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PubMed1999

Automatic implantable cardioverter-defibrillators.

Ventricular fibrillation, a loss of synchronous electrical activity in the heart which leads to hemodynamic collapse, is a leading cause of death. Because of the devastating personal and societal effects of this phenomenon, the automatic cardioverter-defibrillator has been developed for automatic detection and termination of the arrhythmia and is in widespread clinical use. Advances in circuits, leads, waveforms, and signal processing along with increased knowledge of the mechanisms of fibrillation have led to continuing improvements in this device, extending its use to many patients. A device has also been developed for the automatic or semiautomatic treatment of atrial fibrillation, an arrhythmia less life-threatening than ventricular fibrillation, but still a serious health problem. Continued improvement of these devices and the development of qualitatively new approaches hold great promise for exciting therapeutic advances in this area.

Atrial Fibrillation↗
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↗
PubMed2004

Techniques and applications of automatic tube current modulation for CT.

Introduction of slip-ring technology with subsequent development of single- and multi-detector row helical computed tomographic (CT) scanners have expanded the applications of CT, leading to a substantial increase in the number of CT examinations being performed. Owing to concerns about the resultant increase in associated radiation dose, many technical innovations have been introduced. One such innovation is automatic tube current modulation. The purpose of automatic tube current modulation is to maintain constant image quality regardless of patient attenuation characteristics, thus allowing radiation dose to patients to be reduced. This review discusses the principles, clinical use, and limitations of different automatic tube current modulation techniques.

Equipment Design↗
PubMed2001

Reduction of patient motion artifacts in digital subtraction angiography: evaluation of a fast and fully automatic technique.

The performance of an automatic technique for the reduction of patient motion artifacts in digital subtraction angiography was evaluated. Four observers assessed the quality of 104 cerebral digital subtraction angiographic images that were processed by means of both the automatic technique and manual pixel shifting. The automatic technique resulted in better image quality and was considerably less time-consuming.

Adult↗
PubMed1987

Voltage- and time-dependent block of iK1 underlying Ba2+-induced ventricular automaticity.

The mechanism underlying the Ba2+-induced automaticity was studied in isolated guinea pig ventricular myocytes using the whole-cell clamp method and a patch electrode. In the presence of 0.1-0.3 mM Ba2+, application of a weak depolarizing current induced repetitive firing of spontaneous action potentials. Application of tetrodotoxin or Ca2+ channel blockers and removal of external Na+ and Ca2+ did not abolish the rhythmic activity, thereby suggesting that activation of inward currents played no crucial role in the generation of this rhythmicity. Voltage-clamp studies revealed that Ba2+ blocked the inward rectifier K+ current (iK1) in a voltage- and time-dependent manner with a greater and more rapid block at more negative potentials. This Ba2+ action could quantitatively be fitted with a model of the conventional bimolecular adsorption isotherm with a voltage-dependent dissociation constant. Simulation studies using this model showed that a membrane model, in which only the iK1 system and a small leak conductance were incorporated, could reproduce an automatic activity similar to that seen experimentally. Thus, in isolated ventricular cells, the voltage- and time-dependent block of iK1 by Ba2+ appears to be one important mechanism underlying the automaticity.

Action Potentials↗
PubMed2005

Automatic classification of activity and apneas using whole body plethysmography in newborn mice.

An increasing number of studies in newborn mice are being performed to determine the mechanisms of sleep apnea, which is the hallmark of early breathing disorders. Whole body plethysmography is the method of choice, as it does not require immobilization, which affects behavioral states and breathing. However, activity inside the plethysmograph may disturb the respiratory signal. Visual classification of the respiratory signal into ventilatory activity, activity-related disturbances, or apneas is so time-consuming as to considerably hamper the phenotyping of large pup samples. We propose an automatic classification of activity based on respiratory disturbances and of apneas based on spectral analysis. This method was validated in newborn mice on the day of birth and on postnatal days 2, 5, and 10, under normoxic and hypoxic (5% O(2)) conditions. For both activity and apneas, visual and automatic scores showed high Pearson's correlation coefficients (0.92 and 0.98, respectively) and high intraclass correlation coefficients (0.96-0.99), supporting strong agreement between the two methods. The present results suggest that breathing disturbances may provide a valid indirect index of activity in freely moving newborn mice and that automatic apnea classification based on spectral analysis may be efficient in terms of precision and of time saved.

