Mean Dominant Frequency Research Articles

Actigraphy: A new diagnostic tool for hepatic encephalopathy

To assess the actigraphy, an ambulatory and continuous monitoring of wrist motor activity fitted to study sleep/wake patterns in hepatic encephalopathy (HE). Twenty-five cirrhotic patients (17 M, 8 F, mean age 56+/-11 years, 24/25 alcoholic, Child-Pugh A , B, C: 2, 6, 17) were included. The patients were classified into 3 groups: stage 0 group (n = 12), stage 1-2 group (n = 6), and stage 3-4 group (n = 7) of encephalopathy. Over three consecutive days, patients had clinical evaluation 3 times a day with psychometric test, venous ammoniemia, flash visually evoked potentials (VEP), electroencephalogram and continuous actigraphic monitoring for 3 d, providing 5 parameters: mesor, amplitude, acrophase, mean duration of activity (MDAI) and inactivity (MDII) intervals. Serum ammonia and VEP did not differ among the 3 groups. Electroencephalography mean dominant frequency (MDF) correlated significantly with clinical stages of HE (r = 0.65, P = 0.003). The best correlation with HE stage was provided by actigraphy especially with MDAI (r = 0.7, P < 10(-4)) and mesor (r = 0.65, P < 10(-4)). MDAI correlated significantly with MDF (r = 0.62, 0.004) and was significantly shorter in case of HE compared to patients without HE (stage 0: 5.33+/-1.6 min; stage 1-2: 3.28+/-1.4 min; stage 3-4: 2.52+/-1.1 min; P < 0.05). Using a threshold of MDAI of less than 4.9 min, sensitivity, specificity, positive predictive value, negative predictive value for HE diagnosis were 85%, 67%, 73% and 80%, respectively. Actigraphy may be an objective method to identify HE, especially for early HE detection. Motor activity at the wrist correlates well with clinical stages of HE. MDAI and mesor are the most relevant parameters.

Coherent spike-wave oscillations in the cortex and subthalamic nucleus of the freely moving rat

The basal ganglia play a critical role in controlling seizures in animal models of idiopathic non-convulsive (absence) epilepsy. Inappropriate output from the substantia nigra pars reticulata (SNr) is known to exacerbate seizures, but the precise neuronal mechanisms underlying abnormal activity in SNr remain unclear. To test the hypothesis that cortical spike-wave oscillations, often considered indicative of absence seizures, propagate to the subthalamic nucleus, an important afferent of SNr, we simultaneously recorded local field potentials from the frontal cortex and subthalamic nucleus of freely moving rats. Spontaneous spike-wave oscillations in cortex (mean dominant frequency of 7.4 Hz) were associated with similar oscillations in the subthalamic nucleus (mean of 7.9 Hz). The power of oscillations at 5–9 Hz was significantly higher during spike-wave activity as compared with rest periods without this activity. Importantly, spike-wave oscillations in cortex and subthalamic nucleus were significantly coherent across a range of frequencies (3–40 Hz), and the dominant (7–8 Hz) oscillatory activity in the subthalamic nucleus typically followed that in cortex with a small time lag (mean of 2.7 ms). In conclusion, these data suggest that ensembles of subthalamic nucleus neurons are rapidly recruited into oscillations during cortical spike-wave activity, thus adding further weight to the importance of the subthalamic nucleus in absence epilepsy. An increase in synchronous oscillatory input from the subthalamic nucleus could thus partly underlie the expression of pathological activity in SNr that could, in turn, aggravate seizures. Finally, these findings also reiterate the importance of oscillations in these circuits in normal behaviour.

Mood, cognition and EEG changes during interferon α (alpha-IFN) treatment for chronic hepatitis C

