Somatosensory evoked potentials during whole body hyperthermia in humans

Somatosensory evoked potentials (SEPs) and body temperature were recorded in patients subjected to induced total hyperthermia for treatment of advanced neoplasms. Elevation of body temperature up to 42 degrees C for 2 h was achieved using a computer-controlled external heating system. SEPs were recorded continuously on-line during the treatment using finger shock stimulation. Evoked potential components later than 160 msec disappeared in the early part of the treatment, but reappeared quickly during cooling. P50 and P50-N70 amplitudes decreased regularly and significantly over the whole duration of the heating period. During the plateau period, no evoked potential peaks could be detected but short latency peaks reappeared as soon as cooling started. The disappearance of SEPs to finger stimulation during sustained hyperthermia at 42 degrees C confirms the findings obtained by EEG recording that a major neuronal dysfunction occurs under these circumstances which subsides quickly as temperature is dropped.     

Somatosensory evoked potential changes during muscle testing

Fifteen naive subjects with no known neurological problems were tested by means of manual muscle testing to determine two "strong" and one "weak" muscle on a limb contralateral to the stimulated side. Somatosensory evoked potentials (SEP) were then recorded from contralateral median nerve stimulation while a naive tester tested the three previously identified muscles. In all subjects the baseline (no muscle test) and control "strong" muscle test recordings were comparable while the recording from the "weak" muscle test showed increased amplitudes in contralateral layer components. These findings suggest a neurologic basis for manual muscle testing.     

Somatosensory evoked potential in neurosyphilis

Since the development of effective antibiotic therapy, the occurrence of neurosyphilis has become less frequent. The number of syphilitic patients is gradually increasing as a complication in acquired immunodeficiency syndrome, but the diagnosis of neurosyphilis sometimes is difficult. We describe six patients with neurosyphilis and an analysis of their tibial nerve somatosensory evoked potentials. Four of them, including two with no tabes dorsalis symptoms, had delayed P15-N21 or the absence of N21. These abnormalities were ameliorated by treatment for syphilis. Analysis of tibial nerve SEPs provides a useful tool for the diagnosis of neurosyphilis and the evaluation of the extent to which neurosyphilis has progressed. Received: 20 December 2001, Received in revised form: 15 March 2002, Accepted: 18 March 2002     

Measurement of somatosensory evoked potential in the Mongolian gerbil: the effects of cerebral ischaemia

Normal somatosensory evoked potential (SEP) as well as changes after incomplete cerebral ischaemia following bilateral carotid artery occlusion (BCO) were characterized in the Mongolian gerbil. BCO significantly decreased cerebral blood flow (CBF). Reperfusion CBF at 10 min and 2, 3 and 4 h was significantly below preischaemic control values. BCO decreased SEP amplitude but had no effect on EP-P₃ central conduction time. BCO did significantly increase EP-P₁₁ central conduction time. Reperfusion amplitudes at 10 min and 2, 3 and 4 h revealed a significant increase only at 4 h when compared to the ischaemic amplitude. EP-P₁₁ central conduction time at 10 min reperfusion showed dramatic improvement compared to ischaemic values, although values at 2, 3 and 4 h reperfusion were not statistically different from ischaemic values. A separate group of animals prepared identically but without BCO showed no significant changes in either SEP or CBF over time. These studies establish the protocol necessary to measure SEP in the Mongolian gerbil. In the future SEP may be used as an integral tool in the study of the primary determinants of neurophysiological recovery following cerebral ischaemia.     

Measurement of somatosensory evoked potential in the Mongolian gerbil: the effects of cerebral ischaemia

Normal somatosensory evoked potential (SEP) as well as changes after incomplete cerebral ischaemia following bilateral carotid artery occlusion (BCO) were characterized in the Mongolian gerbil. BCO significantly decreased cerebral blood flow (CBF). Reperfusion CBF at 10 min and 2, 3 and 4 h was significantly below preischaemic control values. BCO decreased SEP amplitude but had no effect on EP-P3 central conduction time. BCO did significantly increase EP-P11 central conduction time. Reperfusion amplitudes at 10 min and 2, 3 and 4 h revealed a significant increase only at 4 h when compared to the ischaemic amplitude. EP-P11 central conduction time at 10 min reperfusion showed dramatic improvement compared to ischaemic values, although values at 2, 3 and 4 h reperfusion were not statistically different from ischaemic values. A separate group of animals prepared identically but without BCO showed no significant changes in either SEP or CBF over time. These studies establish the protocol necessary to measure SEP in the Mongolian gerbil. In the future SEP may be used as an integral tool in the study of the primary determinants of neurophysiological recovery following cerebral ischaemia.     

