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PubMed1999

Development and preliminary clinical tests of an impedance sensing VDD recording pacemaker for diagnosis and research.

Episodes of serious but infrequently occurring cardiac arrhythmias can be difficult to detect and analyse, even with modern Holter monitoring. A previous diagnostic pacemaker developed by this group provided VVI pacing therapy and recorded intracardiac ECG signals but had no atrial sensing or impedance measuring capability. A new external diagnostic pacemaker system is described that has been developed to assist in diagnosing intermittent arrhythmias by selectively recording intracardiac signals. Unlike other ambulatory monitors, in addition to recording ECG, the device combines VDD pacing therapy with the capability of monitoring and recording intracardiac impedance and pressure waveforms through a temporary intracardiac lead. A PCMCIA memory card allows storage of 48 arrhythmic events of 21 seconds each. Twelve seconds of waveform are retained before the event occurs and nine seconds after. Data retrieval and processing is performed with a PC which reconstructs each waveform for display. The ECG provides data on cardiac rhythm while cardiac function is inferred from the haemodynamic signals. During simulated trials, 14 event types were presented to the system. All events were successfully detected and recorded. During in vivo clinical tests 83 waveform recordings were made. Impedance fluctuations with typical peak-to-peak values of 64 ohms were successfully recorded.

Arrhythmias, Cardiac↗

PubMed2006

Joint decoding of visual stimuli by IT neurons' spike counts is not improved by simultaneous recording.

Information about visual stimuli such as objects and faces is represented across populations of neurons of the inferior temporal cortex. Does recording from inferotemporal neurons simultaneously tell you more than recording from them sequentially? Equivalently, are neurons conditionally independent given a stimulus? To evaluate these issues, we recorded from two monkeys during a passive viewing task. Multiple neurons were simultaneously recorded on separate electrodes. From spike counts in 50-ms windows, we computed the mutual information between counts and images for each neuron individually and jointly with other simultaneously recorded neurons. To determine the significance of these values, we shuffled the stimulus labels (to test if there was significant information) or shuffled responses across trials involving the same image (to see if there was synergistic coding). We recorded from 127 pairs of neurons where each neuron individually was visually responsive. Depending on the time window, we found up to approximately 90% of these pairs showed significant information about the visual stimulus. Shuffling across trials failed to show evidence for synergistic coding. In summary, if you were given two of our neuronal responses and asked to guess the stimulus which produced them you could not, in principle, do better with two simultaneously recorded spike counts than with any two spike counts selected randomly from trials of the same type.

Algorithms↗

PubMed2002

[The reproducibility of multifocal ERG recordings].

PROBLEM: Multifocal electroretinogram recordings (mfERG) can be used to detect a local dysfunction of the retina. In this study we tested both the intrasessional and inter-sessional reproducibility of mfERG amplitudes. METHODS: MfERGs from 6 eyes of 6 normal subjects were recorded on two different days using DTL electrodes. The relative coefficient of variation ( RCV) was used to quantify the amplitude reproducibility. We tested the effect of (a) session (inter- vs. intrasessional), (b) recording duration (7.3 vs. 3.6 min), (c) trace type (hexagon traces vs. ring averages), and (d) amplitude definition (peak-trough analysis vs. scalar product) on RCV. RESULTS: RCV was 6.5+/-0.4% (Mean+/-SEM, n=96) when averaged across all recording conditions and all subjects. The ANOVA showed a significant difference ( p=0.018) between hexagon traces and ring averages. Another significant effect ( p=0.016) occurred for the interaction of (a) and (b). CONCLUSION: MfERGs can be recorded with a high degree of reproducibility even for short recording durations and single hexagon traces. As the factor (a) did not show a significant effect, the new placement of the DTL electrode in the second session does not necessarily increase the retest variability compared to a second recording within the same session.

Artifacts↗

PubMed2002

In vivo, low-resistance, whole-cell recordings from neurons in the anaesthetized and awake mammalian brain.

