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PubMed2005

Do SpaceLabs ambulatory non-invasive blood pressure recorders measure blood pressure consistently over several years use?

OBJECTIVE: To assess the measurement consistency of SpaceLabs ambulatory recorders (Spacelabs, Washington, USA) that are in regular use. METHODS: A total of 14 SpaceLabs 90207 and one 90217 ambulatory recorders were tested for measurement consistency using the Dynatech CuffLink (Dynatech, Nevada, USA), a commercially available non-invasive blood pressure (NIBP) simulator. The NIBP recorders were tested at a range of pressures with 20 repeated determinations at a simulated 120/80 mmHg and five repeated determinations at simulated pressures of 80/50, 100/80, 150/100, 200/165 and 250/195 mmHg. Tests were carried out in 1998, 2002 and late 2003 or early 2004. CONCLUSIONS: All 15 SpaceLabs recorders measured consistently over the 6 years with 89.5% of the differences in average pressures, recorded by any particular device at each recorded pressure, less than 2 mmHg between successive test episodes. The maximum difference was 4.5 mmHg and 60.1% of the differences were less than 1 mmHg. The measurements for all devices were within the tolerances specified by the supplier for the device when tested with the simulator. Maintenance records also show that most devices required breakdown maintenance less than once every 3 years. The results show that the SpaceLabs devices maintain measurement consistency in the demanding conditions of ambulatory pressure recording over several years.

Aerospace Medicine↗

PubMed2005

Band-tunable and multiplexed integrated circuits for simultaneous recording and stimulation with microelectrode arrays.

Two thin-film microelectrode arrays with integrated circuitry have been developed for extracellular neural recording in behaving animals. An eight-site probe for simultaneous neural recording and stimulation has been designed that includes on-chip amplifiers that can be individually bypassed, allowing direct access to the iridium sites for electrical stimulation. The on-probe amplifiers have a gain of 38.9 dB, an upper-cutoff frequency of 9.9 kHz, and an input-referred noise of 9.2 microV rms integrated from 100 Hz to 10 kHz. The low-frequency cutoff of the amplifier is tunable to allow the recording of field potentials and minimize stimulus artifact. The amplifier consumes 68 microW from +/- 1.5 V supplies and occupies 0.177 mm2 in 3 microm features. In vivo recordings have shown that the preamplifiers can record single-unit activity 1 ms after the onset of stimulation on sites as close as 20 microm to the stimulating electrode. A second neural recording array has been developed which multiplexes 32 neural signals onto four output data leads. Providing gain on this array eliminates the need for bulky headmounted circuitry and reduces motion artifacts. The time-division multiplexing circuitry has crosstalk between consecutive channels of less than 6% at a sample rate of 20 kHz per channel. Amplified, time-division-multiplexed multichannel neural recording allows the large-scale recording of neuronal activity in freely behaving small animals with minimum number of interconnect leads.

Action Potentials↗

PubMed1997

The concurrent recording of electroencephalography and impedance cardiography: effects on EEG.

Three experiments were performed testing the effects of a variety of impedance cardiograph electrode types and recording arrangements on recorded electroencephalography (EEG) using either a monopolar single-ear reference or a physically linked ears reference. EEG was recorded either alone or concurrently with an impedance cardiograph. When the cardiograph was recorded using a spot electrode for the top current-inducing electrode, there was an overall decrease in power density of the EEG, and this effect was dependent on the location of the recording electrode. This effect was diminished when the top cardiograph spot electrode was replaced by a mylar-coated neck band electrode and EEG was recorded using a monopolar, single-ear reference. However, there tended to be an overall increase in log power density of the EEG in each frequency band below 60 Hz when less technologically advanced EEG amplifiers were used. This effect was diminished if the EEG was recorded using a physically linked ears reference. Recommendations for the concurrent recording of EEG and impedance cardiography are discussed.

Adolescent↗

PubMed1991

Diastolic potentials recorded by surface electrocardiographic signal averaging during sustained ventricular tachycardia: possible origin from the reentrant circuit.

