Evaluation of cerebral AVM's using transcranial Doppler ultrasound

Segmentation techniques of brain arteriovenous malformations for 3D visualization: a systematic review

BACKGROUND

Visualization, analysis and characterization of the angioarchitecture of a brain arteriovenous malformation (bAVM) present crucial steps for understanding and management of these complex lesions. Three-dimensional (3D) segmentation and 3D visualization of bAVMs play hereby a significant role. We performed a systematic review regarding currently available 3D segmentation and visualization techniques for bAVMs.

METHODS

PubMed, Embase and Google Scholar were searched to identify studies reporting 3D segmentation techniques applied to bAVM characterization. Category of input scan, segmentation (automatic, semiautomatic, manual), time needed for segmentation and 3D visualization techniques were noted.

RESULTS

Thirty-three studies were included. Thirteen (39%) used MRI as baseline imaging modality, 9 used DSA (27%), and 7 used CT (21%). Segmentation through automatic algorithms was used in 20 (61%), semiautomatic segmentation in 6 (18%), and manual segmentation in 7 (21%) studies. Median automatic segmentation time was 10 min (IQR 33), semiautomatic 25 min (IQR 73). Manual segmentation time was reported in only one study, with the mean of 5-10 min. Thirty-two (97%) studies used screens to visualize the 3D segmentations outcomes and 1 (3%) study utilized a heads-up display (HUD). Integration with mixed reality was used in 4 studies (12%).

CONCLUSIONS

A golden standard for 3D visualization of bAVMs does not exist. This review describes a tendency over time to base segmentation on algorithms trained with machine learning. Unsupervised fuzzy-based algorithms thereby stand out as potential preferred strategy. Continued efforts will be necessary to improve algorithms, integrate complete hemodynamic assessment and find innovative tools for tridimensional visualization.

Transcranial Doppler ultrasound: Clinical applications from neurological to cardiological setting

Transcranial Doppler (TCD) ultrasonography is a rapid, noninvasive, real-time, and low-cost imaging technique. It is performed with a low-frequency (2 MHz) probe in order to evaluate the cerebral blood flow (CBF) and its pathological alterations, through specific acoustic windows. In the recent years, TCD use has been expanded across many clinical settings. Actually, the most widespread indication for TCD exam is represented by the diagnosis of paradoxical embolism, due to patent foramen ovale, in young patients with cryptogenic stroke. In addition, TCD has also found useful applications in neurological care setting, including the following: cerebral vasospasm following acute subarachnoid hemorrhage, brain trauma, cerebrovascular atherosclerosis, and evaluation of CBF and cerebral autoregulation after an ischemic stroke event. The present review aimed to describe the most recent evidences of TCD utilization from neurological to cardiological setting.

Is Intraoperative Ultrasound a Valuable Tool for Brain Arteriovenous Malformation Diagnosis and Treatment? A Case Report

The localization of arteriovenous malformations (AVMs) intraoperatively in the setting of an acute intracerebral hemorrhage (ICH) is crucial to avoid damage of delicate vascular structures that may even further exacerbate the bleed. Currently, surgical mapping using preoperative angiographic is the standard of practice. We report the use of intraoperative ultrasound for the diagnosis and localization of an AVM in the case of a 61-year-old female with reported iodine contrast allergy and previous severe reaction, in a setting with limited resources, without other imaging options or timely transfer to another facility readily available. Immediate surgical care was warranted to avoid further deterioration of the patient; intraoperative diagnosis and localization of the suspected underlying lesion were done using ultrasound. The ultrasound display showed tubular anechoic intertwined structures that demonstrated bidirectional flow, which is suggestive of an AVM. The intraoperative diagnosis allowed the surgeon to avoid an inadvertent approach to the vascular malformation nidus or vessels, which could have further complicated the case. We believe that intraoperative ultrasound may be valuable for the neurosurgeons today in many settings. Despite the fact that this case occurred in a scenario with limited resources and no other imaging method (such as magnetic resonance imaging (MRI), magnetic resonance angiography (MRA)) available, we advise readers not to rely solely on intraoperative ultrasound.

A proposed classification for assessing rupture risk in patients with intracranial arteriovenous malformations

Background:

Whether cerebral arteriovenous malformations (AVMs) should be treated remains an ongoing debate. Nevertheless, there is a need for predictive factors that assist in labelling lesions as low or high risk for future rupture. Our aim was to design a new classification that would consider hemodynamic and anatomic factors in the rapid assessment of rupture risk in patients with AVMs.

Methods:

This was a retrospective study that included 639 patients with ruptured and unruptured AVMs. We proposed a new classification score (1–4 points) for AVM rupture risk using three factors: feeding artery mean velocity (Vm), nidus size, and type of venous drainage. We employed descriptive statistics and logistic regression analysis.

Results:

A total of 639 patients with cerebral AVMs, 388 (60%) had unruptured AVMs and 251 (40%) had ruptured AVMs. Logistic regression analysis revealed a significant effect of Vm, nidus size, and venous drainage type in accounting for the variability of rupture odds (P = 0.0001, R² = 0.437) for patients with AVMs. Based in the odds ratios, grades 1 and 2 of the proposed classification were corresponded to low risk of hemorrhage, while grades 3 and 4 were associated with hemorrhage: 1 point OR = (0.107 95% CI; 0.061–0.188), 2 point OR = (0.227 95% CI; 0.153–0.338), 3 point OR = (3.292 95% CI; 2.325–4.661), and 4 point OR = (23.304 95% CI; 11.077–49.027).

Conclusion:

This classification is useful and easy to use, and it may allow for the individualisation of each cerebral AVM and the assessment of rupture risk based on a model of categorisation.

Hemodynamics Associated With Intracerebral Arteriovenous Malformations: The Effects of Treatment Modalities

The understanding of the physiology of cerebral arteriovenous malformations (AVMs) continues to expand. Knowledge of the hemodynamics of blood flow associated with AVMs is also progressing as imaging and treatment modalities advance. The authors present a comprehensive literature review that reveals the physical hemodynamics of AVMs, and the effect that various treatment modalities have on AVM hemodynamics and the surrounding cortex and vasculature. The authors discuss feeding arteries, flow through the nidus, venous outflow, and the relative effects of radiosurgical monotherapy, endovascular embolization alone, and combined microsurgical treatments. The hemodynamics associated with intracranial AVMs is complex and likely changes over time with changes in the physical morphology and angioarchitecture of the lesions. Hemodynamic change may be even more of a factor as it pertains to the vast array of single and multimodal treatment options available. An understanding of AVM hemodynamics associated with differing treatment modalities can affect treatment strategies and should be considered for optimal clinical outcomes.

