Transcranial Doppler assessment of cerebral perfusion reserve in patients with carotid occlusive disease and no evidence of cerebral infarction

Cerebral autoregulation, spreading depolarization, and implications for targeted therapy in brain injury and ischemia

Cerebral autoregulation is an intrinsic myogenic response of cerebral vasculature that allows for preservation of stable cerebral blood flow levels in response to changing systemic blood pressure. It is effective across a broad range of blood pressure levels through precapillary vasoconstriction and dilation. Autoregulation is difficult to directly measure and methods to indirectly ascertain cerebral autoregulation status inherently require certain assumptions. Patients with impaired cerebral autoregulation may be at risk of brain ischemia. One of the central mechanisms of ischemia in patients with metabolically compromised states is likely the triggering of spreading depolarization (SD) events and ultimately, terminal (or anoxic) depolarization. Cerebral autoregulation and SD are therefore linked when considering the risk of ischemia. In this scoping review, we will discuss the range of methods to measure cerebral autoregulation, their theoretical strengths and weaknesses, and the available clinical evidence to support their utility. We will then discuss the emerging link between impaired cerebral autoregulation and the occurrence of SD events. Such an approach offers the opportunity to better understand an individual patient's physiology and provide targeted treatments.

A narrative review of the pathophysiology of ischemic stroke in carotid plaques: a distinction versus a compromise between hemodynamic and embolic mechanism

Atherosclerotic carotid artery stenosis causes about 10–20% of all ischemic strokes through two main mechanisms: hemodynamic impairment in case of significant stenosis and thromboembolism from an atherosclerotic plaque regardless of the degree of stenosis. The latter is the most frequent mechanism and appear to result from embolization from a vulnerable atherosclerotic plaque or acute occlusion of the carotid artery and propagation of thrombus distally. Downstream infarcts may occur in a territory of major cerebral artery or at the most distal areas between two territories of major cerebral arteries, the so-called watershed (WS), or border zone area. Although WS infarcts, especially deep WS infarct, were historically thought to be due to hemodynamic compromise, the role of microembolism has also been documented, both mechanisms may act synergistically to promote WS infarcts. Routine and more advanced imaging techniques may provide information on the underlying mechanism involved in ipsilateral ischemic stroke. A better understanding of ischemic stroke pathogenesis in carotid stenosis may limit the use of routine non-selective shunt, whose benefit-risk balance is debated, to patients with hemodynamic impairment.

After reviewing existing evidence underpinning the contribution of the two mechanisms in downstream ischemic stroke and the various imaging techniques available to investigate them, we will focus on the pathogenesis of WS infarcts that remains debated.

Cognition and Hemodynamics

The relationship between cerebral hemodynamics and cognitive performance has increasingly become recognized as a major challenge in clinical practice for older adults. Both diabetes and hypertension worsen brain perfusion and are major risk factors for cerebrovascular disease, stroke and dementia. Cerebrovascular reserve has emerged as a potential biomarker for monitoring pressure-perfusion-cognition relationships. Endothelial dysfunction and inflammation, microvascular disease, and mascrovascular disease affect cerebral hemodynamics and play an important role in pathohysiology and severity of multiple medical conditions, presenting as cognitive decline in the old age. Therefore, the identification of cerebrovascular vascular reactivity as a new therapeutic target is needed for prevention of cognitive decline late in life.

Effects of acetazolamide on the micro- and macro-vascular cerebral hemodynamics: a diffuse optical and transcranial doppler ultrasound study

Acetazolamide (ACZ) was used to stimulate the cerebral vasculature on ten healthy volunteers to assess the cerebral vasomotor reactivity (CVR). We have combined near infrared spectroscopy (NIRS), diffuse correlation spectroscopy (DCS) and transcranial Doppler (TCD) technologies to non-invasively assess CVR in real-time by measuring oxy- and deoxy-hemoglobin concentrations, using NIRS, local cerebral blood flow (CBF), using DCS, and blood flow velocity (CBFV) in the middle cerebral artery, using TCD. Robust and persistent increases in oxy-hemoglobin concentration, CBF and CBFV were observed. A significant agreement was found between macro-vascular (TCD) and micro-vascular (DCS) hemodynamics, between the NIRS and TCD data, and also within NIRS and DCS results. The relative cerebral metabolic rate of oxygen, rCMRO(2), was also determined, and no significant change was observed. Our results showed that the combined diffuse optics-ultrasound technique is viable to follow (CVR) and rCMRO(2) changes in adults, continuously, at the bed-side and in real time.

Diastolic blood pressure levels and ischemic stroke incidence in older adults with white matter lesions

BACKGROUND

The optimal blood pressure level to minimize the risk of ischemic stroke (IS) in older adults is undetermined. Cerebral white matter lesions (WML), prevalent in older adults, may be a marker for vulnerability to IS. We aimed at determining the relationship between diastolic blood pressure (DBP) levels and IS in the presence of WML.

METHODS

The Cardiovascular Health Study population (N = 3,345, age ≥ 65 years, N = 3,345) was followed between 1989 and 2002 for IS incidence. Survival analysis included quintiles of DBP analyzed within WML levels controlling for age and cardiovascular disease.

RESULTS

DBP had no effect on IS incidence in low WML levels but had a marginally significant J-curve relationship with IS in high WML levels: the adjusted hazard ratio for IS in the lowest (<63 mmHg) and highest (≥ 80) DBP quintiles compared with the third (nadir, 69-73 mmHg) was 1.64 (95% confidence interval: 0.93-2.9) and 1.83 (95% confidence interval: 1.06-3.15), respectively.