Algorithms↗
PubMedDate not supplied

DDD(R) pacing with automatic mode switch in patients with paroxysmal atrial fibrillation following AV nodal ablation.

Optimal pacing in patients with paroxysmal atrial fibrillation/flutter following AV node ablation remains to be determined because VVIR pacing cannot restore AV synchronization and conventional DDD(R) pacing cannot properly cope with atrial tachyarrhythmias. The objective of the present investigation was to study the clinical outcome of 16 of these patients who received a new DDDR pacemaker with an automatic mode switch (Thera DR; Medtronic) immediately after AV node ablation. Arrhythmia-related symptoms before ablation were palpitations in 12, dizziness in 10, exercise intolerance in 8, and syncope in 6 patients. Pacing modes at hospital discharge were DDDR (n = 14) and DDD (n = 2) with an activated mode switch in all patients. After 1 month 12 patients were symptom free. Clinical events occurred in 4 patients (palpitations in 2, dizziness in 1, chest pain in 1, and fatigue in 1), which could be relieved in 3 patients. At discharge as well as at the 1-month follow-up, Holter ECG recorded a total of 12 episodes of atrial fibrillation in 5 patients, which were correctly detected by the pacemaker and followed by mode switching. At the 3-month follow-up (n = 14), 12 patients were symptom free and 2 continued to report symptoms which could not be resolved. All patients remained on an automatic mode switch in either the DDDR (n = 12) or DDD (n = 2) mode. There were no hints of inappropriate mode switching or reports of pacemaker syndrome, and there were no new symptoms related to automatic mode switching. The patients studied were highly symptomatic before implantation due to paroxysmal atrial fibrillation/flutter. After the first follow-up, 81% of the patients reported no symptoms. Paroxysmal atrial fibrillation/flutter combined with a high-degree AV-block seems no longer to be a contraindication for AV-synchronous pacing.

Atrial Fibrillation↗
PubMed1978

A chronically implanted system for automatic defibrillation in active conscious dogs. Experimental model for treatment of sudden death from ventricular fibrillation.

Ventricular defibrillation was acheived in active conscious dogs with a chronically implanted automatic system composed of a defibrillator and an alternating current fibrillator. The hermetically sealed defibrillator is encased in titanium, weighs 250 g and has a volume of 145 ml. The sensor continuously monitors ventricular electircal activity and recognizes fibrillation by the absence of isoelectric potential segments. Fibrillation is induced by placing a magnet over the implanted fibrillator. The resulting syncope closely resembles the clinical entity of sudden death, while the defibrillator automatically restores normal rhythm with a truncated exponential pulse of 30 J, 15 seconds after the onset of the arrhythmia. The operational status of the defibrillator can be tested in vitro and noninvasively in vivo with an external analyzer. This experimental model allows for the first time a long-term study of the automatic implantable defibrillator approach to prevent sudden death from ventricular fibrillation under a variety of physiopathologic conditions.

Animals↗
PubMed1985

The effects of single premature stimuli on automatic and triggered rhythms in isolated canine Purkinje fibers.

We studied the effects of single premature stimuli on automatic and triggered rhythms occurring in preparations of isolated canine Purkinje fibers. Preparations were made from false tendons, the subendocardial right bundle branch, and infarct zone Purkinje fibers 24 hr after occlusion of the left anterior descending coronary artery, and were studied by standard microelectrode techniques. Single premature impulses almost always produced reset of automatic rhythms, whether the pacemaker had a low (less than -60 mV), intermediate (-61 to -70 mV), or high (greater than -70 mV) maximum diastolic potential. In contrast, single premature impulses imposed on triggered rhythms sometimes were found to alter these rhythms; often, early premature impulses (i.e., during phase 3) resulted in either a shortened first return cycle or a short period of arrest of the rhythm. The results of this study indicate that it may be possible to design simple electrophysiologic tests using single premature stimuli to determine whether an arrhythmia is being caused by an automatic focus or by triggered activity.

Animals↗
PubMed1990

Premature escape beats induced by overdrive pacing in canine Purkinje fibers. Evidence for the role of normal automaticity as an underlying cellular mechanism.

