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Somatosympathetic reflexes were studied in young hyperinsulinemic, insulin-resistant (Zucker fatty) rats (ZFR) and a related control (Zucker lean) strain (ZLR). Glucose metabolism was characterized by minimal model analysis of intravenous glucose tolerance test data. Seven-week-old ZFR (n = 18) and ZLR (n = 17) were studied under pentobarbital anesthesia. Mean body weight and plasma glucose and insulin concentration were significantly greater (P < 0.05) in ZFR than in ZLR, whereas basal values of mean arterial pressure (MAP) and heart rate (HR) were not significantly different. Increments of MAP ([DELTA]MAP) and HR ([DELTA]HR) elicited by electrical stimulation of the sciatic nerve (5-s trains of 100 pulses, 0.5-ms pulse duration, 100- to 400-[micro]A pulse intensity) were significantly higher (ANOVA, P < 0.05) in ZFR at each level of stimulus intensity. Regression analysis showed a linear increase in [DELTA]MAP and [DELTA]HR with increasing sciatic nerve stimulus intensity. Pressor responses to phenylephrine after ganglionic blockade demonstrated that vascular reactivity to adrenergic stimulation is not increased in ZFR compared with ZLR. Thus this factor does not contribute to enhancement of somatosympathetic reflexes observed in this strain. Insulin sensitivity in ZFR was one-fourth (P < 0.05) that in ZLR. These results suggest that stronger sympathetic nervous reactivity in ZFR is associated with a severe insulin-resistant state before the onset of hypertension and support the hypothesis that insulin-mediated stimulation of the sympathetic nervous system is involved in the development of cardiovascular diseases related to alterations of glucose metabolism. sympathetic nervous activity; minimal model analysis; glucose kinetics; hypertension doi:10.1152/ajpregu.00644.2005

The incorporation of a pressure-dependent compliance in the three-element windkessel model (model A) of the systemic arterial system was evaluated to determine the accuracy of the linear model. Comparison of model A with nonlinear versions of the three-element windkessel model (model B1 and B2) indicated the improved data fit due to constant pressure-dependent compliance in model A. Furthermore, model A provided more accurate parameter estimates compared to models B1 and B2.

Open-loop experimental studies of the relationship between mean systemic arterial pressure (SAP) and mean baroreceptor pressure (BP) reveal that analytical data on SAP-BP and open loop gain (G)-BP curves derived from logistic function (LF) and normal-cumulative distribution function (CDF) are identical. Approximations of SAP-BP data using third-order polynomials have to be avoided for quantitative assay SAP-BP curves.

The T-tube arterial model, equipped with the potential to accurately regenerate pressure and flow waves in the ascending aorta and proximal descending aorta, is utilized to determine descending thoracic aortic compliance in anesthetized open-chest dogs. The end of the body tube displays features associated with the branching site of the abdominal aorta. Aortic pulse wave velocity measurements, computed from the calculated pressure in ascending and abdominal aorta, yield the corresponding length of the body tube. Compliance of the body tube average corresponds to the descending thoracic aortic compliance.

