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Biomedical subjects

G Zanette

Publications and source records attributed to G Zanette.

At least 37 records · Page 2Linked to original sources
PubMed1999

Clinical and electrophysiological assessment of inferior alveolar nerve function after lateral nerve transposition.

Inferior alveolar nerve (IAN) transposition surgery may cause some degree of sensory impairment. Accurate and reproducible tests are mandatory to assess IAN conduction capacity following nerve transposition. In this study subjective (heat, pain and tactile-discriminative tests) and objective (electrophysiological) assessments were performed in 10 patients receiving IAN transposition (bilaterally in 8 cases) in order to evaluate any impairment of the involved nerves one year post-operatively. All patients reported a tingling, well-tolerated sensation in the areas supplied by the mental nerve with no anaesthesia or burning paresthesia. Tactile discrimination was affected the most (all but 1 patient). No action potential was recorded in 4 patients' sides (23.5%); 12 sides showed a decreased nerve conduction velocity (NCV) (70.5%) and 1 side normal NCV values (6%). There was no significant difference in NCV decrease between partial and total transposition sides, if examined separately. Nerve conduction findings were related 2-point discrimination scores, but not to changes in pain and heat sensitivity. These findings show that lateral nerve transposition, though resulting in a high percentage of minor IAN injuries, as determined by electrophysiological testing, provides a viable surgical procedure to allow implant placement in the posterior mandible without causing severe sensory complaints. Considering ethical and forensic implications, patients should be fully informed that a certain degree of nerve injury might be expected to occur from the procedure. Electrophysiological evaluation is a reliable way to assess the degree of IAN dysfunction, especially if combined with a clinical examination. Intraoperative monitoring of IAN conduction might help identify the pathogenetic mechanisms of nerve injury and the surgical steps that are most likely to harm nerve integrity.

Action Potentials↗
PubMed1999

Pharmacokinetic and pharmacodynamic effects of high-dose continuous intravenous verapamil infusion: clinical experience in the intensive care unit.

OBJECTIVE: Our study aimed at evaluating the pharmacokinetic, cardiovascular, and metabolic effects of high-dose verapamil continuous intravenous infusion in cancer patients. DESIGN: Prospective clinical and pharmacokinetic study. SETTING: Intensive care unit of a Cancer Research Institute. PATIENTS: Nine patients (age range 31 to 57 yrs) with progressive cancer disease and without cardiovascular, renal, or hepatic dysfunctions. INTERVENTIONS: After a loading dose (0.15 mg/kg followed by 12 hrs of continuous intravenous infusion at 0.20 mg/kg/hr), the infusion rate of verapamil was increased every 24 hrs (0.25, 0.30, 0.35, and 0.40 mg/kg/hr). The highest rate was maintained for 48 hrs. Doxorubicin was given from the 60 th to the 108 th hr. Hydrochlorothiazide (25 mg/day) and potassium (36 mmol/day) were given orally. Altogether, 17 courses were completed. MEASUREMENTS AND MAIN RESULTS: Steady state concentration (C(SS) and systemic clearance of verapamil and nor-verapamil (active metabolite) for each infusion rate were calculated. Mean arterial pressure (MAP), central venous pressure (CVP), heart rate (HR), PR, QT and QTc intervals, and left ventricular ejection fraction (LVEF) were measured, as well as daily body weight, blood glucose and potassium. C(SS) of verapamil and nor-verapamil increased more than proportionally to the infusion rate (p<.001). Systemic clearance of verapamil decreased over the range of the infusion rate (p<.005). MAP and HR decreased at the 12th hr (p<.001) and then plateaued. CVP increased (p<.01). The relationship between MAP, HR, CVP, and verapamil plasma concentrations was significant (r2 = .25, .14, and .35, respectively; p<.0001). LVEF did not change. Six patients (11 courses) developed junctional rhythm. Three patients (six courses) showed a PR interval increase (p<.05). Patients with junctional rhythm had higher Css of verapamil (p<.009). Overall, QT and QTc intervals increased (p<.01). A linear relationship was observed between verapamil plasma concentrations and QT intervals (r2 = .09, p<.01). Cardiovascular side effects did not determine treatment withdrawal in any patient. Body weight, blood glucose, and potassium did not show significant changes. CONCLUSIONS: Our data suggest a capacity-limited clearance of high-dose verapamil. In the absence of heart disease, following a step by step increase of the dosage, the high plasma verapamil concentrations (617 to 2970 ng/mL) produce frequent but well tolerated hemodynamic and electrocardiogram changes.

