Impaired dynamic cerebral autoregulation in middle cerebral artery stenosis

BACKGROUND AND PURPOSE: Analysis of dynamic cerebral autoregulation during transient falls in blood pressure is considered a sensitive and convenient method for evaluating patients with carotid artery stenosis. To this point, there have been few reports on the efficacy of using the thigh cuffs technique to analyse middle cerebral artery (MCA) stenosis. If it could be determined whether cerebral blood flow can be maintained (autoregulated) during sudden falls in arterial blood pressure (ABP), then it might be possible to identify patients with MCA stenosis who are at risk of stroke. METHODS: We used the thigh cuff technique to estimate dynamic cerebral autoregulation in 57 patients with MCA stenosis and 72 normal controls. After a stepwise fall in arterial blood pressure, we determined the rate of the rise of MCA blood velocity and compared it with the rate of the rise of arterial blood pressure. In this manner, the dynamic cerebral autoregulation of 11 patients undergoing MCA M1 stent angioplasty was estimated both pre- and post-operation. RESULTS: The autoregulatory index (ARI) was significantly reduced in patients with stenosed/occluded MCA (3.24 +/- 1.52), as compared with normal controls (5.25 +/- 1.39; p<0.001) (results reported as mean +/- SD). Poor ARI values are usually observed in patients with a higher degree of stenosis and particularly in patients with insufficient collateral compensation. ARI was significantly reduced in severe stroke patients (modified ranking scale>or=1), as compared with asymptomatic or TIA patients (p<0.05). After MCA stent angioplasty was performed, there was a significant improvement in ARI in 11 subjects, which caused a mean increase in ARI from 2.08 +/- 1.10 to 3.80 +/- 1.36 (p=0.008). CONCLUSIONS: Dynamic cerebral autoregulation is impaired in patients with middle cerebral artery stenosis. Assessing dynamic cerebral autoregulation may allow a subgroup of patients with MCA stenosis who are at risk of hemodynamic stroke to be identified. Dynamic cerebral disautoregulation in patients with severe MCA stenosis is mostly remedied by stent angioplasty.     

Rate of vasospasm following the transsylvian versus transcortical approach for selective amygdalohippocampectomy

Abstract

Affection of the cerebral circulation following the extraaxial transsylvian approach has been reported. This study aims at the comparison of the risk for the development of vasospasm in the transparenchymal transcortical versus the transsylvian approach for selective amygdalohippocampectomy in patients with Ammon's horn sclerosis. n = 80 consecutive patients (13–58 years) were randomized and allotted to either the transsylvian (TS) or transcortical (TC) group. Bilateral middle cerebral arteries (MCA) and internal carotid arteries (ICA) were examined with transcranial Doppler pre-operatively, and from post-operative day 1 to 7. Blood flow velocities (BFV) were compared via ANOVA. Post-operatively, ipsilateral (= side of operative approach) mean BFV increased significantly in both groups with a mean ipsilateral increase of 79.2% in the TS group, and 48.8% in the TC group. This intergroup difference was also statistically significant. In addition, contralateral BFV increased significantly to a maximum mean of 26.3% in the TS group with no significant increase in the TC group. The results in the TS group are interpreted as vasospasm and not hyperemia – due to dissection of the sylvian vessels and the breakdown of blood within the basal cisterns. Factors such as the extent of visual field cuts and results from neuropsychological testing must be taken into account before drawing a conclusion leading to a fundamental change in surgical strategy.     

Comparison of transcranial Doppler ultrasonography and positron emission tomography using a three-dimensional template of the middle cerebral artery

Abstract

Objective: Transcranial Doppler (TCD) measures blood flow velocities (BFV) and is an indirect method of assessing cerebral blood flow (CBF). Positron emission tomography (PET) is a direct method to measure CBF. This study evaluates the correlations between TCD and PET findings

Methods: Nine patients with a symptomatic carotid artery stenosis, who underwent CEA, were studied pre- and post-operatively on the ipsi- and contralateral sides. Measurements of the BFV, CO₂ reactivity, CBF, cerebral blood volume (CBV) and mean vascular transit time (MVTT) were performed using a three-dimensional volume of interest (VOI) for the middle cerebral artery (MCA).

