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Two types of abnormal automaticity in canine ventricular muscle fibers.

When ventricular muscle fibers from dog hearts were exposed to different [Ca2+]0 in K+-free solutions, two types of abnormal automaticity were observed. In the K+-free, Ca2+-free, solution, 9 out of 55 preparations developed spontaneous activity at a reduced membrane potential. The maximum diastolic potential was -47.4 +/- 7.68 mV (n = 9) with slow (less than 20 V/s) upstroke velocity of action potentials. The automaticity was based on membrane oscillations with increasing amplitude to become full-sized responses. It was suppressed after reduction of [Na+]0, by an increase in [Ca2+]0 above 3.6 mmol/l and by application of verapamil. In the K+-free, high-Ca2+, solutions (Ca2+ = 3.6-7.2 mmol/l), oscillatory afterpotentials (OAPs) were observed following the driven action potentials at normal membrane potentials in all 55 preparations. Once the OAPs became large enough to attain threshold, there was the appearance of triggered-automaticity. The automaticity was induced by applying premature stimuli or manipulating [Ca2+]0. It was abolished by application of either verapamil or tetrodotoxin by decreasing the amplitude of the OAPs or the fast Na+ current, respectively, or both in combination. These results indicate that the ventricular muscle fibers can develop abnormal automaticity of two different mechanisms in some conditions, and can be a focus of ectopic impulse formation.

Action Potentials↗

Differential effects of sympathetic activity on AV junctional automaticity and AV conduction.

Rapid ventricular response during episodes of supraventricular tachycardia are often followed, on abrupt cessation of the tachycardia, by prolonged pauses terminated by a sluggish and sometimes erratic escape of a supraventricular pacemaker. Such chronotropic-dromotropic paradoxes are readily reproduced in the animal laboratory following elimination of the sinus node and bilateral decentralization of the stellate ganglia and vagi. This study examined whether left stellate stimulation (0.5, 1, 2, 4, 8 and 16 Hz) or lack thereof differentially affected AV junctional automaticity and AV conduction. In the absence of any sympathetic neural activity (maximal sympathetic deficit), the AV junctional rate averaged a mere 22 +/- 2 percent of its peak performance, whereas under the same conditions, anterograde AV conduction averaged 73 +/- 5 percent and retrograde VA conduction 56 +/- 13 percent of their respective peak performances. On comparing the response curve (normalized responses) for AV junctional automaticity with that obtained for anterograde AV conduction the differences were significant at all frequencies between 0 and 4 Hz. Retrograde VA conduction (as assessed by the fastest ventricular pacing rate still conducted 1:1 to the atria) was always significantly less than anterograde AV conduction (as assessed by the fastest atrial pacing still conducted 1:1 to the ventricles). These results indicate that AV junctional automaticity is considerably more affected by sympathetic deficit than are either anterograde or retrograde AV conduction. In other words, AV junctional automaticity is far more dependent upon sympathetic input than AV conduction. While sympathetic influence is critical to the escape and maintenance of AV junctional automaticity both anterograde and retrograde AV conduction are remarkably resilient even under conditions of severe sympathetic deficit.

Animals↗

Local intraarterial thrombolysis: in vitro comparison between automatic and manual pulse-spray infusion.

PURPOSE: Manual and automatic pulse-spray infusion techniques are compared in vitro to evaluate the efficacy of thrombolysis and the distribution of urokinase and saline solution within thrombus using a pulse-spray catheter. METHODS: A pulse-spray catheter was introduced into a human thrombus within a stenotic flow model. Automatic and manual pulsed infusion of urokinase and automatic pulsed infusion of saline solution were compared. To quantify the efficacy of thrombolysis, pressure gradients were recorded proximal and distal to the thrombus and during the course of infusion. Distribution of infused urokinase was assessed radiographically. RESULTS: The fastest and most homogeneous dissolution of the thrombus was achieved with automatic pulsed infusion of urokinase, shown by decreasing transthrombotic pressure gradients (p < 0.001, Wilcoxon, matched pairs). Manual pulsed infusion of urokinase or saline solution resulted in inhomogeneous thrombus dissolution and delayed thrombolysis. CONCLUSION: Application of automatic pulse-spray injectors seems beneficial for more effective and homogeneous intraarterial pulse-spray thrombolysis when compared with conventional manual pulsed technique.