Background This study is aim to investigate concurrent long-term psychiatric, cognitive and neurophysiological measures of α-IFN neurotoxicity in the treatment of chronic viral hepatitis. Methods Twenty patients with HCV hepatitis were enrolled while treated with α-IFN (3–6 MU t.i.w. for 6–12 months). Neurotoxicity was evaluated by psychiatric [Hamilton Depression Rating Scale (HAM-D), Hamilton Scale for Anxiety (HAM-A), Beck Depression Inventory (BDI) and State-Trait Anxiety Inventory (STAI-Y)], complete cognitive and neurophysiological assessments (EEG spectral analysis, P300). Patients were assessed at baseline ( t 0), 2 ( t 1) and 6 months ( t 2) since the beginning of therapy. Results Depression scores significantly increased (HAM-D: t 0=4.4±2.6; t 1=8.9±3.9, p<0.001; and t 2=7.7±3.8, p<0.001). A concurrent increase was shown also for anxiety (HAM-A: t 0=6.0±3.2; t 1=9.6±4.5, p<0.005; and t 2=9.1±4.5, p<0.005). Significant neurophysiological effects were also detected: increase of α power ( p<0.05) in frontal derivations, reduction of the mean dominant frequency ( p<0.005) and increase of theta power ( p<0.05) in parietal derivations. In contrast, no significant cognitive changes occurred. Limitations The study was performed on a relative small sample of patients mainly with observational intentions. Biological data (e.g. blood cytokines samples) are not available: they could have given useful information about biological mechanisms related to the alterations observed. Conclusions α-IFN treatment caused a time-dependent induction of symptoms of mild depression, concurrent anxiety and EEG changes. These psychiatric and neurophysiological changes can better explain the pharmacological profile of α-IFN and could help to address research on at risk population and, particularly, during pegylated-IFN therapy.

Impairment of gastrointestinal motility by nitrate administration: evaluation based on electrogastrographic changes and autonomic nerve activity

Nitrates decrease the tone of the lower oesophageal sphincter, and may thus induce gastro-oesophageal reflux. In the present study, we evaluated electrogastrographic changes and heart-rate variability before and after the administration of nitrates. In 15 patients with chest pain treated with nitrates, electrocardiography and percutaneous electrogastrography were performed before and after administration of nitrates. Autonomic nervous system function was evaluated by spectral analysis of heart-rate variability and serial changes in low frequency and high frequency power, and the low frequency/high frequency ratio were compared. Electrogastrograms were analysed by obtaining peak power amplitudes and their dominant frequencies. After the administration of nitrates (isosorbide dinitrate), high frequency power, an index of parasympathetic nervous activity, was significantly decreased, whereas the low frequency/high frequency ratio, an index of sympathetic nervous activity, was significantly increased. The mean peak amplitude of the electrogastrogram significantly increased postprandially both before and after treatment. After isosorbide dinitrate treatment, however, mean peak amplitudes after a meal were significantly lower than those obtained before treatment. The mean dominant frequency of the electrogastrogram did not vary before and after treatment. The present study suggests that nitrates inhibit gastrointestinal motility by decreasing autonomic nervous activity.

Neuropsychological-neurophysiological alterations and brain atrophy in cirrhotic patients.

Psychometric performance has been reported to be related to brain atrophy in cirrhotics, but the relationship between brain atrophy and EEG findings is still unknown. The aim of this study was to ascertain the relationship among brain atrophy, EEG, and cognitive performance in cirrhotics. Sixty-eight cirrhotics (age = 55 +/- 10 years; males-66%) underwent psychometric evaluation (Symbol Digit Test, Trail Making Test-Part A, Scan test), EEG recording and spectral analysis (S-EEG), and brain CT scan. Central brain atrophy was ascertained by the following indexes of brain atrophy: the Evans' index, the bicaudate index, the cella media index, the bifrontal index, and the ventricular index; cortical brain atrophy by the sulci index. The severity of liver failure was assessed by the Child-Pugh score: 18% of patients were Child-Pugh Class A, 50% Class B, and 32% Class C. Central and cortical atrophies were found to be correlated with age, but not with the Child-Pugh score. Psychometric performance and the EEG mean dominant frequency (MDF) were found to be correlated with brain atrophy. Multivariate analysis showed that a poor psychometric performance was independently predicted by EEG slowing (MDF: p < 0.01) and by central brain atrophy (cella media index: p < 0.01). In conclusion, brain atrophy was associated with a poor psychometric performance and EEG alterations in cirrhosis. Both brain atrophy and EEG alterations independently predicted cognitive dysfunction in cirrhotic patients.

Spectral electroencephalogram analysis in hepatic encephalopathy and liver transplantation.

