Short-term external counterpulsation augments cerebral blood flow and tissue oxygenation in chronic cerebrovascular occlusive disease

Background and purpose

External counterpulsation improves cerebral perfusion velocity in acute stroke and may stimulate collateral artery growth. However, whether (non‐acute) at‐risk patients with high‐grade carotid artery disease may benefit from counterpulsation needs to be validated.

Methods

Twenty‐eight patients (71 ± 6.5 years, five women) with asymptomatic unilateral chronic severe internal carotid artery stenosis (>70%) or occlusion were randomized to receive 20 min active counterpulsation followed by sham treatment or vice versa. Cerebral blood flow velocity (CBFV) (measured bilaterally by transcranial middle cerebral artery Doppler), tissue oxygenation index (TOI) (measured over the bilateral prefrontal cortex by near‐infrared spectroscopy) and cerebral hemodynamic parameters, such as relative pulse slope index (RPSI), were monitored.

Results

Ipsilateral mean CBFV (ΔV_mean +3.5 ± 1.2 cm/s) and tissue oxygenation (ΔTOI +2.86 ± 0.8) increased significantly during active counterpulsation compared to baseline, whilst the sham had little effect (ΔV_mean +1.13 ± 1.1 cm/s; ΔTOI +1.25 ± 0.65). On contralateral sides, neither counterpulsation nor sham control had any effect on either parameter. During counterpulsation, early dynamic changes in ΔRPSI of the ipsilateral CBFV signal predicted improved tissue oxygenation during counterpulsation (odds ratio 1.179, 95% confidence interval 1.01–1.51), whilst baseline cerebrovascular reactivity to hypercapnia failed to show an association.

Conclusions

In patients with high‐grade carotid disease, ipsilateral cerebral oxygenation and blood flow velocity are increased by counterpulsation. This is a necessary condition for the stimulation of regenerative collateral artery growth and thus a therapeutic concept for the prevention of cerebral ischaemia. This study provides a rationale for further clinical investigations on the long‐term effects of counterpulsation on cerebral hemodynamics and collateral growth.

Double solitaire mechanical thrombectomy in acute stroke: effective rescue strategy for refractory artery occlusions?

BACKGROUND AND PURPOSE

Mechanical thrombectomy by using a single stent retriever system has demonstrated high efficacy for recanalization of large-artery occlusions in acute stroke. We aimed to evaluate the feasibility, safety, and efficacy of a novel double Solitaire stent retriever technique as an escalating treatment for occlusions that are refractory to first-line single stent retriever mechanical thrombectomy.

MATERIALS AND METHODS

All patients treated with the double stent retriever technique by using the Solitaire system were retrospectively selected from 2 large neurointerventional centers. Time to recanalization, angiographic (TICI) and clinical outcomes (mRS), and complications were assessed.

RESULTS

Ten patients (median NIHSS score, 16; mean age, 70 years) with MCA M1 segment (n = 5) and terminal ICA (n = 5 including 2 ICA tandem) occlusions were included. Prior single stent retriever mechanical thrombectomy had been performed in 9 patients (median number of passes, 3). Median time to recanalization was 60 minutes (interquartile range, 45-87 minutes). Procedure-related complications occurred in 1 patient; overall mortality was 20%. Recanalization of the target vessel (TICI 2b/3) was achieved in 80%. Good clinical outcome (mRS 0-2) was 50%.

CONCLUSIONS

In this preliminary feasibility study, the double Solitaire stent retriever technique proved to be an effective method for recanalization of anterior circulation large-artery occlusions refractory to standard stent retriever mechanical thrombectomy.

Transcranial sonography and [18F]fluorodeoxyglucose positron emission tomography for the differential diagnosis of parkinsonism: a head-to-head comparison

BACKGROUND AND PURPOSE

Brain imaging with positron emission tomography using [(18) F]fluorodeoxyglucose (FDG-PET) and transcranial B-mode sonography (TCS) improves the differential diagnosis of parkinsonism. The diagnostic merits of these approaches in identifying and differentiating atypical parkinsonian syndromes (APS) are compared.