A blind patch-clamp technique for in vivo whole-cell recordings in the intact brain is described. Recordings were obtained from various neuronal cell types located 100-5,000 microm from the cortical surface. Access resistance of recordings was as low as 10 M Omega but increased with recording depth and animal age. Recordings were remarkably stable and it was therefore possible to obtain whole-cell recordings in awake, head-fixed animals. The whole-cell configuration permitted rapid dialysis of cells with a calcium buffer. In most neurons very little ongoing action potential (AP) activity was observed and the spontaneous firing rates were up to 50-fold less than what has been reported by extracellular unit recordings. AP firing in the brain might therefore be far sparser than previously thought.

Action Potentials↗

PubMed2005

Duodenal acid clearance in humans: observations made with intraluminal impedance recording.

Duodenal acid clearance appears to be involved not only in the pathogenesis of duodenal ulcer disease but also in functional dyspepsia. Duodenal contractile activity can help to maintain neutral pH in the duodenum by mixing acid with bicarbonate or by aborally transporting the acid load. Intraluminal impedance recording, allowing the detection of nonacid liquid boluses, can be carried out concomitantly with antroduodenal manometry and pH recording and may thus provide useful information about the mechanisms involved in duodenal clearance of endogenous acid and volume boluses. Eight H. pylori-negative healthy volunteers were studied with two catheters positioned across the pylorus, allowing the recording of five impedance signals (one antral, one pyloric, and three duodenal) simultaneously with six pressure signals (two antral, one pyloric, and three duodenal) as well as distal antral and proximal duodenal pH. During phase II of the migrating motor complex, which is known to be associated with the highest duodenal acid exposure, each duodenal acidification event (defined as a pH drop >2 pH units) was characterized by its maximal amplitude, duration, temporal relationship with antroduodenal manometric events, and relation to impedance variations. Acid was considered to have been cleared from the duodenum when the preacidification pH was restored (+/-0.2 unit). A total of 164 duodenal pH drops were recorded during the 323 min of phase II recordings. Eleven percent of the duodenal acidification events were short-lived (<10 sec). All of these events were temporally associated with a propagated antroduodenal contraction and a short-lived drop in impedance, suggesting rapid aboral passage of the acid bolus. The long-lived duodenal acidification events lasted a mean of 32 sec (range, 25-66 sec). In 90% of these events an antroduodenal propagated contraction was recorded at the time of onset. Repetitive duodenal contractions followed the onset of the long-lived acidification events in 34% of the cases. These remained present until complete clearance of the acid. In 81% of the long-lived acidification events, recovery of the associated impedance drop occurred simultaneously with the pH recovery, suggesting a complete clearance of the bolus. Less frequently (19%), the duodenal pH recovered while the impedance remained low, suggesting that the bolus was not cleared but neutralized. Interdigestive duodenal acidification events usually last about 30 sec. They evoke duodenal contractions in only one-third of cases. Combined pH and impedance recording makes it possible to distinguish between neutralization of acid boluses and their complete total clearance.

Adult↗

PubMed2006

Influence of recording electrode type and reference electrode position on the canine electroretinogram.

Electroretinography is commonly used to assess the functional integrity of the retina. There are many external variables that can influence the electroretinographic waveforms recorded, and it is important to be aware of these so as not to misinterpret their effects as abnormalities in retinal function. In this study we examined the effect of three different recording electrodes on the ERGs recorded from normal dogs. A bipolar Burian-Allen lens, a monopolar Dawson Trick Litzkow (DTL) fiber electrode, and a monopolar ERG-Jet lens electrode were compared. The effect of altering the distance of the reference electrode from the eye was also examined; using the ERG-Jet lens electrode, the ERG was recorded with the reference electrode placed over the zygomatic arch at 1, 3 and 5 cm caudal to the lateral canthus. The ERGs recorded with the bipolar Burian-Allen lens had significantly lower amplitudes, higher a-wave thresholds and a shallower initial a-wave slope, than those recorded by the two monopolar electrodes. Positioning the reference electrode further from the eye resulted in significantly higher amplitudes. Naka-Rushton fitting and calculation of retinal sensitivity (K) gave significantly different results between the Burian-Allen lens and ERG-Jet lens electrode with the reference electrode 5 cm from the lateral canthus. These results demonstrate that recording electrode type and distance of the reference electrode from the eye significantly affect the ERG tracings of the dog, and may alter the assessment of retinal function that can therefore be derived. Results obtained using these three different types of electrodes cannot be directly compared.

