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ABSTRACT: Background: It is known that dynamic cerebral autoregulation (dCA) is acutely impaired following ischaemic stroke (IS). However, the influence of stroke subtype, the affected (AF) and unaffected (UA) hemispheres, and the effects of a methodological approach on dCA estimates in stroke are all inconclusive. Therefore, we studied cortical and subcortical acute IS (AIS) patients to test the primary hypotheses that (1) dCA is impaired in stroke subtypes when compared to controls, (2) dCA impairment is more pronounced in the AF compared with the UA hemisphere, and (3) similar results are obtained with both spontaneous blood pressure (BP) fluctuation techniques, and sudden induced BP changes by thigh cuff deflation. Methods: We assessed the dCA values in AIS patients and in healthy controls (n = 10). The AIS patient group consisted of anterior circulation cortical (n = 11) and subcortical (n = 11) strokes within 48 h of symptom onset. Cerebral blood flow velocity was measured using transcranial Doppler ultrasound, and BP measurements were recorded before, during and after the release of bilateral thigh cuffs in 10 controls (7 males) of a mean age of 59 ±15 years (range 31-75), 11 cortical strokes (7 males) of a mean of age 65 ± 19 years (range 25-88) and 11 subcortical strokes (7 males) of a mean age of 60 ± 18 years (range 39-85). Autoregulation index (ARI) estimates, calculated using spontaneous fluctuations and thigh cuff manoeuvre, were derived. Differences in ARI (Tiecks' model) were tested with repeated-measures ANOVA. Results: A total of 22 patients were included, comprising 11 subcortical (lacunar clinical syndrome) and 11 cortical strokes (total anterior circulation stroke/partial anterior circulation syndrome). Of the 10 control subjects, 1 later withdrew because of intolerance to the thigh cuffs. Similar ARI estimates were obtained in both groups, whether assessed from spontaneous fluctuations or thigh cuff measurements (p = 0.37). ARI differences were not significantly different between hemispheres for both control and stroke populations. ARI was significantly impaired in AIS patients compared to age-, sex- and BP-matched control subjects, with a greater impairment of dCA observed in cortical IS. Conclusions: The results of this study suggest that both spontaneous fluctuations and thigh cuff deflation techniques are able to provide reliable estimates of ARI, with the estimates from both spontaneous fluctuations and thigh cuff deflation techniques being in keeping with those reported elsewhere in the literature. dCA was impaired following AIS compared to controls when stroke subtype was considered. Importantly, no differences were observed between UA and AF. This has implications for the assessment of CA after stroke and reinforces the need to define a 'gold standard' test for the investigation of CA.
Cerebrovascular Diseases 03/2013; 35(3):257-261. · 2.72 Impact Factor
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ABSTRACT: A novel method is described for mapping dynamic cerebral blood flow autoregulation to assess autoregulatory efficiency throughout the brain, using magnetic resonance imaging (MRI). Global abnormalities in autoregulation occur in clinical conditions, including stroke and head injury, and are of prognostic significance. However, there is limited information about regional variations. A gradient-echo echo-planar pulse sequence was used to scan the brains of healthy subjects at a rate of 1 scan/second during a transient decrease in arterial blood pressure provoked by a sudden release of pressure in bilateral inflated thigh cuffs. The signal decrease and subsequent recovery were analyzed to provide an index of autoregulatory efficiency (MRARI). MRI time-series were successfully acquired and analyzed in eleven subjects. Autoregulatory efficiency was not uniform throughout the brain: white matter exhibited faster recovery than gray (MRARI = 0.702 vs. 0.672, p = 0.009) and the cerebral cortex exhibited faster recovery than the cerebellum (MRARI = 0.669 vs. 0.645, p = 0.016). However, there was no evidence for differences between different cortical regions. Differences in autoregulatory efficiency between white matter, gray matter and the cerebellum may be a result of differences in vessel density and vasodilation. The techniques described may have practical importance in detecting regional changes in autoregulation consequent to disease.
PLoS ONE 01/2013; 8(4):e62588. · 4.09 Impact Factor
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ABSTRACT: Cerebral blood flow velocity (CBFv) and the autoregulation index (ARI) can be reproducibly assessed by noninvasive transcranial Doppler (TCD) methodology using frame-held (FH) ultrasound probes. However, FH techniques may be impractical in severe head injury patients and neonates, where CBFv and ARI estimates are an important component of clinical assessment and management. Therefore, the aim of this study was to investigate the feasibility of an alternative hand-held (HH) approach to CBFv and ARI measurement. In a healthy volunteer population of 11 subjects, mean age 37 years, CBFv and ARI estimates were not significantly different between HH and FH acquisition techniques. In addition, in the hands of a single observer, good reproducibility over two visits, a mean of 6 days apart, was observed: intra-visit coefficient of variation (CV) 5.3% and 15.8%; and intraclass correlation coefficient (ICC) 0.8 and 0.4 for CBFv and ARI, respectively. Further work is required to assess the use of alternative sites to the middle cerebral artery (MCA) for the assessment of CBFv and ARI using HH rather than FH techniques and the applicability of this methodology in patient populations.
Ultrasound in medicine & biology 07/2012; 38(10):1839-44. · 2.02 Impact Factor
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ABSTRACT: Cerebral autoregulation (CA) describes the mechanism responsible for maintaining cerebral blood flow (CBF) relatively constant, despite changes in mean arterial blood pressure (ABP). This paper introduces a novel method for assessing CA using magnetic resonance imaging (MRI). Images are rapidly and repeatedly acquired using a gradient-echo echo-planar imaging pulse sequence for a period of 4 minutes, during which a transient decrease in ABP is induced by rapid release of bilateral thigh cuffs. The method was validated by comparing the observed MRI signal intensity change with the CBF velocity change in the middle cerebral arteries, as measured by transcranial Doppler (TCD) ultrasound, using a standardized thigh cuff maneuver in both cases. Cross-correlation analysis of the response profiles from the left and right hemispheres showed a greater consistency for MRI measures than for TCD, both for interhemisphere comparisons and for repeated measures. The new MRI method may provide opportunities for assessing regional autoregulatory changes following acute stroke, and in other conditions in which poor autoregulation is implicated.
Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 12/2010; 31(5):1302-10. · 5.46 Impact Factor
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ABSTRACT: The baroreflex pathway has a vascular and a neural segment, both being modulated by variations in peripheral blood pressure (BP). Besides overall baroreceptor sensitivity (BRS), defined as the spectral relationship between changes in peripheral BP and R-R interval within the frequency band of 0.05-0.15 Hz, vascular and neural segment contributions to the overall BRS can be distinguished. We test the hypothesis that changes in overall BRS following a postural maneuver mainly originate from the vascular (peripheral pressure to carotid artery diameter) rather than the neural segment (carotid artery diameter to R-R interval).
Peripheral pressure (Finapress), carotid artery diameter (ultrasound in B-/M-mode) and electrocardiogram values of 20 young subjects in supine and upright-seated postures were recorded simultaneously. Transfer gains were computed for the segmental and overall responses.
Postural change significantly increases peripheral BP and carotid artery diameter. The vascular segment has a uniform spectral distribution. Statistical analyses revealed that postural change decreased overall (p < 0.004) and vascular (p < 0.0001) transfer gains, but did not modify neural gain.
Unlike the neural segment, the vascular segment is frequency non-specific. The decrease in overall BRS due to a postural change is mainly explained by the reduced transfer gain of the vascular segment.
Journal of Vascular Research 03/2009; 46(5):469-77. · 2.65 Impact Factor
