The Study Of Assessment On The Severity And Prognosis Of Acute Cerebrovascular Events Based On Flash Visual Evoked Potential

[Background]A cerebrovascular event (stroke) is a clinical syndrome caused by disruption of blood supply to the brain, characterised by rapidly developing signs of focal or global disturbance of cerebral functions, with serious condition leading to death. The stroke includes two types,namely,the hemorrhagic cerebrovascular and the ischemic cerebrovascular diseases, the most common disease is ischemic cerebrovascular diseases. Arteriosclerosis and hypertension are the most commonly basic diseases. vascular malformation and Shedding emboli from Cerebral blood vessel are less common. cerebrovascular accidents are the most common disease in department of neurology,accounting for about70%and90%in city and rural areas,respectively.Severe cerebrovascular accidents are in quick progression and with a high level of death. Without subjective sensation, judging disease severity and prognosis is mainly dependent on scale and iconography.in acute phase, Timely, accurate, objective evaluating the damage degree of brain function and intracranial pressure in seriously cerebrovascular disease has a meaningful significance in guiding the clinical dicision.so far, there is no mature inspection equipment to monitoring the disease condition in the clinic. A stroke, sometimes referred to as a cerebrovascular accident (CVA), cerebrovascular insult (CVI), or colloquially brain attack is the loss of brain function due to disturbance in the blood supply to the brain, especially when it occurs quickly, and is associated with cerebrovascular disease. This can occur following ischemia (lack of blood flow) caused by blockage (thrombosis, arterial embolism), or a hemorrhage of central nervous system (CNS), or intracranial blood-vessels.As a result, the affected area of the brain cannot function normally, which might result in an inability to move one or more limbs on one side of the body, failture to understand or formulate speech, or an vision impairment of one side of the visual field.A stroke is a medical emergency and can cause permanent neurological damage or death. Risk factors for stroke include old age, high blood pressure, previous stroke or transient ischemic attack (TIA), diabetes, high cholesterol, tobacco smoking and atrial fibrillation. High blood pressure is the most important modifiable risk factor of stroke. Cerebrovascular diease was the second leading cause of death worldwide in2004. An ischemic stroke is occasionally treated in a hospital with thrombolysis (also known as a "clot buster"), and some hemorrhagic strokes benefit from neurosurgery. Treatment to recover any lost function is termed stroke rehabilitation, ideally in a stroke unit and involving health professions such as speech and language therapy, physical therapy and occupational therapy. Prevention of recurrence may involve the administration of antiplatelet drugs such as aspirin and dipyridamole, control and reduction of high blood pressure, and the use of statins. Selected patients may benefit from carotid endarterectomy and the use of anticoagulants. Strokes can be classified into two major categories:ischemic and hemorrhagic. Ischemic strokes are those that are caused by interruption of the blood supply, while hemorrhagic strokes are the ones which result from rupture of a blood vessel or an abnormal vascular structure. About87%of strokes are ischemic, the remainder being caused by hemorrhage. Some hemorrhages develop inside areas of ischemia ("hemorrhagic transformation"). It is unknown how many hemorrhagic strokes actually start as ischemic stroke. In the1970s the World Health Organization defined stroke as a "neurological deficit of cerebrovascular cause that persists beyond24hours or is interrupted by death within24hours", although the word "stroke" is centuries old. This definition was supposed to reflect the reversibility of tissue damage and was devised for the purpose, with the time frame of24hours being chosen arbitrarily. The24-hour limit divides stroke from transient ischemic attack, which is a related syndrome of stroke symptoms that resolve completely within24hours. With the availability of treatments that, when given early, can reduce stroke severity, many now prefer alternative concepts, such as brain attack and acute ischemic cerebrovascular syndrome (modeled after heart attack and acute coronary syndrome, respectively), that reflect the urgency of stroke symptoms and the need to act swiftly.Stroke symptoms typically start suddenly, over seconds to minutes, and in most cases do not progress further. The symptoms depend on the area of the brain affected. The more extensive the area of brain affected, the more functions that are likely to be lost. Some forms of stroke can cause additional symptoms. For example, in intracranial hemorrhage, the affected area may compress other structures. Most forms of stroke are