Biomedical subjects

G H Wieneke

Publications and source records attributed to G H Wieneke.

At least 19 recordsLinked to original sources

PubMed2006

Criteria for conduction block based on computer simulation studies of nerve conduction with human data obtained in the forearm segment of the median nerve.

The finding of conduction block (CB) on nerve conduction studies supports the diagnosis of potentially treatable immune-mediated neuropathies. CB in a number of axons may result in reduction of the compound muscle action potential (CMAP) on proximal versus distal stimulation (decrement). Decrement may also result from increased temporal dispersion (TD) as this leads to desynchronization and phase cancellation of the motor unit action potentials (MUAPs) out of which the CMAP is built up; polyphasia of MUAPs possibly yields additional decrement. To prove the occurrence of CB, decrement has to be larger than can be explained by increased TD or increased phase cancellation. This was established previously by simulations using MUAPs recorded in rats assuming maximal TD. Unfortunately, criteria based on human data and criteria for nerves with limited TD are not available. In the present study, criteria for CB were derived using simulations with thenar surface recorded MUAPs affected by collateral reinnervation that were obtained in patients with lower motor neurone disease (LMND). The effect of TD on decrement was determined for a wide range of TDs in the forearm segment of the median nerve and the segment distal to this. Our criteria for CB were based on area decrement because this was less influenced by TD and more by CB than amplitude decrement. The maximal area decrement in the forearm segment increased as TD in the forearm segment increased but decreased as TD in the distal segment increased. This suggests that, when desynchronization and phase cancellation occur in the distal segment due to TD, less phase cancellation and, therefore, less decrement can occur due to TD in the forearm. The finding that duration prolongation on proximal versus distal stimulation reflected TD within the forearm segment and that distal duration reflected TD in the distal segment allowed proposal of a more flexible set of criteria for forearm segments when TD in the forearm segment is limited or TD in the distal segment is pronounced. A separate investigation showed that the maximal TD in chronic inflammatory demyelinating polyneuropathy was within the range of our simulations, indicating that these were realistic. Our criteria were validated retrospectively in patients with multifocal motor neuropathy and patients with LMND. In the forearm segment of the median nerve, our criteria were more sensitive and equally specific for CB as compared with criteria for CB based on the study using rats. Our criteria have to be evaluated prospectively.

Action Potentials↗

PubMed2004

Documentation of progress in voice therapy: perceptual, acoustic, and laryngostroboscopic findings pretherapy and posttherapy.

The effect of voice therapy in a group of chronically dysphonic patients with diverse diagnoses was studied according to the normal clinical procedure. The results were evaluated by perceptual rating, acoustic analysis, and the assessment of laryngostroboscopic recordings. Although the group effects for the differences between posttherapy and pretherapy data were clearly significant, the effects of voice therapy for the individual patients were divergent. For each of the three evaluation methods, a significant improvement was found for about 40% to 50% of the patients. The diversity of the therapy outcome among the patients could not be explained by the pretherapy status nor by age, gender, or diagnosis groups. In general, the perceptual ratings and the acoustic parameters from the baseline data were clearly correlated. However, these characterizations of the voice were only moderately correlated with the visual evaluation of the vocal fold vibrations. Relations among the three evaluation tools for the changes caused by voice therapy were very weak. The low correlation among the three methods suggests that a multidimensional evaluation of the voice is necessary to give a complete picture of the therapy outcome.

Adolescent↗

PubMed2004

Self-assessment of voice therapy for chronic dysphonia.

The effects of voice therapy in a group of chronically dysphonic patients are determined using two quality-of-life (QOL) instruments: the Voice Handicap Index (VHI), and a simple three-item outcome scale (three visual analogue scales). Both instruments measure changes in the quality of the voice itself and in the extent of impairment resulting from the dysphonia as experienced by the patient in social and occupational settings. Statistical tests conducted on pre- and post-treatment data indicated significant improvements on both instruments for the group as a whole. At the individual level, however, the effects were diverse. For roughly 50% of the subjects, a significant improvement could be established. The positive changes as measured with the three-item scale were greater than those measured with the VHI. The results suggest that the two QOL instruments measure slightly different aspects of the subjective perception of the therapy effects. In order to obtain a general evaluation of the patient's handicap, it may suffice to ask some simple questions.

Adolescent↗

PubMed2003

Measurement of the conductivity of skull, temporarily removed during epilepsy surgery.