Activation of coagulation during therapeutic whole body hyperthermia

Coagulation parameters were initially monitored in 8 patients receiving whole body hyperthermia (WBH). Patients were heated by the warm water blanket technique to 41.8 degrees C (Tmax), maintained at this temperature for 2 hours, then allowed to cool. A fall in platelets was apparent by the time Tmax was achieved and continued during the 18 hours after WBH. Levels of beta-thromboglobulin (BTG) and platelet factor 4 rose by 56% and 191% by the end of treatment but returned to baseline 18 hours later. Fibrinogen, plasminogen and alpha 2-antiplasmin levels declined and FDP and fibrinopeptide A (FPA) levels increased during WBH. Factor XII and Factor VIII:C fell moderately during WBH while Factors VIII R:Ag, VIII:RC and V did not change or showed a late rise. Factor VII levels fell in 7 of 8 patients, reaching levels of 30% of normal in four. To better define the sequence of these coagulations perturbations, earlier and more frequent timepoints were studied in an additional 3 patients. This revealed that decreases in fibrinogen and plasminogen and increases in FPA and BTG occur very early (by the time the patient reaches 39 degrees C). On the other hand, a decrease in Factor VII activity was not apparent until patients had reached Tmax. WBH is therefore associated with a consumption coagulopathy. Possible mechanisms are discussed and extrapolations to the situation seen in heat stroke are suggested.     

Posttranslational arginylation of soluble rat brain proteins after whole body hyperthermia

We have previously reported the posttranslational addition of [14C]-arginine in the N-terminus of several soluble rat brain proteins. One of these proteins was identified as the microtubule-associated protein, the stable tubule only polypeptide (STOP). However, despite the fact that the biological significance of arginylation is not completely understood, some evidence associates it with proteolysis via the ubiquitin pathway. Since this degradative via is exacerbated as a response to stress, we studied in vitro the posttranslational [14C]-arginylation of cytosolic brain proteins of rats subjected to hyperthermia in vivo. Immediately after subjecting the animals to hyperthermia, a minor reduction (16%) in the acceptor capacity of [14C]-arginine into proteins was observed in comparison with animals maintained at 28 degrees C. However, in the animals allowed to recover for 3 h, an increase (46%) in the arginylation was observed concomitantly with a significant accumulation of the heat shock protein (70 kDa; hsp 70) when compared to the control animals. These findings suggest that the posttranslational arginylation of proteins participate in the heat shock response. The STOP protein of the soluble brain fraction of control animals, which in Western blot appears as a doublet band (125 and 130 kDa, respectively), is seen, after the hyperthermic treatment, as a single band of 125 kDa. The amount of 125 kDa protein, as well as the in vitro incorporation of [14C]-arginine, increases after hyperthermia in comparison with control animals. Following hyperthermic treatment, we observed a decrease in the amount of in vivo [35S]-methionine-labeled brain proteins. We speculate that, as observed for STOP protein, the increase in the degradation of protein that occurs in hyperthermia, would produce an increase in the amount of arginine acceptor proteins.     

Somatosensory evoked potential recovery in myotonic dystrophy.

OBJECTIVE: To evaluate recovery functions of the sensory cortex using somatosensory evoked potentials (SEPs) elicited by paired stimuli of the median nerve in patients with myotonic dystrophy (MD). SUBJECTS/METHODS: Twelve MD patients were enrolled in the present investigation. Five patients with facioscapulohumeral muscular dystrophy (FSH) and 12 healthy volunteers were studied as control groups. SEP was recorded from the hand sensory area contralateral to the median nerve stimulated at the wrist. Single pulse or paired-pulse stimuli at various interstimulus intervals (ISIs) (10, 20, 40, 60, 80, 100, 150, 200 and 300 ms) were given. Recovery functions of N9, N20onset-N20peak, N20-P25 and P25-N33 components were studied. RESULTS: Conventional SEPs to a single stimulus were normal in the latency and amplitude in all the patients. Recovery functions of both N9 and N20o-N20p components were normal in the patients. In contrast, in MD patients, disinhibited or hyperexcitable recovery pattern was observed in recovery curves of the N20-P25 or P25-N33 components, whereas those were normal in FSH patients. CONCLUSIONS: Disinhibited cortical excitability (or hyperexcitability) is present in the sensory cortex in patients with myotonic dystrophy. This may reflect cortical pathology or functional alteration of the sensory cortex in MD.     