Animals↗

PubMed1980

Method for recording electrical activity of the sinoatrial node and automatic atrial foci during cardiac catheterization in human subjects.

A method for recording electrical activity of the sinoatrial (S-A) node and automatic atrial foci in human subjects is described. To record S-A nodal electrograms, an electrode catheter was inserted percutaneously into the femoral vein and advanced under fluoroscopic control to the superior vena caval-right atrial junction. The distal terminal of the catheter was placed in the area of the S-A node and the proximal terminal on the free right atrial wall or in the right atrial lumen. Polarity was reversed from the conventional electrocardiographic recording; high amplification (about 100 microV/cm) and selective filters (0.1 to 20 hertz) were used. S-A nodal electrograms recorded with this method in human subjects were similar to electrograms obtained previously from the dog and rabbit and revealed negatively directed diastolic and upstroke slopes preceding the P wave of the electrocardiogram. Sinoatrial conduction time measured from the S-A nodal electrograms in 15 cases was 34.9 +/- 2.1 ms(mean +/- standard error of the mean) for a sinus cycle length of 736.4 +/- 38.6 ms. The coronary sinus electrograms in a patient with coronary sinus rhythm were recorded by the same technique except that the distal terminal of the catheter was placed at the coronary sinus ostium. A negatively directed diastolic slope preceding the P wave was consistently recorded. This method for recording electrograms of the S-A node and ectopic automatic atrial foci should prove useful in (1) assessment of both normal and abnormal S-A nodal function, (2) direct determination of conduction time from the S-A nodal pacemaker to the atrium, and (3) localization of automatic atrial foci.

Adolescent↗

PubMed1982

Intra- and interexaminer variability in head posture recorded by dental auxiliaries.

Determination of the natural head position is essential in the esthetic assessment of the facial profile and could be of value in prediction of facial developmental trends. Recording of head posture has previously been performed in university clinics under experimental conditions. The purpose of the present study was to examine the reliability of a method that dental auxiliaries could use for routine recording of the natural head posture in children in an orthodontic clinic. The material comprised thirty orthodontic patients 6 to 15 years of age and recorded on two occasions 1 to 35 days apart. The auxiliary staff consisted of three different operators. The duplicate cephalometric head films were analyzed separately for the groups of patients recorded by each of the three operators. The data were also divided into one group recorded by the same operator and another group recorded by different operators at the first and the second occasions. No systematic difference between the first and the second recordings was found for the patients examined by each of the three operators or for the groups examined by the same or by different operators. The error of the method for the whole group was 2.3 degrees for the position of the head in relation to the true vertical (NSL/VER), 3.1 degrees for the cervical inclination (OPT/HOR), and 3.4 degrees for the craniocervical angulation (NSL/OPT). The method was found to yield sufficient reproducibility and is suggested to be of clinical value in the study of head posture in relation to orthodontic treatment.

Adolescent↗

PubMed1977

Analysis of intracellular recordings from salamander olfactory epithelium.

Intracellular recordings have been obtained from provisionally identified olfactory receptor and sustentacular cells in the salamander olfactory epithelium. Two categories of membrane potential transients were recorded intracellularly in response to odor stimulation. The first category of responses, presumably recorded from receptor cell somas, were monophasis positive spikes 10-50 mV in amplitude which were superimposed on a depolarizing slow potential which ranged from 4 to 8 mV in amplitude. Graded and differential responses were recorded in response to odor stimulation. The second category of responses were depolarizing and hyperpolarizing slow membrane potential transients presumably recorded from sustentacular cells. Spiking was not observed in response to odor stimulation. Pysiological criteria and Procion dye marking in several instances have provided evidence that responses in the first category were recorded from olfactory receptors and that certain of the other responses were recorded from sustentacular cells.

Ambystoma↗

PubMed1991

Compound action potential of nerve recorded by suction electrode: a theoretical and experimental analysis.

