Application of transcranial Doppler sonography to evaluate cerebral hemodynamics in carotid artery disease. Comparative analysis of different hemodynamic variables

Evaluation of Cerebral Vasomotor Reactivity by Transcranial Doppler Ultrasound in Patients with Diabetic Retinopathy

The aim of this study was to assess the correlation between cerebral vasomotor reactivity (CVR) and the grade of diabetic retinopathy. A total of 43 diabetic patients with matched severity of diabetic retinopathy between their right and left eyes were included in this study. Diabetic retinopathy was graded in three groups. Right and left middle cerebral artery CVR was assessed by the breath-holding index (BHI) using transcranial Doppler ultrasound (TCD). The mean age of the patients was 56.51 ± 9.34 years with a mean duration of having diabetes mellitus of 14.49 ± 8.06 years. Diabetic retinopathy was graded as mild, moderately severe, and severe in 27.9%, 34.9%, and 37.2% of the patients, respectively. The grade of diabetic retinopathy was associated with the HbA1c level (p < .049), microalbuminuria (p < .024), and BHI (p = .001). In patients with severe diabetic retinopathy, the right-sided BHI was significantly lower as compared to those with mild or moderately severe retinopathy (p = .001 and p = .008, respectively). The left-sided BHI value in patients with severe diabetic retinopathy was significantly lower as compared to those with mild or moderately severe retinopathy (p = .001 and p = .012, respectively). In subjects with moderately severe diabetic retinopathy, both-sided BHI was significantly reduced compared to those with mild retinopathy (p = .001). Our results indicate that the grade of diabetic retinopathy was associated with impaired CVR.

Transcranial Doppler-derived indices of cerebrovascular haemodynamics are independent of depth and angle of insonation

Continuous measurement of cerebral blood flow velocity (CBFV) of the middle cerebral artery (MCA) using transcranial Doppler (TCD) and arterial blood pressure (ABP) monitoring enables assessment of cerebrovascular haemodynamics. Further indices describing cerebrovascular function can be calculated from ABP and CBFV, such as the mean index (Mxa) of cerebrovascular autoregulation, the 'time constant of the cerebral arterial bed' (tau), the 'critical closing pressure' (CrCP) and a 'non-invasive estimator of ICP' (nICP). However, TCD is operator-dependent and changes in angle and depth of MCA insonation result in different readings of CBFV. The effect of differing CBFV readings on the calculated secondary indices remains unknown. The aim of this study was to investigate variation in angle and depth of MCA insonation on these secondary indices. In eight patients continuous ABP and ipsilateral CBFV monitoring was performed using two different TCD probes, resulting in four simultaneous CBFV readings at different angles and depths per patient. From all individual recordings, the K-means clustering algorithm was applied to the four simultaneous longitudinal measurements. The average ratios of the between-clusters, sum-of-squares and total sum-of-squares were significantly higher for CBFV than for the indices Mxa, tau and CrCP (p < 0.001, p = 0.007 and p = 0.016) but not for nICP (p = 0.175). The results indicate that Mxa, tau and CrCP seemed to be not affected by depth and angle of TCD insonation, whereas nICP was.

Asymmetric TCD Findings in Malignant MCA Infarction, Resolution after Decompressive Hemicraniectomy: A Case Report

Transcranial Doppler (TCD) is a non-invasive method for assessing cerebral hemodynamics in the acute phase of stroke. We report a case of a 33-year-old man who presented with a massive left hemispheric infarct developing into “malignant” MCA infarction. TCD was utilized to monitor intracranial hemodynamics while the clinical and neuroimaging findings were used to help us in the decision to proceed with decompressive craniectomy (DC). Pre-operatively, there was reduced mean flow velocities (MFV) of the middle cerebral artery (MCA) with increasing pulsatility index (PI) ipsilateral to the infarct. The subsequent but smaller rise in the PI in the contralateral MCA was suggestive of very high intracranial pressure (ICP) from massive brain swelling. Serial TCD examinations post-operatively showed normalization of the PI, and subsequent rise in the left MCA MFV. Clinical improvement was also noted as the TCD findings improved. The asymmetry in TCD findings can be attributed to occlusion of the MCA with subsequent spontaneous recanalisation, occlusion of the MCA with subsequent recanalisation due to the DC, or initial occlusion and subsequent pressure effects on the arterioles of the MCA due to the “malignant” edema of that hemisphere that was relieved by DC. This case illustrates the value of TCD as a useful modality in monitoring intracranial hemodynamics in acute stroke.

