Time correction and two channel recording in 24 hour electrocardiographic analysis

An improved technique for automatic monitoring and analysis of ECG recording is described. The system is based on standard commercial equipment but provides improved quantitative measurement of cardiac arrhythmias. This is done by using a simultaneous recording of a 100 Hz clock, which is used to correct for tape speed variations. Also increased immunity to artefacts is achieved by combining two ECG leads, coupled with signal analysis techniques. The problems arising from certain types of artefact are also discussed.     

Pressure measurement in the renal pelvis

An experimental arrangement for the recording of discrete pressure variations in the renal pelvis is described. An amplifier has been designed which permits shifting of the pressure curve to enable the measurement of pressure variations of the order of a few mm Hg. A correlation has been observed between the pressure variations in the pelvis and the action potentials from the ureter associated with the transport of urine.     

Combined measurement of event-related potentials (ERPs) and fMRI

The study investigates the possibility of combined recording event-related potentials (ERPs) and functional MRI (fMRI). Visual evoked potentials (VEPs) were elicited by an alternating black and white checkerboard, which was presented blockwise outside the static 1.5 T magnetic field and during an echo planar imaging (EPI). An fMRI sequence with a time window for interleaved EEG-measurement and a measurement protocol which reduces pulse artifacts and vibrations was used. Thus, during an EPI sequence, it was possible to detect VEPs which had the same structure and latencies as VEPs outside the magnetic field and which corresponded well with the observed activated areas of the visual cortex.     

Semiquantification of fibrillation potentials with intramuscular temperature drop using an animal model.

It has been reported that the quantity of fibrillation potentials (FP) decreases with drop in the intramuscular temperature. However, the quantitative measurement of the FP with intramuscular temperature changes has not been reported. Under anesthesia of intraperitoneal sodium pentobarbital, the sciatic nerve of 6 rats (Sprague-Dawley) was surgically isolated. A 1-cm segment was excised after tying the proximal and distal ends of the nerve segment. A concentric needle electrode and thermometer needle probe were inserted approximately 1-cm apart into the posterior tibial muscles 3 to 4 days after the nerve segment excision. Before and during cooling the muscles with ice, FPs were evoked and printed on paper recording for later analysis. Visually recognizable potentials (30 microV or above) in each printed tracing with temperature changes (range, 37 degrees C to 15 degrees C) were manually counted. A positive linear correlation was found between the intramuscular temperature changes and the quantity of FPs. The recording of FP completely ceased at about 20 degrees C below baseline temperature. In this study, we have successfully semiquantified fibrillation potentials in a wide range of intramuscular temperature changes.     

Electromagnetic interference in intraoperative monitoring of motor evoked potentials and a wireless solution

Intraoperative neurophysiological monitoring (IONM) is utilized to minimize neurological morbidity during spine surgery. Transcranial motor evoked potentials (TcMEPs) are principal IONM signals in which the motor cortex of the subject is stimulated with electrical pulses and the evoked potentials are recorded from the muscles of interest. Currently available monitoring systems require the connection of 40–60 lengthy lead wires to the patient. These wires contribute to a crowded and cluttered surgical environment, and limit the maneuverability of the surgical team. In this work, it was demonstrated that the cumbersome wired system is vulnerable to electromagnetic interference (EMI) produced by operating room (OR) equipment. It was hypothesized that eliminating the lengthy recording wires can remove the EMI induced in the IONM signals. Hence, a wireless system to acquire TcMEPs was developed and validated through bench-top and animal experiments. Side-by-side TcMEPs acquisition from the wired and wireless systems in animal experiments under controlled conditions (absence of EMI from OR equipment) showed comparable magnitudes and waveforms, thus demonstrating the fidelity in the signal acquisition of the wireless solution. The robustness of the wireless system to minimize EMI was compared with a wired-system under identical conditions. Unlike the wired-system, the wireless system was not influenced by the electromagnetic waves from the C-Arm X-ray machine and temperature management system in the OR.     

A system for recording of auditory evoked responses.

A system for recording of evoked potentials from auditory stimulation was developed. The system consists of a PC equipped with an audio bandwidth board with analog input and output channels. The sound stimulus signal is generated in the computer, D/A converted, and via audio amplifier fed to earphones on the test subject. Auditory evoked potentials in response to sound stimuli are recorded via electrodes, amplified and filtered in an EEG recording system and fed to an A/D converter. The signal is analysed in the PC. The modular design of the program makes it a flexible system where stimulus and recording parameters can easily be modified and new applications can be added to standard clinical measurements. Three applications that are not possible with commercially available systems were developed and evaluated. a) A diagnostic procedure to verify hydrops in patients with Meniere's disease. b) Intraoperative recordings of auditory evoked potentials during neurootological surgery. c) Recording of mismatch negativity (MMN) potentials in evaluation of central auditory functions.     

