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W L Young

Publications and source records attributed to W L Young.

At least 37 records · Page 2Linked to original sources
PubMed2000

Can induction of systemic hypotension help prevent nidus rupture complicating arteriovenous malformation embolization?: analysis of underlying mechanism achieved using a theoretical model.

BACKGROUND AND PURPOSE: Nidus rupture is a serious complication of intracranial arteriovenous malformation (AVM) embolotherapy, but its pathogenetic mechanisms are not well described. An AVM model based on electrical network analysis was used to investigate theoretically the potential role of hemodynamic perturbations for elevating the risk of nidus vessel rupture (Rrupt) after simulated AVM embolotherapy, and to assess the potential benefit of systemic hypotension for preventing rupture. METHODS: Five separate hypothetical mechanisms for nidus hemorrhage were studied: 1) intranidal rerouting of blood pressure; 2) extranidal rerouting of blood pressure; 3) occlusion of draining veins with glue; 4) delayed thrombosis of draining veins; and 5) excessively high injection pressures proximal to the nidus. Simulated occlusion of vessels or elevated injection pressures were implemented into the AVM model, and electrical circuit analysis revealed the consequent changes in intranidal flow, pressure, and Rrupt for the nidus vessels. An expression for Rrupt was derived based on the functional distribution of the critical radii of component vessels. If AVM rupture was observed (Rrupt > or = 100%) at systemic normotension (mean pressure [P] = 74 mm Hg), the theoretical embolization was repeated under systemic hypotension (minor P = 70 mm Hg, moderate P = 50 mm Hg, or profound P = 25 mm Hg) to assess the potential benefit of this maneuver in reducing hemorrhage rates. RESULTS: All five pathogenetic mechanisms under investigation were able to produce rupture of AVMs during or after embolotherapy. These different mechanisms had in common the capability of generating surges in intranidal hemodynamic parameters resulting in nidus vessel rupture. The theoretical induction of systemic hypotension during and after treatment was shown to be of significant benefit in attenuating these surges and reducing Rrupt to safer levels below 100%. CONCLUSION: The induction of systemic hypotension during and after AVM embolization would appear theoretically to be of potential use in preventing iatrogenic nidus hemorrhage. The described AVM model should serve as a useful research tool for further theoretical investigations of AVM embolotherapy and its hemodynamic sequelae.

Blood Pressure↗
PubMed1999

Developmental deficits in adult patients with arteriovenous malformations.

BACKGROUND: Cerebral arteriovenous malformations (AVMs) are congenital masses of arteries and veins that appear to undergo an unclear "maturation" for many years. Using structured interviews, we compared developmental history of adult patients with AVM with a comparison group of patients with cerebral tumor or aneurysm. OBJECTIVE: To determine whether a remote history of developmental abnormality in adult patients with AVM might be an early marker of cerebral status. DESIGN: Adult patients with AVM and a comparison group of patients with cerebral aneurysm or low-grade tumor participated in a survey. SETTING: Urban medical school-based tertiary care center. PATIENTS: Forty-four randomly selected patients with AVM from the Columbia-Presbyterian AVM Database. There were 32 comparison patients:15 randomly chosen patients from the institution's Cerebral Aneurysm Database and all 17 patients who underwent a biopsy from 1990 to 1995 with a diagnosis of low-grade tumor and who could be contacted. MAIN OUTCOME MEASURES: A brief, structured interview adapted from the Centers for Disease Control and Prevention for its 1994 study of the prevalence of learning disabilities in American children. We defined the positive occurrence of a condition as an affirmative answer to the question, " Did have (condition) during his/her school-age years?" Each patient was also asked if there had been any problems in the following skill areas: reading, writing, listening, speaking, attention, impulsivity, organization, mathematics, or drawing. The AVM size was calculated on the angiographic film by measuring its longest diameter in any dimension. RESULTS: Patients with AVM were significantly more likely to report a positive occurrence to any survey question (P<.05). Two thirds of all patients with AVM (66%) reported at least 1 skill difficulty during their school years, significantly more than the comparison group (P<.001). Neither the maximum AVM diameter nor the occurrence of hemorrhage as an adult differed between patients with AVM with and without early skill difficulty. CONCLUSIONS: Patients with AVM are more likely to report a developmental learning disorder than patients with tumor or aneurysm despite the absence of other neurologic symptoms of diseases not diagnosed for another 20 years. These data support the notion that disorders of behavioral and intellectual function are sensitive markers of early cerebral status.