Influence of hypertension and type 2 diabetes mellitus on cerebrovascular reactivity in diabetics with retinopathy

BACKGROUND AND OBJECTIVES

Cerebrovascular reactivity (CVR) provides information on the intracerebral arterioles capacity to react to vasodilatory stimuli. The current study aimed to investigate the influence of hypertension and type 2 diabetes mellitus on CVR in diabetics with retinopathy.

DESIGN AND SETTING

Retrospective analysis of data prospectively collected over a 1-year period.

SUBJECT AND METHODS

Subjects were classified into four groups each comprised of 30 participants: diabetic retinopathy with hypertension (DRH), diabetic retinopathy without hypertension (DR), hypertension without diabetes mellitus (H), and healthy controls without diabetes and hypertension (C). CVR was estimated in relation to the increase in the mean flow velocity compared with the basal velocity in both middle cerebral arteries during hypercapnia.

RESULTS

In the DRH group, the mean (SD) increase in CVR was 8.8 (2.49) cm/s, in the H group 14.4 (2.59) cm/s and in the DR group 9.7 (2.97) cm/s. The analysis of variance showed significant differences among the groups in blood flow velocity after a breath-holding test (F=89.83; df=3.116; P < .001).

CONCLUSIONS

Diabetes mellitus influences CVR more than hypertension.

Cerebro vascular reactivity (CVR) of middle cerebral artery in response to CO2 5% inhalation in preeclamptic women

OBJECTIVE

To compare the cerebro vascular reactivity (CVR) of middle cerebral artery (MCA) in response to CO2 5% inhalation between preeclamptic and normotensive pregnant women, also, between mild and severe preeclampsia.

STUDY DESIGN

A comparative study was performed on 61 women with preeclampsia and 65 normotensive pregnant women who were in the third trimester of gestation. MCA transcranial Doppler ultrasound was used to measure CVR in response to CO2 5% inhalation. Pulsatility index (PI), resistance index (RI), blood pressure, maternal age, gestational age and gravidity were also recorded.

RESULTS

Baseline PI and RI were lower in the preeclamptic group (p < 0.05). Inhalation of CO2 5% caused significant increase in CVR among normotensive pregnant women in comparison with preeclamptic group (1.006 ± 0.229 versus 0.503 ± 0.209, p = 0.0001). Significantly, more cerebral vasodilatation was found among mild preeclamptic women in comparison with severe preeclamptic women (0.583 ± 0.193 versus 0.383 ± 0.173, p = 0.0001). The receiver operating characteristics curve analysis revealed acceptable difference between CO2 stimulation test of preeclamptic and normotensive women (Area under curve = 0.973, p = 0.0001).

CONCLUSION

CVR in response to CO2 5% is less in preeclamptic pregnant women than normotensives, also, in severe preeclampsia, it is less than mild preeclampsia.

Selective Occipital Artery Sonography for Dural Arteriovenous Fistulas

Carotid duplex sonography is a useful method for evaluation of dural arteriovenous fistulas. The resistance index of the external carotid artery has been reported to correlate with the efficacy of treatment and recurrence or aggravation of dural arteriovenous fistulas. Herein, we describe a case of dural arteriovenous fistulas mainly supplied by the occipital artery and show that the resistance index of the occipital artery was more sensitive than that of the external carotid artery. To the best of our knowledge, this is the first report to describe the feasibility of occipital artery detection by carotid duplex sonography and clinical application of the resistance index of the occipital artery for dural arteriovenous fistulas.

The comparative effects of equipotent Bispectral Index dosages of propofol and sevoflurane on cerebrovascular carbon dioxide reactivity in elderly patients

STUDY OBJECTIVES

To compare the effects of equipotent Bispectral Index (BIS) doses of propofol and sevoflurane on cerebrovascular carbon dioxide (CO(2)) reactivity in elderly patients.

DESIGN

Prospective, randomized, controlled study.

SETTING

University Hospital.

PATIENTS

30 consecutive elderly patients (older than 70 yrs of age) scheduled for elective orthopedic, cardiac, or thoracic surgery.

INTERVENTIONS

Anesthesia was maintained with either sevoflurane or propofol along with 33% oxygen and 67% nitrous oxide. A BIS monitor was used. Sevoflurane and propofol dosages were controlled to maintain BIS values at target levels of 40-45.