METHODS

Data were included from 36 patients with clinically suspected APS who underwent PET and TCS. FDG-PET scans were analyzed by visual assessment (including voxel-based statistical maps) of a priori defined disease-specific metabolic patterns. Sonographers achieved diagnoses according to pre-defined criteria for echogenicities of the substantia nigra and lenticular nucleus, and third ventricle diameter. Patients with APS were identified and allocated to the subgroups multiple system atrophy (MSA), progressive supranuclear palsy (PSP) or corticobasal degeneration (CBD).

RESULTS

After a median follow-up period of 9 months, the final clinical diagnoses (reference standard) were Parkinson's disease, n = 15; MSA, n = 9; PSP, n = 7; and CBD, n = 5 (n = 21 APS in total). Six patients (4 APS) showed an insufficient bone window for TCS. In the remaining 30 patients, sensitivity/specificity for diagnosing APS were 82%/100% and 82%/85% for FDG-PET and TCS, respectively. Diagnostic accuracies did not differ between FDG-PET (90%) and TCS (83%; P = 0.69). Likewise, overall accuracy of subgroup classification (non-APS, MSA, PSP and CBD) did not differ between modalities (FDG-PET 87% and TCS 83%; P = 1.00).

CONCLUSIONS

FDG-PET and TCS show comparable accuracies for differential diagnosis of neurodegenerative parkinsonism. This preliminary study supports the use of TCS and warrants further prospective validation.

Photooxidation and photoaquation of iron hexacyanide in aqueous solution: A picosecond X-ray absorption study

We present a picosecond Fe K-edge absorption study of photoexcited ferrous and ferric hexacyanide in water under 355 and 266 nm excitation. Following 355 nm excitation, the transient spectra for the ferrous and ferric complexes exhibit a red shift of the edge reflecting an increased electron density at the Fe atom. For the former, an enhanced pre-edge transition is also observed. These observations are attributed to the aquated [Fe(CN)5OH2](3-) species, based on quantum chemical calculations which also provide structural parameters. Upon 266 nm excitation of the ferric complex, a transient reminiscent of the aquated species is observed (appearance of a pre-edge feature and red shift of the edge) but it is different from that obtained under 355 nm excitation. This points to a new reaction channel occurring through an intermediate state lying between these two excitation energies. Finally, 266 nm excitation of the ferrous species is dominated by the photooxidation channel with formation of the ferric complex as main photoproduct. However, we observe an additional minor photoproduct, which is identical to the 266 nm generated photoproduct of the ferric species, suggesting that under our experimental conditions, the pump pulse photooxidises the ferrous complex and re-excites the primary ferric photoproduct.

A wavelet analysis for the X-ray absorption spectra of molecules

We present a Wavelet transform analysis for the X-ray absorption spectra of molecules. In contrast to the traditionally used Fourier transform approach, this analysis yields a 2D correlation plot in both R- and k-space. As a consequence, it is possible to distinguish between different scattering pathways at the same distance from the absorbing atom and between the contributions of single and multiple scattering events, making an unambiguous assignment of the fine structure oscillations for complex systems possible. We apply this to two previously studied transition metal complexes, namely iron hexacyanide in both its ferric and ferrous form, and a rhenium diimine complex, [ReX(CO)(3)(bpy)], where X = Br, Cl, or ethyl pyridine (Etpy). Our results demonstrate the potential advantages of using this approach and they highlight the importance of multiple scattering, and specifically the focusing phenomenon to the extended X-ray absorption fine structure (EXAFS) spectra of these complexes. We also shed light on the low sensitivity of the EXAFS spectrum to the Re-X scattering pathway.

