Changes In Electrode Position Research Articles

Vectorcardiographic diagnosis of high lateral myocardial infarction: Proposal of new criteria based on angiography

To reduce the effect of electrode position variations on the diagnostic interpretation of an ECG, ECG and VCG interpretations were combined. The reduction was assessed by generating ECGs with displaced electrodes for a group of subjects using Body Surface Potential Maps (BSPMs). VCGs were reconstructed from the ECGs. The group consisted of normals, cases with myocardial infarction (MI), and with left ventricular hypertrophy (LVH). The effects of four types of electrode position changes were assessed for the diagnostic categories MI and LVH. The combined interpretation proved to be less sensitive to large changes than either the ECG or the VCG interpretation alone. The number of small changes increased for the combined interpretation. The combined interpretation showed higher agreement with a human expert than the ECG interpretation alone.

Transcutaneous blood gas analysis during sleep and exercise in cystic fibrosis

Forty patients with cystic fibrosis (CF) (mean age, 13 +/- 2.5 years) were studied with transcutaneous (tc) blood gas monitoring (TCM) during sleep and exercise. By comparing arterial blood samples and TCM in 24 of them (27 samples), a mean bias of tcO2 -15.91 mmHg with a precision of 8.4 mmHg was found. The mean bias of tcCo2 was 7.21 mmHg with a precision of 3.9 mmHg. A standardized submaximal exercise test (1.7 W/kg) was performed in all 40 CF patients and in 14 healthy control subjects (mean age, 13 +/- 0.5 years). The typical tc trend during exercise for CF and healthy subjects was a slight increase of tcO2 levels and tcCO2 stability. A minor decrease of tcO2 values occurred in four CF patients (no greater than 7 mmHg). In 28 patients (mean age, 13 +/- 3 years), tcO2 and tcCO2 were recorded during sleep. In 13 of them, apparent hypoxemic episodes were noted, without relation to the degree of airway obstruction. There were simultaneous episodes of hypercapnia in ten patients. Some difficulties were encountered in analyzing long-term recordings. TcO2 drifts upward and tcCO2 decreases during the recordings over several hours. The change in electrode position after 4 h of sleep modified tcO2 and tcCO2 values. Such difficulties limit the usefulness of long-term but not short-term recordings.

Analysis of amplitude and area of concentric needle EMG motor unit action potentials

Computer simulations indicate that measurements of the area of motor unit action potentials (MUAPs) recorded with a concentric needle electrode could be useful in differentiating between neuropathy and myopathy. However, MUAP area varies markedly when the position of the recording electrode is changed only slightly within the motor unit territory, mainly because of the changes in the MUAP amplitude produced by only slight electrode movements. The ratio of MUAP area to amplitude is much less affected by changes in electrode position and measure the ‘thickness’ of the MUAP wave form. We found that the MUAP area: amplitude ratio was reduced in myopathy even when the MUAP amplitude was normal or increased. In patients with neuropathy, the MUAP amplitude and area both tend to be increased while their ratio is normal or increased. The diagnostic yield obtained from MUAP area, amplitude and their ratio in combination was similar to that obtained using measurements of MUAP duration. Unlike the MUAP duration, the MUAP area, amplitude and area: amplitude ratio are robust features of the MUAP in that they are less sensitive to the signal-to-noise ratio and inter-operator differences in signal selection.

The 3-channel Lissajous' trajectory of the auditory brain-stem response. IV. Effects of electrode position in the cat

Three-channel Lissajous' trajectories (3-CLTs) of the auditory brain-stem response (ABR) were recorded from anesthetized adult cats with 2 different orthogonal and 3 different non-orthogonal recording configurations. Click stimuli were presented monaurally at 70 dB impulse SPL. Planar analysis identified 12 planar segments regardless of electrode configurations. Boundaries, apex latencies, and durations of the planar segments were relatively unchanged by changes in recording locations, in contrast to changes in single-channel ABR peak latencies and amplitudes. The 3-CLT orientation and shape were maintained in voltage-space despite changes in electrode positions, provided that the recording axes remained orthogonal and a simple cosine correction was applied. Non-orthogonal recording axes resulted in 3-CLTs which differed in shape from 3-CLTs recorded from orthogonal recording axes, but had similar planar-segment boundaries and durations. We conclude that the 3-CLT has characteristics which are generator-dependent and unaffected by electrode position if appropriate spatial corrections are applied.

Complications in Cases of Epidural Stimulation Electrode Implants

Spinal cord stimulation (SCS) is an effective treatment for pain and motor disturbances. We have performed 124 SCS procedures between 1981 and 1984 at the University of Göttingen. Reoperations were required for 69 cases (56%) for various reasons, most frequently changes in electrode position due to the dislodgement (36 cases, 52%.) Analysis of the development of this postoperative repositioning showed that 67% occurred within 1 month after the implantation. Therefore, if patients can be kept at rest during the granulation period of 1 month after operation, we suggest that the frequency of reoperation may be considerably lessend.