MEASUREMENTS

A 2.5-MHz pulsed transcranial Doppler (TCD) probe was used to measure mean blood flow velocity in the middle cerebral artery (Vmca). After establishing baseline values of Vmca, end-tidal CO(2) was increased by decreasing ventilatory frequency by 4-8 breaths/min.

MAIN RESULTS

Equipotent doses of 2.25% sevoflurane and 6.61 mg/kg/hr of propofol were required to maintain BIS values at target levels. Baseline blood pressure (BP), BP at hypercapnia, baseline PaCO(2), baseline PaCO(2) at hypercapnia, and pulsatile index were essentially identical between the groups. Absolute and relative CO(2) reactivities in the sevoflurane groups were higher than those in the propofol groups (absolute CO(2) reactivity: 3.2 +/- 0.2* vs. 2.2 +/- 0.3 cm/sec/mmHg; relative CO(2) reactivity: 9.4 +/- 0.3* vs. 7.8 +/- 0.3 cm/sec/mmHg; *P < 0.01 vs. propofol group).

CONCLUSIONS

In elderly patients, hypercapnia has less effect on cerebral circulation during propofol anesthesia than with sevoflurane.

Evaluation of cerebrovascular carbon dioxide reactivity in patients with diabetes mellitus under sedative doses of propofol

The present study compared cerebrovascular CO2 reactivity in diabetic patients on different treatment modalities under sedative doses of propofol. Fifteen patients with diabetes mellitus (on three different antidiabetic treatment modalities) who required mechanical ventilation during intensive care therapy were studied, sedation during mechanical ventilation being maintained using propofol. As controls, 6 patients without diabetes were monitored. A 2.5-MHz pulsed transcranial Doppler probe was attached to the head of the patient at the right temporal window for continuous measurement of mean blood flow velocity in the middle cerebral artery (Vmca). After establishing baseline values of Vmca and cardiovascular hemodynamics, end-tidal CO2 was decreased by increasing ventilatory frequency by 5-8 breaths.min(-1). Values for absolute and relative CO2 reactivity in insulintreated patients were lower than those in the other three groups (absolute CO2 reactivity [means +/- SD]: control, 3.1 +/- 0.6 cm.s(-1).mmHg(-1), diet, 3.8 +/- 1.4 cm.s(-1) x mmHg(-1); oral antidiabetic drug 3.2 +/- 0.9 cm x s(-1) x mmHg(-1); insulin, 1.1 +/- 0.6 cm x s(-1) x mmHg(-1); P = 0.002).The present study shows that insulin-treated diabetic patients probably have lower cerebrovascular CO2 reactivity under propofol anesthesia than control patients or diabetics treated with dietary therapy or oral hypoglycemics.

The effects of ageing and passive heating on cardiorespiratory and cerebrovascular responses to orthostatic stress in humans

We tested the hypothesis that older adults, relative to younger adults, would be more prone to critical reductions in cerebral blood flow and oxygenation upon standing during passive heat stress. Six older (70+/-4 years, mean+/-s.d.) and six younger males (29+/-4 years) were heated (oesophageal temperature raised 0.5 degrees C) in a water-perfused suit. Blood flow velocity in the middle cerebral artery (MCAv), cerebral oxygenation, mean arterial pressure (MAP) and end-tidal partial pressure of carbon dioxide (PET,CO2) were measured continuously before and during 3 min standing in each thermal state. At supine normothermic baseline, MCAv was 47% lower in older participants (P<0.001), whilst MAP and cerebral oxygenation were similar between groups (P>0.05). Heating lowered the supine MAP more in younger adults, and elevated heart rate only in this group. Upon initial standing in normothermia, older participants had a greater drop in MCAv (P<0.05 versus young), a lesser drop in MAP (approximately 24 and approximately 42% in older and younger participants, respectively), but slower recovery of MAP (27.3+/-6.8 versus 18.6+/-4.7 s, mean+/-s.d., P=0.004); heating did not exacerbate any postural responses in either age group. During the last minute of standing, MCAv and PET,CO2 were lower in older participants, though age differences were not evident in cerebral oxygenation (normothermic or heated). Thus, independent of heat stress, in addition to lower resting MCAv, there are further age-related reductions in MCAv and slower corrections of MAP following standing. However, these asymptomatic changes seem to represent a physiologically acceptable insult which can be well tolerated in otherwise healthy older participants even during heat stress.

