犬失血性休克及补液过程中肾动脉多普勒血流速度频谱形态、阻力指数、搏动指数的变化

为探讨失血性休克及补液治疗过程中肾动脉多普勒血流速度频谱形态、RI、PI的变化规律及应用价值，本研究将10条太经股静脉放血至休克状态。然后行补液治疗。在实验过程中按失血量定时检测犬肾动脉血流速度频谱，计算RI、PI值，并记录同步血压。结果：（1）失血过程中．肾动脉RI、PI值随着失血量的增加，血压的下降．总体呈现上升趋势。随着补液的进行、MAP逐渐回升，RI、PI逐渐下降；（2）频谱形态出现一些特民改变，如重度失血时频谱舒张期出现小峰及凹陷．补液早期频谱舒张期凸起等。结论：多普勒指标RI、PI能较好地反映肾动脉阻力情况，肾动脉RI、PI可作为临床大出血患者病情观察和疗效判断的实用指标。     

多普勒超声肾血流测定对高血压病早期肾损害的预测性研究

目的 探讨多普勒超声肾血流测定对诊断高血压病早期肾损害的价值。方法 以血、尿β２－微球蛋白（β２－ＭＧ）和尿白蛋白４排泄率（ＵＡＥＲ）作为早期肾损害指标,对６０例高血压病患者和２０例正常人行多普勒超声肾血流检查。结果 叶间动脉舒张期末血流速度（Ｖｄ）的减慢、血流峰速加速时间的延长是高血压病患者最早出现的肾血流动力学异常;有肾脏早期损害的高血压病患者肾血流频谱参数特点是肾段动脉、叶间动脉的收缩期最大血流速度（Ｖｓ）、Ｖｄ减低,搏动指数（ＰＩ）、阻力指数（ＰＩ）明显增高。结论 多普勒超声肾血流测定是诊断和预测高血压病早期肾损害的简便易行、可靠的方法。     

Measurement of blood flow by ultrasound: accuracy and sources of error

Doppler ultrasound has now developed to the point where the rate of flow of blood in a given vessel can be measured with appropriate instrumentation. The theoretical basis of Doppler flow measurement is reviewed in this paper, with particular emphasis on the potential and actual sources of error. Three distinct approaches are identified, and the strengths and weaknesses of each discussed. The separate errors involved in estimating the vessel cross-sectional area, the angle of approach, and the Doppler shift are analyzed, together with the question of the uniformity of scattering from the blood. In vivo and in vitro tests of the accuracy obtained using a number of Doppler flow measuring instruments are then reviewed. It is concluded that the Doppler methods are capable of good absolute accuracy when suitably designed equipment is used in appropriate situations, with systematic errors of 6% of less. There are, however, considerable random errors, attributable primarily to errors in measuring the cross-sectional area and the angle of approach. Repeating the measurement of flow several times and averaging the results can reduce these random errors to an acceptable level.     

Doppler ultrasound measurement of cerebral blood flow in healthy pregnant women

Purpose To compare global cerebral blood supply in healthy pregnant women and nonpregnant women. Materials and Methods Flow volumes in the common, internal, and external carotid, arteries and the vertebral arteries were determined using color Doppler ultrasonography in 17 nonpregnant women, 55 healthy pregnant women at 10 to 40 weeks gestation, and 24 puerperal women within 1 week after spontaneous delivery. Global cerebral blood flow was defined as the sum of flow volumes in the bilateral internal carotid and vertebral arteries. Results In the nonpregnant group, mean flow volumes of the common, internal, and external carotid arteries and the vertebral arteries, and mean global cerebral blood flow volume were (mean±SD) 863±108 ml/min, 554 ±94 ml/min, 386±65 ml/min, 115±24 ml/min, and 669±104 ml/min, respectively. During the second trimester, flow volumes of the common and external carotid arteries increased significantly in the healthy pregnant women, to about 130 percent and 140 percent of the nonpregnant level, respectively. Global cerebral blood flow volume remained unchanged during pregnancy. Conclusion During pregnancy, increase in flow volumes in the common carotid arteries were accompanied by elevated flow volumes of the external carotid arteries but not the internal carotid arteries. This distribution would tend to regulate the volume of global cerebral blood flow throughout the period of pregnancy.     