Adult↗
PubMed1999

Adenosine-induced cardiac pause for endovascular embolization of cerebral arteriovenous malformations: technical case report.

OBJECTIVE: Extremely high flow through arteriovenous malformations (AVMs) may limit the safety and effectiveness of endovascular glue therapy. To achieve a more controlled deposition of glue, we used transient but profound systemic hypotension afforded by an intravenously administered bolus of adenosine to induce rapidly reversible high-degree atrioventricular block. METHODS AND CASE REPORT: A patient with a large high-flow occipital AVM fed primarily by the posterior cerebral artery underwent n-butyl cyanoacrylate glue embolization. Nitroprusside-induced systemic hypotension did not adequately reduce flow through the nidus, as determined by contrast injection in the feeding artery. In a dose-escalation fashion, boluses of adenosine were administered to optimize the dose and verify that there was no flow reversal in the AVM and no other unexpected hemodynamic abnormalities by arterial pressure measurements and transcranial Doppler monitoring of the posterior cerebral artery feeding the AVM. Thereafter, 64 mg of adenosine was rapidly injected as a bolus to provide 10 to 15 seconds of systemic hypotension (approximately 20 mm Hg). Although there were conducted beats and some residual forward flow through the AVM during this time, the mean systemic and feeding artery pressures were roughly similar and remained relatively constant. A slow controlled injection of n-butyl cyanoacrylate glue was then performed, with excellent filling of the nidus. CONCLUSION: Adenosine-induced cardiac pause may be a viable method of partial flow arrest in the treatment of cerebral AVMs. Safe, deep, and complete embolization with a permanent agent may increase the likelihood of endovascular therapy's being curative or may further improve the safety of microsurgical resection.

Adenosine↗
PubMed1999

Higher cerebral function and hemispheric blood flow during awake carotid artery balloon test occlusions.

OBJECTIVES: Measures capable of detecting early alterations of brain function during acute cerebral ischaemia have not been adequately defined. Internal carotid artery (ICA) test occlusions provide a well controlled environment to investigate the effects of reversible acute hemispheric hypoperfusion on brain function. A continuous time estimation task was developed that reliably demonstrated alterations in higher cerebral function before development of any deficits in elementary neurological function during ICA balloon catheter test occlusions. In the present study, we hypothesised that alterations in our behavioural task would correlate significantly with absolute level of ipsilateral CBF. METHODS: Twenty five patients underwent awake ICA test occlusions during which sustained attention and ipsilateral CBF were measured simultaneously using our time estimation task and the intracarotid 133Xe washout method. Alteration in sustained attention was correlated with CBF after occlusion using Fisher's exact test. RESULTS: Deterioration in sustained attention was significantly associated with ipsilateral CBF below 30 ml/g/min (Fisher's exact test, p=0.047). Changes in individual patients' performance on the behavioural task correlated in real time with changes occurring either at the point of occlusion or at a specific threshold of induced hypotension. Sensitivity for our behavioural test in predicting CBF was 75%; specificity 70%. CONCLUSIONS: Monitoring sustained attention during carotid balloon test occlusions seems to be a sensitive means to detect decreases in CBF as measured by 133Xe washout. Correlation between higher cerebral function and CBF can allow more detailed investigations of physiological relations between cerebral haemodynamics and brain function in human conditions of cerebral ischaemia.