Hemodynamic and metabolic changes after carotid endarterectomy in patients with high-degree carotid artery stenosis

In symptomatic stenosis of the internal carotid artery (ICA), the predominant mechanism of ischemic event is considered thromboembolic. Carotid endarterectomy (CEA) removes the embolic source and is accepted as the major benefit from the surgery. Even in high-degree stenosis, hemodynamic compromise as a causal factor for cerebral ischemia remains controversial, however. We used positron emission tomography (PET) to evaluate possible hemodynamic and/or metabolic changes caused by a severe ICA stenosis and the subsequent changes after CEA. Subjects consisted of 10 patients with recent transient ischemic attack and/or minor stroke whose carotid stenosis exceeded 80% (mean, 92%). We measured regional cerebral blood flow (CBF), oxygen extraction fraction (OEF), oxygen metabolic rate (CMRO2), and regional cerebral blood volume (CBV) before and after the CEA. In addition, we calculated CBF/CBV value as an indicator of tissue perfusion reserve. We compared these PET values to those of 15 age-matched normal controls. Significant reductions in CBF, CBF/CBV, and CMRO2 values were observed in the hemisphere not only ipsilateral, but also contralateral to the stenosis. In 4 patients, an increase in OEF and decrease in CBF/CBV were also detected. These variables significantly recovered after CEA. High-degree carotid stenosis in the tested range reduces cerebral hemodynamic and metabolic reserve and forms a vulnerable environment in the brain. Successful CEA benefits not only by removing embolic source, but also by improving hemodynamic status, which may be seen in even the contralateral hemisphere.

Comparative effects of propofol vs dexmedetomidine on cerebrovascular carbon dioxide reactivity in patients with septic shock

BACKGROUND

The use of sedative drugs is reportedly related to altered cerebrovascular CO2 reactivity. The present study examined the comparative effects of propofol vs dexmedetomidine on cerebrovascular CO2 reactivity in patients with septic shock.

METHODS

A total of 20 patients with septic shock who required mechanical ventilation were included in this study. Sedation during mechanical ventilation was maintained using either propofol or dexmedetomidine. A 2.5 MHz pulsed transcranial Doppler probe was attached to the head of the patient at the right temporal window for continuous measurement of mean blood flow velocity in the middle cerebral artery (V(mca)). After establishing baseline values of V(mca) and cardiovascular haemodynamics, end-tidal CO2 was increased by decreasing ventilatory frequency by 5-8 bpm.

RESULTS

The absolute and relative CO2 reactivity values in patients with septic shock were lower for both propofol and dexmedetomidine than those for control groups, with significant differences between these values in the two septic shock groups (absolute CO2 reactivity in septic shock under propofol: 2.6 (sd 0.3) cm s(-1) mm Hg(-1); absolute CO2 reactivity in septic shock under dexmedetomidine: 2.0 (0.3) cm s(-1) mm Hg(-1); P<0.01).

CONCLUSIONS

This study showed that cerebrovascular CO2 reactivity was lower under dexmedetomidine sedation than under propofol sedation during almost identical sedation in patients with septic shock.

Differential effects of propofol on cerebrovascular carbon dioxide reactivity in elderly versus young subjects

STUDY OBJECTIVE

To examine the age-related difference between elderly and young patients in the effect of propofol on cerebrovascular carbon dioxide (CO(2)) reactivity.

DESIGN

Prospective controlled study.

SETTING

University hospital.

PATIENTS

Elderly (older than 70 years, n = 13) and young patients (younger than 25 years, n = 13) scheduled for elective orthopedic surgery.

INTERVENTIONS

After induction of anesthesia, a 2.5-MHz pulsed transcranial Doppler probe was attached to the patient's head at the right temporal window, from which mean blood flow velocity of the middle cerebral artery was measured continuously.

MEASUREMENTS

After obtaining baseline values of velocity of the middle cerebral artery, arterial blood gases, and cardiovascular hemodynamics, end-tidal CO(2) was decreased by increasing the ventilatory frequency by 2 to 5 breaths per minute. Measurements were repeated when end-tidal CO(2) decreased and remained stable for 5 to 10 minutes. Cerebrovascular CO(2) reactivity, at propofol doses of 5 and 10 mg/kg/h, was measured.