Humans↗

Effects of lorazepam and diazepam on conscious and automatic memory processes.

Recent studies exploring benzodiazepine memory effects have used the distinction between explicit and implicit tasks. There is now increasing evidence that implicit tasks can be "contaminated" by conscious uses of memory and that unconscious (automatic) use of memory can contaminate explicit tasks, leading to mistaken estimates of their respective influences on memory performance. The aim of the present double-blind, double-placebo study was to assess the memory effects of diazepam and lorazepam using a process-dissociation procedure in a stem-completion task, this procedure providing uncontaminated estimates of conscious and automatic memory processes. The memory task was administrated to 60 healthy volunteers randomly assigned to one of three parallel groups (placebo, diazepam 0.3 mg/kg, lorazepam 0.038 mg/kg). Lorazepam markedly reduced conscious as well as automatic influences of memory. Diazepam also reduced conscious uses of memory, albeit to a lesser extent than lorazepam, but did not decrease the influence of automatic memory. Secondary analyses showed that when the deleterious effect on conscious uses of memory was equated between a diazepam subgroup and the lorazepam group, only lorazepam impaired the automatic use of memory. This study strongly suggests a qualitative difference in the memory effects of the two benzodiazepines. It has some implications regarding the relationships between states of consciousness and memory processes.

Adult↗

Alcohol effects on inhibitory control of attention: distinguishing between intentional and automatic mechanisms.

RATIONALE: Recent research has begun to explore the possibility that inhibitory mechanisms of selective attention are particularly susceptible to the impairing effects of moderate doses of alcohol. However, literature also suggests that automatic processes might be more resistant to this impairing effect than controlled processes. OBJECTIVE: The present study used a delayed ocular response task and a saccadic interference task to examine the effects of alcohol on both intentionally controlled and automatic inhibitory influences on selective attention. MATERIALS AND METHODS: Twelve healthy adults performed both tasks under three doses of alcohol (0.0, 0.45, and 0.65 g/kg). RESULTS: The results showed that alcohol reduced intentional inhibitory control over selective attention but had no effect on automatic inhibitory influences. CONCLUSION: The present investigation marks the first effort to directly compare alcohol effects on automatic and intentional inhibitory mechanisms of visual attention. The results suggest that attentional processes dependent on intentional inhibitory control may be more susceptible to the impairing effects of a moderate dose of alcohol than processes dependent on automatic inhibition.

Administration, Oral↗

Automatic user customization for improving the performance of a self-paced brain interface system.

Customizing the parameter values of brain interface (BI) systems by a human expert has the advantage of being fast and computationally efficient. However, as the number of users and EEG channels grows, this process becomes increasingly time consuming and exhausting. Manual customization also introduces inaccuracies in the estimation of the parameter values. In this paper, the performance of a self-paced BI system whose design parameter values were automatically user customized using a genetic algorithm (GA) is studied. The GA automatically estimates the shapes of movement-related potentials (MRPs), whose features are then extracted to drive the BI. Offline analysis of the data of eight subjects revealed that automatic user customization improved the true positive (TP) rate of the system by an average of 6.68% over that whose customization was carried out by a human expert, i.e., by visually inspecting the MRP templates. On average, the best improvement in the TP rate (an average of 9.82%) was achieved for four individuals with spinal cord injury. In this case, the visual estimation of the parameter values of the MRP templates was very difficult because of the highly noisy nature of the EEG signals. For four able-bodied subjects, for which the MRP templates were less noisy, the automatic user customization led to an average improvement of 3.58% in the TP rate. The results also show that the inter-subject variability of the TP rate is also reduced compared to the case when user customization is carried out by a human expert. These findings provide some primary evidence that automatic user customization leads to beneficial results in the design of a self-paced BI for individuals with spinal cord injury.

Algorithms↗

Clonidine, but not ritanserin, suppresses kainic acid-induced automatisms in developing rats.

