Prognostic significance of electrophysiological investigations in stroke patients: somatosensory and motor evoked potentials and sympathetic skin response

Analysis of Consciousness Level Using Galvanic Skin Response during Therapeutic Effect

The neurological status of patients in the Intensive Care Units (ICU) is determined by the Glasgow Coma Scale (GCS). Patients in coma are thought to be unaware of what is happening around them. However, many studies show that the family plays an important role in the recovery of the patient and is a great emotional resource. In this study, Galvanic Skin Response (GSR) signals were analyzed from 31 patients with low consciousness levels between GCS 3 and 8 to determine relationship between consciousness level and GSR signals as a new approach. The effect of family and nurse on unconscious patients was investigated by GSR signals recorded with a new proposed protocol. The signals were recorded during conversation and touching of the patient by the nurse and their families. According to numerical results, the level of consciousness can be separated using GSR signals. Also, it was found that family and nurse had statistically significant effects on the patient. Patients with GCS 3,4, and 5 were considered to have low level of consciousness, while patients with GCS 6,7, and 8 were considered to have high level of consciousness. According to our results, it is obtained lower GSR amplitude in low GCS (3, 4, 5) compared to high GCS (7, 8). It was concluded that these patients were aware of therapeutic affect although they were unconscious. During the classification stage of this study, the class imbalance problem, which is common in medical diagnosis, was solved using Synthetic Minority Over-Sampling Technique (SMOTE), Adaptive Synthetic Sampling (ADASYN) and random oversampling methods. In addition, level of consciousness was classified with 92.7% success using various decision tree algorithms. Random Forest was the method which provides higher accuracy compared to all other methods. The obtained results showed that GSR signal analysis recorded in different stages gives very successful GCS score classification performance according to literature studies.

Characterization of Axon Damage, Neurological Deficits, and Histopathology in Two Experimental Models of Intracerebral Hemorrhage

Spontaneous intracerebral hemorrhage (ICH) is one of the most lethal forms of stroke. From the limited previous studies and our preliminary data, white matter is considered a key predictor of the outcome and potential target of recovery. The traditional ICH model induced by injection of autologous blood or bacterial collagenase into striatum (ST) demonstrated a spontaneous functional recovery within one or 2 months. We hypothesis that an internal capsule (IC) lesion might lead to long-term axonal damage and long lasting functional deficits. Thus in this study, a modified internal capsule ICH model was conducted in rats, and the axonal damage, neurological deficits, histopathology as well as electrophysiology were characterized. The finding demonstrated that compared to ST group, the modified IC lesioned model exhibited a relatively smaller lesion volume with consistent axonal loss/degeneration and long-lasting neurological dysfunction at 2 months after ICH. Functionally, the impairment of the mNSS, ratio of contralateral forelimb usage, four limb stand index, contralateral duty cycle and ipsilateral SSEPs amplitude remained significant at 56 days. Structurally, the significant loss of PKCγ in ipsilateral cortical spinal tracts of IC group and the consistent axonal degeneration with several axonal retraction bulbs and enlarged tubular space was observed at 56 days after ICH. This study suggested that a modified IC lesioned model was proved to have long lasting neurological deficits. A comprehensive understanding of the dynamic progression after experimental ICH should aid further successful clinic translation in animal ICH studies, and provide new insights into the role of whiter matter injury in the mechanism and therapeutic targets of ICH.