Results: CBF in the MCA region, as measured with PET, shows a good correlation with BFV, as measured with TCD, with similar pattern for total, gray and white matter MCA territory (Pearson's correlation coefficients: 0.751, 0.748 and 0.748, respectively). This correlation was found in the pre-operative as well as the post-operative state. No association could be demonstrated between CO₂ reactivity and CBV or (Pearson's correlation coefficients: 0.051 and 0.166, respectively).

Conclusion: With PET, it is possible to create three-dimensional VOI of arterial territories. CBF measured in these VOI seems to correlate with BFV before and after CEA on ipsi- and contralateral sides, while CBV shows no association with pre-operative CO₂ reactivity.     

Cerebral and peripheral effects of laserneedle®-stimulation

Abstract

This study comprises scientific-theoretic fundamental investigations of laserneedle® technology, a new and painless method of acupuncture stimulation. Laserneedles® are not inserted in the skin, but are merely placed on the surface of the acupuncture point. The study documents the significant changes in peripheral microcirculation (p = 0.005) and surface temperature of the skin (p = 0.02) induced by laser, in 22 healthy volunteers (mean age 24.4 ± 2.6 years). In addition, a randomised cross-over study to characterise the specific changes in cerebral blood flow velocity with laserneedle® acupuncture (p < 0.001) is presented. These results provide important information for characterising the effects of laserneedle® acupuncture.     

Pseudoparadoxical dissociation of cerebral oxygen saturation and cerebral blood flow velocity after acupuncture in a woman with cerebrovascular dementia: a case report

Abstract

Acupuncture can increase both cerebral oxygen saturation and cerebral blood flow velocity. We describe a 77-year-old woman with cerebrovascular dementia in whom acupuncture reproducibly induced an increase of blood flow velocity but a decrease of regional oxygen saturation. At four of 11 acupuncture sessions, blood flow velocity was measured in the middle cerebral artery with transcranial Doppler sonography and cerebral regional oxygen saturation (rSO₂) with transcranial near infrared spectroscopy. Cerebral blood flow velocity increased by an average of 20% (range: 7–27%) at all four study points whereas rSO₂ consistently decreased by an average of 7% (range: 4–13%). Clinical status and cognitive function improved. These findings in a patient with vascular dementia may suggest increased oxygen extraction by activated neuronal structures.     

The relation between cerebral blood flow velocities as measured by TCD and the incidence of delayed ischemic deficits. A prospective study after subarachnoid hemorrhage

Abstract

Patients (n = 127) with aneurysmal subarachnoid hemorrhage (SAH) were examined by transcranial Doppler ultrasonography (TCD) in a prospective study to follow the time course of the posthemorrhagic blood flow velocity in both the middle cerebral artery (MCA) and in the anterior cerebral artery (ACA). Results were analysed to reveal their relationship and predictive use with respect to the occurrence of delayed ischemic deficits. Mean flow velocities (MFV) higher than 120 cm sec^-1 in MCA and 90 cm sec^-1 in ACA were interpreted as indicative for significant vasospasm. In 20 of our 127 patients (16%) a delayed ischemic deficit (DID) was subsequently diagnosed clinically (DID+ group). Patients in the DID+ group can be characterized as those individuals who presented early during the observation period post-SAH with highest values of MFV, a faster increase and longer persistence of pathologically elevated MFV-values (exceeding 120 cm sec^-1 in MCA and 90 cm sec^-1 in ACA). They also show a greater difference in MFVvalues if one compares the operated to the nonoperated side. Differences in MFV-values obtained in MCA or ACA were statistically significant (p < 0.05) for DID+ and DID- patients. The daily maximal increase of MFV was found between days 9 and 11 after SAH. In the DID+ group, the maximal MFV was 181 ± 26 cm sec^-1 in MCA and 119 ± 14 cm sec^-1 in ACA. In contrast to this, patients in the DID- group were found to present with MFV of 138 ± 11 cm sec^-1 in MCA and 100 ± 7 cm sec^-1 in ACA respectively. Delayed ischemic deficits appeared three times more often in DID+ patients than in patients with MFV < 120 cm sec^-1, if they showed a MFV > 120 cm sec^-1 in MCA. If pathological values were obtained in ACA, this ratio increases to about four times, if DID+ patients presented with MFV > 90 cm sec^-1 versus patients with MFV < 90 cm sec^-1. Daily monitoring of vasospasm using TCD examination is thus helpful to identify patients at high risk for delayed ischemic deficits. This should allow us to implement further preventive treatment regimens. [Neurol Res 2002; 24: 582-592]     