The aim of this study is to evaluate the role of spectral electroencephalogram (EEG) analysis ((S)EEG) in quantitating brain dysfunction in cirrhotic patients, showing conditions of minimal hepatic encephalopathy (HE), and determining the impact of orthotopic liver transplantation (OLT) on its correction. (S)EEG was compared with visual EEG ((V)EEG) in 44 cirrhotic patients waiting for OLT and 44 healthy controls. Eighteen patients had overt HE, and 26 patients had no apparent HE. Twenty-one transplant recipients were reexamined 6 months after OLT. Computerized (S)EEG was performed by mean dominant frequency (MDF) and the occipital alpha-theta ratio, expressed as its logarithmic transformation (LogR). All patients underwent psychometric assessment. MDF and LogR correlated significantly with Child-Pugh score (P <.05) and the presence of HE (P <.0001). (S)EEG and (V)EEG determined minimal HE in 8 (31%) and 6 (23%) of 26 patients without overt HE, respectively. (S)EEG did not correlate with age, sex, cause of liver disease, portal hypertension, or psychometric test results. MDF and LogR improved in many transplant recipients. LogR was significantly lower in OLT candidates who died before OLT compared with OLT survivors. In conclusion, (S)EEG provides reliable quantitative information to evaluate the degree of HE and appears more sensitive than (V)EEG to discriminate a subclinical stage of HE. The improvement in (S)EEG results observed in transplant recipients confirms the reversibility of bioelectric brain dysfunction with restoration of liver functions.

Odorant-Induced Olfactory Receptor Neural Oscillations and Their Modulation of Olfactory Bulbar Responses in the Channel Catfish

Peripheral waves (PWs) in the channel catfish are odorant-induced neural oscillations of synchronized populations of olfactory receptor neurons (ORNs) that appear after the initial approximately 500 msec of the response. The mean dominant frequency during the initial 2 sec of PW activity is approximately 28 Hz, declining to approximately 20 Hz in the last sec of a 5 sec stimulus. Recordings of PWs from different regions of a single olfactory lamella and simultaneously from widely separated lamellae within the olfactory organ suggest that PWs are initiated in the sensory epithelium within each olfactory lamella. Simultaneous recordings in vivo from the olfactory organ [electro-olfactogram (EOG) or integrated neural activity], local field potentials (LFPs) from the olfactory bulb (OB), and single and few-unit activity from OB neurons were performed. Cross-correlation analysis of simultaneously recorded odor-induced OB LFPs and either EOG or ORN neural activity showed that oscillations occurring within the OB were lower (<20 Hz) than those of PWs; however, during PW activity, OB LFPs increased both their magnitude and dominant frequencies and became correlated with the PWs. Also during odorant-induced PW activity, the responses of different OB neurons with similar odorant specificity became phase locked to each other and to both the PWs and OB LFPs. PWs are hypothesized to function to strengthen the synaptic transfer of olfactory information at specific glomeruli within the OB.

Efecto del estiramiento miocárdico sobre las frecuencias de activación determinadas mediante análisis espectral durante la fibrilación ventricular

The aim of this study was to analyze the effects of myocardial stretching on excitation frequencies, as determined by spectral analysis, during ventricular fibrillation. In 12 isolated rabbit heart preparations, ventricular activation during ventricular fibrillation was recorded with multiple electrodes. Recordings were obtained before, during and after ventricular dilatation produced with an intraventricular balloon. The dominant frequency of the signals obtained with each of the electrodes was determined by spectral analysis. During the control phase, the mean, minimum and maximum dominant frequencies were, respectively, 14.3 1.7, 12.5 1.7, and 16.2 1.4 Hz, and the average difference between the maximum and minimum frequencies was 3.6 2.1 Hz. This difference was over 4 Hz in four cases, and in no case did it exceed 8 Hz. During ventricular stretching, the mean dominant frequency increased significantly (21.1 6.1 Hz; p < 0.0001), as did the minimum values (14 2.6 Hz; p < 0.05) and especially the maximum values (26.6 7.7 Hz; p < 0.0001). The difference between the maximum and minimum frequencies (12.6 6.4 Hz; p < 0.001) was over 4 Hz in all cases except one, and over 8 Hz in 9 cases. The maximum values were distributed heterogeneously during ventricular stretching. Upon suppressing ventricular stretching, the dominant frequency did not differ from controls. Myocardial frequency maps during ventricular fibrillation show limited variations in the dominant frequency of the signals recorded in the lateral wall of the left ventricle. During stretching, the patterns were heterogeneous, due mainly to the marked increase in the maximum dominant frequency. In the experimental model used, the effects of stretching remitted after suppressing ventricular dilatation.