Somatosensory evoked potential testing in infants and children.

Somatosensory evoked potentials (SSEPs) provide the means to assess noninvasively the peripheral and central nervous system in infants and young children. As experienced clinicians know, this is the very system most difficult to adequately evaluate in young children. Physical examination is difficult. SSEPs provide information about function of somatosensory systems not otherwise available. In addition to pathologic states, maturation and sleep produce changes in SSEPs that require careful analysis.     

Somatosensory evoked potential and histopathological investigations in ischaemia-induced brain damage: effects of trimetazidine in rats

We studied the protective effects of trimetazidine (TMZ) on brain damage by means of somatosensory evoked potentials (SEP) in rats. The TMZ group did not show any statistically significant difference from the control group with respect to SEPs. However, the percentage of cells with ischaemic cell damage in hippocampal regions was significantly smaller in the TMZ group than the control group. Trimetazidine reduced the number of damaged cells in the cerebral tissue during the ischaemia-reperfusion damage. It was suggested that higher doses of trimetazidine may further reduce the number of cells with ischaemic damage.     

Level of ischemia and brain functions in the Mongolian gerbil in vivo

The Mongolian gerbil (Meriones unguiculatus) provides a very useful animal model to study the effects of ischemia on brain functions. In this model it is possible to induce two levels of ischemia in the same animal. Thus, monitoring the brain in vivo in real-time will provide meaningful information regarding the development of ischemic injury as well as the follow-up during the recirculation period. The aims of the study were as follows: (1) To elucidate the mechanism behind the development of ischemic depolarization under unilateral and bilateral carotid artery occlusion. (2) To exclude the possibility that removal of the dura mater will affect the results. (3) To correlate the kinetics of the recovery processes to the level of ischemia. We tested the correlation between energy depletion level (evaluated by intramitochondrial NADH redox state) and the development of ischemic depolarization (ID) and vasospasm (evaluated by extracellular K+, DC potential and 366 nm reflectance changes, respectively) under partial and complete ischemia (induced by unilateral or bilateral carotid artery occlusion) using the multiparametric monitoring system (MPA). In 12 out of 32 gerbils monitored by the MPA, the dura mater remained intact, while in the other 20, it was removed very gently before connecting the MPA to the brain. Two types of responses to unilateral carotid artery occlusion were recorded and the gerbils were divided into groups according to the development of the ID. In a third group of 5 gerbils we tested the effect of 1-5 min of bilateral occlusion on the various parameters monitored.(ABSTRACT TRUNCATED AT 250 WORDS)     

Somatosensory and brainstem auditory evoked potential studies in nontraumatic coma

We believe that somatosensory and brainstem auditory evoked response studies help in the understanding of the dysfunction of the ascending sensory pathyways at various levels. In some patients where EEGs showed a significant contamination of muscle and background noise, the SEP studies helped to identify the level of dysfunction. The severity of the clinical condition (GCS score) correlated significantly (p = 0.003) with the prolongation of the CCT. Asymmetries in CCTs were more frequent in the stroke group than in the other groups. The presence of asymmetries in CCT in diffuse encephalopathies indicated a variable degree of dysfunction in the ascending sensory pathways, which clinically were not easily identifiable. This fact raised the possibility of either pre-existing lesion(s) or recent insult(s) such as ischemia. The presence or absence of N20 appeared to influence the duration of survival in subgroups. Some degree of difference in duration of survival was noted among the metabolic group with and without N20 potential. The subset of patients with N20 potential survived relatively longer than the group without it. A suggestion of influence was seen in the stroke group, but caution must be exercised because the absence of N20 was compatible with survival. The hypoxic group did not show any difference. A combination of prolonged interpeak EP-N13 and N13-N20 indicated a poor prognosis. A distinct absence of Wave I in BAER limited its usefulness on some occasions. A combination of abnormal interpeak III-V and abnormal CCT seemed to suggest a poor prognosis. Although death generally occurred earlier in the stroke group, age did not seem to influence the mortality in the first 10 days. Similarly, the cause of death also did not seem to influence the course in those 10 days. None of the adult patients survived.     