CONCLUSIONS

In older adults with low-grade WML, low DBP may not pose a risk for IS. However, in high-grade WML, IS risk may increase in DBP less than 69 mmHg but is highest more than 80 mmHg. People with high-grade WML may be at risk of IS in high and low DBP.

The relationship between blood pressure and cognitive function

The relationship between blood pressure (BP) and cognitive outcomes in elderly adults has implications for global health care. Both hypertension and hypotension affect brain perfusion and worsen cognitive outcomes. The presence of hypertension and other vascular risk factors has been associated with decreased performance in executive function and attention tests. Cerebrovascular reserve has emerged as a potential biomarker for monitoring pressure-perfusion-cognition relationships. A decline in vascular reserve capacity can lead to impaired neurovascular coupling and decreased cognitive ability. Endothelial dysfunction, microvascular disease, and mascrovascular disease in midlife could also have an important role in the manifestations and severity of multiple medical conditions underlying cognitive decline late in life. However, questions remain about the role of antihypertensive therapies for long-term prevention of cognitive decline. In this Review, we address the underlying pathophysiology and the existing evidence supporting the role of vascular factors in late-life cognitive decline.

Acetazolamide improves cerebral hemodynamics in CADASIL

BACKGROUND

Acetazolamide (ACZ), a carbonic anhydrase inhibitor, causes a rapid increase in cerebral blood flow (CBF) in patients with cerebrovascular diseases. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a hereditary cerebrovascular disease caused by mutations in the NOTCH3 gene. Recent studies suggest that ACZ infusion significantly increases cerebral perfusion, even within areas of impaired cerebral vasoreactivity in CADASIL patients. This study evaluates the efficacy and tolerance of a 24-week treatment with 250 mg/d ACZ, which could be chronically implemented to improve cerebral hemodynamics in CADASIL.

METHODS

CADASIL patients (n=16) were treated with ACZ (250 mg) daily for 24 weeks. The mean blood flow velocity (MFV) of the middle cerebral artery (MCA) and CO(2)-induced cerebrovascular reactivity (CVR) were tested using transcranial Doppler sonography (TCD) before and after treatment.

RESULTS

After ACZ treatment, the MFV in the MCA was significantly greater at rest (57.68+/-12.7 cm/s versus 67.12+/-9.4 cm/s; P=0.001). Additionally, the CO(2)-induced vasoreactivity increased significantly (13.17+/- 6.9% versus 20.69+/-8.2%, P=0.004), and the pulsatility index (PI) decreased significantly (0.82+/-0.1 versus 0.73+/-0.08; P=0.001). The relative ACZ-induced enhancement of CO(2) vasoreactivity was not correlated with pretreatment MFV (SRCC=-0.122; P=0.659).

CONCLUSIONS

The present study provides the first evidence that ACZ therapy can increase CBF and CVR in CADASIL patients.

The efficacy of direct extracranial-intracranial bypass in the treatment of symptomatic hemodynamic failure secondary to athero-occlusive disease: a systematic review

OBJECTIVE

The 1985 International Extracranial-Intracranial (EC-IC) Bypass Trial failed to show a benefit following surgery in patients with varying degrees of angiographic ICA stenosis. More recent studies using modern technology to identify appropriate candidates, however, have generated promising findings. As a result, controversy exists regarding the role of this technique in the treatment of symptomatic athero-occlusive disease. To this end, we performed a systematic review and quantitative analysis of the literature to determine if a subset of patients with symptomatic hemodynamic failure secondary to athero-occlusive disease may benefit from direct EC-IC bypass.

METHODS

We performed a MEDLINE (1985-2007) database search using the following keywords, singly and in combination: EC-IC bypass, hemodynamic failure and misery perfusion. Additional studies were identified manually by scrutinizing references from identified manuscripts, major neurosurgical journals and texts, and personal files. Our literature search divided studies into three categories: natural history of patients with stage I hemodynamic failure (16 studies, 2320 patients), natural history of patients with stage II hemodynamic failure (3 studies 163 patients), and outcomes of patients with hemodynamic failure treated by EC-IC bypass (23 studies 506 patients).

RESULTS

Patients with severe stage I and stage II hemodynamic failure are at higher risk of cerebral infarction than those with mild disease (p=.014, OR 1.17-4.08 and p=0.10, OR 0.89-3.63, respectively). Additionally, patients with severe hemodynamic failure respond better to surgery than those with mild disease (p=0.03, OR 0.16-0.92).

CONCLUSIONS

Patients with severe hemodynamic failure secondary to athero-occlusive disease appear to benefit from direct EC-IC bypass surgery. As a result, the conclusions of the 1985 International EC-IC Bypass Trial may not be applicable to this subset of patients. A randomized clinical trial involving this patient population is warranted.

