Effect of lung volume on the oesophageal diaphragm EMG assessed by magnetic phrenic nerve stimulation.
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Previous studies have shown conflicting results on the effect of lung volume on the diaphragm compound muscle action potential (CMAP). Consequently, the ability to quantify the oesophageal diaphragm electromyography (EMG) has been questioned. If lung volume changes have little effect on the diaphragm CMAP the accurate measurement of voluntary EMG, as an index of respiratory drive, may be possible. Furthermore, the measurement of CMAP could provide useful clinical information when evaluating patients with neuromuscular disease. To reassess the effect of lung volume on the oesophageal diaphragm CMAP, six normal subjects were studied using an oesophageal catheter incorporating seven electrodes (number one being proximal and seven distal) that were 1 cm in length and 1 cm apart. Electrode number three was positioned at the centre of the electrically active region of the diaphragm (EARdi) at functional residual capacity (FRC). The diaphragm CMAP elicited by bilateral magnetic stimulation of the phrenic nerves was simultaneously recorded from four electrode pairs. Pair one was created from electrodes one and three, pair two from electrodes two and four, pair three from electrodes three and five, and pair four from electrodes five and seven. Phrenic nerve stimulation was at residual volume (RV), FRC, FRC+1.0 L, FRC+2.0 L, and total lung capacity (TLC). The CMAP recorded from pair one was least influenced by changes in lung volume and the amplitude was 2.41+/-0.39 (mean+/-SD), 2.60+/-0.27, 2.64+/-0.29, and 2.71+/-0.45 mV at RV, FRC, FRC+1.0 L and FRC+2.0 L, respectively. At TLC the CMAP was more variable. The CMAP amplitude recorded from pair two increased with increasing lung volume and at FRC+2.0 L was 3.7 times larger than that at FRC. Pair four usually recorded substantially smaller CMAPs at all lung volumes. This study shows that the diaphragm compound muscle action potential recorded from an oesophageal electrode just above the diaphragm is relatively stable over the lung volume range residual volume to functional residual capacity+2.0 L. (+info)
"Virtual" experiment for understanding the electrocardiogram and the mean electrical axis.
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Educators have placed an emphasis on the development of laboratory materials that supplement the traditional lecture format. The laboratory materials should encourage active learning, small group discussion, and problem-solving skills. To this end, we developed a virtual experiment designed to introduce students to the theory and application of the electrocardiogram (ECG) and the mean electrical axis (MEA). After reviewing background material, the students will analyze ECG recordings from two individuals who underwent a series of experimental procedures. The students are challenged to reduce and analyze the data, calculate and plot the MEA, and answer questions related to the theory and application of the ECG. In conducting the virtual experiment, students are introduced to inquiry-based learning through experimentation. (+info)
Operative hysteroscopy for infertility using normal saline solution and a coaxial bipolar electrode: a pilot study.
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The efficacy and safety of a coaxial bipolar electrode surgical system used to treat surgically remediable infertility conditions was investigated. After gaining initial experience with 50 patients with perimenopausal menorrhagia, 40 infertile patients with submucous myomas (n = 12), uterine septum (n = 12), uterine adhesions (n = 11), and uterine hypoplasia (n = 5) were treated. Bipolar electrodes were inserted through a '5' French operating channel of a 5.5 mm hysteroscope without cervical dilatation. Three electrodes were used: ball, twizzle and spring. Power settings ranged from 50 W (desiccation mode) to 200 W (vapour cut mode). Normal saline was used as the distension medium. All the procedures were completed within 30 min using a 1 l bag of normal saline solution. No episodes of cervical laceration, uterine perforation, haemorrhage, fluid overload or thermal injury occurred. Mild cramping, vaginal bleeding and vaginal discharge were common during the first week. No patients were readmitted. This new surgical approach appears to be well tolerated, safe, and is an effective alternative to conventional hysteroscopic surgery in the treatment of intrauterine lesions. (+info)
Inter-ocular interference and circadian regulation of the chick electroretinogram.
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Illumination of a chick's eye allows light to pass through to the retina of the contralateral eye. Electroretinographic (ERG) recording employing the scalp or comb as a reference results in shorter implicit time, higher amplitude and lower sensitivity during the day than during the night in a light:dark (LD) cycle and in constant darkness (DD). ERG recordings employing the contralateral eye as reference abolishes rhythmicity or reverses the phase angle (higher amplitudes at night). This is probably due to light transmission through the eyes to elicit visual responses in the reference. The contralateral eye is a poor choice for reference in birds and obscures physiological analyses of clock control of vision. (+info)
Virtual electrode polarization in the far field: implications for external defibrillation.
