Cerebral Artery Flow Velocity Research Articles

Changes in cerebral blood flow induced by passive and active elbow and hand movements.

Transcranial Doppler ultrasonography (TCD) has been widely used to obtain information about changes in cerebral perfusion during motor activity after stroke. This type of application is greatly limited when severe motor deficits are present that impede the performance of an active motor task. In this study, we explored the effect of performing passive arm movements on cerebral perfusion. Twenty healthy subjects were investigated. A bilateral TCD monitoring of the middle cerebral artery (MCA) flow velocity was performed during the following experimental conditions: 1-min of active and passive flexion-extension elbow movement and 1-min of active and passive dorsal extension hand movement. Each task was performed with both left and right arms. The percentage increase in flow velocity from rest to task performance was calculated. Each task produced a significantly greater increase in mean flow velocity in the contralateral MCA with respect to the ipsilateral. When comparing the effect of passive and active tasks, no significant difference in mean flow velocity changes recorded in the ipsilateral and the contralateral MCA was detected regarding either elbow or hand movements. These findings demonstrate the possibility of obtaining information about changes in hemispheric cerebral perfusion during passive movements involving elbow and hand. This type of application deserves further attention in the study of cerebral functional changes following cerebral lesions.

The influence of ruptured cerebral aneurysm localization on the blood flow velocity evaluated by transcranial Doppler ultrasonography

The relationship between changes of blood flow velocities in cerebral arteries measured by transcranial Doppler ultrasonography and aneurysm localization was investigated in a group of 165 patients after aneurysmal subarachnoid hemorrhage (SAH). Mean blood flow velocities (MFV) in the middle cerebral artery (MCA) and anterior cerebral artery (ACA) were registered. In patients with aneurysm of internal carotid artery and MCA (group A) statistically significant higher values of MFV from the 1st to the 5th day and on the 12th, 13th, 14th, 15th, and 19th day after SAH were found compared to patients with aneurysm of the anterior communicating artery, ACA, and pericallosal artery (group B). Pathological values of MFV exceeding 120 cm sec-1 in MCA were registered during 14 days in group A and during eight days in group B. Blood flow velocities in ACA were statistically significantly higher in group B on the 2nd, 7th, 9th and 11th day compared to group A. Pathological values of MFV exceeding 90 cm sec-1 in ACA were registered during nine days in both groups. MFV differences between group A and group B in 38 patients subjected to delayed surgery were not observed. The influence of aneurysm localization was observed between the 7th and 14th day after SAH. Critical MFV values for vasospasm in the MCA should be 120 cm sec-1 and in the ACA 90 cm sec-1. [Neurol Res 2001; 23: 23-28]

Evaluation of cerebrovascular reactivity in children [corrected] with chronic renal failure.

Developmental disturbances and encephalopathy have been observed in children with chronic renal failure (CRF). The aim of this study was to investigate the efficiency of the cerebral circulation in uremic children. The study group consisted of 10 children with CRF on conservative treatment, 8 children on continuous ambulatory peritoneal dialysis (CAPD), and 8 children on maintenance hemodialysis (HD). Examination was performed using a TC2-64B, EME Doppler flowmeter machine and capnograph Datex, Normocap. Blood flow velocity in both middle cerebral arteries (MCA), at rest and after spontaneous hyperventilation for 30 s, was analyzed. The vascular reactivity coefficient was calculated as the percentage ratio of decline of blood flow velocity in MCA to PCO2 decrease. Baseline mean blood flow velocities of MCA in euvolemic children under conservative treatment and on CAPD were significantly higher than those in children on HD and healthy control children. The highest value of the vascular reactivity coefficient was significantly higher in the group of children with CRF on conservative and CAPD treatment, than in children on HD and healthy controls. We suggest that hyperreactivity of the cerebral circulation could be the result of impaired autoregulation of blood flow. Evaluation of cerebrovascular reactivity in uremic children requires further examination.

Effect of Oral Administration of Dotarizine on Cerebrovasculature Subjected to Constriction Followed by Dilatation in Rabbits

In the study presented the effect of Dotarizine on blood flow velocity in cerebral arteries - in middle cerebral artery (MCA), and basilar artery (BA)- was investigated and compared utilising transcranial Doppler sonography during normoventilation, 15 min hyperventilation with subsequent 3 min anoxia in anaesthetized rabbits. In the Dotarizine treated group (12 rabbits) 25 mg/kg of Dotarizine dissolved in 0,25% agar was administered orally for five days twice daily. In the control group (9 rabbits) animals were fed with agar of the same concentration. The results revealed that decrease of flow velocity caused by hyperventilation and increase during anoxia were less pronounced in the Dotarizine treated group than in control group of animals. A difference between changes of flow velocity in MCA and BA during anoxia was found and the different reactivity of both vessels was established.