not associated with headache, apart from subarachnoid hemorrhage and cerebral venous thrombosis and occasionally intracerebral hemorrhage. Various systems have been proposed to increase recognition of stroke. Different findings are able to predict the presence or absence of stroke to different degrees. Sudden-onset face weakness, arm drift (i.e., if a person, when asked to raise both arms, involuntarily lets one arm drift downward) and abnormal speech are the findings most likely to lead to the correct identification of a case of stroke increasing the likelihood by5.5when at least one of these is present). Similarly, when all three of these are absent, the likelihood of stroke is significantly decreased (-likelihood ratio of0.39). While these findings are not perfect for diagnosing stroke, the fact that they can be evaluated relatively rapidly and easily make them very valuable in the acute setting.Proposed systems include FAST (face, arm, speech, and time), as advocated by the Department of Health (United Kingdom) and the Stroke Association, the American Stroke Association, the National Stroke Association (US), the Los Angeles Prehospital Stroke Screen (LAPSS) and the Cincinnati Prehospital Stroke Scale (CPSS). Use of these scales is recommended by professional guidelines. For people referred to the emergency room, early recognition of stroke is deemed important as this can expedite diagnostic tests and treatments. A scoring system called ROSIER (recognition of stroke in the emergency room) is recommended for this purpose; it is based on features from the medical history and physical examination.An evoked he terms visually evoked potential (VEP), visually evoked response (VER) and visually evoked cortical potential (VECP) are equivalent. They refer to electrical potentials, initiated by brief visual stimuli, which are recorded from the scalp overlying visual cortex, VEP waveforms are extracted from the electro-encephalogram (EEG) by signal averaging. VEPs are used primarily to measure the functional integrity of the visual pathways from retina via the optic nerves to the visual cortex of the brain. VEPs better quantify functional integrity of the optic pathways than scanning techniques such as magnetic resonance imaging (MRI).Any abnormality that affects the visual pathways or visual cortex in the brain can affect the VEP. Examples are cortical blindness due to meningitis or anoxia, optic neuritis as a consequence of demyelination, optic atrophy, stroke, and compression of the optic pathways by tumors, amblyopia, and neurofibromatosis. In general, myelin plaques common in multiple sclerosis slow the speed of VEP wave peaks. Compression of the optic pathways such as from hydrocephalus or a tumor also reduces amplitude of wave peaks.the most commonly used stimuli to initiate visual evoked potentials, the methods of recording, the sources of visual potentials, the effects of maturation and acuity, and sample patients, potential or evoked response is an electrical potential recorded from the nervous system of a human or other animal following presentation of a stimulus, as distinct from spontaneous potentials as detected by electroencephalography (EEG), electromyography (EMG), or other electrophysiological recording method.Most of primary visual cortex in humans is located in fissures, not on the cortical surface of the occipital pole. At most, only about the central10degrees of visual field are located on the surface of the occipital pole. Furthermore, the area located on the surface of the occipital pole is quite variable, even between hemispheres of the same individual. Because most electrical potentials are generated in sulci, simultaneously at multiple locations, and because of the vertical cancellation that occurs between upper and lower fields, lateralization of pathology is difficult. Potentials occurring at different cortical locations in vertical and horizontal planes that vary between hemispheres produce paradoxical lateralization and obscures source localization.Evoked potential amplitudes tend to be low, ranging from less than a microvolt to several microvolts, compared to tens of microvolts for EEG, millivolts for EMG, and often close to a volt for ECG To resolve these low-amplitude potentials against the background of ongoing EEG, ECG, EMG, and other biological signals and ambient noise, signal averaging is usually required. The signal is time-locked to the stimulus and most of the noise occurs randomly, allowing the noise to be averaged out with averaging of repeated responses.Signals can be recorded from cerebral cortex, brain stem, spinal cord and peripheral nerves. Usually the term "evoked potential" is reserved for responses involving either recording from, or stimulation of, central nervous system structures. Thus evoked compound motor action potentials (CMAP) or sensory nerve action potentials (SNAP) as used in nerve conduction studies (NCS) are generally not thought of as evoked