MAIN RESULTS

No significant differences were observed between the 2 groups in baseline absolute and relative CO(2) reactivity. However, there were significant differences between the 2 groups in absolute or relative CO(2) reactivity at a propofol dosage of 5 mg/kg/h. (Absolute CO(2) reactivity in young patients: 2.1 +/- 0.8 cm/s/mm Hg; elderly: 1.6 +/- 0.4* cm/s/mm Hg. Relative CO(2) reactivity in young patients: 7.4% +/- 1.6%/mm Hg; in the elderly: 6.5% +/- 0.9%*/mm Hg; unpaired t test, *P < .05). In contrast, there were no significant differences between the 2 groups in terms of absolute or relative CO(2) reactivity at a propofol dosage of 10 mg/kg/h.

CONCLUSIONS

Cerebrovascular CO(2) reactivity in elderly patients was lower than that in young patients at a propofol dosage of 5 mg/kg/h.

Cerebrovascular hemodynamics in chronic hypertensive pregnant women who later develop superimposed preeclampsia

OBJECTIVE

We have previously shown that normotensive pregnant women who later develop preeclampsia demonstrate lower baseline pulsatility index (PI) and resistance index (RI) but normal vasodilatory responses to stimulation tests. In the current study, we tested the hypothesis that women with chronic hypertension who later developed superimposed preeclampsia behave similarly.

METHODS

Transcranial Doppler ultrasound was performed on 17 women with chronic hypertension during the second trimester of pregnancy to measure middle cerebral artery (MCA) velocities. Superimposed preeclampsia developed in seven patients (SUPER group) while the rest did not develop preeclampsia (CHT group). Measurements were performed in the left lateral position at baseline on room air, during 5% CO2 inhalation, and during a 2-minute isometric handgrip test. Blood pressure, heart rate, O2 saturation, and end-tidal PCO2 were recorded with each Doppler measurement. Mean PI, RI, and cerebral perfusion pressure (CPP) at each time were compared using two-way repeated measures analysis of variance. Statistical significance was set at P < .05.

RESULTS

The women who developed superimposed preeclampsia did this an average of 8.7 +/- 1.3 weeks after the study. MCA PI and RI were lower, and CPP higher, in the SUPER group compared to the CHT group (0.64, 0.46, and 80.7 vs 0.74, 0.51, and 63.6, respectively; P < .05). Both maneuvers caused reduction in MCA PI and RI in both groups, whereas CPP increased only in the SUPER group.

CONCLUSIONS

These findings suggest that women destined to develop preeclampsia have cerebral hemodynamic changes that predate the development of overt preeclampsia.

Cerebrovascular carbon dioxide reactivity with propofol anesthesia in patients with previous stroke

STUDY OBJECTIVE

To examine whether patients with previous stroke have impaired cerebrovascular carbon dioxide (CO2) reactivity when receiving propofol anesthesia.

DESIGN

Prospective, controlled study.

SETTING

University hospital.

PATIENTS

34 consecutive patients, 17 of whom had previous stroke and were scheduled for elective cardiac surgery, and 17 control age-matched patients without previous stroke who were also scheduled for cardiac surgery.

INTERVENTIONS

Anesthesia was induced and a 2.5-MHz pulsed transcranial Doppler probe was attached to the patient's head at the right temporal window. Mean blood flow velocity of the middle cerebral artery (Vmca) was measured continuously.

MEASUREMENTS

After establishing baseline Vmca, arterial blood gases and cardiovascular hemodynamic values, partial pressure of end-tidal CO2 (PETCO2) was increased by changing the ventilatory frequency by 2 to 5 breaths/min. The measurements were repeated when PETCO2 increased and remained stable for 5 to 10 minutes.

MAIN RESULTS

Values for absolute CO2 reactivity in the control patients and in those with previous stroke were 2.6 +/- 0.5 and 2.9 +/- 0.7 cm/sec/mmHg, respectively, a nonsignificant difference in these values. Values for relative CO2 reactivity in control patients and in patients with previous stroke were 6.4 +/- 1.4 and 6.1 +/- 1.4%/mmHg, respectively, with no significant difference noted.

CONCLUSIONS

Cerebrovascular CO2 reactivity in patients with previous stroke is normal during propofol anesthesia.

