CO2 reactivity of cerebral vasospasm after aneurysmal subarachnoid haemorrhage

Trigeminal Nerve Stimulation Improves Cerebral Macrocirculation and Microcirculation After Subarachnoid Hemorrhage: An Exploratory Study

BACKGROUND

Delayed cerebral ischemia (DCI) is the most consequential secondary insult after aneurysmal subarachnoid hemorrhage (SAH). It is a multifactorial process caused by a combination of large artery vasospasm and microcirculatory dysregulation. Despite numerous efforts, no effective therapeutic strategies are available to prevent DCI. The trigeminal nerve richly innervates cerebral blood vessels and releases a host of vasoactive agents upon stimulation. As such, electrical trigeminal nerve stimulation (TNS) has the capability of enhancing cerebral circulation.

OBJECTIVE

To determine whether TNS can restore impaired cerebral macrocirculation and microcirculation in an experimental rat model of SAH.

METHODS

The animals were randomly assigned to sham-operated, SAH-control, and SAH-TNS groups. SAH was induced by endovascular perforation on Day 0, followed by KCl-induced cortical spreading depolarization on day 1, and sample collection on day 2. TNS was delivered on day 1. Multiple end points were assessed including cerebral vasospasm, microvascular spasm, microthrombosis, calcitonin gene-related peptide and intercellular adhesion molecule-1 concentrations, degree of cerebral ischemia and apoptosis, and neurobehavioral outcomes.

RESULTS

SAH resulted in significant vasoconstriction in both major cerebral vessels and cortical pial arterioles. Compared with the SAH-control group, TNS increased lumen diameters of the internal carotid artery, middle cerebral artery, and anterior cerebral artery, and decreased pial arteriolar wall thickness. Additionally, TNS increased cerebrospinal fluid calcitonin gene-related peptide levels, and decreased cortical intercellular adhesion molecule-1 expression, parenchymal microthrombi formation, ischemia-induced hypoxic injury, cellular apoptosis, and neurobehavioral deficits.

CONCLUSION

Our results suggest that TNS can enhance cerebral circulation at multiple levels, lessen the impact of cerebral ischemia, and ameliorate the consequences of DCI after SAH.

Fluid metabolic pathways after subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is a devastating cerebrovascular disease with high mortality and morbidity. In recent years, a large number of studies have focused on the mechanism of early brain injury (EBI) and delayed cerebral ischemia (DCI), including vasospasm, neurotoxicity of hematoma and neuroinflammatory storm, after aSAH. Despite considerable efforts, no novel drugs have significantly improved the prognosis of patients in phase III clinical trials, indicating the need to further re-examine the multifactorial pathophysiological process that occurs after aSAH. The complex pathogenesis is reflected by the destruction of the dynamic balance of the energy metabolism in the nervous system after aSAH, which prevents the maintenance of normal neural function. This review focuses on the fluid metabolic pathways of the central nervous system (CNS), starting with ruptured aneurysms, and discusses the dysfunction of blood circulation, cerebrospinal fluid (CSF) circulation and the glymphatic system during disease progression. It also proposes a hypothesis on the metabolic disorder mechanism and potential therapeutic targets for aSAH patients.

Therapeutic hypercapnia for prevention of secondary ischemia after severe subarachnoid hemorrhage: physiological responses to continuous hypercapnia

Temporary hypercapnia has been shown to increase cerebral blood flow (CBF) and might be used as a therapeutical tool in patients with severe subarachnoid hemorrhage (SAH). It was the aim of this study was to investigate the optimum duration of hypercapnia. This point is assumed to be the time at which buffer systems become active, cause an adaptation to changes of the arterial partial pressure of carbon dioxide (PaCO₂) and annihilate a possible therapeutic effect. In this prospective interventional study in a neurosurgical ICU the arterial partial pressure of carbon dioxide (PaCO₂) was increased to a target range of 55 mmHg for 120 min by modification of the respiratory minute volume (RMV) one time a day between day 4 and 14 in 12 mechanically ventilated poor-grade SAH-patients. Arterial blood gases were measured every 15 min. CBF and brain tissue oxygen saturation (StiO₂) were the primary and secondary end points. Intracranial pressure (ICP) was controlled by an external ventricular drainage. Under continuous hypercapnia (PaCO₂ of 53.17 ± 5.07), CBF was significantly elevated between 15 and 120 min after the start of hypercapnia. During the course of the trial intervention, cardiac output also increased significantly. To assess the direct effect of hypercapnia on brain perfusion, the increase of CBF was corrected by the parallel increase of cardiac output. The maximum direct CBF enhancing effect of hypercapnia of 32% was noted at 45 min after the start of hypercapnia. Thereafter, the CBF enhancing slowly declined. No relevant adverse effects were observed. CBF and StiO₂ reproducibly increased by controlled hypercapnia in all patients. After 45 min, the curve of CBF enhancement showed an inflection point when corrected by cardiac output. It is concluded that 45 min might be the optimum duration for a therapeutic use and may provide an optimal balance between the benefits of hypercapnia and risks of a negative rebound effect after return to normal ventilation parameters.

Trial registration: The study was approved by the institutional ethics committee (AZ 230/14) and registered at ClinicalTrials.gov (Trial-ID: NCT01799525). Registered 01/01/2015.

Time Course of Cerebrovascular Reactivity in Patients Treated for Unruptured Intracranial Aneurysms: A One-Year Transcranial Doppler and Acetazolamide Follow-Up Study

Background

Cerebrovascular reactivity (CVR) is often impaired in the early phase after aneurysmal subarachnoid hemorrhage. There is, however, little knowledge about the time course of CVR in patients treated for unruptured intracranial aneurysms (UIA).

Methods

CVR, assessed by transcranial Doppler and acetazolamide test, was examined within the first postoperative week after treatment for UIA and reexamined one year later.

