blood flow modulations during preparatory attention and proactive inhibition

This study investigated cerebral blood flow modulations during task preparation in a precued saccade paradigm. Bilateral blood flow velocities in the middle cerebral arteries were recorded in 48 subjects using functional transcranial Doppler sonography. Video-based eye-tracking was applied for ocular recording. Antisaccade and prosaccade trials were presented in both block-wise and interleaved order. A right dominant flow response arose during task preparation. While the response was stronger during antisaccade than prosaccade trials, the degree of lateralisation did not differ between the two trial types. Direction error rates were higher and latencies were longer for antisaccades than prosaccades. There were no differences between block-wise and interleaved trials in blood flow or performance. The stronger blood flow increases during antisaccade than prosaccade preparation reflects the complexity of the upcoming task demands as well as proactive inhibition. The right hemispheric lateralisation may be attributed to preparatory attention independent of demands on inhibitory control.

Cerebral blood flow modulations during proactive control in chronic hypotension

In addition to complaints including fatigue, mood disturbance, dizziness or cold limbs, chronic low blood pressure (hypotension) is associated with reduced cognitive performance. Deficiencies in cerebral blood flow regulation may contribute to this impairment. This study investigated cerebral blood flow modulations during proactive control in hypotension. Proactive control refers to cognitive processes during anticipation of a behaviourally relevant event that allow optimization of readiness to react. Using functional transcranial Doppler sonography, bilateral blood flow velocities in the middle cerebral arteries were recorded in 40 hypotensive and 40 normotensive participants during a precued Stroop task. Hypotensive participants exhibited smaller bilateral blood flow increases during response preparation and longer response time. The group differences in blood flow and response time did not vary by executive function load, i.e. congruent vs. incongruent trials. Over the total sample, the flow increase correlated negatively with response time in trials with a higher executive function load. The findings indicate reduced cerebral blood flow adjustment during both the basic and more complex requirements of proactive control in hypotension. They also suggest a general deficit in attentional function and processing speed due to low blood pressure and cerebral hemodynamic dysregulations rather than particular impairments in executive functions.

Changes in Cerebral Blood Flow in Patients with Familial Mediterranean Fever.

It is known that there is a relationship between systemic inflammation and atherosclerosis. Atherosclerosis is one of the best-known causes of cerebrovascular diseases. The aim of this study was to assess cerebral blood flow velocity using transcranial Doppler (TCD) ultrasonography in patients with familial Mediterranean fever (FMF). A total of 30 patients aged from 20 to 50 years with FMF were enrolled in the FMF group consecutively. The control group (non-FMF group) consisted of 30 age- and sex-matched randomly selected patients without FMF who had other diagnoses such as fibromyalgia and did not have risk factors for atherosclerosis. Bilateral peak-systolic, end-diastolic, and mean blood flow velocities in the middle cerebral artery (MCA), values of Gosling's pulsatility index, and values of Pourcelot's resistance index were recorded using TCD ultrasonography by a neurosonologist blinded to the FMF and control groups. There were 30 participants in the FMF group in remission (male/female: 4/26, mean age: 34.7±5.9 years) and 30 participants in the control group (male/female: 4/26, mean age: 32.3±4.7 years). C-reactive protein levels and bilateral blood flow velocities in the MCA were significantly higher in the FMF group than in the control group. This study suggests that persistent clinical and subclinical inflammation in patients with FMF causes an increase in cerebral blood flow velocities. Our findings provide an insight into this association between FMF and cerebrovascular diseases.

Prediction of Minor Head Injured Patients Using Logistic Regression and MLP Neural Network

In this study it is aimed to assess the posttraumatic cerebral hemodynamia in minor head injured patients. Eighty patients with minor head injury (Group 1) evaluated in the early 8 h of posttraumatic period between July 2003 and February 2004. The control group (Group 2) has composed of 32 healthy people. Bilateral blood flow velocities of middle cerebral arteries (MCA) had measured using transtemporal technique while internal carotid arteries were evaluated by submandibular examination. Two different mathematical models such as the traditional statistical method on the basis of logistic regression and a multi-layer perceptron (MLP) neural network are used to classify the age, sex, velocitiy parameters of MCA, mean velocity of extracranial ICAs and V(MCA)/ V(ICA) ratios. The neural network was trained, cross-validated and tested with subject's transcranial Doppler signals. As a result of these classifications, we found the success rate of logistic regression, the success rate of MLP neural network is 88.2 and 89.1%, respectively. The classification results show that MLP neural network is offering the best results in the case of diagnosis.

Correlation between blood flow velocity in the middle cerebral artery and EEG during cognitive effort

Cognitive effort modifies blood flow velocity (BFV) in the middle cerebral artery (MCA) which can be recorded by transcranial Doppler sonography (TCD). EEG parameters can be used as indicators of cortical activation. To find temporal and spatial relation between circulatory and bioelectric phenomena, we used combined EEG and TCD measurements during cognitive experiments. Bilateral BFV in the MCAs and 16-channel scalp EEG were recorded during mental arithmetic (MA) and verbal fluency (VF) tests in 12 healthy volunteers. Temporal profile of BFV, heart rate (HR), EEG central frequency (CF), relative alpha power (rα p), and laterality index (Li) for BFV and CF were statistically analysed. During mental effort, BFV changes showed a reproducible pattern, which was different in MA and VF tests. The Li BFV correlated with handedness in 9/12 subjects (75%) in the VF, and in 6/12 subjects (50%) in the MA test. Significant correlation was found between Li BFV and Li CF during VF ( r 2 = 0.69). Li was more indicative for the hemispheric dominance in the VF than in the MA test. During VF test, correlation between HR and BFV was significant in 7/12 subjects. CF and rα p provide real time assessment of the functional state of the brain tissue during cognition. The correlation between CF and BFV during mental activity suggests a short latency neurogenic and a long latency, supposedly chemical regulation of regional blood flow. Parallel analysis of EEG and flow parameters increases the confidence of determining hemispheric dominance and provides an alternative to study physiological consequences of cognitive processes.