Adult↗
PubMed1998

[Therapy of cerebral arteriovenous malformations].

The rapid development of modern endovascular, microsurgical, and radiation therapies has considerably expanded the treatment options for encephalic arteriovenous malformations (AVMs). Surgery has the longest history. Single or staged intravascular procedures (embolizations) using fast-acting glues, sclerotic agents, and thrombogenic coils serve to reduce the size of AVM to that suitable for extirpation and may reduce the risk of surgery. Radiation ("gamma-knife") therapy, most frequently used in small, non-operable AVMs, is also viewed by some authors as an alternative or even superior tool in small, operable malformations. Partial embolization to reduce the mass-effect of space-occupying AVMs, to reverse diaschisis, and to treat AVM-related seizure disorders is being discussed and practiced. Given the in part competing or even controversial options, the selection of optimal treatment for AVM patients is becoming increasingly difficult. Current management is impeded by the paucity of information on the exact risks of invasive therapies and by insufficient criteria for identifying patients at risk of spontaneous bleeding during the natural course, including the seriousness of such hemorrhage.

Cerebral Angiography↗
PubMed1998

Theoretical modelling of arteriovenous malformation rupture risk: a feasibility and validation study.

PURPOSE: To explore the feasibility of using a theoretical computational model to simulate the risk of spontaneous arteriovenous malformation (AVM) haemorrhage. METHODS: Data from 12 patients were collected from a prospective databank which documented the angioarchitecture and morphological characteristics of the AVM and the feeding mean arterial pressure (FMAP) measured during initial superselective angiography prior to any treatment. Using the data, a computational model of the cerebral circulation and the AVM was constructed for each patient (patient-specific model). Two model risk (Risk(model)) calculations (haemodynamic- and structural-weighted estimates) were performed by using the patient-specific models. In our previously developed method of haemodynamic-weighted estimate, Risk(model) was calculated with the simulated intranidal pressures related to its maximal and minimal values. In the method of structural-weighted estimate developed and described in this paper, the vessel mechanical properties and probability calculation were considered in more detail than in the haemodynamic-weighted estimate. Risk(model) was then compared to experimentally determined risk which was calculated using a statistical method for determining the relative risk of having initially presented with AVM haemorrhage, termed Risk(exp). RESULTS: The Risk(model) calculated by both haemodynamic- and structural-weighted estimates correlated with experimental risks with chi2 = 6.0 and 0.64, respectively. The risks of the structural-weighted estimate were more correlated to experimental risks. CONCLUSIONS: Using two different approaches to the calculation of AVM haemorrhage risk, we found a general agreement with independent statistical estimates of haemorrhagic risk based on patient data. Computational approaches are feasible; future work can focus on specific pathomechanistic questions. Detailed patient-specific computational models can also be developed as an adjunct to individual patient risk assessment for risk-stratification purposes.

Cerebral Hemorrhage↗
PubMed1998

Principles and philosophy of modeling in biomedical research.

Despite widespread applications in biomedical research, the role of models and modeling is often controversial and ill understood. It is usual to find that fundamental definitions, axioms, and postulates used in the modeling process have become tacit assumptions. What is essential, however, is a clear vision of the fundamental principles of modeling. This is even more compelling for new and emerging interdisciplinary fields that use techniques from previously separate scientific disciplines. This article outlines and reviews the central nature and philosophy of modeling, the rules that govern it, and its underlying key integral relationship to the 'scientific method'. A comprehensive understanding of these issues is indispensable to successful research and meaningful progress in all facets of biomedicine.

Communication↗
PubMed1998

The feasibility of intracarotid adenosine for the manipulation of human cerebrovascular resistance.

