Decreased Vasomotor Reactivity in Alzheimer's Disease

BACKGROUND: Reduced cerebral blood flow and microvascular abnormalities have been suggested as the vascular pathogenesis of Alzheimer's disease (AD). Transcranial Doppler sonography (TCD) can be used as a noninvasive method for measuring cerebral vasomotor reactivity (VMR) which represent the capability of arterioles to dilate and constrict in order to maintain cerebral blood flow. OBJECTIVE: The objective of this study was to determine whether VMR is decreased in AD patients. Methods: Seventeen consecutive patients who met NINDS-ADRDA criteria for AD, and 17 age- and sex-matched controls were included in this study. MRI and MRA were performed for the grading of white-matter lesions. Patients with cerebral infarct or stenosis of the middle cerebral artery (MCA) were excluded. The fixed TCD probe was used to monitor the mean flow velocity (MFV) in the MCA. A 6-L rebreathing bag was applied to patients for at least 5 minutes to elevate the CO2 concentration, which was continuously monitored with a capnometer. VMR was calculated as the percentage change in the MFV. RESULTS: Baseline characteristics - including cerebrovascular risk factors, grades of white-matter lesions, baseline MFV, and pulsatility index - did not differ between the two groups. Mini-Mental State Examination score was significantly low in AD group (20.5 vs. 27.5, p<0.05). VMR was significantly reduced in AD group both in the right-side (24.5% vs. 36.6%, p<0.05) and left-side (20.7% vs. 34.1%, p<0.05) MCAs. CONCLUSIONS: Our finding that VMR is reduced in AD may be suggestive of underlying microangiopathic mechanism in AD patients. Future studies should check the validity of these experimental and hypothesis-generating pilot results.

Vasomotor Reactivity of the Basilar Artery in Patients with Occlusive Vascular Diseases in the Anterior Circulation

BACKGROUND: The basilar artery (BA) may act as an important intracranial collateral to supply hypoperfused anterior circulation. We examined the basilar reserve capacity by using transcranial Doppler sonography (TCD) in patients with occlusive vascular diseases in the anterior circulation (OAC) to determine whether vasomotor reactivity (VMR) of the BA can be affected by the presence of OAC. METHODS: Twenty-five patients were given an MRI including an MRA for minor ischemic symptoms, headache, or dizziness and were divided into two groups according to the presence of OAC. The OAC included occlusions of either the internal carotid artery (ICA) or M1 segment of the middle cerebral artery (MCA). The VMR to hypercapnea was calculated by means of the breath-holding index (BHI). We compared the VMR of the BA between those with and without OAC. RESULTS: Patients with OAC (n=8) showed significantly reduced basilar VMR, compared to that of patients without OAC (n=17) (0.57+/-0.49 versus 1.36+/-0.47, P=0.001). The baseline mean flow velocity of BA was also higher in patients with OAC (70.6+/-24.2cm/s) than those without (38.8+/-11.5 cm/s). However, the baseline pulsatility index did not show differences between patients with and without OAC. CONCLUSIONS: Patients with OAC showed decreased VMR of BA, which can be an easily applicable and useful TCD index for assessing the hemodynamic status in patients with OAC.

Evaluation of Cerebral Vasomotor Reactivity using a Transcranial Doppler with Acetazolamide Test in Poor-grade Patients with Aneurysmal Subarachnoid Hemorrhage

