Inhibition of cortical laser-evoked potentials by transcutaneous electrical nerve stimulation.

Objectives. This study attempts to confirm the hypothesis that transcutaneous electrical stimulation (TENS) of peripheral Aß fibers inhibits nociceptive processing, by quantifying the change of laser-evoked potential (LEP) components, using a 980-nm diode laser. Materials and Methods. Cutaneous heat stimuli were delivered to the dorsum of the right hand in 13 volunteers. LEPs and pain intensity ratings were recorded before, during, and after the use of TENS (110 Hz) at the dorsolateral forearm. Area under the curve (AUC), LEP amplitudes (N2P2), and peak latencies (N2, P2) were calculated. The paired samples t-test was used for statistical analysis. Results. A significant reduction of LEP amplitudes and AUC was found during and after the use of TENS (p < 0.05). After 10 min of TENS this was associated with a clinically relevant decrease of pain intensity. Conclusions. Our data suggest that TENS inhibits nociceptive processing. Ten minutes of TENS exerts a clinically relevant pain reduction.

Clinical prospective study of biochemical markers and evoked potentials for identifying adverse neurological outcome after thoracic and thoracoabdominal aortic aneurysm surgery.

BACKGROUND: Neurological deficit after repair of a thoracic or thoracoabdominal aortic aneurysm (TAA/TAAA) remains a devastating complication. The aim of our study was to investigate the clinical value of biochemical markers [S-100B, neurone-specific enolase (NSE) and lactate dehydrogenase (LD)], evoked potentials and their combinations for identifying adverse neurological outcome after TAA/TAAA surgery. METHODS: From 69 patients, cerebrospinal fluid and blood samples for biochemical analysis were drawn after the induction of anaesthesia, during the cross-clamp period, 5 min, 2, 4, 6, 8, and 19 h, respectively, after reperfusion. In addition, continuous perioperative recording of motor-evoked potentials after transcranial electrical stimulation (tcMEP) and somatosensory-evoked potentials was carried out. Furthermore, neurological examinations were performed. RESULTS: In patients with a defined decrease in lower extremity tcMEP during the cross-clamp period, we found that combinations of the serum concentrations of S-100B and tcMEP ratios at 4, 6, and 8 h after reperfusion had a positive and negative predictive value of 100% in predicting adverse neurological outcome after TAA/TAAA surgery. Furthermore, combinations of the serum concentrations of S-100B and NSE or LD at 19 h after reperfusion had both a positive and negative predictive value of 100% in identifying patients with adverse outcome after TAA/TAAA repair. CONCLUSIONS: TcMEP monitoring during TAA/TAAA surgery seems to be an effective but not completely sufficient guide in our protective multi-modality strategy. Combinations of the serum concentrations of S-100B and tcMEP ratios during the early reperfusion period might be associated with adverse neurological complications. Furthermore, biochemical markers could detect central nervous system injury on the first postoperative day and may have prognostic value.

Thoracic and thoracoabdominal aortic aneurysm repair: use of evoked potential monitoring in 118 patients.

PURPOSE: Paraplegia is the most dreaded and severe complication of surgery on the descending thoracic aorta (TAA) and thoracoabdominal aorta (TAAA). The functional integrity of the spinal cord can be monitored by means of intraoperative recording of myogenic-evoked responses after transcranial electrical stimulation (tcMEP) and somatosensory-evoked potential (SEP) monitoring. In this study, we evaluated the results of evoked potential monitoring and the adequacy of the strategy followed. METHOD: The spinal cord of 118 patients (78 men; age, 65 +/- 12 years; 79 TAAAs, 39 TAAs) undergoing surgery on the TAA or TAAA was monitored with tcMEP and SEP. Spinal cord protection was achieved by means of a multimodality approach: moderate hypothermia (32 degrees C rectal temperature), continuous cerebrospinal fluid drainage to keep the pressure less than 10 mm Hg, reimplantation of intercostal arteries, left ventricular bypass grafting, and staged clamping. In the case of evoked potential changes more than 50% of baseline, the strategy was adjusted: reattachment of more segmental arteries when technically feasible, higher distal and proximal perfusion pressures, and enhanced cerebrospinal fluid drainage. RESULTS: Forty-two of 118 patients (35.6%) had a more than 50% of baseline tcMEP reduction during cross-clamping. At this point, only 5 of those 42 cases were also associated with SEP reduction of more than 50% of baseline. On the basis of the tcMEP findings, the strategy was adjusted. Five patients had postoperative paraplegia (4.2%). CONCLUSION: tcMEP monitoring seems to be a useful adjunct of the protective techniques and may cause substantial adjustments in strategy, reducing the incidence of postoperative paraplegia.