Impaired cerebral autoregulation in obstructive sleep apnea

Obstructive sleep apnea (OSA) increases the risk of stroke independent of known vascular and metabolic risk factors. Although patients with OSA have higher prevalence of hypertension and evidence of hypercoagulability, the mechanism of this increased risk is unknown. Obstructive apnea events are associated with surges in blood pressure, hypercapnia, and fluctuations in cerebral blood flow. These perturbations can adversely affect the cerebral circulation. We hypothesized that patients with OSA have impaired cerebral autoregulation, which may contribute to the increased risk of cerebral ischemia and stroke. We examined cerebral autoregulation in patients with and without OSA by measuring cerebral artery blood flow velocity (CBFV) by using transcranial Doppler ultrasound and arterial blood pressure using finger pulse photoplethysmography during orthostatic hypotension and recovery as well as during 5% CO2 inhalation. Cerebral vascular conductance and reactivity were determined. Forty-eight subjects, 26 controls (age 41.0±2.3 yr) and 22 OSA (age 46.8±2.3 yr) free of cerebrovascular and active coronary artery disease participated in this study. OSA patients had a mean apnea-hypopnea index of 78.4±7.1 vs. 1.8±0.3 events/h in controls. The oxygen saturation during sleep was significantly lower in the OSA group (78±2%) vs. 91±1% in controls. The dynamic vascular analysis showed mean CBFV was significantly lower in OSA patients compared with controls (48±3 vs. 55±2 cm/s; P <0.05, respectively). The OSA group had a lower rate of recovery of cerebrovascular conductance for a given drop in blood pressure compared with controls (0.06±0.02 vs. 0.20±0.06 cm·s−2·mmHg−1; P <0.05). There was no difference in cerebrovascular vasodilatation in response to CO2. The findings showed that patients with OSA have decreased CBFV at baseline and delayed cerebrovascular compensatory response to changes in blood pressure but not to CO2. These perturbations may increase the risk of cerebral ischemia during obstructive apnea.

The extracranial-intracranial bypass trial: implications for future investigations

The 1985 International Extracranial-Intracranial (EC-IC) Bypass Trial failed to show a surgical benefit of EC-IC bypass in patients with varying degrees of angiographic stenosis. This study was limited by the technology available at the time it was conducted. In the 20 years since, there has been considerable progress in imaging techniques that now enable the identification of a subset of stroke patients with hemodynamic ischemia. In the present study, the authors review the relevant literature and propose a reevaluation of the benefits of the EC-IC bypass procedure using these new imaging techniques. The authors reviewed the admission criteria for the EC-IC Bypass Trial in the light of more recently discovered neurovascular physiology and showed that the imaging criteria used in that trial are not physiologically adequate. A MED-LINE (1985-2007) database search for EC-IC case studies was conducted, and additional studies were identified manually by scrutinizing references from identified manuscripts, major neurosurgical journals and texts, and personal files.

The impact of carotid stenting on the hemodynamic parameters and cerebrovascular reactivity of the ipsilateral middle cerebral artery

OBJECTIVE

The study was conducted to determine the effect of carotid angioplasty and stenting (CAS) on the hemodynamic parameters and cerebrovascular reactivity (CVR) of the ipsilateral middle cerebral artery (MCA) and examine the relation between preprocedural exhausted CVR and perioperative neurologic events.

METHODS

The study included 29 patients with severe extracranial carotid stenosis undergoing CAS. Transcranial Doppler imaging was performed before the procedure, 2 days, and 2 to 4 months postoperatively. Peak systolic velocity, end-diastolic velocity, mean flow velocity, and pulsatility index of the ipsilateral MCA were recorded at rest. CVR was assessed with the breath holding test: the increase of mean flow velocity and the breath holding index were calculated.

RESULTS

Peak systolic and mean flow velocities increased significantly in both postoperative studies compared to the preoperative values, end-diastolic velocity was significantly elevated only in the first study, and pulsatility index did not change significantly. When stimulated by breath holding, preoperative mean flow velocity did not increase significantly compared with the resting values; however, it did increase significantly during breath holding in both studies after CAS. The breath holding index improved significantly from -0.35 (-0.71 to 0.55) to 0.38 (0.12 to 0.61) at 2 days (P = .049) and 0.44 (0.31 to 0.92) at 2 to 4 months (P = .020). Exhausted CVR of the MCA preoperatively was associated with increased risk of neurological complications during or after the procedure (P = .006).

CONCLUSIONS

CAS may improve the hemodynamic parameters and the vasomotor reactivity in the ipsilateral MCA. Exhausted CVR is associated with an increased risk of periprocedural neurologic complications.

Management of asymptomatic carotid stenosis in patients undergoing general and vascular surgical procedures

Current available data do not seem to support the strategy for carotid endarterectomy prior to surgical intervention in patients with asymptomatic carotid stenosis. However, in patients with coronary artery disease, synchronous carotid endarterectomy and coronary artery bypass grafting should be considered where there is a proven surgical risk of <3% with unilateral asymptomatic stenosis >60% or bilateral carotid stenosis >75% on the same side as the most severe stenosis. Clarification of the optimal strategy requires an adequately powered, multicentre, randomised clinical trial.

Cerebral hemodynamic reserve and early neurologic deterioration in acute ischemic stroke

Early neurological deterioration (END) is associated with increased mortality and morbidity. Although several predictive factors have been reported, there are little data about the hemodynamic factors. Our aim was to determine the capacity of cerebral hemodynamic reserve (CHR) to predict END. We studied 100 hospitalized patients with a first ever ischemic stroke of the middle cerebral artery (MCA) within the first 24 hours of symptoms onset. END was defined as a drop of at least one point in the Canadian Stroke Scale between admission and 72 hours. The mean flow velocity (mV) in the MCA and the CHR were measured by means of transcranial Doppler within the first 24 hours of admission. The CHR was expressed as the percentage increase in the MCA mV divided by the absolute increase in the end-tidal CO2 pressure in mm Hg after carbogen inhalation. END was observed in 23 patients. Reduced values of the mV in the symptomatic MCA (P = 0.043) and of the CHR in the symptomatic hemisphere (P < 0.001) were significantly associated with END. A CHR of less than 2%/1 mm Hg was independently associated with END (OR 8.45, 95% CI 1.82-39.2) after adjusting for potential confounders. CHR impairment within the first 24 hours of acute ischemic stroke is associated with a higher risk of END. This technique may be useful in selecting patients requiring a more intensive management.

