Neurovascular coupling remains unaffected during normal aging

BACKGROUND AND PURPOSE

During normal aging, the cerebral autoregulation mechanism and the CO2-induced cerebral reserve capacity remain unaffected. This led to the suggestion of a wide compensatory range of mechanisms responsible for the cerebral blood flow regulation. The authors investigated the neurovascular coupling mechanism for age-related changes. Because several authors criticized the comparison between higher and younger age groups, the current authors restricted their study on volunteers between 10 and 60 years.

METHODS

Twenty healthy volunteers in the age group of 10 to 20, 20 to 40, and 40 to 60 each without cerebrovascular risk factors were enrolled in this study; they were aged 16.3 +/- 3.4 SD years (9 boys), 32.7 +/- 2.3 SD years (9 men), and 53.1 +/- 5.3 SD years (10 men). A functional transcranial Doppler test was performed using a visual stimulation paradigm. The resultant flow velocity changes in the posterior cerebral artery were analyzed using a control system approach. Resting flow velocity and each of the control system parameters, which were time delay, attenuation, natural frequency, rate time, and gain, were compared between groups statistically.

RESULTS

Control system parameters remained statistically unchanged between groups, whereas the resting flow velocity decreased significantly by age.

CONCLUSIONS

The neurovascular coupling mechanism seems to be unaffected by moderate aging as estimated by Doppler parameters. Vasoregulative dysfunction in patients at vascular risk is more likely to be caused by the risk factor rather than by age.

Peak systolic velocity Doppler index reflects most appropriately the dynamic time course of intact cerebral autoregulation

BACKGROUND

Transcranial Doppler sonography measures blood flow velocity in basal cerebral vessels with high accuracy and time resolution. Dynamic blood flow tests were used to investigate functional integrity of the cerebral autoregulation (CA) mechanism. It is known from cortical activation studies that velocity indices differ in their appropriateness to measure changes in blood flow velocity. We aimed to compare the peak systolic, end diastolic and time-averaged mean flow velocity indices for their use in measuring the effectiveness of the CA mechanism.

METHODS

We performed the leg cuff test to induce in 15 healthy volunteers (aged 24.8 +/- 0.4 years, 9 males) CA due to a sudden arterial blood pressure decrease. Data from the middle and posterior cerebral arteries were measured continuously with transcranial Doppler ultrasound, and the arterial blood pressure with a noninvasive photoplethysmographic method. After transforming all variables to relative changes, velocity-pressure diagrams were calculated for each velocity-pressure index. Additionally, we calculated the autoregulation index.

RESULTS

The step decrease in arterial blood pressure resulted in an initial drop, which is followed by a rapid recovery of cerebral blood flow velocity. The autoregulation index was 5.5 +/- 1. Efficacy of CA is illustrated more accurately by peak systolic velocity-pressure curves, which lie continuously above a passive velocity-pressure relationship assuming CA to be absent.

CONCLUSIONS

Our data show peak systolic blood flow velocity index to be most accurate for measuring effectiveness of the dynamic CA mechanism. No differences in the CA were found between the vascular territory of the middle and posterior cerebral arteries.

Thrombocyte activation increases with the degree of carotid artery stenosis

Thrombocyte activation and subsequent aggregate formation play a pivotal role in arterio-arterial embolism in high grade carotid artery stenosis. The aim of this study was to test the hypothesis that the amount of activated thrombocytes would differ with the degree of stenosis. In 19 patients with asymptomatic carotid artery stenosis > 70%, 11 patients with low grade carotid disease and a luminal narrowing of < 70%, and 13 healthy controls in vivo thrombocyte activation was determined by the surface thrombocyte expression of P-selectin before and after thrombin stimulation by whole blood flow cytometry. Soluble P (sP)-selectin in serum was measured by ELISA. We found that thrombocyte activation significantly increased with the degree of stenosis in a multiple correlation analysis corrected for age, sex, and cardiovascular risk factors. Only thrombocyte P-selectin expression and sP-selectin serum concentrations were able to discriminate the patient groups in a multivariate analysis, however, only thrombocyte P-selectin expression was an independent variable. In vivo thrombocyte activation, then, increases with the degree of carotid stenosis. Flow cytometry is especially useful in the evaluation of the thrombocyte activation state in patients with cerebrovascular disease.