Adult↗
PubMed1999

Cortical excitability in patients after loading doses of lamotrigine: a study with magnetic brain stimulation.

PURPOSE: Transcranial magnetic stimulation (TMS) of the brain allows the pharmacologic effects of anti-convulsant drugs (AEDs) on the excitability of motor corticospinal pathways to be evaluated in patients with epilepsy and normal subjects. However, no study has yet documented the changes in motor excitability in patients treated with lamotrigine (LTG). We aimed to study the effects of loading doses of LTG on TMS recordings in patients with epilepsy at the beginning of their treatment. METHODS: We investigated single-pulse TMS in six patients with complex partial seizures. The TMS recordings were performed in five sessions before and during 5 weeks of treatment. Motor threshold, motor-evoked potential (MEP) amplitude, cortical silent period, and peripheral conduction velocity were used as parameters of evaluation. LTG was started with a dosage of 25 mg/day until a daily maintenance dosage of 200 mg/day was reached. RESULTS: The motor threshold activation of thenar muscles was significantly increased by LTG after 2 weeks of treatment and was increased in a parallel way to the loading dose of the drug at week 3 and 5 of treatment. The MEP size recorded from the thenar muscles did not show significant changes at high- or low-intensity stimulation. The cortical silent period remained unchanged at low- and high-intensity stimulation. The absolute latency of MEPs after cortical and cervical stimulation was unchanged, as was the central motor conduction time. CONCLUSIONS: Our study documents that loading doses of LTG, administered as monotherapy, progressively increases patients' motor thresholds over short periods.

Action Potentials↗
PubMed1998

Modulation of ipsilateral motor cortex in man during unimanual finger movements of different complexities.

To understand the role of the ipsilateral motor cortex in the control of unimanual movements, we evaluated changes in cortical motor evoked potentials (MEP) from the left abductor pollici brevis (APB) to transcranial magnetic stimulation (TMS) of the right hemisphere in nine normal subjects during execution of right finger movements of different complexities. The motor tasks were (a) repetitive opposition movement (thumb tapping the 3rd finger); (b) isolated finger movements in a 'usual' sequence (thumb tapping fingers 2, 3, 4 and 5) and (c) in an 'unusual' sequence (thumb tapping fingers 3, 5, 2 and 4). Subjects were trained before the study up to disappearance of EMG synkinetic activity in the left APB. As compared to the rest condition, MEP amplitude was enhanced in all subjects during paradigm (b) and even more during (c), but remained unchanged during paradigm (a). The MEP increase disappeared in four out of the nine subjects undergoing overtraining. No significant modifications in MEP amplitude were found in the left proximal muscle (biceps, five subjects). The H reflex induced by left median nerve stimulation at the elbow (four subjects) and MEPs from the left APB to transcranial electrical stimulation (three subjects) were not significantly affected by any of the motor paradigms, indicating that the motor cortex was the site of change. These results provide evidence of an increased excitability of cortical motor outputs targeting the unmoving hand muscles during contralateral sequential finger movements which disappears with overtraining. We conclude that during motor learning there is an interhemispheric transfer of information, possibly in order to inhibit the opposite hemisphere from interfering when a fine unimanual movement is required.

Adult↗
PubMed1998

Transcranial magnetic stimulation selectively impairs interhemispheric transfer of visuo-motor information in humans.

We investigated the cerebral cortical route by which visual information reaches motor cortex when visual signals are used for manual responses. Subjects responded unimanually to photic stimuli delivered to the hemifield ipsilateral or contralateral to the moving hand. On some trials, trans-cranial magnetic stimulation (TMS) was applied unilaterally over the occiput, with the aim of stimulating extrastriate visual areas and thereby modifying transmission of visual input. In association with the side of a visual stimulus and a motor response, TMS could change inter- or intra-hemispheric transmission needed to convey visual information to motor areas. Reaction time differences following TMS suggested that TMS exerted an inhibitory effect only when visuo-motor information had to be transferred interhemispherically. This result reinforces evidence for an extrastriate pathway of interhemispheric transfer of visuomotor information.