Ascertaining the Value of Noninvasive Measures Obtained Using Color Duplex Ultrasound and Central Aortic Pressure Monitoring During the Management of Cerebral Arteriovenous Malformation Resection: Protocol for a Prospective, Case Control Pilot Study

BACKGROUND

Dramatic hemodynamic changes occur upon removal of an arteriovenous malformation of the brain (bAVM) with a number of potentially serious perioperative complications, such as intracranial hemorrhage and venous occlusive hypertensive syndrome. As these complications largely occur in the postoperative inpatient period, a rapid, repeatable noninvasive investigation to serially monitor relevant intracranial hemodynamics may be of benefit. Though, transcranial Doppler (TCD) and transcranial color duplex (TCCD) are techniques used and available to provide hemodynamic measurements postoperatively, the time course of hemodynamic sequences following bAVM resection remains uncertain.

OBJECTIVE

This is a prospective, case control pilot study conducted in participants having elective bAVM resection surgery.

METHODS

Each participant will undergo a preoperative color duplex ultrasound (CDU) of the bilateral extracranial carotid arteries, a CDU of the circle of Willis including the bAVM vessels, and a central aortic pressure measurement, repeated daily, postoperatively, for a 2-week period.

RESULTS

Patient accrual has commenced with anticipation of first results in 2018.

CONCLUSIONS

This protocol aims to strengthen the work of previous authors by providing documentation of the time course of hemodynamic changes following bAVM resection. The protocol is designed to determine whether noninvasive technology, including CDU imaging of the extracranial carotid and intracranial arteries in the form of TCCD along with central aortic pressure measurements, can determine whether there are any hemodynamically significant prognostic markers that may provide insight into the process of vessel remodeling, including insight into venous changes following bAVM resection.

Quantitative evaluation of arteriovenous malformation hemodynamic changes after endovascular treatment using parametric color coding: A case series study

Background Brain arteriovenous malformations (AVMs) are complex vascular lesions. Endovascular treatment results are usually measured by calculating the volume reduction of the lesions. Nevertheless, vascular flow quantification seems a more physiologically accurate way of measuring endovascular results. We evaluated the use of parametric color coding (PCC) with digital subtraction angiography (DSA), in order to determine the feasibility of PCC to detect and measure the impact of AVM endovascular treatment-induced changes using real-time hemodynamic parameters. Methods and results Supratentorial brain AVM treatment was evaluated in 29 patients over the course of 38 sessions. Using regions of interest (ROIs) at the carotid siphon, arterial feeder, drainage vein and venous sinus, we found significant increase in time to peak (TTP) values at the arterial feeder, drainage vein and venous sinus. We compared TTP in four different embolization volume groups: I (0-25%), II (26-50%), III (51-75%) and IV (76-100%). We found significant differences between groups and a moderate correlation between embolization percentages, as well as an increase in TTP at the main vein ROI; but not in the arterial side or sinus. Conclusions Brain AVM endovascular treatment results can be quantified in vivo with PCC. PCC is capable of detecting hemodynamic changes after brain AVM endovascular treatment, that may reflect flow drop, and it is correlated with volume embolization.

Relationship of pulsatility and resistance indices to cerebral arteriovenous malformation angioarchitectural features and hemorrhage

The role that hemodynamics plays in the pathophysiology of cerebral arteriovenous malformation (AVM) hemorrhage remains unclear. Here, we examine the relationship of pulsatility and resistance indices to AVM angioarchitectural features and hemorrhage. Records of patients with cerebral AVMs evaluated at our institution between 2007-2014 and with flows obtained before treatment using quantitative magnetic resonance angiography (QMRA) were retrospectively reviewed. Flow volume rate and flow velocity were measured in primary arterial feeders and compared to their contralateral counterparts. Pulsatility index (PI)=[(systolic flow velocity-diastolic flow velocity)/mean flow velocity] and resistance index (RI)=[(systolic flow velocity-diastolic flow velocity)/systolic flow velocity] were calculated for each feeder and compared to the normal contralateral vessel. Relationships between PI, RI and AVM clinical and angioarchitectural features were assessed using linear regression. Seventy-two patients with a total of 101 feeder arteries were included. PI and RI were significantly lower in AVM arterial feeders compared to normal vessels, thereby resulting in significantly higher flow volume rates and flow velocities in feeder vessels. There was no significant association of PI and RI with hemorrhagic presentation, exclusive deep venous drainage, venous stenosis, single draining vein, or deep location. In conclusion, PI and RI can be measured using QMRA and are lower in AVM arterial feeders compared to normal vessels. Although we found no significant correlation between PI, RI, and AVM angioarchitectural characteristics thought to be associated with increased hemorrhage risk, future studies with larger sample sizes may better elucidate this relationship.

Paediatric musculoskeletal interventional radiology

Interventional radiology technique is now well established and widely used in the adult population. Through minimally invasive procedures, it increasingly replaces surgical interventions that involve higher percentages of invasiveness and, consequently, of morbidity and mortality. For these advantageous reasons, interventional radiology in recent years has spread to the paediatric age as well. The aim of this study was to review the literature on the development, use and perspectives of these procedures in the paediatric musculoskeletal field. Several topics are covered: osteomuscle neoplastic malignant and benign pathologies treated with invasive diagnostic and/or therapeutic procedures such as radiofrequency ablation in the osteoid osteoma; invasive and non-invasive procedures in vascular malformations; treatment of aneurysmal bone cysts; and role of interventional radiology in paediatric inflammatory and rheumatic inflammations. The positive results that have been generated with interventional radiology procedures in the paediatric field highly encourage both the development of new ad hoc materials, obviously adapted to young patients, as well as the improvement of such techniques, in consideration of the fact that childrens' pathologies do not always correspond to those of adults. In conclusion, as these interventional procedures have proven to be less invasive, with lower morbidity and mortality rates as well, they are becoming a viable and valid alternative to surgery in the paediatric population.

Quantitative assessment of changes in cerebral arteriovenous malformation hemodynamics after embolization

BACKGROUND AND PURPOSE

Embolization reduces flow in arteriovenous malformations (AVMs) before surgical resection, but achievement of this goal is determined subjectively from angiograms. Here, we quantify effects of embolization on AVM flow.

METHODS

Records of patients who underwent AVM embolization at our institution between 2007 and 2013 and had flow rates obtained pre- and postembolization using quantitative magnetic resonance angiography were retrospectively reviewed. Total flow was estimated as aggregate flow within primary arterial feeders or flow in single draining veins.

