Impaired dynamic cerebral autoregulation in middle cerebral artery stenosis

Abstract

Background and purpose: Analysis of dynamic cerebral autoregulation during transient falls in blood pressure is considered a sensitive and convenient method for evaluating patients with carotid artery stenosis. To this point, there have been few reports on the efficacy of using the thigh cuffs technique to analyse middle cerebral artery (MCA) stenosis. If it could be determined whether cerebral blood flow can be maintained (autoregulated) during sudden falls in arterial blood pressure (ABP), then it might be possible to identify patients with MCA stenosis who are at risk of stroke.

Methods: We used the thigh cuff technique to estimate dynamic cerebral autoregulation in 57 patients with MCA stenosis and 72 normal controls. After a stepwise fall in arterial blood pressure, we determined the rate of the rise of MCA blood velocity and compared it with the rate of the rise of arterial blood pressure. In this manner, the dynamic cerbral autoregulation of 11 patients undergoing MCA M1 stent angioplasty was estimated both pre- and post-operation.

Results: The autoregulatory index (ARI) was significantly reduced in patients with stenosed/occluded MCA (3.24 ± 1.52), as compared with normal controls (5.25 ± 1.39; p<0.001) (results reported as mean ± SD). Poor ARI values are usually observed in patients with a higher degree of stenosis and particularly in patients with insufficient collateral compensation. ARI was significantly reduced in severe stroke patients (modified ranking scale≥1), as compared with asymptomatic or TIA patients (p<0.05). After MCA stent angioplasty was performed, there was a significant improvement in ARI in 11 subjects, which caused a mean increase in ARI from 2.08 ± 1.10 to 3.80 ± 1.36 (p=0.008).

Conclusions: Dynamic cerebral autoregulation is impaired in patients with middle cerebral artery stenosis. Assessing dynamic cerebral autoregulation may allow a subgroup of patients with MCA stenosis who are at risk of hemodynamic stroke to be identified. Dynamic cerebral disautoregulation in patients with severe MCA stenosis is mostly remedied by stent angioplasty.     

动脉粥样硬化相关大脑中动脉狭窄支架植入血管成形术后再狭窄发生情况及危险因素分析

目的 探讨动脉粥样硬化(atherosclerosis,AS)相关大脑中动脉(middle cerebral artery,MCA)狭窄支架植入血管成形术后再狭窄发生情况及危险因素分析。方法 本研究纳入对象为2013年2月-2017年2月于本院行支架植入血管成形术治疗的122例AS相关MCA狭窄患者,术后随访2年; 根据计算机断层扫描血管造影(CTA)以及数字减影血管造影(DSA)检查术后再狭窄发生情况,分别设为再狭窄组与正常组,调查疾病史、狭窄情况、支架植入等病历资料,进行单因素及多因素logistic回归分析。结果 122例AS相关MCA狭窄术后动脉再狭窄25例,再狭窄率20.49%; 2组吸烟史、合并高血压病、糖尿病、高脂血症、术前动脉狭窄程度、饮酒史、动脉狭窄Moil分型、年龄有明显差异(P<0.05); 2组病变血管长度、支架种类、性别无明显差异(P>0.05); 多因素logistic回归分析显示,吸烟史(OR=3.443,95%CI=1.125～11.254)、合并高血压病(OR=4.827,95%CI=1.432～16.763)、合并糖尿病(OR=3.644,95%CI=1.243～12.043)、合并高脂血症(OR=3.923,95%CI=1.443～13.652)、术前动脉狭窄程度>75%(OR=2.787,95%CI=1.032～9.691)是AS相关MCA狭窄支架植入血管成形术后再狭窄的独立危险因素。结论 AS相关MCA狭窄支架植入血管成形术后容易出现动脉再狭窄,吸烟史、合并高血压病、合并糖尿病、合并高脂血症、术前动脉狭窄程度>75%均会增加其复发风险。     

Assessment of the thigh cuff technique for measurement of dynamic cerebral autoregulation