Premature escape beats induced in conscious dogs with chronic complete atrioventricular block have been defined as escape beats occurring on cessation of overdrive pacing and having a coupling interval to the last paced beat shorter than the coupling interval between the premature escape beat and the second postpacing beat. Triggered activity has been proposed as the primary underlying mechanism. We used standard microelectrode techniques to study the effects of overdrive pacing on normal automatic canine Purkinje fibers to determine if premature escape beats could be induced and if so, to define the underlying cellular mechanism(s). For this purpose, we overdrive-paced Purkinje fibers for 10 and 50 seconds and for 10 and 50 beats at a pacing cycle length (PCL) of 1,000-200 msec. In addition, to help distinguish among major arrhythmogenic mechanisms, we used a matrix of drugs consisting of propranolol, nadolol, lidocaine, ethmozin, and doxorubicin. Fifty-second stimulation trains induced "classic" overdrive suppression of the first three postpacing impulses, whereas 10-second overdrive pacing induced significant overdrive suppression only at a PCL of 200 msec. With 50-beat overdrive pacing and a PCL of 1,000-600 msec, there was overdrive suppression of postpacing impulses, whereas reduced overdrive suppression was observed at a PCL of 400-200 msec. Ten-beat stimulation trains induced a "flat response" of postpacing impulses. Ten- and 50-beat overdrive pacing provoked premature escape beats in 66% of the fibers, with the higher incidence at a PCL of 200 msec for 50-beat stimulation trains. No shortening of the coupling interval of premature escape beats was observed at faster pacing rates. Only lidocaine (which suppresses normal automaticity) abolished premature escape beats. We conclude that normal automaticity is the most likely mechanism underlying premature escape beats in Purkinje fibers with high levels of membrane potential.

Animals↗
PubMed1993

On-line assessment of left atrial area and function by echocardiographic automatic boundary detection.

BACKGROUND: Direct assessment of left atrial (LA) function has not been previously performed by noninvasive techniques; rather, LA function has been evaluated only indirectly via the analysis of transmitral flow velocity by Doppler. The recent development of real-time two-dimensional echocardiographic automatic boundary detection suggests that LA dimensions can be measured instantaneously to provide on-line assessment of its systolic and diastolic functions. METHODS AND RESULTS: We performed echocardiographic assessment of LA dimensions and function with automatic boundary detection in 45 patients by using the apical four-chamber view. Thirty-seven patients had structural or functional cardiac abnormalities, 35 patients were in sinus rhythm, and 10 patients had atrial fibrillation. Moderate to severe mitral regurgitation (MR) was noted in 16 patients. We also studied 10 control subjects to assess normal values of LA cavity area and indexes of function. From the instantaneously derived LA area, we derived indexes of systolic atrial expansion and diastolic atrial emptying. There were excellent correlations between the on-line-derived LA areas and those measured off line from videotaped images of conventional echocardiography (r = .91 for end-diastolic and .93 for end-systolic areas; SEE, 4.0 and 3.8 cm2, respectively). Patients in atrial fibrillation had depressed diastolic emptying index (0.17 +/- 0.05) compared with those in sinus rhythm (0.28 +/- 0.12; P < .02). Furthermore, patients with chronic MR exhibited larger LA cavity areas and depressed systolic and diastolic LA function as compared with those without MR. In addition, the Doppler-determined mitral E/A ratio was related to the ratio of early diastolic-to-late diastolic change in LA cavity area (r = .79; SEE 0.6; n = 35). CONCLUSIONS: Instantaneous LA cavity area measurement by echocardiographic automatic boundary detection is accurate and feasible in patients with diverse cardiac disorders. Patients with atrial fibrillation had a depressed diastolic emptying index and those with significant mitral regurgitation had depressed systolic expansion index as well. LA functional indexes in both systole and diastole can be derived providing an approach for quantitative evaluations of left atrial-left ventricular interactions based on geometric assessment noninvasively.

Atrial Fibrillation↗
PubMed1989

Amantadine-induced afterpotentials and automaticity in guinea pig ventricular myocytes.

The ionic mechanisms of amantadine-induced changes in membrane potential and automatic activity in guinea pig ventricular myocytes were studied using the suction-pipette whole-cell clamp method. While 25-100 microM amantadine decreased the action potential amplitude and duration, 200 and 400 microM amantadine lengthened the action potential duration and decreased the maximum diastolic potential with an appearance of diastolic depolarization and automaticity. In the presence of 25-100 microM amantadine, the preparations developed an afterpotential due to incomplete repolarization and a delayed afterdepolarization that eventually brought about triggered automaticity. The former type of afterpotential was abolished by tetrodotoxin (TTX) and the latter by Co2+. Spontaneous activity from the diastolic depolarization was also abolished by Co2+ but not by Cs+. Amantadine suppressed the calcium current to as much as half of the control at the concentrations used (25-200 microM). The drug also produced a depression of the inward rectifier K+ current. The outward current showing time-dependent decay was activated at the plateau voltages by concentrations lower than 100 microM, whereas the delayed outward K+ current was depressed by the drug in a concentration-dependent manner at more positive potentials. Amantadine activated the TTX-sensitive and TTX-insensitive inward currents on repolarization from depolarized states, without producing the transient inward current. These results indicate that the amantadine-induced diastolic depolarization and afterpotentials are caused by changes in multiple ionic currents and that, therefore, the drug can be used as a unique model for the study of arrhythmogenesis.