Relation of cerebral blood flow velocity and level of vigilance in humans.

Blood flow velocities in both middle cerebral arteries (MCA) were measured using transcranial Doppler ultrasound (TCD) in healthy subjects engaged in a continuous static visual vigilance task. Stimuli comprised white vertical gratings on a black background with a size of 5 x 5" (non-targets) or 5 x 3.5" (targets). Button presses were required to the rare (8.5%) targets. Over the 30 min session a decrease in hit rate and an increase in reaction time were seen, indicating a decrease in vigilance. These performance changes were paralleled by a decrease in flow velocity in both MCAs. No hemispheric difference was seen. These data suggest a close coupling of performance and blood flow in vigilance tasks. Modulation of cholinergic activity during the vigilance task might be the common underlying mechanism.

Vascular reactivity in middle cerebral artery and basilar artery by transcranial Doppler in normals subjects during hypoxia.

The anatomical and physiological differences between the carotid and vertebrobasilar circulations suggest the possibility of a different response to variations in systemic pO2. We evaluated cerebrovascular response (CR) in these two systems by monitoring variations in the blood flow velocities in the middle cerebral and basilar arteries during hypoxia. Eighteen healthy, non-smoking volunteers underwent transcranial Doppler study during a state of hypoxia obtained by means of the rebreathing method. Oxyhaemoglobin saturation (SaO2) was monitored using a pulsoxymeter in the 88-94% range. The cerebral blood flow velocity (BFV) was measured in the right middle cerebral artery (MCA) and the basilar artery (BA). Our findings indicate that the mean blood flow velocity (MFV) in the BA changes at a lower rate than that in the MCA during hypoxia.

Slow rhythmic oscillations of blood pressure, intracranial pressure, microcirculation, and cerebral oxygenation. Dynamic interrelation and time course in humans.

Various biological signals show nonpulsatile, slow rhythmic oscillations. These include arterial blood pressure (aBP), blood flow velocity in cerebral arteries, intracranial pressure (ICP), cerebral microflow, and cerebral tissue PO2. Generation and interrelations between these rhythmic fluctuations remained unclear. The aim of this study was to analyze whether stable dynamic interrelations in the low-frequency range exist between these different variables, and if they do, to analyze their exact time delay. In a clinical study, 16 comatose patients with either higher-grade subarachnoid hemorrhage or severe traumatic brain injury were examined. A multimodal digital data acquisition system was used to simultaneously monitor aBP, flow velocity in the middle cerebral artery (FVMCA), ICP, cerebral microflow, and oxygen saturation in the jugular bulb (SjO2). Cross-correlation as a means to analyze time delay and correlation between two periodic signals was applied to a time series of 30 minutes' duration divided into four segments of 2048 data points (approximately 436 seconds) each. This resulted in four cross-correlations for each 30-minute time series. If the four cross-correlations were consistent and reproducible, averaging of the original cross-correlations was performed, resulting in a representative time delay and correlation for the complete 30-minute interval. Reproducible cross-correlations and stable dynamic interrelations were found between aBP, FVMCA, ICP, and SjO2. The mean time delay between aBP and ICP was 6.89 +/- 1.90 seconds, with a negative correlation in 81%. A mean time delay of 1.50 +/- 1.29 seconds (median, 0.85 seconds) was found between FVMCA and ICP, with a positive correlation in 94%. The mean delay between ICP and SjO2 was 9.47 +/- 2.21 seconds, with a positive correlation in 77%. Mean values of aBP and ICP did not influence the time delay and dynamic interrelation between the different parameters. These results strongly support Rosner's theory that ICP B-waves are the autoregulatory response of spontaneous fluctuations of cerebral perfusion pressure. There is casuistic evidence that failure of autoregulation significantly modifies time delay and the correlation between aBP and ICP.

Transcranial Doppler and systemic hemodynamic studies in septic shock.