The conductivity of the human skull plays an important role in source localization of brain activity, because it is low as compared to other tissues in the head. The value usually taken for the conductivity of skull is questionable. In a carefully chosen procedure, in which sterility, a stable temperature, and relative humidity were guaranteed, we measured the (lumped, homogeneous) conductivity of the skull in five patients undergoing epilepsy surgery, using an extended four-point method. Twenty-eight current configurations were used, in each of which the potential due to an applied current was measured. A finite difference model, incorporating the geometry of the skull and the electrode locations, derived from CT data, was used to mimic the measurements. The conductivity values found were ranging from 32 mS/m to 80 mS/m, which is much higher than the values reported in other studies. Causes for these higher conductivity values are discussed.

Adult↗

PubMed2003

Demyelination and axonal loss in multifocal motor neuropathy: distribution and relation to weakness.

Multifocal motor neuropathy (MMN) is characterized by a slowly progressive, asymmetric weakness of the limbs without sensory loss. The arms are usually affected to a greater extent than the legs, and distal muscles more than proximal muscles. The distribution of electrophysiological abnormalities and its correlation with weak muscle groups in MMN have not been investigated systematically. The aim of the present study was to assess whether electrophysiological abnormalities have a preferential or random distribution, whether electrophysiological abnormalities in a nerve correlate with weakness in the innervated muscles, and whether these results are relevant for the development of optimal electrodiagnostic protocols. We compared the pattern of weakness and electrophysiological abnormalities in 39 patients with a lower motoneuron syndrome and a positive response to intravenous immunoglobulins. All patients underwent an extensive standardized electrophysiological examination. Electrophysiological evidence of demyelination was found more often in the nerves of the arms and was distributed randomly over lower arm, upper arm and shoulder segments. Electrophysiological evidence of axonal loss presented more frequently in longer nerves, occurring most often in the leg nerves. For the arm nerves, it is possible that the length dependence of axonal loss is due to the random distribution of demyelinating lesions that lead to axonal degeneration. Weakness was associated with features of demyelination and axonal loss in the nerves of the arm, and with features of axonal loss in leg nerves. However, a substantial number (approximately one-third) of electrophysiological abnormalities were found in nerves innervating non-weakened muscles. These results imply that in MMN, conduction block is most likely to be found in long arm nerves innervating weakened muscles, but if conduction block cannot be detected in these nerves, the electrophysiological examination should be extended to other arm nerves including those innervating non-weakened muscles.

Action Potentials↗

PubMed2002

Diazepam-enhanced beta activity in Sturge Weber syndrome: its diagnostic significance in comparison with MRI.

OBJECTIVES: This study was performed to assess the extent of functional involvement of the affected hemisphere in Sturge Weber syndrome in comparison with the uninvolved hemisphere. To this end beta activity in the electroencephalogram (EEG) was measured, both before and after administration of diazepam intravenously (i.v.). METHODS: In 9 patients asymmetry in beta band activity was studied before and after diazepam administration. Several beta bands and asymmetry parameters were calculated. beta band asymmetries were compared with structural abnormalities (magnetic resonance imaging, MRI). RESULTS: Total beta activity was reduced in the involved hemisphere in all patients after diazepam administration. In 3 patients functional abnormalities were found in brain regions that were structurally intact. CONCLUSIONS: Decreased diazepam-enhanced beta activity in the EEG is a sensitive criterion of functional abnormality. In patients with subtle structural abnormalities diazepam-enhanced EEG may have added value in diagnosing functional involvement and in monitoring disease progression in patients.

Adolescent↗

PubMed2001

A new method for measuring mechanical properties of laryngeal mucosa.

A study of the effect of exogenous hazardous agents or conditions on the mechanical characteristics of vocal fold mucosa should meet three methodological criteria. 1) The outer surface of the mucosa should be exposed to the agent or condition while the inner surface is exposed to a physiological environment. 2) Even slight changes in mechanical characteristics should be detected. 3) The applied strain should be within physiological ranges. To date, no such method has been described in the literature. A method meeting the listed criteria is proposed and evaluated here.

Animals↗

PubMed2001

Laryngeal mucosa elasticity and viscosity in high and low relative air humidity.

In earlier work we showed that low relative humidity (RH) of inhaled air causes acoustic voice parameters such as jitter and shimmer to deteriorate. Other authors have shown negative effects on vocal efficiency. To explain these changes in the mechanical properties of the vocal folds, the effects of changes in RH of the air passing over microdissected mucosa of sheep larynges were studied. The dissected surface of the tissue specimen just touched Ringer solution and air of varying RH was blown over the specimen. The mucosa specimen was subjected to sinusoidal oscillations of length (strain) and the resulting force (stress) was measured. The gain and phase angle between the imposed strain and resulting stress were measured, and elasticity and viscosity were calculated. Two different air conditions were tested: air with high RH (100%) vs air with low RH (0%). Viscosity and stiffness increased significantly in both ambient conditions (P < 0.01). Dry dehydrating air resulted in a stiffer and more viscous cover than humid air (P < 0.001). These changes in mechanical characteristics may contribute to the effects on voice parameters described in earlier work.