The effect of two low-dose propofol infusions on the relationship between six-pulse transcranial electrical stimulation and the evoked lower extremity muscle response.

BACKGROUND: Transcranial stimulation of the motor cortex using high-voltage electrical stimuli given in train is a method of monitoring the integrity of the motor pathways during thoracoabdominal aortic aneurysm surgery. The purpose of this study was to assess the relationship between the stimulus intensity and the corresponding amplitude of the myogenic motor evoked potential (tcMEP) in response to six-pulse transcranial electrical stimulation during two levels of low-dose propofol infusion and stable fentanyl/nitrous oxide anaesthesia. METHODS: Nine patients (37-78 yr) scheduled to undergo surgery on the thoracoabdominal aorta were studied. After achieving a stable anaesthetic state the output voltage was decreased with 50 V intervals from 350 V to 200 V during a target propofol infusion aimed at a plasma steady-state concentration of 0.7 microg x ml(-1) and increased with 50 V intervals from 200 V to 450 V during a target propofol infusion aimed at a plasma steady-state concentration of 1.4 microg x ml(-1). TcMEPs were recorded from the right tibialis anterior muscle. RESULTS: Doubling the target propofol infusion to 1.4 microg x ml(-1) resulted in a 30-50% decrease in tcMEP amplitude. The largest tcMEP amplitude using the six-pulse paradigm was found during a propofol infusion aimed at a plasma concentration of 0.7 microg x ml(-1) and demanded a stimulus output of 350 V, corresponding to a charge density of 7.5 microC x cm(-2) per phase. CONCLUSION: Doubling the target propofol infusion to 1.4 microg x ml(-1) provides less robust, but still recordable tcMEPs in response to six-pulse electrical stimulation. Safety guidelines are discussed.

Effect of nitrous oxide on myogenic motor potentials evoked by a six pulse train of transcranial electrical stimuli: a possible monitor for aortic surgery.

Intraoperative recording of myogenic motor potentials evoked by transcranial electrical stimulation (tcMEP) is a method of monitoring the integrity of the vulnerable motor pathways during thoracoabdominal aortic aneurysm (TAAA) surgery. Deflation of the left lung during TAAA surgery may result in impairment of arterial oxygenation. Ventilation with nitrous oxide may cause further desaturation. We studied the effects of 20%, 40% and 60% nitrous oxide in oxygen on within-patient variability and magnitude of tcMEP in response to six pulse transcranial electrical stimulation during fentanyl-low-dose propofol anaesthesia with partial neuromuscular block. Ten patients (two females; aged 63-74 yr) were studied. After achieving a stable anaesthetic state and before surgery, 10 tcMEP were recorded from the right tibialis anterior muscle during addition of 20%, 40% and 60% nitrous oxide in oxygen in random order. When ventilation with 40% or 60% nitrous oxide in oxygen was performed, there was 50-70% depression of tcMEP amplitude (P < 0.05) and 40-60% reduction in tcMEP area under the curve (P < 0.05) compared with 20% nitrous oxide in oxygen. There was no significant difference in the coefficients of variation for tcMEP between the three nitrous oxide anaesthetic regimens. Our results suggest that increasing doses of nitrous oxide reduce the MEP waveform to six pulse transcranial electrical stimulation, but even with 60% nitrous oxide in oxygen, the tcMEP were recordable and as reproducible as with 20% and 40% nitrous oxide regimens. The method is sufficiently robust for use in aortic surgery.

The relationship between evoked potentials and measurements of S-100 protein in cerebrospinal fluid during and after thoracoabdominal aortic aneurysm surgery.