Acute hypertensive response in patients with intracerebral hemorrhage pathophysiology and treatment

Acute hypertensive response is a common systemic response to occurrence of intracerebral hemorrhage which has gained unique prominence due to high prevalence and association with hematoma expansion and increased mortality. Presumably, the higher systemic blood pressure predisposes to continued intraparenchymal hemorrhage by transmission of higher pressure to the damaged small arteries and may interact with hemostatic and inflammatory pathways. Therefore, intensive reduction of systolic blood pressure has been evaluated in several clinical trials as a strategy to reduce hematoma expansion and subsequent death and disability. These trials have demonstrated either a small magnitude benefit (second intensive blood pressure reduction in acute cerebral hemorrhage trial and efficacy of nitric oxide in stroke trial) or no benefit (antihypertensive treatment of acute cerebral hemorrhage 2 trial) with intensive systolic blood pressure reduction compared with modest or standard blood pressure reduction. The differences may be explained by the variation in intensity of systolic blood pressure reduction between trials. A treatment threshold of systolic blood pressure of ≥180 mm with the target goal of systolic blood pressure reduction to values between 130 and 150 mm Hg within 6 h of symptom onset may be best supported by current evidence.

Somatosensory deficits

The analysis and interpretation of somatosensory information are performed by a complex network of brain areas located mainly in the parietal cortex. Somatosensory deficits are therefore a common impairment following lesions of the parietal lobe. This chapter summarizes the clinical presentation, examination, prognosis, and therapy of sensory deficits, along with current knowledge about the anatomy and function of the somatosensory system. We start by reviewing how somatosensory signals are transmitted to and processed by the parietal lobe, along with the anatomic and functional features of the somatosensory system. In this context, we highlight the importance of the thalamus for processing somatosensory information in the parietal lobe. We discuss typical patterns of somatosensory deficits, their clinical examination, and how they can be differentiated through a careful neurologic examination that allows the investigator to deduce the location and size of the underlying lesion. In the context of adaption and rehabilitation of somatosensory functions, we delineate the importance of somatosensory information for motor performance and the prognostic evaluation of somatosensory deficits. Finally, we review current rehabilitation approaches for directing cortical reorganization in the appropriate direction and highlight some challenging questions that are unexplored in the field.

Disentangling Somatosensory Evoked Potentials of the Fingers: Limitations and Clinical Potential

In searching for clinical biomarkers of the somatosensory function, we studied reproducibility of somatosensory potentials (SEP) evoked by finger stimulation in healthy subjects. SEPs induced by electrical stimulation and especially after median nerve stimulation is a method widely used in the literature. It is unclear, however, if the EEG recordings after finger stimulation are reproducible within the same subject. We tested in five healthy subjects the consistency and reproducibility of responses through bootstrapping as well as test–retest recordings. We further evaluated the possibility to discriminate activity of different fingers both at electrode and at source level. The lack of consistency and reproducibility suggest responses to finger stimulation to be unreliable, even with reasonably high signal-to-noise ratio and adequate number of trials. At sources level, somatotopic arrangement of the fingers representation was only found in one of the subjects. Although finding distinct locations of the different fingers activation was possible, our protocol did not allow for non-overlapping dipole representations of the fingers. We conclude that despite its theoretical advantages, we cannot recommend the use of somatosensory potentials evoked by finger stimulation to extract clinical biomarkers.

Somatosensory and Brainstem Auditory Evoked Potentials Assessed between 4 and 7 Days after Severe Stroke Onset Predict Unfavorable Outcome

Our objective was to explore the best predictive timing of short-latency somatosensory evoked potentials (SLSEP) and brainstem auditory evoked potentials (BAEP) for unfavorable outcomes in patients with early stage severe stroke. One hundred fifty-six patients with acute severe supratentorial stroke were monitored according to SLSEP, BAEP, and the Glasgow Coma Scale (GCS) at 1-3 days and 4-7 days after the onset of stroke. All patients were followed up for outcomes at 6 months after onset using the modified Rankin Scale (mRS), with a score of 5-6 considered unfavorable. The predictive values of SLSEP, BAEP, and the GCS at 1-3 days were compared with 4-7 days after onset. Our results show that, according to the analysis of prognostic authenticity, the predictive values of SLSEP and BAEP at 4-7 days after stroke onset improved when compared with the values at 1-3 days for unfavorable outcomes. Most of the patients with change of worsening evoked potentials from 1-3 days to 4-7 days after onset had unfavorable outcomes. In conclusion, SLSEP and BAEP assessed at 4-7 days after onset predicted unfavorable outcomes for acute severe stroke patients. The worsening values of SLSEP and BAEP between 1-3 days and 4-7 days also present a prognostic value.