Solvent-induced luminescence quenching: static and time-resolved X-ray absorption spectroscopy of a copper(I) phenanthroline complex

We present a static and picosecond X-ray absorption study at the Cu K-edge of bis(2,9-dimethyl-1,10-phenanthroline)copper(I) ([Cu(dmp)2](+); dmp = 2,9-dimethyl-1,10-phenanthroline) dissolved in acetonitrile and dichloromethane. The steady-state photoluminescence spectra in dichloromethane and acetonitrile are also presented and show a shift to longer wavelengths for the latter, which points to a stronger stabilization of the excited complex. The fine structure features of the static and transient X-ray spectra allow an unambiguous assignment of the electronic and geometric structure of the molecule in both its ground and excited (3)MLCT states. Importantly, the transient spectra are remarkably similar for both solvents, and the spectral changes can be rationalized using the optimized ground- and excited-state structures of the complex. The proposed assignment of the lifetime shortening of the excited state in donor solvents (acetonitrile) to a metal-centered exciplex is not corroborated here. Molecular dynamics simulations confirm the lack of complexation; however, in both solvents the molecules come close to the metal but undergo rapid exchange with the bulk. The shortening of the lifetime of the title complex and nine additional related complexes can be rationalized by the decrease in the (3)MLCT energy. Deviations from this trend may be explained by means of the effects of the dihedral angle between the ligand planes, the solvent, and the (3)MLCT-(1)MLCT energy gap.

[Innovations in neuro-monitoring using transcranial ultrasound]

This review describes transcranial ultrasound-based neuromonitoring by assessing changes of brain structures or cerebral blood flow over time. Some of the presented ultrasound techniques are still experimental. They are advantageous as they provide non-invasive and bed-side imaging. Thus, time, costs and potentially hazardous side effects due to transportation of acutely ill patients to CT or MRI scanners can be avoided. An assessment of increased cerebral pressure can be achieved by repeated determination of individual pulsatility index, cerebral venous blood flow, midline shift and transorbital optic sheath measurements. Moreover, transcranial duplex sonography offers the possibility to detect intracranial haemorrhage and to guide neurosurgical interventions. Finally, the value of measuring cerebral autoregulation and the current state of the art regarding sonothrombolysis in acute intracranial arterial thrombosis is presented.

Dynamic cerebral autoregulation associates with infarct size and outcome after ischemic stroke

OBJECTIVES

Cerebral autoregulation is particularly challenged in acute ischemic stroke. We investigated (1) clinical and radiological factors related to dynamic cerebral autoregulation (DCA) in acute stroke and (2) the relationship between DCA and clinical outcome of stroke.

METHODS

A total of 45 patients with middle cerebral artery (MCA) stroke were analyzed pooling two previous studies. DCA was measured by transcranial Doppler in both MCAs early (within 48 h from onset) and late (day 5-7) using low-frequency phase and correlation analysis (index Mx). Outcome was assessed by modified Rankin scale after a mean period of 4 months.

RESULTS

Mx increased (i.e. autoregulation worsened) between the early and late measurement, more so on affected (P = 0.005) than on unaffected sides (P = 0.014). Poorer autoregulation as indicated by lower ipsilateral phase (early and late) and higher Mx (late measurement) were significantly related to larger infarction. More severe stroke was significantly related to poorer ipsilateral Mx and phase. Ipsilateral phase in the early (P = 0.019) and Mx in the late measurement (P =0..016) were related to poor clinical outcome according to univariate analysis.

CONCLUSIONS

Impairment of DCA ipsilateral to acute ischemic stroke is associated with larger infarction. Dysautoregulation tends to worsen and spread to the contralateral side over the first days post-stroke and is associated with poor clinical outcome.

[Imaging techniques for giant cell arteritis. Ultrasound and MRI]

This article summarizes the examination technique, typical findings, interpretation and limitations of ultrasound diagnosis in patients with giant cell arteritis. Colour-coded sonography of the temporal artery has gained increasing attention. If experienced ultrasound examiners are available, diagnosis of giant cell arteritis in patients with a typical clinical constellation can be made based solely on sonographic findings, in particular by a hypoechogenic halo. The hitherto probably under-diagnosed large vessel variant of giant cell arteritis shows characteristic findings with a simple and quick ultrasound examination of the proximal arm arteries. High resolution MRI has been shown to be a promising technique for non-invasive imaging of giant cell arteritis. Mural inflammatory changes of the superficial temporal arteries can be depicted and the cranial involvement pattern can be readily assessed and in combination with MR angiography extracranial involvement can be determined within the same investigation. Aortitis is a feared complication of giant cell arteritis but can be detected and inflammatory stenoses of the aortic branch vessels can also be revealed. In the hands of an experienced operator ultrasonography can be regarded as the non-invasive imaging modality of first choice whereas MRI is more expensive and may not be as widely available. However, its imaging acquisition is standardized and is more observer-independent. Reading of the images is a routine task for a vascular radiologist and larger areas of the vasculature can be simultaneously assessed.