BACKGROUND AND PURPOSE: Dynamic methods of measuring cerebral autoregulation have become an accepted alternative to static evaluation. This article aims to describe a set of data collected from healthy volunteers by a dynamic method, the purpose being to qualify and quantify expected results for those who may be designing a study using this technique. METHODS: Cerebral blood flow velocity (CBFV) (measured by transcranial Doppler) and arterial blood pressure (Finapres) were recorded in 16 normal subjects before, during, and after the induction of a blood pressure drop (release of bilateral thigh cuffs). This procedure was repeated 6 times for each subject. A mathematical model was applied to the data to generate an autoregulatory index (ARI) with values between 0 and 9. RESULTS:The ARI values for this sample population follow a normal distribution, with a mean+/-SD of 4.98+/-1.06 (n=15). Analysis of the cumulative mean ARI values of all subjects showed an exponential-type convergence of ARI toward the sample mean as the number of test iterations increased. The population average blood pressure drop on thigh cuff release was 26.4+/-7.1 mm Hg (n=16), occurring in 4.6+/-1. 7 seconds. The corresponding population average drop for CBFV was 15. 6+/-5.8 cm/s, taking 2.5+/-1.0 seconds. No significant trend was noted in the measurements as the number of test iterations increased. The correlation between the predicted and actual CBFV, having a mean value of 0.76+/-0.19, showed evidence of a nonlinear relationship to ARI values. Significant correlation was also found between ARI and (1) arterial blood pressure before cuff release and (2) the magnitude of the drop in CBFV on cuff release. CONCLUSIONS: The distribution of ARI values is not significantly different from normal. At least 3 iterations of the test procedure should be performed and averaged to obtain the mean ARI for each subject. There is no significant evidence of physiological accommodation as the number of test iterations increases. The effects of mean blood pressure and the magnitude of the change in CBFV should be considered as possible covariates when ARI data are analyzed.     

Elective stenting for symptomatic middle cerebral artery stenosis presenting as transient ischaemic deficits or stroke attacks: short term arteriographical and clinical outcome

BACKGROUND: Although stent assisted angioplasty is an effective treatment for coronary and peripheral arterial disease, its efficacy in intracranial arteriosclerotic disease has not been verified. OBJECTIVES: To assess the radiographic and clinical outcome of stent assisted angioplasty for symptomatic middle cerebral artery (MCA) stenosis. METHODS: We attempted stent assisted angioplasty in 14 patients with symptomatic high grade stenosis (>60%) on the proximal portion of the MCA, who had experienced either recurrent transient ischaemic attacks (TIAs) resistant to medical therapy or one or more stroke attacks. Patient records were analysed for angiographic characteristics, degree of stenosis, pre-procedural regimen of anti-platelet and/or anti-coagulation agents, use of devices, procedure related complications, pre-operative and post-operative single photon emission computed tomography (SPECT) findings, and clinical and radiographic outcomes. RESULTS: Stent assisted angioplasty was successfully performed in 8 of 14 patients without any serious complications and unsuccessful in 2 of 14 patients due to the tortuous curve of the internal carotid artery siphon. Four patients had complications. Two patients had an arterial rupture; one patient was rescued by an additional stent and balloon tamponade, the other patient died. Complications in the other two patients included thrombotic occlusion and distal thrombosis. Residual stenosis was less than 50% in diameter in all the patients. All eight patients who underwent follow up cerebral angiography had no restenosis. Follow up SPECT showed improved perfusion in the affected MCA territory in all the tested patients with TIA and in one of three stroke patients. Using the modified Rankin Scale at follow up, four of five TIA patients and five of six stroke patients were assessed as functionally improved or having a stable clinical status. CONCLUSION: Although the re-stenosis rate in stent assisted angioplasty seems to be better than in primary balloon angioplasty as reported previously, the complication rate is still high. Elective stenting is an alternative therapeutic method for the prevention of secondary ischaemic stroke in stroke patients with MCA stenosis, and seems to be a potentially effective but also hazardous therapeutic technique in patients with recurrent TIAs. This study indicates the need for randomised control trial data of this intervention. Additionally, long term follow up data and additional clinical experience are required to assess the durability of this procedure.     

