Predictive Value of Dynamic Cerebral Autoregulation Assessment in Surgical Management of Patients with High-Grade Carotid Artery Stenosis

NO Deficiency Compromises Inter- and Intrahemispheric Blood Flow Adaptation to Unilateral Carotid Artery Occlusion

Carotid artery stenosis (CAS) affects approximately 5-7.5% of older adults and is recognized as a significant risk factor for vascular cognitive impairment (VCI). The impact of CAS on cerebral blood flow (CBF) within the ipsilateral hemisphere relies on the adaptive capabilities of the cerebral microcirculation. In this study, we aimed to test the hypothesis that the impaired availability of nitric oxide (NO) compromises CBF homeostasis after unilateral carotid artery occlusion (CAO). To investigate this, three mouse models exhibiting compromised production of NO were tested: NOS1 knockout, NOS1/3 double knockout, and mice treated with the NO synthesis inhibitor L-NAME. Regional CBF changes following CAO were evaluated using laser-speckle contrast imaging (LSCI). Our findings demonstrated that NOS1 knockout, NOS1/3 double knockout, and L-NAME-treated mice exhibited impaired CBF adaptation to CAO. Furthermore, genetic deficiency of one or two NO synthase isoforms increased the tortuosity of pial collaterals connecting the frontoparietal and temporal regions. In conclusion, our study highlights the significant contribution of NO production to the functional adaptation of cerebrocortical microcirculation to unilateral CAO. We propose that impaired bioavailability of NO contributes to the impaired CBF homeostasis by altering inter- and intrahemispheric blood flow redistribution after unilateral disruption of carotid artery flow.

Assessment of cerebral autoregulatory function and inter-hemispheric blood flow in older adults with internal carotid artery stenosis using transcranial Doppler sonography-based measurement of transient hyperemic response after carotid artery compression

Unhealthy vascular aging promotes atherogenesis, which may lead to significant internal carotid artery stenosis (CAS) in 5 to 7.5% of older adults. The pathogenic factors that promote accelerated vascular aging and CAS also affect the downstream portion of the cerebral microcirculation in these patients. Primary treatments of significant CAS are eversion endarterectomy or endarterectomy with patch plasty. Factors that determine adequate hemodynamic compensation and thereby the clinical consequences of CAS as well as medical and surgical complications of carotid reconstruction surgery likely involve the anatomy of the circle of Willis (CoW), the magnitude of compensatory inter-hemispheric blood flow, and the effectiveness of cerebral microcirculatory blood flow autoregulation. This study aimed to test two hypotheses based on this theory. First, we hypothesized that patients with symptomatic and asymptomatic CAS would exhibit differences in autoregulatory function and inter-hemispheric blood flow. Second, we predicted that anatomically compromised CoW would associate with impaired inter-hemispheric blood flow compensation. We enrolled older adults with symptomatic or asymptomatic internal CAS (>70% NASCET criteria; n = 46) and assessed CoW integrity by CT angiography. We evaluated transient hyperemic responses in the middle cerebral arteries (MCA) after common carotid artery compression (CCC; 10 s) by transcranial Doppler sonography (TCD). We compared parameters reflecting autoregulatory function (e.g., transient hyperemic response ratio [THRR], return to baseline time [RTB], changes of vascular resistance) and inter-hemispheric blood flow (residual blood flow velocity). Our findings revealed that CAS was associated with impaired cerebral vascular reactivity. However, we did not observe significant differences in autoregulatory function or inter-hemispheric blood flow between patients with symptomatic and asymptomatic CAS. Moreover, anatomically compromised CoW did not significantly affect these parameters. Notably, we observed an inverse correlation between RTB and THRR, and 49% of CAS patients exhibited a delayed THRR, which associated with decreased inter-hemispheric blood flow. Future studies should investigate how TCD-based evaluation of autoregulatory function and inter-hemispheric blood flow can be used to optimize surgical techniques and patient selection for internal carotid artery revascularization.

