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Variability Parameters (variability + parameter)
Selected AbstractsTHE ECONOMICS OF MARINE RESERVESNATURAL RESOURCE MODELING, Issue 3 2002RÖGNVALDUR HANNESSON ABSTRACT. Marine reserves can be a useful supplement to other methods of fisheries management, but marine reserves alone are not likely to achieve a great deal in economic terms andperhaps not even in terms of conservation. The effects of marine reserves with open access elsewhere are analyzed, using a logistic model for a population with a patchy distribution. It is assumedthat a marine reserve is establishedfor the territory of one of two sub-populations which interact through migrations. The total population increases while the total catch declines for the most part. A high rate of migration would, however, dilute the conservation effect. Examining a stochastic variant of the model shows that the variability (sum of squareddeviations) of catches may decrease as a result of protecting one of the sub-populations. Even if all rents disappear by assumption, it is possible to identify this as an economic benefit, particularly when the average catch increases. The variability of the catch falls for a range of values of the population migration parameter and variability of growth, both when the stochastic disturbances are independent and when they are perfectly correlated for the two sub-populations, andalso when the growth variability parameter differs between the sub-populations. [source] Refined analysis of genetic variability parameters in hepatitis C virus and the ability to predict antiviral treatment responseJOURNAL OF VIRAL HEPATITIS, Issue 8 2008J. M. Cuevas Summary., Hepatitis C virus (HCV) infects approximately 3% of the world population. The chronicity of hepatitis C seems to depend on the level of genetic variability. We have recently (Torres-Puente et al., J Viral Hepat, 2008; 15: 188) reported genetic variability estimates from a large-scale sequence analysis of 67 patients infected with HCV subtypes 1a (23 patients) and 1b (44 patients) and related them to response, or lack of, to alpha-interferon plus ribavirin treatment.. Two HCV genome regions were analysed in samples prior to antiviral therapy, one compressing the three hypervariable regions of the E2 glycoprotein and another one including the interferon sensitive determining region and the V3 domain of the NS5A protein. Haplotype and nucleotide diversity measures showed a clear tendency to higher genetic variability levels in nonresponder than in responder patients. Here, we have refined the analysis of genetic variability (haplotype and nucleotide diversity, number of haplotypes and mutations) by considering their distribution in each of the biologically meaningful subregions mentioned above, as well as in their surrounding and intervening regions. Variability levels are very heterogeneous among the different subregions, being higher for nonresponder patients. Interestingly, significant differences were detected in the biologically relevant regions, but also in the surrounding regions, suggesting that the level of variability of the whole HCV genome, rather than exclusively that from the hypervariable regions, is the main indicator of the treatment response. Finally, the number of haplotypes and mutations seem to be better discriminators than haplotype and nucleotide diversity, especially in the NS5A region. [source] Relationship Between Abnormal Microvolt T-Wave Alternans and Poor Glycemic Control in Type 2 Diabetic PatientsPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 10 2007GIULIO MOLON M.D. Background:Abnormal microvolt T-wave alternans (TWA) predicts the risk of ventricular arrhythmias and sudden cardiac death. Although type 2 diabetes is associated with an increased risk of these events, there is a dearth of available data on microvolt TWA measurements in type 2 diabetic populations. Methods:We studied 59 consecutive type 2 diabetic outpatients without manifest cardiovascular disease (CVD) and 35 non-diabetic controls who were matched for age, sex, and blood pressure values. Microvolt TWA analysis was performed non-invasively using the CH-2000 system during a sub-maximal exercise with the patient sitting on a bicycle ergometer. Results:The frequency of abnormal TWA was significantly higher in diabetic patients than in controls (25.4 vs 5.7%; P < 0.01). Among diabetic patients, those with abnormal TWA (n = 15) had remarkably higher hemoglobin A1c (HbA1c) (8.1 ± 0.9 vs 7.1 ± 0.8%, P < 0.001) and slightly smaller time-domain heart rate variability parameters (i.e., RMSSD, root mean square of difference of successive R-R intervals) than those with normal TWA (n = 44). Gender, age, body mass index, lipids, blood pressure values, cigarette smoking, diabetes duration, microvascular complication status, QTc interval, and current use of medications did not significantly differ between the groups. In multivariate regression