The present study outlines the relationship between cerebral and systemic hemodynamics in patients with septic shock. Sepsis is an immune mediated systemic disease in which the systemic vascular resistance (SVR) often decreases as a result of a Gram negative sepsis. The result is a hyperdynamic systemic circulation with redistribution phenomena in different organ systems. In order to study the effect of sepsis on cerebral vessels 20 patients with septic shock (12 men, 8 women, mean age 57.9 years) were subjected to both pulmonary artery catheter and transcranial Doppler (TCD) monitoring. The data were correlated to the APACHE II score and outcome. The study showed that cerebral mean and end-diastolic blood flow velocities (BFV) in the middle cerebral arteries significantly enhanced if the SVR-index decreases. In some patients a severely reduced SVRI (below 500 dynes.s/cm5.m2) was observed in combination with a downstroke latent steal phenomenon. TCD abnormalities were strongly related to disease severity and outcome. The increased BFV are explained by a mild vasospasm of the basal cerebral arteries. TCD appears to be a valuable tool to monitor the cerebral hemodynamics in these patients. They are particularly at risk for ischemic brain damage if they are subjected to therapeutic or spontaneous hyperventilation, which can potentially be detected by TCD.

The Relationship Between Cerebral Blood Flow and Transcranial Doppler Blood Flow Velocity During Hypothermic Cardiopulmonary Bypass in Adults

A noninvasive, simple, and continuous method to assess cerebral perfusion during cardiopulmonary bypass (CPB) could help prevent cerebral ischemia. Transcranial Doppler sonography (TCD) allows a noninvasive, on-line measurement of blood flow velocity in cerebral arteries. The correlation of TCD-estimated and actual cerebral blood flow (CBF) has not been well studied during CPB. We determined the correlation of middle cerebral artery (MCA) mean velocity and CBF determined by the Kety-Schmidt method during nonbypass and two hypothermic bypass flow conditions. Sixteen patients undergoing hypothermic (27 degrees C) CPB for coronary artery bypass grafting and/or valve replacement surgery were enrolled in the study. We were able to determine MCA velocity in only 12 patients. We determined CBF and MCA velocity in each patient during four 15-min study periods: 1) prebypass after sternotomy before aortic cannulation; 2) hypothermic (27 degrees C) CPB with 1.2 L.min-1.m-2 pump flow; 3) hypothermic CPB with 2.4 L.min-1.m-2 pump flow, and 4) 30 min after weaning from CPB. There was no difference in the mean arterial pressure between the two CPB pump blood flows. The pooled change in MCA velocity and CBF as percentage of baseline (prebypass) for all patients and at all time points had a correlation of 0.33 (r). A decrease or increase in MCA velocity did not necessarily indicate a corresponding decrease or increase in CBF. This technology may be of limited usefulness during the circulatory condition of hypothermic, nonpulsatile CPB.

Transcranial Doppler during neurocardiogenic syncope

The purpose of the present study was to investigate changes in cerebral circulation during neurocardiogenic syncope (NCS). Twenty patients with a history of unexplained syncopes were studied over a 45 min period in a tilted position. Heart rate and arterial blood pressure were recorded non-invasively using Finapres. Cerebral blood flow velocity of both middle cerebral arteries was measured with transcranial Doppler (TCD). Ten patients (50%) developed a NCS during the tilt test, with a strong reduction in blood pressure (mean, 48/34 mmHg) and heart rate (mean, 54 beats/min). Simultaneously, diastolic blood flow velocities dropped to values close to zero. However, systolic blood flow velocities did not decrease. In consequence, the pulsatility index (PI) increased considerably from 0.93 to 2.01. The increase in PI suggests that there is a constriction of cerebral resistance vessels during NCS. Despite the drop in blood pressure and the putative increase in cerebrovascular resistance, systolic blood flow velocities remained unchanged in the TCD records. This fact can be explained by a lumen narrowing of the middle cerebral artery at the site of insonation. In conclusion, the typical changes in cerebral blood flow velocity during NCS are probably due to a strong constriction of both the proximal and the peripheral segments of cerebral arteries. It is clear that, in addition to vasodepression and cardiac inhibition, cerebral vasoconstriction is a further mechanism in the pathogenesis of a NCS.

Transcranial Doppler assessment of cerebral blood flow velocity in term newborns.

Using the transcranial Doppler technique to assess postnatal changes in cerebral blood flow velocity, we studied the anterior cerebral artery, middle cerebral artery, and internal carotid artery of 31 healthy, term newborn infants. Normative values for the 1st, 3rd, and 5th days of life were determined. Cerebral blood flow velocity values in all three arteries examined correlated well with each other and we observed a statistically significant increase only in middle cerebral artery blood flow velocity between the 1st and 3rd, and 1st and 5th postnatal days. Thus, if we assume that flow velocities in various cerebral arteries undergo similar change, only one representative artery need be examined. The middle cerebral artery appears to be the vessel of choice. This choice simplifies the recording procedure, particularly in repeated examinations.