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We recently suggested that failure of implantable defibrillation therapy may be explained by the virtual electrode-induced phase singularity mechanism. The goal of this study was to identify possible mechanisms of vulnerability and defibrillation by externally applied shocks in vitro. We used bidomain simulations of realistic rabbit heart fibrous geometry to predict the passive polarization throughout the heart induced by external shocks. We also used optical mapping to assess anterior epicardium electrical activity during shocks in Langendorff-perfused rabbit hearts (n = 7). Monophasic shocks of either polarity (10-260 V, 8 ms, 150 microF) were applied during the T wave from a pair of mesh electrodes. Postshock epicardial virtual electrode polarization was observed after all 162 applied shocks, with positive polarization facing the cathode and negative polarization facing the anode, as predicted by the bidomain simulations. During arrhythmogenesis, a new wave front was induced at the boundary between the two regions near the apex but not at the base. It spread across the negatively polarized area toward the base of the heart and reentered on the other side while simultaneously spreading into the depth of the wall. Thus a scroll wave with a ribbon-shaped filament was formed during external shock-induced arrhythmia. Fluorescent imaging and passive bidomain simulations demonstrated that virtual electrode polarization-induced scroll waves underlie mechanisms of shock-induced vulnerability and failure of external defibrillation. (+info)
A multifilamented electrode in the middle cardiac vein reduces energy requirements for defibrillation in the pig.
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OBJECTIVE: To compare the defibrillation efficacy of a novel lead system placed in the middle cardiac vein with a conventional non-thoracotomy lead system. METHODS: In eight pigs (weighing 35-71 kg), an electrode was advanced transvenously to the right ventricular apex (RV), with the proximal electrode in the superior caval vein (SCV). Middle cardiac vein (MCV) angiography was used to delineate the anatomy before a three electrode system (length 2 x 25 mm + 1 x 50 mm) was positioned in the vein. An active housing (AH) electrode was implanted in the left pectoral region. Ventricular fibrillation was induced and biphasic shocks were delivered by an external defibrillator. The defibrillation threshold was measured and the electrode configurations randomised to: RV-->AH, RV+MCV-->AH, MCV-->AH, and RV-->SCV+AH. RESULTS: For these configurations, mean (SD) defibrillation thresholds were 27.3 (9.6) J, 11.9 (2.9) J, 15.2 (4.3) J, and 21.8 (9.3) J, respectively. Both electrode configurations incorporating the MCV had defibrillation thresholds that were significantly less than those observed with the RV-->AH (p < 0.001) and RV-->SCV+AH (p < 0.05) configurations. Necropsy dissection showed that the MCV drained into the coronary sinus at a location close to its orifice (mean distance = 2.7 (2.2) mm). The MCV bifurcated into two main branches that drained the right and left ventricles, the left branch being the dominant vessel in the majority (6/7) of cases. CONCLUSIONS: Placement of specialised defibrillation electrodes within the middle cardiac vein provides more effective defibrillation than a conventional tight ventricular lead. (+info)
Cardiovascular, orthopedic, and physical medicine diagnostic devices; reclassification of cardiopulmonary bypass accessory equipment, goniometer device, and electrode cable devices. Food and Drug Administration, HHS. Final rule.
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The Food and Drug Administration (FDA) is reclassifying from class I into class II the cardiopulmonary bypass accessory equipment device that involves an electrical connection to the patient, the goniometer device, and the electrode cable. FDA is also exempting these devices from the premarket notification requirements. FDA is reclassifying these devices on its own initiative based on new information. FDA is taking this action to establish sufficient regulatory controls that will provide reasonable assurance of the safety and effectiveness of these devices. (+info)
Pacing induced sustained atrial fibrillation in a pony.
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A transvenous, screw-in electrode was implanted in the right atrium of a healthy pony and connected with an implantable pulse generator programmed to deliver bursts of electrical stimuli to the atrium. Initially, cessation of burst pacing resulted in short (less than 1 minute), self-terminating episodes of atrial fibrillation. As burst pacing continued, the episodes of induced atrial fibrillation became longer. After 3 weeks of continuous atrial pacing, atrial fibrillation became sustained (56 hours). This model of pacing induced atrial fibrillation can be used to study the mechanisms leading to atrial fibrillation, its perpetuation and therapy. Our preliminary observations support the concept that once atrial fibrillation starts, it sets up changes in the electrical characteristics of the atrium that favor its own perpetuation. (+info)