ECG signal averaging can detect low amplitude diastolic potentials in sinus rhythm. We, therefore, recorded signal-averaged ECGs during eight episodes of inducible uniform sustained VT with coincident atrial pacing to look for continuous diastolic electrical activity. Simultaneous AV pacing in seven patients served as controls. The number of QRS complexes averaged (187 +/- 47 vs 183 +/- 63), the noise level (1.26 +/- 0.88 vs 1.39 +/- 0.47) and cycle length (385 +/- 52 vs 404 +/- 40) did not differ between VT and paced recordings. In each lead the difference in onset between the unfiltered surface recording and the filtered data (40 Hz bidirectional) was significantly greater in VT than the paced recordings (25 +/- 16 vs 11 +/- 8 msec, P = 0.0012). These late diastolic (pre-QRS) potentials were greater than 15 msec duration in 65% of the leads in VT versus 20% of paced recording (P = 0.021). The maximum value was greater than 20 msec in six VT (75%) versus one (14%) paced recording (P = 0.019). The earliest filtered onset in any lead preceeded the earliest surface activity by greater than 12 msec, in 6 VT versus one paced recording (P = 0.019). Early diastolic (post-QRS) potentials were also longer in VT than pacing (49 +/- 40 versus 5 +/- 20, P = 0.001) and exceeded 38 msec in seven of the VTs but none of the paced recordings (P = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Atrioventricular Node↗

PubMed1980

Diagonal half-mouth recording of restorative and exodontic needs.

Partial recording of dental caries prevalence and incidence has been frequently recommended and employed. The aim of this study was to test the hypothesis that the partial recording of restorative and exodontic needs using an alternating diagonal half-mouth examination gives results which can accurately represent complete recording. Diagonal half-mouth recording was simulated by computer and gave results which closely represented the complete recording of the same sample of subjects. Partial recording lost a low proportion of the information collected by complete recording. Less frequently observed items of treatment showed highest proportions of information loss. If increases in the number of subjects in a sample can be achieved due to reductions in resources required for each subject, a proportional loss of information may be turned to a proportional gain of information. Reasons for the current recommendations against a diagonal half-mouth examination for the recording of restorative and exodontic needs are postulated and discussed.

Adolescent↗

PubMed1985

Partial recording of gingivitis and dental plaque in children of different ages and in young adults.

In epidemiologic studies, total recordings of the amount of dental plaque and the degree of gingival inflammation tend to be too time-consuming. Various partial recording methods have accordingly been suggested. However, the validity of these methods when applied to different age groups has not been investigated sufficiently. The aim of the present study was to test whether different systems for partial recording of plaque and gingivitis can take the place of a full-mouth recording in children of different ages and in young adults. Ninety children, divided into three age groups (4-6, 7-9, 14-16 yr), and 30 adults (20-22 yr) were examined. The degree of gingival inflammation was recorded using the Gingival Index and the amount of dental plaque using the Plaque Index. Two partial recording methods were tested. One of these covered the teeth suggested by Ramfjord, modified for children with a primary dentition, and the other the front segment of the maxilla. The results were compared with those from an examination of all tooth surfaces. In all age groups excellent agreement was found between the partial recording method suggested by Ramfjord and a full-mouth recording of both the gingival state and the amount of dental plaque. Examination of the maxillary front segment was less accurate and resulted in a systematic underestimate.

Adolescent↗

PubMed2003

Assessment of an ECG event recorder in healthy dogs in a hospital environment.