Association Between Evoked Potentials and Balance Recovery in Subacute Hemiparetic Stroke Patients

Objective

To investigate the association between baseline motor evoked potential (MEP) and somatosensory evoked potential (SSEP) responses in the lower extremities and balance recovery in subacute hemiparetic stroke patients.

Methods

MEPs and SSEPs were evaluated in 20 subacute hemiparetic stroke patients before rehabilitation. Balance (static posturography and Berg Balance Scale [BBS]), motor function (Fugl-Meyer Assessment [FMA]) and the ability to perform activities of daily living (Modified Barthel Index [MBI]) were evaluated before rehabilitation and after four-weeks of rehabilitation. Posturography outcomes were weight distribution indices (WDI) expressed as surface area (WDI-Sa) and pressure (WDI-Pr), and stability indices expressed as surface area (SI-Sa) and length (SI-L). In addition, all parameters were evaluated during eyes open (EO) and eyes closed (EC) conditions.

Results

The MEP (+) group showed significant improvements in balance except WDI-Sa (EC), FMA, and MBI, while the MEP (-) group showed significant improvements in the BBS, FMA, and MBI after rehabilitation. The SSEP (+) group showed significant improvements in balance except SI-Sa (EO), FMA, and MBI, while the SSEPs (-) group showed significant improvements in the BBS, MBI after rehabilitation. The changes in the SI-Sa (EO), SI-L (EO), total MBI, and several detailed MBI subscales in the MEP (+) group after rehabilitation were significantly larger than those in the MEP (-) group.

Conclusion

Our findings suggest that initial assessments of MEPs and SSEPs might be beneficial when predicting balance recovery in subacute hemiparetic stroke patients.

Sympathetic skin responses in adult humans during sequential swallowing

STUDY AIMS

Autonomic changes, especially those of sympathetic skin responses (SSR), during sequential water swallowing (SWS) have not been systematically investigated. This study aims to electrophysiologically examine these autonomic changes (SSR and heart rate) that occur during 50 ml sequential water swallowing from a cup.

MATERIALS AND METHODS

Fifty-eight normal healthy adults were included in the study. Their submental muscle activity, respiratory activity, heart rate changes, and sympathetic skin responses were recorded during 50 ml water swallowing. In addition, we requested subjects to imagine drinking water as they did just before. The same recordings were performed during this imagination period.

RESULTS

SSR appeared at the beginning and at the end of SWS in 52% of subjects. A first sympathetic skin response was evoked at the onset of SWS, and a second one appeared 8.6±1.7 seconds after the first one and at the end of swallowing. Similar double SSRs were also obtained during imagination in most investigated subjects (33 out of 35 of selected subjects in a total group of 58 subjects). Swallowing tachycardia was observed during the SWS-associated apnea period, but not during the imagination period. Heart rate significantly increased during the SWS-associated apnea period.

CONCLUSION

The first SSR that appeared at the onset of swallowing is likely related to arousal. The appearance of a second response is a novel finding, which is probably related to the activity of subtil corticosubcortical networks. While discrete/single swallows can be used to evoke SSRs, SWS is unlikely to be clinically useful in its current form. In contrast, swallowing tachycardia could be a useful tool to examine dysphagic patients.