UNLABELLED: To assess the feasibility of manipulating human cerebrovascular resistance with adenosine, we measured cerebral blood flow (CBF) by determining the initial slope (IS) of tracer washout 20-80 s after intracarotid 133Xe injection (standard IS) during sequential 3-min intracarotid infusions of (a) saline; (b) adenosine 1.2-mg bolus followed by an infusion of 1 mg/min (bolus + infusion); (c) saline; and (d) nicardipine (0.1 mg/min). During 133Xe washout, adenosine caused a rapidly clearing compartment. Therefore, tracer washout was also analyzed 5-25 s after injection (early IS). Nicardipine (n = 8) increased both standard IS (from 39+/-12 to 53+/-16 mL 100g.min(-1); P < 0.005) and early IS (from 40+/-9 to 55+/-20 arbitrary units; P < 0.02) to a similar degree. Adenosine bolus + infusion increased early IS (from 33+/-6 to 82+/-43 arbitrary units; P < 0.02) but did not increase standard IS (from 41+/-12 to 43 +/-16 mL 100g(-1) min(-1)). Standard and early IS values were then determined before and after adenosine delivered either by infusion alone (2 mg/min for 3 min, n = 5) or bolus alone (2 mg in 1 s, n = 3). Neither standard nor early IS changed after adenosine infusion alone. Early IS increased after adenosine bolus alone. Increase in early IS, but not standard IS, suggests a transient (<30 s) increase in CBF. IMPLICATIONS: Intracarotid adenosine, in the 1- to 2-mg dose range, may cause a transient, but not a sustained, increase in cerebral blood flow. Intracarotid adenosine in such a dose range does not seem to be an appropriate drug for sustained manipulation of cerebrovascular resistance.

Adenosine↗
PubMed1998

Cerebral blood flow and CO2 reactivity is similar during remifentanil/N2O and fentanyl/N2O anesthesia.

BACKGROUND: Remifentanil, a rapidly metabolized mu-opioid agonist, may offer advantages for neurosurgical procedures in which prolonged anesthetic effects can delay assessment of the patient. This study compared the effects of remifentanilnitrous oxide on cerebral blood flow (CBF) and carbon dioxide reactivity with those of fentanyl-nitrous oxide anesthesia during craniotomy. METHODS: After institutional approval and informed patient consent were obtained, 23 patients scheduled to undergo supratentorial tumor surgery were randomly assigned to remifentanil or fentanyl infusion groups in a double-blinded manner. Midazolam, thiopental, and pancuronium induction was followed by equipotent narcotic loading infusions of remifentanil (1 microg x kg(-1) x min(-1)) or fentanyl (2 microg x kg(-1) x min(-1)) for 5-10 min. Patients were ventilated with 2:1 nitrous oxideoxygen, and opioid rates were reduced and then titrated to a stable hemodynamic effect. After dural exposure, CBF was measured by the intravenous 133xenon technique at normocapnia and hypocapnia. Reactivity of CBF to carbon dioxide was calculated as the absolute increase in CBF per millimeters of mercury increase in the partial pressure of carbon dioxide (PaCO2). Data were analyzed by repeated-measures analysis of variance, unpaired Student's t-tests, or contingency analysis. RESULTS: In the remifentanil group (n = 10), CBF decreased from 36+/-11 to 27+/-8 ml x 100 g(-1) x min(-1) as PaCO2 decreased from 33+/-5 to 25+/-2 mmHg. In the fentanyl group (n = 8), CBF decreased from 37+/-11 to 25+/-6 ml x 100 g(-1) x min(-1) as PaCO2 decreased from 34+/-3 to 25+/-3 mmHg. Absolute carbon dioxide reactivity was preserved with both agents: 1+/-1.2 ml x 100 g(-1) x min(-1) x mmHg(-1) for remifentanil and 1.5+/-0.5 ml x 100 g(-1) x min(-1) x mmHg(-1) for fentanyl (P = 0.318). CONCLUSION: Remifentanil and fentanyl have similar effects on absolute CBF, and cerebrovascular carbon dioxide reactivity is maintained.

Adult↗
PubMed1998

A prospective evaluation of clinical tests for placement of laryngeal mask airways.

