Hideki Etani

Rate of successful recording of blood flow signals in the middle cerebral artery using transcranial Doppler sonography.

Background and Purpose To assess the usefulness of transcranial Doppler sonography, we investigated the rate of blood flow signal recording failure in the middle cerebral artery in Japanese subjects. Furthermore, we studied the effect of increased emitted power on the rate of successful recording in some of the patients in whom recording failure had been detected at the standard transducer power of 100 mW/cm2. Methods To evaluate the rate of successful recording, we measured blood flow signals in 597 patients (age range, 16 to 89 years) for screening of cerebrovascular disease by using a 2-MHz range-gated, pulsed-wave Doppler instrument at the standard transducer power. In 18 elderly patients with recording failure at the standard power, we assessed the effect of increased emitted power of 400 mW/cm2 on flow signal recording. Results Blood flow signals were recorded in 920 (77.1%) of the 1194 middle cerebral arteries of the 597 patients studied. The rate of successful recording of bilateral middle cerebral artery flow signals (70.9%; 423 of 597 patients) decreased with age, especially in females (17.0% in women aged 70 years or older). In 12 of 18 elderly patients with recording failure at the standard power, blood flow signals could be detected at the increased emitted power of 400 mW/cm2. Conclusions The rate of successful recording of blood flow signals in Japanese subjects decreases with advancing age, especially in females. Increasing the emitted power markedly improves the successful recording rate.

Efficacy of echo-doppler examination for the evaluation of renovascular disease

The accuracy of the diagnosis of renal artery stenosis using noninvasive echo-Doppler velocimetry was compared with that of angiography in 40 renal arteries. The duplex-Doppler signals were detected through the muscle of the back (the translumbar approach). Renal artery stenosis was diagnosed by three objectively defined Doppler parameters, the acceleration index (AI), the acceleration time (AT), and the acceleration time ratio (ATR). The normal range obtained on 11 control subjects was defined as AI greater than or equal to 3.78, AT less than or equal to 0.07 s, and ATR less than or equal to 1.35. High technological success (98%) was obtained using the translumbar approach. In comparison with angiography (cases of significant stenosis), the accuracy of the echo-Doppler method using the criteria of the AI was 95%, the sensitivity was 100%, and the specificity was 93%. This noninvasive method may be one of the most accurate screening methods for diagnosing significant renal artery stenosis.

A validation study on the reproducibility of transcranial doppler velocimetry

The transcranial Doppler method for the measurement of intracranial arterial blood flow velocity is a useful noninvasive technique with a number of applications. The present study validated the reproducibility of this method for repeated measurements of flow velocity in the middle cerebral and basilar arteries. Fifteen healthy volunteers were studied. Measurements were made twice by one examiner and once by another in a single day and again by the first examiner on another day. The reproducibility was evaluated by calculating the correlation coefficient (r) and the coefficient of variation (CV) of the difference between the values obtained from each pair of measurements. Although depending on the examiner, the time interval between the examinations and the vessels studied some differences were noted in the reproducibility, both the r (0.69-0.95) and CV (6.7%-19.5%) values in the whole study were good enough to warrant the applicability of this method for the repeated measurements of the intracranial arterial blood flow velocity in future studies.

Carotid Intima-Media Thickness and Risk of Cardiovascular Events in High-Risk Patients

Background and Purpose: There is epidemiological evidence that increased carotid intima-media thickness (IMT) is a predictor of cardiovascular disease (CVD) events. However, the significance of carotid IMT in high-risk patients in whom risk factors are managed clinically has not been adequately investigated. The purpose of this study was to determine the usefulness of carotid IMT measurement in such patients. Methods: The study comprised 900 outpatients with cardiovascular risk factors or established atherosclerosis. Carotid IMT was calculated as the mean bilateral IMT of the common carotid artery, bifurcation, and internal carotid artery. Baseline vascular risk factors, medications, and history of CVD were recorded at the time of enrollment. The incidence of CVD events was determined prospectively. Results: During a mean follow-up period of 2.6 years, there were 64 CVD events. The relative risk (RR) of a CVD event increased with increased IMT. Association between CVD events and carotid IMT was significant after adjustment for risk factors and history of CVD, showing an increased risk per IMT tertile from the middle tertile (RR, 2.5; 95% confidence interval [CI]: 1.0–6.3) to the highest (RR, 3.6; 95% CI: 1.4–9.0). When patients with a history of CVD were excluded (n = 574), the predictive value of IMT was significant even after adjustment for risk factors (hazard ratio per 1 SD IMT increase was 1.57 [95% CI: 1.11–2.20]). Conclusions: Carotid IMT is an independent predictor of vascular events in high-risk patients in whom risk factors are managed clinically.