Eye and brain growth in the Mongolian gerbil (Meriones unguiculatus)

Eye and brain growth were evaluated by measures of weight and surface dimensions at 11 ages spanning the period from birth to 150 days of age in the Mongolian gerbil (Meriones unguiculatus). Brain weight was found to increase very rapidly until day 18, followed by a more gradual increase to asymptote by 70 days of age. Eye growth follows overall body growth more closely than brain growth. Eye shape was found to change from ovoid to spherical over the first 70 days of life. The possible relationship between eye growth and retinal specialization is considered, and brain growth is compared across several rodent species.     

Somatosensory evoked potential of the lower extremity in the premature neonate

The morphology of SEP is a good index of cortical maturation. Cerebral SEP is elicited by stimulation of the posterior tibial nerve at 38 wk post-conceptional age in 37 neonates distributed in 3 groups: I = gestational age (GA) at birth less than 31 wk; II = GA 23-36 wk; III = full-term neonates (FTN). A somatosensory response was identified in only 21 cases (56.8%). The presence of SEP in 3 groups, ie I, II, III, was 45.5%, 53.8% and 69.2% respectively. The morphological characteristics studied (latencies, amplitude and rising time) in these neonates were different: the peak latencies of major positive wave (P1) and rising time were not significantly different between I and III. These parameters were statistically different between II and III. SEP development is linked to some morphological factors-height, and growth-but also to the maturation of the central nervous system (myelinisation and central pathway organization). These results indicate that until 38-39 wk post-conceptional age, the maturation of the central somatosensory pathway is variable at different birth periods; this suggest the possible role of extra-uterine factors of in the acceleration of neurological development.     

Somatosensory evoked potentials following severe head injury: loss of the thalamic potential with brain death

The thalamic component (P17) of the short-latency somatosensory evoked potential (SEP) was assessed to determine its usefulness in patients with severe head injury. Subjects were a group of patients admitted to the Auckland Hospital Critical Care Unit who subsequently died from head injury. In all instances where brain death was unequivocally established and a SEP recording made in close temporal proximity to the time of brain death the P17 potential was absent. When there was evidence of continuing brainstem activity and particularly where prolonged survival occurred following the last SEP recording the P17 potential remained intact bilaterally. This study shows that the presence or absence of the thalamic component of the short-latency SEP provides a reliable electrophysiological measure of brainstem function in patients where brain death has been suspected.     

Somatosensory evoked potential studies in internal capsule and corona radiata infarction

To document the somatosensory evoked potential (SEP) changes in capsular and corona radiata infarction and correlate these with clinical and radiological findings, 15 patients with corona radiata and 16 with internal capsular infarction were studied. The mean age of the patients was 55 years (range 26–80), and 6 of them were female. In the patients with corona radiata infarction, median N9–N20 conduction time was abnormal in 4 cases, which correlated with sensory abnormalities in 1. In 3 of these patients, infarction was located in the anterior two-thirds and in 1 there was total corona radiata infarction. The amplitude of N20 potential on the affected side was reduced in 1 patient. In the capsular infarction group, N9–N20 conduction time was abnormal in 1 patient only who had total involvement of the posterior limb of the internal capsule. The amplitude of N20 was reduced in another patient. There were 4 patients who had abnormal sensory findings, but their SEPs were normal. At 3 months, the SEP changes remained stable in all of the patients who were followed up. The SEP changes did not correlate with changes in sensation or 3-month outcome as assessed by the Barthel index score. The lack of clinicoradiological and SEP correlation may be owing to variation on the organisation of sensory pathways in the corona radiata and internal capsule. Received: 3 July 1997 Received in revised form: 15 January 1998 Accepted: 27 January 1998     

Somatosensory evoked potential in man: far field potentials.

Three short latency positive potentials evoked by median nerve stimulation were recorded from the scalp, nose and ear of 11 normal adult subjects in leads where the hand or knee contralateral to the side of stimulation was used as the reference site. The short latencies and positive polarity of these components suggest that they are volume conducted far field potentials. Evidence is presented which suggests that the first potential arises in peripheral nerve fibers. Brain stem and dicencephalic structures are suggested as possible sources for the second and third potentials. The configuration of the response to median nerve stimulation recorded over the cervical spine in ear and hand reference recordings was different. Evidence is presented which suggests that this occurs because the electrode placed on the ear records the far field potentials described in the above paragraph. A far field potential was also recorded in hand--knee leads contralateral to the stimulated median nerve.     

Central hyperthermia, brain hyperthermia and low hypothalamus temperature

Introduction, Patients and Methods

We measured brain temperature in a case of central hyperthermia.

Results

Brain temperature was increased except for hypothalamus that was colder.

Conclusion

We suppose that central hyperthermia is driven by cold hypothalamus.