Electrogastrographic Norms in Children: Toward the Development of Standard Methods, Reproducible Results, and Reliable Normative Data

ABSTRACTBackgroundSurface electrogastrography (EGG) is a noninvasive technique that detects gastric myoelectrical electric activity, principally the underlying pacemaker activity generated by the specialized interstitial cells of Cajal. Interest in the use of this methodology has grown because of its potential applications in describing functional gastrointestinal disorders, particularly as a tool in the evaluation of nausea, anorexia, and other dyspeptic symptoms.MethodsFifty‐five healthy volunteers (27 female), ranging in age from 6 to 18 years (mean, 11.7 years), were studied for a 1‐hour baseline preprandial period and a 1‐hour postprandial period after consumption of a standard 448‐kcal meal. Recordings were obtained with an EGG Digitrapper or modified Polygraph (Medtronic‐Synectics, Shoreview, MN). Spectral analysis by an autoregressive moving average method was used to extract numerical data on the power and frequency of gastric electrical activity from the EGG signal.ResultsThe authors present normative data for healthy children and adolescents studied under a standardized protocol. Mean dominant frequency was found to be 2.9 ± 0.40 cycles per minute preprandially and 3.1 ± 0.35 postprandially, with 80% ± 13% of test time spent in the normogastric range (2–4 cycles per minute) before and 85% ± 11% after the test meal. The response of several key parameters to meal consumption was considered, and the effects of age, gender, and body mass index (BMI) on the EGG were sought.ConclusionsThere is a postprandial increase in the rhythmicity and amplitude of gastric slow waves, as other investigators have shown in adults. Key normative values are not dependent on age, gender, or BMI. The authors discuss limitations in the data set and its interpretability. The authors establish a normative data set after developing a standardized recording protocol and test meal and show that EGG recordings can be obtained reliably in the pediatric population. Development of similar norms by investigators using the EGG is crucial for future exploration of the validity and clinical application of the EGG. Differences in test conditions of signal detection and analytic methods influence EGG results substantially, and caution should be used when comparing results across centers.

Electrogastrographic norms in children: toward the development of standard methods, reproducible results, and reliable normative data.

Surface electrogastrography (EGG) is a noninvasive technique that detects gastric myoelectrical electric activity, principally the underlying pacemaker activity generated by the specialized interstitial cells of Cajal. Interest in the use of this methodology has grown because of its potential applications in describing functional gastrointestinal disorders, particularly as a tool in the evaluation of nausea, anorexia, and other dyspeptic symptoms. Fifty-five healthy volunteers (27 female), ranging in age from 6 to 18 years (mean, 11.7 years), were studied for a 1-hour baseline preprandial period and a 1-hour postprandial period after consumption of a standard 448-kcal meal. Recordings were obtained with an EGG Digitrapper or modified Polygraph (Medtronic-Synectics, Shoreview, MN). Spectral analysis by an autoregressive moving average method was used to extract numerical data on the power and frequency of gastric electrical activity from the EGG signal. The authors present normative data for healthy children and adolescents studied under a standardized protocol. Mean dominant frequency was found to be 2.9 +/- 0.40 cycles per minute preprandially and 3.1 +/- 0.35 postprandially, with 80% +/- 13% of test time spent in the normogastric range (2-4 cycles per minute) before and 85% +/- 11% after the test meal. The response of several key parameters to meal consumption was considered, and the effects of age, gender, and body mass index (BMI) on the EGG were sought. There is a postprandial increase in the rhythmicity and amplitude of gastric slow waves, as other investigators have shown in adults. Key normative values are not dependent on age, gender, or BMI. The authors discuss limitations in the data set and its interpretability. The authors establish a normative data set after developing a standardized recording protocol and test meal and show that EGG recordings can be obtained reliably in the pediatric population. Development of similar norms by investigators using the EGG is crucial for future exploration of the validity and clinical application of the EGG. Differences in test conditions of signal detection and analytic methods influence EGG results substantially, and caution should be used when comparing results across centers.