Dynamics of cerebral blood flow autoregulation in hypertensive patients

In hypertensive patients, the upper and lower limits of cerebral autoregulation are shifted to higher levels. However, the dynamics of cerebral autoregulation in hypertensive patients are less well known. We compared the dynamics of cerebral autoregulation in 21 treated hypertensive patients (13 men and 8 women; mean age: 48.9+/-13.6 years) and in 21 normotensive subjects (13 men and 8 women; mean age: 51+/-14.5 years) by transcranial Doppler (TCD) of the middle cerebral artery (MCA) during the acute decrease in blood pressure induced by standing up after 2 min in squatting position. MCA maximal outline blood flow velocity (FV), blood pressure (Finapres) and end-tidal PCO2 were continuously monitored and computerised. A cerebral vascular resistance index (CR) was calculated as follows: mean arterial BP/MCA mean FV with normalised changes in CR per second during the blood pressure decrease (CR slope). The CR slope reflecting the rate of cerebral autoregulation did not differ between the two groups and within the hypertensive patients [well controlled (8 patients) and not controlled (13 patients)]. The time to maximum decrease of CR (T1) and the time to full recovery of CR after the initial drop (T2) were also similar in the two groups (controls T1: 11.3+/-3.1 s, T2: 12+/-5.9 s; hypertensive T1: 11.7+/-2.5 s, T2: 10.7+/-4.5 s) and within hypertensive patients. These findings suggest that the dynamics of cerebral autoregulation are well preserved in hypertensive patients, with no difference according to the efficiency of treatment of hypertension.     

Dynamic cerebral autoregulation and beat to beat blood pressure control are impaired in acute ischaemic stroke

OBJECTIVES: Hypertension and chronic cerebrovascular disease are known to alter static cerebral autoregulation (CA) but the effects of acute stroke on dynamic CA (dCA) have not been studied in detail. Those studies to date measuring dCA have used sympathetically induced blood pressure (BP) changes, which may themselves directly affect dCA. This study assessed whether dCA is compromised after acute stroke using spontaneous blood pressure (BP) changes as the stimulus for the dCA response. METHODS: 56 patients with ischaemic stroke (aged 70 (SD 9) years), studied within 72 hours of ictus were compared with 56 age, sex, and BP matched normal controls. Cerebral blood flow velocity was measured using transcranial Doppler ultrasound (TCD) with non-invasive beat to beat arterial BP levels, surface ECG, and transcutaneous CO(2) levels and a dynamic autoregulatory index (dARI) calculated. RESULTS: Beat to beat BP, but not pulse interval variability was significantly increased and cardiac baroreceptor sensitivity (BRS) decreased in the patients with stroke. Dynamic CA was significantly reduced in patients with stroke compared with controls (strokes: ARI 3.8 (SD 2.2) and 3.2 (SD 2.0) for pressor and depressor stimuli respectively v controls: ARI 4.7 (SD 2.2) and 4.5 (SD 2.0) respectively (p<0.05 in all cases)). There was no difference between stroke and non-stroke hemispheres in ARI, which was also independent of severity of stroke, BP, BP variability, BRS, sex, and age. CONCLUSION: Dynamic cerebral autoregulation, as assessed using spontaneous transient pressor and depressor BP stimuli, is globally impaired after acute ischaemic stroke and may prove to be an important factor in predicting outcome.     

Serial changes in static and dynamic cerebral autoregulation after acute ischaemic stroke

BACKGROUND: The longitudinal changes in static and dynamic cerebral autoregulation (CA) following acute ischaemic stroke are unknown and were assessed in this study. METHODS: Fifty-four ischaemic stroke patients were studied within 96 h of ischaemic stroke and again 7-14 days later, using transcranial Doppler techniques to measure CA. Results were compared to an age-, sex- and blood pressure (BP)-matched control group. Static BP pressor stimulus was produced by thigh cuff inflation and dynamic stimulus by rapid thigh cuff release. RESULTS: Dynamic, but not static, CA was globally impaired at initial (mean dynamic CA index 3.9 +/- 3.1 vs. 6.2 +/- 2.3, p < 0.005) and follow-up studies (dynamic CA 3.9 +/- 2.8 vs. 6.2 +/- 2.3, p < 0.01) in stroke patients compared to controls. Static CA was similar in stroke patients and controls and was unchanged during follow-up. CONCLUSIONS: Dynamic, but not static, CA is impaired after acute ischaemic stroke and remains abnormal for at least 1-2 weeks post ictus. These changes are present in both the affected and non-affected hemispheres and are unrelated to previous antihypertensive treatment, baseline BP levels or BP changes after stroke, age or stroke type.     