Preserved dynamic cerebral autoregulation in the middle cerebral artery among persons with migraine

Migraine affects the autonomous nervous system and a recent investigation has also proposed a severe disturbance of dynamic cerebral blood flow regulation in the middle cerebral artery during spontaneous blood pressure oscillations. This study investigates whether dynamic cerebral autoregulation is impaired in persons with migraine among a normal cohort. Out of 94 adults studied to establish normal values for dynamic autoregulation, 19 suffered from migraine according to IHS criteria (10 of them with aura). Transcranial Doppler sonography and fingerplethysmography were used to determine dynamic autoregulation of both middle cerebral arteries following spontaneous low frequency (0.06-0.12 Hz) blood pressure fluctuations (phase and gain of transfer function, correlation coefficient indices Dx and Mx). No significant differences were found for the low frequency variability of blood pressure (power spectral density) and various indices of dynamic cerebral autoregulation between persons with and without migraine. Moreover, no differences were observed between persons with migraine, with and without aura. This study based on a normal cohort does not support the presence of generally impaired cerebral autoregulation dynamics in persons with migraine. Future studies should focus on posterior circulation and particular cerebellar autoregulation.

Natural attenuation potential of downwelling streams for perfluorochemicals and other emerging contaminants

Stream augmentation with tertiary treated municipal wastewater-i.e., recycled water-is increasingly considered as an ecologically beneficial way to utilize recycled water, especially in semi-arid regions of the American Southwest. There is concern that emerging contaminants, i.e. unregulated but biologically active organic compounds, may be present in recycled water and will impact on the aquatic environment and the underlying groundwater. Emerging contaminants include a wide variety of chemically disparate compounds, including pharmaceuticals, endocrine disruptors, and residues of perfluorochemical surfactants (PFCs). This paper presents background data on the occurrence and transport of PFC in Upper Silver Creek (USC) and Coyote Creek, in San Jose, California. USC feeds into Coyote Creek, which discharges into San Francisco Bay. Augmenting the natural flow of Coyote Creek with highly treated recycled water is currently being considered as a means to provide more freshwater to the river ecosystem. The reach of interest is approximately 1,000 m where USC flows on alluvial fan deposits. Data indicate that some PFCs are refractory.

Bildgebende Verfahren bei Riesenzellarteriitis (M. Horton)

This review article highlights several diagnostic imaging modalities in giant cell arteritis. Color-coded Duplex sonography is a relatively cost-efficient but strongly observer-dependent imaging modality. It may be difficult to distinguish inflammatory from atherosclerotic mural changes. Positron emission tomography with (18)F-fluoro-2-deoxy-D-glucose is very sensitive in detecting extracranial involvement of large vessel vasculitis. However, it provides no information on inflammatory changes of the superficial cranial arteries. High-resolution MRI is a new observer-independent method that allows visualizing and assessing the superficial cranial arteries in high detail. Extracranial large artery involvement can be evaluated during the same investigation. At present, only single-center experiences with this promising but rather complex procedure exist. A comparative multicenter trial is about to be initiated.

Charge collection imaging of a monolithic DeltaE-E telescope for radiation protection applications

The development of microdosimeters and particle telescopes is important for risk assessment in space and aviation applications. The charge collection properties of a monolithic particle telescope, suitable for both microdosimetry and fluence based approaches, were studied using an ion microprobe.

Dynamic Cerebral Autoregulation in Acute Ischemic Stroke Assessed From Spontaneous Blood Pressure Fluctuations

Background and Purpose— This study investigates dynamic cerebral autoregulation assessed from spontaneous blood pressure (ABP) and cerebral blood flow velocity (CBFV) fluctuations and its time course in acute ischemic stroke.