Results

Of 37 patients initially assessed, 34 were reexamined after one year. Bilaterally, baseline and acetazolamide-induced blood flow velocities were higher in the postoperative week compared with one year later (p < 0.001). CVR on the ipsilateral side of treatment was lower in the initial examination compared with follow-up (58.9% versus 66.1%, p = 0.04). There was no difference in CVR over time on the contralateral side (63.4% versus 65.0%, p = 0.65). When mean values of right and left sides were considered there was no difference in CVR between exams. Larger aneurysm size was associated with increased change in CVR (p = 0.04), and treatment with clipping was associated with 13.8%-point increased change in CVR compared with coiling (p = 0.03).

Conclusion

Patients with UIA may have a temporary reduction in CVR on the ipsilateral side after aneurysm treatment. The change in CVR appears more pronounced for larger-sized aneurysms and in patients treated with clipping. We recommend that ipsilateral and contralateral CVR should be assessed separately, as mean values can conceal side-differences.

Controlled Hypercapnia Enhances Cerebral Blood Flow and Brain Tissue Oxygenation After Aneurysmal Subarachnoid Hemorrhage: Results of a Phase 1 Study

BACKGROUND

This study investigated if cerebral blood flow (CBF) regulation by changes of the arterial partial pressure of carbon dioxide (PaCO2) can be used therapeutically to increase CBF and improve neurological outcome after subarachnoid hemorrhage (SAH).

METHODS

In 12 mechanically ventilated poor-grade SAH-patients, a daily trial intervention was performed between day 4 and 14. During this intervention, PaCO2 was decreased to 30 mmHg and then gradually increased to 40, 50, and 60 mmHg in 15-min intervals by modifications of the respiratory minute volume. CBF and brain tissue oxygen saturation (StiO2) were the primary and secondary endpoints. Intracranial pressure was controlled by an external ventricular drainage.

RESULTS

CBF reproducibly decreased during hyperventilation and increased to a maximum of 141 ± 53 % of baseline during hypercapnia (PaCO2 60 mmHg) on all days between day 4 and 14 after SAH. Similarly, StiO2 increased during hypercapnia. CBF remained elevated within the first hour after resetting ventilation to baseline parameters and no rebound effect was observed within this time-span. PaCO2-reactivities of CBF and StiO2 were highest between 30 and 50 mmHg and slightly decreased at higher levels.

CONCLUSION

CBF and StiO2 reproducibly increased by controlled hypercapnia of up to 60 mmHg even during the period of the maximum expected vasospasm. The absence of a rebound effect within the first hour after hypercapnia indicates that an improvement of the protocol is possible. The intervention may yield a therapeutic potential to prevent ischemic deficits after aneurysmal SAH.

Multimodal MRI characterization of experimental subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is associated with significant morbidity and mortality. We implemented an in-scanner rat model of mild SAH in which blood or vehicle was injected into the cistern magna, and applied multimodal MRI to study the brain prior to, immediately after (5min to 4h), and upto 7days after SAH. Vehicle injection did not change arterial lumen diameter, apparent diffusion coefficient (ADC), T2, venous signal, vascular reactivity to hypercapnia, or foot-fault scores, but mildly reduce cerebral blood flow (CBF) up to 4h, and open-field activity up to 7days post injection. By contrast, blood injection caused: (i) vasospasm 30min after SAH but not thereafter, (ii) venous abnormalities at 3h and 2days, delayed relative to vasospasm, (iii) reduced basal CBF and to hypercapnia 1-4h but not thereafter, (iv) reduced ADC immediately after SAH but no ADC and T2 changes on days 2 and 7, and (v) reduced open-field activities in both SAH and vehicle animals, but no significant differences in open-field activities and foot-fault tests between groups. Mild SAH exhibited transient and mild hemodynamic disturbances and diffusion changes, but did not show apparent ischemic brain injury nor functional deficits.

Controlled transient hypercapnia: a novel approach for the treatment of delayed cerebral ischemia after subarachnoid hemorrhage?

Object

The authors undertook this study to investigate whether the physiological mechanism of cerebral blood flow (CBF) regulation by alteration of the arterial partial pressure of carbon dioxide (PaCO2) can be used to increase CBF after aneurysmal subarachnoid hemorrhage (aSAH).

Methods

In 6 mechanically ventilated patients with poor-grade aSAH, the PaCO2 was first decreased to 30 mm Hg by modification of the respiratory rate, then gradually increased to 40, 50 and 60 mm Hg for 15 minutes each setting. Thereafter, the respirator settings were returned to baseline parameters. Intracerebral CBF measurement and brain tissue oxygen saturation (StiO2), measured by near-infrared spectroscopy (NIRS), were the primary and secondary end points. Intracranial pressure (ICP) was controlled by external ventricular drainage.

Results

A total of 60 interventions were performed in 6 patients. CBF decreased to 77% of baseline at a PaCO2 of 30 mm Hg and increased to 98%, 124%, and 143% at PaCO2 values of 40, 50, and 60 mm Hg, respectively. Simultaneously, StiO2 decreased to 94%, then increased to 99%, 105%, and 111% of baseline. A slightly elevated delivery rate of cerebrospinal fluid was noticed under continuous drainage. ICP remained constant. After returning to baseline respirator settings, both CBF and StiO2 remained elevated and only gradually returned to pre-hypercapnia values without a rebound effect. None of the patients developed secondary cerebral infarction.

Conclusions

Gradual hypercapnia was well tolerated by poor-grade SAH patients. Both CBF and StiO2 reacted with a sustained elevation upon hypercapnia; this elevation outlasted the period of hypercapnia and only slowly returned to normal without a rebound effect. Elevations of ICP were well compensated by continuous CSF drainage. Hypercapnia may yield a therapeutic potential in this state of critical brain perfusion. Clinical trial registration no.: NCT01799525 (ClinicalTrials.gov).