Sonographic harmonic grey scale imaging of brain perfusion: scope of a new method demonstrated in selected cases

AIM

Transient response harmonic transcranial sonography is a new bed-side technique which provides information on brain tissue perfusion. This paper demonstrates the scope of perfusion transcranial sonography (p-TCS).

METHODS

P-TCS was performed in an axial insonation plane through the thalamus and third ventricle in a case with Moyamoya disease and a patient with bilateral thalamic oedema due to thrombosis of the internal cerebral veins, and compared to results in 10 healthy controls. Signal increase induced by a bolus of an echo-contrast agent (Optison trade mark ) was quantified in regions of interest (ROI) in the thalamus (TH), lentiform nucleus (LN) and the cerebral white matter (WM).

RESULTS

In Moyamoya disease p-TCS could demonstrate a decreased perfusion in the WM and LN as a result of bilateral, high-grade stenoses of the intracranial part of the internal carotid artery. Peak intensity was increased in the TH due to collateral cross-over flow from the vertebrobasilar system. TH perfusion was decreased in thrombosis of the internal cerebral vein thrombosis with normal LN perfusion. The extention of the thalamic oedema into the white matter could also be demonstrated by decreased perfusion in the adjacent WM. ROI ratios of different tissues proved helpful in quantifying the perfusion results.

CONCLUSION

P-TCS is a new, promising technique that can supply information on pathological brain tissue perfusion at the patient's bed-side.

[Heart and brain]

The heart and the brain are closely related, not only proverbially but also anatomically and pathogenetically. Cerebral circulation begins in the heart, through which a major pathomechanism of stroke is predestined: 20-30% of all cerebral infarctions are cardioembolically related. Both organs are equally affected by atherosclerotic processes. Despite this close relationship, generalizing extrapolations from heart to cerebral infarction are usually not applicable. The occurrence of coronary infarction is almost exclusively due to atherosclerosis with plaque rupture, whereas embolic mechanisms such as in cerebral infarction or microangiopathic processes play almost no role. On the other hand, the brain also influences the cardiovascular system. Thus, infarctions particularly in the region of the right insular cortex can induce cardiac arrhythmia and ECG and blood pressure changes. Additionally, vegetative crises with increased sympathicotonia and increased parasympathicotonia are common clinical observations in severe brain disease. A close relation between the two organs can also be observed in preventive pharmacotherapy. Similar principles, however, stand in contrast to considerations of various clinical risks and values, as can be seen for example in anticoagulation or thrombolysis. In this study, special attention is paid to cardioembolic stroke and preventive medicine aspects of coronary and cerebral vascular disorders. In particular, stress is placed on the discerning of commonalities and various evaluations of test results.

Feasibility and validity of transcranial duplex sonography in patients with acute stroke

OBJECTIVES

To evaluate in a prospective multicentre setting the feasibility of transcranial colour coded duplex sonography (TCCS) for examination of the middle cerebral artery (MCA) in patients with acute hemispheric stroke, and to assess the validity of sonographic findings in a subgroup of patients who also had a correlative angiographic examination.

METHODS

TCCS was performed in 58 consecutive patients within six hours of the onset of a moderate to severe hemispheric stroke. Ultrasound contrast agent (Levovist) was applied if necessary. Thirty two patients also had computed tomography angiography (n=13), magnetic resonance angiography (n=18), or digital subtraction angiography (n=1). In 14 of these patients, both the sonographic and corresponding angiographic examination were performed within six hours of stroke onset (mean time difference between TCCS and angiography 0.8 hours). Eighteen patients, in whom angiography was carried out more than 24 hours after stroke onset, had a follow up TCCS for method comparison (mean time difference 6.1 hours).

RESULTS

Initial unenhanced TCCS performed 3.4 (SD 1.2) hours after the onset of symptoms depicted the symptomatic MCA mainstem in 32 patients (55%) (13 occlusions, one stenosis, 18 patent arteries). After signal enhancement, MCA status could be determined in 54 patients (93%) (p<0.05), showing an occlusion in 25, a stenosis in two, and a patent artery in 27 patients. In 31 of the 32 patients who had correlative angiography, TCCS and angiography produced the same diagnosis of the symptomatic MCA (10 occlusions, three stenoses, 18 patent arteries); TCCS was inconclusive in the remaining one.