Cerebral blood flow and dynamic cerebral autoregulation during ethanol intoxication and hypercapnia.

More than one-third of patients diagnosed with head injury are intoxicated with ethanol. Most clinical and animal studies have shown alcohol to have a deleterious impact in the setting of cerebrovascular trauma; however, there are also data showing neuroprotective effects in low ethanol doses. Human studies using imaging modalities suggest that small doses of alcohol produce cerebral vasodilatation and higher doses cerebral vasoconstriction. The aim of this study was to investigate the effect of ethanol intake on dynamic cerebral autoregulation and velocities in the middle cerebral arteries, and compare these changes with the effects of hypercapnia. Dynamic cerebral autoregulation and cerebral blood flow velocities were analysed before and after alcohol intake (1.1 g/kg of body weight) in six adult volunteers. Cerebral blood flow velocities in both middle cerebral arteries were monitored continuously by transcranial Doppler. A value for dynamic cerebral autoregulation was calculated from the rate of increase in middle cerebral artery velocities after a rapid-step decrease in arterial blood pressure. A sudden decrease in blood pressure was achieved by the release of previously inflated large blood pressure cuffs around the subject's thighs. Three volunteers were also tested before alcohol intake with CO(2) challenge (breathing 6% CO(2)) during the autoregulation procedure. Blood alcohol level reached 90 mg/dl approximately 60 min after ethanol ingestion. Cerebral blood velocities increased by 8% from baseline for uncorrected end-tidal (et) CO(2) and by 24% for correction to et CO(2)=40. Dynamic cerebral autoregulation measured as an autoregulation index decreased from 4.3+/-1.3 to 2.9+/-1.1 (p=0.089), which did not reach statistical significance. During hypercapnic conditions, dynamic cerebral autoregulation dropped from 4+/-0.8 to 0.9+/-0.9. In conclusion, mild alcohol intoxication caused cerebral vasodilatation with a subsequent increase in cerebral blood flow of 8-24%. Dynamic cerebral autoregulation was not found to be significantly impaired by ethanol. Hypercapnia almost completely destroys the physiological autoregulatory mechanism. A mild hyper-ventilation to etCO(2)=34-36 may be a compensatory contra-measure for ethanol-induced vasodilatation in the setting of head trauma.     

Dynamic but not static cerebral autoregulation is impaired in acute ischaemic stroke

It remains unclear as to whether dynamic and static cerebral autoregulation (CA) are impaired in acute ischaemic stroke, and whether these changes are related to stroke subtype. This could have important implications with regard to post-stroke prognosis and the management of blood pressure (BP) in the acute post-ictal period. Using transcranial Doppler ultrasonography and non-invasive manipulation of BP, we compared both mechanisms in 61 patients with ischaemic stroke within 96 h of ictus, and 54 age- and sex-matched controls. There was no difference in static and dynamic CA indices between the various stroke subtypes. Combining all stroke subtypes dynamic autoregulation, as measured using thigh cuff release, was significantly impaired in both the affected and non-affected stroke hemispheres compared to controls (mean autoregulation index 4.1 +/- 3.3, 4.8 +/- 3.1 and 6.2 +/- 2.3, respectively, p < 0.05). By comparison static autoregulation, assessed using isometric hand grip and thigh cuff inflation, was not significantly different. In conclusion, dynamic but not static CA appears to be globally impaired in acute ischaemic stroke. This deserves further study and may identify possibilities for therapeutic intervention.     

Cerebral autoregulation is preserved in multiple system atrophy: A transcranial Doppler study.