Animals↗

PubMed2001

The existence of two sources in rolandic epilepsy: confirmation with high resolution EEG, MEG and fMRI.

In benign rolandic epilepsy seizure semiology suggests that the epileptic focus resides in the lower sensorimotor cortex. Previous studies involving dipole modeling based on 32 channel EEG have confirmed this localization. These studies have also suggested that two distinct dipole sources are required to adequately describe the typical interictal spikes. Since in benign epilepsy invasive validation is prohibited, this study tries to further establish these results using a multi-modal approach, involving 32 channel EEG, high resolution 84 channel EEG, 151 channel MEG and fMRI. From one patient interictal spikes were recorded and analyzed using the MUSIC algorithm in a realistic volume conductor model. In an fMRI experiment the same patient performed voluntary tongue movements, thus mimicking a typical seizure. Results show that EEC, MEG and fMRI localization converge on the same area in the lower part of the sensorimotor cortex, and that high resolution EEG clearly reveals two distinct sources, one in the post- and one in the pre-central cortex.

Brain Mapping↗

PubMed2001

Flow redistribution in the major cerebral arteries after carotid endarterectomy: a study with transcranial Doppler scan.

PURPOSE: This open single-center prospective study aimed to determine the redistribution of blood flow within the circle of Willis and through collateral pathways after carotid endarterectomy. Blood flow velocity and flow direction in the major cerebral arteries were determined, both at rest and during CO(2) inhalation. METHODS: Carotid endarterectomy was performed in 148 patients with a 70% or greater diameter stenosis of the internal carotid artery while patients were under general anesthesia. Arteriotomy closure was done with a venous patch. Selective shunting was performed with an electroencephalogram. Baseline blood flow velocity of the basal cerebral arteries was measured by means of transcranial Doppler sonography preoperatively (within 1 week before surgery) and 3 months postoperatively. At the same times, cerebrovascular reactivity was calculated during CO(2) inhalation insonating both middle cerebral arteries. RESULTS: Baseline blood flow velocity in the ipsilateral middle cerebral artery hardly changed 3 months postoperatively, but there was a considerable redistribution of flow in the circle of Willis. This was characterized by a decrease in contribution from the contralateral hemisphere through the anterior communicating artery, reduced cerebropetal flow rates in the ophthalmic artery, and smaller contribution of the posterior collateral sources. The CO(2) reactivity on the side of surgery increased in all patients. In patients with a contralateral occlusion, CO(2) reactivity increased on both sides. The redistribution of flow was most pronounced in patients who needed intraoperative shunting and in patients with a contralateral internal carotid artery occlusion. CONCLUSION: After carotid endarterectomy, flow redistribution, as expressed by changes in blood flow velocity values, occurs in the circle of Willis. The contribution of collateral sources is diminished, and the CO(2) reactivity increases, both of which reflect improvement of the hemodynamic condition. The most improvement occurs in patients with contralateral occlusion.

Aged↗

PubMed2001

The development of spectral EEG changes during short periods of circulatory arrest.

The EEG was monitored in 56 patients during implantation of an internal cardioverter defibrillator. The purpose of this study was to determine the main EEG frequency ranges that represent ischemic changes during short periods of circulatory arrest. The EEG was recorded with a 16-channel common reference montage (Cz). After onset of circulatory arrest, the log spectral changes of three-epoch moving averages were calculated relative to the baseline spectrum. For factor analysis, 17 EEG periods were selected that showed changes progressing to an isoelectrical period. Topographic differences and the time course of quantitative EEG (qEEG) changes were studied in all 56 patients. For each patient the EEG period with the longest duration of circulatory arrest was chosen. Factor analysis revealed four factors that represented the spectral EEG changes occurring during circulatory arrest and recovery. The frequency intervals of these factors were 0 to 0.5 Hz, 1.5 to 3 Hz, 7.5 to 9.5 Hz, and 15 to 20 Hz for all channels. Only minor topographic differences were found in the power of the spectral changes; the sequence of events was similar for all electrode positions. The first EEG change after circulatory arrest was an initial increase in alpha power and a decrease in beta power. On average, after approximately 15 seconds alpha power started to decrease, beta power decreased further, delta-1 power started to increase, and delta-2 power started to decrease. After approximately 25 seconds, the delta-1 power increase appeared to plateau or to decrease. A circulatory arrest longer than approximately 30 seconds resulted in an isoelectrical EEG. After restoration of the circulation, there was a fast transient increase in delta-1 and delta-2 power, followed by a decrease to baseline. alpha and beta power showed a more gradual increase in power toward baseline and were the last to restore after 60 to 90 seconds. In general, the spectral changes in the alpha and beta frequency ranges were most pronounced and consistent. In conclusion, to detect intraoperative cerebral ischemia, monitoring of changes in the four frequency ranges found is preferable to monitoring changes in the classically defined frequency bands. Furthermore, these results stress the importance of the alpha and beta ranges in detecting cerebral ischemia.