Effects of low doses of erythromycin on the 13C Spirulina platensis gastric emptying breath test and electrogastrogram: a controlled study in healthy volunteers

OBJECTIVE: Electrogastrography and stable isotope gastric emptying breath tests (GEBTs) are relatively simple, noninvasive tests of gastric motor function that may be useful in monitoring the effects of therapeutic interventions. It was our primary objective to examine the effects of low dose i.v. erythromycin on the results of the 13C Spirulina platensis GEBT and electrogastrography. We were also interested in evaluating the reproducibility of these tests. METHODS: In 10 healthy subjects (five female, ages 23–37 yr), we simultaneously performed the GEBT, using a prepackaged meal (340 kcal), and electrogastrography on each of four different occasions separated by at least 1 wk. After performance of baseline studies, they were repeated in random order after the infusion of 50 mg of erythromycin (Er50), 100 mg erythromycin (Er100), and a placebo (saline). Breath samples were obtained at baseline and at 75, 90, and 180 min after the meal and T 1/2 and T lag calculated. Electrogastrography recordings began 30 min before the test meal and continued for 2 h after the meal. RESULTS: Baseline and placebo T 1/2 and T lag were similar. Er50 resulted in a modest acceleration of gastric emptying ( T 1/2 Er50 vs baseline vs placebo = 104.0 vs 132.7 vs 125.5 min) and reduction in lag time ( T lag Er50 vs baseline vs placebo = 47.2 vs 61.5 vs 56.2 min). A similar decrease was seen in response to Er100. The baseline and placebo fasting and fed electrogastrography parameters were similar. After infusion of Er100, the percentage of normal slow waves in the first postprandial hour decreased relative to baseline and placebo (percent normogastria Er100 vs baseline vs placebo = 64.1 ± 7.5 vs 82.4 ± 6.4 vs 79.7 ± 5.5). This corresponded with an increase in percent tachygastria during the same period and an overall decrease in the mean dominant frequency. Similar but less striking changes were seen after administration of Er50. Replicate GEBTs showed a high degree of reproducibility both within and between individuals for T 1/2 and T lag. In contrast, replicate electrogastrograms revealed moderate to high variability for all parameters except the dominant frequency. CONCLUSION: The stable isotope GEBT utilizing 13C S. platensis demonstrates responsiveness to the prokinetic effects of low dose i.v. erythromycin and good reproducibility.

Acoustics, context and function of vibrational signalling in a lycaenid butterfly–ant mutualism

Juveniles of the Australian common imperial blue butterfly, Jalmenus evagoras, produce substrate-borne vibrational signals in the form of two kinds of pupal calls and three larval calls. Pupae stridulate in the presence of conspecific larvae, when attended by an ant guard, and as a reaction against perturbation. Using pupal pairs in which one member was experimentally muted, pupal calls were shown to be important in ant attraction and the maintenance of an ant guard. A pupa may use calls to regulate levels of its attendant ants and to signal its potential value in these mutualistic interactions. Therefore substrate-borne vibrations play a significant role in the communication between J.evagoras and its attendant ants and pupal calls appear to be more than just signals acting as a predator deterrent. Similarly, caterpillars make more sound when attended by Iridomyrmex anceps, suggesting that larval calls may be important in mediating ant symbioses. One larval call has the same mean dominant frequency, pulse rate, bandwidth and pulse length as the primary signal of a pupa, suggesting a similarity in function.

Temporal organization of atrial activity and irregular ventricular rhythm during spontaneous atrial fibrillation: an in vivo study in the horse.

Atrial fibrillation (AF) is common in healthy horses. We studied the temporal organization of AF to test the hypothesis that the arrhythmia is governed by a high degree of periodicity and therefore is not random in the horse. Further, we surmised that concealed conduction of AF impulses in the AV node results in an inverse relationship between AF frequency and ventricular frequency. Fast Fourier transform (FFT) analysis of atrial activity was done on signal-averaged ECGs (n = 11) and atrial electrograms (n = 3) of horses with AF at control (C), after quinidine sulfate (22 mg/kg by mouth every 2 hours) at 50% time to conversion (T50), and immediately before conversion (T90) to sinus rhythm. FFT always revealed a single dominant frequency peak. The mean dominant frequency decreased until conversion (C = 6.84 +/- 0.85 Hz, T50 = 4.87 +/- 1.5 Hz, T90 = 3.41 +/- 1.18 Hz; P < 0.001). Mean AA intervals (n = 500) gradually increased after quinidine. Mean RR intervals (n = 500), standard deviation of the mean (SDM), Poincaré plots, and serial autocorrelograms (SACs) of 500 RR intervals were measured at C and T90 to determine the ventricular response to AF and quinidine-induced changes in the variability of the ventricular response. Mean RR interval and SDM were reduced after quinidine (C = 1431 +/- 266 msec and 695 +/- 23 msec; T90 = 974 +/- 116 msec and 273 +/- 158 msec, respectively; P < 0.01). Poincaré plots and SAC at C and at T90 revealed a significant correlation of consecutive RR intervals typical of a system with a deterministic behavior. At T90, the variability of RR intervals was reduced and the overall periodicity of RR intervals was increased after quinidine administration. In the horse, AF is a complex arrhythmia characterized by a high degree of underlying periodicity. The inverse AA-to-RR interval relationship and reduced variability of RR intervals after quinidine suggest that the ventricular response during AF results from rate-dependent concealment of AF wavelets bombarding the AV node, which nevertheless results in a significant degree of short-term predictability of beat-to-beat changes in RR intervals.

