Duplex scanning of the internal carotid artery: an assessment of cerebral blood flow

Effect of pneumoperitoneum and Trendelenburg position on internal carotid artery blood flow measured by ultrasound during robotic prostatectomy

INTRODUCTION

Robotic prostatectomy requires pneumoperitoneum and a steep Trendelenburg position; however, this condition may compromise cerebral blood flow. Here, we evaluated the effect of pneumoperitoneum and the steep Trendelenburg position on internal carotid artery (ICA) blood flow measured by Doppler ultrasound during robotic prostatectomy.

METHODS

Patients who underwent robotic prostatectomy were prospectively recruited. The ICA blood flow was measured at the following five time-points: with the patient awake and in the supine position (Ta), 10 min after anaesthetic induction in the supine position (T1), 10 (T2) and 30 (T3) min after pneumoperitoneum in the steep Trendelenburg position, and at the end of surgery in the supine position after desufflation of the pneumoperitoneum (T4). Hemodynamic and cerebrovascular variables were measured at each time-point.

RESULTS

A total of 28 patients were evaluated. The ICA blood flows were significantly lower at T2 and T3 than at T1 (162.3±44.7 [T2] vs. 188.0±49.6 mL/min [T1], P=0.002; 163.1±39.9 [T3] vs. 188.0±49.6 mL/min [T1], P=0.009). The ICA blood flow also differed significantly between Ta and T1 (236.8±58.3 vs. 188.0±49.6 mL/min, P<0.001). Heart rates, cardiac indexes, peak systolic velocity, and end-diastolic velocity were significantly lower at T2 and T3 than at T1. However, ICA diameter, mean blood pressure, and end-tidal carbon dioxide partial pressure did not differ significantly at all time-points.

CONCLUSION

Pneumoperitoneum and the steep Trendelenburg position caused decreased ICA blood flow, suggesting that they should be carefully performed during robotic prostatectomy, especially in patients at risk of postoperative cerebrovascular accident. This article is protected by copyright. All rights reserved.

STUDY ON THE RELATIONSHIP BETWEEN WALL SHEAR STRESS AND ASPECT RATIO OF CEREBRAL ANEURYSMS WITH DIFFERENT PRESSURE DIFFERENCES USING CFD SIMULATIONS

CFD simulations were performed for 60 human cerebral aneurysms (30 previously ruptured and 30 previously unruptured) to study the behavior of the time-averaged wall shear stress (TAWSS) with respect to the aspect ratio (AR), implementing a set of low, normal, and high-pressure differences between the inlet and the outlets of each artery. It is well known that there exists a direct relationship between TAWSS and the rupture. In this investigation, we presented an important result because the condition of the pressure among the branches and the AR may be measured in any patient, then a slope may be associated, and finally a TAWSS may be estimated. We found that when the pressure difference increased, the absolute slopes between TAWSS and AR increased as well. Also, the magnitude of the slope in the previously unruptured aneurysms was 4.7 times the slope in the previously ruptured aneurysms. On the other hand, TAWSS was higher in the previously unruptured aneurysm than previously ruptured aneurysms due to the unruptured aneurysms that have a smaller surface area. Furthermore, we analyzed the relationship between TAWSS and other geometric parameters of the aneurysm, such as bottleneck and non-sphericity index; however, no correlation was found for either cases.

Maternal cerebral blood flow during normal pregnancy: a cross-sectional study

OBJECTIVE

Pregnancy is associated with substantial changes in the maternal circulatory physiology. Our aim was to investigate maternal cerebral blood flow (CBF) during normal pregnancies.

STUDY DESIGN

We prospectively measured maternal CBF in 210 low-risk pregnant women at different gestational ages, and in 15 nonpregnant women. CBF was assessed by measuring blood flow volume in the internal carotid artery (ICA) by dual-beam angle-independent digital Doppler ultrasound.

RESULTS

ICA blood flow volume increased during pregnancy from 318 mL/min ± 40.6 mL/min in the first trimester to 382.1 mL/min ± 50.0 mL/min during the third trimester, corresponding to CBF values of 44.4 and 51.8 mL/min(-1)/100 g(-1), respectively (P < .0001). CBF changes were associated with progressive decrease in cerebral vascular resistance and moderate increase in ICA diameter.

CONCLUSION

Maternal CBF is gradually increasing during normal pregnancy. Vasorelaxing impact of estrogens and other factors on cerebral vessels may explain the changes in CBF during pregnancy.