RESULTS

Twenty-one patients were included (mean age 35 years, 24% hemorrhagic presentation) with Spetzler-Martin grades 1 to 4. Fifty-four total embolization sessions were performed. The mean AVM flow was 403.4±262.4 mL/min at baseline, 285.3±246.4 mL/min after single session (29% drop, P<0.001), and 102.0±103.3 mL/min after all sessions of embolization (75% drop, P<0.001). Total number of pedicles embolized (P<0.001) and embolization of an intranidal fistula during any session (P=0.002) were significantly associated with total decreased flow postembolization. On multivariate analysis, total pedicles embolized was predictive of total flow drop (P<0.001). However, pedicles embolized per session did not correlate with flow drop related to that session (P=0.44).

CONCLUSIONS

AVM flow changes after embolization can be measured using quantitative magnetic resonance angiography. The total number of pedicles embolized after multiple embolization sessions was predictive of final flow, indicating this parameter is the best angiographic marker of a hemodynamically successful intervention. The number of pedicles embolized per session, however, did not correlate with flow drop in that session, likely because of flow redistribution after partial embolization.

Invasive and ultrasound based monitoring of the intracranial pressure in an experimental model of epidural hematoma progressing towards brain tamponade on rabbits

INTRODUCTION

An experimental epidural hematoma model was used to study the relation of ultrasound indices, namely, transcranial color-coded-Doppler (TCCD) derived pulsatility index (PI), optic nerve sheath diameter (ONSD), and pupil constriction velocity (V) which was derived from a consensual sonographic pupillary light reflex (PLR) test with invasive intracranial pressure (ICP) measurements.

MATERIAL AND METHODS

Twenty rabbits participated in the study. An intraparenchymal ICP catheter and a 5F Swan-Ganz catheter (SG) for the hematoma reproduction were used. We successively introduced 0.1 mL increments of autologous blood into the SG until the Cushing reaction occurred. Synchronous ICP and ultrasound measurements were performed accordingly.

RESULTS

A constant increase of PI and ONSD and a decrease of V values were observed with increased ICP values. The relationship between the ultrasound variables and ICP was exponential; thus curved prediction equations of ICP were used. PI, ONSD, and V were significantly correlated with ICP (r² = 0.84 ± 0.076, r² = 0.62 ± 0.119, and r² = 0.78 ± 0.09, resp. (all P < 0.001)).

CONCLUSION

Although statistically significant prediction models of ICP were derived from ultrasound indices, the exponential relationship between the parameters underpins that results should be interpreted with caution and in the current experimental context.

Pulsatile Flow Effects on the Hemodynamics of Intracranial Aneurysms

High-resolution numerical simulations are carried out to systematically investigate the effect of the incoming flow waveform on the hemodynamics and wall shear stress patterns of an anatomic sidewall intracranial aneurysm model. Various wave forms are constructed by appropriately scaling a typical human waveform such that the waveform maximum and time-averaged Reynolds numbers, the Womersley number (α), and the pulsatility index (PI) are systematically varied within the human physiologic range. We show that the waveform PI is the key parameter that governs the vortex dynamics across the aneurysm neck and the flow patterns within the dome. At low PI, the flow in the dome is similar to a driven cavity flow and is characterized by a quasi-stationary shear layer that delineates the parent artery flow from the recirculating flow within the dome. At high PI, on the other hand, the flow is dominated by vortex ring formation, transport across the neck, and impingement and breakdown at the distal wall of the aneurysm dome. We further show that the spatial and temporal characteristics of the wall shear stress field on the aneurysm dome are strongly correlated with the vortex dynamics across the neck. We finally argue that the ratio between the characteristic time scale of transport by the mean flow across the neck and the time scale of vortex ring formation can be used to predict for a given sidewall aneurysm model the critical value of the waveform PI for which the hemodynamics will transition from the cavity mode to the vortex ring mode.

Observations on the flow characteristics of blood flow in arteriovenous fistulae (experimental)

Hemodynamic play a very significant role in the pathophysiology of intracranial arteriovenous malformation. The surgical decisions are based on the understanding of the complexities of the flow. Quantification of the abnormal flow is difficult. The mathematical models provide limited information due to the simplicity of the design of these models. Flow of fluid in a tube is very sensitive to small changes in the diameter. We studied the flow characteristics of a fistula by introducing accurately machined acrylic fistulae between the femoral arteries and veins of dogs. The influences of systemic arterial pressure, diameter of the arterial feeders, volume of blood flow, velocity of flow and the diameter of the shunt on the flow of blood across the shunt were studied. Our experiments suggest that the flow characteristics of an arteriovenous fistulae are complex and are influenced by small changes in the diameters of the fistula and the feeding artery. Our model demonstrates the occurrence of the anomalous flow reduction in the fistula and steal phenomenon and is therefore a more realistic representation of the clinical situation. The design of a mathematical model should include the diameter of the fistula if it is intended to replicate the hemodynamic characteristics of an arteriovenous malformation more faithfully.

The application of ultrasound in the management of cerebral arteriovenous malformation

Ultrasound is used in the diagnosis, treatment and follow-up of cerebral arteriovenous malformation (AVM). Several parameters including flow velocity, flow volume, resistance index, pulsatility index, vasomotor reactivity and their influencing factors are reviewed. The applications of ultrasound in the preoperative evaluation, intraoperative monitor and postoperative follow-up of AVM, are summarized. Although some limits exist, ultrasound can provide more reliable information about AVM, if lesions are classified according to their characteristics, compared in different conditions between preoperation and postoperation, feeding and non-feeding side, patients and healthy adults, and if ultrasound method is combined with other examinations and different developed ultrasound techniques. With the appearance and development of new ultrasound technique, its application will be wider in management of AVM.

Transcranial Doppler study of cerebral arteriovenous malformations after gamma knife radiosurgery

The aim of this study was to evaluate the clinical value of the Transcranial Doppler (TCD) in follow-up examinations after gamma knife radiosurgery (GKS) for arteriovenous malformations (AVM). We performed TCD after GKS in 18 patients who had cerebral AVMs to evaluate the hemodynamic effects of the procedure. Ten patients underwent TCD within 12 months after GKS, and eight between 12 and 24 months. The mean blood velocity (Vm) and pulsatility index (PI) were primarily analyzed in the feeding arteries (FAs) and non-FAs. Fifteen healthy volunteers served as control patients. The Vm values in the FAs after GKS ranged from 31 cm/s to 90 cm/s, with PI values ranging from 0.48 to 1.03. The Vm values in the comparable normal arteries ranged from 28 cm/s to 87 cm/s, and the PI values in these arteries ranged from 0.62 to 1.02. The Vm and PI values in every FA in all patients were normal compared to the values in the non-FAs (p=0.67 and 0.38, respectively). Our results suggest that AVM vessels with high Vm and low PI values return to normal as the nidus of the AVM is obliterated after GKS. Although there was a trend toward a reduction of the Vm values after obliteration, this trend was not significant, except when the < 12 month subgroup was compared to the 12-24 month subgroup. In our limited study, TDC proved to be a reliable, safe and non-invasive method to monitor the outcome of GKS for cerebral AVMs.