Distribution of artificial cerebral microemboli in stroke patients with patent foramen ovale

Abstract

Objectives: Patent foramen ovale (PFO) is considered as an important risk factor for cerebrovascular diseases. Nevertheless, the relationship between the distribution of highintensity transient signals (HITS), resulting from injection of air mixed with saline and detected by transcranial Doppler (TCD), and clinical cerebrovascular syndromes in these patients has not been investigated.

Methods: Using TCD, we screened 40 patients with stroke or transient ischemic attack (TIA), in whom PFO was proven by transesophageal echocariography (TEE). Of these, 30 patients (75%) with artificially produced HITS either in the middle cerebral artery (MCA) or the basilar artery (BA) were included in the analysis.

Results: Nineteen patients had a stroke or TIA in the carotid territory and 11 patients in the vertebro-basilar territory. HITS were found in the MCA in all 30 patients and in 21 of the 30 patients in the BA. Of the latter, ten patients were in the carotid group and 11 patients were in the veretebro-basilar group, p=0.011.

Conclusion: There is a significant association between the distribution of artificial HITS and the clinical cerebrovascular syndromes.     

Regional cerebral 18FDG uptake during subarachnoid hemorrhage induced vasospasm

Abstract

Objectives: The aim was to elucidate whether aneurysmal subarachnoid hemorrhage (SAH)-induced vasospasm induces changes of regional glucose uptake in surgically treated, asymptomatic cases.

Methods: ¹⁸FDG uptake (standardized uptake value, SUV) was analysed with PET in eight surgically treated aneurismal patients with a mean middle cerebral artery flow velocity >120 cm/seconds measured with transcranial Doppler ultrasound. Data were compared with a healthy control group using Statistical Parametric Mapping (SPM99b).

Results: Six of the eight patients had no focal neurological signs. The inhomogeneous bilateral increase in SUV (p<0.0001) was asymmetrical, with an almost 70% larger volume on the operated side. Reduced glucose uptake was found in the frontal and temporobasal regions of the two patients with neurological deficits (p<0.0001); the affected volume was 40% larger on the operated side.

Discussion: SAH-induced vasospasm results in widespread increase of glucose uptake—probably reflecting increased glycolysis. This was earlier than neurological focal signs appear. Decreased glucose uptake can be detected in severe cases of vasospasm reflected by neurological deficit. Although the changes are more prominent where surgery had taken place our results suggest that not only the surgery, but also subarachnoid blood might have resulted in our findings.     

Symptomatic middle cerebral artery stenosis.

The clinical course of 16 consecutive patients with stenosis of the middle cerebral artery angiographically diagnosed between 1970 and 1977 was reviewed. All were managed nonsurgically with medical treatment including anticoagulation. Prior to therapy, transient ischemic attacks had occurred in 15 and cerebral infarction in 11. Initially, none exhibited more than a minor neurological deficit. Follow-up from one month to six years showed a benign course in 14 patients: 13 experienced no subsequent transient attacks or new stroke; 1 had repeated transient attacks for two years but not in the following four years. Two of the 16 developed a severe stroke early in the course, before medical therapy was started. No distinctive clinical or radiographic features were identified that permitted prediction of the outcome. This small series supports the need for a randomized study of bypass efficacy in these patients.     