CONCLUSION

TCCS is a feasible, fast, and valid non-invasive bedside method for evaluating the MCA in an acute stroke setting, particularly when contrast enhancement is applied. It may be a valuable and cost effective alternative to computed tomography and magnetic resonance angiography in future stroke trials.

Disturbance in the serum IgG subclass distribution in patients with anti-Hu positive paraneoplastic neurological syndromes

Autoantibodies in patients with paraneoplastic neurological syndromes (PNS) have been reported to be predominantly IgG1 and IgG3 isotypes. However, no data are available about the IgG subclass distribution of the total serum IgG in these patients. Therefore, we investigated the IgG subclass distribution (given as percentage of total IgG) in 15 anti-Hu positive PNS patients, 15 patients with small cell lung cancer (SCLC) without PNS and 23 healthy controls using a commercial enzyme-linked immunosorbant assay test. Although IgG1 (and to a lower extent IgG3) are the predominant subclasses of the anti-Hu antibodies, PNS and SCLC showed a significant decrease in IgG1 and a concomitant increase in IgG2 compared with healthy controls (P < 0.05, respectively). In contrast, only SCLC patients, but not PNS patients, had higher IgG3 and IgG4 values compared with controls (P < 0.05, respectively). There was no correlation between IgG subclass levels and the titre or the predominant isotype of the antineuronal antibodies. PNS patients with autonomic disturbances had lower IgG4 levels than PNS patients without autonomic disturbances (P < 0.05). Our study demonstrates a disturbance in the IgG subclass distribution in PNS patients which is partly different from SCLC patients. The isotype regulation of the anti-Hu antibody seems to be independent from this phenomenon.

Circulating microemboli after composite replacement or valve-sparing aortic root surgery

BACKGROUND

The purpose of this study was to determine whether microembolic signals (MES) occur after valve-sparing operations on the aortic root. One of the advantages of these procedures relates to the freedom of macroemboli without anticoagulation. Whether this holds true for circulating microemboli has not yet been verified.

METHODS

For comparison, 8 male patients (mean age: 51.8 +/- 12.8 years) were investigated 20.5 +/- 8.4 months after implantation of a mechanical composite graft (group I) and 9 female and 7 male patients (mean age 55.0 +/- 13.4 years) 23.5 +/- 20.0 months after valve-sparing replacement of the aortic root (group II). The middle cerebral artery was insonated for 2 periods of 30 min, breathing room air or O 2 at 9 l/min.

RESULT

Breathing room air, the amount of MES was considerably smaller in group II (0.94 +/- 1.95 vs. 56.1 +/- 58.9 per 30 min, p = 0.006). The difference was less pronounced (0.5 +/- 1.3 vs. 28.9 +/- 42.6 per 30 min, p = 0.009) breathing oxygen. Breathing oxygen reduced MES significantly in group I (p < 0.05) but not in group II (p > 0.05).

CONCLUSIONS

Aortic valve-sparing operations induce MES at a significantly lower rate than composite aortic valve replacement using a mechanical valve.

Vertebrobasilar transcranial color-coded duplex ultrasonography: improvement with echo enhancement

BACKGROUND AND PURPOSE

The diagnostic yield of vertebrobasilar transcranial color-coded duplex ultrasonography (US) is often hampered by insufficient acoustic penetration, anatomic variations, and vessel tortousity. The purpose of this study was to evaluate the effect of echo enhancement on vertebrobasilar transcranial color-coded duplex US.

METHODS

In 23 consecutive patients (mean age, 61.0 +/- 11.1 years) with vertebrobasilar stroke, the vertebrobasilar system (P1 segment of the posterior cerebral artery [PCA], basilar head, V4 segment of the vertebral artery, and basilar artery) was examined with transcranial color-coded duplex US before and after injection of an echo-enhancer. The acoustic window was graded according to visibility of parenchymal structures, and vessel imaging was graded according to the appearance of the color mode signal. Maximum depth of the basilar color signal was recorded. All patients with an abnormal or inconclusive US finding underwent either digital subtraction angiography or MR angiography.