The role of arterioles and the microcirculation in the development of vasospasm after aneurysmal SAH

Cerebral vasospasm of the major cerebral arteries, which is characterized by angiographic narrowing of those vessels, had been recognized as a main contributor to delayed cerebral ischemia (DCI) in subarachnoid hemorrhage (SAH) patients. However, the CONSCIOUS-1 trial revealed that clazosentan could not improve mortality or clinical outcome in spite of successful reduction of relative risk in angiographic vasospasm. This result indicates that the pathophysiology underlying DCI is multifactorial and that other pathophysiological factors, which are independent of angiographic vasospasm, can contribute to the outcome. Recent studies have focused on microcirculatory disturbance, such as microthrombosis and arteriolar constriction, as a factor affecting cerebral ischemia after SAH. Reports detecting microthrombosis and arteriolar constriction will be reviewed, and the role of the microcirculation on cerebral ischemia during vasospasm after SAH will be discussed.

Lower Incidence of Transcranial Doppler and Symptomatic Vasospasm After Aneurysmal Subarachnoid Hemorrhage and Aneurysm Clipping in the Elderly Patient?

BACKGROUND:

Vasospasm is the major cause of morbidity and mortality after aneurysmal subarachnoid hemorrhage. It is well known that the vasoreactivity decreases with advancing age, but it is not well investigated in a large patient cohort whether, as a consequence, the incidence of vasospasm is lower in elderly patients.

OBJECTIVE:

To investigate whether transcranial Doppler vasospasm, delayed ischemic neurological deficits, and vasospasm-associated ischemic lesions are less frequent in older patients.

METHODS:

Seven hundred fifty-eight patients who suffered from subarachnoid hemorrhage were included in this study. Clinical presentation, Hunt and Hess score, Fisher grade, incidence of vasospasm, neurological deficits and ischemic lesions on radiographic imaging, transcranial Doppler blood flow velocities, medical complications, and outcome were registered.

RESULTS:

Four hundred seventy-eight patients &lt; 60 years of age and 280 patients ≥ 60 years of age were identified; 55.2% of the younger and 25.7% of the older age group developed post-hemorrhagic vasospasm (P &lt; .001). Older patients developed less vasospasm (P = .00), fewer neurological deficits (P &lt; .001), and fewer ischemic lesions on computed tomography imaging (P = .06). On the other hand, older patients had significantly worse outcomes than younger patients (P = .01) and more frequently died of medical complications (P = .01).

CONCLUSION:

Vasospasm, delayed ischemic neurological deficits, and vasospasm-associated ischemic lesions are more likely to occur in patients &lt; 60 years of age than in older patients. The lower incidence of vasospasm and vasospasm-related ischemia in the elderly patient does not translate into better outcome because of the higher rate of fatal medical complications in patients ≥ 60 years of age.

Continuous neuromonitoring using transcranial Doppler reflects blood flow during carbon dioxide challenge in primates with global cerebral ischemia

OBJECTIVE

At present, there is no consensus on the optimal monitoring method for cerebral blood flow (CBF) in neurointensive care patients. The aim of the present study was to investigate whether continuous transcranial Doppler (TCD) monitoring with modulation of partial pressure of CO2 reflects CBF changes. This hypothesis was tested in 2 pathological settings in which cerebral ischemia can be imminent: after an episode of cerebral ischemia and during vasospasm after subarachnoid hemorrhage.

METHODS

Sixteen cynomolgus monkeys were divided into 3 groups: 1) chemoregulation in control animals to assess the physiological range of CBF regulation, 2) chemoregulation during vasospasm after subarachnoid hemorrhage, and 3) chemoregulation after transient cerebral ischemia. We surgically placed a thermal CBF probe over the cortex perfused by the right middle cerebral artery. Corresponding TCD values were acquired simultaneously while partial pressure of CO2 was changed within a range of 25 to 65 mm Hg (chemoregulation). A correlation coefficient of CBF with TCD values of greater than r equals 0.8 was considered clinically relevant.

RESULTS

CBF and CBF velocity correlated strongly after cerebral ischemia (r = 0.83, P < 0.001). Correlations were poor in chemoregulation controls (r = 0.2) and in the vasospasm group (r = 0.55).

CONCLUSION

The present study provides experimental support that, in clearly defined conditions, continuous TCD monitoring combined with chemoregulation testing may provide an estimate of CBF in the early postischemic period.

Perfusion-weighted MRI to evaluate cerebral autoregulation in aneurysmal subarachnoid haemorrhage

INTRODUCTION

The aim of this study was to evaluate autoregulatory mechanisms in different vascular territories within the first week after aneurysmal subarachnoid haemorrhage (SAH) by perfusion-weighted magnetic resonance imaging (PW-MRI). For this purpose, regional cerebral blood flow and volume (rCVF and rCBV) were measured in relation to different degrees of angiographically visible cerebral vasospasm (CVS).

MATERIALS AND METHODS

In 51 SAH patients, PW-MRI and digital subtraction angiography were performed about 5 days after onset of SAH. Regional CBF and rCBV were analysed in the territories of the anterior cerebral artery (ACA), the middle cerebral artery (MCA) and the basal ganglia of each hemisphere in relationship to the degree of CVS in the particular territory. Correlations between rCBF, rCBV and CVS were analysed.

RESULTS

CVS was found in 22 out of 51 patients in at least one territory. In all territories, rCBV decreased with increasing degree of CVS, correlated with a decrease of rCBF. In the ACA territories, SAH patients with severe CVS had significantly lower rCBF compared to healthy subjects and to SAH patients without CVS. In the basal ganglia, rCBF and rCBV of the control group were significantly higher compared to the patients without and with moderate vasospasms.