In young rats, systemic or local administration of kainic acid (KA) elicits scratching as the prevailing automatism whereas in adult rats, wet dog shakes (WDS) are usually recorded. We tested the effects of the alpha 2-adrenergic agonist clonidine (0.25 mg/kg, IP; also acting, however, on imidazoline receptors), which has been reported to block KA-induced WDS in adult rats and the 5-HT2 antagonist ritanserin (20 mg/kg, IP) in rats aged 7, 12, 18, 25, and 90 days treated IP with doses of KA that induce maximum number of automatisms with minimal early lethal effects (i.e., 4, 6, 8, 10, and 14 mg/kg, respectively). Both WDS and scratching were frequently recorded together in one animal. Neither ritanserin nor its solvent had significant effects on the total number of automatisms or on their distribution between WDS and scratching. In contrast, clonidine suppressed automatisms throughout the development studied. In 90-day-old (adult) rats clonidine decreased the incidence of both WDS and scratching, whereas it usually attenuated scratching at younger ages. Kainic acid-induced seizures were also recorded because of reported incompatibility between tonic-clonic seizures and WDS in adult rats. In 18-90-day-old rats, tonic-clonic seizures and WDS were found incompatible. In 7-18-day-old pups, scratching and KA-induced tonic-clonic seizures occurred together. Moreover, in 7-day-old rats, clonidine was anticonvulsant. We have demonstrated that KA-induced automatisms develop from scratching in pups to prevailing WDS in adult rats, whereas the incidence of scratching rather decreases during development.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗

The beta-agonist drug tulobuterol decreases cardiac automaticity in the rat: comparison with isoproterenol.

The effect of the new beta-agonist drug tulobuterol, has been compared with isoproterenol in an experimental model of ectopic cardiac automaticity induced by local injury in the isolated right ventricle of the rat. Isoproterenol significantly increases ventricular automaticity even with the lowest concentrations tested (10(-9)M). Tulobuterol, at concentrations ranging from 10(-9)M to 10(-6)M do not induce any change on the automatic ventricular frequency. Nevertheless, at higher concentrations (10(-5) and 5 X 10(-5)M), tulobuterol decreases the experimentally induced ventricular automaticity. Our results suggest that the new beta-agonist drug tulobuterol does not increase ventricular automaticity but, in fact, decreases it.

Adrenergic beta-Agonists↗

Core-based portal image registration for automatic radiotherapy treatment verification.

PURPOSE: Portal imaging is the most important quality assurance procedure for monitoring the reproducibility of setup geometry in radiation therapy. The role of portal imaging has become even more critical in recent years due to the migration of three-dimensional (3D) treatment planning technology, including high-precision conformal therapy, from the research setting to routine clinical practice. Unfortunately, traditional methods for acquiring and interpreting portal images suffer from a number of deficiencies that contribute to the well-documented observation that many setup errors go undetected, and some persist for a clinically significant portion of the prescribed dose. Significant improvements in both accuracy and efficiency of detecting setup errors can, in principle, be achieved by using automatic image registration for on-line screening of images obtained from electronic portal imaging devices (EPIDs). METHODS AND MATERIALS: This article presents recent developments in a method called core-based image analysis that shows great promise for achieving the desired improvements in error detection. Core-based image analysis is a fundamental computer vision method that is capable of exploiting the full power of EPIDs by providing for on-line detection of setup errors via automatic registration of user-selected anatomical structures. We describe a robust method for automatic portal image registration based on core analysis and demonstrate an approach for assessing both accuracy and precision of registration methods using realistic, digitally reconstructed portal radiographs (DRPRs) where truth is known. RESULTS: Automatic core-based analysis of a set of 20 DRPRs containing known, random field positioning errors was performed for a patient undergoing treatment for prostate cancer. In all cases, the reported translation was within 1 mm of the actual translation with mean absolute errors of 0.3 mm and standard deviations of 0.3 mm. In all cases, the reported rotation was within 0.6 degree of the actual rotation with a mean absolute error of 0.18 degree and a standard deviation of 0.23 degree. CONCLUSION: Our results, using digitally reconstructed portal radiographs that closely resemble clinical portal images, suggest that automatic core-based registration is suitable as an on-line screening tool for detecting and quantifying patient setup errors.

Humans↗

Automatic left ventricular volume measurements on contrast-enhanced ultrafast cine magnetic resonance imaging.