BACKGROUND: Reliable tests of correct anatomic placement of the laryngeal mask airway (LMA) may enhance safety during use and minimize the need for fiberoptic instrumentation during airway manipulation through the device. This study assessed the correlation between the outcomes of nine clinical tests to place the LMA and the anatomic position of the device as graded on a standard fiberoptic scale. METHODS: During 150 anesthetics, the outcome of nine clinical tests of correct placement was individually scored as satisfactory (positive) or unsatisfactory (negative) for clinical use of the LMA. Anatomic placement was assessed (by fiberoptic evaluation) by an anesthesiologist, who was blinded to the placement of the device, as grade 1, vocal cords not seen; grade 2, cords plus the anterior epiglottis seen; grade 3, cords plus the posterior epiglottis seen; and grade 4, only vocal cords seen. The outcomes of clinical tests were correlated with fiberoptic grade. RESULTS: Tests that correlated with the fiberoptic grade were the ability to generate an airway pressure of 20 cm water, the ability to ventilate manually, a black line on the LMA in midline, anterior movement of the larynx, outward movement of the LMA on inflation of the cuff, and movements of the reservoir bag with spontaneous breathing. Two tests, ability to generate airway pressure of 20 cm water and ability to ventilate manually, correlated with fiberoptic grades 4 and 3 combined (i.e., the epiglottis was supported by the LMA) and grade 2 (the epiglottis was not supported by the LMA). Tests with poor correlation with fiberoptic grade were the presence of resistance at the end of insertion, inability to advance LMA after inflation of the cuff, and presence of a capnographic trace. CONCLUSIONS: The outcome of clinical tests correlates with the anatomic placement of LMAs, as judged by fiberoptic examination. Two tests that best correlated with the fiberoptic grade were the ability to generate airway pressure of 20 cm water and the ability to ventilate manually.

Adult↗
PubMed1998

Complex intracranial aneurysms: combined operative and endovascular approaches.

OBJECTIVE: Endovascular management of complex intracranial aneurysms is increasingly being considered as an alternative to standard surgical clipping. However, little attention has been paid to the complementary nature of surgery and endovascular therapy. METHODS: Between September 1992 and May 1997, 12 patients with complex intracranial aneurysms were treated with combined operative and endovascular methods. Seven patients demonstrated subarachnoid hemorrhage (two of Grade II, two of Grade III, and three of Grade IV). Five patients demonstrated unruptured aneurysms, i.e., three giant aneurysms (one vertebrobasilar junction aneurysm, one middle cerebral artery bifurcation aneurysm, and one internal carotid artery-ophthalmic artery aneurysm), one large internal carotid artery-ophthalmic artery aneurysm, and one middle cerebral artery serpentine aneurysm. Management strategies involved either surgery followed by endovascular therapy (S-E; n = 5) or endovascular therapy followed by surgery (E-S; n = 7). S-E paradigms included aneurysm exploration followed by endovascular treatment (S-E1; n = 3), partial aneurysm clipping followed by endovascular aneurysm packing (S-E2; n = 1), and extracranial-to-intracranial bypass followed by endovascular parent vessel occlusion (S-E3; n = 1). E-S paradigms included superselective angiography followed by surgical clipping (E-S1; n = 2), Guglielmi detachable coil partial dome packing followed by delayed surgical clipping (E-S2; n = 2), proximal temporary vessel balloon occlusion followed by aneurysm clipping (E-S3; n = 2), and proximal permanent vessel occlusion followed by surgical aneurysm decompression for mass effect treatment (E-S4; n = 1). RESULTS: Eleven aneurysms (92%) were completely eliminated. The remaining aneurysm was 90% obliterated and remained quiescent at the 34-month follow-up examination, despite presenting with subarachnoid hemorrhage. No patient experienced repeat bleeding (follow-up period, 23+/-28 mo). There were no deaths. One patient achieved a fair outcome (Glasgow Outcome Scale score of III); all other patients experienced excellent outcomes (Glasgow Outcome Scale score of I). In all cases, the aneurysm management paradigm chosen had a positive effect on definitive therapy. CONCLUSION: Several factors can contribute to the complexity of intracranial aneurysms. Management strategies that combine operative and endovascular techniques in a complementary way, for the best possible outcomes for these patients, can be designed accordingly.