Comparative overview of brain perfusion imaging techniques

Numerous imaging techniques have been developed and applied to evaluate brain hemodynamics. Among these are: Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), Xenon-enhanced Computed Tomography (XeCT), Dynamic Perfusion-computed Tomography (PCT), Magnetic Resonance Imaging Dynamic Susceptibility Contrast (DSC), Arterial Spin-Labeling (ASL), and Doppler Ultrasound. These techniques give similar information about brain hemodynamics in the form of parameters such as cerebral blood flow (CBF) or volume (CBV). All of them are used to characterize the same types of pathological conditions. However, each technique has its own advantages and drawbacks. This article addresses the main imaging techniques dedicated to brain hemodynamics. It represents a comparative overview, established by consensus among specialists of the various techniques. For clinicians, this paper should offers a clearer picture of the pros and cons of currently available brain perfusion imaging techniques, and assist them in choosing the proper method in every specific clinical setting.

Comparative overview of brain perfusion imaging techniques

BACKGROUND AND PURPOSE

Numerous imaging techniques have been developed and applied to evaluate brain hemodynamics. Among these are positron emission tomography, single photon emission computed tomography, Xenon-enhanced computed tomography, dynamic perfusion computed tomography, MRI dynamic susceptibility contrast, arterial spin labeling, and Doppler ultrasound. These techniques give similar information about brain hemodynamics in the form of parameters such as cerebral blood flow or cerebral blood volume. All of them are used to characterize the same types of pathological conditions. However, each technique has its own advantages and drawbacks.

SUMMARY OF REVIEW

This article addresses the main imaging techniques dedicated to brain hemodynamics. It represents a comparative overview established by consensus among specialists of the various techniques.

CONCLUSIONS

For clinicians, this article should offer a clearer picture of the pros and cons of currently available brain perfusion imaging techniques and assist them in choosing the proper method for every specific clinical setting.

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.

Flow velocity and flow volume measurements in the extracranial carotid and vertebral arteries in healthy adults: reference data and the effects of age

To establish reference data and to investigate the development of haemodynamics in the extracranial carotid and vertebral arteries, we performed a prospective study in 78 age- and gender-matched healthy adults from 20 to 85 y old. Angle-corrected flow velocities and luminal diameters were measured and waveform parameters and flow volumes calculated in all the arteries. Side-to-side differences and the influence of age on these parameters were also investigated. In the common carotid arteries, the internal carotid arteries and the vertebral arteries (CCA, ICA and VA, respectively) all flow velocities decreased significantly during ageing. The luminal diameter remained constant in all the carotid arteries, but increased slightly with age in the VA. An age-related decline of intravascular flow volume was observed in the ICA. Due to a pronounced decrease in end-diastolic flow velocity, the resistance index decreased in ICA and VA during ageing. There were no significant side-to-side differences in flow velocities and flow volumes in any of the extracranial arteries. The luminal diameters of the CCA, ICA and ECA were significantly smaller in women than in men. No relevant gender-related differences in flow velocities or waveform parameters were found in the extracranial arteries. There was no gender-linked difference in the flow volumes of the brain-feeding arteries and, in the ECA, flow volumes were significantly higher in men. Reference data on all flow velocities and waveform parameters, luminal diameters and flow volumes were established for different age groups between 20 and 85 y old. These data allow us to outline the development of cerebral haemodynamics during "benign ageing" and to utilise flow volume measurements in clinical practice, especially in patients with cerebrovascular diseases.

Color duplex measurement of cerebral blood flow volume in healthy adults

BACKGROUND AND PURPOSE

Global cerebral blood flow (CBF) is an important yet largely unknown quantity in the treatment of neurological intensive care patients. Color duplex sonography of the extracranial cerebral arteries can be used to measure global CBF volume directly at the bedside. To establish reference data on global CBF volume and to test the influence of sex and age on this parameter, a prospective study was performed in a group of 78 healthy adults aged 20 to 85 years (39 women, 39 men; mean age, 52+/-19 years in either sex).

METHODS

The common, external, and internal carotid arteries and the vertebral arteries were examined with the use of a 7.0-MHz transducer of a computed sonography system. Angle-corrected time-averaged flow velocity and the diameter of the vessel were measured. Intravascular flow volumes were calculated as the product of angle-corrected time-averaged flow velocity and the cross-sectional area of the circular vessel. CBF volume was determined as the sum of flow volumes in the internal carotid and vertebral arteries of both sides.

RESULTS

From 20 to 85 years of age, CBF volume decreased significantly (P</=0.0001), on average by approximately 3 mL/min per year. There were no sex-linked differences in CBF volume. The mean relative contributions of the internal carotid artery and the vertebral arteries to global CBF volume remained constant with age (76% versus 24%). The reference data on CBF volume established for the groups aged 20 to 39 years, 40 to 59 years, and 60 to 85 years were 727+/-102, 656+/-121, and 603+/-106 mL/min, respectively.