OBJECTIVE: A greater reduction in cerebral blood flow has been shown in poor-grade patients with aneurysmal subarachnoid hemorrhage. The present study is designed to evaluate cerebral vasomotor reactivity(VMR) using a transcranial doppler(TCD) with acetazolamide(AZ) challenge in those patients and to investigate its predicting value for outcome. METHODS: Firstly, we compared the effect of AZ and most extensively using CO2 stimuli(breath-holding method) on middle cerebral artery flow velocity(FV) in the same control adults(n=12) to examine the reproducibility of AZ test. Secondly, the changes of FV of lesional and contralateral hemispheres after injection of AZ, which was measured one week after early surgery of poor-grade patients with aneurysmal subarachnoid hemorrhage, were compared between patients who showed good outcome(Group 1, n=22) and poor outcome(Group 2, n=22). RESULTS: There was a close correlation between both stimulation methods, indicating a strong similarity of the vasodilatory effects of CO2 and AZ. The FV at rest(lesional: 71.5+/-38.6cm/s, contralateral: 49.4+/-22.6cm/s) increased significantly after administration of AZ(lesional: 90.5+/-40.1cm/s, contralateral: 66.5+/-25.4cm/s, P<0.01, Student's t test) in Group 1. However, all had an insignificant increase of FV after AZ challenge compared with the baseline values in Group 2. The difference between the values at rest and after AZ had an increasing tendency but it was not significant, between Group 1 and 2(repeated measures ANOVA, P=0.06). CONCLUSION: These results demonstrate that the assessment of VMR by the change of FV using TCD together with AZ test in poor-grade patients with aneurysmal subarachnoid hemorrhage seems clinically helpful for predicting surgical outcome.

Effect of Extracranial-Intracranial Bypass on Cerebral Blood Flow and Vasomotor Reactivity in patients with Compromised Cerebral Hemodynamics

BACKGROUND: The obstruction of intracranial arteries causes cerebral hemodynamic impairment. It is now evident that patients with cerebral hemodynamic compromise have a higher risk of stroke than those with normal cerebral blood flow. The purpose of this study is to investigate the changes of cerebral blood flow and vascular reactivity after extra-intracranial arterial bypass (EIAB) surgery in patients with cerebral hemodynamic compromise. METHODS: We enrolled 16 consecutive patients (8 female and 8 male patients) with transient ischemic attack or cerebral infarction resulted from the occlusion of distal internal carotid artery (ICA) or middle cerebral artery (MCA). We measured the relative regional cerebral blood flow (rrCBF) at rest and after Diamox infusion, and vasomotor reactivity by using single photon emission computed tomography (SPECT). We performed extra-intracranial arterial bypass (EIAB) surgery in patients with impaired vasomotor reactivity. Follow-up brain SPECT was done at 3months after EIAB. We compared the rrCBF and vasomotor reactivity before and after EIAB, and evaluated the effect of collateral vessels on the cerebral hemodynamic after surgery. RESULTS: EIAB increases the vasomotor reactivity significantly (-19.6+/-10 before EIAB, 11.2+/-27 after EIAB, p=0.003) but does not increase the cerebral blood flow at rest (70.5% before EIAB, 70.9% after EIAB). The degree of collateral vessel development did not influence on the restoration of vasomotor reactivity. CONCLUSIONS: These results demonstrate that EIAB increases the vasomotor reactivity of the distal part on the occluded ICA or MCA, but does not increase the cerebral blood flow at rest.

The Reference Values and Influencing Factors of TCD Measurements in 200 Normal Korean Adults

The clinical utility of transcranial doppler ultrasonography (TCD) in cerebrovascular disease has been extended recently. Although number of studies have been performed to define normal reference values of TCD measurements, they have some limitations to be used as reference values which include relatively small number of subjects, lack of data about some cerebral vessels and/or parameters. This study was aimed to obtain clinically useful reference values of TCD measurements with consideration of the influence of age and sex in Korean adults, particularly who are in stroke-prone age group. We measured flow velocities, pulsatility indecies, side-to-side differences and vasomotor reactivities of all intra-and extracranial cerebral arteries using TCD in 209 normal Korean adults (age, 23-78 years; 94 men and 115 women), and analyzed the influence of age and sex on those measurements. With advancing age, subjects showed significant reduction in velocity measurements and increase in pulsatility indecies of most examined arteries. Females showed hight velocities of middle cerebral, internal carotid, vertebral and basilar artery and lower pulsatility indecies of middle cerebral arteries compared with males. Asymmetry measurements including side-to-side differences and asymmetry index, and ,breath holding index testing vasomotor reactivity were also measured and the normal range of those parameters were calculated. Since present study included large number of subjects, and checked paramenters of TCD in both extra- as well as intracranial cerebral arteries, we are convinced that these results can be used as a reference data of TCD measurements in Korean adults.