Adult↗
PubMed1998

Mathematical considerations for modeling cerebral blood flow autoregulation to systemic arterial pressure.

The shape of the autoregulation curve for cerebral blood flow (CBF) vs. pressure is depicted in a variety of ways to fit experimentally derived data. However, there is no general empirical description to reproduce CBF changes resulting from systemic arterial pressure variations that is consistent with the reported data. We analyzed previously reported experimental data used to construct autoregulation curves. To improve on existing portrayals of the fitting of the observed data, a compartmental model was developed for synthesis of the autoregulation curve. The resistive arterial and arteriolar network was simplified as an autoregulation device (ARD), which consists of four compartments in series controlling CBF. Each compartment consists of a group of identical vessels in parallel. The response of each vessel category to changes in perfusion pressure was simulated using reported experimental data. The CBF-pressure curve was calculated from the resistance of the ARD. The predicted autoregulation curve was consistent with reported experimental data. The lower and upper limits of autoregulation (LLA and ULA) were predicted as 69 and 153 mmHg, respectively. The average value of the slope of the CBF-pressure curve below LLA and beyond ULA was predicted as 1.3 and 3.3% change in CBF per mmHg, respectively. Our four-compartment ARD model, which simulated small arteries and arterioles, predicted an autoregulation function similar to experimental data with respect to the LLA, ULA, and average slopes of the autoregulation curve below LLA and above ULA.

Animals↗
PubMed1998

Morbidity of intracranial hemorrhage in patients with cerebral arteriovenous malformation.

BACKGROUND AND PURPOSE: Decisions on invasive arteriovenous malformation (AVM) treatment are currently based on natural-course risk estimates of AVM bleeding and assumptions on morbidity from cerebral hemorrhage in general. However, morbidity of AVM hemorrhage has rarely been reported. We sought to assess the morbidity of intracranial hemorrhage in patients with cerebral AVMs. METHODS: From a prospective AVM database, 119 patients were analyzed: 115 had a hemorrhage as the diagnostic event, and 27 of them suffered a second hemorrhage during follow-up; an additional 4 patients had other diagnostic symptoms but bled during follow-up. The type (parenchymal, subarachnoid, intraventricular) and location of AVM hemorrhage were determined by CT/MR brain imaging. Disability and neurological impairment were assessed with the Barthel Index, the Rankin Scale, and the National Institutes of Health Stroke Scale, with a mean follow-up time of 16.2 months. RESULTS: Of the 115 incident hemorrhages, 34 (30%) were subarachnoid, 27 (23%) parenchymal, 18 (16%) intraventricular, and 36 (31%) in combined locations. In 54 patients (47%; 95% confidence interval [CI], 38% to 56%) the incident hemorrhage resulted in no neurological deficit, and an additional 43 patients (37%; 95% CI, 28% to 46%) were independent in their daily activities (Rankin 1). Fifteen patients (13%; 95% CI, 7% to 19%) were moderately disabled (Rankin 2 or 3), and 3 (3%; 95% CI, 0% to 6%) were severely disabled (Rankin > or =4). Parenchymal hemorrhages were most likely to result in a neurological deficit (52%). Type and morbidity of hemorrhage during follow-up were similar to incident events. Twenty (74%) of 27 patients with both incident and follow-up hemorrhages were normal or independent (Rankin 0 or 1). None of the patients with a hemorrhage during follow-up died during the observation period. CONCLUSIONS: Hemorrhage from cerebral AVMs appears to have a lower morbidity than currently assumed. This finding encourages a reevaluation of the risks and benefits of invasive AVM treatment.