The effect of cortico-spinal tract damage on primary sensorimotor cortex activation after rehabilitation therapy

Recently, it was shown that patients have different functional activation patterns within affected primary sensorimotor cortex (SMC) after intensive rehabilitation therapy. This individual difference was supposed to depend on the integrity of the cortico-spinal fibres from the primary motor cortex. In this study, we considered whether patients with different fMRI activation patterns after intensive rehabilitation therapy suffered from different cortico-spinal fibre lesions. To comprehend this circumstance a lesion subtraction analysis was used. To verify these results with the use of transcranial magnetic stimulation motor evoked potentials was also derived. Patients were treated after a modified version of constraint-induced movement therapy (modCIMT; 3 h daily for 4 weeks). Increased and decreased SMC activation showed similar individual patterns as described previously. These activation differences depend on the integrity of the cortico-spinal tract, which was measured via lesion subtraction analysis between patient groups, and was supported by affected motor evoked potentials.

Outcome prediction in acute monohemispheric stroke via magnetoencephalography

BACKGROUND

Following an ischemic stroke a highly variable clinical outcome is commonly evident despite similar onset symptoms as well as lesion characteristics. The aim of this study was to identify indexes providing early prediction of functional recovery, in addition to clinical severity and lesion dimension at onset of stroke.

METHODS

In 32 patients, magnetoencephalographic (MEG) parameters collected in the acute phase (<10 days from symptoms onset, T0) from affected (AH) and unaffected (UH) hemispheres at rest and evoked by sensory stimuli were evaluated in association with the clinical outcome in a stabilized phase (T1, median 7.8 months) classified with three levels: worsening, partial and full recovery.

RESULTS

Multiple multinomial logistic regression indicated AH gamma and UH delta band powers able to prognosticate clinical outcome at T1. After inclusion in this analysis, lesion volume had the strongest predictive ability, and UH delta band power remained as a predictive factor with a measurable cut-off, maximizing both sensitivity and specificity of the prediction: a patient with UH delta below cut-off would recover to some extent; a patient with UH delta above cut-off would have a probability of about 70% to worsen.

CONCLUSIONS

MEG UH delta and AH gamma band powers were found to provide useful information about long-term outcome prognosis. Only the increase of delta band activity in the unaffected hemisphere contains information about the outcome in addition to the lesion volume.

Transcranial magnetic stimulation and stroke: A computer-based human model study

This paper explores how transcranial magnetic stimulation (TMS) induced currents in the brain are perturbed by electrical and anatomical changes following a stroke in its chronic stage. Multiple MRI derived finite element head models were constructed and evaluated to address the effects that strokes can have on the induced stimulating TMS currents by comparing stroke models of various sizes and geometries to a healthy head model under a number of stimulation conditions. The TMS induced currents were significantly altered for stimulation proximal to the lesion site in all of the models analyzed. The current density distributions were modified in magnitude, location, and orientation such that the population of neural elements that are stimulated will be correspondingly altered. The current perturbations were minimized for conditions tested where the coil was far removed from the lesion site, including models of stimulation contralateral to the lesioned hemisphere. The present limitations of TMS to the peri-lesional cortex are explored, ultimately concluding that conventional clinical standards for stimulation are unreliable and potentially dangerous predictors of the site and degree of stimulation when TMS is applied proximal to infarction site.

Two different reorganization patterns after rehabilitative therapy: an exploratory study with fMRI and TMS

We used two complementary methods to investigate cortical reorganization in chronic stroke patients during treatment with a defined motor rehabilitation program. BOLD ("blood oxygenation level dependent") sensitive functional magnetic resonance imaging (fMRI) and intracortical inhibition (ICI) and facilitation (ICF) measured with transcranial magnetic stimulation (TMS) via paired pulse stimulation were used to investigate cortical reorganization before and after "constraint-induced movement therapy" (CI). The motor hand function improved in all subjects after CI. BOLD signal intensity changes within affected primary sensorimotor cortex (SMC) before and after CI showed a close correlation with ICI (r = 0.93) and ICF (r = 0.76) difference before and after therapy. Difference in number of voxels and ICI difference before and after CI also showed a close correlation (r = 0.92) in the affected SMC over the time period of training. A single subject analysis revealed that patients with intact hand area of M1 ("the hand knob") and its descending motor fibers (these patients revealed normal motor evoked potentials [MEP] from the affected hand) showed decreasing ipsilesional SMC activation which was paralleled by an increase in intracortical excitability. This pattern putatively reflects increasing synaptic efficiency. When M1 or its descending pyramidal tract was lesioned (MEP from the affected hand was pathologic) ipsilesional SMC activation increased, accompanied by decreased intracortical excitability. We suggest that an increase in synaptic efficiency is not possible here, which leads to reorganization with extension, shift and recruitment of additional cortical areas of the sensorimotor network. The inverse dynamic process between both complementary methods (activation in fMRI and intracortical excitability determined by TMS) over the time period of CI illustrates the value of combining methods for understanding brain reorganization.