Methods— Forty patients admitted with acute ischemic stroke in the territory of the middle cerebral artery (MCA) were enrolled. Admission National Institutes of Health Stroke score was 6±4. Study 1 was performed within 22 (±11) hours and study 2 was performed within 134 (±25) hours of ictus. The final analysis comprised 33 and 29 patients for study 1 and study 2, respectively. Twenty-five age- and sex-matched controls were studied. ABP (Finapres method) and CBFV in both MCAs (transcranial Doppler) were recorded over 10 minutes. Correlations between diastolic and mean ABP and CBFV fluctuations were averaged, yielding the correlation coefficient indices (Dx, Mx). Transfer function analysis was applied to obtain phase shift and gain between ABP and CBFV oscillations.

Results— No disturbance of autoregulation was indicated by all parameters at study 1. Separate analyses for clinical severity, stroke side, and size did not reveal significant differences for the various autoregulatory indices at study 1 and 2. At study 2, MCA flow velocity was significantly increased on both sides, the autoregulation index Mx was slightly but significantly ( P <0.05) worse on both sides in comparison to study 1, and phase showed a trend toward poorer values on affected sides. No significant differences to controls occurred. Clinical outcome in patients completing both studies was good in all but one patient.

Conclusions— Dynamic cerebral autoregulation assessed from spontaneous blood pressure fluctuations does not seem to be relevantly disturbed in early minor MCA stroke. At the subacute stage, slight autoregulatory disturbance may be present.

Complete Biological Dehalogenation of Chlorinated Ethylenes in Sulfate Containing Groundwater

The ability of dehalogenating bacteria to compete with sulfate reducing bacteria for electron donor was studied in microcosms that simulated groundwater contaminated with both chlorinated ethylenes and fuel hydrocarbon compounds. Results demonstrate that reductive dehalogenation of perchloroethylene to ethylene can proceed in the presence of > 100 mg l(-1) sulfate. The hydrogen concentration, which was 2.5 nM in the presence of approximately 150 mg l(-1) sulfate and in the absence of chlorinated compounds, decreased to 0.7 nM during the dechlorination of trichloroethylene and increased to 1.6 nM during the dechlorination of cis-dichloroethylene and vinyl chloride. With only sediment associated donor ("historical" donor) present, dechlorination of trichloroethylene proceeded slowly to ethylene (on a time scale of several years). Addition of toluene, a model hydrocarbon compound, stimulated dechlorination indirectly. Toluene degradation was rapid and linked to sulfate utilization, and presumably formed fermentable substrates that served as hydrogen donors. Dehalogenation was inhibited in soil free microcosms containing 5 mM sulfide, but inhibition was not observed when either aquifer sediment or 5 mM ferrous chloride was added.

Effect of Carotid Endarterectomy or Stenting on Impairment of Dynamic Cerebral Autoregulation

Background and Purpose— Analysis of dynamic cerebral autoregulation (DCA) from spontaneous blood pressure fluctuations might contribute to prognosis of severe internal carotid artery stenosis, but its response to carotid recanalization has not been investigated so far. This study investigates the effect of carotid endarterectomy or stenting on various DCA parameters.

Methods— In 58 patients with severe unilateral stenosis undergoing carotid endarterectomy (n=41) or stenting (n=17), cerebral blood flow velocity (CBFV, transcranial Doppler) and arterial blood pressure (ABP, Finapres method) were recorded over 10 minutes before and on average 3 days after carotid recanalization. Nineteen patients were additionally examined after 7 months. Correlations between diastolic and mean ABP and CBFV fluctuations were averaged to form the correlation coefficient indices (diastolic [Dx] and mean values [Mx]). Transfer function parameters (low-frequency phase and high-frequency gain between ABP and CBFV oscillations) were calculated over the same 10 minutes. CO 2 reactivity was assessed via inhalation of 7% CO 2 .

Results— Before recanalization, all DCA parameters were clearly impaired ipsilaterally compared with contralateral sides. Phase, Dx, and Mx indicated early normalization of DCA after both endarterectomy and stenting. By multiple regression, the degree of DCA improvement was highly significantly related to the extent of impairment before recanalization. No significant change in DCA was found at follow-up. Ipsilateral gain and CO 2 reactivity increased significantly less after endarterectomy than after stenting ( P <0.05).