Ambulatory electrocardiography techniques are superior to standard electrocardiography in evaluating rhythm disturbances in dogs with episodic weakness or collapse. Disadvantages include cumbersome equipment, short recording periods and an inherent delay in trace analysis. A small programmable cardiac event recorder with combined automatic and owner-triggered recording capability was evaluated in 13 healthy dogs in a hospital environment. The unit was well tolerated and produced diagnostic recordings directly to a personal computer, with useful information about continuous heart rate. It detects premature complexes, pauses and bradycardias according to programmed detection thresholds. These events were counted frequently but trace review revealed concerns regarding specificity. Recordings were often triggered by sinus arrhythmia, sinus tachycardia and unclassifiable rate changes rather than by clinically significant arrhythmias. Correct detection of ventricular ectopic complexes, a single supraventricular premature complex, sinus arrest and second-degree atrioventricular block occurred in individual dogs. Visual review of all automatically recorded events was essential and significantly increased the time required for event recording analysis. Manual recordings might be more useful and the overall results suggest that further studies are warranted to evaluate the system in clinical cases in the home environment.

Animals↗

PubMed1994

The perception of speech sounds recorded within the uterus of a pregnant sheep.

The intelligibility of speech stimuli recorded within the uterus of a pregnant sheep was determined perceptually using a group of untrained judges. The intrauterine sound environment of the ewe was intended to simulate that of a pregnant woman. Two separate lists, one of meaningful and one of nonmeaningful speech stimuli, were delivered through a loudspeaker to the side of the ewe and were simultaneously recorded with an air microphone located 15 cm from the flank and with a hydrophone previously sutured to the neck of the fetus. Perceptual test tapes generated from these recordings were played to 102 judges. The intelligibility of the phonemes recorded in the air was significantly greater than the intelligibility of phonemes recorded from the uterus. A male talker's voice was more intelligible than a female talker's voice when recorded from within the uterus, but not so when recorded in the air. An analysis of the feature information transmission from recordings inside and outside the uterus revealed that voicing information is better transmitted in utero than place or manner information.

Animals↗

PubMedDate not supplied

Fluoroscopy: recording of fluoroscopic images and automatic exposure control.

Some means of recording images is a necessary part of most fluoroscopic systems. Several methods are available for recording images during fluoroscopy. Screen-film recording methods such as use of spot film devices and automatic film changers provide high-spatial-resolution images. Recording images by using the image intensifier (fluorography) provides film or digital images at relatively lower doses but with poorer spatial resolution. Digitally recorded images have better contrast resolution than analog images but lower spatial resolution and represent a compromise between dose and image quality. Motion picture (cine fluorographic) recording requires extremely high dose rates compared with those of lower-resolution videotape recording of motion. Recording systems in fluoroscopy require automatic exposure control for optimum image quality. The same feedback system used to control fluorographic exposures can be used to control exposure rates during fluoroscopy as well. Automatic brightness control maintains intensifier exposure rates on the basis of subject thickness by adjusting various technique factors. The type of control mechanism depends on the imaging task and the complexity (age and cost) of the equipment. The operator can choose between better image quality (higher contrast) or lower radiation dose.

Fluoroscopy↗

PubMed1994

Serosal and cutaneous recordings of gastric myoelectrical activity in patients with gastroparesis.

The aims of this study were to 1) investigate gastric myoelectrical activity in patients with gastroparesis, 2) validate the cutaneous electrogastrogram (EGG) in tracking the frequency change of the gastric slow wave, and 3) investigate the effect of electrical stimulation on gastric myoelectrical activity. Gastric myoelectrical activity was recorded in 12 patients with documented gastroparesis using serosal electrodes for > 200 min in each subject. All recordings were made at least 4 days after surgery. Each session consisted of a 30-min recording in the fasting state and a 30-min recording after a test meal. The test meal (liquid or mixed) was selected according to patient's tolerance. Electrical stimulation was performed in three subjects via the serosal electrodes at a frequency of 3 cycles/min. Gastric myoelectrical activity was recorded using serosal electrodes in each session. The serosal recording showed slow waves of 2.5 to 4.0 cycles/min in all 12 subjects. Absence of spikes was noted in 11 of the 12 subjects. The simultaneous serosal and cutaneous recording of gastric myoelectrical activity showed that the frequency of the EGG was exactly the same as that of the serosal recording. Liquid meals resulted in a significant decrease in slow-wave frequency (Student's t test, P = 0.006), and the EGG accurately reflected this change. Electrical stimulation had no effect on the frequency of the gastric slow wave and did not induce spikes.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2002

Transmural recording of monophasic action potentials.