Continuous Positive Airway Pressure Breathing Increases Cerebral Blood Flow Velocity in Humans

The effect of a continuous positive airway pressure (CPAP) of 12 cm H2O on mean middle cerebral artery flow velocity (CBFV) was studied in nine human volunteers by means of transcranial Doppler sonography (TCD). During CPAP breathing, CBFV increased (45 +/- 9 vs 59 +/- 11 cm/s; P < 0.001; mean +/- SD), and pulsatility index (PI) decreased (0.87 +/- 0.1 vs 0.74 +/- 0.2; P < 0.05), indicating an increase in cerebral blood flow due to cerebral vasodilation. This phenomenon should be taken into account when CPAP is applied to patients with intracranial disease or when assessing CBFV patterns of patients during CPAP respiration.

Ketanserin does not impair the validity of transcranial flow velocity measurements as an index of cerebral blood flow

Introduction: Transcranial Doppler sonograpby (TCD) increasingly is employed not onfy for diagnostic purposes but also for cerebral haemodynamic monitoring during surgery or intensive care. Most clinical and scientific applications of TCD measurements as an index of flow are based on the assumption that at least intraindividualiy the relation between flow and flow velocity remains constant during the period of investigation. However, drug-induced changes of the diameter of the insonated vessel may impair the validity of serial TCD measurements. This investigation was designed to study the influence of ketanserin on the relationship between global cerebral blood flow (CBF) and red blood cell (RBC) velocity in basal cerebral arteries.

Effects of partial plasma exchange transfusion on blood flow velocity in large arteries of arm and leg, and in cerebral arteries in polycythaemic newborn infants.

Continuous wave Doppler velocimetry was performed in brachial, femoral and cerebral arteries in four preterm, four small-for-gestational-age (SGA) and eight appropriate-for-gestational age (AGA) polycythaemic newborns before and at 3 and 24 h after partial plasma exchange transfusion and in 18 matched controls at 3 and 24 h after birth. In peripheral arteries, end-diastolic flow velocity was zero in all eight AGA controls, but only in two of the other infants. Consequently, mean flow velocity and red cell transport in AGA controls were significantly lower than in the other five groups, which did not differ. Partial plasma exchange transfusion did not influence flow velocities and red cell transport in peripheral arteries, but normalized the flow velocities in cerebral arteries in all three subgroups of polycythaemic infants, which were lower than in control infants. Cerebral red cell transport in controls increased significantly between 3 and 24 h, and in polycythaemic infants between 0 and 3 h after partial plasma exchange transfusion. In conclusion, reduction in haematocrit had different effects on blood flow velocity and red cell transport of peripheral and cerebral vessels, suggesting that the increased cerebral blood flow velocity after partial plasma exchange transfusion is not simply due to a reduction in viscosity or oxygen content of the blood. The lower peripheral blood flow velocities in normocythaemic AGA infants as compared to all other groups, suggest that the level of maturity is an important determinant for the capacity to regulate blood flow.

Monitoring of severe head-injured patients with transcranial Doppler (TCD) ultrasonography.

Intracranial haemodynamics were studied in 36 patients with severe head injury and experimental animals with acute intracranial hypertension by the use of TCD ultrasound. The mean flow velocity (FV) in the basal cerebral arteries commonly decreased on the side of the haematoma depending on intracranial pressure (ICP) elevation and cerebral perfusion pressure (CPP) reduction in focal brain injury. The FV decreased bilaterally and there was no difference between the right and left sides in diffuse brain injury without a clear relationship between the FV and CPP. The FV of the middle cerebral artery and blood flow in the internal carotid artery exhibited flow patterns which changed correlatively depending on CPP reduction in experimental animals. Monitoring with TCD ultrasound is valuable in evaluating compression ischaemia in focal brain injury. But many complicated factors are considerable in diffuse brain injury.

Transcranial Doppler Evaluation of Cerebral Infarction in the Neonate*

We recorded cerebral artery flow velocities (CAFV) in two neonates with cerebral infarction, using transcranial Doppler sonography (TCD). Cerebral infarction was diagnosed by brain imaging. The arteries investigated were the middle cerebral artery (MCA), the internal carotid artery (ICA) and the anterior cerebral artery (ACA). The whole territory of right MCA was involved. A decrease in CAFV was noted in MCA and ICA of the affected side. Furthermore, early recordings of CAFV allowed us to distinguish perinatal infarction from antenatal infarction: in the former, Doppler signal was completely absent during the first days of life whereas in the latter, Doppler signal was reduced but present. The process of recanalization could be followed. The asymmetry of CAFV recorded in the neonatal period seems to persist definitively at least in MCA. These Doppler data correlate well with the evolutive stages of cerebral infarction shown by brain imaging. Beside US, CT and MRI scans, TCD may be a useful adjunct for identifying and following infants with suspected occlusion of major cerebral vessels.

