Biomedical subjects

V Häkkinen

Publications and source records attributed to V Häkkinen.

At least 19 recordsLinked to original sources

PubMed1999

Implementation of three-dimensional EEG brain mapping.

The electroencephalogram (EEG) visualization software was developed containing two-dimensional (2D) and three-dimensional (3D) brain mapping modules. The input to the program is standard clinical individual patient data recorded using digital EEG and magnetic resonance imaging (MRI). The software utilizes several techniques, such as heuristic triangulation, ray casting, Gouraud shading, and image fusion to form multimodal 3D images. The program has been applied to the 3D visualization of various EEG signals, "cortical" EEG signals, and potential fields generated by a computer model. The developed program appears to operate efficiently and intuitively in PC/Windows environment.

Algorithms↗

PubMed1998

Cortical silent period evoked by transcranial magnetic stimulation in ischemic stroke.

OBJECTIVES: Transcranial magnetic stimulation (TMS) of the motor cortex produces motor evoked potentials (MEPs). Besides this excitatory response, TMS has inhibitory effects. When TMS is performed during voluntary muscle contraction, the MEP is followed by a pause in electromyographic activity (cortical silent period, SP). The aim of this study was to evaluate the clinical usefulness of the SP. METHODS: We studied SP changes in 50 patients with acute hemispheric brain infarction. A stimulator with a round coil and a fixed intensity of 90% of maximum was used to evoke MEPs. RESULTS: SP was elicited on the affected side in 29 of the 50 patients. The mean SP duration was markedly longer on the affected side in the patient group. There were no significant differences between left and right sides in the means of the MEP amplitude ratio (amplitude related to corresponding amplitudes to peripheral electric stimulation) and MEP latencies in the patient group. Prolonged SP was found in 25 of the 29 patients (86%) whereas only 4 (14%) had abnormalities in MEP latency or amplitude ratio. The mean SP duration was significantly prolonged also in a subgroup of 14 patients with normal hand function. CONCLUSIONS: The SP measurement is an easily performed and sensitive method to detect even subclinical disturbances in motor system function in ischemic stroke.

Adult↗

PubMed1998

Clonidine does not attenuate median nerve somatosensory evoked potentials during isoflurane anesthesia.

BACKGROUND: Clonidine, an alpha2 agonist, reduces the requirements of several anesthetics. However, the effects of clonidine on somatosensory evoked potentials (SEPs) are unclear. These effects on cortical SEPs during isoflurane anesthesia were studied in 20 ASA I-II patients scheduled for elective surgery. Furthermore, the isoflurane concentration required to induce electroencephalogram (EEG) burst-suppression with and without clonidine was studied. METHODS. Anesthesia was maintained with isoflurane at a FiO2 of 0.4. At 1 MAC isoflurane the patients were randomly given either intravenous clonidine 2 microg kg(-1) (ten patients) or saline (ten patients). Finally, the isoflurane concentration was increased to a point at which a burst-suppression pattern appeared in the EEG. SEPs upon median nerve stimulation were recorded (1) before induction of anesthesia, (2) at 1 MAC before clonidine/saline, (3) at 1 MAC after clonidine/saline, (4) at EEG burst-suppression. RESULTS: The cortical SEP amplitude was attenuated from 3.7 (2.0) microV to 2.1 (1.3) microV (p < 0.001) and the peak latency increased from 19.3 (1.1) ms to 22.0 (1.3) ms (p < 0.0001) during 1 MAC isoflurane anesthesia, but the addition of clonidine did not further increase these changes. The isoflurane end-tidal concentration needed to induce burst-suppression EEG was not significantly different in the clonidine group compared with the placebo group (2.0% vs. 2.1%, p = 0.07). CONCLUSIONS: The effect of clonidine in reducing the requirements of anesthetics during general anesthesia is not seen in the cortical SEPs. The isoflurane-induced burst-suppression in the EEG was not affected by clonidine, suggesting that the EEG effects of clonidine and isoflurane were not additive. If SEPs are monitored intraoperatively, clonidine can be used as an adjuvant during isoflurane anesthesia without harmful effects on SEP monitoring.

Adrenergic alpha-Agonists↗

PubMed1997

Motor involvement in acute herpes zoster.