Spontaneous pial single-channel arteriovenous fistulae with angiographically occult small feeding arteries: case report

BACKGROUND

Pial single-channel arteriovenous (AV) fistulae are usually cured by interrupting only the feeding arteries identified in cerebral angiography.

CASE DESCRIPTION

A 27-year-old woman presented after 3 complex partial seizures due to a pial single-channel AV fistula with the varix located in the right temporal lobe. When all feeding arteries identified by preoperative cerebral angiography were temporarily occluded, varix blood flow was confirmed with Doppler ultrasonography. Many small feeding arteries were identified, and the varix was dissected and removed. The postoperative course was uneventful and postoperative cerebral angiography revealed no abnormal vascular lesions.

CONCLUSION

Pial single-channel AV fistulae are not always cured by interrupting only the feeding arteries identified in cerebral angiography and might require varix removal.

Intravascular pressure measurements in feeding pedicles of brain arteriovenous malformations

Pressure measurements in arterial feeders of arteriovenous malformations (AVMs) can be easily acquired during endovascular treatment procedures. In this study, mean arterial pressure values in arterial feeders (Pfed) of brain AVMs were determined using a pressure measuring system connected to a standard microcatheter. A total of 148 measurements were performed in 139 patients. Mean systemic arterial pressure values were subtracted for correction. The levels of correlation between the pressure values and various clinical parameters (i.e., AVM location, size, previous hemorrhage) and pathoanatomical features of the AVM (e.g., nidus structure, number of draining veins) were determined. Pfed values were 54.5 mmHg on average. Pfed was lower in more distally located AVMs, in larger lesions and in AVMs with multiple drainage veins. Pressure values were significantly higher in patients with previous hemorrhage and in smaller AVMs. Our results support the importance of hemodynamic parameters in determining the presentation of AVMs. More extensive studies using this simple technique may further elucidate these mechanisms and may result in improved criteria for patient selection and reduction of complications.

Evaluation of arteriovenous malformations (AVMs) with transcranial color-coded duplex sonography: does the location of an AVM influence its sonographic detection?

OBJECTIVE

The clinical value of transcranial color-coded duplex sonography (TCCS) in the evaluation of arteriovenous malformations (AVMs) has not yet been fully investigated. In this study, 54 intracranial AVMs confirmed by angiography were prospectively examined over 6 years. The purpose of the study was to describe their typical sonographic features and to define sensitivity for diagnosis with regard to the location of an AVM.

METHODS

Transcranial color-coded duplex sonographic findings for 54 patients with intracranial AVMs are presented. The vessels of the circle of Willis were identified by location, course, and direction of flow on color flow images.

RESULTS

In accordance with digital subtraction angiography, the intracranial AVMs could be visualized in 42 cases (sensitivity, 77.8%). The pathologic vessels were coded in different shades of blue and red, corresponding to varying blood flow directions in the AVM. The major feeding vessels could be easily identified. Hemodynamic parameters showing increased systolic and diastolic flow velocities and a decreased pulsatility index were better attainable with TCCS than with conventional transcranial Doppler sonography. Arteriovenus malformations located near the cortex, that is, in the parietal, frontal, occipital, and cerebellar regions of the brain, could not be visualized. In contrast, AVMs located in the basal regions were very easy to image (sensitivity, 88.9%). Additionally, TCCS proved useful for follow-up examinations postoperatively or after embolization.

CONCLUSIONS

Transcranial color-coded duplex sonography is a valuable noninvasive method for the diagnosis and long-term follow-up of intracranial AVMs. Arteriovenous malformations located in the axial imaging plane can be more easily detected. Nevertheless, TCCS should not be used as a screening method.

Intraoperative Doppler to Measure Cerebrovascular Resistance as a Guide to Complete Resection of Arteriovenous Malformations

OBJECTIVE:

Intraoperative color Doppler ultrasound has been used to locate arteriovenous malformations (AVMs). We describe the use of spectral Doppler to measure flow resistance and resistive index (RI) of vessels around the nidus to distinguish feeding arteries from en passant and normal vessels. This is particularly helpful in small AVMs and aids in the identification of normal vessels and completeness of resection by ruling out persistent low RI flow.

METHODS:

Seven patients with AVMs underwent resection. Spectral Doppler applied to the vessels in proximity to the AVM, along with calculated RI, was used to identify feeding arteries and draining veins. After presumed surgical resection of the AVM, pre-resection and postresection RIs were compared to identify residual AVM. Postoperative angiography was performed in all seven patients to confirm complete resection of the AVM.

RESULTS:

The mean pre-resection RI of vessels feeding the AVM was 0.34 (±0.01). In five patients without residual nidus on the basis of postresection color Doppler and postoperative angiogram, the postresection RI was 0.62 (±0.04). In two patients, the postresection scan identified a nidus with persistent low RI flow. Once residual AVM was resected, the RI became significantly higher. A postoperative angiogram confirmed complete resection of the AVM in all patients.

CONCLUSION:

Intraoperative duplex Doppler allowed more accurate localization of the AVM nidus. RI of the vessels around the AVM helped to distinguish vessels feeding the AVM from en passant vessels. Furthermore, comparison of pre-resection and postresection RI accurately indicated the completeness of resection.

Cerebral blood flow velocity alterations, under two different carbon dioxide management strategies, during sevoflurane anesthesia in gynecological laparoscopic surgery

In this study, 33 female patients, scheduled for operative gynecological laparoscopies, were enrolled. Our aim was prospective, randomized comparison of the influence of two different management strategies, regarding end tidal CO2, on cerebral blood flow velocities and on pulsatility index, examined by means of transcranial Doppler ultrasonography, under sevoflurane anesthesia 1.3 MAC: permissive hypercapnia (up to 45 mmHg, Group I, n = 17) versus intervention to ensure mild hypocapnia, (around 33 mmHg, Group II, n = 16). Baseline measurements of investigated parameters were recorded and CO2 insufflation started. In Group I no further adjustment was performed and CO2 partial pressure rose, while in Group II it was kept stable, by ventilatory patterns adjustment. Hemodynamic, acid base balance and cerebrovascular variables were recorded during pneumoperitoneum and in post-desufflation period, at eight checking time points. In Group I cerebral blood flow velocities increased according to CO2 elevation (2.3%-3.9% per mmHg of increase in CO2 partial pressure), whereas in Group II no significant alterations were noticed. Pulsatility index was constant over time without clinical differences between groups. Our study suggests that under sevoflurane anesthesia 1.3 MAC, prophylactic hyperventilation limits the cerebral blood flow velocities enhancing effect of CO2 insufflation, during laparoscopies.