CONCLUSION

PW-MRI showed simultaneous decrease of rCBF and rCBV in patients with SAH. The fact that rCBV did not increase in territories with CVS to maintain rCBF reveals dysfunctional vascular autoregulation. Vasospasms in the microvasculature are most evident in the basal ganglia, showing decreased rCBV and rCBF even in SAH patients without CVS.

ADMISSION ANGIOGRAPHIC CEREBRAL CIRCULATION TIME MAY PREDICT SUBSEQUENT ANGIOGRAPHIC VASOSPASM AFTER ANEURYSMAL SUBARACHNOID HEMORRHAGE

OBJECTIVE

Angiographic cerebral vasospasm occurs in approximately 70% of patients hospitalized after aneurysmal subarachnoid hemorrhage (SAH) and is associated with poor outcome. In this study, we examined whether or not cerebral circulation time (CCT) measured with digital subtraction angiography was associated with angiographic vasospasm.

METHODS

Patients who underwent cerebral angiography within 24 hours of SAH were analyzed. Contrast dye transit time from the arterial to the venous phase was measured to obtain CCT (supraclinoid internal carotid artery to parietal cortical veins) and microvascular CCT (cortical middle cerebral artery to parietal cortical veins). Patients with ruptured anterior circulation aneurysms and vasospasm on follow-up angiography (Group A) were compared with patients with SAH without vasospasm (Group B) and with normal control subjects (Group C).

RESULTS

There were 20 patients in Group A (mean age, 51 ± 13 yr), 17 patients in Group B (56 ± 12 yr), and 98 patients in Group C (52 ± 12 yr). CCT in patients in Group A (7.7 ± 1.9 s) was significantly longer than those in Groups B (6.6 ± 1.2 s; P = 0.005) and C (5.9 ± 1 s; P &lt; 0.001). Microvascular CCT in patients in Group A (7.1 ± 1.8 s) was significantly longer than those in Groups B (6.1 ± 1.2 s; P = 0.003) and C (5.4 ± 0.9 s; P &lt; 0.001).

CONCLUSION

Prolonged CCT, a measurement of increased small vessel resistance, can be identified within 24 hours after SAH and is associated with subsequent angiographic vasospasm. These results suggest that microcirculation changes may be involved in vasospasm.

Using CT in the Diagnosis and Management of Patients with Cerebral Vasospasm

Cerebral vasospasm remains a serious complication of aneurysmal subarachnoid hemorrhage. Efforts in improving its clinical outcome have been focused on early diagnosis and applying effective treatment regimens. Standard diagnostic modalities currently used do not fully address this complex disease. The use of CT angiography and CT perfusion are discussed, with emphasis on its potential role in not only detecting vasospasm, but also in guiding management decisions and assessing clinical outcome.

Intro-arterial Administration of Fasudil Hydrochloride for Vasospasm Following Subarachnoid Hemorrhage-Analysis of Time-Density Curve With Digital Subtraction Angiography-

The cerebral circulatory dynamics were evaluated before and after intra-arterial administration of fasudil hydrochloride in 20 patients with angiographic vasospasm after subarachnoid hemorrhage (SAH). The region of interest time-density curves obtained before and after intra-arterial administration of fasudil hydrochloride were compared in the proximal portion of the middle cerebral artery in the early arterial phase, the distal portion of the middle cerebral artery in the late arterial phase, and the transverse sinus in the venous phase. In the early arterial phase, the time to peak and the time to half-peak were significantly reduced. In the late arterial phase and venous phase, the time to peak was significantly reduced. These results suggest that intra-arterial administration of fasudil hydrochloride induced dilation of the proximal arteries, and improved cerebral microcirculation. The present study suggests that intra-arterial administration of fasudil hydrochloride is effective as a treatment for vasospasm following SAH.

Role of single photon emission computed tomography and transcranial Doppler ultrasonography in clinical vasospasm

This report presents our experience with Transcranial Doppler (TCD) ultrasonography and Single Photon Emission Computed Tomography (SPECT) in the assessment of patients with aneurysmal subarachnoid haemorrhage (SAH). It was designed to evaluate clinical vasospasm with both TCD and SPECT and determine their diagnostic value. Twenty-eight consecutive patients were examined with both TCD and SPECT, performed within 24 hours of each other. They had a total of 45 TCDs and 46 SPECT scans. Eight patients (29%) developed clinical vasospasm, noted from day 2 to day 11 post subarachnoid haemorrhage; these patients underwent TCDs and SPECT scans when the diagnosis of vasospasm was made. Twenty patients (71%) did not demonstrate clinical vasospasm throughout their hospital stay and underwent TCDs and SPECT scans within the first 2 weeks of their SAH, mostly between day 2 and day 10, the period of greatest risk for vasospasm. TCD and SPECT sensitivity for clinical vasospasm was 100% and 50% respectively, their specificity was only 20% and 60%. TCD sensitivity for symptomatic vasospasm was found to be excellent, whereas SPECT was not found to be as useful. We conclude that TCD is the preferred method in the evaluation of patients with subarachnoid haemorrhage.

Cerebral blood flow and vascular physiology

The cerebral circulation is tightly regulated to meet the brain's metabolic demands. Although the mechanism is not fully understood, the major physiologic influences on cerebral blood flow have been well documented. In this chapter the basic vascular anatomy, and physiologic control of the cerebral circulation are reviewed. Clinical implications are emphasized.

Effect of age on cerebral blood flow velocity and incidence of vasospasm after aneurysmal subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Current transcranial Doppler criteria for vasospasm after aneurysmal subarachnoid hemorrhage are not age specific. We analyzed the effect of age on cerebral blood flow velocity changes after subarachnoid hemorrhage and constructed an age-adjusted predictive model of cerebral blood flow velocity in subarachnoid hemorrhage patients.