Motor involvement in acute herpes zoster is considered rare, but its incidence is unknown. In a sample of 40 patients with acute herpes zoster of varying severity, an abnormal electromyogram (EMG) (fibrillation, positive waves, high-frequency discharges) was found in 21 (53%), suggesting extension of inflammation to the anterior horn and/or anterior motor roots. In the majority of patients these changes were not confined to the segment invaded by the rash but were widespread, extending several segments cranially and caudally, and both ipsi- and contralaterally. In 5 (13%) patients these changes became more extensive on repeat EMG over a period of months. There was no association between severity of rash, pain, postherpetic neuralgia, and EMG changes. We conclude that widespread subclinical motor involvement is relatively common in herpes zoster, may last for months, and is easily detectable by EMG.

Acute Disease↗

PubMed1997

Median nerve somatosensory evoked potentials during isoflurane anaesthesia.

PURPOSE: The effect of isoflurane on the subcortical P14 component of the median nerve somatosensory evoked potential (SEP) is poorly known. We studied whether the P14 wave from the upper brainstem, recorded with a nasopharyngeal electrode, was attenuated at the isoflurane-induced EEG burst-suppression level. We also compared the effect of isoflurane on the P14, cervical N13 and cortical N20, N35 and N6, components. METHODS: Seventeen elective patients were anaesthetized with isoflurane. Somatosensory evoked potentials were recorded prior to anaesthesia, at 0.5 MAC and 1 MAC end-tidal isoflurane as well as at the level when EEG was in burst-suppression (mean 1.9 vol% end-tidal isoflurane). RESULTS: Isoflurane had varying effects on the subcortical components of median SEP. The amplitude of nasopharyngeal P14 was stable, but the mean latency increased from 14.4 +/- 1.2 msec at 0.5 MAC to 15.2 +/- 1.1 msec at burst-suppression level (P < 0.05). In contrast, the N13 neck response amplitude was attenuated from 3.3 +/- 0.6 microV to 2.6 +/- 0.5 microV (P < 0.005) without latency changes. The latency of the cortical N20 wave was increased from 19.7 +/- 1.1 msec at awake to 24.4 +/- 1.6 msec at burst-suppression level (P < 0.0001) and amplitude was reduced from 3.3 +/- 1.1 microV to 1.3 +/- 0.6 microV (P < 0.0001). The later cortical components were attenuated even during 0.5 MAC isoflurane and were not recordable during EEG burst-suppression. CONCLUSION: We conclude that P14 can reliably be recorded with nasopharyngeal electrodes during isoflurane anaesthesia, even during EEG burst-suppression, when the N20 wave is attenuated. In contrast, the middle-latency SEP components are sensitive to isoflurane anaesthesia.

Adolescent↗

PubMed1997

The detection of drowsiness and sleep onset periods from ambulatory recorded polygraphic data.

A 30 min sample recording at the sleep onset of 7 healthy male subjects was used to further develop a computer-scoring algorithm applied earlier for the analysis of MSLT recordings. The performance of this algorithm was tested on 7 patients with obstructive sleep apnea by using 6 h daytime recordings including drowsiness and sleep episodes. The total epoch-by-epoch agreement between visual and computer scoring was over 90% and the accurate detection rate of non-REM sleep was 64%. The hypnograms produced by the computer scoring corresponded sufficiently to those obtained by visual scoring. Our automatic scoring system can give a good estimation of the daytime vigilance profile but for clinical diagnosis the results have to be verified visually. However, by using modern digital recording, analyzing and scoring techniques the speed of analysis and thus the costs can markedly been reduced as compared to traditional visual analysis.

Adult↗

PubMed1997

Nitrous oxide has different effects on the EEG and somatosensory evoked potentials during isoflurane anaesthesia in patients.