To assess the accuracy of automatic extraction of the left ventricular inner contour on contrast-enhanced ultrafast cine magnetic resonance (MR) images, we compared the values obtained by this method with those obtained using intravenous digital subtraction left ventriculography. High-quality single breath-hold contrast-enhanced ultrafast cine MR images were obtained in all cardiac phases on horizontal and vertical long axis sections of the left ventricle. For ultrafast cine MR imaging, a phase-rewind gradient-echo (rewind-SMASH) sequence was used. Automatic extraction of the left ventricular inner contour on contrast-enhanced ultrafast cine MR images was performed in all cardiac phases. High-quality left ventricular images of the horizontal long axis section were obtained in 127 of 160 patients (79%). The automatic extraction of the left ventricular contour was easily performed on high-quality images with very short processing time (4 s/frame). The values for left ventricular volumes obtained with the automatic extraction method on contrast-enhanced ultrafast cine MR imaging were correlated well with those obtained with the manual extraction method and IV-DSA in high quality cardiac images. The biplane modified Simpson's method using automatic extraction is an accurate and highly reproducible method for evaluating left ventricular volumes.

Cardiac Volume↗

Measuring automatic retrieval: a comparison of implicit memory, process dissociation, and speeded response procedures.

Using the stem completion task, we compared estimates of automatic retrieval from an implicit memory task, the process dissociation procedure, and the speeded response procedure. Two standard manipulations were employed. In Experiment 1, a depth of processing effect was found on automatic retrieval using the speeded response procedure although this effect was substantially reduced in Experiment 2 when lexical processing was required of all words. In Experiment 3, the speeded response procedure showed an advantage of full versus divided attention at study on automatic retrieval. An implicit condition showed parallel effects in each study, suggesting that implicit stem completion may normally provide a good estimate of automatic retrieval. Also, we replicated earlier findings from the process dissociation procedure, but estimates of automatic retrieval from this procedure were consistently lower than those from the speeded response procedure, except when conscious retrieval was relatively low. We discuss several factors that may contribute to the conflicting outcomes, including the evidence for theoretical assumptions and criterial task differences between implicit and explicit tests.

Analysis of Variance↗

Automatic analysis of auditory nerve electrically evoked compound action potential with an artificial neural network.

The auditory nerve's electrically evoked compound action potential is recorded in deaf patients equipped with the Nucleus 24 cochlear implant using a reverse telemetry system (NRT). Since the threshold of the NRT response (NRT-T) is thought to reflect the psychophysics needed for programming cochlear implants, efforts have been made by specialized management teams to develop its use. This study aimed at developing a valid tool, based on artificial neural networks (ANN) technology, for automatic estimation of NRT-T. The ANN used was a single layer perceptron, trained with 120 NRT traces. Learning traces differed from data used for the validation. A total of 550 NRT traces from 11 cochlear implant subjects were analyzed separately by the system and by a group of physicians with expertise in NRT analysis. Both worked to determine 37 NRT-T values, using the response amplitude growth function (AGF) (linear regression of response amplitudes obtained at decreasing stimulus intensity levels). The validity of the system was assessed by comparing the NRT-T values automatically determined by the system with those determined by the physicians. A strong correlation was found between automatic and physician-obtained NRT-T values (Pearson r correlation coefficient >0.9). ANOVA statistics confirmed that automatic NRT-Ts did not differ from physician-obtained values (F = 0.08999, P = 0.03). Moreover, the average error between NRT-Ts predicted by the system and NRT-Ts measured by the physicians (3.6 stimulation units) did not differ significantly from the average error between NRT-Ts measured by each of the three physicians (4.2 stimulation units). In conclusion, the automatic system developed in this study was found to be as efficient as human experts for fitting the amplitude growth function and estimating NRT-T, with the advantage of considerable time-saving.

Cochlear Implants↗

Evaluation of speech intelligibility for children with cleft lip and palate by means of automatic speech recognition.