RESULTS

In the P1 PCA, V4 vertebral artery, basilar artery, and basilar head, image quality was insufficient in 65%, 82%, 83%, and 38%, respectively, before echo enhancement, and in 15%, 30%, 35%, and 9%, respectively, after echo enhancement. In all graded vessels, the improved image quality with echo enhancement was statistically significant. Compared with the reference examinations in the 15 cases of occlusion or stenosis, definite diagnosis was possible in 60% (nine cases) with nonenhanced transcranial color-coded duplex US and in 93% of (14 cases) after echo enhancement.

CONCLUSION

Echo enhancement resulted in improved image quality of the vertebrobasilar system and markedly increased diagnostic confidence.

Intracranial venous hemodynamics is a factor related to a favorable outcome in cerebral venous thrombosis

BACKGROUND

In recent studies, coma, cerebral hemorrhage, older age, and infectious origin have been identified as prognostic factors in cerebral venous thrombosis (CVT). However, no studies of the prognosis of CVT have evaluated hemodynamic factors. However, it is conceivable that the presence or absence and the efficiency of venous collaterals, as well as recanalization, may have an impact on brain tissue damage and hence on the prognosis of acute CVT.

METHODS

Twenty-six patients with acute CVT (mean age, 40+/-15 years) were recruited prospectively. All patients were treated with intravenous heparin, followed by oral anticoagulation for 12 months, except for 2 patients who were lost to follow-up after hospital discharge. Neurological deficits were graded on the National Institute of Health Stroke Scale on admission, at hospital discharge, and at 90+/-14 days after admission. The functional clinical outcome was graded on the modified Rankin Scale on day 90 after admission. All patients received a venous transcranial duplex sonography (TCCS) on admission and were followed up in case of a pathological result until normalization was recorded (mean follow-up, 316+/-395 days; range, 13 to 1180 days).

RESULTS

Initial TCCS was pathological in 18 of 26 patients (69%). Four distinct venous drainage types were identified: increased drainage to the cavernous sinus and to the deep cerebral veins, flow reversal in the basal veins, and either compensatory increased or reversed flow in the transverse sinus. Initially normal venous TCCS or normalized TCCS within 90 days was significantly related to favorable outcome.

CONCLUSIONS

TCCS can be used to evaluate venous drainage patterns in acute CVT. Furthermore, initially normal and normalization of initially pathological venous TCCS within 90 days is related to a favorable outcome in this disease.

Cerebral autoregulation in middle cerebral artery territory precedes that of posterior cerebral artery in human cortex

OBJECTIVE

Cerebral autoregulation tends to compensate changes in arterial blood pressure. This mechanism of cerebral blood flow regulation appears to be insufficient in orthostatic dysregulation in which mainly vertebrobasilar symptoms occur. To investigate this hypothesis, we compared cerebral autoregulation in the vascular territory of the carotic and vertebrobasilar vessel system using a leg cuff test to induce a drop in cerebral perfusion pressure.

METHODS

We measured blood flow velocity in 10 healthy young volunteers (aged 26.7 +/- 0.3 years, 7 male) simultaneously in the middle and posterior cerebral artery with transcranial Doppler sonography. A leg cuff test was used to induce a sudden decrease in arterial blood pressure. Arterial blood pressure was measured with a non-invasive photoplethysmographic method. The averaged relative blood flow velocity changes due to the pressure step were compared between both vessel territories.

RESULTS

After cuff release systolic (diastolic) blood flow velocity increased with a latency of 1.1 +/- 0.3 s (1.8 +/- 0.4 s). Due to a smaller decrease and identical time courses cerebral blood flow velocity recovery in the posterior cerebral artery precedes blood flow recovery in the middle cerebral artery by 0.9 +/- 0.3 s.

DISCUSSION

Cerebral autoregulation in the carotid and vertebrobasilar system does not differ in the time course of the blood flow velocity recovery. Due to a smaller decrease in blood flow velocity recovery in the posterior cerebral artery precedes recovery in the middle cerebral artery by nearly 1 s.