Nimodipine tested in a human model of cerebral ischaemia

The anti-ischaemic properties of nimodipine 30 mg and 60 mg t.i.d. for 4 days has been tested in a double-blind, placebo-controlled, cross-over study based on the use of hyperventilation to reduce flow velocity in cerebral arteries. Whether the anti-ischaemic properties were due to a vasodilatator action on cerebral blood vessels or to an anti-ischaemic effect on cerebral neurons was studied. There was a slight cardiovascular effect, without any significant change in the EEG at rest. During standardized hyperventilation, there was no difference in the reduction in the blood flow velocity in the nimodipine and placebo groups (namely 56%, 56% and 59%). Both doses of nimodipine, however, significantly attenuated the hyperventilation-induced increase in slow EEG activity in the 1.5-6.0 Hz range. It is concluded that the anti-ischaemic properties of nimodipine are due to an effect on the central nervous system rather than to an effect on cerebral blood flow.

Cerebral blood flow velocities in the anterior cerebral arteries and basilar artery in hydrocephalus before and after treatment

We studied Pourcelot's index (PI), which shows cerebral vascular resistance, in the anterior cerebral arteries and basilar artery, and the PI ratio (Pourcelot's index in the anterior cerebral artery/Pourcelot's index in the basilar artery) in 11 measurements of hydrocephalus. The mean values of PI in the anterior cerebral artery, basilar artery, and the PI ratio before treatment were significantly higher than those after treatment and those in normal infants. Before treatment, the mean PI in the anterior cerebral arteries was significantly higher than the mean PI in the basilar artery. All PI ratios increased to 1.00 or more. After treatment and in normal infants, the mean PI in the anterior cerebral arteries was significantly lower than the mean PI in the basilar artery. All PI ratios decreased to less than 1.00. We believe that the PI ratio is useful to evaluate the need or effect of treatment in hydrocephalus.

Prediction of brain blood flow using pulsed Doppler ultrasonography in newborn lambs

The purpose of this study was to evaluate the ability of pulsed Doppler ultrasonography to predict brain blood flow by comparing measurements made in basal cerebral arteries using a pulsed Doppler system with measurements of brain blood flow using radioactive microspheres in lambs. We measured the instantaneous maximum velocity during peak systole and end diastole and the mean velocity over the pulse cycle in basal cerebral arteries, calculated Pourcelot's index of resistance and Gosling's pulsatility index, and used regression analysis to compare the pulsed Doppler measurements with brain blood flow measured with radioactive microspheres. Pulsed Doppler measurements of the peak systolic, end diastolic, and mean flow velocity in basal cerebral arteries were directly related to brain blood flow. In contrast, no linear relationship was detected between the resistance or pulsatility indices and brain blood flow measured by microspheres (p greater than 0.14). Prediction of brain blood flow for individual subjects lacks the quantitative precision necessary for use as a clinical tool. However, the direct relationship between brain blood flow and the peak systolic, end diastolic, and mean flow velocities in basal cerebral arteries supports the use of these measurements in clinical research for the qualitative assessment of change in brain blood flow.

Dose-Dependent Blood Flow Velocity Changes in the Basal Cerebral Arteries Following Low-Dose Ketamine

The effects of low-dose ketamine on blood flow velocity and pulsatility index (PI) in the basal cerebral arteries were studied in two groups of healthy volunteers (group A: 0.25 mg/kg, n = 10; group B: 0.5 mg/kg, n = 10) by means of a 2 MHz pulsed transcranial Doppler ultrasonic system (TCD) for an observation period of 70 min. In addition, mean arterial pressure (MAP), heart rate (HR), end-tidal CO2 (petCO2), and oxygen saturation (saO2) were recorded. The mean blood flow velocity (Vmean) increased significantly by 28% in group A and by 68% in group B within 2-9 min. In group B, the PI was reduced by 32% for a period of 2-7 min (p < 0.05). MAP (group A: -20%; group B: -26%) and HR (group A: -39%; group B: -54%) increased significantly (p < 0.05). Vmean and PI were significantly different between groups A and B, suggesting a dose-dependent stimulation of cerebral hemodynamics. The flow velocity increases cannot be entirely explained by systemic hemodynamic changes since there was no intergroup difference with respect to MAP and HR. No significant differences were observed with regard to petCO2 and saO2. With the assumption that the diameter of the insonated vessel is not changed by ketamine, the dose-dependent increase in Vmean with a concomitant decrease in PI may be interpreted as indicating an increase in cerebral blood flow.