To investigate the possibility of transmural recording of repolarization through the ventricular wall, KCl monophasic action potential (MAP) electrodes positioned along plunge needles were developed and tested. The MAP electrode consists of a silver wire surrounded by agarose gel containing KCl, which slowly eluted into the adjacent tissue to depolarize it. In six dogs, a plunge needle containing three KCl MAP electrodes was inserted into the left ventricle to simultaneously record from the subepicardium, midwall, and subendocardium. In six pigs, eight plunge needles containing three KCl MAP electrodes and two plunge needles containing similar electrodes except for the absence of KCl were inserted into the ventricles. In three guinea pig papillary muscles, a KCl electrode was used to record MAPs along with two microelectrodes for recording transmembrane potentials. Transmural MAP recordings could be made for >1 h in dogs and >2 h in pigs with a significant decrease in MAP amplitude over time but without a significant change in MAP duration. With the electrodes without KCl in pigs, the injury potentials subsided in <30 min. When the pacing rate was changed to alter the action potential duration and refractory period in dogs, the MAP duration correlated with the local effective refractory period (r = 0.94). The time course of the MAP duration recorded with a KCl MAP electrode in guinea pig papillary muscles corresponded well with that of the transmembrane potential recorded with an adjacent microelectrode. It is possible to record transmural repolarization of the ventricles with KCl MAP electrodes on plunge needles. The MAP is caused by the KCl rather than being a nonspecific injury potential.

Action Potentials↗

PubMed1989

Specificity of esophageal electrode recordings of posterior cricoarytenoid muscle activity.

Esophageal electrodes have been used for recording the electromyographic (EMG) activity of the posterior cricoarytenoid muscle (PCA). To determine the specificity of this EMG technique, esophageal electrode recordings were compared with intramuscular recordings in eight anesthetized mongrel dogs. Intramuscular wire electrodes were placed in the right and left PCA, and the esophageal electrode was introduced through the nose or mouth and advanced into the upper esophagus. On direct visualization of the upper airway, the unshielded catheter electrode entered the esophagus on the right or left side. Cold block of the recurrent laryngeal nerve (RLN) ipsilateral to the esophageal electrode was associated with a marked decrease in recorded activity, whereas cold block of the contralateral RLN resulted only in a small reduction in activity. After supplemental doses of anesthesia were administered, bilateral RLN cold block essentially abolished the activity recorded with the intramuscular electrodes as well as that recorded with the esophageal electrode. Before supplemental doses of anesthesia were given, especially after vagotomy, the esophageal electrode, and in some cases the intramuscular electrodes, recorded phasic inspiratory activity not originating from the PCA. Therefore, one should be cautious in interpreting the activity recorded from esophageal electrodes as originating from the PCA, especially in conditions associated with increased respiratory efforts.

Animals↗

PubMed1984

Intradendritic recordings from neurons of motor cortex of cats.

The properties of neuronal spike potentials ranging from 20 to 60 mV in size were studied in stable recordings made from the motor cortex of unanesthetized, unparalyzed cats. Histologic evidence that injection of horseradish peroxidase (HRP) was confined to single neurons and appropriately high levels of potassium measured with K+ ion-sensitive electrodes indicated that these recordings were obtained from single, intracellularly penetrated neurons. Pressure injection of small volumes of 4% HRP in 1 M KC1, intracellularly, was characteristically associated with transient increases in spike size and decreases in input resistance. Recoveries of HRP-filled dendritic processes without filling of somata were obtained from penetrations giving spikes smaller than the recorded resting potential (spike-undershoot recordings). Recordings with dendritic recoveries had higher input resistances and showed greater increases in spike size during pressure injection than did recordings with both somata and dendrites recovered. The activity in response to a weak click elicited in cells with spike potentials between 20 and 40 mV was as great or greater than that elicited in cells with larger spike potentials or in extracellularly recorded units. We conclude that many stable spike-undershoot recordings of neurons of the motor cortex of awake cats reflect penetrations of dendritic processes as opposed to injury because they show a) a normal functional response to weak auditory stimuli delivered over periods of many minutes, b) a reversible increase in spike size during pressure injection of small volumes of HRP in KC1 consistent with penetration of a cable remote from the site of spike generation, and c) the frequent recovery of HRP-marked dendrites without somata.