Doppler echocardiographic approach to the blood flow of the left anterior descending coronary artery

Assessment of flow in the left anterior descending coronary artery by Doppler echocardiography appeared to be possible in some patients in which the coronary artery system might be wide and/or the displacement of the coronary artery might be reduced because of cardiac enlargement or of impaired cardiac function. A study of this possibility was carried out in 78 patients, 20 cases with hypertrophic cardiomyopathy, 10 with dilated cardiomyopathy, 20 with aortic valve disease, and 28 following valve replacement for aortic valve disease. The anterior interventricular sulcus was a helpful landmark to search for the left anterior descending artery. The characteristic feature of the coronary flow pattern, that the flow ran mainly during diastole, was also helpful in finding the coronary artery. Complementary roles of ultrasonic imaging and Doppler ultrasound evaluation should be emphasized for identifying a thin echo-free space in the sulcus as the coronary artery. The left anterior descending coronary artery was imaged in 26 of the 78 patients. The peak velocity ranged 24 cm/s to 75 cm/s in different patients. Because the present study was carried out in patients with some particular diseases, these results do not indicate that current techniques can be routinely used for assessing the coronary flow. The detection rate will be increased with improvements in image resolution and the Doppler sensitivity. Although the detection rate of the coronary artery was not satisfactory in the present stage, the effect of sublingual administration of nitroglycerin on coronary circulation was noninvasively assessed in some patients, where reduction of the flow velocity by about 27% was observed in real time.     

Reproducibility of ultrasonic fetal volume blood flow measurements

The intraobserver reproducibility of ultrasonic volume blood flow measurements in the human fetus was evaluated in this study. A new approach, simultaneous measurement of the vessel diameter and the flow velocity with a pulsed-wave Doppler ultrasound synchronized with a real-time ultrasound phase-locked echo-tracking system, was used to estimate volume blood flow (VBF) in the fetal descending aorta. Measurements were performed in a longitudinal study on 20 normally grown fetuses. Intraobserver reproducibility of repeated estimations of mean blood flow velocities throughout gestation was very good, with high values of intraclass correlation coefficient (IntraCC 0·80–0·91) and low values of coefficient of variation (CV 4–11%). The IntraCC of repeated vessel diameter measurements throughout gestation was low (0·30–0·68), whereas the values of CV were acceptable (< 12%), with the exception of the period between 140 and 167 gestational days (CV > 12%). The lower reproducibility of vessel diameter measurement contributed directly to the relatively low reproducibility of VBF estimations overall (IntraCC 0·25–0·70; CV 17–28%), as these are calculated from a formula using both flow velocity and vessel diameter. Nevertheless, the synchronized approach gives absolute values of vessel diameter, flow velocity and VBF comparable with values reported in the human fetus previously. The new method provides, by taking the vessel wall pulsations into consideration and by measuring diameter and velocity simultaneously, a more complete information on fetal haemodynamics and fetal physiology.     

Functional assessment of high-grade ICA stenosis with duplex ultrasound and transcranial Doppler

Background: Duplex ultrasound (DUS) has shown a >90% accuracy compared to angiography, concerning the degree of internal carotid artery (ICA) stenosis. However, uncertainty may occur in a severe stenosis, in which peak systolic velocity (PSV) may decrease owing to high flow resistance or high backward pressure. We investigated intracranial collateral flows using transcranial Doppler (TCD) to further evaluate the hemodynamic significance of high‐grade ICA stenosis. Methods: In this retrospective study, 320 consecutive symptomatic patients were examined. The degree of ICA stenosis and collateral capacity in the circle of Willis was investigated by DUS and TCD. In addition, magnetic resonance angiography (MRA) was added in a subgroup of 204 patients. The criterion for hemodynamic significant ICA stenosis was established collateral flow. Results: In 91% of all symptomatic vessels (291 vessels), an ICA stenosis of ≥70% was found. Established collateral flow always indicated precerebral carotid artery disease of ≥70%. Furthermore, in 11% of the whole study material, collateral reserve capacity was found despite high‐grade (≥70%) ICA stenosis. PSV in ICA <2·5 m s^?1 was combined with established collateral flow and MRA stenosis of ≥70% in 9% (19 arterial systems). In 4%, doubt existed concerning the degree of stenosis after DUS. Conclusion: Transcranial Doppler helps to determine whether an ICA stenosis is of hemodynamic significance and to assess collateral patterns. Established collateral blood flow will help to identify patients with ≥70% (ECST) carotid artery disease. TCD might be of value when flow velocity criteria combined with plaque assessment by DUS are inclusive. Other diagnostic methods may also be considered.     