OBJECTIVE: Cleft lip and palate (CLP) may cause functional limitations even after adequate surgical and non-surgical treatment, speech disorders being one of them. Interindividually, they vary a lot, showing typical articulation specifics such as nasal emission and shift of articulation and therefore a diminished intelligibility. Until now, an objective means to determine and quantify the intelligibility does not exist. METHOD: An automatic speech recognition system, a new method, was applied on recordings of a standard test to evaluate articulation disorders (psycholinguistic analysis of speech disorders of children PLAKSS) of 31 children at the age of 10.1+/-3.8 years. Two had an isolated cleft lip, 20 a unilateral cleft lip and palate, 4 a bilateral cleft lip and palate, and 5 an isolated cleft palate. The speech recognition system was trained with adults and children without speech disorders and adapted to the speech of children with CLP. In this study, the automatic speech evaluation focussed on the word accuracy which represents the percentage of correctly recognized words. Results were confronted to a perceptive evaluation of intelligibility that was performed by a panel of three experts. RESULTS: The automatic speech recognition yielded word accuracies between 1.2 and 75.8% (mean 48.0+/-19.6%). The word accuracy was lowest for children with isolated cleft palate (36.9+/-23.3) and highest for children with isolated cleft lip (72.8+/-2.9). For children with unilateral cleft lip and palate it was 48.0+/-18.6 and for children with bilateral cleft lip and palate 49.3+/-9.4. The automatic evaluation complied with the experts' subjective evaluation of intelligibility (p<0.01). The multi-rater kappa of the experts alone differed only slightly from the multi-rater kappa of experts and recognizer. CONCLUSION: Automatic speech recognition may serve as a good means to objectify and quantify global speech outcome of children with cleft lip and palate.

Adolescent↗

High-resolution transthoracic real-time three-dimensional echocardiography: quantitation of cardiac volumes and function using semi-automatic border detection and comparison with cardiac magnetic resonance imaging.

OBJECTIVES: We sought to validate high-resolution transthoracic real-time (RT) three-dimensional echocardiography (3DE), in combination with a novel semi-automatic contour detection algorithm, for the assessment of left ventricular (LV) volumes and function in patients. BACKGROUND: Quantitative RT-3DE has been limited by impaired image quality and time-consuming manual data analysis. METHODS: Twenty-four subjects with abnormal (n = 14) or normal (n = 10) LVs were investigated. The results for end-diastolic volume (EDV), end-systolic volume (ESV), and ejection fraction (EF) obtained by manual tracing were compared with the results determined by the semi-automatic border detection algorithm. Moreover, the results of the semi-automatic method were compared with volumes and EF obtained by cardiac magnetic resonance imaging (CMRI). RESULTS: Excellent correlation coefficients (r = 0.98 to 0.99) and low variability (EDV -1.3 +/- 8.6 ml; ESV -0.2 +/- 5.4 ml; EF -0.1 +/- 2.7%; p = NS) were observed between the semi-automatically and manually assessed data. The RT-3DE data correlated highly with CMRI (r = 0.98). However, LV volumes were underestimated by RT-3DE compared with CMRI (EDV -13.6 +/- 18.9 ml, p = 0.002; ESV -12.8 +/- 20.5 ml, p = 0.005). The difference for EF was not significant between the two methods (EF 0.9 +/- 4.4%, p = NS). Observer variability was acceptable, and repeatability of the method was excellent. CONCLUSIONS: The RT-3DE, in combination with a semi-automatic contour tracing algorithm, allows accurate determination of cardiac volumes and function compared with both manual tracing and CMRI. High repeatability suggests applicability of the method for the serial follow-up of patients with cardiac disease.

Aged↗

Automatic analysis of medical dialogue in the home hemodialysis domain: structure induction and summarization.

Spoken medical dialogue is a valuable source of information for patients and caregivers. This work presents a first step towards automatic analysis and summarization of spoken medical dialogue. We first abstract a dialogue into a sequence of semantic categories using linguistic and contextual features integrated in a supervised machine-learning framework. Our model has a classification accuracy of 73%, compared to 33% achieved by a majority baseline (p<0.01). We then describe and implement a summarizer that utilizes this automatically induced structure. Our evaluation results indicate that automatically generated summaries exhibit high resemblance to summaries written by humans. In addition, task-based evaluation shows that physicians can reasonably answer questions related to patient care by looking at the automatically generated summaries alone, in contrast to the physicians' performance when they were given summaries from a naïve summarizer (p<0.05). This work demonstrates the feasibility of automatically structuring and summarizing spoken medical dialogue.