OBJECTIVE: This study was performed to correlate the changes in concentration of S-100 protein in the cerebrospinal fluid (CSF) during and after thoracoabdominal aortic aneurysm (TAAA) surgery with the results of somatosensory and motor evoked potential monitoring. METHODS: The study was designed as a prospective study at St Antonius Hospital in Nieuwegein, The Netherlands. The participants were 19 patients who were undergoing elective TAAA surgery. CSF samples for analysis of S-100 protein were drawn after the induction of anesthesia, during the cross-clamp period of the critical aortic segment, after 5 minutes of reperfusion of this segment, during the closure of the skin, and 24 hours after the closure of the skin. In all the patients, continuous intraoperative recording of myogenic motor potentials evoked by transcranial electrical stimulation (tcMEP) and somatosensory potentials evoked by stimulation of the posterior tibial nerve took place to monitor the integrity of the spinal cord. The operative technique consisted of staged or sequential clamping to maximize the beneficial effect of the distal perfusion by the left heart bypass, continuous CSF drainage to keep the CSF pressure below 10 mm Hg, and moderate hypothermia (32 degrees C rectal temperature). We correlated the measured concentrations of S-100 protein in CSF with the results of evoked potential monitoring during surgery and the number of intercostals reimplanted and oversewn. RESULTS: In all the patients, the concentration of S-100 protein was increased in CSF. The highest concentration of S-100 protein was found in the CSF sample taken 5 minutes after reperfusion of the critical aortic segment. There was a good (negative) correlation between the changes in S-100 protein in CSF and the changes in motor evoked potential monitoring during the cross-clamp period. The best (negative) correlation was detected between the S-100 protein elevation in the CSF sample drawn 5 minutes after reperfusion and the tcMEP amplitude reduction during clamping (r = -0.73; P =.007). No relation was found between the S-100 protein dynamics in CSF and somatosensory evoked potential monitoring. A positive (r = 0.58; P =.05) correlation was found between the change in tcMEP amplitude during clamping and the number of reattached intercostals. A moderate to good (r = -0.5 to -0.7; P <.05) correlation between the number of reattached intercostals and the changes in S-100 protein concentration in CSF during TAAA surgery was found. Our data show that transient elevations in S-100 protein after cross clamping are larger in those patients with marked decrease in tcMEP from baseline during the cross-clamp period. CONCLUSION: A correlation is shown between an increasing concentration of S-100 protein in CSF and a reduction in tcMEP amplitude during cross clamping of the aorta. The S-100 protein in CSF seems to be a marker of potential clinical value in the evaluation of the effects of procedures to detect and reduce spinal cord ischemia.

Within patient variability of lower extremity muscle responses to transcranial electrical stimulation with pulse trains in aortic surgery.

Intraoperative recording of myogenic motor responses evoked by transcranial electrical stimulation is a method of controlling the integrity of the motor pathways during clamping of the aorta. It is important to know the within patient variability of the transcranial motor evoked potential (tcMEP), before changes within the variability range are interpreted as abnormal during the period of aortic cross clamping. Lower limb muscle responses were obtained in 11 patients, following transcranial electrical stimulation with pulse trains, of 4, 6 and 8 pulses. Under the conditions of partial neuromuscular blockade and a stable low dose propofol/fentanyl/nitrous oxide anaesthetic state, this study shows that multipulse transcranial electrical stimulation reliably produces muscle responses of the lower limb in all patients tested with a coefficient of variation (CV) of around 20%. Eight pulses in the stimulation train produce neurophysiological facilitation that exceeds a 4 pulse train in terms of area under the curve (AUC) and response duration. The use of multipulse stimulation rather than double or single pulse stimulation is recommended in order to increase the clinical efficacy of tcMEP monitoring in aortic surgery.

Impact of left heart bypass on the results of thoracoabdominal aortic aneurysm repair.