Serum cytokine levels do not correlate with disease activity and severity assessed by brain MRI in multiple sclerosis

OBJECTIVE

Chronic and acute dysregulation of the cytokine network has been described in multiple sclerosis (MS). Inflammatory lesions in the central nervous system of MS patients can be assessed by brain magnetic resonance imaging (MRI). This study has been performed to investigate whether changes of cytokines correlate with morphological changes as determined by MRI.

MATERIALS AND METHODS

We included 46 patients with relapsing-remitting MS in the study. The serum concentrations of tumor necrosis factor-beta (TNF-beta), TNF receptor-1 (TNFR-1; 55 kDa) and TNFR-2 (75 kDa), interleukin-4 (IL-4), interleukin-10 (IL-10) and interferon-gamma (IFN-gamma) were measured by enzyme linked immunosorbent assay in all patients. Each parameter was correlated with clinical findings and brain MRI parameters. We measured both the number (lesion load) and cumulated area (disease burden) of all lesions on brain MRI. In addition, the number and cumulated area of those lesions showing signs of activity [Gadolinium (Gd)-enhancement, perifocal edema] were determined.

RESULTS

A non-significant trend (P < 0.05) was found only for the correlation of serum IFN-gamma levels and the number of active MRI lesions showing both Gd-enhancement and perifocal edema in the subgroup of patients (n=21) with active lesions. When corrected for multiple comparisons, this correlation was not significant anymore, as it was above the corrected P-value of 0.001. We could not observe any further correlation of cytokine levels and MRI parameters. However, TNF-beta serum levels were significantly (P < 0.05) elevated in the patient subgroups with higher number of lesions and disease burden, respectively.

CONCLUSION

Our data show that the determination of serum levels of the investigated cytokines and cytokine receptors is not useful as a tool to determine subclinical disease activity and severity as assessed by brain MRI.

Assessment of intracranial collateral flow by transcranial color-coded duplex sonography using a temporal and frontal axial insonation plane

BACKGROUND AND PURPOSE

The insonation of the posterior communicating artery (PcomA) is often hampered by the unfavorable insonation angle when the temporal acoustic bone window (TBW) is used. This problem may be ameliorated by a lateral frontal bone window (LFBW). This study evaluated the TBW and LFBW for the assessment of collateral intracranial flow conditions and aimed at defining diagnostic transcranial color-coded duplex sonography (TCCS) criteria that do not need compression maneuvers.

METHODS

The A1 segment of the anterior cerebral artery (ACA), the PcomA, and the P1 segment of the posterior cerebral artery (PCA) were insonated by TCCS in 40 controls and 20 patients (16 internal carotid artery [ICA] occlusions or high grade stenoses, 3 middle cerebral artery stenoses or occlusions, 1 PCA stenosis).

RESULTS

Detection rates for the A1 ACA and P1 PCA were higher for the TBW (94%, 98%) compared to the LFBW (86%, 81%) in controls. The PcomA was identified more frequently through the LFBW (86%) compared to the TBW (80%). Through the LFBW angle, corrected flow velocity (FV) measurements were possible for the PcomA with an average correction of 6.5 degrees. In controls, in > 80% of identified PcomAs, flow was directed towards the ICA. Side to side differences were below 7% for peak systolic FVs. In the patients with ICA disease, a flow reversal in the ipsilateral A1 ACA and a FV difference of > 30% seemed feasible for diagnosis of anterior communicating artery crossflow. Criteria for PcomA crossflow were side differences of FVs in the PcomA of > or = 30% and in the P1 PCA of > or = 20%.

CONCLUSIONS

The LFBW proved useful as a complementary insonation plane to assess intracranial crossflow conditions, especially via the PcomA. We were able to define TCCS criteria for functional relevant collateralization without the need of compression maneuvers.

Intracranial venous hemodynamics in patients with midline dislocation due to postischemic brain edema

BACKGROUND AND PURPOSE

Cerebral venous pressure is governed by intracranial pressure, cerebral perfusion pressure, and venous outflow resistance. Therefore, changes in venous flow velocities are to be expected because of changes in intracranial pressure and brain tissue dislocation in patients with ischemic stroke and space-occupying brain edema.

METHODS

In 21 prospectively recruited patients with middle cerebral artery stroke and postischemic edema, flow velocities in the basal veins, the vein of Galen, the straight sinus, and the P2 segment of the posterior cerebral artery were recorded every 0.9+/-0.5 days during the first 5 days after symptom onset with the use of transcranial color-coded duplex sonography. The midline shift of the third ventricle was determined by B-mode imaging.