METHODS

We identified patients with aneurysmal subarachnoid hemorrhage admitted between 1991 and 1999 with a prospective transcranial Doppler database. Eighty-one patients, with complete medical records and transcranial Doppler examinations of the vessels of interest, were included. Patients were subdivided into 2 groups by age: younger, <68 years of age (n=47) and older, >/=68 years of age (n=34). Maximum mean flow velocity and incidence of symptomatic vasospasm were reported. Linear and nonlinear regression analyses were performed.

RESULTS

Middle cerebral artery and internal carotid artery mean flow velocity were lower in older patients (median 76 versus 114 cm/s and 76 versus 126 cm/s, respectively; P<0.003). Incidence of symptomatic vasospasm was lower in older patients (44% versus 66%; P=0.05). Older patients developed symptomatic vasospasm at lower middle cerebral artery (median 57 versus 103 cm/s; P=0.04) and internal carotid artery (median 54 versus 81 cm/s, P=0.02) mean flow velocity. Relationship between middle cerebral artery and internal carotid artery mean flow velocity and age was quadratic (ANOVA, P<0.0001).

CONCLUSIONS

Older patients have a lower incidence of symptomatic vasospasm, and such vasospasm develops at lower cerebral blood flow velocity than younger patients. A quadratic relationship was found between age and cerebral blood flow velocity. This model could be used to create an age-adjusted nomogram that might improve diagnostic capabilities of transcranial Doppler.

Impact of cerebral microcirculatory changes on cerebral blood flow during cerebral vasospasm after aneurysmal subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Cerebral microcirculatory changes during cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH) are still controversial and uncertain. The aim of this study was to investigate the changes of cerebral microcirculation during cerebral vasospasm and to clarify the roles of microcirculatory disturbances in cerebral ischemia by measuring cerebral circulation time (CCT) and regional cerebral blood flow (rCBF).

METHODS

In 24 cases with aneurysmal SAH, rCBF studies by single-photon emission CT and digital subtraction angiography (DSA) were performed on the same day between 5 and 7 days after SAH and/or within 4 hours after the onset of delayed ischemic neurological deficits. CCT was obtained by analyzing the time-density curve of the contrast media on DSA images and was divided into proximal CCT, which was the circulation time through the extraparenchymal large arteries, and peripheral CCT, which was the circulation time through the intraparenchymal small vessels. They were analyzed in association with rCBF and angiographic vasospasm.

RESULTS

Severe angiographic vasospasm statistically decreased rCBF, and correlation between the degree of angiographic vasospasm and rCBF was seen (r=0.429, P=0.0006). Peripheral CCT showed strong inverse correlation with rCBF (r=-0.767, P<0.0001). Even in none/mild or moderate angiographic vasospasm, prolonged peripheral CCT was clearly associated with decreased rCBF.

CONCLUSIONS

In addition to the marked luminal narrowing of large arteries detected as severe angiographic vasospasm, microcirculatory changes detected as prolonged peripheral CCT affected cerebral ischemia during cerebral vasospasm. These results suggested that impaired autoregulatory vasodilation or decreased luminal caliber in intraparenchymal vessels may take part in cerebral ischemia during cerebral vasospasm.

Cerebrovascular reserve capacity many years after vasospasm due to aneurysmal subarachnoid hemorrhage. A transcranial Doppler study with acetazolamide test

BACKGROUND AND PURPOSE

Vasospasm in aneurysmal subarachnoid hemorrhage results in proliferative vasculopathy. Systemic hypertension also causes vascular hypertrophy. Both of these histological changes can lead to rigidity of the cerebrovascular system, reducing its autoregulatory capacity.

METHODS

Blood flow velocity (BFV) in the middle cerebral artery at rest and cerebrovascular reserve capacity (CVRC) (percent rise in BFV after acetazolamide stimulation) measured by means of transcranial Doppler sonography were studied many years after aneurysmal subarachnoid hemorrhage in patients with proven cerebral vasospasm (mean BFV > 160 cm/s). The BFV under resting conditions and the CVRC values of the ipsilateral and the contralateral hemispheres were measured in 29 patients (mean age, 43 years; mean follow-up, 4.6 years) and compared with those of control subjects.

RESULTS

Persistent high BFV (> 120 cm/s) was found in three patients in the peripheral branch of the ipsilateral middle cerebral artery. In the main trunks of the arteries of the anterior circle of Willis, BFV was normal in all cases. CVRC was normal in all patients (ipsilateral, 52 +/- 21%; contralateral, 56 +/- 17%); values did not differ significantly from each other or from the control value (45 +/- 18%). The higher value of CVRC on the contralateral side was found to be statistically significant in selected groups (hypertensive patients and patients with residual infarct on late CT).

CONCLUSIONS

Proliferative vasculopathy developed at the time of vasospasm must have resolved and did not reduce late vasoreactivity. Comorbidity with hypertension also did not seem to influence the late vasoreactivity toward normalization.

Morphological changes of intraparenchymal arterioles after experimental subarachnoid hemorrhage in dogs

OBJECTIVE

Morphological and microcirculatory changes in intraparenchymal vessels after subarachnoid hemorrhage (SAH) have not yet been fully clarified. We conducted this experimental study to investigate the serial morphological changes of intraparenchymal arterioles after SAH.

METHODS

SAH was produced by injecting autologous arterial blood into the cisterna magna twice at 48-hour intervals in 30 dogs. The dogs were killed 3, 7, or 14 days after SAH, and then perfusion-fixed specimens of both anterior sylvian giri were obtained by using two methods. Microvascular corrosion casts produced by arterial injection of polyester resin were examined using scanning electron microscopy, and the widths of 40 arterioles of each animal were measured. Sectioned slices from the brain surface to 500 microns deep were examined by light microscopy, and external diameter, internal diameters, and wall thickness of the arterioles at depths of 50, 200, and 500 microns from the brain surface were morphometrically evaluated in 40 arterioles of each animal. In control animals receiving cisternal injections of mock cerebrospinal fluid (n = 10) and in healthy control animals (n = 10), the same examination and evaluation were performed.