logistic analysis, HbA1c (OR 13.6, 95% CI 2.0,89.1; P = 0.0076) predicted abnormal TWA independent of RMSSD values and other potential confounders. Conclusions:Our findings suggest that abnormal TWA is a very common condition (,25%) among people with type 2 diabetes without manifest CVD and is closely correlated to glycemic control. [source] Multichannel mapping of fetal magnetocardiogram in an unshielded hospital settingPRENATAL DIAGNOSIS, Issue 5 2005Donatella Brisinda Abstract Objectives To evaluate the feasibility of unshielded in-hospital multichannel mapping of fetal magnetocardiogram (FMCG), with a 36-channel system for standard adult magnetocardiographic (MCG) recordings, and its reliability according to the recommended standards for FMCG. Methods FMCG was ambulatory mapped with a 36-channel MCG system, in six normal pregnancies at different gestational ages. MCG analysis included adaptive digital filtering of 50 Hz, signal averaging, reconstruction of magnetic field distribution (MFD) and source localization. Fixed Point Independent Component Analysis algorithm (FastICA) was used to reconstruct the FMCG, separating them from maternal contamination and noise. Results The quality of FMCG recorded after the 32nd gestational week and reconstructed with FastICA was close to FMCG obtained in shielded rooms, and good enough to measure cardiac intervals and heart rate variability parameters. In two cases, reconstruction of the MFD during the QRS allowed three-dimensional localization of ventricular sources. Conclusions A first demonstration has been given that multichannel mapping of FMCG can be performed in unshielded clinical environments, with resolution good enough for contactless assessment of fetal cardiac electrophysiology. FastICA processing on unshielded FMCG, recorded after the 32nd week, provided beat-to-beat analysis and heart rate variability assessment. Further work is needed to improve signal reconstruction in early pregnancy. Copyright © 2005 John Wiley & Sons, Ltd. [source] The effects of experimental muscle and skin pain on the static stretch sensitivity of human muscle spindles in relaxed leg musclesTHE JOURNAL OF PHYSIOLOGY, Issue 11 2008Ingvars Birznieks Animal studies have shown that noxious inputs onto ,-motoneurons can cause an increase in the activity of muscle spindles, and it has been proposed that this causes a fusimotor-driven increase in muscle stiffness that is believed to underlie many chronic pain syndromes. To test whether experimental pain also acts on the fusimotor system in humans, unitary recordings were made from 19 spindle afferents (12 Ia, 7 II) located in the ankle and toe extensors or peronei muscles of awake human subjects. Muscle pain was induced by bolus intramuscular injection of 0.5 ml 5% hypertonic saline into tibialis anterior (TA); skin pain was induced by 0.2 ml injection into the overlying skin. Changes in fusimotor drive to the muscle spindles were inferred from changes in the mean discharge frequency and discharge variability of spindle endings in relaxed muscle. During muscle pain no afferents increased their discharge activity: seven afferents (5 Ia, 2 II) showed a decrease and six (4 Ia, 2 II) afferents were not affected. During skin pain of 13 afferents discharge rate increased in one (Ia) and decreased in two (1 Ia, 1 II). On average, the overall discharge rate decreased during muscle pain by 6.1% (P < 0.05; Wilcoxon), but remained essentially the same during skin pain. There was no detectable correlation between subjective pain level and the small change in discharge rate of muscle spindles. Irrespective of the type of pain, discharge variability parameters were not influenced (P > 0.05; Wilcoxon). We conclude that, contrary to the ,vicious cycle' hypothesis, acute activation of muscle or skin nociceptors does not cause a reflex increase in fusimotor drive in humans. Rather, our results are more aligned with the pain adaptation model, based on clinical studies predicting pain-induced reductions of agonist muscle activity. [source] Relationship Between Myocardial Beta-Adrenergic Sensitivity and Heart Rate VariabilityANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2 2000Philippe Cabrol M.D. Background: In congestive heart failure, despite activation of the sympathetic nervous system, heart rate variability parameters reflecting sympathetic modulation on sinus node are decreased. Our goal was to assess the role of beta-adrenergic sensitivity in the modulation of heart rate variability (HRV) in patients with valvular heart diseases. Methods and results: Ten patients with aortic stenosis, 10 patients with heart failure, and 12 controls were included. Baroreflex sensitivity was calculated by the sequency method. Noradrenaline plasma levels were assayed by HPLC. HRV was studied using 24-hour Holter monitoring. Cardiac beta-adrenergic receptivity was assessed by the chronotropic response to dobutamine. Right auricular samples were obtained