Predictive value of median-SSEP in early phase of stroke: a comparison in supratentorial infarction and hemorrhage

OBJECTIVE

To compare the prognostic value of median somatosensory evoked potentials (M-SSEP) changes in the early phase of supratentorial infarction and hemorrhage.

MATERIAL AND METHODS

This study includes 130 patients (mean age 62+/-11.4 years, 43 women, large middle cerebral artery territory infarction in 36 patients, restricted/lacunar in 55, massive supratentorial hemorrhage in 10, small/medium size hemorrhage in 31). M-SSEP were recorded early (0-7 days in ischemia, 0-21 days in hemorrhage) and patients stratified into groups with absent, abnormal, normal response. Clinical state was determined by the Medical Research Council (MRC) scale, Barthel Index and Rankin score and followed for at least 6 months.

RESULTS

Moderate prognostic correlation was established between N20-P25 amplitudes (r=0.34, p<0.05) and N20-P25 amplitude ratio (r=0.45, p<0.01) and Barthel Index at 6 months in patients with ischemic stroke. Moderate relationship (r=-0.34, p<0.05) exists also between N20-P25 ratio and Rankin score at 6 months in patients with small/medium size hemorrhage. In large infarctions and small/medium size cerebral hemorrhages correlations with all clinical indices of outcome are weak. In massive hemorrhage, only a weak correlation (r=-0.19, p<0.05) between amplitude ratio and Rankin score was found. The combination of initial MRC and N20-P25 amplitude ratio has 10% (in hemorrhage) to 15% (in infarction) greater prognostic value (p<0.05) than initial alone.

CONCLUSIONS

M-SSEP have independent predictive value regarding functional recovery in ischemic stroke and small/medium size cerebral hemorrhage. Combined assessment of initial MRC and M-SSEP substantially improves prognosis in acute stroke.

Cervical spinal cord stimulation improves neurological dysfunction induced by cerebral vasospasm

The effect of cervical spinal cord stimulation on the cerebral blood flow has been investigated both experimentally and clinically since 1986. Although the effect of the spinal cord stimulation on cerebral ischemia induced by cerebral vasospasm after subarachnoid hemorrhage has been investigated widely, neurological dysfunction induced by cerebral vasospasm and the effect of the spinal cord stimulation on neurological dysfunction have not been investigated so far. The aim of this study is to investigate the neurological dysfunction induced by cerebral vasospasm after subarachnoid hemorrhage and whether the spinal cord stimulation improves this neurological dysfunction or not in New Zealand albino rabbits. The animals were divided into sham and experiment groups: Sham group. Motor evoked potentials were recorded before experimental procedure was performed in this group. Just after, intracisternal saline was injected and 3 days later a stimulation electrode was placed in the cervical epidural space. Motor evoked potentials were recorded but electrical stimulation was not applied. Experiment group. Firstly, motor evoked potentials had been recorded before experimental procedure was performed in also this group. After then a stimulation electrode was placed in the cervical epidural space of the animals in which subarachnoid hemorrhage procedure was performed 3 days ago. Motor evoked potentials were recorded both before and after spinal cord stimulation. Motor evoked potential latencies and amplitudes did not change in the sham operation group. But, motor evoked potential latencies extended and the amplitudes decreased in the experiment group before spinal cord stimulation. Spinal cord stimulation improved the changes occurring in latencies and amplitudes in the experiment group. Spinal cord stimulation improves the neurological dysfunction induced by cerebral vasospasm and motor evoked potentials recording is a reliable electrophysiological method to detect cerebral vasospasm and to assess the effects of different treatments in cerebral vasospasm.