Animals↗

PubMed2006

Assessment of quality of continuous intracranial pressure recordings in children.

BACKGROUND: Bad quality of continuous intracranial pressure (ICP) recordings may potentially give wrong diagnostic information. METHOD: This study examined the ICP recordings of 33 children undergoing ICP monitoring during a 12-month period. Their ICP recordings were stored as raw data files and analyzed retrospectively. An automatic algorithm applied to every subsequent 6-second time window of each recording assessed the quality of ICP recordings. Time windows containing 4-18 cardiac beat-induced single ICP waves were accepted; time windows containing artifact-induced pressure waves due to noise in the signal were rejected. For every ICP recording, the number of accepted and rejected time windows were determined. In addition, the raw data ICP signal was assessed by visual inspection to verify the automatic algorithm. Two methods of computing mean pressure of a time window are compared; mean ICP was either computed according to current practice independent of the presence or absence of single ICP waves or computed only for single ICP waves within the time window (mean(SW) ICP). RESULTS: In 4 of the 33 patients (12%), more than 70% of the time windows of their ICP recordings were rejected; in 3 patients 95-100% of time windows were rejected. Visual inspection of the raw ICP signals confirmed the absence of single ICP waves. In these cases, computing mean(SW) ICP, not by mean ICP, revealed the bad signal quality. CONCLUSIONS: This retrospective study showed that in 3 of 33 patients (9%) the quality of the ICP recordings was so bad that they gave wrong diagnostic information. One way of obtaining quality control is to compute mean(SW) ICP, determined only for cardiac beat-induced single ICP waves within a time window.

Adolescent↗

PubMed1989

Short-latency sinusoidal wavelets to bright flashed stimuli: studies with corneal lens, nasopharyngeal, retrobulbar and scalp recordings.

Short-latency flash visual evoked potentials (VEPs) and electroretinograms (ERGs) were recorded in 30 healthy volunteers and 14 patients (7 with retrobulbar neuritis and 7 with retinitis pigmentosa). Simultaneous recordings were performed by corneal, scalp, nasopharyngeal and retrobulbar (5 patients) electrodes. In 18 out of 30 healthy controls a brief sequence of oscillating wavelets was recorded between 15 and 40 ms on the scalp sites behind the vertex. In retrobulbar neuritis (RBN) patients normal responses were recorded by lens, retrobulbar, nasopharyngeal and frontal scalp electrodes. On the contrary none of these patients displayed short-latency activity behind the Cz scalp position. In 5 out of the 7 patients with retinitis pigmentosa, corneal, nasopharyngeal and scalp electrodes failed to detect any reliable waveform time-locked to the flash onset. In the remaining 2, a small lens ERG was recorded, while all other electrodes recorded a sequence of low-volted wavelets initiating 30 ms after the stimulus onset. In these patients an occipital VEP reduced in amplitude and with prolonged latency was also recorded. It is concluded that in presence of a normal corneal ERG because of the presence of volume spread oscillating retinal activity, it is hard to define while part of the scalp recorded, short latency, oscillating potentials is generated in subcortical visual structures.

Adolescent↗

PubMedDate not supplied

Thresholds of intracranially recorded auditory field potentials in the pigeon compared with compound action potential thresholds.