Suction electrodes are widely used for recording compound action potentials (CAPs) from peripheral nerves or central tracts. Unfortunately, the recordings obtained with suction electrodes often vary over time, making quantitative measurement of CAP amplitude difficult. We developed an equivalent electrical model which predicts that the magnitude of a recorded potential will be linearly related to the resistance of the electrode with a nerve inserted. Mathematical procedures were developed that allow correction of virtually all variability inherent in this type of recording; this variability may arise from resistance drift, variable stimulus artifact, or potentials generated as a result of the current of injury. The validity of the theoretical analysis was confirmed experimentally using rat optic nerves. The magnitude of the CAP and electrode resistance varied spontaneously by as much as 100% over time, due to changes in electrode resistance and size of the stimulus artifact. Because the CAP was linearly related to resistance, it was therefore best quantified by the slope computed from this relationship. The stimulus artifact, unlike the CAP itself, was shown to be independent of recording electrode resistance and therefore only resulted in a variable offset to the area vs resistance linear relationship; the slope of this relationship was unaffected. In the absence of stimulation, a steady negative DC potential was recorded from the optic nerve, which was greatest immediately after dissection, and was also a linear function of electrode resistance. In contrast to CAP amplitude, the latencies of the component peaks within the CAP were not significantly altered by changes in electrode resistance. The experimental results confirmed the validity of the electrical model and demonstrated that suction electrodes can be a very reliable and quantitative recording method if the signals are properly corrected.

Action Potentials↗

PubMedDate not supplied

Conduction properties of epidurally recorded spinal cord potentials following lower limb stimulation in man.

Spinal somatosensory evoked potentials were recorded in 35 neurologically normal patients undergoing surgery for scoliosis. During posterior procedures the recording electrodes were placed in the dorsal epidural space and during anterior operations in the intervertebral discs. Stimulation was of the tibial nerve in the popliteal fossa and the posterior tibial and sural nerves at the ankle. At thoracic levels the response consisted of at least 3 components with different peripheral excitation thresholds and spinal conduction velocities (range 35-85 m/sec). All components were conducted mainly in tracts ipsilateral to the stimulus, component 1 being most laterally located. At low stimulus intensity only the fastest activity was recorded but this was markedly delayed over low thoracic segments and was recorded as a repetitive discharge rostrally. Higher intensities elicited additional components which were conducted at a slower but relatively uniform velocity; consequently they might overlap with or even overtake the fast activity at mid-to-low thoracic levels. Component 1 was much less prominent when the posterior tibial nerve was stimulated at the ankle and absent from the (cutaneous) sural nerve response; remaining potentials were conducted at velocities similar to those of components 2 and 3 following tibial nerve stimulation at the knee. Small 'stationary' potentials were recorded at all thoracic levels, probably due to the change in conductivity as the volley entered the spinal cord. Efferent activity was recorded at and below the thoraco-lumbar junction, possibly related to the H-reflex or F-wave. Similar, although smaller, afferent potentials were recorded from the anterior side of the vertebral column. Component 1 is likely to be due to the stimulation of group 1 muscle afferents which terminate in the dorsal horn and activate second order neurones, many of whose axons go to form the ipsilateral dorsal spinocerebellar tract. Components 2 and 3 are believed to be largely cutaneous in origin and to be conducted mainly in the dorsal columns.

Adolescent↗

PubMedDate not supplied

Influence of medial septal and entorhinal cortex lesions on theta activity recorded from the hippocampus and median raphe nucleus.

The electrophysiological relationship between the hippocampus (HP) and the median raphe nucleus (MRN) was examined in the freely moving rat. Bilateral HP recording electrodes were implanted in all animals (n = 15). In the first group of animals, placement of a monopolar recording electrode in the MRN allowed for simultaneous recording of field activity from the HP and MRN, both prior to and following electrolytic destruction of the medial septum (MS) (n = 10). Immediately following MS lesions, theta activity recorded from both sites was abolished. These data suggest that the MS may serve as a pacing input to both the HP and MRN. In a second group of animals, field activity was recorded from the HP and MRN, both prior to and following electrolytic destruction of the entorhinal cortex (EC) (n = 5). Type 1 theta activity recorded from both the HP and MRN was attenuated by EC lesions; however, detomidine-induced immobility-related theta activity was unaffected by destruction of the EC. In light of these findings, the plausibility of EC inputs to the MRN was discussed. The present results suggest that theta activity recorded from the MRN is dependent on the same neural mechanisms that control theta production in the HP.