Adolescent↗

PubMed2001

Activation of interictal spiking in mesiotemporal lobe epilepsy by propofol-induced sleep.

The objective of this study was to test whether low-dose propofol increases the number of interictal spikes in patients with mesiotemporal lobe epilepsy, and to determine whether this is the result of intrinsic properties and is restricted to the primary epileptogenic focus. Controlled infusion of propofol in step-up/-down target concentrations of 0, 0.3, 0.6, and 0.8 mg/L was administered to 10 patients during a 3.5-hour daytime EEG registration. The number of spikes were counted and related to propofol concentration and sleep level. Results were compared with a spontaneous, nocturnal first sleep cycle in 9 of 10 patients. All patients entered nonrapid eye movement 1 sleep during propofol administration, and 8 reached nonrapid eye movement 2 sleep. In 7 patients who showed spikes, spikes were related to sleep (P < 0.05) and not to increasing (P = 0.1) or decreasing (P = 0.5) propofol concentration. Six of nine patients showed more spikes during spontaneous (nocturnal) sleep than during propofol-induced sleep. Contralateral spiking was not suppressed selectively. Low-dose propofol is a safe means of increasing spiking in these patients because it induces sleep. There were no signs of an intrinsic epileptogenicity of propofol or a selective effect on ipsilateral spikes. Controlled sleep induction will increase the yield of interictal spikes during short interictal recordings such as in magnetoencephalography.

Adult↗

PubMed2001

EEG evidence for shunt requirement during carotid endarterectomy: optimal EEG derivations with respect to frequency bands and anesthetic regimen.

Currently there is no consensus on the derivations that should be used for EEG monitoring during carotid endarterectomy (CEA). The aim of this study was to determine which derivations distinguish the best between patients requiring a shunt and patients who do not need a shunt. Four predefined frequency bands and two regimens for general anesthesia (isoflurane versus propofol) were used. EEG data (16 channels) were obtained from 152 EEGs recorded during carotid endarterectomy. Analog EEG signals of preclamp and clamp periods of 100 seconds were digitized to compute power spectra. Changes in power during clamping were calculated for all possible derivations in four predefined frequency bands and were expressed as Z-scores. For each derivation, the area under the receiver operating characteristics curve was calculated. Derivations with the greatest area under the receiver operating characteristics curve were considered to distinguish the best between the shunt and the nonshunt groups formed in retrospect on the basis of consensus between three independent and experienced board-certified electroencephalographers. The two different anesthetic regimens resulted in different patterns of EEG changes because of clamping. The optimal derivations to differentiate between the shunt and the nonshunt groups also differed for the two anesthetic regimens, although for both conditions, anterior head regions were especially preferred. The optimal derivations are given for each anesthetic regimen.

Adult↗

PubMed2000

Observer variations in short period spectral analysis of heart rate variability.

25% of the corresponding mean LF/HF ratio. The smallest interobserver variations were found for the 'fixed frequency' method. The data showed that it is advantageous to select the 3-min ECG periods but not to select the frequency regions. Selection of the latter led to an increase in interobserver variation. The results of this study give a realistic impression of the intrasubject and interobserver variation to be expected when measuring the LF/HF ratio. This variation is considerable.

Analysis of Variance↗

PubMed2000

Increase in alpha rhythm frequency after carotid endarterectomy.

OBJECTIVES: Besides preventing stroke, carotid endarterectomy (CEA) is reported to improve cerebral circulation and brain function. We tested whether this improvement is reflected by changes in the qEEG. METHODS: qEEG changes in 166 patients with a >70% stenosis of the internal carotid artery (ICA) were assessed after subtraction of the preoperative and postoperative spectra (eyes closed condition) before and 3 months after CEA. The mean frequency of the alpha band (MFA), the peak frequency of the alpha band (F alpha), and bands with limits relative to each patient's F alpha were studied in relation to neurological symptoms, patency or occlusion of the contralateral ICA, shunt requirement, and side of surgery. RESULTS: MFA and F alpha significantly increased over both hemispheres. After alignment on F alpha, a decrease of spectral band power was seen below F alpha, and a band power increase above F alpha. The group of patients with a contralateral ICA occlusion showed significantly more improvement than the group without. The group of patients with neurological deficits showed a tendency for improvement. No differences were found concerning shunt requirement or the side of surgery. CONCLUSIONS: After CEA the alpha rhythm frequency increases. In general, patients with a contralateral ICA occlusion improve more than other patients, in agreement with data from the literature on cerebral circulation and brain function.