The effect of diabetes on the interrelationship between jugular venous oxygen saturation responsiveness to phenylephrine infusion and cerebrovascular carbon dioxide reactivity

In this study, we examined whether cerebrovascular carbon dioxide (CO(2)) reactivity was related to the response of jugular venous oxygen saturation (SjvO(2)) to phenylephrine infusion in diabetic patients during cardiopulmonary bypass. Forty diabetic patients scheduled for coronary artery bypass graft surgery were studied, and 40 age-matched nondiabetic cardiopulmonary bypass patients served as controls. Cerebrovascular CO(2) reactivity was measured continuously using transcranial Doppler. Mean arterial blood pressure (MAP) was increased by repeated phenylephrine infusion until reaching 100% of baseline values. There was a significant difference in absolute CO(2) reactivity between the diabetic and control groups (controls, 2.8 +/- 0.7 cm. s(-1). mm Hg(-1); diabetics, 2.2 +/- 1.1 cm. s(-1). mm Hg(-1); P = 0.02). Among the diabetics, absolute CO(2) reactivity in insulin-dependent patients was less than that in noninsulin-dependent patients (diet therapy group, 3.2 +/- 0.7; glibenclamide group, 2.6 +/- 0.7; insulin-dependent group, 1.0 +/- 0.7; P < 0.01). There was a correlation between absolute CO(2) reactivity and the mean slope of SjvO(2) versus MAP for increasing MAP (r = 0.54; P < 0.0001). In conclusion, we found that the interrelationship between SjvO(2) responsiveness to phenylephrine infusion and cerebrovascular CO(2) reactivity, as well as impaired cerebrovascular autoregulation, were associated with previous hyperglycemia.

Cerebrovascular Hemodynamics in Pregnant Women With Mild Chronic Hypertension

OBJECTIVE

To evaluate and compare the cerebrovascular autoregulation in pregnant normotensive and mild chronic hypertensive patients without preeclampsia.

METHODS

Transcranial Doppler ultrasound was used to measure peak, end-diastolic, and mean velocities in the middle cerebral arteries of 34 normotensive and 17 mild chronic hypertensive women in the third trimester of pregnancy. Measurements were performed in the left lateral position at baseline, during 5% CO(2) inhalation, and during an isometric handgrip test. Mean pulsatility index, resistance index, and cerebral perfusion pressure at each time were compared using 2-way repeated measures analysis of variance. Using an alpha error of 5%, the statistical power to identify differences in middle cerebral artery indices in response to the two maneuvers was at least 90% and 50% in comparison between the two groups. Significance was P <.05.

RESULTS

Pregnant women with mild chronic hypertension had higher baseline mean blood pressure but similar pulsatility index (0.73 versus 0.75), resistance index (0.50 versus 0.50), and cerebral perfusion pressure (59.9 versus 61.8 mm Hg) compared with normotensive pregnant women. Both maneuvers caused a significant reduction in pulsatility index and resistance index and higher cerebral perfusion pressure. No significant differences were noted in the response to either 5% CO(2) inhalation or isometric handgrip test between the two groups.

CONCLUSION

Pregnant women with mild chronic hypertension show normal cerebral vasomotor reactivity to CO(2) breathing and isometric handgrip. This suggests that the abnormal cerebrovascular autoregulation in preeclampsia is not directly linked to the elevated blood pressure but rather is determined by a separate pathophysiologic pathway.

LEVEL OF EVIDENCE

II-2

Improvement of carotid blood flow after carotid endarterectomy--evaluation using intraoperative ultrasound flow measurement

OBJECTIVES

to examine the relationship between the degree of extracranial internal carotid artery (ICA) stenosis and changes in the ipsilateral ICA blood flow after carotid endarterectomy (CEA).

MATERIALS AND METHODS

in a prospective study we studied 51 patients with unilateral 60-99% ICA stenosis (median degree 84%, asymptomatic stenosis n = 13, symptomatic stenosis n = 38). The degree of ICA diameter stenosis was determined by ex-vivo plastination of the surgically removed atherosclerotic specimen and video-assessed planimetry. Intraoperative transit time ultrasound flow measurements of the carotid arteries were performed before and after CEA. Blood flow changes were assessed by mathematical approximations. Statistics were done by use of the Wilcoxon signed Rank test.

RESULTS

common carotid artery (CCA) and ICA median blood flow increased after CEA from 370 and 130 ml/min to 450 and 282 ml/min, respectively (p <.001). The relative increase of ICA blood flow was 5% and 18% for 60-69% and 70-79% ICA stenosis (n.s.) but 70% and 247% for 80-89% and 90-99% stenosis (p <.001 each). Mathematical evaluation (fourth-polynomal function) determined a significant increase of carotid blood flow after CEA in ICA stenosis of > or =82.3%.

CONCLUSIONS

in the absence of severe contralateral ICA occlusive disease a significant increase of ipsilateral ICA blood flow by CEA can be expected in patients with an ICA stenosis of > or =82.3% (linear degree of stenosis, ECST criteria).