Amantadine↗
PubMed1990

Effects of alpha-adrenergic stimulation on intracellular sodium activity and automaticity in canine Purkinje fibers.

Approximately 60% of adult canine Purkinje fibers respond to alpha 1-adrenergic stimulation with a decrease in automaticity. Recent studies of disaggregated Purkinje myocytes have suggested that this negative chronotropic effect results from alpha 1-adrenergic activation of the Na-K pump. In this study we evaluated 1) whether Na-K pump activation is associated with the negative chronotropic effect of alpha 1-adrenergic stimulation in adult canine Purkinje fibers and 2) if the effect of alpha-agonists on the pump is direct or mediated by an increase in intracellular sodium activity (aNai). We used sodium selective microelectrodes to determine the effects of 5 x 10(-9) and 5 x 10(-8) M phenylephrine on aNai. Phenylephrine decreased automaticity in five of eight Purkinje fibers while an increase occurred in the other three. The rate decrease was always accompanied by a decrease in aNai (-3.9 mM; p less than 0.05), whereas in fibers showing an increase in rate, aNai was unchanged. To evaluate the effect of phenylephrine in the absence of changes in automaticity, 10 Purkinje fibers were studied during pacing. A clear-cut reduction in aNai (-2.8 mM) was present in six fibers; no change was seen in the other four. The effect of phenylephrine was blocked by prazosin but not by propranolol. We conclude that the effect of alpha 1-adrenergic stimulation to reduce aNai is consistent with activation of the Na-K pump. Moreover, this action of alpha 1-adrenergic stimulation is closely linked to its negative chronotropic effect.

Adrenergic alpha-Antagonists↗
PubMed1996

Automatic embolus detection compared with human experts. A Doppler ultrasound study.

BACKGROUND AND PURPOSE: Transcranial Doppler ultrasound (TCD) reliably detects the occurrence of microembolic signals (MES). Unfortunately, TCD monitoring is a time-consuming and mentally strenuous procedure. The purpose of this study was to assess whether automatic embolus detection software devices acting as a "stand-alone system" are able to identify MES in patients with solid cerebral microemboli. METHODS: Ten records of TCD monitoring of the middle cerebral artery in patients with symptomatic high-grade carotid artery stenosis were analyzed for the moments at which MES occurred by four observers and three automatic detection software devices (RB11 on TC2000, Pioneer Version 2.10, and Embotec). The results of the three software systems were assessed on the basic assumption that MES were present if at least three of the four observers agreed. RESULTS: The average number of 1-second periods in which MES were detected by the four observers per tape ranged from 5 to 39. The overall kappa values (and SEs) for chance-corrected interobserver agreement between the four observers ranged from .94 (.02) to .99 (.01). The agreement between the software devices and the observers was lower, with kappa values (and SEs) ranging from .18 (.17) to .93 (.07). The RB11 and Embotec systems achieved a kappa value higher than 0.4 in all tapes. The Pioneer system failed to reach a kappa value of 0.4 in three tapes. The RB11 showed a sensitivity of 70% for detecting MES, the Embotec 62%, and the Pioneer 44%. CONCLUSIONS: In patients with symptomatic high-grade carotid artery stenosis, a high degree of agreement in the detection of moments of MES can be achieved between observers. The three automatic detection software devices reached less agreement. Supervision of TCD monitoring and assessment of MES by an experienced observer is still necessary.

Carotid Stenosis↗
PubMed2001

Functional anatomical correlates of controlled and automatic processing.