Doppler assessment of renal blood flow velocity waveforms in the anemic fetus before and after intravascular transfusion for severe red cell alloimmunization.

Image-directed pulsed Doppler ultrasonography demonstrated a decrease in the pulsatility index of the renal artery in 9 anemic fetuses (less than 30 weeks, menstrual age) soon after intravascular transfusion. The pulsatility index returned to pretransfusion values the day following the transfusion. End diastolic blood velocity in the renal artery could not be measured before the transfusion, was detectable immediately after the procedure, and was again nonmeasurable one day after the transfusion. These data suggest an increase in renal blood flow in the anemic fetus soon after intravascular transfusion to eliminate excess fluid.     

乳腺癌患者高频彩色多普勒超声血流特点及阻力系数的变化

目的探讨乳腺癌患者采用高频彩色多普勒超声检查的血流阻力指数（RI）、血流特点、声像特征及其诊断价值。方法选取2019年1月~2021年1月安徽省肿瘤医院甲乳外科经病理学确诊的96例乳腺癌患者（病例组）、同期经病理学检查确诊的乳腺良性疾病患者100例（良性组）,对两组患者的高频彩色多普勒超声检查资料进行分析,对比两组的RI、血流特点、声像特征差异,并以病理学结果作为金标准计算各项指标在诊断乳腺癌中的价值。结果病例组的肿块呈不规则形状、边缘毛刺征、微钙化病灶、边界模糊的检出率均高于良性组（P < 0.05）;肿块形状特征诊断乳腺癌与乳腺良性疾病的敏感度为66.67%,特异性为60.00%,ROC曲线下面积为0.633;边缘毛刺征诊断乳腺癌与乳腺良性疾病的敏感度为73.96%,特异性为58.00%,ROC曲线下面积为0.660;微钙化病灶诊断乳腺癌与乳腺良性疾病的敏感度为31.25%,特异性为91.00%,ROC曲线下面积为0.611;边界模糊诊断乳腺癌与乳腺良性疾病的敏感度为27.08%,特异性为89.00%,ROC曲线下面积为0.580;病例组的血流分级主要为Ⅱ级（48.96%）、Ⅲ级（27.08%）,良性组的血流分级主要为0级（53.00%）、Ⅰ级（24.00%）,两组差异有统计学意义（P < 0.05）;血流分级诊断乳腺癌与乳腺良性疾病的敏感度为76.04%,特异性为77.00%,ROC曲线下面积为0.765;病例组的RI值低于良性组（P < 0.05）;病灶RI值诊断乳腺癌与乳腺良性疾病的敏感度为77.03%,特异性为55.17%,ROC曲线下面积为0.681。结论根据高频彩色多普勒超声检查的声像特征、血流分级、RI参数鉴别诊断乳腺癌及乳腺良性疾病均具有一定的临床价值,临床上可以综合几种指标分析,提高临床的诊断效率。     

彩色多普勒超声诊断早期糖尿病肾病临床价值的研究

目的探讨彩色多普勒超声对诊断早期糖尿病肾病的临床价值。方法以24小时微量尿蛋白排泄率（UAER）作为糖尿病肾病的诊断指标,将60例糖尿病患者,分为三组,20例正常人为对照组,以彩色多普勒超声分别检测肾体积及肾各级动脉的血流参数进行统计学分析。结果随着肾功能损害加重,肾动脉的收缩期峰值流速、舒张末血流速度下降,血流阻力指数（RI）增高,以RI增高与肾功能损害程度相关最密切。大量蛋白尿组体积缩小。与各组差异非常显著,余各组间无显著差异。结论彩色多普勒超声测定肾动脉血流参数,能反映糖尿病肾病肾损害程度,可作为早期糖尿病肾病诊断的参考指标。     

彩色多普勒超声血流阻力指数联合糖链抗原125对卵巢肿瘤的诊断价值

目的探讨彩色多普勒超声血流阻力指数（resistance index,RI）联合血清糖链抗原125（carbohydrate antigen 125,CA125）检测在卵巢良、恶性肿瘤鉴别诊断中的价值。方法检测60例卵巢肿瘤患者血清CA125水平,并行彩色多普勒超声检查记录RI,与手术组织病理结果进行对照,比较RI及RI联合CA125诊断卵巢肿瘤的效能。结果手术组织病理诊断卵巢良性肿瘤45例,恶性肿瘤15例;RI联合CA125诊断良性、恶性卵巢肿瘤的准确率（93.33%、86.67%）高于RI（66.67%、53.33%）（P〈0.05）。结论彩色多普勒超声RI联合血清CA125检测鉴别诊断良、恶性卵巢肿瘤优于单独应用彩色多普勒超声RI。     