Impaired Dynamic Cerebral Autoregulation in Patients With Cerebral Venous Sinus Thrombosis: Evaluation Using Transcranial Doppler and Silent Reading Stimulation

OBJECTIVE

Cerebral venous sinus thrombosis (CVST) may impair dynamic cerebral autoregulation (dCA) of the middle cerebral artery (MCA). However, most studies have focused on dCA of the MCA; a few studies are based on the posterior cerebral artery (PCA) during silent reading and neurovascular coupling (NVC). This study explored the effects of CVST on dCA of the MCA and PCA during silent reading and NVC.

METHODS

From January 2021 to August 2022, 60 CVST patients and 30 controls were enrolled in this study. Non-invasive continuous beat-to-beat blood pressure, cerebral blood flow velocity and other associated information on the MCA and PCA during silent reading were collected using a transcranial Doppler. NVC assessment was performed by opening and closing the eyes periodically based on voice prompts, and eye-opening visual stimulation was achieved by silently reading Chinese tourism materials. Visual stimulation signals can selectively activate Brodmann's areas 17, 18, and 19 of the occipital when reading silently with open eyes, prompting them to release neurotransmitters and dilate PCA. dCA was determined by transfer function analysis.

RESULTS

In dCA of the PCA during silent reading, the CVST group's very low frequency phase was lower than that of the control group (p = 0.047). In NVC, the difference in the indexes of the cerebrovascular conductance and visually evoked flow response of the CVST group were lower than those of the control group (p = 0.017 and p = 0.019, respectively).

CONCLUSION

Compared with the control group, dCA and NVC of the PCA during silent reading were impaired in CVST patients.

Risk of perioperative stroke and cerebral autoregulation monitoring: a systematic review

BACKGROUND

Perioperative stroke, delirium, and cognitive impairment could be related to management and to variations in blood pressure control, cerebral hypoperfusion and raised blood volume. Cerebral autoregulation (CAR) is a mechanism to maintain cerebral perfusion through the control of the vascular tone and hemodynamic reactions in the circulation.

OBJECTIVE

The present systematic review addresses the relationship between impaired CAR and perioperative stroke by evaluating the rate of neurological complications after surgery in studies in which perioperative CAR was tested or monitored.

METHODS

We included randomized clinical trials and prospective observational studies. All studies had adjusted the relative risk, hazard ratio or 95% confidence interval (95%CI) values. These estimation effects were tested using random-effects models. Heterogeneity among the selected studies was assessed using the Higgins and Thompson I² statistics.

RESULTS

The Web of Science, PubMed and EMBASE electronic databases were searched to retrieve articles. A total of 4,476 studies published between 1983 and 2019 were analyzed, but only 5 qualified for the data extraction and were included in the final analysis. The combined study cohort comprised 941 patients who underwent CAR monitoring during surgical procedures. All studies provided information about perioperative stroke, which equated to 16% (158 of 941) of the overall patient population.

CONCLUSION

The present meta-analysis showed evidence of the impact of CAR impairment in the risk of perioperative stroke. On the pooled analysis, blood fluctuations or other brain insults large enough to compromise CAR were associated with the outcome of stroke (odds ratio [OR]: 2.26; 95%CI: 1.54-2.98; p < 0.0001).

Advances in Neuroimaging and Monitoring to Defend Cerebral Perfusion in Noncardiac Surgery

Noncardiac surgery conveys a substantial risk of secondary organ dysfunction and injury. Neurocognitive dysfunction and covert stroke are emerging as major forms of perioperative organ dysfunction, but a better understanding of perioperative neurobiology is required to identify effective treatment strategies. The likelihood and severity of perioperative brain injury may be increased by intraoperative hemodynamic dysfunction, tissue hypoperfusion, and a failure to recognize complications early in their development. Advances in neuroimaging and monitoring techniques, including optical, sonographic, and magnetic resonance, have progressed beyond structural imaging and now enable noninvasive assessment of cerebral perfusion, vascular reserve, metabolism, and neurologic function at the bedside. Translation of these imaging methods into the perioperative setting has highlighted several potential avenues to optimize tissue perfusion and deliver neuroprotection. This review introduces the methods, metrics, and evidence underlying emerging optical and magnetic resonance neuroimaging methods and discusses their potential experimental and clinical utility in the setting of noncardiac surgery.