Embolism in acute middle cerebral artery stenosis

OBJECTIVE: To investigate the frequency of middle cerebral artery (MCA) stenosis in a series of nonselected patients and the coexistence of microembolic signals with stenosis. METHODS: MCA stenosis was sought by transcranial Doppler (TCD) in 387 patients admitted consecutively with acute ischemic cerebrovascular disease within the first 48 hours of the onset of symptoms and again at 6 months. TCD monitoring for microembolic signals was performed on all patients with MCA stenosis. RESULTS: MCA stenoses were found in 29 patients (7%), although in only 20 patients (5%) was the stenosis symptomatic. Microembolic signals were detected in five of 14 symptomatic stenoses (36%) monitored at the acute phase, but none were found in the chronic phase or in asymptomatic stenosis. Despite one third of symptomatic patients having had a further source of emboli, microembolic signals were detected only distally to the MCA stenosis. In the symptomatic group, 25% of stenoses had completely disappeared 6 months after stroke. Microembolic signal detection at the acute phase was associated with the subsequent disappearance of the stenosis. CONCLUSIONS: The frequency of symptomatic MCA stenosis in acute ischemic stroke was 5% in the population studied. Many stenoses are transient, and microembolic signals are often detectable at the poststenotic segment in the acute phase. The origin of at least 25% of symptomatic acute MCA stenoses may be embolic rather than atherosclerotic.     

Impaired dynamic cerebral autoregulation at extreme high altitude even after acclimatization

Cerebral blood flow (CBF) increases and dynamic cerebral autoregulation is impaired by acute hypoxia. We hypothesized that progressive hypocapnia with restoration of arterial oxygen content after altitude acclimatization would normalize CBF and dynamic cerebral autoregulation. To test this hypothesis, dynamic cerebral autoregulation was examined by spectral and transfer function analyses between arterial pressure and CBF velocity variabilities in 11 healthy members of the Danish High-Altitude Research Expedition during normoxia and acute hypoxia (10.5% O₂) at sea level, and after acclimatization (for over 1 month at 5,260 m at Chacaltaya, Bolivia). Arterial pressure and CBF velocity in the middle cerebral artery (transcranial Doppler), were recorded on a beat-by-beat basis. Steady-state CBF velocity increased during acute hypoxia, but normalized after acclimatization with partial restoration of SaO₂ (acute, 78%±2% chronic, 89%±1%) and progression of hypocapnia (end-tidal carbon dioxide: acute, 34±2 mm Hg; chronic, 21±1 mm Hg). Coherence (0.40±0.05 Units at normoxia) and transfer function gain (0.77±0.13 cm/s per mm Hg at normoxia) increased, and phase (0.86±0.15 radians at normoxia) decreased significantly in the very-low-frequency range during acute hypoxia (gain, 141%±24% coherence, 136%±29% phase, −25%±22%), which persisted after acclimatization (gain, 136%±36% coherence, 131%±50% phase, −42%±13%), together indicating impaired dynamic cerebral autoregulation in this frequency range. The similarity between both acute and chronic conditions suggests that dynamic cerebral autoregulation is impaired by hypoxia even after successful acclimatization to an extreme high altitude.     

Cerebral autoregulation in middle cerebral artery territory precedes that of posterior cerebral artery in human cortex.

OBJECTIVE: Cerebral autoregulation tends to compensate changes in arterial blood pressure. This mechanism of cerebral blood flow regulation appears to be insufficient in orthostatic dysregulation in which mainly vertebrobasilar symptoms occur. To investigate this hypothesis, we compared cerebral autoregulation in the vascular territory of the carotic and vertebrobasilar vessel system using a leg cuff test to induce a drop in cerebral perfusion pressure. METHODS: We measured blood flow velocity in 10 healthy young volunteers (aged 26.7 +/- 0.3 years, 7 male) simultaneously in the middle and posterior cerebral artery with transcranial Doppler sonography. A leg cuff test was used to induce a sudden decrease in arterial blood pressure. Arterial blood pressure was measured with a non-invasive photoplethysmographic method. The averaged relative blood flow velocity changes due to the pressure step were compared between both vessel territories. RESULTS: After cuff release systolic (diastolic) blood flow velocity increased with a latency of 1.1 +/- 0.3 s (1.8 +/- 0.4 s). Due to a smaller decrease and identical time courses cerebral blood flow velocity recovery in the posterior cerebral artery precedes blood flow recovery in the middle cerebral artery by 0.9 +/- 0.3 s. DISCUSSION: Cerebral autoregulation in the carotid and vertebrobasilar system does not differ in the time course of the blood flow velocity recovery. Due to a smaller decrease in blood flow velocity recovery in the posterior cerebral artery precedes recovery in the middle cerebral artery by nearly 1 s.     