BACKGROUND: This study evaluated the role of left heart bypass on the results of thoracoabdominal aortic aneurysm (TAAA) operations. METHODS: Two hundred fifty-eight patients had surgical repair of a thoracoabdominal aortic aneurysm between 1981 and 1998 using the inlay technique. Simple cross-clamping was used in 47.7% and left heart bypass (atriodistal) in 52.3%. Further surgical technique was identical: liberal intercostal or lumbar artery reimplantation, cerebrospinal fluid drainage (since 1989), administration of a renal cooling solution, permissive mild hypothermia, and no pharmacologic protection. Both univariate and multivariate analysis were used. RESULTS: The hospital mortality rate was 10.1% overall: 14.6% in the cross-clamp group, and 5.9% in the bypass group (p = 0.02). The risk of hospital death increased with aneurysm rupture (odds ratio 5.6) and when the patient needed postoperative dialysis (odds ratio 7.5). The use of left heart bypass had a mild protective effect on hospital death (odds ratio 0.56). The incidence of postoperative renal failure requiring dialysis was 8.3% overall: 10.9% in the cross-clamp group, and 5.9% in the bypass group (p = 0.16). After multivariate analysis, a longer operative procedure (odds ratio 1.01 per minute) and a longer reappearance time of blue dye in the urine (odds ratio 1.05 per minute) increased the risk of dialysis, whereas the use of atriodistal bypass reduced that risk (odds ratio 0.08). Paraplegia or paraparesis occurred in 10.9% of patients overall: 13.2% in the cross-clamp group, and 8.8% in the bypass group (p = 0.27). After logistic regression, rupture increased the risk of paraplegia or paraparesis (odds ratio 3.2) and dissection reduced it (odds ratio 0.23). CONCLUSIONS: The use of atriodistal bypass is beneficial in patients who had thoracoabdominal aortic aneurysm repair. Hospital mortality rates, postoperative dialysis, and paraplegia/paraparesis were reduced.

The influence of nitrous oxide to supplement fentanyl/low-dose propofol anesthesia on transcranial myogenic motor-evoked potentials during thoracic aortic surgery.

OBJECTIVE: Intraoperative monitoring of myogenic motor evoked potentials to transcranial electrical stimulation (tc MEPs) is a new method to assess the integrity of the motor pathways. The authors studied the effects of 50% nitrous oxide (N2O) and a low-dose propofol infusion on tc MEPs paired electrical stimulation during fentanyl anesthesia with partial neuromuscular blockade. DESIGN: Cross-over study. SETTING: St Antonius Hospital, Nieuwegein, The Netherlands. PARTICIPANTS: Ten patients scheduled to undergo surgery on the thoracoabdominal aorta were studied; 6 women aged 54 to 69 years and 4 men aged 68 to 77 years. INTERVENTIONS: After achieving a stable anesthetic state and before surgery, tc MEPs were recorded during four 15-minute periods: (I) air/oxygen (O2; F(I)O2 = 50%); propofol target blood concentration, 0.5 microg/mL; (II) N2O/O2 (F(I)O2 = 50%); propofol target blood concentration, 0.5 microg/mL; (III) N2O/O2 (F(I)O2 = 50%; propofol target blood concentration, 1.0 microg/mL; and (IV) air/O2 (F(I)O2 = 50%); propofol target blood concentration, 1.0 microg/mL. MEASUREMENTS AND MAIN RESULTS: Tc MEPs were recorded from the right extensor digitorum communis muscle and the right tibialis anterior muscle. The right thenar muscle was used for recording the level of relaxation; the T1 response was maintained at 40% to 70% of the control compound muscle action potential. There was no significant difference in onset latency among the four phases. The addition of N2O and doubling the target propofol infusion to 1.0 microg/mL resulted in a 40% to 50% reduction of tc MEP amplitude recorded in the extensor digitorum communis muscle and tibialis anterior muscle (p < 0.01). During each phase, tc MEPs could be elicited and interpreted, except in one patient, in whom no tc MEPs could be elicited in the leg because of technical problems. CONCLUSION: The data indicate that tc MEP monitoring is feasible during low-dose propofol, fentanyl/50% N2O in 02 anesthesia and partial neuromuscular blockade.

Within-patient variability of myogenic motor-evoked potentials to multipulse transcranial electrical stimulation during two levels of partial neuromuscular blockade in aortic surgery.