Acoustic Stimulation↗
PubMed1998

Scalp topography and source analysis of interictal spontaneous spikes and evoked spikes by digital stimulation in benign rolandic epilepsy.

OBJECTIVES: We report the analysis of scalp topography and dipole modeling of the rolandic spikes in 6 patients suffering of benign rolandic epilepsy of childhood with extremely high amplitude SEP by tapping stimulation of the finger of the hand. METHODS: EEG and BESA analysis were performed for both rolandic spontaneous interictal spikes and high amplitude scalp activity evoked by tapping and electrical stimulation of the first finger of the right hand. RESULTS: The evoked responses showed a morphology characterized by a rapid phase (spike) followed by a slow phase (slow wave). The spike presented an early small positive component followed by a main negative component. Similar morphology, dipole configuration and source localization were observed for both rolandic spikes and evoked high amplitude scalp responses. Dipole localization showed an overlap of spatial coordinates between rolandic and evoked spikes. CONCLUSIONS: These findings suggest that the extremely high amplitude SEPs could be evoked spikes which probably had the same cortical generators of the spontaneous rolandic spikes.

Brain Mapping↗
PubMed1998

Spike topography and functional magnetic resonance imaging (fMRI) in benign rolandic epilepsy with spikes evoked by tapping stimulation.

We performed a spike topography study and a functional magnetic resonance imaging (fMRI) in a female patient with benign rolandic epilepsy presenting single high-amplitude evoked spikes in response to somatosensory peripheral stimulation. The stimulus was delivered to the first finger of the right hand using a tendon hammer, which evoked a single spike followed by a slow wave, showing the maximal amplitude over the left central regions. fMRI showed that the contralateral sensory cortices (S1 and S2) and the motor cortex (M I) were activated during tapping stimulation. In 3 normal subjects, tapping stimulation produced no fMRI activation. This fMRI study documents a highly focal activation of sensorimotor areas related to subclinical evoked spikes in benign rolandic epilepsy.

Acoustic Stimulation↗
PubMed1998

Systemic manifestations and liver disease in patients with chronic hepatitis C and type II or III mixed cryoglobulinaemia.

The aim of this study was to evaluate the prevalence of cryoglobulins in patients with chronic hepatitis B and C virus infection and to investigate the association of type II and type III mixed cryoglobulinaemia with systemic manifestations and liver disease stage and outcome in hepatitis C virus (HCV)-positive patients. We analysed the prevalence of cryoglobulinaemia in a cohort of patients with chronic liver disease and compared the systemic manifestations and liver involvement in HCV-positive patients with type II or type III mixed cryoglobulinaemia. The prevalence of serum cryoglobulins was significantly higher in HCV-positive patients than in hepatitis B surface antigen (HBsAg)-positive patients (55.4 vs 20.6%). In HCV-positive patients, stage of liver disease correlated with the prevalence of cryoglobulinaemia. Patients with type II cryoglobulins showed a significantly higher risk of cirrhosis and of extrahepatic manifestations while patients with type III cryoglobulins had a significantly higher prevalence of hepatocellular carcinoma. During follow-up the former had an odds ratio of 11.9 of death from extrahepatic complications while the latter had an odds ratio of 3.4 of dying from hepatic disease. Our study confirms the high frequency of mixed cryoglobulinaemia in patients with chronic hepatitis C virus infection. The presence and type of cryoglobulins seem to be associated with different clinical manifestations and outcome.

Adolescent↗
PubMed1998

The usefulness of routine preoperative laboratory tests for one-day surgery in healthy children.

Since 1984, laboratory tests have not been routinely required for healthy paediatric patients scheduled for one-day surgery in our Paediatric Surgery Department. We reviewed the medical charts of all children ASA physical status 1 and 2 who underwent a minor surgical procedure in the last 15 years. We excluded all former preterm infants of less than 60 weeks postconceptual age. The series under examination includes two groups of patients: group A includes 1884 children who underwent routine preoperative laboratory tests; group B includes 8772 children who had preoperative, selected laboratory tests performed only when the child's history and/or clinical examination revealed some abnormalities. The following data were collected: demographic data, ASA physical status classification, surgical procedure, anaesthetic technique, major and minor complications, length of hospital stay, the difference between the expected length of hospitalization and the actual length, number and reasons for cancellations of surgery. On the basis of our experience we believe that a thorough clinical assessment of the patient is more important than routine preoperative laboratory screening, which should be required only when justified by real clinical indications. Moreover, this practice eliminates unnecessary costs without compromising the safety and the quality of care.