Perception of female reproductive state from vocal cues in a mammal species.

While acoustic signalling by males is known to affect male-male competition, mate attraction and the timing of ovulation, the extent to which sexual selection has shaped the evolution of female acoustic signals is poorly understood. Among mammals, experimental evidence indicates that females attract mating partners by using olfactory and visual signals to advertise their reproductive state. Whether or not males ascertain female reproductive state from vocal signals has, however, never been systematically tested. In this study, we use playbacks of recorded vocalizations to demonstrate that male Barbary macaques, Macaca sylvanus, can discriminate between female copulation calls given at different stages of the oestrous cycle, responding more strongly to those given around the time when conception is most likely to occur. Acoustic analysis suggests that the mean dominant frequency of call units and a number of temporal parameters could provide males with the information necessary to discern the proximity of ovulation in this way Our results provide the first experimental evidence that the calls of female mammals may contain information on reproductive state, which males can perceive and use in such a way as to increase their reproductive success.

Electrogastrography in gastrostomy-tube-fed children.

Following gastrostomy tube placement some children develop gagging, retching, vomiting, pain, or irritability during feedings. Conventional medical management is not always successful. It is possible that intolerance of gastrostomy tube feedings reflects an underlying motility disorder of the foregut. The study aim was to determine whether children with gastrostomy tube feeding difficulties demonstrate abnormal gastric electrical control activity as measured by electrogastrography. Cutaneous electrogastrography of interpretable quality was performed in 25 feeding-tolerant and 23 feeding-intolerant children less than 10 years of age. Dominant frequencies, rhythm indices, and postprandial power measurements were recorded during the fasting and postprandial periods. Differences between groups were compared using the Student's t test. The groups were similar in method of gastrostomy tube placement, antireflux surgery, neurological impairment, duration of gastrostomy feeding dependence, formula type, volume, and administration. The feeding-tolerant group was significantly older (P<0.01). There were no significant differences between groups in the mean dominant frequencies or rhythm indices. The feeding-intolerant children had a mean postprandial power change that was significantly lower than that of the feeding tolerant group (P<0.003), although overlap was present. Children who are intolerant of gastrostomy tube feeding have an abnormal postprandial power decrease. EGG dominant frequency and rhythm indices are not predictive of gastrostomy feeding tolerance in predominantly neurologically impaired children.

Probability of Induction and Stabilization of Ventricular Fibrillation with Epinephrine

Clinical studies suggest that epinephrine facilitates ventricular fibrillation (VF) although mechanisms remain unclear. We tested the hypothesis that epinephrine increases the probability of inducing VF and stabilizes VF in association with shortening of fibrillation action potential duration. VF was induced in isolated, New Zealand White rabbit hearts (n=16) under control conditions and in the presence of 0.9μm/l epinephrine. Monophasic action potentials were recorded during sinus rhythm, pacing, and fibrillation. Epinephrine reduced fibrillation p80by 80%, from 23±4 to 4.6±1 V (P<0.05); and reduced fibrillation p90by 82%, from 29.3±5.4 to 5.4±1.9 V (P<0.05). Epinephrine also reduced the probability of spontaneous termination of VF during the first 5 s of VF from 29 to 8% (P<0.05). Epinephrine significantly decreased mean fibrillation cycle length from 104.5±2 to 75.7±2.3 ms (P<0.001). Mean action potential duration (60% repolarization) decreased from 76±3 to 40±3 ms (P<0.0003). Frequency analysis showed a mean dominant frequency during VF of 10.0±0.2 Hz under control conditions and 13.3±0.3 Hz with epinephrine (P<0.0001). These results suggest that epinephrine increases the probability of VF induction and decreases the probability of spontaneous defibrillation. Stabilization of fibrillation is associated with shortening of action potential duration and fibrillation cycle length, which may allow a greater number of fibrillation waves in the ventricle.