Transcranial doppler measurement of cerebral velocity indices as a predictor of preeclampsia

OBJECTIVE

We have previously shown that women with preeclampsia demonstrate cerebral hyperperfusion and abnormal cerebrovascular autoregulation. In the current study, we tested the hypothesis that abnormal cerebrovascular function can be detected before the clinical onset of preeclampsia.

STUDY DESIGN

Transcranial Doppler ultrasonography was performed for 166 women in the second trimester of pregnancy to measure peak, end-diastolic, and mean velocities in the middle cerebral arteries. Preeclampsia developed in 10 patients who were initially normotensive. In a nested case-controlled design, each patient with preeclampsia who was initially normotensive was matched for gestational age at the time of initial examination, maternal age, and parity with two pregnant women who remained normotensive and who were delivered at term. All measurements were performed with the subject in the left lateral position at baseline, during 5% carbon dioxide inhalation, and during a 2-minute isometric handgrip test. Blood pressure, heart rate, oxygen saturation, and end-tidal PCO (2) were recorded with each Doppler measurement. The mean pulsatility index, resistance index, and cerebral perfusion pressure at each time were calculated and compared. Statistical significance was set at a probability value of <.05.

RESULTS

The studies were performed at 19 to 28 weeks of gestation. Preeclampsia developed an average of 13.6 +/- 1.0 weeks after the study. Baseline mean blood pressure and heart rate were similar, but middle cerebral arteries pulsatility and resistance indices were lower in the women with preeclampsia who were initially normotensive compared with the pregnant women who were normotensive (0.83 and 0.54 vs 0.73 and 0.50, respectively; P <.05). Both maneuvers caused a significant reduction in the pulsatility and resistance indices. With the use of baseline values as covariates, no significant differences were noted in the response to either carbon dioxide inhalation or handgrip between the group of women who remained normotensive and the group of women with preeclampsia who were initially normotensive.

CONCLUSION

Normotensive pregnant women who later have preeclampsia demonstrate lower baseline pulsatility and resistance indices but normal vasodilatory responses to challenge tests. These findings suggest that women who are destined to have preeclampsia experience cerebral hemodynamic changes that predate the development of overt preeclampsia symptoms.

Twenty-four-hour non-invasive monitoring of systemic haemodynamics and cerebral blood flow velocity in healthy humans

Acute short-term changes in blood pressure (BP) and cardiac output (CO) affect cerebral blood flow (CBF) in healthy subjects. As yet, however, we do not know how spontaneous fluctuations in BP and CO influence cerebral circulation throughout 24 h. We performed simultaneous monitoring of BP, systemic haemodynamic parameters and blood flow velocity in the middle cerebral artery (MCAV) in seven healthy subjects during a 24-h period. Finger BP was recorded continuously during 24 h by Portapres and bilateral MCAV was measured by transcranial Doppler (TCD) during the first 15 min of every hour. The subjects remained supine during TCD recordings and during the night, otherwise they were seated upright in bed. Stroke volume (SV), CO and total peripheral resistance (TPR) were determined by Modelflow analysis. The 15 min mean value of each parameter was assumed to represent the mean of the corresponding hour. There were no significant differences between right vs. left, nor between mean daytime vs. night time MCAV. Intrasubject comparison of the twenty-four 15-min MCAV recordings showed marked variations (P < 0.001). Within each single 15-min recording period, however, MCAV was stable whereas BP showed significant short-term variations (P < 0.01). A day-night difference in BP was only observed when daytime BP was evaluated from recordings in the seated position (P < 0.02), not in supine recordings. Throughout 24 h, MCAV was associated with SV and CO (P < 0.001), to a lesser extent with mean arterial pressure (MAP; P < 0.005), not with heart rate (HR) or TPR. These results indicate that in healthy subjects MCAV remains stable when measured under constant supine conditions but shows significant variations throughout 24 h because of activity. Moreover, changes in SV and CO, and to a lesser extent BP variations, affect MCAV throughout 24 h.

Ophthalmic artery flow direction on color flow duplex imaging is highly specific for severe carotid stenosis

BACKGROUND/PURPOSE

Collateral flow patterns are important risk factors for brain ischemia in the presence of internal carotid artery (ICA) stenosis or occlusion. Ophthalmic artery (OA) flow reversal, routinely studied by transcranial Doppler sonography, is an important marker for high-grade ICA stenosis or occlusion. The authors sought to define the value of assessing OA flow direction with color flow duplex ultrasonography (CDUS) in the setting of significant ICA disease.