Multi-modal monitoring of acute brain injury

OBJECTIVE

To review the scientific basis for and utility of the traditional cerebral monitors used currently in neurointensive care, together with research techniques that are soon likely to become used in managing severe head injury and subarachnoid haemorrhage.

DESIGN AND CONTENT

Firstly, the pathophysiology of acute brain injury including cerebral haemodynamics, oxygen and metabolism and the role of secondary insults are discussed. Secondly, the importance of assessment of cerebrovascular autoregulation and reactivity is reviewed together with methods for its continuous non-invasive measurement using transcranial Doppler and intracranial pressure/arterial pressure recordings. Thirdly, the respective roles of jugular venous oxygen and brain tissue oxygen monitoring are analysed. Fourthly, the use of cerebral microdialysis is described, together with an overview of its utility.

CONCLUSION

Cerebral multimodal monitoring can be helpful for the optimal management of acute brain injury and essential for future exploratory trials of neuroprotective drugs.

Steal affecting the central nervous system

Steal is a pathophysiological process in which increased blood flow through a low-resistance vascular bed is sufficient to divert flow away from a region of the central nervous system. Three disease states in which steal may cause neurological deficits due to central nervous system ischemia are reviewed. Subclavian steal occurs when stenosis of the subclavian artery proximal to the vertebral origin causes retrograde flow in the left vertebral artery. Patients with anatomic subclavian steal usually do not develop neurological symptoms but may rarely present with posterior circulation ischemia. Arteriovenous malformations alter cerebral blood flow patterns and regional perfusion pressure. It has been hypothesized that cerebral arteriovenous malformations may cause neurological deficits due to steal and that these deficits may be cured with arteriovenous malformation treatment. Intra-arterial pressure measurements and transcranial velocity studies show regional hemodynamic alterations. However, these changes have not been correlated with presenting symptoms. Evidence from single-photon emission computed tomography does suggest a relationship between regional hypoperfusion and neurological deficits. Coarctation of the aorta may divert flow from the spinal cord circulation through intercostal arteries distal to the stenosis. This is a possible but unproven mechanism of myelopathology. Steal syndromes may be amenable to treatment by open surgical or endovascular approaches. Experimental studies of the pathophysiology of steal are strengthened by precise definitions of the measured parameters and innovative applications of technology.

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.

The role of transcranial Doppler in the management of patients with subarachnoid haemorrhage--a review

Introduced 15 years ago, transcranial Doppler (TCD) recordings of blood-velocity in patients with recent subarachnoid haemorrhage (SAH) have two objectives: to detect elevated blood velocities suggesting cerebral vasospasm (VSP) and to identify patients at risk for delayed cerebral ischemic deficits (DID). The pathophysiological cascade causing DID is complex. Discrepancies between blood velocities and DID (presuming that there actually is an "ischemic threshold" for blood velocity in absolute terms, which seems most unlikely) have been demonstrated, particularly in patients with elevated intracranial pressure (ICP) levels. Furthermore, the vessel showing the highest blood velocity is not always the one perfusing the area where ischemic symptoms arise, nor does the site of the greatest subarachnoid blood clot always relate to the ischemic brain region. Moreover, it is probable that the complex haemodynamic changes following SAH and the subsequent development of VSP may be underestimated if only considering the crude intracranial artery blood velocities. Cerebral blood flow measurements combined with TCD to assess both flow and velocity have emphasised this point. Despite these findings and ignoring the basic principles of cerebral haemodynamics, cerebral vasospasm is still being assessed from the intracranial velocity measurement alone. The addition of at least a careful measurement from the extracranial internal carotid artery--using the same TCD equipment and taking only a few short minutes to perform--allows a much more accurate assessment of the degree and the effects of vasospasm. This probably explains why the clinical value of TCD is still debated. There is still uncertainty as to the best method to prevent and to treat VSP, and the overall outcome after SAH depends on so many factors besides VSP. Conclusive evidence may therefore be hard to obtain, and it appears sound to conclude that even with advanced investigation technology available, proper selection, pre- peri- and postoperative care and timing of surgery remain cornerstones in the management of these patients,--equal in importance to their treatment in the operating room or in the interventional angiography suite.

A tribute to Helge Nornes

This supplement of the Acta Neurochirurgica is dedicated to professor Helge Nornes on the occasion of his retirement. Helge Nornes started his neurosurgical training in Oslo in 1965. In 1980 he was offered the neurosurgical chair of Bern, Switzerland, where he stayed until 1983 when his old university called him back to the chair at the National Hospital in Oslo, a position he filled until he retired last year. The present paper briefly reviews examples of his contributions to neurosurgery and to the understanding of intracranial pathophysiology, including the transcranial doppler, the miniature transducer for intracranial pressure monitoring, his observations on intracranial pressure and internal carotid blood flow during subarachnoid haemorrhage, intracranial arterial blood flow in patients undergoing aneurysm surgery, his studies of the pathophysiology of arteriovenous malformations, the introduction of intraoperative Doppler recordings during surgery for aneurysms and arteriovenous malformations, and his methods for evaluating collateral circulation prior to internal carotid artery occlusion.

Hemodynamic changes in arterial feeders and draining veins during embolotherapy of arteriovenous malformations: an experimental study in a swine model

OBJECTIVE

Transcatheter assessment of changes in draining vein (DV) flow velocity has been proposed recently as a potentially useful procedure for hemodynamic monitoring of the progression of embolotherapy in cerebral arteriovenous malformations (AVMs). We compared and contrasted changes in hemodynamic parameters of arterial feeders (AFs) and DVs during experimental AVM embolotherapy.

METHODS

Carotid-jugular fistula-type AVM models were surgically created in eight swine. Pre- and postembolization transcatheter mean AF and DV pressures, DV-time average spectral peak velocity, and AF and DV pulsatility indices were assessed. An expression, the peak systolic velocity minus end-diastolic velocity (Vs - Ved), was also used in evaluating the transvenous Doppler spectra. Pre- and postembolization hemodynamic parameters were compared statistically.