Echo-Doppler velocimeter in the diagnosis of hypertensive patients: the renal artery Doppler technique

The renal blood flow velocity characteristics in 8 normal controls, 19 essential hypertensive patients and 8 hypertensive patients with renovascular disease were evaluated using echo-Doppler velocimetry. Two different approaches for ultrasonic detection of the renal artery, the translumbar and the transabdominal approach, were used. Renal Doppler sonograms were analyzed by measuring the acceleration index and the peak-systolic frequency/end-diastolic frequency (S/D) ratio. Renovascular patients who required surgery were examined before and after angioplasty. Doppler signals could be detected in all 35 subjects by using the translumbar approach. The acceleration index of the affected renal arteries significantly correlated to the percent stenosis of the renal artery determined by angiography. The acceleration index in the affected renal artery was improved by surgical treatment. The S/D ratio in essential hypertensives was significantly higher than that in the normal controls. There was a significant inverse correlation between the S/D ratio and creatinine clearance. Echo-Doppler velocimetry is considered to be useful in the diagnosis of renovascular disease and also in the evaluation of abnormalities of renal vascular resistance in hypertensive patients.

Effect of small deep hemispheric infarction on the ipsilateral cortical blood flow in man.

The effect of small, deep ischemic lesions on the ipsilateral cortical circulation was investigated in 10 patients with persistent mild or moderate neurological deficits due to infarcts in the internal capsule. rCBF studies by the 133Xe intracarotid injection method were performed 14-180 days after the onset of the infarction. The rCBF functional image was made up from the data of 133Xe dynamic images measured by an Anger-type gamma camera and the rCBF values were calculated by the initial slope method. The average value of mean rCBFs (mCBF) in 10 patients was 44.9 +/- 7.1 ml/100g/min (average PaCO2; 39.9 +/- 4.3 mm Hg). In the rCBF functional images, a focal hypoperfusion area was observed in all cases and localized around the central sulcus, especially in the precentral and central areas. Significant decreases of mCBF and the tendency to decrease of the rCBFs in the hypoperfusion focus were noted in the patients with the larger infarcts in comparison with those with the smaller ones. These results suggest that a small, deep ischemic lesion such as a capsular infarct may have remote effects on the ipsilateral cortical circulation, due probably to the damage of a number of fibers passing through the lesion.

Computer-Assisted Analysis of Heterogeneity on B-Mode Imaging Predicts Instability of Asymptomatic Carotid Plaque

Background: Computerized assessment of plaque echogenicity by B-mode ultrasonography has demonstrated that the gray-scale median (GSM) pixel intensity of the entire plaque predicts future ischemic stroke in patients with symptomatic carotid stenosis, but not those with asymptomatic stenosis. This study investigated whether plaque heterogeneity (i.e., the distribution of pixel intensities) could predict the instability of asymptomatic plaque. Methods: By comparison with carotid endarterectomy specimens and the GSM values of known tissues on B-mode images, the GSM values for blood, lipid, muscle/fibrous tissue, and calcification were determined. Then we estimated the percent area of each tissue component for 297 asymptomatic plaques causing 40–99% carotid artery stenosis in 250 patients, and monitored the incidence of atherothrombotic cerebral infarction due to carotid stenosis during follow-up. Results: Eight infarcts occurred during a follow-up period of 22 ± 15 months. Plaques in the top tertile for the percent area of lipid-like echogenicity (p < 0.05) and in the lowest tertile for calcification (p = 0.06) showed an association with future infarction according to Kaplan-Meier analysis. This association remained significant after adjustment for the severity of carotid stenosis (hazard ratio 4.4 for lipid-like and 0.24 for calcification-like component, both p < 0.05) according to Cox proportional hazards analysis. Conclusions: The distribution of pixel intensities in carotid plaque on B-mode ultrasonography can be employed to predict instability of asymptomatic plaque and possibly to select patients for interventional procedures. A large-scale investigation will be needed to confirm that estimating the percentage of plaque components relative to the total plaque area can predict ischemic stroke.