RESULTS

We observed an initial increase of flow velocity in the basal vein ipsilateral to the lesion, followed by a significant decrease within 5 days after symptom onset and with increasing midline shift in patients with brain herniation. In the straight sinus, flow velocity showed a biphasic U-shaped response to increasing dislocation of the third ventricle, with an initial decrease followed by an increase in the course of mass movement (midline shift 1 to 1.5 cm). A steep increase of flow velocity in the vein of Galen took place with a midline shift >1.5 cm. In the survivors these changes could not be observed. Flow velocity in the P2 segment of the posterior cerebral artery followed a typical course in neither the fatal cases nor the survivors.

CONCLUSIONS

Monitoring of flow velocities in the basal cerebral veins and in the straight sinus can provide additional pathophysiological information in patients with space-occupying brain edema after acute stroke.

Prognostic value of soluble tumor necrosis factor receptors 1 and 2 in multiple sclerosis patients treated with interferon beta-1b

The objective of this study was to investigate the effect of interferon (IFN) beta-1b on the serum levels of soluble tumor necrosis factor receptor 1 (sTNF-R1) and sTNF-R2 in patients with multiple sclerosis (MS) in correlation with clinical and magnetic resonance image (MRI) activity. Serum samples were obtained every 3 months from 24 patients treated with 8 x 10(6) U of IFN beta-1b every other day (treatment group) and from 21 patients without any immunomodulatory therapy (control group) over a 15-month observation period. The cytokine receptor levels were assessed by ELISA. Cranial MRI was performed every 6 months to determine the burden of disease. In the treatment group, the MRI responders had significantly larger mean values for the area under the concentration-time curve of sTNF-R1 (p = 0.04) and sTNF-R2 (p = 0.01) when compared to the MRI nonresponders during the 15-month observation period. With regard to an increase in sTNF-R1 and -2 of more than 20% during the first 3 months of treatment, we observed a sensitivity of 33 and 58%, respectively, a specificity of 90 and 60%, respectively, and a positive predictive value of 80 and 64%, respectively, for MRI response during the 15-month observation period. A decrease in sTNF-R1 and -2 of more than 20% during the first 3 months of treatment had a sensitivity of 40 and 20%, respectively, a specificity of 100 and 100%, respectively, and a positive predictive value of 100 and 100%, respectively, for further MRI nonresponse (during the 15-month observation period). The present data suggest that assessment of sTNF-Rs may contribute to the identification of subgroups of patients who are likely to respond better than others to treatment with IFN beta-1b. This could help to establish a cost-effective prescription pattern for this expensive treatment, which is of importance for the future management of patients with MS.

Cell surface bound and soluble adhesion molecules in CSF and blood in multiple sclerosis: correlation with MRI-measures of subclinical disease severity and activity

BACKGROUND

The expression of soluble cell adhesion molecules (AM) in cerebrospinal fluid (CSF) and blood and their significance as measures of disease activity has been extensively studied in patients with multiple sclerosis (MS). In previous studies, we found that cell surface bound AM on mononuclear cells (MNC) in CSF and blood might be useful markers of clinical disease activity in MS patients.

OBJECTIVE

To analyze the correlation of cell surface bound and soluble AM in CSF and blood with magnetic resonance imaging (MRI) markers of subclinical disease severity and activity in patients with MS.

METHODS

Expression levels of cell surface bound AM on peripheral blood and CSF MNC were determined by flow cytometry analysis in 77 (CSF: 33) MS patients. Concentration levels of the soluble forms of AM were measured by enzyme-linked immunosorbent assay (ELISA). In corresponding cerebral gadolinium (Gd)-enhanced MRI scans, we determined both measures of subclinical disease severity and subclinical disease activity.

RESULTS

The expression levels of cell surface bound AM in peripheral blood correlated inversely with parameters for subclinical disease severity and activity on cerebral MRI scans as well as with the disease duration. Furthermore, we found significant correlations between serum levels of soluble AM and patient age but not with disease duration.