Behavioral studies have shown that consistent practice of a cognitive task can increase the speed of performance and reduce variability of responses and error rate, reflecting a shift from controlled to automatic processing. This study examines how the shift from controlled to automatic processing changes brain activity. A verbal Sternberg task was used with continuously changing targets (novel task, NT) and with constant, practiced targets (practiced task, PT). NT and PT were presented in a blocked design and contrasted to a choice reaction time (RT) control task (CT) to isolate working memory (WM)-related activity. The three-dimensional (3-D) PRESTO functional magnetic resonance imaging (fMRI) sequence was used to measure hemodynamic responses. Behavioral data revealed that task processing became automated after practice, as responses were faster, less variable, and more accurate. This was accompanied specifically by a decrease in activation in regions related to WM (bilateral but predominantly left dorsolateral prefrontal cortex (DLPFC), right superior frontal cortex (SFC), and right frontopolar area) and the supplementary motor area. Results showed no evidence for a shift of foci of activity within or across regions of the brain. The findings have theoretical implications for understanding the functional anatomical substrates of automatic and controlled processing, indicating that these types of information processing have the same functional anatomical substrate, but differ in efficiency. In addition, there are practical implications for interpreting activity as a measure for task performance, such as in patient studies. Whereas reduced activity can reflect poor performance if a task is not sensitive to practice effects, it can reflect good performance if a task is sensitive to practice effects.

Adult↗
PubMedDate not supplied

Posttraining sleep enhances automaticity in perceptual discrimination.

Perceptual learning can develop over extended periods, with slow, at times sleep-dependent, improvement seen several days after training. As a result, performance can become more automatic, that is, less dependent on voluntary attention. This study investigates whether the brain correlates of this enhancement of automaticity are sleep-dependent. Event-related potentials produced in response to complex auditory stimuli were recorded while subjects' attention was focused elsewhere. We report here that following training on an auditory discrimination task, performance continued to improve, without significant further training, for 72 hr. At the same time, several event-related potential components became evident 48-72 hr after training. Posttraining sleep deprivation prevented neither the continued performance improvement nor the slow development of cortical dynamics related to an enhanced familiarity with the task. However, those brain responses associated with the automatic shift of attention to unexpected stimuli failed to develop. Thus, in this auditory learning paradigm, posttraining sleep appears to reduce the voluntary attentional effort required for successful perceptual discrimination by facilitating the intrusion of a potentially meaningful stimulus into one's focus of attention for further evaluation.

Adult↗
PubMed2006

Attentional modulation of unconscious "automatic" processes: evidence from event-related potentials in a masked priming paradigm.

Automatic processes are usually thought to occur independently of any cognitive resources. This traditional view has been recently challenged by showing that temporal attention to a target stimulus is a prerequisite for "automatic" response priming. The event-related potential (ERP) study reported here extends this research by pursuing a somewhat different approach. In two experiments, it was investigated whether masked semantic priming effects can be modulated by temporal attention to the prime using a cueing procedure. We hypothesized that masked priming is amplified when attention is directed to the stimulus stream in the time window of masked prime presentation, even in the absence of any prime awareness. ERPs were recorded while subjects performed a primed lexical decision task. Target words were preceded by semantically related or unrelated masked prime words, which were not consciously identified. A cue stimulus prompted subjects to direct their attention to the stimulus stream either shortly before the masked prime (short cue interval) or a long time interval before. Priming affected the amplitude of the N400 ERP component, an electrophysiological index of semantic processing. Unrelated prime-target pairs elicited a larger N400 than related pairs (N400 priming effect). Most importantly, this masked N400 priming effect was strongest when the cue interval and the stimulus onset asynchronies were short. The present results show that temporal attention to the prime is a prerequisite for obtaining masked N400 priming effects. They also demonstrate that unconscious automatic processes are susceptible to attentional modulation.

Adolescent↗
PubMed2000

Automatic detection of open and closed eye states in the electroencephalographic (EEG) record for background EEG interpretation by the trigger method.

Automatic detection of open and closed eye states in electroencephalographic (EEG) records was investigated in this study as a part of procedures for the precise interpretation of the background EEG to achieve a comprehensive automatic EEG interpretation system. The features of eye open and closure were extracted from the EEG using a Markov process amplitude (MPA) EEG model, which could efficiently express the features of the EEG using a small number of parameters. A new technique, named the trigger method, was also developed to overcome the difficulty resulting from large differences in the EEG features among different subjects, because an accurate detection could not be obtained by using the conventional threshold method. The proposed method gave satisfactory results which conformed with those of visual inspection by a qualified EEGer and could be clinically used as a preprocessing method for the automatic interpretation of the awake background EEG.

Adult↗