Diminished Reserve for Cerebral Vasomotor Response to L-Arginine in the Elderly: Evaluation by Transcranial Doppler Sonography

Background: Nitric oxide is pivotal in endothelially dependent vasodilatory regulation. An association of endothelial dysfunction with aging has been documented in the forearm and coronary vascular beds. However, the influence of aging in the human cerebral circulation, where regulation is particularly complex, is incompletely understood. Objective: We systematically administered L-arginine, a precursor of nitric oxide, to evaluate the influence of aging on nitric oxide-mediated cerebral vasomotor regulation. Methods: Among healthy volunteers, 20 older subjects (10 men, 10 women; age: 70.2 ± 2.8 years) and 22 younger subjects (10 men, 12 women; age: 28.8 ± 1.9 years) received intravenous infusions of L-arginine monochloride (500 mg/kg) over 30 min. Hemodynamic parameters were monitored continuously during and after infusion. The cerebral vasomotor response was estimated by transcranial Doppler sonography of the right middle cerebral artery. Results: Infusion of saline as a control brought little change in the mean blood pressure, heart rate or cerebral blood flow velocity in either group. On administration of L-arginine, cerebral blood flow velocity increased and mean blood pressure decreased. After completion of infusion, both parameters rapidly normalized. While reduction of mean blood pressure did not differ between older and younger groups, the cerebral circulation in the older group showed a blunted, smaller, and more easily saturated vasomotor response compared to the younger group, though both groups had similar baseline values. Conclusion: Our results indicate a diminished nitric oxide-mediated cerebral vasomotor response in aging subjects. Additionally, transcranial Doppler sonography can be used to reliably evaluate age-related changes in the physiologic responses of the human cerebral circulation.

Carbondioxide reactivity of the blood flow in human basilar artery estimated by the transcranial doppler method in normal men: A comparison with that of the middle cerebral artery

Using the transcranial Doppler technique, the carbondioxide reactivity of the blood flow velocity in the human basilar artery (BA) was investigated in healthy volunteers for comparison with that in the middle cerebral artery (MCA). An exponential curve with an exponent of 0.044 mmHg-1 was found to be a good fit to the BA data and 0.040 mmHg-1 to the MCA data, respectively. While the response of both arteries showed a good correlation to the end-tidal carbondioxide partial pressure (PETCO2), there was no significant difference observed between the carbondioxide (CO2) reactivity of each artery. In both arteries, the end-diastolic flow velocity decreased significantly with the reduction of PETCO2, which may represent the increasing resistance of cerebral microvasculature in hypocapnia. Because of the reliability and noninvasiveness of this method, this normal value should be quite helpful for the bed-side evaluation of an altered CO2 response in the patients with cerebrovascular disease.

Relationship between plasma (D)-dimer level and cerebral infarction volume in patients with nonvalvular atrial fibrillation.

Background: Plasma D-dimer level may reflect the activity of thrombus formation in the left atrium of patients with nonvalvular atrial fibrillation (NVAF). Proper anticoagulation with warfarin dramatically decreases the rate of cerebral embolism, reduces stroke severity and subsequent risk of death, as well as the level of D-dimer in NVAF patients. However, the predictive value of D-dimer level on cerebral embolism severity has not been examined. Thus, the purpose of this study was to investigate the association between plasma D-dimer level at admission and infarct size in NVAF patients. Methods: We identified 124 patients with consecutive ischemic stroke and NVAF who were admitted within 48 h of symptom onset. We measured infarction volume from CT taken after 3 ± 1 days from the onset. Plasma D-dimer levels were measured at the time of admission. Relationships were analyzed between infarction volume and plasma D-dimer levels, cardiovascular risk factors, preadmission medications and admission conditions. We also assessed the influence of D-dimer level on functional outcome in patients with preadmission modified Rankin Scale (mRS) score of 0–1 and patients by tertile of D-dimer level (≤0.83, 0.83–2.16 and ≥2.16 µg/ml). Results: Infarction volume significantly correlated with D-dimer level (r = 0.309, p < 0.001), systolic blood pressure (r = 0.201, p = 0.026), diastolic blood pressure (r = 0.283, p = 0.002), National Institutes of Health Stroke Scale (NIHSS) score on admission (r = 0.546, p < 0.001) and mRS score at discharge (r = 0.557, p < 0.001). Multivariate regression analyses showed that the D-dimer level was significantly associated with infarction volume after adjusting for age, sex, current smoker or not, prothrombin time-international normalized ratio ≥1.6, diastolic blood pressure, CHADS2 score and NIHSS score on admission. In patients with a preadmission mRS score of 0–1 (n = 108), D-dimer level was significantly associated with NIHSS score at admission (r = 0.318, p < 0.001) and mRS score at discharge (r = 0.310, p = 0.001). Patients in the highest D-dimer tertile group showed worse outcome than those in the middle (p = 0.041) and lowest (p < 0.001) tertiles. Conclusions: Plasma D-dimer level on admission is significantly related to infarction volume and functional outcome, following cardioembolic stroke in NVAF patients.