RESULTS

Corrosion casts of arterioles showed tapered narrowing with folding after SAH, and the width of the arterioles significantly decreased 3 and 7 days after SAH (P < 0.01). Morphometric examination by light microscopy showed a significant decrease of internal diameter of arterioles associated with a significant increase of wall thickness at any depth from the brain surface 3 and 7 days after SAH (P < 0.05 or P < 0.01). These findings improved 14 days after SAH. Control animals receiving cisternal injections of mock cerebrospinal fluid showed no significant differences compared with healthy control animals.

CONCLUSION

These results suggest that constriction of intraparenchymal arterioles occurs after SAH and may contribute to delayed cerebral ischemia.

Transcranial Doppler ultrasonography in the neurocritical care unit

TCD ultrasonography is a noninvasive means to study the cerebral vasculature. By varying the depth and angle of insonation of a pulsed sound wave, the direction and velocity profile of the cerebral arteries can be ascertained. This can be used to identify areas of focal stenosis and increased resistance and to estimate the adequacy of cerebral flow. TCD ultrasonography commonly is used in SAH to detect cerebral vasospasm. Many centers interpret rising velocities as increasing vessel narrowing and initiate medical strategies based on these values. TCD use in head trauma is less clearly defined. TCD ultrasonography is considered an acceptable confirmatory test for the determination of brain death. TCD ultrasonography is capable of studying dynamic cerebrovascular processes. By being able to determine vessel patency, TCD may become a useful adjuvant to thrombolytic therapy. Continuous monitoring of flow velocities and profiles along with testing to cerebrovascular reserve promises to be a future active area of research.

Clinical relevance and frequency of transient stenoses of the middle and anterior cerebral arteries in bacterial meningitis

BACKGROUND AND PURPOSE

We sought to examine the frequency and clinical relevance of intracranial artery stenoses in patients with bacterial meningitis in whom the occurrence of stroke has angiographically been reported to be associated with stenoses or occlusions of the large basal cerebral arteries.

METHODS

Thirty-five unselected patients (24 men, 11 women; mean age, 51 +/- 18 years) with bacterial (n = 33) or fungal (n = 2) meningitis prospectively underwent serial transcranial Doppler sonography recordings of mean blood velocity (MBV) and pulsatility index in the middle (MCA) and anterior (ACA) cerebral arteries, as well as recordings of the ratio of the MBV of the MCA and internal carotid artery (MCA/ICA ratio) on days 1, 3, 5, 8, 14, and 21 after admission. The results were correlated with the Glasgow Coma Scale (days 1 to 14), the occurrence of focal cerebral signs, and the Glasgow Outcome Scale (short-term outcome, day 21). An MCA stenosis was diagnosed by an MBV of 120 cm/s or more or an MCA/ICA ratio of more than 3. An ACA stenosis was diagnosed by an MBV of 100 cm/s or more.

RESULTS

Transient stenoses occurred most frequently between days 3 and 5 and were detected in 18 patients (51%). Seventeen patients remained without a stenosis. Patients with stenoses showed a significantly poorer mean Glasgow Coma Scale score from day 3 (9 +/- 4) to day 14 (11 +/- 4) than patients without a stenosis (day 3: 13 +/- 4, P < .01 by t test; day 14: 14 +/- 1, P < .05). The mean Glasgow Outcome Scale score was not significantly different between both groups. The occurrence of mainly transient focal cerebral signs was significantly related to the number of narrowed vessels per patient (P < .05, chi 2 test).

CONCLUSIONS

Stenoses of the intracranial arteries occur frequently in bacterial meningitis and are associated with a complicated course of the disease.

Effects of intravenous anesthetic agents on middle cerebral artery blood flow velocity during induction of general anesthesia

OBJECTIVE

Our objective was to quantify the effects of intravenous anesthetics on values measured by or derived from transcranial Doppler sonography (TCD) during induction of general anesthesia.

METHODS

We recorded blood flow velocity in the middle cerebral artery (V-MCA) before, during, and after induction of general anesthesia in six groups of young patients without intracranial pathology (n = 10 each) using TCD. Patients were randomized to receive either 2 mg/kg propofol, 1.5 mg/kg methohexital, 5 mg/kg thiopental, 0.3 mg/kg etomidate, 2 micrograms/kg fentanyl and 0.15 mg/kg midazolam, or 1.5 mg/kg ketamine and 0.15 mg/kg midazolam intravenously. At 2 min after injection, each patient was intubated and given isoflurane 0.8% and nitrous oxide 66% in oxygen. Ventilation was set to achieve an end-tidal PCO2 of 40 mm Hg. V-MCA, arterial blood pressure, heart rate, hematocrit, and PCO2 (venous samples) were measured before and 1, 3, 5, 10, and 30 min after induction of anesthesia.

RESULTS

The preinduction data were not different between groups. At 1 min after injection, propofol, thiopental, methohexital, and etomidate significantly decreased V-MCA. TCD values were only slightly affected following fentanyl/midazolam. Ketamine/midazolam induced a modest rise in V-MCA. After endotracheal intubation, V-MCA increased in all groups, and slowly declined thereafter.

CONCLUSIONS

Under the circumstances of our study, values derived from TCD measurements responded differently to the agents used to induce general anesthesia in nonneurosurgical patients.