Aged↗

PubMed2000

The use of preoperative transcranial Doppler variables to predict which patients do not need a shunt during carotid endarterectomy.

OBJECTIVES: to analyse whether preoperative transcranial Doppler (TCD) variables can predict intraoperative shunt requirement. DESIGN AND METHODS: the blood-flow velocity (BFV) in the major basal cerebral arteries was measured preoperatively with TCD, in 178 patients scheduled for CEA. Carotid artery compression and CO2 reactivity tests were also performed. Intraoperative electroencephalography was used to decide whether a shunt was needed. Differences in the probability of shunt requirement between the categories of variables were assessed with crosstabs statistics. RESULTS: preoperative TCD criteria clearly identified a subgroup of 59 patients (33%) who did not require a shunt. In general, these patients appeared to have adequate collateral flow through the anterior communicating artery. In contrast, prediction of the need for a shunt was less reliable. TCD variables could predict the need for a shunt with a probability of only 60%. CONCLUSIONS: preoperative TCD can be used to identify patients who do not require a shunt during carotid endarterectomy.

Aged↗

PubMed1999

Reduction of sympathetic hyperactivity by enalapril in patients with chronic renal failure.

BACKGROUND: Inhibition of angiotensin-converting enzyme (ACE) reduces the risk of cardiovascular problems in patients with chronic renal failure. This effect may be due in part to a decrease in sympathetic nervous activity, but no direct evidence of such an action is available. METHODS: We studied muscle sympathetic-nerve activity in 14 patients with hypertension, chronic renal failure, and increased plasma renin activity before, during, and after administration of the ACE inhibitor enalapril. Ten other patients with similar clinical characteristics were studied before and during treatment with the calcium-channel blocker amlodipine. Normal subjects matched for age and weight were included in both studies. RESULTS: At base line, mean (+/-SD) muscle sympathetic-nerve activity was higher in the group of patients who received enalapril than in the control subjects (35+/-17 vs. 19+/-9 bursts per minute, P=0.004). The baroreflex curve, which reflects changes in muscle sympathetic-nerve activity caused by manipulations of blood pressure with sodium nitroprusside and phenylephrine, was shifted to the right in the patients, but baroreflex sensitivity was similar to that in the control subjects (-2.1+/-1.9 and -2.7+/-1.3 bursts per minute per mm Hg, respectively; P=0.36). A single dose of the sympatholytic drug clonidine caused a greater fall in blood pressure in the patients than in the control subjects. Treatment with enalapril normalized blood pressure and muscle sympathetic-nerve activity (at 23+/-10 bursts per minute) in the patients and shifted the baroreflex curve to the left, reflecting normal blood-pressure levels, without significantly changing sensitivity (-2.3+/-1.8 bursts per minute per mm Hg, P=0.96). In the patients who received amlodipine, treatment also lowered blood pressure but increased muscle sympathetic-nerve activity, from 41+/-19 to 56+/-14 bursts per minute (P=0.02). CONCLUSIONS: Increased sympathetic activity contributes to hypertension in patients with chronic renal disease. ACE inhibition controls hypertension and decreases sympathetic hyperactivity.

Amlodipine↗

PubMed1999

The influence of temperature on conduction block.

In nerve conduction studies, it may be difficult to distinguish conduction block from increased temporal dispersion. We assessed whether a better distinction is possible by warming, because this increases the number of blocked nerve fibers and decreases temporal dispersion. We investigated 11 patients with conduction block in the median or ulnar nerve. Motor conduction was studied at 25 degrees C and at 40 degrees C. The amplitude reduction and area reduction were significantly greater at 40 degrees C than at 25 degrees C. Significantly more nerve segments fulfilled criteria for conduction block at 40 degrees C than at 25 degrees C. The duration prolongation was slightly smaller at 40 degrees C. These results indicate that, in demyelinating neuropathies, an increase in temperature increases the number of blocked nerve fibers and decreases temporal dispersion. Conduction block may therefore be missed when the investigated limb is too cold. Based on our study, we also propose a criterion for conduction block that is based on the influence of temperature.

Adult↗