Conclusions— Dynamic cerebral dysautoregulation in patients with severe carotid obstruction is readily and completely remedied by carotid recanalization.

Estimation of Delay Times in Biological Systems

The problem of delay time estimation in biological systems is addressed with the focus on practical applicability of methods. Four delay time estimators are described: a cross correlation method and three increasingly sophisticated interpretations of the phase spectrum, ranging from a pointwise interpretation of the phase spectrum in terms of a delay to a Hilbert transform method. The four methods are compared through simulation studies showing that, in general, the Hilbert transform method performs best. The methods are then used to estimate delay times in three physiological systems: vestibular stimulation, cerebral autoregulation, and human orthostatic tremor. In all three cases, the Hilbert transform method yields the best results, leading in some cases to physiologically more sensible interpretations of experiments than the other methods.

Bilateral severe carotid artery stenosis or occlusion - cerebral autoregulation dynamics and collateral flow patterns

BACKGROUND

Bilateral severe obstruction of the internal carotid artery is a hemodynamically critical state. We aimed to (1) analyze dynamic cerebral autoregulation (DCA) in affected patients, and (2) to correlate DCA data with different collateral flow patterns.

METHODS

DCA was assessed noninvasively by transfer function analysis (phase shift) of respiratory-induced oscillations at 0.1 Hz of arterial blood pressure (Finapres method) and cerebral blood flow velocity (transcranial Doppler) in 30 patients with severe bilateral carotid stenosis (> or =75%) or occlusion. CO(2)-reactivity was measured via inhalation of 7% CO(2). 30 patients with unilateral stenosis were recruited as controls.

RESULTS

Patients with bilateral 75-89% stenosis had a virtually preserved phase shift. A pronounced reduction was found in bilateral critical stenosis or obstruction (90-100%). Patients with ipsilateral 90-100% and contralateral 75-89% stenosis had a significantly less severe reduction of phase shift on the ipsilateral side. CO(2)-reactivity showed a less marked reduction in patients with bilateral critical stenosis or occlusion. Phase shift was best if "Willisian" collaterals were present. Significantly reduced values were found if only secondary collaterals (ophthalmic artery, leptomeningeal flow) were detected. Poorest values occurred with recruitment of functionally stenosed "Willisian" collaterals. CO(2)-reactivity showed poor values with sole recruitment of secondary collaterals, whereas functionally stenosed primary collaterals did not show values as poor as for phase shift. Clinically symptomatic patients had significantly lower phase shift and CO(2)-reactivity values.

CONCLUSIONS

DCA is severely impaired in bilateral critical carotid stenosis or occlusion. Sole recruitment of secondary collaterals and signs of a functional stenosis in primary ("Willisian") collaterals reflect insufficient collateral supply with a poor hemodynamic status. CO(2)-reactivity assessing the vasodilatory reserve and DCA represent different information for characterizing cerebral hemodynamic impairment. Determining transfer function phase might be a physiologically well supported approach for analysis of cerebral hemodynamic compromise.

Impaired dynamic cerebral autoregulation in eclampsia

Eclampsia is frequently associated with brain edema, cerebral infarction or hemorrhage. Its underlying cerebrovascular pathophysiology is still poorly understood. We examined cerebral autoregulation by a non-invasive multimodal assessment in a 28-year-old primaparous woman with postpartal eclampsia. Transcranial Doppler sonography showed considerably increased cerebral blood flow velocity (CBFV) of all basal cerebral vessels. Magnetic resonance imaging demonstrated multifocal vasogenic brain edema. Using transfer function analysis, a severely decreased phase shift between respiratory-induced 0.1-Hz oscillations of arterial blood pressure and CBFV was observed, indicating substantial disturbance of dynamic cerebral autoregulation (DCA). In contrast, CO(2)-vasomotor reactivity of the right middle cerebral artery was only slightly reduced. We therefore assume that the cerebral arteriolar dysfunction in eclampsia leads primarily to an impairment of the autoregulatory mechanism that is followed by different degrees of arteriolar vasodilation. Because of its probably high sensitivity to hemodynamic disturbances, assessment of DCA might be of great value in early pre-eclampsia for risk prediction of cerebral arteriopathy and eclampsia.