RESULTS

Pre-embolization DV flow was pulsatile (Vs - Ved, 12 +/- 4.8 cm/s), with a mean DV velocity of 39.3 +/- 11.4 cm per second. Postembolization, this changed to a less/nonpulsatile pattern (Vs - Ved, 5.4 +/- 2.7 cm/s; P = 0.0035) with a lower mean DV-average spectral peak velocity of 7.0 +/- 3.1 cm per second (P = 0.0001). The mean DV pressure was also reduced from 52.0 +/- 8.2 to 45.5 +/- 8.7 mm Hg (P = 0.0023). The mean AF pressure increased from a mean of 79.5 +/- 15.5 to 96.8 +/- 16.2 mm Hg (P = 0.0004). The DV pulsatility index values also increased from a mean of 0.3 +/- 0.2 to 1.1 +/- 0.5 (P = 0.0003). Periembolization objective hemodynamic changes were detected in the DVs earlier than were the visually subjective angiographic changes observed within the nidus.

CONCLUSION

This preliminary study indicates that transvenous assessment of average spectral peak velocity and wave pattern (Vs - Ved) may be useful in the hemodynamic evaluation of AVM shunting. The convergence of these two parameters to a range less than 10 cm per second after nidus embolization may afford a theoretical advantage over AF pressure measurements when used for objective and quantitative monitoring of endovascular embolotherapy.

Early haemodynamic changes in the ophthalmic artery, siphon and intracranial arteries after carotid endarterectomy estimated by transcranial Doppler and duplex scanning

OBJECTIVES

To study early haemodynamic changes in connection with carotid endarterectomy (CE).

METHODS

Sixty-three consecutive patients, average age 64, with symptomatic stenosis in the internal carotid artery (ICA) > or = 70% were examined clinically and by transcranial Doppler (TCD) 1 day before and within 48 h after CE. Duplex scanning of extracranial vessels was performed within 1 week after CE.

RESULTS

After CE, all retrograde systolic velocities (SV) in the ophthalmic artery (OA) and 9/10 retrograde mean velocities (MV) in the siphon changed to antegrade. Antegrade SV in the OA increased significantly (p < 0.001) only on the operated side. SV in the OA on the operated side correlated (p < 0.05) with MV in the siphon, and pulsatility index (PI) in the middle cerebral artery (MCA, p < 0.001). MV in the MCA increased from 46 +/- 12 cm/s to 59 +/- 21 cm/s after CE and in the ACA with normal flow from 54 +/- 19 cm/s to 62 +/- 28 cm/s (p < 0.001 and < 0.05, respectively) only on the operated side. Stump pressure correlated (p < 0.01) with SV in the OA and PI in the MCA and was higher (59 +/- 16 mmHg, p < 0.01) in the group with antegrade flow in the OA compared to the group with retrograde flow in the OA (43 +/- 15 mmHg).

CONCLUSION

TCD and duplex gives important early information about patency of the ICA and haemodynamic intracranial changes after CE.

Transvenous hemodynamic assessment of arteriovenous malformations and fistulas. Preliminary clinical experience in Doppler guidewire monitoring of embolotherapy

BACKGROUND AND PURPOSE

Transvenous monitoring of blood flow through intracranial vascular malformations was performed with an intravascular Doppler guidewire to assess hemodynamic changes during endovascular embolotherapy.

METHODS

Flow velocity was assessed in the intracranial venous sinuses of two patients with arteriovenous malformations and seven patients with dural arteriovenous fistulas. In all cases, the Doppler guidewire was positioned in the dural sinuses coaxially through a 2.1F microcatheter. The Doppler guidewire was then advanced to the site of arteriovenous shunting for sampling of venous average peak velocity (APV) and pulsatility index. In two cases, simultaneous feeding artery flow velocity was monitored by transcranial color-coded duplex sonography.

RESULTS

Before embolotherapy, the flow pattern in the venous sinuses was pulsatile, with a mean (+/-SD) APV of 39.0 +/- 22.5 cm/s. Total or near-total embolization was achieved in six of the nine cases. After embolization, the flow pattern became less pulsatile and the APV was reduced to a mean of 21.2 +/- 14.6 cm/s (P = .0123, one-tailed paired t test). The pulsatility index was used to calculate the maximum minus the minimum peak velocity (MxPV-MnPV). This was reduced from an average of 27.0 +/- 8.7 cm/s to 13.5 +/- 8.3 cm/s after treatment (P = .0456). A parallel reduction in APV of the feeding arteries was observed with embolization.

CONCLUSIONS

Preliminary clinical experience indicates that transvenous assessment of two parameters, APV and MxPV-MnPV, is useful in the hemodynamic evaluation of intracranial arteriovenous shunts. This valuable hemodynamic information may be used for objective and quantitative monitoring during embolotherapy of intracranial vascular malformations.

Transvenous hemodynamic assessment of experimental arteriovenous malformations. Doppler guidewire monitoring of embolotherapy in a swine model

BACKGROUND AND PURPOSE

A Doppler guidewire was used to monitor progressive changes in draining vein flow parameters during experimental embolotherapy in a swine arteriovenous malformation (AVM) model.

METHODS

A microcatheter was positioned superselectively in the main arterial feeder and main draining vein in each of 10 AVM models in swine. With use of the Doppler guidewire, preembolization arterial and venous average peak velocities (APVs) and pulsatility indices were recorded. The device was left in the draining vein during transarterial particulate (in 8 swine) or liquid adhesive (in 2 swine) embolization, and continuous transvenous flow during and after treatment was monitored. Periembolization Doppler flow parameters were correlated qualitatively with angiographic changes in the nidus.

RESULTS

Preembolization draining vein flow was pulsatile, with a mean APV of 38.9 +/- 13.7 cm/s. After embolization, this changed significantly to a less pulsatile or nonpulsatile pattern, with a lower mean APV of 9.2 +/- 4.9 cm/s (P = .0001). A novel expression, the maximum minus the minimum peak velocity (MxPV-MnPV), was used in evaluating the transvenous Doppler spectra. This was reduced significantly after embolization from a mean of 11.1 +/- 3.5 cm/s to 6.7 +/- 2.5 cm/s (P = .0025). Objective periembolization hemodynamic changes were detected in the draining veins earlier than the visually subjective angiographic changes within the nidus.

CONCLUSIONS

Transvenous Doppler guidewire assessment of two parameters, APV and MxPV-MnPV, is useful in the hemodynamic evaluation of experimental arteriovenous shunting and may be used for future objective and quantitative monitoring during endovascular AVM embolotherapy.