Perioperative Dynamics of Intracranial B-waves of Blood Flow Velocity in the Basal Cerebral Arteries in Patients with Brain Arteriovenous Malformation

Intracranial B-waves (8-30 mHz) of blood flow velocity (BFV) in the cerebral arteries are observed in various pathologies of the brain. Changes in B-waves of BFV in pathological arteriovenous shunting and "steal" syndrome remain poorly understood. The aim of this study was to evaluate the dynamics of the B-wave amplitude of BFV (BWA) in patients with an arteriovenous malformation (AVM) in the brain. In 38 such patients, cerebral autoregulation (CA) was assessed using a cuff test and transfer function analysis of the mean blood pressure (BP) and BFV in the basal cerebral arteries within the range of Mayer waves (80-120 mHz). BWA was calculated with spectral analysis. Reliable CA impairment was denoted on the AVM side as compared with the contralateral side prior to intervention. BWA was greater on the AVM side (4.5 ± 2.7 cm/s) than on the contralateral side (2.2 ± 1.4 cm/s, p < 0.05). After embolization, there was a reliable improvement (p < 0.05) in CA and a decrease in BWA on the AVM side (2.7 ± 1.8 cm/s). Thus, a considerable increase in BWA on the AVM side that is not induced by BP fluctuations may indicate additional compensation for blood flow under conditions of reduced perfusion pressure. This assumption is supported by a reduction in BWA after AVM embolization.

Hemodynamics in acute stroke: Cerebral and cardiac complications

Hemodynamics is the study of blood flow, where parameters have been defined to quantify blood flow and the relationship with systemic circulatory changes. Understanding these perfusion parameters, the relationship between different blood flow variables and the implications for ischemic injury are outlined in the ensuing discussion. This chapter focuses on the hemodynamic changes that occur in ischemic stroke, and their contribution to ischemic stroke pathophysiology. We discuss the interaction between cardiovascular response and hemodynamic changes in stroke. Studying hemodynamic changes has a key role in stroke prevention, therapeutic implications and prognostic importance in acute ischemic stroke: preexisting hemodynamic and autoregulatory impairments predict the occurrence of stroke. Hemodynamic failure predisposes to the formation of thromboemboli and accelerates infarction due to impairing compensatory mechanisms. In ischemic stroke involving occlusion of a large vessel, persistent collateral circulation leads to preservation of ischemic penumbra and therefore justifying endovascular thrombectomy. Following thrombectomy, impaired autoregulation may lead to reperfusion injury and hemorrhage.

Dynamic cerebral autoregulation is an independent outcome predictor of acute ischemic stroke after endovascular therapy

Background

Endovascular therapy (EVT) is increasingly used to improve cerebral reperfusion after moderate-to-severe acute ischemic stroke (AIS). However, the influence of hemodynamic factors on clinical outcome is still unclear after EVT. Dynamic cerebral autoregulation (dCA) is an important brain reserve mechanism and is impaired after AIS. This study aimed to explore the role of dCA in predicting the outcome of AIS patients after EVT.

Methods

AIS patients with severe stenosis/occlusion of unilateral middle cerebral artery (MCA) or internal carotid and treatment with EVT were enrolled to receive dCA examinations at the 24 h, 72 h and 7th day after stroke onset. Healthy volunteers were also recruited as controls. DCA was recorded from spontaneous fluctuations of blood pressure and MCA flow velocity. Transfer function analysis was used to derive dCA parameters, including phase difference (PD) and coherence in the low-frequency range (0.06–0.12 Hz). The clinical outcome was measured using the modified Rankin Scale (mRS) at 90 days after onset. Multivariate logistic regression was performed to reveal the correlation between dCA and clinical outcomes. The receiver operation characteristics (ROC) curve was performed to determine the cut-off point of PD.

Results

A total of 62 AIS patients and 77 healthy controls were included. Compared with controls, dCA were impaired bilaterally till to 7th day after onset in patients, presenting as much lower PD value on the ipsilateral side. During follow-up, we found that PD on the ipsilateral side at 24 h after onset was significantly lower in patients with unfavourable outcome (n = 41) than those with favourable outcome (n = 21), even after adjustment of confounding factors (p = 0.009). ROC curve analysis revealed that PD < 26.93° was an independent predictor of unfavourable-outcome.