Patients with multiple system atrophy (MSA) present large changes in blood pressure (BP) due to autonomic disturbances. We analyzed how this change may influence dynamic cerebral autoregulation (DCA). Simultaneous recordings of arterial BP (Finapres) and middle cerebral artery (MCA) blood flow velocity (BFV) (transcranial Doppler) were performed in 10 patients with MSA (61 +/- 12 yr of age) and 12 healthy volunteers (61 +/- 11 yr of age): cerebral BFV response to oscillations in mean BP was studied in the supine position by cross-spectral analysis of mean BP and mean MCA BFV. The DCA was also studied during the decrease in BP the first seconds when standing up from a sitting position by the assessment of the cerebrovascular resistance index (CR; mean BP/mean MCA BFV ratio). The MCA BFV/BP cross-spectral analysis showed a phase for the mid-frequency band (0.07-0.2 Hz) significantly larger in MSA, suggesting more active autoregulation in response to larger changes in BP. Changes in CR reflecting the rate of autoregulation, when standing did not differ between the two groups. These data suggest that dynamic cerebral autoregulation is preserved in MSA.     

Transcranial Doppler sonographic studies of cerebral autoregulation in Shy-Drager syndrome

Summary A study is reported of mean arterial blood pressure and heart rate in four patients suffering from Shy-Drager syndrome. Blood flow velocity in the middle cerebral artery (MCA) was recorded by transcranial Doppler sonography. Concomitant changes in cerebral blood flow and the effect of cerebral autoregulation were thus examined. During tilt (60°, head up) mean arterial blood pressure decreased by 40 mm Hg or 35%, while MCA blood flow velocity dropped by 14 cm/s or 28% (mean values). The lower percentage reduction in flow velocity may indicate a preserved cerebral autoregulation in central autonomic insufficiency.     

Wingspan stenting of symptomatic middle cerebral artery stenosis and perioperative evaluation using high-resolution 3 Tesla MRI

High-resolution MRI (HR MRI) was employed to study intracranial arterial walls in a patient who underwent angioplasty and stenting for middle cerebral artery (MCA) stenosis using the Wingspan stent (Boston Scientific, Natick, MA, USA). HR MRI clearly depicted the wall structure of the MCA. As a complementary method, HR MRI may improve intracranial atherosclerotic stenosis diagnosis and therapy.     

Bendrofluazide fails to reduce elevated blood pressure levels in the immediate post-stroke period

INTRODUCTION: Blood pressure (BP) levels, beat-to-beat blood pressure variability, dynamic cerebral autoregulation and cardiac baroreceptor sensitivity are frequently abnormal following acute stroke and are associated with an adverse short- and long-term prognosis. Thiazide diuretics are effective antihypertensive agents in preventing primary and secondary stroke, but their hypotensive and cerebral autoregulatory effects in the immediate post-stroke period have not been studied. METHODS: Thirty-seven hypertensive neuroradiologically proven ischaemic stroke patients were randomized in a double-blind, placebo controlled, parallel group study to bendrofluazide 2.5 mg daily or matching placebo, within 96 h of stroke onset, for a 7-day period. Casual and non-invasive beat-to-beat arterial BP levels, cerebral blood flow velocity, ECG and transcutaneous carbon dioxide levels were measured within 70 +/- 20 h of cerebral infarction and again 7 days later. Dynamic cerebral autoregulatory indices, pulse interval, BP variability and cardiac baroreceptor sensitivity were also calculated. RESULTS: Small, non-significant falls were seen in casual and beat-to-beat BP levels over the 7-day period in both active and placebo-treated patients with no differences between treatments. No significant changes were seen in dynamic cerebral autoregulation or in cardiac baroreceptor sensitivity during the follow-up in either group. CONCLUSION: Following acute ischaemic stroke, the standard dose of bendrofluazide at 2.5 mg daily in this study sample did not lower systemic BP levels over the subsequent 7-day period. There was no evidence that bendrofluazide significantly altered cerebral autoregulation or improved cardiac baroreceptor sensitivity post-ictus. Bendrofluazide appears to be an ineffective hypotensive agent at the standard dosage in the initial post-stroke period.     