Voltage-clamp-controlled current-clamp recordings from neurons: an electrophysiological technique enabling the detection of fast potential changes at preset holding potentials

Investigations of the properties of fast, transient potential changes (e.g. receptor potentials or synaptic potentials) in excitable cells by means of current-clamp recording techniques require the exact adjustment and control of membrane potentials. Usually, the desired membrane potential values are set by current injection via the recording electrode and are controlled manually by regulating the current strength necessary to maintain a constant potential. However, this technique is associated with a number of disadvantages. A single-electrode current- and voltage-clamp amplifier was therefore modified to compensate for slow membrane potential changes without affecting faster voltage responses. Basically, low-pass filters with selectable time constants were incorporated into the voltage-clamp feedback circuit to control the amplifier's response speed. In addition, the amplifier's electronic circuits were altered to enable current pulse injection into the cells. Thus, while recording at preset and controlled membrane potentials, it was possible to monitor the cell's input resistance or current/voltage relationship. This new recording technique has been designated "voltage-clamp-controlled current clamp" (VCcCC) and its performance was tested by intracellular recordings from neocortical and neostriatal neurons in vitro using either conventional microelectrodes or patch-clamp electrodes.     

The influence of the surface electrogram on the rising phase of the mammalian cardiac action potential

1. When guinea pig cardiac tissue is stimulated, the rising phase of the action potential is influenced by the shape of the concomitant local surface electrogram. This, in turn, depends on the direction of the wave of excitation passing the recording microelectrode. 2. A symmetrical biphasic surface electrogram yields sigmoid upstrokes with masimum upstroke velocity (Vmax) lower than when it is either zero or uniphasic and negative. 3. When the main direction of the depolarization wave in guinea pig ventricular myocardium is receding from the recording microelectrode, giving rise to negative uniphasic extracellular potentials, a notch might distort the registration of the rising phase of the action potential. 4. When the main direction of the depolarization wave is approaching the recording microelectrode, giving rise to positive uniphasic extracellular potentials, Vmax is transferred to less negative membrane potentials. 5. The extracellular surface electrogram influences the overshoot of the action potentials of the normal atrial and depressed (D-600) ventricular myocardium and is changed, depending on how the wave of excitation passes the recording microelectrode.     

Reversal potential for Ia excitatory post synaptic potentials in spinal motoneurones of cats

A technique permitting the introduction of two separate microelectrodes into spinal motoneurones of cats has been used to study the effect of injections of large depolarizing currents on membrane properties and on synaptic potentials. By using one electrode for passage of current, and the other for recording, continuous measurement of membrane potentials was possible. The Ia excitatory postsynaptic potential has been reversed in twelve motoneurones, and the reversal level in most of-these has been measured at between 0 and +10mV. During continuous injection of strong depolarizing currents, large variations in membrane potential and input resistance, sometimes of a repetitive nature, were observed.The results indicate that the characteristics of the Ia excitatory postsynaptic potential are explainable by a chemically mediated increase in ionic conductance, a concept which has been challenged by other recent studies in which reversal of these potentials could not be obtained.     

A tethering system for direct measurement of cardiovascular function in the caged baboon.

A device suitable for the continuous measurement of physiological activity in large, conscious monkeys has permitted the direct recording of systemic arterial blood pressure and heart rate in caged baboons. The device comprises a lightweight fiberglass backpack, retained in place on the baboon by a thoracic elastic band and shoulder straps, and a flexible stainless steel tether connecting the pack to an electrocannular slip-ring in the top center of the baboon's cage. A chronically indwelling arterial catheter inserted retrograde into the abdominal aorta via the internal iliac artery and connected to a small pressure transducer on the pack provides direct measurement of blood pressure and heart rate. Body fluids can be sampled or drugs administered via an indwelling catheter in the inferior vena cava. Electrical and fluid connections between the fiberglass pack and recording and infusion equipment located outside the cage pass through the flexible tether and remain protected from the subject. The reliability of the tethering system has been demonstrated in physiological, pharmacological, and behavioral experiments with baboons.     

A simple method for the routine assessment of heart-rate variation in autonomic neuropathy

A simple method is described for the rapid assessment of respiratory heart-rate variation (HRV) by making use of an EMG machine to record the RR-interval of the electrocardiogram. The built-in software for single-fibre EMG usually incorporated in modern EMG equipment is sufficient for a rapid data analysis based on the difference between the shortest and longest RR-intervals recorded over a period of 60 to 100 s. Measurements of HRV obtained by our new method correlate well with those obtained by the more tedious conventional manual measurement of an ECG recording (r = 0.88).     