UNLABELLED: Intraoperative recording of myogenic motor responses evoked by transcranial electrical stimulation (tcMEPs) is a method of assessing the integrity of the motor pathways during aortic surgery. To identify conditions for optimal spinal cord monitoring, we investigated the effects of manipulating the level of neuromuscular blockade (T1 response of the train-of-four (TOF) stimulation 5%-15% versus T1 response 45%-55% of baseline), as well as the number of transcranial pulses (two versus six stimuli) on the within-patient variability and amplitude of tcMEPs. Ten patients (30-76 yr) scheduled to undergo surgery on the thoracic and thoracoabdominal aorta were studied. After achieving a stable anesthetic state and before surgery, 10 tcMEPs were recorded from the right extensor digitorum communis muscle and the right tibialis anterior muscle in response to two-pulse and six-pulse transcranial electrical stimulation with an interstimulus interval of 2 ms during two levels of neuromuscular blockade. The right thenar eminence was used for recording the level of relaxation. The tcMEP amplitude using the six-pulse paradigm was larger (P < 0.01; leg and arm) compared with the amplitude evoked by two-pulse stimulation during both levels of relaxation. The within-patient variability, expressed as median coefficient of variation, was less when six-pulse stimulation was used. At a T1 response of 45%-55% of baseline, larger, less variable tcMEPs were recorded than at a T1 response of 5%-15%. Our results suggest that the best quality of tcMEP signals (tibialis anterior muscle) is obtained when the six-pulse paradigm is used with a stable level of muscle relaxation (the first twitch of the TOF-thenar eminence-at 45%-55% of baseline). IMPLICATIONS: This study shows that six-pulse (rather than two-pulse) transcranial electrical stimulation during a stable anesthetic state and a stable neuromuscular blockade aimed at 45%-55% (rather than 5%-15%) of baseline provides reliable and recordable muscle responses sufficiently robust for spinal cord monitoring in aortic surgery.

Normal serum concentrations of S-100 protein and changes in cerebrospinal fluid concentrations of S-100 protein during and after thoracoabdominal aortic aneurysm surgery: Is S-100 protein a biochemical marker of clinical value in detecting spinal cord ischemia?

PURPOSE: This study was performed to determine the concentration of S-100 protein in serum and in the cerebrospinal fluid (CSF) during and 24 hours after thoracoabdominal aortic aneurysm repair. METHODS: This prospective study was performed at St. Antonius Hospital in Nieuwegein, The Netherlands. Eight patients who underwent elective thoracoabdominal aortic surgery participated in the study. Arterial blood and CSF samples for analysis of S-100 protein were drawn after induction of anesthesia, during the cross-clamp period of the critical segment, after 5 minutes of reperfusion, during the closure of the skin, and 24 hours after closure of the skin. RESULTS: No increase in S-100 protein concentration could be detected in serum (< 0.2 microg/L). The S-100 protein concentration in CSF increased during the procedure in all patients (4.2 +/- 3.1 microg/L). However, in one patient, who became paraplegic, the S-100 protein concentration in CSF increased even further after 24 hours (10 microg/L). CONCLUSIONS: The preliminary results suggest that S-100 protein in CSF may be a marker of clinical value in evaluating the effects of measures to detect and reduce spinal cord ischemia.

Cerebellitis as an uncommon complication of infectious mononucleosis.

Cerebellitis is an uncommon complication of infectious mononucleosis. We describe such a patient with infectious mononucleosis and cerebellitis as a major feature of a more global encephalitis. In the discussion the cerebral complications are reviewed.

Delirium and cognitive disorders after cardiac operations: relationship to pre- and intraoperative quantitative electroencephalogram.