Recovery of somatosensory deficits in acute stroke

OBJECTIVES

To study the recovery of somatosensory deficits after acute stroke.

MATERIAL AND METHODS

A detailed clinical examination of sensation, median nerve somatosensory evoked potentials (SEP), quantitative sensory tests (QST), and subjective evaluation were performed in five acute stroke patients at three control time points up to 12 months after the stroke.

RESULTS

The deficit recovered at least partially in all patients, mostly within 3 months after stroke. The improvement in warm and vibration detection thresholds occurred between 3 and 12 months. The SEP improved both by 3 and 12 months.

CONCLUSION

The recovery of subjective sensory disturbance occurred in line with the improvement of the clinical sensory tests and QST. The most sensitive measure for somatosensory dysfunction at the early phase was graphesthesia. In our patients, initially normal SEP with a sensory deficit resulted in excellent clinical recovery, whereas initially absent SEP did not necessarily predict poor outcome.

Prognostic value of median and tibial somatosensory evoked potentials in acute stroke

The predictive values of early somatosensory evoked potentials (SSEPs) for the functional outcome after stroke are investigated. Ninety-four stroke patients (mean age: 61.2, S.D.: 11.8) with CT confirmed diagnoses of middle cerebral artery (MCA) infarction in 71 and supratentorial intracerebral hemorrhage in 23. Median and tibial SSEPs were recorded within 3 days of onset. SSEP parameters were compared to motor (MRC) and functional ability (Barthel index) followed up at 1, 3, 6 and 12 months. Upper limb MRC remains the strongest single predictor of functional outcome, determining 54.3% of Barthel index value at 12 months. The highest predictive value among SSEP parameters has N20-P25 amplitude ratio-34.5%. Combined application of upper limb MRC and N20-P25 amplitude ratio provided significantly stronger prognostic information-66%. Combined assessment of SSEP parameters and muscle power in acute stroke considerably improves prediction of functional outcome.

Motor evoked potentials following transcranial magnetic stimulation after middle cerebral artery and/or basilar artery occlusions in rats

To clarify the significance of motor evoked potentials following transcranial magnetic stimulation (MMEPs) in acute stage of cerebral ischemia, MMEPs were recorded in rats with the right middle cerebral artery (MCA) and/or the basilar (BA) artery occlusions. MMEPs from bilateral forelimb muscle and regional cerebral blood flow (rCBF) of the pons were recorded simultaneously. After MCA occlusion, the amplitudes of MMEPs from left forelimb were increased up to approximately 184-221% of the pre-ischemic value for 60 min, though the latencies were unchanged. On the other hand, in the rats of BA occlusion and both BA and MCA occlusion groups, MMEPs amplitudes were decreased to 8-25% of the pre-ischemic value for 60 min. Pontine rCBF was decreased to 28-44% in both groups. As a mechanism of the facilitation of MMEPs after MCA occlusion, the affection of the inhibitory mechanism between the cerebral cortex and the generator of MMEPs by MCA occlusion is speculated.