Animals↗

PubMed1987

Adaptation, plant evolution, and the fossil record.

The importance of adaptation in determining patterns of evolution has become an important focus of debate in evolutionary biology. As it pertains to paleobotany, the issue is whether or not adaptive evolution mediated by natural selection is sufficient to explain the stratigraphic distributions of taxa and character states observed in the plant fossil record. One means of addressing this question is the functional evaluation of stratigraphic series of plant organs set in the context of paleoenvironmental change and temporal patterns of floral composition within environments. For certain organ systems, quantitative estimates of biophysical performance can be made on the basis of structures preserved in the fossil record. Performance estimates for plants separated in time or space can be compared directly. Implicit in different hypotheses of the forces that shape the evolutionary record (e.g. adaptation, mass extinction, rapid environmental change, chance) are predictions about stratigraphic and paleoenvironmental trends in the efficacy of functional performance. Existing data suggest that following the evolution of a significant structural innovation, adaptation for improved functional performance can be a major determinant of evolutionary changes in plants; however, there are structural and development limits to functional improvement, and once these are reached, the structure in question may no longer figure strongly in selection until and unless a new innovation evolves. The Silurian-Devonian paleobotanical record is consistent with the hypothesis that the succession of lowland floodplain dominants preserved in the fossil record of this interval was determined principally by the repeated evolution of new taxa that rose to ecological importance because of competitive advantages conferred by improved biophysical performance. This does not seem to be equally true for Carboniferous-Jurassic dominants of swamp and lowland floodplain environments. In these cases, environmental disruption appears to have been a major factor in shaping the fossil record. This does not mean that continuing adaptation was not important during this interval, but it may indicate that adaptive evolution was strongest in environments other than those best represented in the paleobotanical record.

Adaptation, Biological↗

PubMed1986

Urodynamic appraisal of vaginal versus rectal pressure recordings as indication of intra-abdominal pressure changes.

To compare intravaginal versus intrarectal pressure recordings as an indication of intra-abdominal pressure changes, simultaneous recording of the vaginal, bladder, and rectal pressures were obtained in 20 women. The transmitted pressure changes recorded from the inner and middle thirds of the vagina strongly correlated with the transmitted pressure changes recorded from the bladder (r = 0.99) when compared with the observed correlation between bladder and rectal pressure recordings (r = 0.91). The vaginal pressure recording is an easier and accurate alternative to intrarectal pressure recordings for approximating abdominal pressure changes during urodynamic testing.

Adult↗

PubMed1990

Long term recordings in the cat motor cortex: unit activity and field potentials from sensory and brain stem stimulation as a means of identifying electrode position.

A method of chronically implanting microwires (25 microns diameter, 90% Pt/10% Ir wire) in the cat pericruciate cortex is described. These wires can obtain simultaneous recordings of single and multiunit activity from different sites and multiple recordings from the same site on different postoperative days. The electrodes were permanently implanted in the anaesthetized animal and left in place. Recordings were carried out in the awake, unrestrained cat. Different units were recorded as a result of spontaneous electrode movement in the cortex. Movement was documented with field potential recording from the implanted electrodes and resulted in changes in the latency and polarity of the initial components of the cutaneous field potential and changes in the number of components of the field potential elicited from brain stem stimulation. Changes in the receptive fields of the units, changes in the number of units antidromically invaded from brain stem stimulation, and in the threshold and occurrence of muscle activity elicited from intracortical microstimulation supported the evidence of electrode movement obtained from field potential recordings and could be used to document electrode movements tangential to the plane of the cortical laminae. Movement was a slow gradual process throughout the period of implantation. The longest period from which a single unit could be recorded was 2 days. The need for this neurophysiological analysis is supported by evidence for irregular electrode movement which could not have been reconstructed from histological examination of the cortex.