We examined the incidence of delirium and cognitive disorders after cardiac operations and the related risk factors. The value of pre- and intraoperative QEEG was determined. Using the Mini-Mental State Examination and the Saskatoon Delirium Checklist, 321 patients were tested during the immediate postoperative period. Forty-four patients (14%) showed delirium, 68 (23%) cognitive disorders and 26 (9%) both. Significant risk factors for the development of cognitive disorders were age > or = 70 yr, female gender, duration of cardiopulmonary bypass > or = 2.5 h and aorta-cross-clamping > 70 min. Risk factors for delirium were age > or = 70 yr, female gender and Hb < 5 mmol 1(-1) intraoperatively. The preoperative QEEG showed significant differences between the groups with and without a cognitive disorder, while the intraoperative QEEG showed significant differences between the groups with and without delirium. Different risk factors for delirium and cognitive disorders are a possible explanation for the controversies in the literature, where neuropsychologic complications were grouped together. A low intraoperative Hb is an important risk factor for the development of delirium and can be treated. The preoperative QEEG may have prognostic significance in the occurrence of cognitive disorders, while the intraoperative QEEG may have prognostic significance in the occurrence of delirium.

Upper and lower extremity somatosensory evoked potential recording during surgery for aneurysms of the descending thoracic aorta.

Since tibial nerve somatosensory evoked potentials (SEPs) recording is influenced by hemodynamic changes and anesthetics, alterations cannot always be attributed to spinal cord ischemia, so causing false positive results. Additional recording of median nerve SEPs facilitates interpretation. From January 1988 to July 1993, 60 consecutive patients (44 men, 16 women, mean age 66 years, ranging from 26 to 83 years) underwent surgery for an aneurysm of the descending thoracic aorta using a non-heparinized left heart bypass (Biomedicus pump). In 40 patients recording of the tibial and median nerve SEPs was performed intraoperatively by stimulating both nerves alternately. In 32 patients (80%) both recordings were uneventful. In three patients (7.5%) the tibial nerve SEP temporarily disappeared due to peripheral ischemia on termination of the bypass for the creation of an open distal anastomosis. In three patients (7.5%) near loss of both tibial and median SEP recordings was caused by low blood pressure and/or anesthetics. In two patients (5%) isolated loss of the tibial nerve SEP was due to ischemia in the spinal pathway of the tibial nerve. The tibial nerve SEP signal returned to normal: in one patient after reperfusion of intercostal arteries localized within the aneurysm, in the other patient after drainage of cerebrospinal fluid (CSF). Continuous recording of both tibial and median nerve SEPs gives consistent information on spinal cord ischemia, reducing the false positive rate of the lower extremity SEP to 7.5%.

Unexplained somatic complaints in relation to paroxysmal EEG phenomena and localised abnormalities in the electroencephalogram.

UNLABELLED: A positive significant relationship (p<0,01) is found between a psychiatric judgement on autonomic nervous system complaints and a "blind" neurological judgement on paroxysmal EEG phenomena. CLASSIFICATION: Somatization Disorder (DSM-III-R; IV 300.81). Diagnoses: nervous functional complaints, hyperventilation syndrome, Da Costa's disease (irritable heart syndrome, neurocirculatory asthenia) and irritable bowel syndrome. A positive significant relationship (p<0,001) is found between a diagnosis of "Da Costa's disease" and a "blind" neurological judgement on PEF. A positive significant relationship (p<0,001) is found between a psychiatric judgement on neurasthenia (atypical headache and atypical tiredness) classified as dysthymia DSM-IH-R 300.40 and a neurological judgement on localised (cortical) abnormalities by "blind" EEG evaluation. No medication in the last half year. Logistic regression analysis (n=116) revealed that sex and age are of no importance. No medication in the last half year before EEG registration.

Somatosensory evoked potentials during exclusion and reperfusion of critical aortic segments in thoracoabdominal aortic aneurysm surgery.

Forty-three patients undergoing repair of a thoracoabdominal aortic aneurysm were monitored to evaluate spinal cord ischemia, as evidenced by somatosensory evoked potentials (SEPs). All patients were operated on using left heart bypass. In 34 patients (80%), staged clamping was used. Except for cerebrospinal fluid (CSF) drainage in 15 patients (35%), no other protective measures to preserve spinal cord function were used. The overall incidence of immediate onset paraplegia was 7%, and of immediate onset paraparesis was 5%; neither was limited only to those patients in whom potentials were lost. In 18 patients (42%), no change in the evoked potentials occurred; one of these patients (5%) awoke paraplegic after operation, and two others had a delayed onset paraplegia. In 13 patients (30%), evoked potentials were lost despite adequate perfusion; in 12 of them, potentials returned gradually, with one immediate paraplegia (8%), and in one potentials did not return at all, with subsequent immediate paraplegia (100%). In 12 patients (28%), evoked potentials decreased without being lost completely, and then recovered; in this group there were no immediate paraplegias. No relationship could be demonstrated between the extinction time, the recovery time, or the duration of loss of evoked potentials with postoperative neurological outcome. Intraoperative monitoring of SEPs is a good indicator of spinal cord ischemia, although we found a 5% incidence of false negatives. SEP monitoring offers an improvement in surgical strategy, and allows safer operations for thoracoabdominal aneurysms.