On the neuromuscular effects of pindolol and sotalol in the rat

The effects of pindolol and sotalol on neuromuscular transmission were tested using intracellular micro-electrode recording of resting membrane potentials, miniature end-plate potentials and end-plate potentials, and recording of muscle contractions upon nerve stimulation of rat phrenic nerve-hemidiaphragm preparations. Both pindolol and sotalol reduced the amplitudes of miniature end-plate potentials and end-plate potentials in a dose-dependent manner without significantly affecting their time-courses. Pindolol, but not sotalol, also increased the frequency of the miniature end-plate potentials and decreased the number of acetylcholine quanta released by nerve impulses. Neither of the drugs significantly affected resting membrane potentials of the muscle fibres or excitability of the motor nerve to electric stimulation.     

Click evoked neurogenic vestibular potentials (NVESTEPs): a method of assessing the function of the vestibular system

OBJECTIVES: To obtain neurogenic vestibular evoked potentials (NVESTEPs) with surface scalp recording using high intensity auditory clicks. The same stimulus is used in myogenic vestibular evoked potentials which has been shown to evoke potentials in the vestibular division of the vestibulocochlear nerve. METHODS: A whole head recording with surface EEG electrodes was performed using high intensity clicks in one normal volunteer to determine the best recording position for vestibular evoked potentials. The results were compared to responses at moderate click intensities used for brainstem auditory evoked potentials (BAEPs). The difference in the location of the two responses on the scalp was assumed to be from the vestibular system. RESULTS: Responses specific to the high intensity clicks were best obtained in the parietal areas, with no reproducible responses obtained in the same area with moderate intensity clicks normally used in BAEPs. Recordings in neurologically normal volunteers showed a consistent response with a negative polarity at around 3 ms, which we therefore called N3. Two case studies are presented. The first case is a patient with unilateral sensorineural hearing loss with NVESTEPs present, suggesting that NVESTEPs is not a cochlear response. The second case is a patient with multiple sclerosis with demyelinating lesions in the pons and an unobtainable NVESTEP response. CONCLUSION: NVESTEPs is a possible new diagnostic technique that may be specific for the vestibular pathway. It has potential use in patients with symptoms of dizziness, subclinical symptoms in multiple sclerosis, and in disorders specific for the vestibular nerve.     

Intracellular study of electrical activity of Auerbach's plexus in guinea-pig small intestine

Intracellular recording revealed two general categories of ganglion cells in Auerbach's plexus. The characteristics of one category were relatively low resting potentials, high input resistance, discharge of spikes throughout a depolarizing current pulse, stimulus-evoked synaptic potentials and spontaneous electrical activity. Characteristics of the second category were high resting potentials, low input resistance, spikes only at the onset of a depolarizing current pulse and long duration hyperpolarizing after-potentials. Responses to extracellular electrical stimulation of the ganglia and interganglionic fiber tracts consisted of electrotonic spread of spikes from the processes to the cell soma, somal action potentials and depolarizing and hyperpolarizing responses that were probably EPSPs and IPSPs. Some of the neurons which received excitatory synaptic input responded with a prolonged train of spikes that outlasted by many seconds the duration of the stimulus to the fiber tract. Spontaneous electrical activity consisted of single EPSPs, patterned bursts of spikes that originated in the cell processes and spread electrotonically to, the recording site, IPSPs and action potentials. The burst-type activity showed periodic conversions from a burst pattern to a trainlike pattern of continuous discharge. Spontaneous discharge of single action potentials was superimposed upon a background of continuous synaptic input to the cell. Spontaneously occurring hyperpolarizing potentials were converted to depolarizing potentials when the membrane was hyperpolarized by current injected through the recording electrode. This work was supported by BMVg In San and National Institutes of Health AM 16813     

Electromyographic validation of the double pulley equipment during movements of the lower limbs

The double pulley equipment was tested on ten male volunteers during contraction of the semitendinosus and biceps femoris (caput longum) muscles in the following movements of the lower limbs: 1) hip extension with extended knee and erect trunk, 2) hip extension with flexed knee and erect trunk, 3) hip extension with flexed knee and erect trunk, 3) hip extension with extended knee and inclined trunk, 5) hip abduction along the midline, 7) hip abduction with extension beyond the midline, 8) adduction with hip flexion beyond the midline, 8) adduction with hip flexion beyond the midline, and 9) adduction with hip extension beyond the midline. The myoelectric signals were taken up by Lec Tec surface electrodes connected to a 6-channel Lynx electromyographic signal amplifier coupled with a computer equipped with a model CAD 10/26 analogue digital conversion board and with a specific software for signal recording and analysis. The semitendinosus and biceps femoris muscles presented the highest potentials in movements 1; 2; 7, 8 and 9, whereas the potentials in the remaining movements were negligible. The pattern of activity of the semitendinosus and the biceps femoris was similar in exercises 1, 2, 3, 4 and 8. The potentials of the semitendinosus prevailed in movements 5, 6 and 7, and the strongest potentials observed in movement 9 were those of the biceps femoris.     