Neonatal intracranial hemorrhage due to rupture of arteriovenous malformation

Two cases of neonatal intracerebral hemorrhage secondary to rupture of arteriovenous malformation are reported and the pertinent literature is reviewed. Despite the limited number of cases, review of the literature and our results demonstrate that the outcome of surgical removal of an arteriovenous malformation in the neonatal period is not as poor as was previously believed.

Cerebral hyperemia after arteriovenous malformation resection is related to "breakthrough" complications but not to feeding artery pressure. The Columbia University Arteriovenous Malformation Study Project

To study the pathophysiology of idiopathic postoperative brain swelling or hemorrhage after arteriovenous malformation resection, termed normal perfusion pressure breakthrough (NPPB), we performed cerebral blood flow (CBF) studies during 152 operations in 143 patients, using the xenon-133 intravenous injection method. In the first part of the study, CBF was intraoperatively measured (isoflurane/N2O anesthesia) during relative hypocapnia in 95 patients before and after resection. The NPPB group had a greater increase (P < 0.0001) in mean +/- standard deviation global CBF (28 +/- 6 to 47 +/- 16 ml/100 g/min, n = 5) than did the non-NPPB group (25 +/- 7 to 29 +/- 10 ml/100 g/min, n = 90); both arteriovenous malformation groups showed greater increase (P < 0.05) than did controls undergoing craniotomy for tumor (23 +/- 6 to 23 +/- 6 ml/100 g/min, n = 22). Ipsilateral and contralateral CBF changes were similar. In a second cohort of patients with arteriovenous malformations, CBF was measured at relative normocapnia and it increased (P < 0.002) from pre- to postresection (40 +/- 13 to 49 +/- 15 ml/100 g/min, n = 57). There were no NPPB patients in this latter cohort. The feeding mean arterial pressure was measured intraoperatively before resection or at the last embolization before surgery (n = 64). The feeding mean arterial pressure (44 +/- 16 mm Hg) was 56% of the systemic arterial pressure (78 +/- 12 mm Hg, P < 0.0001) and was not related to changes in CBF from pre- to postresection. There was an association between increases in global CBF from pre- to postresection and NPPB-type complications, but there was no relationship of these CBF changes to preoperative regional arterial hypotension. These data do not support a uniquely hemodynamic mechanism that explains cerebral hyperemia as a consequence of repressurization in hypotensive vascular beds.

Complications after multidisciplinary treatment of cerebral arteriovenous malformations

PATIENTS AND TECHNIQUES

A series of 67 patients treated for cerebral AVMs with a multidisciplinary approach is reported, with special attention for the complications due to treatment. The malformations were classified after the Spetzler Grading Scale, with 67% low-grade and 33% high-grade AVMs. Three modes of treatment were used: surgical resection, endovascular embolization, and radiosurgery (linear accelerator technique). The actual treatment was: resection alone (25% of cases), embolization plus resection (24%), embolization alone (21%), and radiosurgery (30%), either alone or after embolization or surgery. The following eradication rates were obtained: overall 80%, after resection (with or without embolization) 91%, after embolization alone 13%, after radiosurgery 87%.

CLINICAL OUTCOME

The outcome was evaluated in terms of deterioration due to treatment. A deterioration after treatment occurred in 19 patients (28%), and was a minor deterioration (19%), a neurological deficit (4%), or death (4%). As far as the mode of treatment is concerned, surgical resection was responsible for deterioration (minor) in 17% of all cases operated upon. Radiosurgery was followed by a minor deterioration in 10% of irradiated cases. Embolization gave a complication in 25% of all embolized cases (minor or neurological deficit, or death). The mechanism of the complications was: resection or manipulation of an eloquent area during surgery, radionecrosis after radiosurgery, ischaemia and haemorrhage (50% each) following embolization. In most cases of haemorrhage due to embolization, occlusion of the main venous drainage could be demonstrated.

DISCUSSION

The haemodynamic disturbances to AVMs and to their treatment are reviewed in the literature. The main haemodynamic mechanisms admitted at the beginning of a complication after treatment of cerebral AVMs are the normal perfusion pressure breakthrough syndrome, the disturbances of the venous drainage (venous overload or occlusive hyperaemia), and the retrograde thrombosis of the feeding arteries.

CONCLUSIONS

According the authors' experience, the emphasis of treatment for cerebral AVMs has now shifted from surgical resection to endovascular embolization. One of the explanations is that endovascular techniques are now employed in the most difficult cases (high grade AVMs). As severe complications of endovascular embolization may also occur for low-grade malformations, the question arises whether surgery or radiosurgery should not be used first for this low-grade group even if embolization is feasible.

Low pulsatility signals through the orbits

BACKGROUND AND PURPOSE

Low pulsatility signals (LPS) on transcranial Doppler ultrasonography are detected (1) with arteriovenous malformations, (2) distal to hemodynamically significant stenosis, and (3) in venous structures. We describe focal LPS in the territory of the internal carotid artery siphon that do not represent any of the above conditions.

METHODS

We performed retrospective and prospective reviews of transcranial Doppler studies on 3225 patients over 5 years. Clinical and radiological data of all patients with focal LPS were extracted. LPS was defined as a focal signal identified through the orbital windows with a low pulsatility index (< 0.6).

RESULTS

Sixteen LPS (mean flow velocity [mean +/- SD], 62 +/- 11 cm/s; pulsatility index [mean +/- SD], 0.41 +/- 0.08; depth range, 46 to 72 mm) from 15 patients (mean +/- SD age, 45 +/- 15 years; 4 men, 11 women) were identified. LPS flow direction was away from the probe in 13 cases and toward it in 3. Presenting symptoms included headache, focal neurological deficits, dizziness, and pulsatile tinnitus. All patients had cranial MRI (MRI and MR angiography in 11). Three patients underwent conventional cerebral angiography. Arteriovenous malformations or significant arterial stenoses were not detected on any study.

CONCLUSIONS

A focal signal from the internal carotid artery siphon region with low pulsatility index and normal mean flow velocity, identified in the absence of other transcranial Doppler abnormalities, is not related to an arteriovenous malformation or proximal arterial stenosis. LPS, as defined, are not of venous origin since mean flow velocity was in the arterial range. LPS are likely related to prominent venous flow in the cavernous sinus secondary to unusually strong pulsation of the intracavernous internal carotid artery.