颈动脉支架术高灌注损伤因素分析

目的 探讨颈内动脉狭窄支架置入术后高灌注损伤的危险因素.方法 颈内动脉狭窄经过颈动脉支架成形术治疗的患者中术后出现高灌注损伤12例和未出现高灌注损伤的56例患者的临床资料进行分析,研究高灌注损伤与高血压、糖尿病、狭窄程度、侧枝代偿情况、血压变化情况、狭窄同侧大脑中动脉血流速度变化的相关性.结果 结果 提示狭窄程度(B=0.637;P=0.034;OR=1.891)、侧枝代偿情况(B=-1.955;P=0.021;OR=0.142)、血压变化(B=-1.818;P=0.011;OR=0.162)和血流速度的变化(B=1.278;P=0.031;OR=3.59)与高灌注损伤密切相关.结论 患者的颈动脉狭窄程度越高,侧枝循环代偿越差,术后血压控制不好,术后同侧大脑中动脉的血流速度越快,则高灌注损伤的危险就越大.     

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.     

Dynamic cerebral autoregulation in stroke patients with a central sympathetic deficit

Gierthmühlen J, Allardt A, Sawade M, Baron R, Wasner G. Dynamic cerebral autoregulation in stroke patients with a central sympathetic deficit.
Acta Neurol Scand: 2011: 123: 332–338.
© 2010 John Wiley & Sons A/S. Objective – To investigate the functional role of the sympathetic innervation on cerebral autoregulation. Materials and methods – Seventeen patients with infarction of the dorsolateral medulla oblongata affecting central sympathetic pathways (Wallenberg′s syndrome) and 21 healthy controls were included in the study. Cerebral blood flow velocity (CBFV) in the medial cerebral artery was investigated using transcranial Doppler ultrasound during decrease in cerebral perfusion pressure induced by leg‐cuff test and tilt table. Results – Upon leg‐cuff test, changes of cerebral blood flow and mean arterial blood pressure as well as autoregulatory index did not differ between patients or controls. No differences were found in changes of CBFV, mean arterial blood pressure and heart rate between patients or controls during the tilt table test. Conclusions – We suggest that the sympathetic nervous system does not have an influence on cerebral autoregulation after decrease in perfusion pressure under normotonous conditions.     

Association between intracranial, arterial pulse pressure amplitudes and cerebral autoregulation in head injury patients

OBJECTIVE: To explore whether intracranial pulse pressure amplitudes relate to arterial pulse pressure amplitudes and whether correlations between time-related changes in intracranial and arterial pulse pressure amplitudes associate with indices of cerebral autoregulation. METHODS: A total of 257 continuous and simultaneous intracranial pressure (ICP), arterial blood pressure (ABP) and middle cerebral artery (MCA) blood velocity recordings were obtained 1-14 days after ictus in 76 traumatic head injury patients and analysed retrospectively. Clinical outcome was assessed using the Glasgow outcome scale (GOS). Pulse pressure amplitudes of corresponding single ICP and ABP waves were correlated in consecutive 200 wave pairs. Mean ICP, mean ABP and mean ICP wave amplitudes, and mean and systolic MCA blood flow velocities, were computed in consecutive 6 second time windows. The indices of cerebral autoregulation PRx (moving correlation between mean ICP and mean ABP), and Mx and Sx (moving correlation between mean and systolic MCA blood velocity and cerebral perfusion pressure) were calculated over 4 minute periods and averaged over each recording. RESULTS: Intracranial pulse pressure amplitudes were not related to arterial pulse pressure amplitudes (mean of Pearson's correlations coefficients: 0.04). Outcome was related to mean ICP, PRx and Sx (p 相似文献   

2型糖尿病患者无症状的大脑中动脉狭窄的危险因素分析

目的 探讨住院2型糖尿病患者无症状大脑中动脉（MCA）狭窄的相关危险因素。方法回顾性总结227例2型糖尿病住院患者的病历资料，排除合并中风或中风史以及其他颅内疾病患者。用TCD诊断MCA狭窄。结果227例患者中MCA狭窄者共61例，狭窄率（26．9％），狭窄组病人年龄、病程、收缩压、尿酸水平、合并高血压和心电图异常率明显高于非狭窄组；Logistic回归分析显示糖尿病病人的病程以及合并高血压是无症状颅内动脉狭窄的独立危险因素。结论糖尿病病程延长及合并高血压是无症状MCA狭窄的独立危险因素。     

Acute exposure to normobaric mild hypoxia alters dynamic relationships between blood pressure and cerebral blood flow at very low frequency.