Animals↗

PubMed1991

Recording of simultaneous single-unit activity in the dragonfly ganglia.

A technique for discriminating simultaneously active single units from multiple-unit data records has been developed. Multiple-unit records were obtained extracellularly from the dragonfly mesothoracic ganglion using two paired-electrode sets. The multiple-unit records were post processed based on the unique physical characteristics imparted to each spike via the tissue medium and spatial geometry of cells. It was assumed that the action potential amplitude falls off roughly as the inverse of distance squared from the recording electrode. Further, it was assumed that the tissue RC characteristics coupled with action potential amplitudes and neuron dipole characteristics impart a spike waveform unique to each cell. Accordingly, spikes were sorted by amplitude ratio as well as by matching of spike waveforms. Additional waveform characterization was derived from the spike angle (width) within grouped spikes. Decomposition of the multiple-unit records based on these parameters yielded clustered spike records from defined cellular sources. The defined clusters were combined to provide the cumulative record for a large number of simultaneously active single units.

Action Potentials↗

PubMed1991

Coincident recording and stimulation of single and multiple neuronal activity with one extracellular microelectrode.

This paper describes how an extracellular microelectrode may be used to stimulate neurons with brief, rectangular pulses and afterwards directly record the resultant activity. Two obstacles are the stimulus artifact lingering in the electrical circuitry and transient tip potentials (TTPs) arising from ion depletion at the electrode-tissue interface. Electronic switching between the stimulus source and the recording amplifier eliminates direct stimulus artifact from the electrical circuitry, although high but acceptable switching artifact remains. TTPs revert with time constants that are prominent in the desired recording (0.1-1 ms) and can reach 50 mV when more than 1 microA passes through a typical electrolyte-filled micropipette (for example 2-4 M omega, filled with 3 M NaCl, and placed in 0.1 M NaCl). They are always negative when cations flow into the tip, they are accompanied by a rise in microelectrode impedance, and they increase as a function of the resting electrode impedance, the duration and amplitude of applied current, and the dilution of the external electrolyte. TTPs were substracted by differential recording and stimulation through matched micropipettes (one in the brain and one in contiguous electrolyte) and in addition were reduced by pressure ejection of electrolyte. Directly elicited spikes (single or multiple) were detected about 0.5 ms after delivery of a rectangular stimulus pulse in the cerebellar cortex of pentobarbital-anesthetized rats. Typically, 3-4 units could be excited by less than 3 microA cathodal currents at any recording site. All-or-nothing properties, thresholds, and refractoriness to a second pulse within 2-4 ms verified the neuronal nature of the recorded signals. Complex wave forms, probably generated synaptically, were also seen. The technique of coincident extracellular recording and stimulation can be used as a universal search stimulus during microelectrode penetrations through the brain and in determining threshold-distance relations for extracellular stimulation. Where cell penetrations are unstable, it might be usefully substituted for intracellular technique in testing a neuron's behavioral or physiological influences or in exploring a cell membrane's response to drugs (in terms of excitability rather than voltage and impedance).

Animals↗

PubMed1986

Sleep-wake behavior of newborn rats recorded with movement sensitive method.

The aim of this study was to determine criteria for classification of sleep-wake behavior in newborn rats by recording total body and respiratory movements with a static charge sensitive bed (SCSB). Initially, the sleep-wake behavior was simultaneously observed visually and recorded by the SCSB mattress, from the fourth to the twenty-second postnatal days. Thus, the criteria for scoring the SCSB recordings were obtained by comparison of the behavioral scorings with the SCSB tracings. To further validate this movement sensitive method for neonatal sleep studies in rats, deep neck muscle electrograms were studied at the age range of 8-13 days, and electroencephalograms as well as electromyograms from the age of 12-17 days, simultaneously with the SCSB recordings. Finally, the sleep-wake behavior of other rat pups was recorded only with the SCSB from the fourth to the twenty-second postnatal days. These latter recordings were afterwards scored by using the criteria defined in the first part of this study. The results thus obtained indicate that the SCSB method is sensitive and reliable in recording and classifying the sleep-wake behavior of newborn rats.

Animals↗