糖尿病肾病肾实质剪切波速度与肾动脉血流参数的相关性分析

目的探讨糖尿病肾病(DN)患者肾实质剪切波速度(SWV)与各级肾动脉血流参数的相关性。方法收集DN患者28例,根据尿白蛋白与肌酐比值将DN患者分为早期阶段DN组15例(DN1组)和进入临床期后DN组13例(DN2组);另选择健康体检者28例作为对照组。依次进行频谱多普勒超声和声触诊组织定量(VTQ)技术检查,比较各组各级肾动脉血流参数和肾实质SWV的变化,并分析二者间的相关性。结果 DN1组和DN2组各级肾动脉阻力指数(RI)均较对照组升高,收缩期最大峰值流速(PSV)和舒张期末血流速度(EDV)均较对照组降低,除DN1组主肾动脉PSV与对照组比较差异无统计学意义外,余各级肾动脉RI、PSV、EDV DN1组和DN2组与对照组比较差异均有统计学意义(均P0.05)。对照组、DN1组及DN2组SWV分别为(3.56±0.53)m/s、(2.99±0.63)m/s及(2.62±0.74)m/s,三组两两比较差异均有统计学意义(均P0.05)。肾实质SWV与主肾动脉和段动脉RI均呈负相关(r=-0.39、-0.37,均P0.05),与段动脉和叶间动脉PSV,以及各级肾动脉EDV均呈正相关(均P0.05)。结论肾实质SWV随肾损害程度加重而减低,肾实质SWV与肾动脉血流参数存在一定相关性;VTQ有助于评估DN患者肾实质的损害程度。     

Noninvasive monitoring of renal blood flow characteristics during acute renal failure in man

Duplex Doppler ultrasound (DDU) was used to study the blood flow characteristics of the renal interlobar artery in 20 subjects with acute renal failure (ARF), 14 subjects with transient impairment of renal function and 23 control subjects with normal function. Renovascular resistance was assessed by pulsatility index (PI) and change in flow velocity by change in mean frequency shift (f). The 99% confidence intervals for PI in the three groups were 3.32–5.46, 1.58–2.34 and 0.99–1.33 respectively. Values for f were 0.2–0.38, 0.5–0.62 and 0.7–1.02 kHz respectively. Ten ARF patients recovered function, 99% confidence intervals for PI just prior to recovery were 0.9–1.48 and for f 0.52–1.02 kHz. There was increased renovascular resistance and reduced intrarenal blood flow velocity at the onset of ARF. These changes persisted during ARF; recovery of function occurred after they returned to normal. Similar, but less marked, changes were found in patients with a transient impairment of function.This study was conducted at Charing Cross Hospital, London     

彩色多谱勒对IUGR脐动脉血流的检测

目的：应用彩色多谱勒检测正常妊娠和胎儿宫内发育迟缓（以简称ＩＵＧＲ）的脐动脉血流指标ＰＩ、ＲＩ、Ｓ／Ｄ值。材料和方法：应用彩色多谱勒检测了２００例正常妊娠和１１１例ＩＵＧＲ的脐动脉血流,孕周从２６－４１周。结果：正常妊娠组及ＩＵＧＲ组的脐动脉血流指标均随妊娠周数的增高而降低,但ＩＵＧＲ组的脐动脉血流ＰＩ、ＲＩ、Ｓ／Ｄ值明显高于正常妊娠组（Ｐ〈０．０１）。孕３０周后,脐动脉血流Ｓ／Ｄ值〉４,揭示胎儿预后不良。结论：脐动脉血流检测不仅是胎儿监护的一种方法,而且可作为诊断ＩＵＧＲ的一个指标及对估计胎儿预后有一定的临床价值。     

Measurement of aortic blood velocity in acute myocardial infarction by Doppler ultrasound

Aortic blood velocity was measured by a transcutaneous continuous wave Doppler technique in thirty-five patients with proven acute myocardial infarction. Measurements were made on the first and seventh day following admission to hospital. Group I comprised 21 patients who had sustained a first myocardial infarction of moderate size, uncomplicated by hypoperfusion. Group II comprised 14 patients who had had a large rise in cardiac enzymes, a previous myocardial infarction or were clinically hypoperfused. The mean value for peak aortic velocity for Group I on Day 1 was 88±12.9 cm/s. This was significantly lower than the mean value of 101.8±23.1 cm/s for a group of 85 normal subjects. By Day 7 the mean value for Group I of 105.1±19.8 cm/s was not significantly different from normal. For Group II patients on Day 1 the mean value for peak aortic velocity was 67.9±11.7 cm/s and was significantly lower than that for both Group I and the normal group. By the seventh day the mean value for Group II was 76.5±17.1 cm/s which was not significantly different from Day 1.     

