Noxious stimuli do not modify myogenic motor evoked potentials by electrical stimulation during anesthesia with propofol-based anesthesia

PURPOSE: To investigate whether motor evoked potentials (MEP) to transcranial electrical stimulation under constant blood propofol concentration are affected by the arousing effect of surgical noxious stimuli. METHODS: Twenty patients who underwent elective spinal surgery were studied. Patients were anesthetized with 50% nitrous oxide in oxygen, fentanyl, and propofol to maintain the bispectral index (BIS) score around 50. MEP in response to a multipulse transcranial electrical stimulation at stimulus sites of C3-C4 were recorded over the right abductor pollicis brevis muscle. Changes of peak-to-peak amplitude and onset latency of MEP, BIS score before and after surgical stimuli were evaluated. Propofol plasma concentration was measured at the same time points. RESULTS: Both MEP amplitude and latency did not change significantly after surgical stimuli although BIS increased significantly (48 +/- 6 to 58 +/- 5; P < 0.05). Plasma propofol concentration was maintained at the same level between the two measurement points (3.3 +/- 0.7 to 3.3 +/- 0.7 micro g*mL(-1)). There was no relation between BIS change and changes of MEP amplitude and latency, and propofol plasma concentration. CONCLUSION: MEP to the transcranial electrical stimulation under a constant and clinically appropriate blood propofol concentration are not affected by surgical noxious stimuli.     

A method linking statistics and knowledge engineering for making medical consulting systems

There are two methods of making medical consulting systems: the statistical method and the knowledge engineering method. Since both of these methods seem to be very different from each other, they have been recognized and applied separately. We contend, however, that a combination of statistics and knowledge engineering is a more effective and suitable way to create a medical consulting system than is the use of either method alone. In order to justify this contention, we created a medical consulting system, AUTSVR-V1.1, which detects auditory slow vertex responses (SVR) through observing and identifying background activities of the electroencephalogram (EEG) automatically during measurement of SVRs for the purpose of objective electric response audiometry (ERA), and compared it with AUTSVR-V1.0, which depends on statistics only.     

A detecting method for the fetal QRS complex with a small amplitude

It is often impossible to determine the presence of the fetal QRS waves from leads on the maternal abdomen because the amplitude is small or noise interferes. Yet, clinically, confirmation is highly necessary. Clinicians face a great difficulty when the fetal QRS waves are not identifiable: when, for example, they are not apparent owing either to the fetal death or to the poor recording system. We therefore developed the fetal QRS complex detecting system for computer use. This system was developed through the use of two procedures. First, possible fetal QRS waves were detected by computing slopes of moving regression lines. Second, the location of the fetal QRS waves was determined from possible fetal QRS waves by using the weighted periodgram method. We recognized that this system can detect fetal QRS complex from fetal ECGs that are affected by mixture noises in the fetal ECGs accompanying both cephalic and breech presentations.     

Histamine effects on the 5-HT1c receptor expressed in Xenopus oocytes.

To analyze the cross-reactivity between serotonin (5-HT) and histamine, the in vitro transcribed RNA for the 5-HT1c receptor was functionally expressed in Xenopus oocytes. 5-HT significantly increased 45Ca2+ efflux in RNA-injected oocytes, but not in uninjected and water-injected control oocytes. Furthermore, histamine and the H1 receptor agonists, but not the H2 and H3 agonists, significantly induced 45Ca2+ efflux in 5-HT1c receptor RNA-injected oocytes, but not in uninjected and water-injected oocytes. However, the H1, H2, and H3 antagonists failed to inhibit histamine-induced 45Ca2+ efflux at 10(-6) M. This finding suggests that the 5-HT1c receptor can be activated by both 5-HT and histamine, although the action of histamine is different from classic histamine pharmacology.     

Artificial neural networks for source localization in the human brain

Summary Source localization in the brain remains an ill-posed problem unless further constraints about the type of sources and the head model are imposed. Human head is modeled in various ways depending critically on the computing power available and/or the required level of accuracy. Sophisticated and truly representative models may yield more accurate results in general, but at the cost of prohibitively long computer times and huge memory requirements. In conventional source localization techniques, solution source parameters are taken as those which minimize an index of performance, defined relative to the model-generated and clinically measured voltages. We propose the use of a neural network in the place of commonly employed minimization algorithms such as the Simplex Method and the Marquardt algorithm, which are iterative and time consuming. With the aid of the error-backpropagation technique, a neural network is trained to compute source parameters, starting from a voltage set measured on the scalp. Here we describe the methods of training the neural network and investigate its localization accuracy. Based on the results of extensive studies, we conclude that neural networks are highly feasible as source localizers. A trained neural network's independence of localization speed from the head model, and the rapid localization ability, makes it possible to employ the most complex head model with the ease of the simplest model. No initial parameters need to be guessed in order to start the calculation, implying a possible automation of the entire localization process. One may train the network on experimental data, if available, thereby possibly doing away with head models.     

Tetanic Stimulation of the Peripheral Nerve before Transcranial Electrical Stimulation Can Enlarge Amplitudes of Myogenic Motor Evoked Potentials during General Anesthesia with Neuromuscular Blockade

Background: Neuromuscular blockade can suppress myogenic motor evoked potentials (MEPs). The authors hypothesized that tetanic stimulation (TS) of the peripheral nerve before transcranial stimulation may enhance myogenic MEPs during neuromuscular blockade. In the current study, the authors evaluated MEP augmentations by TS at different levels of duration, posttetanic interval, neuromuscular blockade, and stimulus intensity.

Methods: Thirty-two patients undergoing propofol-fentanyl-nitrous oxide anesthesia were examined. Train-of-five stimulation was delivered to C3-C4, and MEPs were recorded from the abductor hallucis muscle. In study 1, TS with a duration of 1, 3, or 5 s was delivered at 50 Hz to the tibial nerve 1, 3, or 5 s (interval) before transcranial stimulation, and the effects of TS on MEP amplitude were evaluated. In study 2, TS-induced MEP augmentations were evaluated at the neuromuscular blockade level (%T1) of 50% or 5%. In study 3, MEP augmentations by TS at stimulus intensities of 0, 5, 25, and 50 mA were evaluated.

Results: The application of TS significantly enlarged the amplitudes of MEPs at the combinations of duration (3, 5 s) and interval (1, 3, 5 s) compared with those without TS. TS-induced MEP augmentations were similarly observed at %T1 of both 50% and 5%. TS-induced MEP augmentations were observed at stimulus intensities of 25 and 50 mA.