Adolescent↗
PubMed1998

Influence of somatosensory input on paroxysmal activity in benign rolandic epilepsy with 'extreme somatosensory evoked potentials'.

We studied six patients suffering from benign rolandic epilepsy of childhood with central temporal spikes who presented so-called 'extreme somatosensory evoked potentials (SEPs)' following peripheral somatosensory stimulation. Stimuli were delivered to the fingers of one hand using both a triggered tendon hammer and low-intensity electrical stimulation. The electrical stimulation was delivered in sequences in different conditions (i.e. random order, 1, 3 and 10 Hz). Both tapping and electrical stimulation produced scalp evoked potentials in all subjects, characterized by a spike followed by a slow wave, similar in morphology and scalp distribution to the spontaneously occurring spikes. This paroxysmal activity was sensitive to stimulus rate; the number of evoked spikes was inversely related to the frequency of stimulation, being maximal at 1 Hz and disappearing at high frequencies (10 Hz). Spontaneous spikes disappeared during high-frequency stimulation but were present during low-frequency stimulation. Averaged SEPs at 3-Hz stimulation showed a late high-amplitude component, identical in morphology and distribution to the single evoked spike. We therefore conclude that, in these subjects, the so-called 'extreme SEPs' are evoked spikes and that evoked and spontaneous spikes share common cortical sensorimotor generators. The evidence that these generators can be influenced by afferent input provides important information regarding the functional mechanisms involved in modulating cortical excitability in benign rolandic epilepsy. Moreover, we suggest that peripheral electrical stimulation can be used as an additional activation test in this kind of epilepsy.

Age of Onset↗
PubMed1998

Neurophysiological evidence of neuroplasticity at multiple levels of the somatosensory system in patients with carpal tunnel syndrome.

The human somatosensory cortex (S1) is capable of modification after partial peripheral deafferentation, but it is not known whether spinal and brainstem changes contribute to this process. We recorded spinal, brainstem and cortical somatosensory evoked potentials following ulnar nerve stimulation in patients affected by unilateral carpal tunnel syndrome with EMG evidence of chronic alterations in median nerve sensorimotor conduction at the wrist lasting at least 4 weeks, and compared them with those from the unaffected hand and with those obtained in a control group. Amplitudes of spinal N13 and brainstem P14 potentials following stimulation of the ulnar nerve ipsilateral to the deafferented median nerve were greater than those following stimulation of the contralateral ulnar nerve. Side-to-side amplitude differences in N13 and P14 were greater in patients than in the control group. Parietal N20 and P27 potentials, supposedly generated in S1, were also significantly increased. The present results suggest that a chronic pathological modification of peripheral sensorimotor inputs is associated with changes in neural activity at multiple sites of the somatosensory system. Changes in spinal and brainstem structures could contribute to the mechanisms subserving changes in the S1. Changes in synaptic strength and unmasking inputs secondary to disconnection of the normally dominant inputs to the 'median nerve' cortex may be the mechanisms underlying ulnar nerve SEP changes.

Adult↗
PubMed1998

Effects of voluntary contraction on tibial nerve somatosensory evoked potentials: gating of specific cortical responses.

We evaluated vertex-parietal P37, N50, and contralateral N37 somatosensory evoked potentials (SEPs) to posterior tibial nerve stimulation during weak (20 to 30%) and strong (80 to 90%) ipsilateral gastrocnemius-soleus contraction. The results were compared with data obtained during full relaxation. P37 and N50 were attenuated significantly during weak contraction and then abolished during strong contraction, whereas the contralateral N37 was not. The N37 potential spreads over the vertex and over the ipsilateral parietal region during strong contraction. The Cz'-F3 montage was not appropriate for detecting these SEP patterns. These findings suggest that thalamic or cortical gating mechanisms affect specific cortical responses. P37 and N50 could reflect the arrival of the afferent volley into the motor areas from thalamic and cortical (subareas 1 and 2 of S1) projections. N37 could be generated in subarea 3b. Differential analysis of N37 and P37 is required in clinical practice, mainly in those conditions that involve the motor system and in those conditions in which tonic muscular activity is increased.