Magnetoencephalography in stroke: a 1-year follow-up study

Recovery after stroke is closely linked to cerebral plasticity. Magnetoencephalography (MEG) is a non-invasive technique, which allows location of cerebral cells activities. In the present work, a cohort of patients has been studied with MEG. Twelve patients with a recent ischemic or hemorragic stroke were included as soon as possible after onset of stroke. Neurologic assessment, including standard neurologic examination, functional independence measure (FIM) and Orgogozo's scale was performed for 1 year in addition to a study of the somatosensory evoked field (SEF) using a 37-channel Biomagnetometer system. No response could be recorded in five patients at the first SEF exploration. In three cases, no response was ever recorded during the study. All these patients had a bad recovery. The location of the SEF sources was always in the normal non-infarcted cortex of the postcentral gyrus. Sensory recovery seemed to be linked to the reorganization of the persistent functional cortex, which was a limiting factor for recovery. These observations confirm the experimental results obtained in animal models. After stroke it can be assumed that in the case of incomplete lesion, an intensive sensory peripheral stimulation could maximize the use of residual sensory function and then contribute to improve the sensory deficit. In case of total sensory loss other techniques have to be used, such as visual monitoring of hand activity in order to improve hand function.

Systematic review for the early prediction of motor and functional outcome after stroke by using motor-evoked potentials

OBJECTIVE

To clarify the prognostic value of motor-evoked potentials (MEPs) in predicting motor and functional outcomes after acute stroke.

DATA SOURCES

A computer-aided search to identify original prognostic studies published from 1988 through 2000; relevant references cited in the retrieved articles were also included.

STUDY SELECTION

A preliminary screening selected studies in which transcranial magnetic stimulation was assessed as a prognostic determinant for outcome at the level of impairments (motor recovery) and disabilities (functional recovery). The studies were then subjected to a critical review according to a priori methodologic criteria.

DATA EXTRACTION

Data from the studies were used to construct contingency tables with MEPs as a prognostic determinant. The distribution of cells was statistically assessed with the Fisher exact test. The prognostic test properties were expressed as sensitivity and specificity. The clinical significance was determined by odds ratios.

DATA SYNTHESIS

Of 85 potentially relevant studies, 20 met the criteria for the preliminary screening; after the critical review, 5 studies were included for analysis and discussion.

CONCLUSIONS

Analysis of the data from the 5 studies indicated obvious evidence for the prognostic value of MEPs for both motor and functional recovery. The prognostic test properties for subgroups of patients could be established. In predicting motor recovery of the upper extremity, the specificity was consistently very high for subgroups of patients with paralysis or severe paresis; this test property might be used in clinical practice. We discuss the prognostic value of MEPs and offer suggestions for further research.

Value of somatosensory and motor evoked potentials in predicting arm recovery after a stroke

OBJECTIVES

Prediction of motor recovery in the arm in patients with stroke is generally based on clinical examination. However, neurophysiological measures may also have a predictive value. The aims of this study were to assess the role of somatosensory (SSEPs) and motor (MEPs) evoked potentials in the prediction of arm motor recovery and to determine whether these measures added further predictive information to that gained from clinical examination.

METHODS

Sixty four patients who had had a stroke and presented with obvious motor deficit of the arm were examined in terms of three clinical variables (motor performance, muscle tone, and overall disability) and for SSEPs and MEPs. Clinical and neurophysiological examinations were done at entry to the study (2 to 5 weeks poststroke), and at about 2 months after stroke. Further clinical follow up was conducted at 6 and 12 months after stroke.

RESULTS

Neurophysiological measures made in the acute phase were of little use alone in predicting motor recovery of the arm at 2, 6, and 12 months after stroke. At 2 months, the absence of SSEPs and MEPs indicated a very poor outcome. Conversely, if the responses were preserved, a great variation in motor outcome was found. Multiple regression analysis showed that the addition of SSEPs and MEPs to the clinical examination increased the possibility of predicting arm recovery in the long term. In the acute phase, the combination of the motor score and SSEPs were best able to predict outcome. The long term outcome based on variables taken at 2 months, was best predicted through incorporating the three clinical measures and MEPs.

CONCLUSIONS

Neurophysiological measures alone are of limited value in predicting long term outcome. However, predictive accuracy is substantially improved through the combined use of both of these measures and clinical variables.