Cerebral autoregulation in carotid artery occlusive disease assessed from spontaneous blood pressure fluctuations by the correlation coefficient index

BACKGROUND AND PURPOSE

Estimation of dynamic cerebral autoregulation from spontaneous fluctuations of arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) is an attractive monitoring option for cerebral hemodynamic impairment. We evaluated the correlation coefficient index method in patients with severe obstructive carotid disease and compared it with transfer function analysis (frequency domain approach to cerebral autoregulation) and CO2 vasomotor reactivity.

METHODS

In 139 patients with severe unilateral carotid stenosis (>or=70%) or occlusion, CBFV (transcranial Doppler) and ABP (Finapres method) were recorded over 10 minutes. Correlations between systolic pressure, diastolic pressure, and mean ABP and CBFV oscillations over 1-minute epochs were averaged over 10 minutes to form the correlation coefficient indexes (Sx, Dx, Mx, respectively). Transfer function parameters (phase shift and gain between ABP and CBFV oscillations) were determined from the entire 10-minute period. CO2 reactivity was assessed by inhalation of 7% CO2.

RESULTS

The correlation indexes Dx and Mx were significantly higher ipsilateral to stenosis and increased with degree of stenosis, indicating increasing dependence of CBFV on ABP and thus impairment of cerebral autoregulation. Dx and Mx correlated moderately but highly significantly with transfer function parameters and CO2 reactivity and showed a good level of agreement in detecting pathological values. Patients with a small variance of the 1-minute source correlations of Dx and Mx showed clearly better correlation values. Transfer function parameters and CO2 reactivity but not Dx and Mx were significantly poorer in patients with symptomatic stenosis or occlusion.

CONCLUSIONS

The potential of the correlation coefficient indexes Dx and Mx in detecting hemodynamic impairment in patients with carotid stenosis is comparable to that of transfer function analysis and CO2 reactivity testing. In future, a combination of various hemodynamic tests might help to identify patients at risk for ischemic events.

Dynamic cerebral autoregulation and collateral flow patterns in patients with severe carotid stenosis or occlusion

The quality of collateral blood supply in carotid disease is pivotal for the resulting hemodynamic compromise. However, the interrelation between different patterns of collateral blood flow and actual impairment of cerebral autoregulation (CAR) has not been analyzed so far. Dynamic CAR was assessed noninvasively by the phase shift between respiratory-induced 0.1-Hz oscillations of arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) in 101 patients with severe unilateral carotid stenosis (> or = 75%) or occlusion. CO(2)-vasomotor reactivity was assessed via inhalation of 7% CO(2). Spontaneously activated collaterals via primary (anterior/posterior communicating artery, type I, n = 65) and secondary (ophthalmic artery / leptomeningeal with or without primary pathways, group II, n = 24) pathways were assessed by transcranial Doppler/duplex sonography. Signs of functional stenosis in the anterior collateral pathways were subsumed under type III (n = 12). Best dynamic CAR (phase shift) on affected sides was observed for type I (n = 65), in which values did not differ significantly from contralateral sides. Reduced phase shift values were present in type II; poorest values were observed for type III. CO(2)-reactivity differed mainly between type I and the other types. A less distinct differentiation of autoregulatory impairment was found when dividing patients into groups of different degrees of stenosis. Symptomatic patients (previous TIA/stroke) were significantly less frequent in the group with type I collateral flow and had significantly lower phase shift and CO(2)-reactivity values. In conclusion, we found that dynamic CAR is substantially impaired if secondary collateral pathways are activated or if functional stenosis in the activated anterior collateral pathway is present. These hemodynamic constellations are also associated with a higher proportion of clinically symptomatic patients. Determination of dynamic CAR by transfer function analysis represents a convenient, sensitive method for detection of cerebral hemodynamic compromise in obstructive carotid disease.