Acute hypoxia directly causes cerebral arteriole vasodilation and also stimulates peripheral chemoreceptors to change autonomic neural activity. These changes may alter cerebral vascular modulation. We therefore hypothesized that dynamic cerebral autoregulation would be altered during acute exposure to hypoxia. Fifteen healthy men were examined under normoxic (21%) and hypoxic conditions. Oxygen concentrations were decreased in stepwise fashion to 19%, 17%, and 15%, for 10 mins at each level. Mean blood pressure (MBP) in the radial artery was measured via tonometry, and cerebral blood flow velocity (CBFV) in the middle cerebral artery was measured by transcranial Doppler ultrasonography. Dynamic cerebral autoregulation was assessed by spectral and transfer function analysis of beat-by-beat changes in MBP and CBFV. Arterial oxygen saturation decreased significantly during hypoxia, while end-tidal CO2 and respiratory rate were unchanged, as was steady-state CBFV. With 15% O2, very-low-frequency power of MBP and CBFV variability increased significantly by 185% and 282%, respectively. Moreover, transfer function coherence (21% O2, 0.46+/-0.04; 15% O2, 0.64+/-0.04; P=0.028) and gain (21% O2, 0.61+/-0.05 cm/secs/mm Hg; 15% O2, 0.86+/-0.08 cm/secs/mm Hg; P=0.035) in the very-low-frequency range increased significantly by 53% and 48% with 15% O2, respectively. However, these indices were unchanged in low- and high-frequency ranges. Acute hypoxia thus increases arterial pressure oscillations and dependence of cerebral blood flow (CBF) fluctuations on blood pressure oscillations, resulting in apparent increases in CBF fluctuations in the very-low-frequency range. Hypoxia may thus impair dynamic cerebral autoregulation in this range. However, these changes were significant only with hypoxia at 15% O2, suggesting a possible threshold for such changes.     

Association between intracranial,arterial pulse pressure amplitudes and cerebral autoregulation in head injury patients

Abstract

Objective: To explore whether intracranial pulse pressure amplitudes relate to arterial pulse pressure amplitudes and whether correlations between time-related changes in intracranial and arterial pulse pressure amplitudes associate with indices of cerebral autoregulation.

Methods: A total of 257 continuous and simultaneous intracranial pressure (ICP), arterial blood pressure (ABP) and middle cerebral artery (MCA) blood velocity recordings were obtained 1–14 days after ictus in 76 traumatic head injury patients and analysed retrospectively. Clinical outcome was assessed using the Glasgow outcome scale (GOS). Pulse pressure amplitudes of corresponding single ICP and ABP waves were correlated in consecutive 200 wave pairs. Mean ICP, mean ABP and mean ICP wave amplitudes, and mean and systolic MCA blood flow velocities, were computed in consecutive 6 second time windows. The indices of cerebral autoregulation PRx (moving correlation between mean ICP and mean ABP), and Mx and Sx (moving correlation between mean and systolic MCA blood velocity and cerebral perfusion pressure) were calculated over 4 minute periods and averaged over each recording.

Results: Intracranial pulse pressure amplitudes were not related to arterial pulse pressure amplitudes (mean of Pearson's correlations coefficients: 0.04). Outcome was related to mean ICP, PRx and Sx (p ≤ 0.04, multiple regression analysis). Correlations between intracranial and arterial pulse pressure amplitudes were weakly related to PRx (Pearson's correlation coefficient: 0.16; p=0.01), but were not related to the indices of cerebral autoregulation Mx (Pearson's correlation coefficient: 0.07) and Sx (Pearson's correlation coefficient: 0.04).

Conclusions: In this cohort of pressure recordings, we found no evidence of a correlation between intracranial and arterial blood pressure amplitudes. The correlation appeared not to be related to the state of cerebral autoregulation, although a weak correlation was found with pressure reactivity index PRx.