Acetazolamide as a vasodilatory stimulus in cerebrovascular diseases and in conditions affecting the cerebral vasculature

Pathologic processes affecting the brain vessels may damage cerebral vasodilatory capacity. Early detection of cerebral dysfunction plays an important role in the prevention of cerebrovascular diseases. In recent decades acetazolamide (AZ) has frequently been used for this purpose. In the present work the mechanism of action and the previous studies are reviewed. The authors conclude that AZ tests are useful in cerebrovascular research. Further investigations are recommended to prove how impaired reserve capacity and reactivity influence the stroke risk in patients and whether these tests may indicate therapeutic interventions.

Assessment of cerebrovascular reserve capacity in asymptomatic and symptomatic hemodynamically significant carotid stenoses and occlusions

BACKGROUND

Cerebrovascular reactivity measurements are believed to be a helpful tool for selecting patients who are at higher risk for hemodynamic strokes. The aim of this study was to compare cerebral vasoreactivity among patients suffering from internal carotid artery stenosis of different severity (asymptomatic stenosis, asymptomatic occlusion, symptomatic stenosis, symptomatic occlusion).

METHODS

Sixty-two patients with asymptomatic and symptomatic internal carotid artery stenoses and occlusions underwent transcranial Doppler-acetazolamide tests. Absolute velocities of the middle cerebral arteries (MCAV), percent increases of the MCAV at different time points of the test (cerebrovascular reactivity, CVR) and maximal percent increase after administration of acetazolamide (cerebrovascular reserve, CRC) were compared on the affected and non-affected sides. Asymmetry indices (CRC (affected side)/CRC (non-affected side)) were compared between the groups of different severity of obstructive lesion.

RESULTS

Resting MCAV was similar on both sides in all groups. A significant side-difference of the MCAV values after acetazolamide was observed only in the symptomatic groups. Difference of cerebrovascular reserve capacity between the affected and non-affected side was statistically significant only in the symptomatic groups (CRC symptomatic stenosis 36.6 +/- 20.9% vs. 71.1 +/- 27.9%, CRC symptomatic occlusion: 31.2 +/- 24.6% vs. 64.5 +/- 29.7%). Asymmetry index of the CRC was near to 1 in the asymptomatic stenosis group only, while in all the other groups this index referred to a significant hemispheric asymmetry of the vasoreactivity.

CONCLUSIONS

Although in general cerebrovascular reserve capacity is compromised in cases of hemodynamically significant carotid lesions, there is a large individual variability within the subgroups. Further randomized studies are needed to clarify whether the clinical efficiency of carotid endarterectomy and extra-intracranial bypass may be improved by selecting the patients using hemodynamic criteria.

Cerebrovascular reserve in patients with carotid occlusive disease assessed by stable xenon-enhanced ct cerebral blood flow and transcranial Doppler

BACKGROUND AND PURPOSE

Cerebrovascular reserve (CVR) by both transcranial Doppler ultrasonography (TCD) and quantitative cerebral blood flow (CBF) can identify subgroups of patients at increased risk for stroke. A direct comparison of CVR measurements obtained with both technologies in patients with cerebrovascular occlusive disease is lacking.

METHODS

CVRs before and after acetazolamide administration (1 g IV) were measured by TCD insonation of the middle cerebral artery (MCA) and CBF obtained with stable xenon CT (Xe/CT) in 38 patients with carotid occlusive disease. Sensitivity/specificity calculations were based on 2 Xe/CT MCA values: an average over 4 levels and the level with the lowest percent change in CBF. Compromised CVR was defined as no reactivity or a decrease in reactivity.

RESULTS

Using the analysis of the systolic TCD, we found that velocity changes compared with the average Xe/CT MCA CVR showed a sensitivity of 33%, specificity of 90.6%, positive predictive value of 54.5%, and negative predictive value of 80%. The sensitivity of TCD compared with the lowest Xe/CT CBF CVR was 35.5%, specificity and positive predictive values were 100%, and negative predictive value was 66.7%. The index of validity was between 72% and 76%.

CONCLUSIONS

TCD is much less sensitive than Xe/CT CBF in identifying patients with compromised CVR. This may be a result of the inability of TCD to identify patients with compromised reserves when their MCA blood flow comes from collateral sources. The lack of correlation between TCD and Xe/CT CBF for identifying patients with compromised CVR should be considered when stroke risk assessments are made by TCD.

An association between anxiety and neurocardiogenic syncope during head-up tilt table testing

To study the association between anxiety and neurocardiogenic syncope as determined by head-up tilt table testing (HUT) in men and women with presyncope or syncope, patients with unexplained syncope or presyncope undergoing HUT were asked to complete the Burns Anxiety Inventory (BAI), a validated inventory of 33 questions with responses graded from 0 to 3. HUT consisted of a 30-minute tilt to 60 degrees, which if negative, was repeated with an isoproterenol infusion. A positive HUT was defined as symptomatic hypotension and/or bradycardia. Of the 66 patients who completed the BAI and underwent HUT, 33 were men and 33 were women. The mean age was 57 +/- 18 years (17-91 years). Patients with a positive HUT had a higher BAI score than those with a negative HUT (22 +/- 12 vs 14 +/- 13, P = 0.017). This association was stronger in women with a BAI score of 24 +/- 11 in those with a positive HUT versus 13 +/- 8 in those with a negative HUT (P = 0.005). In contrast, the mean BAI score for men with a positive HUT was 19 +/- 13, as compared to 15 +/- 16 for a negative HUT (P = 0.5). In conclusion, the present study demonstrates a statistical association between anxiety (as determined by BAI) and HUT result. Gender-based analysis revealed a more statistically significant relationship between anxiety and HUT outcome for women as compared to men.