Clinically silent dysfunction of dorsal columns and dorsal spinocerebellar tracts in hereditary spastic paraparesis.

Hereditary spastic paraparesis (HSP) is a neurodegenerative disorder, of which progressive spastic paraparesis is the clinical hallmark. Given the neuropathological evidence of degeneration of pyramidal tracts, dorsal columns, and dorsal spinocerebellar tracts, it is surprising that sensory symptoms are so indistinct compared to motor symptoms. We investigated the involvement of peripheral conduction and spinal proprioceptive pathways by nerve conduction studies, somatosensory evoked potentials of the median and tibial nerves, and quantitative assessment of the vibration perception thresholds of the hands and feet respectively in 32 patients suffering from HSP and healthy control groups. We did not find peripheral conduction abnormalities in HSP patients. Log-transformed vibration perception thresholds of the feet were abnormal in 13/32 HSP patients and in 0/64 controls (p < 0.00001), while tibial nerve somatosensory evoked potentials were abnormal in 20/32 patients and in 1/17 controls (p = 0.00001). The values for the upper extremities were within normal limits for nearly all subjects. In the HSP group, the neurophysiological disturbances did not correlate significantly with duration or severity of the disease, when age was controlled for, except for median nerve SSEP latency, which was affected by severity (p = 0.0072). We conclude that neurophysiological methods detected proprioceptive, subclinical abnormalities in several HSP patients, which may reflect degeneration of the dorsal columns, and/or dorsal spinocerebellar tracts. Since we found no correlation with several disease variables, the fact that not all HSP patients displayed these abnormalities may be caused by anatomical variations in proprioceptive pathways, rather than by phenotypical heterogeneity.

Influence of changes in arterial carbon dioxide tension on the electroencephalogram and posterior tibial nerve somatosensory cortical evoked potentials during alfentanil/nitrous oxide anesthesia.

The effects of variation of arterial CO2 tension (PaCO2) on the electroencephalogram (EEG) and posterior tibial nerve somatosensory cortical evoked potentials (PTN-SCEP) during opioid/N2O anesthesia have not been well documented. We studied the effects of hypocapnia (PaCO2 approximately 23 mmHg) and hypercapnia (PaCO2 approximately 50 mmHg) during steady-state alfentanil/N2O anesthesia in 16 patients. EEG and PTN-SCEP were recorded continuously, while PaCO2 was altered in 15-min intervals by varying the inspired CO2 concentration. Hypocapnia caused significant increases in power in the delta, theta, and beta bands (P less than 0.01), with the greatest increase observed in the alpha band. Relative power increased in the alpha band but remained unchanged in the delta, theta, and beta bands. Median frequency and 95% spectral edge frequency were unaltered during hypocapnia. In contrast, hypercapnia caused a significant decrease of power in the alpha and beta bands, whereas delta and theta power remained unchanged. This was reflected in a significant decrease of the 95% spectral edge frequency, from 8.9 (6.7-11.6) to 7.0 (5.6-8.6) Hz. All EEG parameters returned to normal upon restoration of normocapnia. There was a significant negative correlation between power in the alpha band and end-tidal CO2 in all patients (r = 0.47 to -0.89). PTN-SCEP latencies and amplitudes were not significantly different from control values during hypocapnia and hypercapnia. It is concluded that variations in PaCO2 within the limits 20-50 mmHg produce substantial changes in the EEG power spectrum, especially in the alpha band (8-12 Hz), but do not alter PTN-SCEP.