METHODS

Of all patients having routine carotid ultrasound in the neurosonology laboratory between July 1995 and November 2000, 152 had both carotid and orbital (OA flow direction by reduced power orbital CDUS) examinations as well as angiographic confirmation of stenosis to which North American Symptomatic Carotid Endarterectomy Trial criteria could be applied. Degree of angiographic stenosis in these 152 patients (304 arteries) was correlated with OA flow direction.

RESULTS

Of 304 arteries, 101 had greater than 80% stenosis by angiogram. In 56 of these 101 arteries with high-grade stenosis or occlusion, the ipsilateral OA was reversed; however, OA flow direction was never reversed ipsilateral to arteries with less than 80% stenosis (sensitivity 55%, specificity 100%, negative predictive value 82%, and positive predictive value 100% for OA flow reversal as a marker of high-grade carotid lesions).

DISCUSSION/CONCLUSIONS

OA flow direction is easily studied with CDUS. Reversed OA flow direction is highly specific (100%) for severe ipsilateral ICA stenosis or occlusion, with excellent positive predictive value, moderate negative predictive value, and limited sensitivity. OA flow reversal is not only quite specific for severe ICA disease, which may be helpful if the carotid CDUS is difficult or inadequate, but may also provide additional hemodynamic insights (i.e., the inadequacy of other collateral channels such as the anterior communicating artery). OA evaluation can provide important hemodynamic information and should be included as part of carotid CDUS if there is any evidence of ICA stenosis or occlusion.

Transcranial Doppler ultrasonography: year 2000 update

In this update, the main clinical applications of transcranial Doppler ultrasonography are reassessed. A specific format for technology assessment, personal experience, and an extensive review of the literature form the basis of the evaluation. The document is approved by the American Society of Neuroimaging and the Neurosonology Research Group of the World Federation of Neurology.

Transcranial Doppler sonography guided by magnetic resonance angiography for improved monitoring of intracranial arteries

Transcranial Doppler (TCD) sonography combines the advantages of real-time hemodynamic information, cost-effectiveness, and bedside application. However, measurements can be difficult to reproduce because the spatial resolution and the determination of insonation angles are limited. The purpose of this study was to use the high anatomic resolution of three-dimensional (3D) magnetic resonance angiography (MRA) images for the stereotactic guidance of TCD in order to improve the accuracy and reproducibility of TCD examinations. The MRA examinations were performed on a 1.5 T scanner using a 3D flow compensated gradient-echo sequence. A noninvasive stereotactic mask was used for image registration. The MRA data were then transferred to a personal computer. An infrared tracking system registered the position of the head and the ultrasound probe during TCD. This enabled the authors to superimpose a virtual ultrasound beam onto the MRA projections of the intracranial arteries displayed on the monitor of the personal computer. This allows the examiner to easily identify the insonated intracranial artery and displays the insonation angle. In volunteer examinations (n = 10), the accuracy and reproducibility for the localization of specific vessel segments was 2.48 mm for the middle cerebral artery and 2.81 mm for all insonated intracranial arteries (middle cerebral artery, anterior cerebral artery, internal carotid artery, and posterior cerebral artery). Without navigation the reproducibility of vessel segment insonation dropped to 4.7 mm for the middle cerebral artery and to 4.84 mm for all vessels. The authors conclude that 3D MRA, acquired as an initial procedure in patients with intracranial vascular disorders, can be used to provide stereotactic guidance for repeated TCD examinations. This facilitates the reproducible insonation of specific vessel segments.

CO2 reactivity in patients after subarachnoid haemorrhage

CO2 reactivity was tested in patients with transcranial Doppler sonography (TCD) and endtidal CO2 measurements after an average time interval of ten months after subarachnoid haemorrhage (SAH). After deliberately changing breathing there was a significant change in endtidal CO2 and in flow velocities in all three examination groups. Comparing 27 patients with SAH and 5 patients treated for incidental aneurysms and 20 patients without cerebrovascular disease there were no significant differences in CO2 reactivity. Furthermore, there were no right to left differences. In 12 patients with vasospasm, two of them treated by percutaneous transluminal angioplasty for delayed ischaemic deficits, CO2 reactivity was normal at the time of investigation. Furthermore, normal CO2 reactivity was found in patients after SAH and surgery for ruptured aneurysms regardless of the severity of the SAH.