Altered cerebral vasoregulation in hypertension and stroke.

Autoregulation of blood flow that maintains steady perfusion over the range of systemic blood pressure is compromised by stroke. To determine whether cerebral vasoregulation is impaired in stroke during orthostatic stress. Subjects included 30 control subjects, 30 with hypertension, and 20 with minor stroke and were studied using transcranial Doppler. Bilateral blood flow velocities (BFVs) from middle cerebral arteries, heart rate, blood pressure (BP), and CO2 were obtained during hyperventilation and CO2 rebreathing during supine rest and tilt at 80 degrees. Side-to-side BFV difference, vasomotor range (VMR), and cerebrovascular resistance (CVR) were calculated during normo-, hypo-, and hypercapnia. Mean BFVs were similar between groups in supine position but differed during tilt. BFV diminished on the stroke side during tilt with hyperventilation and CO2 rebreathing (p < 0.0001). CVR increased (p < 0.0001) and VMR decreased (p < 0.01) on the stroke side. Vasoregulation was preserved on the normal side. BFV asymmetry differentiated patients with stroke from the other groups (p < 0.0001). BFV difference between the normal vs stroke side was the largest in stroke-normotensive (n = 7) compared with stroke-hypertensive (n = 13) patients and the two other groups (p < 0.0001). BFV asymmetry in stroke was associated with lower orthostatic BP (p < 0.0001). Cerebral vasoregulation is impaired with minor stroke, and cerebral blood flow depends on blood pressure. Decline of blood flow velocities during orthostatic stress may pose a risk of silent hypoperfusion.

Changes in middle cerebral artery blood flow after carotid endarterectomy as monitored by transcranial Doppler

Objective: By using transcranial Doppler (TCD) it is possible to measure blood flow velocities within the circle of Willis. In this study, TCD was performed before and after carotid endarterectomy (CEA) with the aim to describe cerebral hemodynamics after normalization of the carotid artery blood flow. Methods: Thirty CEA patients were consecutively entered into the TCD study, whereas 15 patients were referred for postoperative TCD for various clinical reasons. All 45 patients were investigated by using TCD: first preoperatively, then during the first few days after CEA before discharge from the hospital, and finally 3 to 12 months later. In addition, all patients underwent duplex investigation of the internal carotid artery the day before surgery and 3 months postoperatively. For the analysis, the patients were divided into two groups, one with (S-group), suspected postoperative neurologic complications/symptoms and another one without (C-group). Six patients were assigned to the S-group and 37 to the C-group, the latter including two patients who underwent bilateral CEAs. Results: In the whole study group,a significant postoperative increase in systolic flow velocity was recorded bilaterally in the middle cerebral artery (MCA) as measured some days after surgery. The patients in the S-group showed high blood flow velocities mainly in the MCA on the ipsilateral side. A contralateral flow velocity increase did not occur in patients with very severe contralateral stenosis or occlusion (n = 9) if the late follow-up investigation was chosen as a reference value. Twenty patients in the C-group formed a subgroup with high blood pressure and/or headache postoperatively (CB-group) The other 19 patients were referred to as the CA-group. The CB- and S-groups showed more pronounced vessel disease in internal carotid artery on the contralateral side combined with lower collateral capacity in the circle of Willis compared to the CA-group. In the S-group the mean ± standard deviation peak systolic velocity in ipsilateral MCA increased from a preoperative value of 0.71 ± 0.22 m/sec to 2.23 ± 0.72 m/sec ( P < .005). In the CB-group, we observed a bilateral MCA blood flow velocity increase from 0.72 ± 0.18 to 1.35 ± 0.56 m/sec ( P < .0001) on the ipsilateral side and from 0.82 ± 0.37 to 1.28 ± 0.66 m/sec ( P < 0.001) on the contralateral side. In the CA-group, we observed minor bilateral blood flow velocity increases in the MCA, from 0.79 ± 0.25 m/sec to 1.03 ± 0.33 m/sec on the ipsilateral ( P < .001) and from 0.70 ± 0.17 m/sec to 0.93 ± 0.26 m/sec on the contralateral side ( P < .005). At the follow-up 3 to 12 months after surgery, the MCA flow velocities had returned to normal. Conclusions: Soon after surgery, blood flow velocity increases often bilaterally in the MCA. However a contralateral flow velocity increase did not occur in patients with very severe contralateral stenosis or occlusion if the late follow-up investigation was chosen as a reference value. The clinical significance of bilateral flow velocity increases is uncertain, but very high blood flow velocities might be a signal for cerebrovascular hyperperfusion. In those patients, increased postoperative surveillance is recommended. (J Vasc Surg 2002;36:285-90.)