BACKGROUND: Electroencephalogram (EEG) and somatosensory evoked potentials (SEPs) are altered by inhalation anaesthesia. Nitrous oxide is commonly used in combination with volatile anaesthetics. We have studied the effects of nitrous oxide on both EEG and SEPs simultaneously during isoflurane burst-suppression anaesthesia. METHODS: Twelve ASA I-II patients undergoing abdominal or orthopaedic surgery were anaesthetized with isoflurane by mask. After intubation and relaxation the isoflurane concentration was increased to a level at which an EEG burst-suppression pattern occurred (mean isoflurane end-tidal concentration 1.9 (SD 0.2) %. With a stable isoflurane concentration, the patients received isoflurane-air-oxygen and isoflurane-nitrous oxide-oxygen (FiO2 0.4) in a randomized cross-over manner. EEG and SEPs were simultaneously recorded before, and after wash-out or wash-in periods for nitrous oxide. The proportion of EEG suppressions as well as SEP amplitudes for cortical N20 were calculated. RESULTS: The proportion of EEG suppressions decreased from 53.5% to 34% (P < 0.05) when air was replaced by nitrous oxide. At the same time, the cortical N20 amplitude was reduced by 69% (P < 0.01). CONCLUSION: The results suggest that during isoflurane anaesthesia, nitrous oxide has a different effect on EEG and cortical SEP at the same time. The effects of nitrous oxide may be mediated by cortical and subcortical generators.

Adolescent↗

PubMed1997

Effects of hypothermia and sternal retractors on median nerve somatosensory evoked potentials.

BACKGROUND: Somatosensory evoked potentials (SEPs) are altered by hypothermia, which is often used during cardiopulmonary bypass (CPB). However, the effect of hypothermia on SHP amplitudes is unclear. Also, the sternal retractors used during open heart surgery are reported to cause brachial plexus distension and SEP changes. METHODS: Median nerve SEPs under hypothermic CPB were studied in 29 elective patients scheduled for open heart surgery. In 23 patients who underwent left internal mammary artery (IMA) dissection, the effects of sternal retractors on cortical SEP before the initiation of CPB were investigated. RESULTS: A latency shift of all SEP components was detected when nasopharyngeal temperature decreased from 35.7(SD 0.4) degrees C to 27.8(SD 0.25) degrees C. The mean cortical N20 latency was increased by 39% (P < 0.0001), cervical N13 by 33% (P < 0.0001), and peripheral N9 by 27% (P < 0.0001). The latency changes were reversible when normothermia was restored. The effect of hypothermia on SEP amplitudes was more complex. The mean amplitude of N20 decreased from 2.7 microV to 2.2 microV (P < 0.05) and the amplitude of N13 from 2.5 microV to 2.0 microV (P < 0.0001). In contrast, the N9 component showed an increase from 1.4 microV to 2.1 microV (P < 0.0001) during hypothermia. The sternal retractors did not cause significant cortical SEP amplitude changes during IMA dissection or sternotomy. Also, the latency changes were small, although significant (P < 0.05). CONCLUSION: Despite the moderate amplitude changes produced by hypothermia, SEPs can be successfully monitored during hypothermia. Theoretically, the different behaviour of amplitude in peripheral and cranial components of SEP during hypothermia is interesting. Hypothermia has a more profound effect on synaptic transmission, represented by the cortical N20 latency, than on the peripheral nerve conduction velocity. Intraoperative monitoring of temperature is essential whenever SEPs are recorded. The sternal retractors were not responsible for the intraoperative SEP changes.

Cardiopulmonary Bypass↗

PubMed1997

Distributed clinical neurophysiology.

We have developed a consultation forum for clinical neurophysiology in Finland. The system connects local digital electroencephalography (EEG) recording and analysing networks using a high-speed asynchronous transfer mode (ATM) network. Clinicians can obtain a second opinion using interactive data and video consultations or using data-only consultations. In addition, the system can be used for off-line review of pre-recorded data. During a one-month evaluation, 66 EEG recordings were made altogether in Satakunta Central Hospital and consultations were required on 12 occasions. Nine of them were data-only consultations and three were data and video consultations. A data consultation lasted 15-20 min and a data and video consultation 35-45 min. Clinically, there were numerous benefits for the hospitals. The system established a link to a centre of excellence for second opinions or continuing education. It also helped with on-duty arrangements and enabled the construction of national data banks.

Electroencephalography↗

PubMed1996

Nonlinear eye movement detection method for drowsiness studies.

