O39	THE CLINICAL USE OF CEREBROVASCULAR REACTIVITY MEASUREMENTS HUGH MARKUS, ST GEORGE’S HOSPITAL , MEDICAL SCHOOL, LONDON, UK Cerebrovascular reactivity looks at the ability of cerebral circulation to increase in response to a vasodilatory stimulus such as carbon dioxide or acetazolamide. Cerebral perfusion can be measured in a number of ways including PET, SPECT, MRI, Xenon CT and transcranial Doppler. A subgroup of patients with carotid stenosis, have impaired reactivity in the ipsilateral middle cerebral artery territory. This correlates with the absence of good collateral supply, principally via the Circle of Willis. An increasing number of studies have demonstrated that impaired reactivity is an independent predictor of subsequent stroke risk. Many of these have been underpowered or had methodological difficulties, but more recent methodologically better studies have confirmed this association. It is possible that this technique may be useful in identifying at risk patient groups for surgical intervention; possible groups include patients with carotid occlusion who may benefit from EC-IC by-pass, and patients with asymptomatic carotid stenosis for carotid endarterectomy. However this needs to be confirmed in prospective trials. Cerebrovascular reactivity measurements may also be useful in selecting which patients with carotid stenosis and occlusion require revascularisation prior to major surgical procedures such as coronary artery by-pass grafting. The technique has also been used to look at patients with more diffuse cerebrovascular disease such as CADASIL and patients with small vessel disease. This data does suggest an impairment of autoregulation in this ischaemic stroke subtype.
O40	Tilt table testing, TCD and cerebral autoregulation Rolf R. Diehl, Dept. of Neurology, Krupp Hospital Essen Tilt table testing (TTT) is an established method in diagnosing neurocardiogenic syncope (NCS) and postural tachycardia syndrome (POTS). Usually, the diagnostic decision is based on typical arterial blood pressure and heart rate changes during the course of head-up tilting: sudden hypotension and bradycardia in NCS and excessive tachycardia in POTS. Several studies have shown that both NCS and POTS are also characterized by typical TCD changes. During NCS the TCD curves show a strong resistance pattern with nearly zero flow during diastole. During POTS there is a continuous decline in blood flow velocities and an increase in pulsatility. For both conditions it was supposed that autoregulatory failure may be responsible for these typical TCD changes. Using continuous autoregulation testing by the cross spectrum analysis method it has been shown that cerebral autoregulation is neither affected in NCS nor in POTS. Other pathological mechanisms were discussed to explain the characteristic TCD changes: hypocapnea and/or an increase in sympathetic vasomotor tone in POTS, and a cerebral perfusion pressure decrease below the threshold of the critical closure pressure (at least during diastole) in NCS. TCD monitoring during TTT may be of clinical value in cases with orthostatic intolerance if blood pressure and heart rate do not show clear enough the typical pathological pattern. For example, sometimes heart rate during tilting does not exceed the pathological limit of 30 beats/min above supine values as required for POTS while TCD shows the characteristic progressive decline. In those cases the diagnosis of POTS can be supported by the TCD finding.
O41	CONTINUOUS ASSESSMENT OF AUTOREGULATION- AN UPDATE M.Czosnyka, L.Steiner, M.Ballestri,S.Piechnik, Z.Czosnyka, E.Lang* I.Gooskens, E.Schmidt, JD Pickard Academic Neurosurgical Unit, University of Cambridge, U.K. *Dept of Neurosurgery, Christian-Albrechts University, Kiel, Germany Background: The method for continuous assessment of cerebral autoregulation from MCA blood flow velocity and cerebral perfusion pressure (CPP) or arterial pressure (AP) slow waveform has bee introduced 7 years ago. We intend to review clinical applications of this method in various scenarios. Method: Moving correlation coefficient (3 min window), called Mx index, is calculated between low-pass filtered (0.05 Hz) signals of FV and CPP or AP (when intracranial pressure is not measured directly). Material: 243 ventilated head injured patients, 15 patients after subarachnoid haemorrhage (poor grade, all patients were ventilated), 38 patients with Common Carotid Artery stenotic disease, 35 patients suffering from hydrocephalus undergoing infusion test and fourteen volunteers. Results: Good agreement between Aaslid’s cuff test and Mx has been confirmed in healthy volunteers during CO2 inhalation (R=0.81).It also correlated significantly with static rate of autoregulation in 16 head injured patients (R= 0.78; p<0.005). Poor autoregulation (Mx) proved to be correlated with decreased CO2 reactivity in patients with carotid artery stenosis (R=0.46; p<0.005). Reactivity occurred to be significantly (p<0.021) disturbed by vasospsm after SAH and worse in patients with ventricular dilatation in whom CSF dynamics was normal (p<0.02). In head injury autoregulation was worse for low CPP (CPP<55 Hg) and for too high CPP(>105 mmHg) than for normal CPP (between 60 and 100 mmHg; p<0.05). It was significantly disturbed by intracranial hypertension (ICP>25 mmHg; p<0.00006). It strongly differed between patients with favourable and unfavourable outcome (p<0.00002). Conclusion: Mx can be used in many clinical scenarios for continuous monitoring of cerebral autoregulation, predicting outcome and optimising therapeutical strategies.