Improvement of chronic hepatic encephalopathy in dogs by the benzodiazepine-receptor partial inverse agonist sarmazenil, but not by the antagonist flumazenil.

Therapeutic modulation of the increased GABAergic tone in chronic hepatic encephalopathy (HE) by the benzodiazepine receptor (BR) antagonist flumazenil (F) has led to conflicting results in humans and animal models for HE. The BR inverse agonist sarmazenil (S) has only been used in animal models of acute HE. Therefore we investigated the effects of intravenous injection of F and S in dogs with chronic HE 8 to 12 weeks after placement of a portocaval shunt and 40% hepatectomy (n=7), compared to sham-operated pair-fed controls (n=7). The HE dogs had hyperammonemia (298 +/- 48 microM v 33 +/- 3 before surgery (mean +/- SEM)) and signs of HE at the start of the experiments (0.9 +/- 0.1 (scale 0-4)). Three (S3) and 8 (S8) mg/kg of S resulted in a significant improvement of encephalopathy (grade 0.9 +/- 0.2 immediately before v 0.5 +/- 0.1 after injection (S3) and 0.7 +/- 0.1 v 0.3 +/- 0.1 (S8)) and increase in mean dominant frequency of the EEG (MDF; 9.1 +/- 0.7 Hz v 11.1 +/- 0.3 (S3) and 8.9 +/- 0.5 v 11.0 +/- 0.3 (S8)) in HE dogs, whereas 15 mg/kg of S, 3 and 8 mg/kg of F, and the vehicle had no significant effects. The efficacy of S in these dogs is consistent with an increased GABAergic tone in the pathogenesis of chronic HE. The lack of effects of F makes a role for endogenous benzodiazepines herein unlikely.

Tymbal mechanics and the control of song frequency in the cicada Cyclochila australasiae

The anatomy of the tymbal of Cyclochila australasiae was re-described and the mass of the tymbal plate, ribs and resilin pad was measured. The four ribs of the tymbal buckle inwards in sequence from posterior to anterior. Sound pulses were produced by pulling the tymbal apodeme to cause the tymbal to buckle inwards. A train of four sound pulses, each corresponding to the inward buckling of one rib, could be produced by each inward pull of the apodeme, followed by a single pulse as the tymbal buckled outwards after the release of the apodeme. Each preparation produced a consistent sequence of pulses. Each of the pulses produced had its maximum amplitude during the first cycle of vibration. The waveform started with an initial inward-going rarefaction followed by a larger outward compression, followed by an approximately exponential decay, as is typical of a resonant system. The mean dominant frequencies of the pulses produced during the inward movement were 4.37, 4.19, 3.92 and 3.17 kHz respectively. The pulse produced during the outward movement had a mean resonant frequency of 6.54 kHz. This suggests that the mass-to-stiffness ratio that determines the resonant frequencies of the various pulses differs from pulse to pulse. If succeeding pulses followed rapidly, the next pulse tended to start on the inward-going half-cycle of its predecessor and to produce a coherent waveform. Coherence was lost if the preceding pulse had decayed to below approximately one-tenth of its peak amplitude. When the tymbal plate was loaded by a 380 &micro;g wire weight, the resonant frequency of all sound pulses was reduced. Pulses produced later in the inward buckling sequence were less affected by the loading than earlier ones. This suggests that the effective mass determining the resonance in the later pulses is greater than that in the earlier pulses. The frequency of the pulses produced in the outward movement was affected most, suggesting that the mass involved was less than that in any of the pulses produced by the inward movement. The quality factor, Q, of the pulses produced by the inward buckling of the unloaded tymbal was approximately 10. For the outward buckling, Q was approximately 6. The Q of loaded tymbals was higher than than that of unloaded tymbals. The Q of the resonances varied approximately as the reciprocal of the resonant frequency. Experimental removal of parts of the tymbal showed that the thick dorsal resilin pad was an important elastic determinant of the resonant frequency, but that the mass and elasticity of the tymbal ribs were also determinants of the resonant frequency. The major element of mass is the tymbal plate. The integrity of the tymbal ribs was essential if the buckling movement were to occur. The force required to cause inward buckling of the tymbal was approximately 0.25 N. The force required to hold the tymbal in the buckled-in position was approximately 0.05 N. This asymmetry in the tymbal compliance, together with the different masses involved in inward and outward buckling, may account for the difference between the resonant frequencies of the inward-going and outward-going clicks. The tymbal appears to act as an energy storage mechanism that releases energy as the tymbal ribs buckle inwards in sequence. Each pulse provides a large initial impulse to the abdominal resonator, followed by a sustaining resonant vibration at, or close to, the song frequency. Subsequent pulses maintain the coherent resonance of the song pulse.