Automatic long-term vigilance analysis systems require information about the occurrence and type of eye movements, in addition to information about other physiological signals. This paper presents a method to detect different types of eye movements in ambulatory recordings. The method is based on the application of a weighted FIR-median-hybrid filter in the preprocessing of the signal and on the novel use of linear correlation between two EOG signals which are obtained using a new, improved electrode montage. The evaluation of the method showed that it performed well in detecting isolated unambiguous eye movements, but differences were observed in comparison to visual scoring in borderline cases. The method was found to be suitable for use as part of a signal analysis system for drowsiness studies.

Electrooculography↗

PubMed1995

A comparison of transcranial magnetic stimulation with electroneuronography as a predictive test in patients with Bell's palsy.

The aim of this study was to examine the neuronographic findings of electrical and transcranial magnetic stimulation of the facial nerve and to compare their ability to predict clinical recovery from idiopathic facial nerve palsy (Bell's palsy). Eighty-six patients were examined clinically and neurophysiologically immediately on presentation to Tampere University Hospital. Electroneuronography (ENoG) and transcranial magnetic stimulation (TMS) were performed 1-6 times for each patient. The time interval between each examination varied from 2 to 7 days. Seventy-eight patients were followed for a median period of 13 months after the onset of palsy. Facial nerve function was graded according to the House-Brackmann grading system. Relative amplitude differences of ENoG and TMS during the acute phase were then correlated with clinical outcome. Statistical analysis of the results showed that a TMS response elicitable during the first 5 days of the palsy was correlatable with a good prognosis. ENoG results correlated with clinical outcome at a later time from onset of symptoms. TMS was well tolerated and no adverse effects were seen. These results indicate that TMS is a useful method for the early prediction of outcome in patients with Bell's palsy.

Acute Disease↗

PubMed1995

Multi-centre comparison of five eye movement detection algorithms.

Although various investigators have suggested algorithms for the automatic detection of eye movements during sleep, objective comparisons of the proposed methods have previously been difficult due to different recording arrangements of different investigators. In this study the results of five eye movement detection algorithms applied to the same data were compared to visually scored data. The percentages of true and false detections are given for various threshold levels in rapid and slow eye movement detections. The methods gave best results when they were used with the same electrode montage they were designed for but the performance decreased when other montages were used. Subtracting the cross-talk of EEG delta activity improved the correctness of eye movement detections.

Journal Article↗

PubMed1995

Which structures are sensitive to painful transcranial electric stimulation?

Electric transcranial stimulation (TCS) is useful for clinical studies. It is, however, painful and not generally used for awake subjects. By means of topical anaesthesia and nerve blockades we wanted to find out which structures of the scalp and cranium are sensitive to electric TCS. Altogether 21 subjects participated in the present study. Our data show that pain experienced by the subjects during electric TCS is brought about by activation of the pain receptors in the scalp under the stimulating electrodes. Topical anaesthetic cream is incapable of attenuating this pain. The periosteum does not seem to be much more sensitive electric stimulation than rest of the scalp. Furthermore, contractions of facial and neck muscles do not seem to have a significant role in pain generation in electric TCS. Pain can be prevented if sufficiently large areas of the scalp are properly anaesthetized before stimulation by e.g. blockade of the major nerves responsible for the sensation of the stimulus area.

Adult↗

PubMed1994

Evaluation of a computerized system for recognition of epileptic activity during long-term EEG recording.

A new method of recognition of epileptic activity using adaptive segmentation in EEG during long-term intensive monitoring was developed in Tampere. The performance of the system was validated and compared to the commercially available discharge recognition system of Gotman. Twelve approximately 30 min EEG segments recorded during intensive monitoring from 6 patients were analysed. On these EEG segments two EEG specialists marked the occurrence of epileptic activity independently. Later they re-evaluated any differences in their scoring. This consensus file was used as a reference in validating the performance of the two computer programs. We found that the program developed in Tampere detected discharge activity more often than the Gotman system. Both systems performed poorly in spike recognition. In the specificity of the recognized segments, the Gotman system was better.

Computer Systems↗

PubMed1994

Somatosensory evoked potentials during isoflurane anaesthesia.