Is the acetazolamide test valid for quantitative assessment of maximal cerebral autoregulatory vasodilation? An experimental study

BACKGROUND AND PURPOSE

The cerebral vasodilating effect of acetazolamide (ACZ) injection has been used as an index of the autoregulatory vasodilation (or cerebral perfusion reserve). The question of whether the ACZ test assesses the maximal autoregulatory vasodilating capacity is not definitely resolved. The effects of ACZ injection on this reserve at a dose producing maximal vasodilation have never been evaluated and may help to resolve this problem.

METHODS

The effect of ACZ injection on cerebral blood flow (CBF) autoregulation was tested in anesthetized rats. A pilot experiment evaluated the dose-effect relationship of injected ACZ, cumulative doses (n=4, group 1), and independent bolus doses (n=6, group 2). CBF was estimated by laser-Doppler flowmetry, and cerebrovascular resistance (CVR) was calculated from mean arterial blood pressure (MABP) and from CBF (expressed as a percentage of baseline CBF). A bolus of ACZ of 21 mg/kg produced the maximal cerebral vasodilation that could be obtained by ACZ administration. In the main experiment, MABP was lowered from 110 to 20 mm Hg by stepwise bleeding in 3 groups of 6 animals treated 10 minutes before bleeding by injection of saline (group 3), 7 mg/kg ACZ (group 4), or 21 mg/kg ACZ (group 5).

RESULTS

The CVR-MABP relationship was linear in all groups, indicating that CBF autoregulation was still effective after ACZ administration.

CONCLUSIONS

These results indicate that maximal ACZ-induced cerebral vasodilation is not quantitatively equivalent to maximal autoregulatory vasodilating capacity in anesthetized rats.

Cerebrovascular reactivity and reserve capacity in type II diabetes mellitus

The aim of the study was to test the hypothesis that cerebrovascular reserve capacity and cerebrovascular reactivity are impaired in patients suffering from non insulin-dependent diabetes mellitus. We also intended to investigate factors which may influence resting cerebral blood flow velocity and cerebrovascular reserve capacity. A total of 28 patients suffering from type II diabetes mellitus and 20 healthy control subjects were studied. Based on diabetes duration patients were divided into two groups: subjects with > 10 years and those with < or = 10 years disease duration. Middle cerebral artery mean blood flow velocities were measured at rest and after intravenous administration of 1g acetazolamide. Cerebrovascular reactivity and reserve capacity were calculated. Blood glucose, insulin, glycosylated hemoglobin, hemostatic factors (fibrinogen, alpha-2 macroglobulin and von Willebrand factor antigen) were determined. Cerebrovascular reactivity and reserve capacity values were compared between the two diabetic subgroups and controls. Correlations between laboratory parameters and cerebrovascular reserve were investigated by linear regression analysis. Resting cerebral blood flow velocity was similar in controls and in the two diabetic subgroups. Cerebrovascular reactivity was elevated for a shorter time in patients with > 10 years disease duration than in controls and short-term diabetic patients. Cerebrovascular reserve capacity was lower in the long-term diabetes group (means +/- SD: 39.6 +/- 20.7%) than in patients with < or = 10 years disease duration (63.3 +/- 17.4%, p < 0.02 after Bonferroni correction). Cerebrovascular reserve capacity was inversely related to the duration of the disease (R = 0.53, p < 0.003). None of the determined laboratory factors had any relation with resting cerebral blood flow and cerebrovascular reserve capacity. The vasodilatory ability of cerebral arterioles is diminished in long-standing type II diabetes mellitus.

Age and sex differences in cerebral hemodynamics: a transcranial Doppler study

BACKGROUND AND PURPOSE

Hemodynamic factors seem to play an important role in the pathogenesis of cerebral ischemic events. The aim of this study was to evaluate whether changes in cerebrovascular reactivity occur in women after menopause.

METHODS

Using transcranial Doppler ultrasonography, we studied the changes of flow velocity after hypercapnia in the middle cerebral arteries of 45 healthy premenopausal women (mean age, 32.3 years; range, 20 to 47 years) and 40 postmenopausal women (mean age, 54.4 years; range, 48 to 64 years). The same measurements were recorded in two groups of healthy male subjects age matched with premenopausal (45 subjects) and postmenopausal women (40 subjects). Moreover, a subgroup of postmenopausal women aged 48 to 53 years (15 subjects) were compared with a group of 15 premenopausal women of the same age. We obtained hypercapnia with breath holding and evaluated cerebrovascular reactivity with the breath-holding index (BHI).

RESULTS

BHI was significantly lower in postmenopausal women (0.89+/-0.3) than in premenopausal women (1.59+/-0.3; P<0.0001) and in young (1.34+/-0.5; P<0.001) and old men (1.20+/-0.4; P<0.04). In the latter group, BHI was significantly lower than in premenopausal women (P<.0001). BHI values were also significantly lower in postmenopausal than in premenopausal women of the same age (0.81+/-0.1 versus 1.34+/-0.1; P<0.0001).