Adult↗
PubMed1997

Transient deafferentation in humans induces rapid modulation of primary sensory cortex not associated with subcortical changes: a somatosensory evoked potential study.

Human somatosensory cortex (S1) is capable of rapid modification after temporary peripheral deafferentation but it is not known whether subcortical changes contribute to this modulation. We recorded spinal, brainstem and cortical somatosensory evoked potentials (SEPs) to median nerve stimulation following anaesthetic block of the ipsilateral ulnar nerve. Spinal N13 and subcortical P14, N18 potentials remained unchanged during the experiment. N20/P20, P27 and N30 cortical potentials, which are generated in different subareas of the S1 (N20/P20, N30 in area 3b; P27 in area 1), showed different increases in amplitude during the anaesthesia, which were more marked for N20/P20 and N30 than for P27 potentials. These results suggest that changes in S1 neural activity induced by transient deafferentation may be primarily intracortical in origin and appear to be segregated within the different subareas of the somatosensory cortex. Unmasking of pre-existing thalamo-cortical projections from median nerve territories, induced by ipsilateral ulnar nerve deafferentation, may be the mechanism underlying cortical SEP enhancement.

Adult↗
PubMed1997

Binocular interaction in normal vision studied by pattern-reversal visual evoked potential (PR-VEPS).

Monocular and binocular visual evoked potentials (VEPs) in response to different check size (15-21-38-84 minutes or arc) were studied in 14 subjects with normal visual acuity and stereopsis. The binocular VEP amplitude is slightly higher than the VEP amplitude on stimulation of the "better eye" and significantly higher than the VEP amplitude on stimulation of the "worse eye"; this effect is observed using small checks and almost exclusively involved N75-P100. Both the N75 and P100 peaks occur earlier after binocular than monocular stimulation. The shortening of the N75 mean latency is significantly greater than that of the P100 mean latency when larger check sizes are used. The mean latency of the N145 potential is not significantly different in monocular and binocular stimulus conditions. The slight summation effect and latency shortening in the binocular VEPs are not consistent with the hypothesis that it is the sum of separate monocular signals originating from the visual cortex that gives rise to the response. The early components of both monocular and binocular VEPs are thought to be of post-synaptic origin (outside layer 4c of area 17), where the inputs become mixed so that most cells receive information from both eyes. The amplitude enhancement of binocular VEPs, which mainly occurs when using small checks, may be related to the increase in the total amount of cortical activity representing the macular region; this may account for binocular superiority in fine spatial resolution. The latency shortening in binocular conditions can be explained by considering that the critical determinant of the latency is the fundamental spatial frequency of the pattern. When coarse patterns are used, their effectiveness in parafoveal stimulation may affect the VEPs, with a significant contribution coming from the more peripheral retina. The enlargement of the visual field when the eyes see simultaneously may therefore further reduce the latency of the response when using the larger checks suitable for eccentric stimulation.

Adult↗
PubMed1997

Selective gating of lower limb cortical somatosensory evoked potentials (SEPs) during passive and active foot movements.

We evaluated subcortical and cortical somatosensory evoked potentials (SEPs) in response to posterior tibial nerve stimulation in 4 experimental conditions of foot movement and compared them with the baseline condition of full relaxation. The experimental conditions were: (a) active flexion-extension of the stimulated foot; (b) active flexion-extension of the non-stimulated foot; (c) passive flexion-extension of the stimulated foot in complete relaxation; (d) tonic active flexion of the stimulated foot. We analyzed latencies and amplitudes of the subcortical P30 potential, of the contralateral pre-rolandic N37 and P50 responses and of the P37, N50 and P60 potentials recorded over the vertex. Latencies did not vary in any of the paradigms. The amplitude of subcortical P30 potential did not change during any of the paradigms. Among the cortical waves, P37, N50 and P60 amplitudes were significantly attenuated in all conditions except active movement of the non-stimulated foot (b). This attenuation was less during passive (c) than during active movements of the stimulated foot (a and d). The contralateral pre-rolandic waves N37 and P50 showed no significant decrease during any of the paradigms. These results suggest that gating occurs rostrally to the cervico-medullary junction, probably at cortical level. The different behavior of N37, P50 and P37, N50 cortical responses during movement of the stimulated foot provides evidence suggestive of a highly localized gating process occurring at cortical level. These potentials could reflect activation of separate, functionally distinct generators.

Adult↗