potentials, though they do meet the above definition. In1934, Adrian and Matthew noticed potential changes of the occipital EEG can be observed under stimulation of light. Ciganek developed the first nomenclature for occipital EEG components in1961. During that same year, Hirsch and colleagues recorded a visual evoked potential (VEP) on the occipital lobe (externally and internally), and they discovered amplitudes recorded along the calcarine fissure were the largest. In1965, Spehlmann used a checkerboard stimulation to describe human VEPs. An attempt to localize structures in the primary visual pathway was completed by Szikla and colleagues. Halliday and colleagues completed the first clinical investigations using VEP by recording delayed VEPs in a patient with retrobulbar neuritis in1972. A wide variety of extensive research to improve procedures and theories has been conducted from the1970s to today. Visually evoked potentials are useful to quantitate nerve dysfunction from retina to visual cortex. VEP recordings are done by a number of methods to evaluate visual pathway function. Choices of which VEP stimuli and protocol to apply need to be made based on the patient’s symptoms, history and other information available. Abnormalities seen in VEPs are symptomatic, but not diagnostic. VEP abnormalities do not specify etiology. For example, retinal disease alone will drastically alter VEPs. Interpretation of VEPs must be considered within the context of the patient’s clinical appearance and information available from other tests and examinations. Whereas stimulus patterns for multifocal electroretinograms (mfERGs) are an array of flickering patterns, multifocal visually evoked potentials (mfVEPs) are better elicited with reversing check patterns (Sutter,2010).Four occipital scalp electrodes are required to record mfVEPs. A common mfVEP montage is to first place two electrodes on the midline. One just below the inion and another3-4centimeters above the inion; and laterally place electrodes4centimeters off the midline several centimeters above inion. The ground lead can be anywhere on the body. See Hood et al.(2008) for suggested International Standard for recording mfERGs.The stimulus for multifocal electroretinograms is a focal pattern stimulation m-sequence modulated flicker (See chapter on The Electroretinogram:Clinical Applications by Donnell Creel). The common stimulus for multifocal visually evoked potentials (mfVEPs) is a dartboard pattern with each sector a contrast reversing check patternflash visual evoked potential(FVEP)is that Exogenous flash stimulate the photosensory cell,producing bioelectricity and successively activate the pathways for vision. NIP-200of Noninvasive monitoring of intracranial pressure could record the Potential response at the place of occipital tuberosity. FVEP can reflect the function of macular area, the optical conductivity in visual pathway and function of visual cortex. FVEP is sensitive to the change in the visual pathway,especially,with the increased intracranial pressure under the condition of Brain tissue necrosis.with induced prolongation of latency, FVEP play an important role in the disease progression and prognosis with the advantage of uninvasive, continuous, timely, convenient prediction on the evolution of disease. Our study mainly focuse on the clinical applicability of the FVEP on the seriousness and prognosis of patients with Critical cerebral vascular disease.[Methods]88patients in the Neurology intensive care unit are divided by two groups,with56cases are large-area cerebral infarction and32cases are Large area cerebral hemorrhage, endpoint events are checked when patients leave the wards,with two endpoints,namely,death and survival.the subjects both are Monitored the condition by FVEP for three day,meanwhile, APACHE score, Glasgow Pittsburgh coma scale and USA National Institutes of Health Stroke Scale (NIHSS) score are also in use. The calculation method for the amount of necrosis of the brain is base on the The volume of infarction.namely,the Infarction area with each layer mutiply the depth of the scanning spacer thickness by layer. The volume of cerebral hemorrhage is dependent on the CT,with fomula raised by Tian:T (mL)=π/6xL(long_axis)xS(short axis)xSlice(slice thickness)(cm).the detection method of FVEP is as follows:Yellow neon light with frequecy1.0Hz,2ms for Flash pulse width and Flash60times per second.the subject lay down,with eye closed, recording electrodes are placed on the occipital tuberosity with upper space of3cm with both sides, reference electrodes are placed on the center of the forehead hairline.ground electrode are on the glabella.we separately measures the latency period of the waves of P2、N2、P3、N3. measured values are based on latency period on each stage of the FVEP. statistical analyses are used to assess the relevance between latency period of each stage and above indictors that can predict the severity of stroke. Data are expressed as means±SD. Statistical analysis was conducted by chi-square test (qualitative data)or T test (quantitative data).All analyses were performed using SPSS11.5statistical software package (SPSS Inc., Chicago, IL, USA) Probability values<0.05were considered statistically significant.