CONCLUSIONS

These findings suggest that the large reduction of cerebrovascular reactivity in postmenopausal women cannot be considered a simple factor related to aging but is probably influenced by hormonal changes. The alteration in cerebrovascular regulation could be involved in the increase of cerebrovascular disease in postmenopausal women.

Neurologic complications of vascular surgery

Technological advances in the management of cardiovascular disorders have resulted in an expansion of eligibility criteria for treatment, as well as an increased demand for improved outcomes. Neurologic complications after coronary artery bypass surgery, particularly stroke and cognitive dysfunction, substantially increase mortality, strain health care resources, and reduce the clinical effectiveness of the procedure. Carotid endarterectomy can be both the optimum stroke preventative strategy as well as a cause of stroke. The trend toward minimally invasive endovascular procedures, which has provided non-surgical options for both coronary and cerebral vascular occlusive lesions, is slowly being compared to conventional surgical and medical therapies. The identification of risk factors and mechanisms of adverse cerebral outcomes of these myriad vascular procedures is essential in improving their clinical effectiveness and patient applicability.

Symptomatic carotid artery occlusion. A reappraisal of hemodynamic factors

BACKGROUND

Over the last several years evidence has accumulated that in addition to embolism, a compromised cerebral blood flow may play an important role in causing transient ischemic attacks and ischemic stroke in patients with occlusion of the internal carotid artery. This evidence is found in both clinical features and ancillary investigations, particularly measurements of cerebral blood flow.

SUMMARY OF REVIEW

On the basis of 20 follow-up studies in patients with transient ischemic attacks or minor ischemic stroke associated with an occluded carotid artery, the annual risk of stroke was 5.5% (95% confidence interval [CI], 5.0% to 6.0%), and that of ipsilateral stroke (distinguished in 11 of the 20 studies) was 2.1% (95% CI, 1.6% to 2.8%). Patients with a compromised cerebral blood flow as measured by positron emission tomography, single-photon emission CT, transcranial Doppler, or stable xenon CT (six studies) have an even higher annual risk of stroke (all strokes: 12.5%; 95% CI, 8.9% to 17.6%; ipsilateral stroke: 9.5%; 95% CI, 6.4% to 14.0%).

CONCLUSIONS

Because a compromised cerebral blood flow may be an important causal factor in patients with symptomatic carotid artery occlusion, medical and surgical options for treatment are reviewed in this light.

Bilateral increase in CO2 reactivity after unilateral carotid endarterectomy

BACKGROUND AND PURPOSE

A low or absent CO2 reactivity is considered indicative of a compromised hemodynamic compensatory capacity in patients with internal carotid artery (ICA) stenosis or occlusion. The aim of the present study was to investigate whether patients with preoperatively decreased or absent CO2 reactivity show an improvement of CO2 reactivity 3 months after carotid endarterectomy (CEA) and whether the preoperative CO2 reactivity is correlated with clinical classification and hemodynamic factors.

METHODS

A group of 65 patients with > 70% ICA stenosis was studied. CO2 reactivity was measured by bilateral transcranial Doppler sonography before and 3 months after CEA.

RESULTS

The preoperative CO2 reactivity was not significantly different in subgroups formed according to the presenting clinical symptoms. Patients with severe ICA stenosis with contralateral ICA occlusion had mean low preoperative CO2 reactivity on both sides. Furthermore, patients with reversed flow in the ophthalmic artery had low mean preoperative CO2 reactivity on the same side. The CO2 reactivity was not significantly different in the subgroups of patients with signs of collateral blood flow through the anterior or posterior communicating artery. In particular, patients with low preoperative CO2 reactivity (approximately < 30%) showed an evident increase after the operation. Such an inverse correlation was found bilaterally, although it was more pronounced on the CEA side.

CONCLUSIONS

CEA can increase CO2 reactivity in both hemispheres. This effect is most pronounced in patients with low (< 30%) preoperative CO2 reactivity. If this group represents patients who would be at risk from low-flow stroke, then testing of CO2 reactivity might help select a subset of patients with an especially high probability of benefit from CEA.

Transcranial Doppler assessment of cerebrovascular reactivity in symptomatic and asymptomatic severe carotid stenosis

BACKGROUND AND PURPOSE

Some studies have suggested a link between impaired cerebral hemodynamics and stroke in patients with carotid stenosis. The aim of this study was to assess the effects of severe carotid stenosis on cerebrovascular reactivity and the possible changes after endarterectomy.

METHODS

Using bilateral transcranial Doppler ultrasound, we studied the changes of flow velocity after hypercapnia in the middle cerebral arteries of 10 control subjects and 24 patients (13 symptomatic and 11 asymptomatic) with unilateral severe carotid stenosis before and after endarterectomy. Cerebrovascular reactivity was evaluated with the breath-holding index (BHI).

RESULTS

Before endarterectomy, BHI (mean value +/- SD) was significantly lower (P < .001) in the stenotic side of symptomatic patients (0.40 +/- 0.2) than in control subjects (1.12 +/- 0.3), the stenotic side of asymptomatic patients (0.80 +/- 0.4), and the normal side of both symptomatic (0.93 +/- 0.3) and asymptomatic ultrasonics (1.03 +/- 0.2) patients. On the other hand, no significant difference in BHI was detected in control subjects, on the normal side of symptomatic and asymptomatic patients, and the stenotic side of asymptomatic patients. After endarterectomy, BHI significantly increased (P < .0001) on the stenotic side of symptomatic patients (1.06 +/- 0.2) while remaining substantially stable on the normal side of both symptomatic and asymptomatic patients and on the stenotic side of asymptomatic patients.