Diagnostic tools for the detection of subclinical hepatic encephalopathy: comparison of standard and computerized psychometric tests with spectral-EEG.

The prevalence of subclinical hepatic encephalopathy (SHE) varies according to the diagnostic tool used in its detection. Since a standardised approach to the diagnosis of SHE is not yet available, we compared psychometric tests and EEG spectral analysis. On the same day 32 cirrhotic patients without overt hepatic encephalopathy and 18 controls were assessed by psychometric tests, both standard and computerized (CPT), and by EEG spectral analysis (EEG-SA). The CPT, measuring reaction time (Rt) and errors (er), were Font, Choice1, Choice2 and Scan test. The standard psychometric tests were the number connection test (NCT), the Reitan-B test, the Line Tracing Test [for time: LTT(t) and for errors: LTT(er)], and the Symbol Digit test (SD). Both psychometric tests [Reitan-B test, LTT(er) and CPT but Font (Rt) and Choice2 (er)] and EEG-SA parameters [mean dominant frequency (MDF) and theta power (theta %)] significantly correlated (p < 0.05) with albumin plasma levels. LTT(er), Scan, Font, Choice1 and Choice2 were significantly related to theta % and MDF. There was no control with positive EEG-SA, though one control was positive with LTT(t) and with the number of errors made during Font and Scan tests. The percentage of cirrhotics with positive EEG-SA was 34% (CI95% = 19-53), while 9-66% were positive with psychometric tests, depending on the test considered. In spite of the correlation between neuropsychological and neurophysiological parameters, the diagnostic agreement between EEG-SA and each psychometric test was not high. 1) neurophysiological and neuropsychological impairment in cirrhotics without overt hepatic encephalopathy were found linked to each other and to hepatic dysfunction; 2) psychometric tests were not sufficiently good predictors of EEG alterations; therefore, neuropsychological tools can not substitute neurophysiological ones to detect CNS dysfunction in liver disease.

Effects of blockade of fast and slow inward current channels on ventricular fibrillation in the pig heart.

To determine the contribution of fast and slow inward channels to the electrocardiogram (ECG) of ventricular fibrillation. Ventricular fibrillation was induced by endocardial electrical stimulation in pigs anaesthetised with pentobarbitone sodium (30 mg/kg intravenously). ECGs simultaneously recorded from the body surface (lead II) and from the endocardium were studied by power spectrum analysis (0-40 Hz). The mean (SEM) dominant frequency of fibrillation (9.0 (1.1) Hz in lead II at 0-40 s) did not change significantly with time in pigs given intravenous saline. However, the dominant frequency was significantly reduced by intravenous pretreatment with the class I antiarrhythmic drugs, lignocaine (3 mg/kg, 6.5 (0.5) Hz; 10 mg/kg, 4.2 (0.6) Hz), mexiletine (3 mg/kg, 6.2 (0.4) Hz; 10 mg/kg, 5.5 (0.4) Hz), and disopyramide (2.5 mg/kg, 5.4 (0.6) Hz). After flecainide (3 mg/kg, 6.9 (0.5) Hz) the reduction in frequency was not significant. Similar data were obtained with endocardial recordings. In contrast pre-treatment with verapamil (0.2 mg/kg, 11.7 (0.8) Hz; and 1.0 mg/kg, 12.9 (1.6) Hz) produced a significantly higher dominant frequency of fibrillation than saline and widened the bandwidth of frequencies around the dominant frequency. These results indicate that voltage-dependent sodium channel currents contribute to the rapid frequencies of ventricular fibrillation. Blockade of L-type inward calcium channel activity increases the fibrillation frequency and fractionates the frequencies of the fibrillation wavefronts.