CONCLUSIONS

The data presented here provide additional information on the natural development of global cerebral perfusion in "benign aging." CBF volume reference data for different age groups were also established. These data provide a basis for the clinical application of CBF volume measurements at the bedside, especially in the monitoring of CBF volume in neurological intensive care patients.

Color duplex measurement of cerebral blood flow volume: intra- and interobserver reproducibility and habituation to serial measurements in normal subjects

Color duplex flowmetry of internal carotid and vertebral arteries permits estimation of intravascular flow volumes and global cerebral blood flow volume (CBFV) by summing the flow volumes measured in each of the four extracranial vessels. Intravascular flow volumes were calculated as the product of angle-corrected time-averaged flow velocity and the cross-sectional area of the vessel. The reliability of this new method was tested in a prospective, intra- and interdiane, intra- and interobserver reproducibility study of 32 healthy subjects aged 7-57 years. In each subject, CBFV was tested by each observer twice on day 1 and once on day 2 in consecutive recordings. In each artery, both examiners found closely similar mean intravascular flow volumes. Intradiane interobserver reproducibility of CBFV was high on both days (correlation coefficient, CC, 0.90 and 0.85, p < or = 0.0001; coefficient of variance, CV, 10.0 and 10.4%, respectively), as was the interdiane comparison (CC = 0.81, p < or = 0.0001; CV < or = 13.3%). Intraobserver reproducibility was even higher. On both days, there was a progressive decrease in CBFV from each subject's first to the last examination within a 1-h examination period (day 1: 717 +/- 150 ml/min to 690 +/- 120 ml/min; difference, p < or = 0.05; day 2: 700 +/- 120 ml/min to 665 +/- 126 ml/min; difference, p < or = 0.01). This habituation effect was more pronounced in subjects with high initial CBFV. Reproducibility of CBFV is comparable to that of mean CBF measurements with 133Xe inhalation and H2 15(O) positron emission tomography techniques reported by other groups. This method makes serial bedside-monitoring of CBFV feasible without posing the risks of radiation exposure.

Intraoperative measurement of Javid shunt flow with transit-time ultrasound

Transit-time ultrasound methods were used to measure blood flow in 37 patients undergoing carotid endarterectomy. Internal carotid flow before (ICFbef) and after (ICFaft) endarterectomy was measured with a 6 mm perivascular probe, and Javid shunt flow (SF) was measured with a clamp-on probe. For the entire group ICFbef averaged 117 +/- 67 ml/min and ICFaft was 173 +/- 67 ml/min. Shunt flow averaged 123 +/- 51 ml/min. The differences between ICFbef and ICFaft and between SF and ICFaft were significant (ANOVA, p < 0.01) but the difference between ICFbef and SF was not. The relationship between ICFbef and SF appeared to define two groups of patients. Those in whom SF was greater than ICFbef (SF > ICFbef) had more stenosis evident on preoperative arteriograms (64.7% +/- 14.55% maximum single diameter stenosis) and a greater average increase in ICF (151% +/- 159%) than those with SF < or = ICFbef (43.3% +/- 20.9% stenosis and 34% +/- 54% increase in ICF), suggesting that the relationship between SF and ICFbef defines groups with different hemodynamic responses. The similarity between SF and ICFbef indicates that Javid shunt flow offers adequate protection from cerebral ischemia. A practical benefit of the shunt clamp-on flow probe is the ability afforded to recognize shunt occlusions.

Legal and ethical aspects of driving and working in patients with an implantable cardioverter defibrillator

Automobile driving is essential to work and leisure for many people, and patients with implantable cardioverter defibrillators (ICDs) are no exception. Whether patients who may suffer sudden incapacitation should be allowed to drive raises important ethical and legal issues. The opinion of physicians regarding when or if it is safe to drive with an ICD varies, and most countries have no regulations to assist such decisions. Such regulations can best be developed by actuarial analysis of the risks involved, although the limited volume of published data on the ICD hinders this process. A policy based on very low levels of social risk from driving by patients with ICDs or a comparison with epileptic patients suggests a ban on driving for 12 to 24 months after ICD implantation. Patients who have received therapy from the ICD within this period would not be granted a driver's licence. As further data from actuarial studies become available, these guidelines could be relaxed for patients at low risk of therapy delivery.