应用ROC曲线评价彩色多普勒血流显像对肾动脉狭窄的诊断价值

目的用受试者工作特征(receiver operating characteristic,ROC)曲线评价彩色多普勒血流显像(CDFI)诊断肾动脉狭窄(RAS)的价值。方法选择同时行肾动脉CDFI及数字减影血管造影(DSA)检查的RAS患者56例,以DSA检查结果为“金标准”,绘制CDFI诊断RAS的正确率及RAS狭窄程度的ROC曲线并计算曲线下面积(AUC)。根据经过培训的检查者从事彩色多普勒超声诊断工作的年资及所使用的仪器分组,比较各组间的诊断符合率。结果CDFI诊断RAS正确率ROC曲线的AUC达0.756±0.048,用CDFI诊断RAS具有统计学意义(P<0.001);CDFI诊断RAS狭窄程度ROC曲线的AUC仅为0.512±0.065,即用CDFI诊断RAS狭窄程度无统计学意义(P>0.05)。不同年资超声医师对RAS的诊断符合率差异无统计学意义(P>0.05),不同仪器组对RAS的诊断符合率差异无统计学意义(P>0.05)。结论在规范化检查的条件下,CDFI可作为诊断RAS的有效筛选手段,为临床提供重要的诊断信息,但对RAS程度的判断则价值有限。     

经颅多普勒超声监测OSAS患者睡眠呼吸暂停期间的脑血流变化

目的采用经颅多普勒超声(TCD)对阻塞性睡眠呼吸暂停综合征(OSAS)患者的睡眠呼吸暂停期间脑血流变化进行监测。方法选取符合OSAS诊断标准的50例患者,并选取同时期就诊的正常人50例作为对照组,对上述研究者采用TCD仪2 MHz脉冲波探头监测大脑中动脉平均血流速度(MFV),观察有无出现狭窄、闭塞、血流频谱的改变。结果 50例患者中,TCD检查共发现39例异常,发生率为78.0%(39/50),其中有29例为血流速度减慢,发生率为58.0%(29/50),9例为血管狭窄,发生率为18.0%(9/50);12例正常,概率为24.0%(12/50)。50例对照组中,共有10例患者出现TCD检查异常,发生率为20.0%(10/50),OSAS患者TCD异常检出率相比于正常对照组显著升高(P0.01)。中重度OSAS患者的脑血流异常情况发生率显著高于轻度患者。随访1年,OSAS组共出现8例脑血管事件,发生率为16.0%(8/50),对照组仅有1例,发生率为2.0%(1/50),组间比较差异有统计学意义(P0.05)。OSAS患者屏气前后大脑中动脉血流速度均相对于正常者升高(P0.01),屏气后的增加率明显低于正常人群(P0.01),随着OSAS疾病的严重程度上升,其屏气前后大脑中动脉血流速度明显上升(P0.05)。结论 OSAS患者由于长期的缺氧而使其容易出现动脉硬化改变,引起脑血流下降或是出现脑动脉狭窄。OSAS越严重,则出现脑血流动力学的异常发生率也就越高,越容易发生脑血管事件。     

Strain gauge plethysmography and Doppler ultrasound in the measurement of limb blood flow