for determination of beta-adrenergic receptor density by binding study with [125I]-iodocynaopindolol, and beta 1 and beta 2 densities, measured by competition between 125ICP binding by isoprenaline. In multivariate analysis, the dose of dobutamine that increases basal heart rate for 25 beats/min (ED25) is correlated with a parameter of global HRV: SDNN (r = 0.6, P < 0.001) and with indexes reflecting rather sympathetic modulation of HRV: SDANN (r = 0.62, P < 0.001) or SD (r = 0.47, P < 0.0001). All these relations were independent from mean NN, spontaneous baroreflex sensitivity, and noradrenaline plasma levels. No significant correlation existed between dobutamine ED25 and HRV indexes reflecting parasympathic tone. No relationship existed between HRV and beta-adrenergic receptor-binding characteristics. Conclusion: Cardiac beta-adrenergic sensitivity explored by dobutamine ED25 is an important determinant of HRV independent from mean NN, spontaneous baroreflex sensitivity, and noradrenaline plasma levels. [source] Relevance of anaesthesia for dofetilide-induced torsades de pointes in ,1 -adrenoceptor-stimulated rabbitsBRITISH JOURNAL OF PHARMACOLOGY, Issue 1 2008D Vincze Background and purpose: No information is available concerning the effects of anaesthetics in the most frequently used in vivo pro-arrhythmia model. Accordingly, in this study we examined the effect of pentobarbital, propofol or ,-chloralose anaesthesia on the pro-arrhythmic activity of the class III anti-arrhythmic dofetilide in ,1 -adrenoceptor-stimulated rabbits. Experimental approach: Rabbits anaesthetized intravenously with pentobarbital, propofol or ,-chloralose were infused simultaneously with the ,1 -adrenoceptor agonist phenylephrine (15 ,g kg,1 min,1, i.v.) and dofetilide (0.04 mg kg,1 min,1, i.v.). The electrocardiographic QT interval, the Tpeak,Tend interval and certain QT variability parameters were measured. The heart rate variability and the baroreflex sensitivity were utilized to assess the vagal nerve activity. The spectral power of the systolic arterial pressure was calculated in the frequency range 0.15,0.5 Hz to assess the sympathetic activity. Key results: Pentobarbital considerably reduced, whereas propofol did not significantly affect the incidence of dofetilide-induced torsades de pointes (TdP) as compared with the results with ,-chloralose (40% (P=0.011) and 70% (P=0.211) vs 100%, respectively). In additional experiments, neither doubling of the rate of the dofetilide infusion nor tripling of the rate of phenylephrine infusion elevated the incidence of TdP to the level seen with ,-chloralose. None of the repolarization-related parameters predicted TdP. The indices of the parasympathetic and sympathetic activity were significantly depressed in the ,-chloralose and propofol anaesthesia groups. Conclusions and implications: In rabbits, anaesthetics may affect drug-induced TdP genesis differently, which must be considered when results of different studies are compared. British Journal of Pharmacology (2008) 153, 75,89; doi:10.1038/sj.bjp.0707536; published online 29 October 2007 [source] Respiratory effects on the reproducibility of cardiovascular autonomic parametersCLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 4 2007Éva Zöllei Summary The aim of this study was to assess the influence of breathing pattern on the reproducibility of the most commonly used heart rate and blood pressure variability parameters and baroreflex indices. 5,5 min ECG and blood pressure recordings were made and repeated for 10 healthy volunteers in supine rest on 10 consecutive days during spontaneous and 6 min,1 patterned breathing. We investigated the following parameters: mean RR interval (RRI); the standard deviation of RR intervals (SDRR); the root mean square of successive differences in RRI (RMSSD); the percentage of RRIs which differed by 50% from the proceeding RRI (PNN50); mean systolic arterial pressure (SAP); the standard deviation of SAP (SAP SD); mean mean arterial pressure (MAP); mean diastolic blood pressure (DAP) and baroreflex indices from spontaneous sequence method (upBRS and downBRS) and from cross spectral analysis (LF alpha, HF alpha). To assess reproducibility for each parameter within- and between-subject variability values were calculated and the ratio of within- and between-subject variability was assessed. In addition, we calculated intraclass correlation coefficient (ICC). Compared to spontaneous respiration during 6 min,1 patterned breathing the heart rate and blood pressure variability increased; upBRS, LF alpha and HF alpha increased, downBRS did not change. However, ICC showed good reproducibility for most parameters, which did not improve further with controlled breathing. In conclusion, respiration had a strong influence on the most widely used cardiovascular autonomic parameters. The controlling of breathing did not result in consistent improvement in their reproducibility. [source] | |||||||||||||