Cortical blood flow recorded during early or delayed surgery for ruptured intracranial aneurysms

Forty-three patients were operated on for ruptured intracranial aneurysms during a 12-month-period. Intraoperative evaluation of cortical blood flow by means of a thermal diffusion probe was performed in 23 out of the 41 patients who were operated on for aneurysms of the anterior circulation. The autoregulation index was determined at the time of raising the systemic blood pressure after clipping of the aneurysm(s). No statistically significant difference was found between the averages of the autoregulation indexes calculated in the subgroups of patients submitted respectively to early or delayed surgery. There was no correlation of both cortical blood flow and autoregulation with either age of the patients, or preoperative neurological grade. On the contrary, the autoregulation index showed a statistically significant correlation with outcome.

Transcranial Doppler diagnosis of cerebral vasospasm following subarachnoid haemorrhage: correlation and analysis of results in relation to the age of patients

A retrospective analysis was undertaken to determine whether cerebral vasospasm following subarachnoid haemorrhage (SAH) correlates with the age of patients. For at least 3 weeks after bleeding 80 subjects underwent very close follow-up with clinical examination and transcranial Doppler records of the blood velocities within the basal cerebral arteries. Firstly a correlation between measured maximal mean blood flow velocities and age was made. Secondly, according to their age and the maximum of recorded mean velocities (v), the patients were divided into groups as follows: age 55 years or less, age more than 55 years; and maximum velocity v1 < 90 cm/s, 90 cm/s < v2 < 120 cm/s, 120 cm/s < v3 < 160 cm/s, v4 > 160 cm/s. There was a significant correlation of the measured maximum mean velocities and the age of the patients (r = -0.525, p < 0.01). With regard to the velocity groups there was a significant (chi-squared statistic for contingency tables, p < 0.01) difference between both age-groups: 32% (n = 18) of the younger fell into group v4 with maximum mean velocities of more than 160 cm/s, but none of the older had such. Vice versa, 63% (n = 15) of the older compared with only 14% (n = 8) of the younger fell into group v1 with maximum mean velocities of less than 90 cm/s. Clinical follow-up also depicted differences between both age groups. 13 of 18 younger patients with maximum mean velocities > 160 cm/s exhibited symptomatic vasospasm with a delayed neurological deficit. This typical course did not occur in the older age group.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered cerebrovascular CO2 reactivity following subarachnoid hemorrhage in cats

The authors tested the hypothesis that cerebral blood flow (CBF) reactivity to CO2 was blunted following subarachnoid hemorrhage (SAH). Subarachnoid hemorrhage was produced in five cats by performing four cisterna magna injections of blood in each (SAH Group). A second group of six cats was treated with an antifibrinolytic agent (AF) in addition to four cisterna magna blood injections (SAH+AF Group). Four cats received AF and four cisterna magna injections of saline (Control Group). The presence or absence of basilar artery vasospasm was determined by comparing baseline and follow-up selective angiograms. Cerebral blood flow reactivity was determined by randomly varying the concentration of inspired CO2 to alter PaCO2 from 20 to 75 mm Hg. Regional CBF was measured with radiolabeled microspheres. Basilar artery vasospasm was seen following subarachnoid injection of blood but not of saline. Normocapnic CBF was similar in all three groups in the brain stem (mean +/- standard error of the mean: SAH Group 46 +/- 6, SAH+AF Group 46 +/- 6, and Control Group 44 +/- 9 ml/min/100 gm) and in the supratentorial compartment (SAH Group 53 +/- 8, SAH+AF Group 61 +/- 9, and Control Group 51 +/- 13 ml/min/100 gm). At intermediate levels of hypercarbia (PaCO2 50 +/- 3 mm Hg), CBF increased similarly in all three groups (SAH Group 161% +/- 32%, SAH+AF Group 118% +/- 33%, and Control Group 174% +/- 19% compared to baseline); at higher levels of PaCO2 (60 +/- 3 mm Hg), CBF values were SAH Group 265% +/- 50%, SAH+AF Group 205% +/- 47%, and Control Group 159% +/- 30% of baseline. At the highest level of PaCO2 (75 +/- 6 mm Hg), supratentorial CBF did not increase as much in the SAH+AF Group as in the Control Group (179% +/- 59% vs. 463% +/- 58% of baseline, respectively). The authors conclude that, in this model of SAH, there is no change in normocapnic CBF; however, blood flow reactivity to hypercarbia is blunted. It is possible that this may result from a combination of narrowing of proximal large vessels and globally impaired reactivity of small vessels.

Use of transcranial Doppler sonography to predict development of a delayed ischemic deficit after subarachnoid hemorrhage

Blood flow velocity was recorded from the middle or anterior cerebral and extracranial internal carotid arteries using transcranial Doppler sonography (TCD) in 121 unselected consecutive patients with acute aneurysmal subarachnoid hemorrhage (SAH). Recordings were made daily or every 2nd day after SAH for a 14-day period. The highest recorded velocity was greater in the 47 patients who developed a delayed ischemic neurological deficit (186 +/- 6 cm sec-1; mean +/- standard error of the mean) than in the 74 patients who did not develop a neurological deficit (149 +/- 5 cm sec-1) (p < 0.001, Mann-Whitney test). Peak velocity recordings can thus assist in the diagnosis of delayed ischemic neurological deficit; however, peak velocity was often recorded only after the onset of neurological deficit. When only those readings made before the onset of neurological deficit were considered, there was no significant difference in peak velocity between the groups (157 +/- 8 cm sec-1 vs. 149 +/- 5 cm sec-1, respectively). Alternative TCD parameters for predicting delayed neurological deficit were therefore sought. The rate of increase in TCD velocity, recorded during the first few days after SAH, was significantly higher in the patients who later developed a neurological deficit. A maximum velocity increase of 65 +/- 5 cm sec-1 per 24-hour period was recorded in patients who later developed a neurological deficit, compared to 47 +/- 3 cm sec-1 24 hrs-1 in patients who did not develop a delayed neurological deficit (p = 0.003). A rise of more than 50 cm sec-1 24 hrs-1 identifies those patients who are most likely to develop a delayed ischemic neurological deficit after SAH. This can be applied prospectively to individual cases. Serial TCD studies in the early period after SAH are thus of value to identify patients who can be selected for prophylactic therapy, which may prevent or ameliorate development of delayed ischemic neurological deficits.