CONCLUSIONS

Our results suggest that subclinical disease progression may be associated with a decrease of the expression of cell surface bound AM on peripheral blood MNC. This might be a result of activated MNC migration into the CNS.

Comparison of visually evoked peak systolic and end diastolic blood flow velocity using a control system approach

Transcranial Doppler sonography measures blood flow velocity in basal cerebral vessels with high accuracy. For quantification, time averaged mean blood flow velocities are used most because the peak systolic and end diastolic blood flow velocities mark the velocity extremes of one heart cycle. It is known, from hemodynamic measurements of the neurovascular coupling mechanism, that the end diastolic velocity is more sensitive for change in hemodynamics than the peak systolic velocity. Thus, we used a recently introduced control system approach to compare both indices for their use in functional transcranial Doppler tests focusing on hemodynamics of blood flow velocity change. We enrolled 65 healthy young volunteers without a medical history of cardiovascular risk factors, and performed a visual stimulation test. Peak systolic and end diastolic maximal blood flow velocities were used after transformation to relative data for control-system analysis. Due to Doppler artefacts, 95% of peak systolic and 86% of end diastolic data sets were analyzed. Results showed statistically significant differences for resting blood flow velocity and the control system parameter gain, attenuation and rate time, whereas the parameters' natural frequency and time delay were equal. Increase in relative blood flow velocity in the posterior cerebral artery due to visual-cortical stimulation was higher in end diastolic values than peak systolic data. Using a complex visual stimulation paradigm, the higher sensitivity of the end diastolic index is of no practical use. Being less influenced by Doppler artefacts, the peak systolic velocity index is more feasible for control-system analysis of dynamic blood flow regulation.

Interobserver and intraobserver reliability of venous transcranial color-coded flow velocity measurements

BACKGROUND AND PURPOSE

Venous transcranial color-coded duplex sonography is a new technique for noninvasive evaluation of the intracranial venous system. However, the interobserver and intraobserver reliability of this method is unclear.

METHODS

In 23 healthy volunteers (30 +/- 7.3 years of age), the deep middle cerebral vein (dMCV), basal vein (BV), vein of Galen (VG), and straight (SRS), transverse (TS), and superior sagittal (SSS) sinuses in addition to the arterial segments of the circle of Willis were insonated through the temporal bone window on 2 consecutive days by 2 experienced examiners. The examiners were blinded to each other's results. The interobserver and intraobserver reliability was calculated using a method described by Bland and Altman, resulting in 2-SD confidence intervals.

RESULTS

Non-angle-corrected and angle-corrected systolic and end diastolic venous flow velocities (FV) were in good accordance with published normal values, ranging between 8.6 and 19.2 cm/s. The interobserver reliabilities for non-angle-corrected systolic FVs in the dMCV, BV, VG, SRS, and TS were +/- 1.8, 2.4, 2.6, 3.3, and 4.6 cm/s; for angle-corrected systolic FVs, the interobserver reliabilities were +/- 2.5, 3.1, 13.9, 11.6, and 7.7 cm/s. The intraobserver reliabilities for non-angle-corrected systolic FVs in the dMCV, BV, VG, SRS, and TS were +/- 2.9, 3.2, 2.6, 3.2, and 6.1 cm/s; for angle-corrected systolic FVs, the intraobserver reliabilities were 3.2, 3.7, 13.9, 11.6, and 7.5 cm/s. Angle correction was not attempted for the SSS. The interobserver and intraobserver reliabilities for systolic FVs in the SSS were +/- 3.3 and +/- 3.3 cm/s, respectively.

CONCLUSIONS

Intracranial venous FVs can be measured with a high interobserver and intraobserver reliability in healthy human subjects. Intraobserver reliability was higher for cerebral veins than for dural sinuses, predisposing them for follow-up examinations; however, angle correction for venous FVs in the VG and the SRS is not advisable.