Short latency somatosensory evoked potentials (SEPs) to median nerve stimulation during isoflurane anaesthesia were recorded in 12 elective-surgery patients. The effect of isoflurane on the shape, amplitude and latency of SEPs was evaluated. SEPs were recorded at awake, 1 MAC, 1.5 MAC, at electroencephalogram (EEG) burst suppression and at continuous suppression levels. Finally, SEPs were recorded when anaesthesia was lightened back to 1 MAC. The peak latency and amplitude of the first cortical N20 wave were measured. The latencies increased with increasing isoflurane concentrations. At high concentrations only an almost monophasic N20 wave was recorded, reduced in shape and amplitude. No specific changes could be correlated with the burst suppression or suppression patterns. This suggests that EEG and SEP generators are differently affected with increasing isoflurane concentration. The results indicate that SEPs can also be recorded in drug-induced EEG suppression.

Adult↗

PubMed1993

The effect of small differences in electrode position on EOG signals: application to vigilance studies.

The primary aim of the study was to determine the best electrode positions for EOG signals in vigilance studies. Two-channel recordings were conducted in analogy to the Rechtschaffen and Kales (1968) system. Twenty electrodes (10 electrode pairs) were compared. Both EOG amplitudes and amplitude asymmetries within an electrode pair were studied. The amplitude of the EOG signal is sensitive to relatively small differences in electrode position. This concerns especially distance from the eye, the direction of eye movement and the effect of the upper eye lid movement. Larger and more symmetrical EOG amplitudes were obtained for different eye movements by placing the electrodes more medially than in the conventionally used system. EOG asymmetry in different electrode positions was dependent on the eye movement direction and even on the starting and end points of a movement with equal angular degrees. Most of the data could be explained by a simple monopolar model when combined with the effects of the upper eye lid movements. The most unexpected finding was that the EOG amplitudes of the horizontal and oblique eye movements were significantly larger when the eyes were moving towards an electrode than when they were moving to the opposite direction.

Adult↗

PubMed1993

Validation of computer analysed polygraphic patterns during drowsiness and sleep onset.

A computer system for the automatic analysis of polygraphic records was validated. Records from 9 subjects made during routine MSLT tests were analysed both by two preliminary and one consensus scorer and by a computer system. Special attention was paid to the analysis of drowsiness periods. Therefore a classification system including 7 stages, three for wakefulness and movement, one for drowsiness and three for the sleep stages S1, S2 and SREM was used. Adaptive segmentation was used to divide the records into short segments of variable length (mean 1.6 sec, range 0.5-13.7 sec). The agreements between the computer and visual scores were relatively good for 5 subjects having a prominent occipital alpha activity during wakefulness (range 70-79%) but less promising (range 64-70%) for the other 4 subjects with "poor" occipital alpha activity. The values obtained corresponded to the inter-scorer agreements. Most of the discrepancies were between adjacent stages. At times in the presence of strongly fluctuating EEG amplitudes and especially with the "low-alpha" subjects it was very difficult to determine exactly even by visual scoring when, for instance, drowsiness became sleep. It is concluded that the reliability of the system is sufficient for practical purposes especially if critical parts of the records are visually reexamined. It was found to be difficult to define unambiguous scoring criteria for subjects with poorly defined EEG rhythms giving insufficient landmarks for stage determination.

Adult↗

PubMed1992

Magnetic facial nerve stimulation in Bell's palsy.

The transcranial magnetic stimulation (TMS) technique makes it possible to stimulate the intracranial part of the facial nerve. In a total of 51 patients with acute Bell's palsy, TMS was performed, and the responses were compared with those elicited by conventional extracranial electric stimulation (EES). Clinical recovery was evaluated at 258-539, mean 410, days from the beginning of the palsy. With both techniques the motor evoked potentials (MEPs) could always be elicited on the healthy side, the mean latency being 4.7 ms with TMS and 3.7 ms with EES. In the acute phase, TMS elicited MEPs on the paralyzed side in 47% of the patients, and EES in 98%. The patients with TMS elicitable MEPs during the first 4 days of the palsy had significantly better recovery than those without response (p less than 0.05). The difference in recovery between patients with or without elicitable TMS responses on days 5-8 and 9-14 was not significant. In EES, the amplitude difference between the two sides within the first 4 days was not significantly (p greater than 0.05) different. On days 9-14 the patients with a less than 80% difference between the two sides recovered significantly (p less than 0.05) better than those with a difference of greater than or equal to 80%, So, TMS may be of help in the early prognosis of Bell's palsy.

Adolescent↗