Activities of Daily Living↗
PubMed1998

Feeding artery pressure and venous drainage pattern are primary determinants of hemorrhage from cerebral arteriovenous malformations.

PURPOSE: The purpose of this study was to define the influence of feeding mean arterial pressure (FMAP) in conjunction with other morphological or clinical risk factors in determining the probability of hemorrhagic presentation in patients with cerebral arteriovenous malformations (AVMs). METHODS: Clinical and angiographic data from 340 patients with cerebral AVMs from a prospective database were reviewed. Patients were identified in whom FMAP was measured during superselective angiography. Additional variables analyzed included AVM size, location, nidus border, presence of aneurysms, and arterial supply and venous drainage patterns. The presence of arterial aneurysms was also correlated with site of bleeding on imaging studies. RESULTS: By univariate analysis, exclusively deep venous drainage, periventricular venous drainage, posterior fossa location, and FMAP predicted hemorrhagic presentation. When we used stepwise multiple logistic regression analysis in the cohort that had FMAP measurements (n = 129), only exclusively deep venous drainage (odds ratio [OR], 3.7; 95% confidence interval [CI], 1.4 to 9.8) and FMAP (OR, 1.4 per 10 mm Hg increase; 95% CI, 1.1 to 1.8) were independent predictors (P < 0.01) of hemorrhagic presentation; size, location, and the presence of aneurysms were not independent predictors. There was also no association (P = 0.23) between the presence of arterial aneurysms and subarachnoid hemorrhage. CONCLUSIONS: High arterial input pressure (FMAP) and venous outflow restriction (exclusively deep venous drainage) were the most powerful risk predictors for hemorrhagic AVM presentation. Our findings suggest that high intranidal pressure is more important than factors such as size, location, and the presence of arterial aneurysms in the pathophysiology of AVM hemorrhage.

Adult↗
PubMed1997

Risk of spontaneous haemorrhage after diagnosis of cerebral arteriovenous malformation.

BACKGROUND: A small proportion of strokes are caused by cerebral arteriovenous malformations (AVM). Treatment to prevent intracranial haemorrhage itself carries risks, and untreated AVM may in many cases have a good prognosis. We investigated the risk of subsequent symptomatic bleeding in the clinical course of AVM in patients with and without an initial haemorrhage. METHODS: 281 unselected, consecutive, prospectively enrolled patients with cerebral AVM were grouped according to their initial clinical presentation--142 presented with and 139 without haemorrhage. The frequency of AVM haemorrhages during the subsequent clinical course (before the start of endovascular, surgical, or radiation treatment) in the two groups was compared by means of Kaplan-Meier life-tables, log-rank test, and multivariate proportional-hazards regression models. Haemorrhage was defined as a clinically symptomatic event with signs of acute bleeding on computed tomography or magnetic resonance brain imaging. FINDINGS: During mean follow-up of 8.5 months for the haemorrhage group and 11.9 months for the non-haemorrhage group, haemorrhages occurred in 18 (13%) of the former patients and in three (2%) of the latter (p=0.0002). The annual risk of haemorrhage was 17.8% and 2.2%, respectively. In the multivariate regression model, the adjusted hazard ratio for haemorrhage at initial presentation was 13.9 (95% CI 2.6-73.8; p=0.002). Deep venous drainage (hazard ratio 4.1 [1.2-14.9], p=0.029) and male sex (9.2 [2.1-41.3], p=0.004) were also significantly associated with subsequent haemorrhage, but no significant association was found for age or AVM size. The annual rate of spontaneous haemorrhage was 32.6% for men and 10.4% for women in the haemorrhage group compared with 3.3% for men and 1.3% for women in the non-haemorrhage group. Among patients with haemorrhage at initial presentation, the risk of haemorrhage fell from 32.9% in year 1 to 11.3% in subsequent years (34.2% to 31.0% in men; 31.1% to 5.5% in women). INTERPRETATION: In AVM, patients initially presenting with haemorrhage have a higher risk of subsequent bleeding than those presenting with other symptoms. The risk is higher in men than in women.