O42	Dynamic cerebral autoregulation AND collateral flow patterns In PATIENTS WITH severe carotid ARTERY DISEASE M. Reinhard, T. Müller*, B. Guschlbauer, J. Timmer*, and A. Hetzel Dept. of Neurology and Clinical Neurophysiology, University of Freiburg, Germany Freiburg Centre for Data Analysis and Modeling (FDM), Dept. of Physics, University of Freiburg, Germany Background: Transfer function analysis of spontaneous oscillations of arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) has become an attractive tool for graduating cerebral autoregulation (CA) dynamics. However, the interrelation between different patterns of collateral blood flow and actual impairment of dynamic CA in patients with obstructive carotid disease has not been analyzed so far. Methods: 96 patients with severe unilateral carotid stenosis (³ 80%) or occlusion were studied. Phase shift between oscillations of ABP (Finapres) and CBFV of middle cerebral artery over the affected side was determined in the low frequency range (0.06-0.15 Hz). Spontaneously activated collateral flow patterns via primary pathways (anterior/posterior communicating artery, ACoA/PCoA, group I, n=65) and secondary pathways (ophthalmic artery, leptomeningeal, group II, n=14) were assessed by transcranial Doppler/Duplex sonography. The concomitant activation of primary and secondary pathways was subsumed under group III (n=18). Results: Best dynamic CA (phase shift) was observed in group I (34 ± 23°). Reduced values were present in group II (21 ± 19°), and poorest values in group III (9 ± 13°). Differences between all groups were significant (p<0.05). CO2-vasomotor reactivity was preserved in group I (1.4 ± 0.7 %/mmHg) and reduced in groups II (0.8 ± 0.5) and III (0.6 ± 0.6, no significant difference between groups II and III). 7 patients of group III and 4 patients of group I had a recruited but stenosed anterior collateral pathway with very poor phase shift values (5 ± 11°). CO2-reactivity of this subgroup was 0.8 ± 0.8 %/mmHg. Conclusions: Severely impaired dynamic cerebral autoregulation as measured by transfer function phase was observed in (1) patients with concomitant activation of primary and secondary collateral pathways or (2) the presence of a stenosed but recruited anterior collateral pathway. Patients with concomitant activation are likely to have insufficiency of primary (reflected in the high prevalence of a stenosed anterior pathway) and secondary collateral pathways (reflected in still recruited primary pathways). This significant differentiation was not found with CO2-vasomotor reactivity.
O43	Time delay as a parameter for cerebrovascular reactivity – INFLUENCE of CAROTID ENDARTERECTOMY A. Hetzel, B. Guschlbauer, M. Reinhard Dept. of Neurology and Clinical Neurophysiology, University of Freiburg, Germany Background: Responsiveness to CO2 is an established test of cerebrovascular reserve capacity. The amplitude response of cerebral blood flow velocity (CBFV) has mainly been considered so far. We found the off-delay between the decrease of endtidal PCO2 and the consequent decrease in CBFV as an additional simple parameter in the time domain. The aim of the present study was to evaluate the influence of carotid endarterectomy (CEA) on these parameters in patients with severe carotid stenosis. Methods: 89 patients with severe (³ 80%) unilateral (n=75) or bilateral (n=14) carotid stenosis underwent CO2-reactivity testing prior to and 3 days after CEA. Both middle cerebral arteries were insonated using transcranial Doppler sonography, blood pressure was monitored using the Finapres device. Hypercapnia was induced by inhalation of 7% CO2. Results: The off time delay decreased significantly from 17.4 ± 7.4 s to 12.2 ± 5.1 s (p<0.001) ipsilateral to the affected side after CEA. No significant changes were found on the contralateral side even in patients with bilateral stenosis. Conventional CO2-reactivity significantly increased (p<0.001). Again no changes on the contralateral side were observed. Conclusions: Analysis of the time course during CO2-reactivity testing reveals a significant delay parameter between withdrawal of hypercapnia and decrease of CBFV. Our hypothesis is that there might be a delayed clearance of local hypercapnia and the vasodilating local perivascular ion changes due to reduced local blood flow on the side of the stenosis. As expected, carotid endarterectomy leads to restoration of physiological blood flow conditions, which is reflected not only by an increase in amplitude CO2-reactivity, but also by a decrease of the time delay to values comparable with that of the unaffected side. The lacking benefit for the contralateral side in patients with bilateral stenosis is probably due to the early measurement point after CEA.