ARTMEM—An interactive graphical program simulating membrane potential measurements across artificial membranes

This paper describes ARTMEM, an interactive graphical simulation program, and its use for teaching students the concept of membrane potentials and the measurement of electrical potentials across an ion-selective membrane. The program, written in Borland C++, and specifically designed for IBM-PC-compatible equipment, can also run on fast Macintosh computers using SoftPC emulation software. It demonstrates how an ion-selective membrane separating two different salt solutions automaticallygenerates a potential across the membrane, as well as how such electrical potentials can be measured simply and the underlying permeability ratio determined. The program was developed to replace a previous experiment with actual artificial resin membranes; virtually every feature of the experiment has been simulated (e.g., unstirred-layer effects, solutionmixing contamination, liquid junction potential effects). In addition, a number of these features and the procedure for data fitting are more clearly demonstrated using the computer simulation. The efficacy of such a simulation is discussed in comparison with the real experiment and other types of simulations.     

Comparative evaluation of methods for quantification of neural activity

Electrograms of single- and few-fibre baro- and chemoreceptor preparations from the carotid sinus nerve of rabbits were recorded monophasically at different levels of activation, as well as complete absence of potentials during temporary cold block of the preparation. The neural activity of every neurogram was determined by a PDP-12 computer using three different methods: (i) Determining all maxima and minima in the electrogram and distinguishing action potentials by comparing the amplitude changes to discriminator values derived from previous analysis of noise; (ii) counting transitions of the electrogram across a constant-voltage threshold just above the baseline noise; (iii) integrating the electrogram with or without rectification with reference to the electrical zero level. The results provided evidence that, in single- as in few-fibre preparations if methods (ii) in part, and (iii) generally, yield erroneous values and, consequently, distorted activity response curves due to measurement of baseline or superimposed noise, loss of summated potentials, baseline shifts and/or the presence of different types of potentials in the recording. Most satisfactory results were obtained by method (i). However, since even the latter becomes incorrect if the neural frequency exceeds several hundred to about 1000 impulses/s, none of these methods can be considered for exact quantification of neural activity in multi-fibre preparations or whole nerves.     

Action potential threshold of hippocampal pyramidal cells in vivo is increased by recent spiking activity

Understanding the mechanisms that influence the initiation of action potentials in single neurons is an important step in determining the way information is processed by neural networks. Therefore, we have investigated the properties of action potential thresholds for hippocampal neurons using in vivo intracellular recording methods in Sprague-Dawley rats. The use of in vivo recording has the advantage of the presence of naturally occurring spatio-temporal patterns of synaptic activity which lead to action potential initiation. We have found there is a large variability in the threshold voltage (5.7+/-1.7 mV; n=22) of individual action potentials. We have identified two separate factors that contribute to this variation in threshold: (1) fast rates of membrane potential change prior to the action potential are associated with more hyperpolarized thresholds (increased excitability) and (2) the occurrence of other action potentials in the 1 s prior to any given action potential is associated with more depolarized thresholds (decreased excitability). We suggest that prior action potentials cause sodium channel inactivation that recovers with approximately a 1-s time constant and thus depresses action potential threshold during this period.     

Effect of electrical coupling on ionic current and synaptic potential measurements

Recent studies have found electrical coupling to be more ubiquitous than previously thought, and coupling through gap junctions is known to play a crucial role in neuronal function and network output. In particular, current spread through gap junctions may affect the activation of voltage-dependent conductances as well as chemical synaptic release. Using voltage-clamp recordings of two strongly electrically coupled neurons of the lobster stomatogastric ganglion and conductance-based models of these neurons, we identified effects of electrical coupling on the measurement of leak and voltage-gated outward currents, as well as synaptic potentials. Experimental measurements showed that both leak and voltage-gated outward currents are recruited by gap junctions from neurons coupled to the clamped cell. Nevertheless, in spite of the strong coupling between these neurons, the errors made in estimating voltage-gated conductance parameters were relatively minor (<10%). Thus in many cases isolation of coupled neurons may not be required if a small degree of measurement error of the voltage-gated currents or the synaptic potentials is acceptable. Modeling results show, however, that such errors may be as high as 20% if the gap-junction position is near the recording site or as high as 90% when measuring smaller voltage-gated ionic currents. Paradoxically, improved space clamp increases the errors arising from electrical coupling because voltage control across gap junctions is poor for even the highest realistic coupling conductances. Furthermore, the common procedure of leak subtraction can add an extra error to the conductance measurement, the sign of which depends on the maximal conductance.