Adult↗
PubMed1997

Deliberate systemic hypotension to facilitate endovascular therapy of cerebral arteriovenous malformations: a computer modeling study.

With the aid of a computer model, this investigation describes the relationship between mean arterial pressure (MAP) reduction and its effect on total arteriovenous malformation (AVM) shunt flow, feeding artery velocities, and cerebral blood flow in hypotensive, structurally normal vascular beds adjacent to the AVM nidus. Simulations were performed for two feeding artery sizes (2 and 4 mm in diameter) and two AVM shunt flows (500 and 1000 ml/minute) with and without the presence of autoregulation in normal brain. Systemic arterial hypotension was simulated in a stepwise fashion by reducing aortic pressure from 100 to 10 mm Hg in 10-mm Hg steps. The percentage of MAP that resulted in a 50% reduction of shunt flow was calculated (%MAP reduction at half-maximal shunt flow). As the MAP decreased, the shunt flow decreased in a nearly linear fashion; the cerebral blood flow remained constant in neighboring brain until the MAP dropped below 60 and 80 mm Hg for the medium and large AVMs, respectively. The %MAP reductions at half-maximal shunt flow for the medium and large AVMs were not significantly different from 50%: 44% and 47%, respectively. Results for 2 and 4 mm AVM feeding artery sizes were similar. The decrease in both total shunt flow and flow velocity in feeding artery pedicles, potentially embolized by glue injection, were nearly linear with the institution of systemic hypotension. The presence or absence of autoregulation in normal brain, or different variations in the simulated angioarchitecture of the AVMs, did not affect this relationship in the model.

Journal Article↗
PubMed1997

Manipulation of cerebrovascular resistance during internal carotid artery occlusion by intraarterial verapamil.

UNLABELLED: Occlusion of the internal carotid artery (ICA) results in acute cerebral hypotension. We hypothesized that during acute cerebral hypotension, in addition to physiological autoregulation, further arteriolar relaxation is possible by pharmacological means. We tested the feasibility of using intracarotid verapamil, a calcium channel blocker, to decrease the cerebrovascular resistance (CVR) and augment cerebral blood flow (CBF) at low postocclusion distal ICA pressures (PICA). Eleven patients undergoing trial occlusion of ICA were enrolled. Distal ICA or stump pressure, hemispheric CBF, and CVR were determined before and after carotid occlusion. During ICA occlusion, CBF and other physiological variables were determined before and after intracarotid verapamil. Two patients were excluded from the study. Carotid occlusion (n = 9) significantly decreased PICA (mean +/- SD, from 82 +/- 22 to 46 +/- 11 mm Hg, P = 0.001) and CBF (from 42 +/- 11 to 33 +/- 11 mL.100 g-1.min-1, P < 0.05). During occlusion, after intracarotid verapamil (3.9 +/- 1.6 mg), hemispheric CBF tended to increase from 31 +/- 11 to 35 +/- 14 mL.100 g-1.min-1 (P = 0.067). However, the percent increase in CBF after verapamil was a linear function of PICA (y = 1.01 x -32, n = 9, r2 = 0.84, P = 0.006). The decrease in CBF during carotid occlusion suggests that near maximal cerebral autoregulatory vasodilation had occurred, although our results indicate that it may be feasible to further augment CBF by pharmacological means during acute cerebral hypotension. IMPLICATIONS: When the internal carotid artery is occluded during neurosurgical procedures, there may be a significant reduction in cerebral perfusion. The authors have demonstrated that the intraarterial administration of verapamil increases cerebral blood flow as a linear function of cerebral artery pressure. Intracarotid injection of vasodilators may augment cerebral blood flow during acute cerebral hypotension.

Adult↗