CONCLUSIONS

These findings suggest that the study of cerebrovascular reactivity to hypercapnia may be relevant in evaluating the functional effects of carotid stenosis. Further investigations are needed to confirm the reliability of the breath-holding method in the selection of patients who might benefit most from carotid endarterectomy.

Non-invasive testing for cerebrovascular disease

Selecting the appropriate investigation for diagnosing occlusive cerebrovascular disease depends on the availability, cost, accuracy, invasiveness and the purpose of the test. Intraarterial digital subtraction angiography remains the gold standard, but for accuracy the stenosis should be measured rather than estimated. Duplex ultrasonography is almost as accurate and can additionally analyse plaque morphology. Of 2651 duplex tests carried out in our laboratory, 12.2% were for reversible ischaemic attacks, 2.7% for amaurosis, 12.1% for cervical bruit and 4.3% for vertebrobasilar ischaemia. Duplex within 30 days of operation was carried out on 607 patients (22.9%) and surveillance on 1000 others (37.7%). Asymptomatic carotid stenosis > 60% should be confirmed by intra-arterial digital subtraction angiography, magnetic resonance angiography or spiral computed tomography angiography. For typical transient ischaemic attacks, duplex or angiography alone is adequate but when the clinical presentation is atypical, a confirming test is required. Routine preoperative brain computed tomography is not cost-effective, being equivalent to US$ 4300-11840 per perioperative stroke in our institution. Postoperative surveillance is justified, costing only US$ 505 per patient over 4 years.

Orthostatic intolerance and orthostatic tachycardia: a heterogeneous disorder

A series of autonomic function tests were performed in eight patients who had orthostatic intolerance and orthostatic tachycardia (> 36 bpm). All eight had an abnormal tilt-table test (mean tachycardia 50 bpm compared with 22 +/- 7 bpm in 31 normal subjects). Plasma volume was low in four out of six patients. There was a subnormal response to the cold pressor test in three out of eight patients. Intravenous atropine-induced tachycardia was subnormal in two out of eight patients. A segmental or patchy anhidrosis was present in six out of eight patients. Pilocarpine (0.0625%) induced miosis (three out of six) and exaggerated Valsalva ratio (one out of eight) were observed. A follow-up of six patients, 8-17 years after the autonomic evaluation, showed spontaneous and complete improvement in two out of six, partial improvement in one out of six, and persistence of symptoms in three out of six patients. A repeat autonomic evaluation in two patients with persistent symptoms, 2 and 5 years after the initial assessment, showed mild progression of sympathetic and parasympathetic dysfunction. This syndrome appears characterized by orthostatic tachycardia, low plasma volume, lack of adrenergic supersensitivity, and sudomotor abnormalities. A longitudinal follow up demonstrates patients with and without recovery. The syndrome appears heterogeneous in terms of onset, clinical manifestations, laboratory studies and outcome.

Assessment of cerebral vasomotor reactivity by transcranial Doppler ultrasound and breath-holding. A comparison with acetazolamide as vasodilatory stimulus

BACKGROUND AND PURPOSE

Evaluating cerebrovascular vasomotor reactivity seems to be of prognostic relevance for patients with occlusive internal carotid artery disease. To evaluate its clinical usefulness, the recently introduced breath-holding maneuver as a carbon dioxide-dependent vasodilatory stimulus was compared with the acetazolamide challenge by means of transcranial Doppler ultrasound and stable xenon-enhanced computed tomography.

METHODS

In a total of 134 middle cerebral arteries of 74 patients (mean +/- SD age, 62 +/- 9 years) with unilateral or bilateral occlusive carotid artery disease, vasomotor reactivity was estimated by the increase of middle cerebral artery mean blood velocity by transcranial Doppler ultrasound, comparing the breath-holding maneuver and 1 g IV acetazolamide as vasodilatory stimuli. The carotid artery findings were classified as normal, stenosis of 50% to < 70%, 70% to < 90%, 90% to 99%, and occlusion. Eighteen of the 74 patients additionally underwent stable xenon-enhanced computed tomography to calculate the increase of mean cortical regional cerebral blood flow in the middle cerebral artery territory after acetazolamide stimulation.

RESULTS

The percentage of mean regional cerebral blood flow changes (n = 36 hemispheres) correlated best with the absolute mean blood velocity changes while breath-holding (P = .007, r = .4332). The absolute mean regional cerebral blood flow changes correlated best with the percentage of mean blood velocity changes after acetazolamide stimulation (P = .004, r = .4580). On all 134 middle cerebral arteries, both vasodilatory stimuli correlated highly significantly (P < .0001) when comparing increases in absolute (r = .5448) or relative (r = .3516) mean blood velocity. Both stimulation techniques similarly indicated significantly reduced vasomotor reactivity with increasing degree of internal carotid artery lesions (P < or = .01). However, the acetazolamide challenge differentiated more accurately between the various groups of internal carotid artery findings.

CONCLUSIONS

The assessment of vasomotor reactivity by transcranial Doppler ultrasound correlates with cerebral blood flow changes even when different vasodilatory stimuli are used. In cooperative patients the breath-holding maneuver as vasodilatory stimulus seems clinically useful for a first estimation of cerebral vasomotor reactivity.