Abstract The maintenance of adequate oxygen delivery (DO₂) and tissue uptake (VO₂) has become central dogma in the management of the critically ill. However, these parameters are derived using gas tensions measured in mixed venous blood and may not reflect changes in regional blood flow. Therefore, it has become necessary to provide estimates of blood flow to specific organs and to evaluate the most adequate techniques available. In order to define the best means of assessing blood flow to the lower limb noninvasively in normal subjects, measurements of superficial femoral arterial blood flow using Doppler ultrasound (DU) and strain gauge plethysmography (SGP) were compared in 10 normal volunteers at rest and during exercise. To evaluate the effect of strain gauge positioning, results of measurements made under four different combinations of cuff/strain gauge placement were compared in 15 other volunteers. The correlation of the limb blood flow obtained using the two methods at rest and exercise was 0·57 and 0·62 and the limits of agreement (d±2SD) were 0·40±2·49 and -0·86±5·22 ml 100 ml^-1 tissue min^-1 at rest and on exercise, respectively. Results obtained using SGP were more reproducible (Coef. repeat. 0·45 vs. 0·94 ml 100 ml^-1 tissue min^-1, for SGP and DU, respectively). The various combinations of cuff/strain gauge positioning showed a tendency to over-read when the latter was placed on the thigh, but were not significantly different (P<0·05). Measurements of limb blood flow obtained using DU and SGP correlate poorly over a wide range of blood flow and do not agree, the results from the latter being more reproducible. Although the same position of cuff and strain gauge should be maintained throughout an experiment, varying the positions studied yields comparable results.     

Measurement of renal blood flow in human subjects using the ultrasound velocity profiling technique

Purpose To (1) assess the accuracy of the ultrasound velocity profiling (USVP) technique of renal blood flow (RBF) measurement in normal subjects and (2) compare renal blood flow measurements obtained using USVP and renal clearance rate in patients with renal diseases. Methods First, we calculated unilateral renal blood flow (unil-RBF) using USVP and the clearance rate of para-aminohippuric acid (C_PAH) simultaneously in six healthy male subjects. We then compared unil-RBF_USVP and unil-RBF_PAH in nine patients with chronic glomerulonephritis (CGN). Results In the first study, the limits of agreement in a Bland-Altman plot ranged from −325.3 to 32.0 ml/min per 1.48 m². The mean bias was −146.7 ml/min per 1.48 m². Subdivision for values of unil-RBF_USVP by flow showed small discrepancies in values above 280 ml/min per 1.48 m²: mean bias, −98.2 ml/min per 1.48 m²; limits of agreement, −223.3 to 26.8 ml/min per 1.48 m². The three patients in the second study had immunoglobulin A (IgA) nephropathy, in whom unil-RBF_PAH was estimated as being markedly lower than unil-RBF_USVP, contrary to the primary result. Conclusion Despite its consistent negative bias, USVP may be a reliable method of quantifying renal blood flow noninvasively when measured values exceed 280 ml/min per 1.48 m². We assumed that the p-aminohippurate extraction rate (E_PAH) was profoundly impaired in the three patients with IgA nephropathy.     

A new angle-independent Doppler ultrasonic device for assessment of blood flow volume in the extracranial internal carotid artery.

OBJECTIVE: To evaluate a new angle-independent ultrasonic device for assessment of blood flow volume in the internal carotid artery. METHODS: In vitro, a pulsatile pump was set to provide an outflow of physiological fluid at 500 mL/min through an 8-mm-diameter tube. Flow volume rates were measured 10 times by 10 different operators and compared with time-collected flow volume rates. In vivo, internal and common carotid artery blood flow volumes were measured in 28 volunteers by 2 operators using a FlowGuard device (Biosonix Ltd). Internal and common carotid artery diameters and blood flow volumes were also assessed by Duplex sonography and compared with FlowGuard measurements. In 10 volunteers, internal carotid artery blood flow volume changes in response to monitored breath manipulations were recorded. RESULTS: In vitro, intraoperator variability was 4.04% (range, 2%-5.7%). The mean error rate +/- SD was 3.54% +/- 0.8% (range, 2.7%-5.2%). In vivo, the mean common carotid artery blood flow volume was 456 +/- 39 mL/min (range, 417-583 mL/min) with a mean diameter of 6.7 +/- 0.7 mm (range, 5.8-8.7 mm). The mean internal carotid artery blood flow volume was 277 +/- 25 mL/min (range, 239-338 mL/min) with a mean diameter of 5 +/- 0.5 mm (range, 4.1-6.1 mm). No significant difference was found between operators. Internal carotid artery diameter and blood flow volume measured by the FlowGuard were closely correlated with the results of Duplex sonography. Repeated shifts of end-tidal CO2 induced reproducible changes in internal carotid artery flow volume: 187.5 +/- 18.1 mL/min at 26.8 +/- 1.9 mm Hg and 382.1 +/- 18.2 mL/min at 47 +/- 2.2 mm Hg. CONCLUSIONS: The FlowGuard showed that volume flow studies in the internal carotid artery could be easily performed, with results compatible with those of previous clinical reports. Duplex comparative results and breath-induced changes in internal carotid artery flow volume justify further evaluation of the system.