Artificial Intelligence↗

Effect of premature ventricular beats on manual and automatic repolarization measurements.

OBJECTIVE: To compare QT interval and QT dispersion in ventricular ectopic beats with measurements from the preceding and the immediately following sinus beats, and investigate differences between manual and automatic measurements. PATIENTS: Eleven chronic uremic patients. MAIN OUTCOME MEASURES: ECGs were recorded during hemodialysis treatment and 12-lead sections containing five consecutive beats were extracted, each containing four sinus beats and one centrally-positioned premature ventricular beat. QT measurements were performed both manually and with a computer-automated technique. RESULTS: T wave amplitude was greater in the ectopic beats compared to the sinus beats (0.61 +/- 0.18 vs. 0.23 +/- 0.06 mV, P <.001). The ectopic beats had a greater QT than the sinus beats when measured manually (415 +/- 35 ms vs. 386 +/- 28 ms, P <.001), or automatically (375 +/- 30 vs. 366 +/- 27 ms, P<.01). The sinus beats following the ectopics had a greater QT than the preceding sinus beats (400 +/- 27 vs. 386 +/- 28 ms, P<.001, manual; 382 +/- 24 vs. 366 +/- 27 ms, P<.001, automatic). Differences in QT dispersion were seen only between the ectopic and sinus beats (91 +/- 31 vs. 58 +/- 27 ms, P <.001, manual; 68 +/- 33 vs. 49 +/- 35 ms, P <.001, automatic). CONCLUSIONS: Manual measurement resulted in greater QT values than automatic measurement. Both techniques identified differences between sinus and ectopic beats. The ventricular ectopic beats resulted in an increase in the QT of the immediately following sinus beats. These results confirm the need to interpret QT measurements with care in the presence of ectopic beats.

Aged↗

Automatic detection of slow wave sleep using two channel electro-oculography.

An automatic method was developed for detecting slow wave sleep (SWS). The automatic method is based on a two-channel electro-oculography (EOG) with left mastoid (M1) as reference. Synchronous electroencephalographic (EEG) activity was detected by calculating cross-correlation between the two EOG channels by using 0.5-6 Hz band. An amplitude criterion was used for detecting slow waves and beta power 18-30 Hz was used to exclude artefacts. The automatic scoring was compared to a standard visual sleep scoring based on EOG, central EEG and submental EMG. Sleep EEG and EOG were recorded from 265 subjects. The optimal cross-correlation, amplitude and beta thresholds were derived using data from 133 training subjects and then applied to the data from different 132 validation subjects. Results were most sensitive to the changes in the amplitude criteria. Cohen's Kappa between the visual and the new developed automatic scoring in separating non-SWS and SWS was substantial (0.70) with epoch-by-epoch agreement of 93%. SWS epoch detection sensitivity was 75% and specificity was 96%. Also the total amount of slow waves, slow wave time (SWT), was estimated. The advantage of the automatic method is that it could be applied during online recordings using only four disposable self-adhesive electrodes.

Adult↗

Automatic affective stimulus processing is intact after unilateral resection of the anterior temporal lobe in humans.

Only hundreds of milliseconds after an incoming stimulus is perceived, we make an evaluation of whether it is good or bad. This evaluation seems to occur automatically and can significantly influence behavior. According to several functional imaging studies, the amygdala, which is localized in the temporal lobes of the brain, is an important structure for the automatic processing of affective stimuli. To investigate how critical a role the amygdala plays in this process, we had 20 participants with unilateral resection of the temporal lobe and 20 controls perform an affective priming task. Both controls and patients demonstrated shorter response latencies on trials where prime and target had the same valence than on trials where prime and target had the opposite valence. This finding is generally known as the affective priming effect and is considered to reflect automatic stimulus evaluation. More specifically, it is assumed that the valence of the prime stimulus is activated automatically and exerts an influence on the speed by which the target stimulus is evaluated. Given that the affective priming effect is equally large in both groups, our results suggest that the automatic processing of stimulus valence is intact in participants who sustained unilateral resection of the temporal lobe.

Adult↗