The compound action potential (CAP) thresholds provide a reliable indicator for cochlear functional integrity during experimentation in birds as well as in mammals. However, if experimental manipulations are necessary in the middle ear/inner ear spaces, the round window electrodes are often inconvenient. In search for an alternative for CAP recordings, intracranial recordings of acoustically evoked field potentials from the nucleus angularis/magnocellularis were made in pigeons using stereotactically placed electrodes. The responses were compared with those recorded from intracranial surface electrodes placed on the dura mater and compared with CAP responses recorded from the round window. The field potentials recorded from the nucleus angularis/magnocellularis contain a significant contribution from the auditory nerve, as large in amplitude as the CAP recorded at the round window. The recordings from the intracranial surface electrodes were noisier and the contribution from the auditory nerve was too small to be used as a fast monitor of the condition of the inner ear. Threshold curves as a function of frequency could be determined with an automated method from the nucleus angularis/magnocellularis with the same sensitivity and accuracy as from the round window CAP within a few minutes. These results demonstrate that stereotactic recordings of field potentials from the nucleus magnocellularis/angularis region are a suitable alternative to reliably monitor the condition of the inner ear when round window electrodes cannot be used.

Animals↗

PubMedDate not supplied

Remote extracochlear versus intracochlear recordings in the guinea pig.

A comparison was made of the whole-nerve action potential recorded from a wire electrode placed on the tympanic membrane (TM) (remote extracochlear recording) and than recorded from intracochlear electrodes in the first and third turn scala tympani of the guinea pig. Cochlear microphonics and summating potentials were also studied. The expected decreased sensitivity at the TM site was observed in all responses, although the microphonic (CM) was diminished more that the action potential (AP) as compared to the responses monitored via the ST1 electrode. Nevertheless, the TM-recorded cochlear potentials largely mimicked the ST1-recorded potentials in a qualitative manner, i.e., similar configurations of the CM pseudo-threshold functions. It was consistently observed that the N2 of the AP is proportionally larger (relative to N1) in the TM recording than in the ST1 recording. These phenomena were attributed to the complex spread of the bioelectrical potentials in the nonhomogeneous volume conductor formed by the tissues of the temporal bone. It was suggested that the observed change in the N1/N2 ratio at the different sites of recording is due to the different contributions of second-order neuronal discharges to the compound AP. In effect, the TM electrode "sees" proportionally more activity from second-order fibers than does the ST1 electrode, and the ST3 electrode, less.

Action Potentials↗

PubMed1998

In vitro circadian rhythms of the mammalian suprachiasmatic nuclei: comparison of multi-unit and single-unit neuronal activity recordings.

The circadian clock in the mammalian suprachiasmatic nuclei (SCN) expresses 24-h rhythms when isolated in vitro. Numerous studies have demonstrated that recordings of SCN single-unit neuronal activity (SUA), when expressed as a population rhythm, can be used to reliably estimate SCN circadian clock phase in vitro. The main disadvantage of this technique is its laborious nature. Thus, the present experiments were designed to investigate whether in vitro multi-unit neuronal activity (MUA) recordings from the SCN could reliably substitute for SUA recordings. The results show that an MUA rhythm can be recorded from rat SCN for 3 days in vitro but that this rhythm is extremely variable; times of peak MUA in control experiments vary by 7 to 9 h each day. They also show that several serotonergic agents previously shown to consistently advance the SUA rhythm 2 to 3 h when applied during the day induce apparent advances in the MUA rhythm in some experiments; in other cases, however, there appears to be a delay or no change in the phase of the rhythm. Thus, the mean change in time of peak seen after these treatments was an advance of about 1 h. Finally, the results show that glutamate and optic chiasm stimulation applied during early subjective night can induce apparent delays in the MUA rhythm. The results of these experiments were less variable, so that the overall effect was a delay in peak MUA of 2.5 to 3.5 h. Nevertheless, these experiments still exhibited more variability than that generally seen in SUA experiments. Taken together, these results indicate that MUA recordings of the SCN exhibit significantly more variability than do SUA recordings. The extent of this variability leads to the conclusion that, using the techniques and equipment outlined here, MUA recordings are not an adequate substitute for SUA recordings when trying to estimate the phase of the SCN circadian clock.

Animals↗