Conclusion

In AIS patients after EVT, dCA was impaired on both sides over the first 7 days. PD on the ipsilateral side at 24 h after onset is an independent unfavourable-outcome predictor for AIS after EVT.

Cerebrovascular function in patients with chronic obstructive pulmonary disease: the impact of exercise training

This study examined cerebral blood flow (CBF) and its regulation before and after a short-term periodized aerobic exercise training intervention in patients with chronic obstructive pulmonary disease (COPD). Twenty-eight patients with COPD (forced expiratory volume in 1 s/forced vital capacity < 0.7 and <lower limit of normal) and 24 healthy control subjects participated in the study. Extracranial CBF (duplex ultrasound), middle cerebral artery velocity (MCAv; transcranial Doppler), cerebrovascular reactivity to hypocapnia and hypercapnia, and dynamic cerebral autoregulation (transfer function analysis) were quantified. These tests were repeated in both patients with COPD ( n = 23) and control subjects ( n = 20) after 8 wk of periodized upper and lower body aerobic exercise training (3 sessions/wk). At baseline, global extracranial CBF was comparable between the COPD and control groups (791 ± 290 vs. 658 ± 143 ml/min, P = 0.25); however, MCAv was lower in patients with COPD compared with control subjects (46 ± 9 vs. 53 ± 10 cm/s, P = 0.05). Although there were no group differences in dynamic cerebral autoregulation or the MCAv response to hypercapnia, patients with COPD had a lower MCAv response to hypocapnia compared with control subjects (−1.1 ± 1.5 vs. −1.6 ± 1.3 cm·s−1·mmHg−1, P = 0.02). After aerobic training, absolute peak O2 consumption increased in both groups, with a greater improvement in control subjects (1.7 ± 0.4 vs. 4.1 ± 0.2 ml·kg−1·min−1, respectively, P = 0.001). Despite these improvements in peak O2 consumption, there were no significant alterations in CBF or any measures of cerebrovascular function after exercise training in either group. In conclusion, patients with COPD have a blunted cerebrovascular response to hypocapnia, and 8 wk of aerobic exercise training did not alter cerebrovascular function despite significant improvements in cardiorespiratory fitness.

NEW & NOTEWORTHY No study to date has investigated whether exercise training can alter resting cerebral blood flow (CBF) regulation in patients with chronic obstructive pulmonary disease (COPD). This study is the first to assess CBF regulation at rest, before, and after aerobic exercise training in patients with COPD and healthy control subjects. This study demonstrated that while exercise training improved aerobic fitness, it had little effect on CBF regulation in patients with COPD or control subjects.

Cerebral Autoregulation in Stroke

PURPOSE OF REVIEW

Cerebral autoregulation (CA) is a mechanism that maintains cerebral blood flow constant despite fluctuations in systemic arterial blood pressure. This review will focus on recent studies that measured CA non-invasively in acute cerebrovascular events, a feature unique to the transcranial Doppler ultrasound. We will summarize the rationale for CA assessment in acute cerebrovascular disorders and specifically evaluate the existing data on the value of CA measures in relation to clinical severity, guiding management decisions, and prognostication.

RECENT FINDINGS

Existing data suggest that CA is generally impaired in various cerebrovascular disorders. In patients with small vessel ischemic stroke, CA has been shown to be impaired in both hemispheres, whereas in large territorial strokes, CA impairment has been limited to the affected hemisphere. In these latter patients, impaired CA is also predictive of secondary complications such as hemorrhagic transformation and cerebral edema, hence worse functional outcome. In patients with carotid stenosis, impaired CA may also be associated with a higher ipsilateral hemispheric stroke risk. CA is also strongly linked to outcome in patients with intracranial hemorrhage. In patients with intraparenchymal hemorrhage, CA impairment correlated with clinical and imaging severity, whereas in those with subarachnoid hemorrhage, CA measures have a predictive value for development of delayed cerebral ischemia and radiographic vasospasm. Assessment of CA is increasingly more accessible in acute cerebrovascular disorders and promises to be a valuable measure in guiding hemodynamic management and predicting secondary complication, thus enhancing the care of these patients in the acute setting.