Pharmacokinetics of echocontrast agent infusion in a dog model

Ultrasound contrast agents (UCAs) have a distinct diagnostic impact on transcranial Doppler (TCD) and duplex sonography. In addition to the properties of the UCA and ultrasound imaging modes, the duration of contrast enhancement depends on the administration mode. Infusion of UCAs may be appropriate for prolonging the diagnostically useful time of elevated Doppler intensity. Five sedated dogs were investigated by TCD during infusion with SonoVue, a new UCA consisting of sulfur hexafluoride microbubbles. The infusion rate was varied, and the time-intensity curves were analyzed. Infusion rate of 70 ml/h provided a stable mean level of increased Doppler intensity up to 24 to 26 dB over baseline, whereas a rate of 35 ml/h did not result in a stable plateau (range 8-19 dB over baseline [5 minutes after starting time]). The maximum increases in Doppler mean intensity (18.2 dB [35 ml/h] and 25.6 dB [70 ml/h]) were significantly different (P = .025). Pharmacokinetic analysis of SonoVue during inflow (by exponential functional fitting of the time-mean intensity curves) and elimination (by linear regression analysis) revealed no dose-related differences. This study demonstrated a dose-dependent level of increased Doppler mean intensity within the brain circulation during infusion of SonoVue. Unlike the bell-shaped course of Doppler signal enhancement seen after bolus injection, infusion generates a stable plateau, which is an important prerequisite for more advanced contrast applications.

SonoVue in transcranial Doppler investigations of the cerebral arteries

BACKGROUND AND PURPOSE

The authors investigated the safety and diagnostic potential of a new ultrasound contrast agent (SonoVue) using transcranial color-coded duplex sonography (TCCS).

METHODS

Forty patients were enrolled in a multicenter, open-label (on-site), blind (off-site), randomized, dose-ranging crossover study. SonoVue was administered as an intravenous bolus injection of 4 different dosages (0.3, 0.6, 1.2, and 2.4 mL). Efficacy was evaluated as (1) off-site assessment of global quality of the Doppler investigation (based on color or power Doppler images and spectral analysis) at baseline and following each dose of SonoVue according to a 4-point scale (from very poor to excellent imaging of blood flow) and (2) duration of clinically useful signal enhancement and color or power Doppler visualization of blood flow. Additional on-site efficacy assessments performed following each dose of SonoVue included confidence in diagnosis and global consequences of contrast enhancement on diagnosis. Safety evaluations included clinical laboratory tests, neurological examination, injection site tolerability, and incidence of adverse events and their relationship to the study agent.

RESULTS

All doses of SonoVue significantly improved the global quality of Doppler examinations (P < .05). The median duration of clinically useful enhancement was dose related (P < .001) and ranged from 2 to 6 minutes at the highest dose. The administration of the contrast agent changed a nondiagnostic study to a diagnostic one in 66% of patients and increased the confidence in diagnosis in 74% of cases. No serious adverse events were recorded following SonoVue administration. The observed adverse reactions were all transient and mild in intensity.

CONCLUSIONS

The results obtained from this multicenter study demonstrate that the administration of SonoVue to patients with ischemic cerebrovascular disease who undergo TCCS examination of cerebral vessels improves the visualization of intracranial arteries, providing a dose-dependent contrast enhancement and a clinically useful duration of signal enhancement related to the dose. During this multicenter study, SonoVue proved to be a safe and well-tolerated compound.

Neurovascular coupling in terms of a control system: validation of a second-order linear system model

Neurovascular coupling (NC) adapts cerebral blood flow to cortical activity. Functional transcranial Doppler (f-TCD) investigations revealed a typical time course of evoked blood flow responses with an initial overshoot and a stabilization at a lower, but stable, level. This blood flow reaction can be described in terms of a control-system model. We tested reliability and validity of this new approach using different stimulation paradigms. The P2 segment of the posterior cerebral artery was insonated in 14 healthy volunteers and, subsequently, NC was stimulated using two tests, a checkerboard stimulus of 1 s with different repetition rates and a reading test. Data were analyzed according to algorithms of control-system theory. The reading test was used to measure test reliability and side differences. A second-order linear system can describe blood flow regulation of NC. Different stimulation protocols of the checkerboard test and the related evoked blood flow curves could be described by the same control-system model. Further, there were no differences between the checkerboard and reading test nor between right and left side or test and retest of the reading test. NC can be described in a much more detailed manner using control-system analysis. We were able to show that blood flow response due to different visual stimuli follow one common control-system model. Unlike quantification of NC using overshoot, parameters of the control system have smaller SDs, increasing the statistical power and, thereby, usefulness of f-TCD as a diagnostic instrument.