Prognosis of asymptomatic stenosis of the middle cerebral artery

BACKGROUND: The risk of ischaemic events in asymptomatic intracranial atherosclerosis is unknown. OBJECTIVE: To follow up patients with asymptomatic atherosclerotic middle cerebral artery stenosis (MCAS) to evaluate the long term stroke risk in its territory. METHODS: Consecutive white patients with asymptomatic atherosclerotic MCAS were enrolled. Patients with MCAS of possible or proven non-atherosclerotic origin were excluded. MCAS was assessed by transcranial colour duplex sonography according to published angiography validated criteria. Medical treatment was given at the discretion of the treating physician. RESULTS: 50 patients were included and followed for (mean (SD)) 815 (351) days; three were lost to follow up. MCAS was < 50% in 38 and > or = 50% in 12. No patient suffered an ischaemic event in the MCAS territory; one had a transient ischaemic attack in the contralateral hemisphere. Three patients died, one from a subdural haematoma in the contralateral hemisphere, and two from non-stroke-related causes. Medical treatment at baseline included antithrombotic drugs in 42 cases (antiplatelet agent, n = 39; warfarin, n = 3), and statins in 22; at the end of follow up 45 of the 47 survivors were on antithrombotic drugs (antiplatelet agent, n = 37; warfarin, n = 8), and 30 were on statins. CONCLUSIONS: Asymptomatic MCAS of atherosclerotic origin appears to have a benign long term prognosis with a low risk of ipsilateral stroke in medically treated white patients.     

Impaired dynamic cerebral autoregulation is associated with the severity of neuroimaging features of cerebral small vessel disease

AimsCerebral small vessel disease (CSVD) is characterized by functional and structural changes in small vessels. We aimed to elucidate the relationship between dynamic cerebral autoregulation (dCA) and neuroimaging characteristics of CSVD.MethodsA case‐control study was performed. Cerebral blood flow velocity (CBFV) of bilateral middle cerebral arteries and spontaneous arterial blood pressure were simultaneously recorded. Transfer function analysis was used to calculate dCA parameters (phase, gain, and the rate of recovery of CBFV [RoRc]). Neuroimaging characteristics of CSVD patients were evaluated, including lacunes, white matter hyperintensities (WMH), cerebral microbleeds (CMBs), perivascular spaces (PVS), and the total CSVD burden.ResultsOverall, 113 patients and 83 controls were enrolled. Compared with the control group, the phase at low frequency and the RoRc in CSVD patients were lower, and the gain at very low and low frequencies were higher, indicating bilaterally impaired dCA. Total CSVD burden, WMH (total, periventricular and deep), severe PVS, and lobar CMBs were independently correlated with the phase at low frequency.ConclusionsOur findings suggested that dCA was compromised in CSVD patients, and some specific neuroimaging characteristics (the total CSVD burden, WMH, severe PVS and lobar CMBs) might indicate more severe dCA impairment in CSVD patients.     

Effect of chronic middle cerebral artery stenosis on the local cerebral hemodynamics

In 36 patients with angiographically proven middle cerebral artery (MCA) stenosis, local cerebral hemodynamics were studied employing angiography, 133Xe inhalation regional cerebral blood flow (rCBF) measurements and CT scans. They had transient ischemic attacks in 8 and completed stroke in 28. The patients with less than 50% stenosis (n = 16) had no hemodynamic abnormality in angiographical and rCBF examinations. The infarction in this group was small and located in the basal ganglia area. The patients with 50 to 74% stenosis (n = 9) often revealed a delayed filling of MCA branches in the angiography, however, they showed no significant rCBF reduction. The infarction in this group was also small and located in the basal ganglia area. The patients with 75 to 99% stenosis (n = 11) exhibited a significant flow depression both in angiographical and rCBF examinations. Three of them had large cerebral infarction in the watershed zone or the cerebral cortex. The results of the present study suggest that the hemodynamic effect of MCA stenosis begins to manifest at 50% in grade and becomes apparent at 75%. The danger of hemodynamic crisis as well as the risk of large cerebral infarction may increase when MCA stenosis exceeds 75% in grade.