O44	TRANSCRANIAL DOPPLER AND NEAR INFRARED SPECTROSCOPY CAN EVALUATE THE HEMODYNAMIC EFFECT OF CAROTID ARTERY OCCLUSION F Vernieri, F Tibuzzi, P Pasqualetti, N Rosato, F Passarelli, PM Rossini, M Silvestrini* AFaR Dipartimento di Neuroscienze, Ospedale Fatebenefratelli, Isola Tiberina, Roma *Clinica Neurologica, Università degli Studi di Ancona Background. The hemodynamic effect of an occlusion of the internal carotid artery (ICA) on the distal circulation has been categorized into three stages. When collateral vessels (stage 0) are not adequate, reflex autoregulatory vasodilatation of arterioles (stage I) can maintain normal cerebral blood flow (CBF). Transcranial Doppler (TCD) follow-up studies demonstrated the importance of collaterals and of cerebral vasomotor reactivity (VMR) on the outcome of patients with ICA occlusion. When the first two stages of hemodynamic compromise fail to occur and CBF begins to fall, the brain can increase the oxygen it extracts from the blood to maintain normal cerebral oxygen metabolism (stage II). At present, measurement of this stage is only possible with positron emission tomography. Methods. Near infrared spectroscopy (NIRS) is a non-invasive technique that, by providing a real time assessment of fluctuations in cerebral hemoglobin, has been used to estimate the cerebral blood volume and to measure cerebral VMR. Moreover, NIRS technology, which enables the absolute measurement of absorption and scattering coefficients of brain, can determine in-situ the oxy- and deoxy-hemoglobin concentration in the blood stream. In order to evaluate all three stages of cerebral hemodynamic status, 23 subjects with symptomatic and asymptomatic carotid artery occlusion individually underwent a simultaneous examination by means of TCD and NIRS at rest condition and after CO2 reactivity test. Results. The main result of this study is that a difference exists between asymptomatic and symptomatic patients (6.94 vs 3.83; p=0.027) in terms of hemoglobin saturation increase measured by NIRS. Conclusion. The possibility of simultaneously undertaking NIRS and TCD enables obtaining comprehensive information about the cerebral hemodynamic status in patients with occlusive disease in a simple, non–invasive and reliable way.
O45	ARTERIAL BLOOD PRESSURE AND CEREBRAL BLOOD FLOW Lepic T, Raicevic R, Lukic-Kostic L**, Pesic V**, Cosic Z***. Dpt. of Neurology, Dpt. of Radiology**, Dpt. of Cardiology*** Military Medical Academy, Belgrade, Yougoslavia Background and purpose: Cerebral blood flow (CBF) is an important variable in cerebrovascular disorders. A noninvasive measurement of global CBF is approved with color duplex sonography of the extra cranial cerebral arteries. In aim to determine the influence of arterial blood pressure (ABP) on CBF was performed the study in a group of 124 aged 20 to 85 years; mean age, 58 years in either sex). Methods: The internal carotid arteries and the vertebral arteries were examined with the use of a 7.0-MHz transducer of a computed sonography system. Angle-corrected time-averaged flow velocity and the diameter of the vessel were measured. Intravascular flow volumes were calculated automatically as the product median mean flow velocity and the cross-sectional area of the circular vessel. CBF volume was determined as the sum of flow volumes in both internal carotid and vertebral arteries. Arterial blood pressure was measured by digital blood pressure monitor during the sonographic examination. Results: The mean global CBF was 676+/-98 mL/min. Mean ABP was 112+/-23 mmHg. Relative contributions of the carotid and the vertebral arteries to global CBF volume were 78% versus 22%. CBF correspond significantly with ABP (p < .0001). Increasing of the mean ABP for 10 mm Hg was resulting in increasing of the mean CBF for 32 mL/min in normotensive patient. In early hypertensive patients increasing of CBF was 39 mL/min. Conclusion: Our results of noninvasive sonographic measurement of CBF according to ABP in normotensive and hypertensive patients providing to possible impairment of auto regulation of CBF in hypertensive patients