Studies of biologic parameters for denture design. Part III: Effects of occlusal adjustment, base retention, and fit on masseter muscle activity and masticatory performance

EMG recordings of ipsilateral and contralateral masseter muscles and standardized masticatory performance tests were made in 20 denture wearers before and after modifications were made to their clinically unsatisfactory dentures. The improvement of retention and stability by correction of gross occlusal prematurities and by the use of a denture adhesive or base reline with a soft tissue-conditioning material did not significantly alter the chewing performance or muscle activity during mastication in denture wearers. The results support our previous findings that the influence of denture factors on chewing ability of denture wearers is limited. To avoid variations in EMG activity caused by changes in electrode positions, all tests for a given subject were made at the same sitting. Thus the study design did not provide time to denture wearers for their neuromuscular mechanism to adapt to the modifications prior to testing masticatory function. A replication of this study that permits sufficient adaptation time after each modification is suggested to validate the findings.

Effects of electrode position on esophageal diaphragmatic EMG in humans.

The effects of electrode position and gastric-balloon anchoring on esophageal diaphragmatic EMG (EMGdi) responses to CO2 rebreathing were studied in seven normal sitting humans using an esophageal catheter that consisted of four platinum wire coils enabling simultaneous recording of three EMGdi signals from three different sites in the esophagus. A gastric balloon attached to the distal end of the catheter allowed anchoring of the catheter. EMGdi signals were quantitated as a moving time average. Two rebreathing experiments were performed with and without balloon anchoring on the same day. Changes in electrode position of at least 2 cm above the site of maximum EMGdi activity caused minimal changes in the moving average EMGdi and did not significantly effect the quantitated EMGdi response to CO2 rebreathing. The maximum EMGdi activity was approximately 2 cm above the gastroesophageal junction in sitting humans. Stabilization of the catheter with an inflated gastric balloon did not improve the reproducibility of the EMGdi data. Finally, the EMGdi response to two CO2 rebreathing runs done at the same sitting showed intraindividual reproducibility.

Human ability to discriminate various parameters in afferent electrical nerve stimulation with particular reference to prostheses sensory feedback

Afferent electrical nerve stimulation is an approach showing many promises with regard to sensory feedback for powered prostheses. It is well tolerated, can transmit fairly high amounts of information, and has several characteristics making it superior to electrocutaneous and vibrotactile devices when applied to prostheses. The feedback information is transferred in modulated form either by means of the current pulse amplitude (a.m.) or by the current pulse frequency (f.m.) A.M. stimulation should be applied in such a way that it gives rise to characteristic changes in the distribution of paresthesias with changing current. Used in this way it is not dependent upon minor changes in electrode position, it is easy to learn and gives high rates of information, even in untrained subjects. The number of channels that can be used in each nerve is, however, limited because of the large amount of axons necessary to achieve the spatial spread. F.M. stimulation is more difficult to learn than a.m. but gives the same rate of information transfer when used in trained individuals. Like a.m. it is not dependent upon minor changes in electrode position, but a smaller number of axons is needed to achieve discrimination. Thus several channels can be used in each nerve. Both with a.m. and f.m. stimulation a trained subject can discriminate five or six discrete levels with a rate of correct recognition of more than 75%, the amount of transmitted information being about 1·8 bits per symbol.

Distribution of activity in spinal pathways evoked by experimental dorsal column stimulation.

Experiments were performed in rhesus monkeys to determine the distribution of activity evoked in spinal pathways by dorsal column stimulation. It was shown that many pathways in both the dorsal and ventral quadrants of the cord can be activated either directly or transsynaptically by stimulation with electrodes of the type implanted clinically. Moreover, the transsynaptically evoked responses recorded in each quadrant had somewhat different characteristics. Therefore, since the activation of each group of pathways may have differing effects in modifying the preception of noxious stimuli, the authors believe that changes in electrode position and stimulus parameters may be important in obtaining the therapeutic value of spinal cord stimulation for relief of pain.

Differences caused by changes in electrode positions in two corrected orthogonal lead systems

Frank and McFee corrected orthogonal lead systems were compared for electrode displacement errors on 10 normal and 12 abnormal (enlarged hearts) individuals. All of the normal and 6 of the abnormal subjects were recorded using both lead systems. Chest and back electrodes were individually and collectively displaced 2.5 centimeters from their correct locations and errors in scalar and vector amplitudes were measured using a digital computer. The McFee lead showed some superiority over the Frank lead for scalar amplitudes when percentage errors were compared but no significant difference between the systems was observed when comparing absolute magnitude of errors. For the Frank lead the normal group performed better than the abnormal group while no such difference occurred for the McFee lead. The Frank lead was most sensitive to longitudinal electrode displacement while the McFee lead was most sensitive to lateral displacement of the left side and anterior chest wall electrodes. For the Frank lead it appears that a level slightly below the 4th interspace was optimum for the majority of subjects.