Transcranial Doppler in neurosurgery

This chapter describes the use of the transcranial Doppler apparatus in neurosurgery. The principles of Doppler insonation, the techniques of recording and the use of activation techniques is described. The relationship between blood flow and blood velocity is discussed, and the interaction of various pharmacological agents. The establishment of normal values for the laboratory and various vessels insonated is emphasised. The use of indices particularly the pulsatility index is described together with its variations. Cerebral vascular reactivity measurements and the interaction of Doppler recordings with raised intracranial pressure, useful in assessment of cerebral perfusion pressure as in head injury and in terminal cases, is documented. The use of transcranial Doppler in management of head injury and subarachnoid haemorrhage is described. The latter is probably the most useful routine place for Doppler measurement in neurosurgical practice and the documentation of the onset and progress of vasospasm is the final portion of the chapter.

Transcranial Doppler in spontaneous attacks of migraine

BACKGROUND AND PURPOSE

Our aim in this study was to compare headache-free and spontaneous migraine measurements of blood flow velocity and the pulsatility index in the anterior cerebral artery, middle cerebral artery, and posterior cerebral artery.

METHODS

Thirty-one patients (nine having experienced migraine with aura and 22 migraine without aura) were studied in headache-free periods and during spontaneous migraine attacks with transcranial Doppler ultrasonography.

RESULTS

During attacks of migraine with aura, blood flow velocities (particularly the diastolic velocity [p = 0.05]) were reduced while the pulsatility index increased (p = 0.05), whereas a generalized increase in diastolic velocity (p less than 0.02) and a decrease in the pulsatility index (p = 0.05) were observed during attacks of migraine without aura. Significant variations of blood pressure and heart rate were never found.

CONCLUSIONS

These findings are consistent with constriction of resistance vessels in migraine with aura and dilatation of the vessels in migraine without aura. This disparity could be due to a difference between the two migraine types or could be related to the fact that in this study the time interval between headache onset and transcranial Doppler was shorter in the migraine-with-aura group. The latter explanation would apply if, in fact, both types of migraine evolve from hypoperfusion to hyperperfusion during their time course, although perhaps with a difference in intensity.

Cerebral blood flow velocity changes after ventricular taps and ventriculoperitoneal shunting

Transcranial Doppler ultrasonography (TCD) was performed on 14 patients with hydrocephalus (age range 1 day to 12 years old) before and after ventriculoperitoneal shunting. TCD was also performed with simultaneous intracranial pressure (ICP) measurements during ventricular taps through a reservoir in 7 patients. Measurements of the resistance index (RI) = (S-D)/S, peak systolic (S), enddiastolic (D) and time-averaged mean flow velocities were made. After ventricular taps and ventriculoperitoneal shunting there was a significant decrease in RI in all patients. This was due to a greater increase in D compared to S, which suggests a decreased distal cerebrovascular resistance. There was a significant correlation between RI and ICP in the older infants and children and in individual neonates. Successful cerebrospinal fluid diversion reduces ICP and cerebrovascular resistance, thus improving cerebral perfusion. The RI is a reliable index for serial monitoring of cerebrohaemodynamic change in patients with hydrocephalus.

Acetazolamide reactivity on cerebral blood flow in patients with subarachnoid haemorrhage

Cerebral vasodilatory capacity was evaluated by acetazolamide-activated N-isopropyl-p-[123I]iodoamphetamine (123I-IMP) single photon emission computed tomography (SPECT) in 42 patients with subarachnoid haemorrhage (SAH). A low perfusion area was present in the corresponding region of haematoma seen on the CT and continued to be noted throughout the time courses. Deteriorated acetazolamide reactivity affected by surgical intervention was seen in 100% of the patients who underwent aneurysm repair in the 1st postoperative week, 92% in the second week, 73% in the third week, and 47% in the fourth week. Three patients with acute diffuse brain swelling seen on CT showed intracranial non-filling of 123I-IMP on SPECTs performed on Day 6, and all three died by Day 10. Some low perfusion areas, due to probable vasospasm, were present in 77% of Hunt and Hess grades I and II patients and in 100% of grades III, IV, and V patients throughout their time courses. Overall, low perfusion areas, due to probable vasospasm, were seen in 10 patients (31%) of 32 who underwent SPECT between Day 4 and 8,23 (77%) of 30 between Day 9 and 14, 21 (72%) of 29 between Day 15 and 21, and 11 (48%) of 23 between Day 22 and 28. The results suggest acetazolamide-activated 123I-IMP study is of value in evaluating changes in vasodilatory capacity in SAH patients in the acute and subacute stages.

Traumatic occlusion of the internal carotid artery in a healthy young male: effects on the regional cerebral blood flow

The effects of acute right internal carotid artery occlusion in a previously healthy young male, was studied over a period of 10 months, with angiography, TransCranial Doppler ultrasonography (TCD) and SPECT-rCBF. A clinically observed inability to meet increased metabolic demand in the right hemisphere was concommitant to a decreased Pulsatility Index (PI) in the right middle cerebral artery (MCA). Autoregulation studies showed almost dilatation of the resistance vessels in the right middle cerebral artery territory, at rest. A decreased blood flow velocity, in the right middle cerebral artery 7 months after the accident, suggesting a decreased rCBF, could not be confirmed by SPECT-rCBF studies. This finding strongly cautions against interpretation of chronical blood flow velocity changes in terms of changes in regional blood flow. The present study shows the benefits in the combined use of angiography, SPECT-rCBF, and TCD.