Relationship between transcranial Doppler-determined pulsatility index and cerebrovascular resistance: an experimental study

Clinical studies with transcranial Doppler suggest that the pulsatility of the flow velocity (FV) waveform increases when the distal cerebrovascular resistance (CVR) increases. To clarify this relationship, the authors studied animal models in which the resistance may be decreased in a controlled manner by an increase in arterial CO2 tension, or by a decrease in cerebral perfusion pressure (CPP) in autoregulating animals. Twelve New Zealand white rabbits were anesthetized, paralyzed, and ventilated. Transcranial Doppler basilar artery FV, laser Doppler cortical blood flow, arterial pressure, intracranial pressure, and end-tidal CO2 concentration were measured continuously. Cerebrovascular resistance (CPP divided by laser Doppler cortical flux) and Gosling Pulsatility Index (PI, defined as an FV pulse amplitude divided by a timed average FV) were calculated as time-dependent variables for each animal. Four groups of animals undergoing controlled manipulations of CVR were analyzed. In Group I, arterial CO2 concentration was changed gradually from hypocapnia to hypercapnia. In Group II, gradual hemorrhagic hypotension was used to reduce CPP. In Group III, the short-acting ganglion blocking drug trimetaphan was injected intravenously to induce transient hypotension. Intracranial hypertension was produced by subarachnoid saline infusion in Group IV. During the hypercapnic challenge the correlation between the cortical resistance and Doppler flow pulsatility was positive (r = 0.77, p<0.001). In all three groups in which cerebral perfusion pressure was reduced a negative correlation between pulsatility index and cerebrovascular resistance was found (r = -0.84, p<0.001). The authors conclude that PI cannot be interpreted simply as an index of CVR in all circumstances.

Clinical cerebrovascular applications of arterial ultrasound volume flow rate estimates

A variety of disorders affect cerebral hemodynamics. Volume flow rate (VFR) estimates now allow accurate quantification of the effect of cerebrovascular lesions on the conduit vessels, with excellent in vivo and in vitro correlation. Four selected cases with VFR data and angiographic correlation are presented to illustrate potential clinical uses of this method. The VFR estimates were obtained with a color M-mode-based velocity imaging technique, which uses time-domain processing (P-700 Color Velocity Imaging System, Philips Ultrasound International, Irvine, CA). In a patient awaiting coronary artery surgery, with unilateral internal carotid artery occlusion and contralateral angiographic stenosis (50-80%, reader variation), the baseline and acetazolamide-challenged common carotid artery VFRs showed excellent conduit function ipsilateral to this stenosis. Thus, the angiographic stenosis did not have significant hemodynamic effects and endarterectomy was avoided. In a patient with an arteriovenous malformation fed by the left vertebral and left external carotid arteries, high in the left cervical region, VFR estimates of two to three times normal predicted the feeding vessels, influenced management, and proved helpful in follow-up. In a patient with subclavian steal syndrome, VFR estimates quantified the steal after brachial hyperemia. Finally, in a patient with delayed vasoconstriction after subarachnoid hemorrhage, very low VFR estimates preceded clinical deterioration. Quantification of hemodynamic changes with VFR estimates was useful for the diagnosis, management, and follow-up of these patients with four types of cerebrovascular disease, and should be applicable in many others.

Transcranial color-coded duplex sonography in cerebral arteriovenous malformations

BACKGROUND AND PURPOSE

It is well known that significant changes in cerebral hemodynamics may occur during the treatment of cerebral arteriovenous malformations with the complication of intracerebral hemorrhage and parenchymal edema. We used transcranial color-coded duplex sonography to study alterations in blood flow velocities during staged embolization.

METHODS

Forty-one patients aged 40 +/- 13 years (mean +/- SD) with angiographically proven cerebral arteriovenous malformations were studied. The blood flow velocities of the anterior, middle, and posterior cerebral arteries were measured in 16 patients with supratentorial arteriovenous malformations, both before the first and then after each successive embolization (three to seven treatments).

RESULTS

In 29 of 41 patients (71%), transcranial color-coded duplex sonography satisfactorily revealed the malformations and their main feeders. After the final embolization, we found a reduction in the peak flow velocity in treated feeders of 23 +/- 28% compared with the values before the first embolization. The untreated feeders showed an increase in peak flow velocities of 12 +/- 23% as an expression of increased collateral flow. After the treatment of the supplying feeders, we observed a reduction in flow velocity of 25 +/- 13% in seven patients, with cross-filling of the arteriovenous malformation through the contralateral anterior cerebral artery and the anterior communicating artery.

CONCLUSIONS

The technical advantage of transcranial color-coded duplex sonography compared with transcranial Doppler sonography is that it allows the exact identification of different feeding arteries in arteriovenous malformations. Repeated measurements during stepwise embolization with corrected insonation angle are easily achieved, and noninvasive quantification of hemodynamic changes is possible. The method may be helpful in the planning of the different steps of embolization.

Phase relationship between cerebral blood flow velocity and blood pressure. A clinical test of autoregulation

BACKGROUND AND PURPOSE

This study investigates the usefulness, as a test of dynamic autoregulation, of phase shift angle analysis between oscillations in cerebral blood flow velocity (CBFV) and in arterial blood pressure (ABP) during deep breathing.

METHODS

Fifty healthy volunteers, 20 patients with occlusive cerebrovascular diseases (OCD), and 10 patients with arteriovenous malformations (AVM) took part in the study. All subjects received transcranial Doppler monitoring of both middle cerebral arteries (MCAs). In addition, continuous blood pressure monitoring was performed with the use of noninvasive servo-controlled infrared finger plethysmography during deep breathing at a rate of 6/min. With the use of a high-pass filter model of autoregulation, autoregulation was quantified as phase shift angle between oscillations in CBFV and ABP at a frequency of 6/min. A phase shift angle of 0 degrees indicates total absence of autoregulation, while 90 degrees can be gauged as optimal autoregulation. In addition, vasomotor reactivity of both MCAs to CO2 stimulation was assessed among patients and calculated as percent increase in CBFV per millimeter of mercury of increase in CO2.

RESULTS

All normal subjects showed positive phase shift angles between CBFV and ABP (mean +/- SD, 70.5 +/- 29.8 degrees). OCD patients presented with significantly decreased phase shift angles for the MCA only on the pathological side (51.7 +/- 35.1 degrees; P < .05). Patients with AVM showed significantly reduced phase shift angles on both the affected side (26.8 +/- 13.5 degrees; P < .001) and the unaffected side (40.6 +/- 26.6 degrees; P < .01). In patients' groups, phase shift angle and vasomotor reactivity correlated significantly (r = .66; P < .001) after results from all MCAs were pooled.

CONCLUSIONS

Results confirm the high-pass filter model of cerebral autoregulation: Normal subjects showed predicted positive phase shift angles between CBFV and ABP oscillations. Patients with expected autoregulatory disturbances showed significant decreases in phase shift angles. Close correlations existed between autoregulation and CO2-induced vasomotor reactivity.