[Results]1compare with the survivors, non-survivors are more elderly,having a higher level of headache and with more volume of infarction or hemorrhage.2the relation between the results of FVEP and Rating scales compare with the first day, subjects in the the second and third day have a higher score of APAcHEⅡ、 NIHSS and a lower score of GPCS, with a prolonged latency period.compared with the second day.subjects in the third day have the same result as above.compare with the same time points in the survivors,the non-survivors in the first day have a higher socre of APAcHEⅡ、NIHSS and a lower score of GPCS,with no significance on the prolonged latency period.subjects in the second and third day have a higher socre of APAcHE Ⅱ、NIHSS and a lower score of GPCS,with significance on the prolonged latency period.3correlation analysis between prolonged latency period of FVEP and severity of stroke correlation analysis is carried out between prolonged latency period and the severity of stroke,which N2wave prolonged latency period has a much significant correlation with the Rating scales,with p<=0.000,especially in the third day. N2wave prolonged latency period has a positive correlation with APAcHE Ⅱ、 NIHSS,and a negative correlation with GPCS.4the value of prediction by N2wave prolonged latency period on the prognosis of the patients with severe cerebrovascular diseases. Variables include N2wave prolonged latency period, APAcHE Ⅱ score,NIHSS score and GPCS score,as well as the endpoint events to draw the ROC curve. Maximum Youden index are the point of cut-off. N2wave prolonged latency period has the largest areas in the third under the ROC curve,with a better sensitivity and specificity. APAcHE Ⅱ score has the largest areas in the third under the ROC curve,with a better sensitivity and specificity. NIHSS score has the largest areas in the third under the ROC curve,with a better sensitivity but a worse specificity. GPCS score has the largest areas in the third under the ROC curve,with a general sensitivity but strong specificity.[Conclusion]There are some methods, including Neurological signs, Imaging and electrophysiological examination and Rating scales, play a role in evaluating the prognosis of patients with severe stroke.there are a few studys evaluating the value of FVEP on the disease assessment and prognosis of stroke in China.our study adopts FVEP on88patients in the Neurology intensive care unit in successive three days, while beta,evluating the illness severity score, as well as the correlation analysis with the prognosis. Compare the baseline data between the survival and non-survival,we find the non-survivals are with higher age, morefrequent headache,much more volume of cerebral infarction or hemorrhage.these suggest that the age and intracranial hypertension are important indicators for prognosis.the higher intracranial hypertension,the longer N2wave prolonged latency period.the recent study reveals that the intracranial hypertension predicted by FVEP in accord with sarsinvasive Intracranial hypertension.the result as above suggest that Rating scales and FVEP latency period could accurately evaluate the disease conditon and prognosis.Futher study reveals that FVEP latency periods have a bearing on the severity of disease.especially, N2wave prolonged latency period have a higher correlation,and could reflect the ecrosis of the brain occupying effect and the extent of coma.according the results above.in acute period,the intensity of anomaly of FVEP is in parellel with severity and progression of disease. N2wave prolonged latency period in the third day could reflect the severity and prognosis of stroma to the most degree.Higher scores of APAcHE Ⅱ and NIHSS,lower scores of GPCS,as well as the longer N2wave prolonged latency period,in general,predicts worse clinical outcome. ROC curve has a high popularity in the medical field,the areas under the curve could exactly reflects the authenticity of prognosis,with larger areas indicating the higher value. N2wave prolonged latency period has the largest areas in the third under the ROC curve,with a better sensitivity and specificity. These data suggests that the N2wave prolonged latency period in the third could exactly predict the prognosis of patients,and this is also in accord with physiopathologic process of stroma and the Rating scales.in the view of prognosis,although the areas under the curve of the N2wave prolonged latency period has the smallest areas comparing with other methods, There was no significant difference between them in statistics.so to some extent,the N2wave prolonged latency period could strongly supplement the current methods,with a higher prognostic value.