Regional dynamic cerebral autoregulation across anterior and posterior circulatory territories:A detailed exploration and its clinical implications

Cerebral autoregulation(CA)is the mechanism that maintains stable cerebral blood flow(CBF)despite fluctuations in systemic blood pressure,crucial for brain homeostasis.Recent evidence highlights distinct regional variations in CA between the anterior(carotid)and posterior(vertebrobasilar)circulations.Noninvasive neuromonitoring techniques,such as transcranial Doppler,transfer function analysis,and near-infrared spectroscopy,facilitate the dynamic assessment of CBF and autoregulation.Studies indicate a robust autoregulatory capacity in the anterior circulation,characterized by rapid adjustments in vascular resistance.On the contrary,the posterior circulation,mainly supplied by the vertebral arteries,may have a lower autoregulatory capacity.in acute brain injuries such as intracerebral and subarachnoid hemorrhage,and traumatic brain injuries,dynamic CA can be significantly altered in the posterior circulation.Proposed physiological mechanisms of impaired CA in the posterior circulation include:(1)Decreased sympathetic innervation of the vasculature impairing compensatory vasoreactivity;(2)Endothelial dysfunction;(3)Increased cerebral metabolic rate of oxygen consumption within the visual cortex causing CBFmetabolism(i.e.,neurovascular)uncoupling;and(4)Impaired blood-brain barrier integrity leading to impaired astrocytic mediated release of vasoactive substances(e.g.nitric oxide,potassium,and calcium ions).Furthermore,more research is needed on the effects of collateral circulation,as well as the circle of Willis variants,such as the fetal-type posterior cerebral artery,on dynamic CA.Improving our understanding of these mechanisms is crucial to improving the diagnosis,prognosis,and management of various cerebrovascular disorders.

The utility of therapeutic hypothermia on cerebral autoregulation

Cerebral autoregulation(CA)dysfunction is a strong predictor of clinical outcome in patients with acute brain injury(ABI).CA dysfunction is a potential pathologic defect that may lead to secondary injury and worse functional outcomes.Early therapeutic hypothermia(TH)in patients with ABI is controversial.Many factors,including patient selection,timing,treatment depth,duration,and rewarming strategy,impact its clinical efficacy.Therefore,optimizing the benefit of TH is an important issue.This paper reviews the state of current research on the impact of TH on CA function,which may provide the basis and direction for CA-oriented target temperature management.

The impact of central and obstructive respiratory events on cerebral oxygenation in adults with sleep disordered breathing

Obstructive sleep apnea(OSA)and central sleep apnea(CSA)are two main types of sleep disordered breathing(SDB).While the changes in cerebral hemodynamics triggered by OSA events have been well studied using near-infrared spectroscopy(NIRS),they are essentially unknown in CSA in adults.Therefore,in this study,we compared the changes in cerebral oxygenation between OSA and CSA events in adult patients using NIRS.Cerebral tissue oxygen saturation(StO_(2))in 13 severe SDB patients who had both CSA and OSA events was measured using frequency-domain NIRS.The changes in cerebral StO_(2)desaturation and blood volume(BV)in the¯rst hour of natural sleep were compared between different types of respiratory events(i.e.,277 sleep hypopneas,161 OSAs and 113 CSAs)with linear mixed-effect models controlling for confounders.All respiratory events occurred during non-rapid eye movement(NREM)sleep.We found that apnea events induced greater cerebral desaturations and BV°uctuations compared to hypopneas,but there was no difference between OSA and CSA.These results suggest that cerebral autoregulation in our patients are still capable to counteract the pathomechanisms of apneas,in particularly the negative intrathoracic pressure(ITP)caused by OSA events.Otherwise larger BV°uctuations in OSA compared to CSA should be observed due to the negative ITP that reduces cardiac stroke volume and leads to lower systematic blood supply.Our study suggests that OSA and CSA may have similar impact on cerebral oxygenation during NREM sleep in adult patients with SDB.

COHERENT HEMODYNAMICS SPECTROSCOPY BASED ON A PACED BREATHING PARADIGM-REVISITED

A novel hemodynamic model has been recently introduced,which provides analytical relation-ships between the changes in cerebral blood volume(CBV),cerebral blood flow(CBF),andcerebral metabolic rate of oxy gen(CMRO2),and associat ed changes in the tissue concentrationsof oxy-and deoxy-hemoglobin(AO and AD)measured with near-infrared,spectroscopy(NIRS)[S.Fantini,Neuroimage 85,202-221(2014)].This novel model can be applied tomeasurements of the amplit ude and phase of induced hemodynamic oscillations as a function ofthe frequency of oscillation,realizing the novel technique of coherent hemodynamics spectroscopy(CHS)[S.Fantini,Neuroimage 85,202-221(2014);M.L.Pierro et al.,Neuroimage 85,222-233(2014)]:In a previous work,,we have demonstrated an in vivo application of CiHS on hunanSubjects during paced breat hing[M.L.Pierro et al,Neuroimage 85,222-233(2014)].In thiswork,we present a new analysis of the collected data duringpaced breat hing based on a slightlyrevised formulation of the hemodynamic model and ann efficient fitting procedure.While we haveinitially treated all 12 model parameindeependent,we have found that,in this new in-plementation of CHS,the number of independent is eight.In this article,we identifythe eight independent model parameters and,we show that our previous results are consistentwith the new formulation,once the individual parameters of the earlier analysis are combinedinto the new set of independent parameters.