Acetazolamide reactivity on 123I-IMP single photon emission computed tomography in patients with major cerebral artery occlusive disease: correlation with positron emission tomography parameters

Single photon emission computed tomography (SPECT) with acetazolamide challenge has increasingly been used for evaluating hemodynamic reserve in stroke patients. The accuracy of this test, however, has not been validated with positron emission tomography (PET). In 14 patients who had occlusive disease of the internal carotid artery or the trunk of the middle cerebral artery (MCA) with minimal or no infarction on computed tomography (CT) and magnetic resonance imaging (MRI), we compared acetazolamide reactivity on SPECT with N-isopropyl-p-[123I]-iodoamphetamine to hemodynamic parameters determined with gas inhalation labeled 15O steady-state PET studies. The asymmetry index (AI)--i.e., the percentage of the activity rate of the ischemic MCA territory versus the contralateral one, was determined by SPECT. Acetazolamide reactivity expressed as delta AI, or change in AI after acetazolamide challenge, was significantly lower in seven patients than -8.4%, the lower limit of the 95% confidence interval for the normal reactivity. Values of ipsilateral CBF, cerebral blood volume (CBV)/CBF, and oxygen extraction fraction (OEF) and contralateral OEF were significantly different between patients with normal and reduced acetazolamide reactivity. Values of delta AI were correlated with OEF (r = -0.87; p < 0.001) and CBV/CBF (r = -0.56; p < 0.05). All patients with OEF > 0.52, the mean + 2 SD calculated from five normal volunteers, also had reduced acetazolamide reactivity, while the patients with normal OEF values had normal reactivity. The present study has demonstrated that SPECT studies with an acetazolamide challenge can detect the Stage II hemodynamic failure.

Cerebral blood flow reserve assessment in symptomatic versus asymptomatic high-grade internal carotid artery stenosis

BACKGROUND AND PURPOSE

Thromboembolic stroke is likely to occur in patients with a restricted cerebral blood flow reserve. Our aims were to determine (1) whether symptomatic patients had any significant hemodynamic restriction ipsilateral to carotid occlusive disease compared with patients whose carotid stenosis is asymptomatic and (2) whether patients with carotid occlusive disease have impaired cerebral perfusion reserve compared with control subjects.

METHODS

We compared cerebral blood flow and collateral capacity using the 133Xe inhalation method and acetazolamide test in symptomatic (n = 10) and asymptomatic (n = 10) patients who had a high-grade internal carotid artery stenosis (range, 70% to 99%). Results were compared with those from 10 healthy control subjects.

RESULTS

Mean baseline cerebral blood flow was 40.29 +/- 1.38 mL/100 g per minute on the symptomatic side in symptomatic patients versus 45.20 +/- 2.53 mL/100 g per minute on the lesion side in asymptomatic patients (control subjects, 46.91 +/- 2.11 mL/100 g per minute in the right hemisphere versus 46.17 +/- 1.93 mL/100 g per minute in the left). There was no statistical difference between patients in symptomatic and asymptomatic groups versus control subjects (P > .10). Mean cerebral blood flow increase after acetazolamide was in the same range in symptomatic (52.89 +/- 2.54 mL/100 g per minute) and asymptomatic (56.22 +/- 3.35 mL/100 g per minute) patients (P > .10), and no difference was observed regarding control subjects (54.25 +/- 2.94 mL/100 g per minute; P > .10). Three asymptomatic and two symptomatic patients and three control subjects had no significant cerebral blood flow increase after acetazolamide.

CONCLUSIONS

An additional hemodynamic factor in thromboembolic ischemia related to severe unilateral carotid stenosis might be an unusual finding in patients without apparent hemodynamic induction of symptoms. The lack of significant variation in postacetazolamide cerebral blood flow in some patients and control subjects implies that this procedure may be inconsistent in assessing the cerebral perfusion reserve in the individual case.

Cerebral vasoreactivity in unilateral carotid artery disease. A comparison of blood flow velocity and regional cerebral blood flow measurements

BACKGROUND AND PURPOSE

Hemodynamic information obtained by assessing cerebral vasoreactivity is of clinical interest and may have prognostic significance in patients with occlusive carotid disease. The aim of this study was to compare the results of transcranial Doppler and regional cerebral blood flow studies when used to assess cerebral vasoreactivity.

METHODS

Blood flow velocities in both middle cerebral arteries and regional cerebral blood flow in their respective perfusion territories were compared in 52 patients with severe unilateral carotid stenosis or occlusion. The studies were first performed under basal conditions and repeated after the intravenous administration of 1 g acetazolamide.

RESULTS

Asymmetry (normal compared with pathological side) in middle cerebral artery blood velocity increase was significantly greater than the asymmetry in cerebral blood flow increase in the perfusion territories of the arteries. A significant correlation (r = .63, P < .0001) was found between asymmetry in percent velocity increase and asymmetry in absolute cerebral blood flow increase. The two methods agreed in their assessment of either a normal or a reduced vasoreactivity in 38 subjects and disagreed in 14. In six of the latter patients, who had no evidence of cerebral infarction, the asymmetry in velocity increase was abnormal, whereas asymmetry in flow increase was assessed as normal.

CONCLUSIONS

We found a good correlation between the asymmetry in regional cerebral blood flow increase in the middle cerebral artery perfusion territories and asymmetry in the velocity increase in the middle cerebral arteries after administration of acetazolamide. These results suggest that transcranial Doppler examination combined with the acetazolamide test may be used in clinical situations to assess cerebral vasoreactivity.