Sleep stage-related changes in sympathetic sudomotor and vasomotor skin responses in man

OBJECTIVES

The aim of the study was to evaluate the characteristics of the spontaneous and evoked sympathetic skin responses (SSR) during sleep and wakefulness in comparison with the skin vasomotor responses (SVR).

METHODS

Five healthy subjects underwent a night of videopolysomnographic recording. Spontaneous SSR were recorded via surface electrodes placed on the dorsal and ventral aspect of the hand while SVR were evaluated by means of an infrared photoelectric transducer placed on the index finger. SSR and SVR were evoked via electrical stimuli applied to the left supraorbital nerve.

RESULTS

Spontaneous SSR frequency was highest during stage 4 of NREM sleep and lowest during REM phases. On the contrary, spontaneous SVR frequency reached its lowest value during stage 4 and its highest value during stage 2 of NREM sleep, remaining at levels above waking values during REM. SSR could be elicited by stimuli inducing arousal during light sleep but it was absent during deep NREM and REM sleep. SVR could be evoked throughout NREM and REM sleep.

CONCLUSIONS

Spontaneous SSR and SVR act differently during physiological modifications of vigilance. Evoked SSR is strictly dependent upon the state of vigilance, whereas evoked SVR shows no modifications during the different stages of the wake-sleep cycle.

Functional correlates with left-right asymmetry of visual evoked potentials in stroke patients: modeling and experimental results

OBJECTIVE

To determine the correlation between a clinical measure of function in patients after first stroke and left-right scalp amplitude of visual evoked potentials using a theoretical model of the head.

DESIGN

A random sample of first-stroke patients underwent routine function measurement and investigation of left-right scalp potential asymmetry. Results of the encephalographic tests were compared with those of a healthy subject. To examine the effect of the conductivity in the damaged area on the potential asymmetry, numerical calculations were performed on a model, with four concentric circular compartments representing the brain, cerebrospinal fluid layer, skull, and scalp. The damaged region was modeled as a circular section.

SETTING

Neurologic rehabilitation ward of a major rehabilitation hospital and university-affiliated biomedical engineering laboratory.

PATIENTS

Four men aged 58 to 71 years, 3 with brain thrombosis and 1 with hemorrhagic stroke. The patients were admitted for rehabilitation an average of 3 weeks after the stroke and stayed for an average of 137 days. Damage was confined to the right brain in all cases; three of the patients had neglect syndrome and/or sensory disturbances. A healthy subject without stroke was also examined.

MEASURES

Function was measured with the Functional Independence Measure (FIM) at 48 to 72 hours from admission and during the last week before discharge. Functional gain was calculated by subtracting the FIM admission score from the discharge score. Left-right scalp visual evoked potential amplitude was studied with flash stimuli according to the 10-20 international system and a theoretical model of the head based on two-dimensional computed tomography images; the volume conductor equation was solved numerically using the finite volume method. Left-right potential asymmetry and the damaged-region-to-brain-area ratio were calculated and correlated with the FIM values by linear regression analysis. Negative asymmetry indicates that the activity in the right damaged hemisphere is lower than in the undamaged one.

RESULTS

A negative correlation was noted between the FIM score on admission and the left-right scalp potential amplitude asymmetry, and between the FIM gain and the damaged-region-to-brain-area ratio obtained from the computed tomography image. Asymmetry was negative in the thrombotic patients and positive in the hemorrhagic one. The healthy subject showed nonsignificant asymmetry.

CONCLUSION

A relationship might exist between the left-right asymmetry of the scalp visual evoked potential and both the damaged-region-to-brain-area ratio and the functional outcome of rehabilitation in poststroke patients. The modeling study shows that the left-right asymmetry is most likely the result of changes in the conductivity at the damaged area, which, in turn, are probably associated with patient functional status and evolution. Further validation in larger groups of patients and normal subjects is needed before these parameters can serve as useful indices for clinical purposes.