Extracranial carotid artery flow measurement during carotid endarterectomy using a Doppler ultrasonographic flowmeter

A study was performed to evaluate immediate changes in carotid artery blood flow after carotid endarterectomy using a Doppler ultrasonographic flowmeter. Forty-seven consecutive patients aged 49-78 (median 64) years with symptomatic internal carotid artery (ICA) stenosis underwent carotid endarterectomy. Volume flow, resistance and pulsatility index were measured in the common carotid artery (CCA) and ICA both before and after operation. ICA flow increased by 54 per cent (P < 0.01) and resistance decreased by 58 per cent (P = 0.01). CCA flow rose by 17 per cent (P = 0.1) and resistance fell by 21 per cent (P = 0.02). The pulsatility index did not change significantly. The Doppler ultrasonographic flowmeter offers a simple, non-invasive and convenient means of improving understanding of the immediate haemodynamic effects of carotid endarterectomy. It is useful in everyday practice to confirm the adequacy of endarterectomy, particularly in the absence of other methods of quality control. Duplex ultrasonography might still be necessary after surgery if the flowmeter does not demonstrate an increase in flow compared with the preoperative value.

Continuous measurement of jugular venous oxygen saturation in response to transient elevations of blood pressure in head-injured patients

Following traumatic brain injury, continuous jugular venous oxygen saturation (SjvO2) measurements have been made and used to assess cerebral oxygenation. Transients of SjvO2 may reflect cerebral blood flow (CBF) changes if measurements are made over a short period of time during which cerebral metabolic rate for oxygen is assumed unchanged. In response to alterations in perfusion pressure, transients of SjvO2 may indicate the extent to which autoregulation has been preserved after injury. The effect of arterial pressure changes on SjvO2 was measured in 14 severely head-injured patients (Glasgow Coma Scale score < 8) within 36 hours of injury. Mean arterial blood pressure (MABP), arterial oxygen saturation, and intracranial pressure (ICP) data were also continuously recorded by a computer at the patients' bedside. The reliability of the SjvO2 oximetry measurements varied among patients, and an average 38% of SjvO2 measurements were off by more than 6% saturation, necessitating recalibration. During periods of satisfactory catheter performance, 120 instances were found in which MABP was elevated more than 8 torr (mean +/- standard deviation: 32 +/- 13 torr) due to endotracheal suctioning. In 94 of these measurements, there was an associated increase in the ICP of 5 torr or more, averaging 16.6 +/- 10.2 torr. The SjvO2 was 0.62 +/- 0.10 before the increase in MABP and rose to a peak of 0.77 +/- 0.10 during the maximum MABP elevation, suggesting increased CBF during the transient hypertension. In 34 of 37 instances of persistent blood pressure elevations lasting for more than 10 minutes (mean 16.0 +/- 8.0 minutes), the SjvO2 elevation persisted (average duration 15.0 +/- 12.4 minutes), suggesting impaired or lost autoregulatory vasoconstriction. The presence or absence of hyperemia was unrelated to the extent of the autoregulation response. Results indicate that SjvO2 rises with increasing perfusion pressure during and after endotracheal suctioning, suggesting a feeble or absent autoregulatory response following traumatic brain injury.

Estimation of cerebral blood flow through color duplex sonography of the carotid and vertebral arteries in healthy adults

BACKGROUND AND PURPOSE

To noninvasively estimate cerebral blood flow volume, a prospective study of color duplex sonography of the common, external, and internal carotid arteries and vertebral arteries of healthy adults was done. Cerebral blood flow was calculated with the sum of flow volumes in the internal carotid and vertebral arteries of both sides.

METHODS

Using a 7.0-MHz linear transducer of a computed sonography system, cervical arteries of 48 volunteers (23 women, 25 men; mean age, 35 +/- 12 years) were examined. We measured angle-corrected time-averaged velocities and the diameter of the vessels and calculated the flow volumes of all arteries. In addition, peak systolic, maximum end-diastolic, and time-averaged maximum velocities and the resistance, pulsatility, and spectral broadening indexes were determined. Furthermore, we analyzed the side-to-side difference, age dependence, and long-term reproducibility of these parameters.

RESULTS

The mean +/- SD values of flow volumes in the common, internal, and external carotid and vertebral arteries were 470 +/- 120, 265 +/- 62, 160 +/- 66, and 85 +/- 33 mL/min on either side, respectively. Total cerebral blood flow was 701 +/- 104 mL/min (corresponding to 54 +/- 8 mL/100 g per minute), with no variation in age or sex. Long-term reproducibility of cerebral blood flow and flow volumes in all vessels was significant (P < .01).

CONCLUSIONS

We conclude that color duplex sonography of cervical arteries is potentially a practical method for estimating total cerebral blood flow. This noninvasive technique may be ideally suited for bedside and follow-up examinations of the critically ill patient. In future studies it should be compared with established radionuclide techniques.