Abstract: Background and purpose: Left ventricular ejection fraction lacks specificity to predict sudden cardiac death in heart failure. T-wave alternans (TWA; beat-to-beat T-wave instability, often measured during exercise) is deemed a promising noninvasive predictor of major cardiac arrhythmic event. Recently, it was demonstrated that TWA during recovery from exercise has additional predictive value. Another mechanism that potentially contributes to arrhythmogeneity is exercise-recovery hysteresis in action potential morphology distribution, which becomes apparent in the spatial ventricular gradient (SVG). In the current study, we investigated the performance of TWA amplitude (TWAA) during a complete exercise test and of exercise-recovery SVG hysteresis (SVGH) as predictors for lethal arrhythmias in a population of heart failure patients with cardioverter-defibrillators (ICDs) implanted for primary prevention. Methods: We performed a case-control study with 34 primary prevention ICD patients, wherein 17 patients (cases) and 17 patients (controls) had no ventricular arrhythmia during follow-up. We computed, in electrocardiograms recorded during exercise tests, TWAA (maximum over the complete test) and the exercise-recovery hysteresis in the SVG. Statistical analyses were done by using the Student t test, Spearman rank correlation analysis, receiver operating characteristics analysis, and Kaplan-Meier analysis. Significant level was set at 5%. Results: Both SVGH and TWAA differed significantly (P < .05) between cases (mean ± SD, SVGH: −18% ± 26%, TWAA: 80 ± 46 μV) and controls (SVGH: 5% ± 26%, TWAA: 49 ± 20 μV). Values of TWAA and SVGH showed no significant correlation in cases (r = −0.16, P = .56) and in controls (r = −0.28, P = .27). Receiver operating characteristics of SVGH (area under the curve = 0.734, P = .020) revealed that SVGH less than 14.8% discriminated cases and controls with 94.1% sensitivity and 41.2% specificity; hazard ratio was 3.34 (1.17-9.55). Receiver operating characteristics of TWA (area under the curve = 0.699, P = .048) revealed that TWAA greater than 32.5 μV discriminated cases and controls with 93.8% sensitivity and 23.5% specificity; hazard ratio was 2.07 (0.54-7.91). Discussion and conclusion: Spatial ventricular gradient hysteresis bears predictive potential for arrhythmias in heart failure patients with an ICD for primary prevention, whereas TWA analysis seems to have lesser predictive value in our pilot group. Spatial ventricular gradient hysteresis is relatively robust for noise, and, as it rests on different electrophysiologic properties than TWA, it may convey additional information. Hence, joint analysis of TWA and SVGH may, possibly, improve the noninvasive identification of high-risk patients. Further research, in a large group of patients, is required and currently carried out by our group. [Copyright &y& Elsevier]

Aortic impedance data of infants, children and adults (age range 0.8-54 yr), previously reported by others, were interpreted by means of three alternative four-element windkessel models: W4P, W4S, and IVW. The W4P and W4S are derived from the three-element windkessel (W3) by connecting an inertance (L) in parallel or in series, respectively, with the aortic characteristic resistance (Rc). In the IVW, L is connected in series with a viscoelastic windkessel (VW). The W4S and IVW (same input impedance) fit the data best. The W4S, however, suffers from the assumption that Rc is part of total peripheral resistance (Rp). The IVW model offers a new paradigm for interpretation of resistive properties in terms of viscous (Rd) properties of vessel wall motion, distinguished from Rp. Results indicated that rapid reduction of Rd/Rp during early development is functional to modulation of decay time constant (τd) of pressure in diastole, such that normalization over heart period (τd/T) is independent of body size. Estimates of total arterial compliance (C) vs. age were fitted by a bell-shaped curve with a maximum at 33 yr. With body weight (BW) factored out by normalization, the C/BW data scattered about a bell-shaped curve centered at 66 mmHg. Inertance was significantly higher in pediatric patients than in adults, in accordance with a lower cross-sectional area of the vasculature, commensurate to a lower aortic flow. Changes of arterial properties appear functional to control the ratio of pulsatile power to active power and keep arterial efficiency as high as 97% in infants and children. [ABSTRACT FROM AUTHOR]

Background: This study examined the relative role of age and hypertension in deterioration of insulin-dependent (insulin sensitivity, SI ) and insulin-independent (glucose effectiveness, SG ) actions on glucose tolerance. Methods: We applied the minimal model of glucose kinetics to estimate SI and SG indexes from insulinemia and glycemia data detected during a frequently sampled intravenous glucose tolerance test performed in 21 normoglycemic subjects who were not affected by the metabolic syndrome (MS): seven young normotensive subjects (YN; mean age 29.3 ± 1.5 years), six elderly normotensive subjects (EN; mean age 57.0 ± 3.4 years) and eight elderly hypertensive patients (EH; mean age 62.1 ± 2.1 years). Results: Both normotensive subject groups (YN and EN) showed no significant difference in SI estimates despite significantly different age, whereas a significant reduction was evident in the EH patients compared with these groups. Mean estimates of SG showed no significant difference in elderly subject groups (EN and EH), irrespective of hypertension, whereas a significant increase was evident in the YN (analysis of variance followed by Scheffé test, P < .05). Conclusions: Our study demonstrates that, in the absence of MS: 1) insulin sensitivity in normotensive subjects is independent of age; b) hypertension is associated with insulin resistance in elderly subjects; and c) age is a primary predictor of deterioration in glucose effectiveness, independent of hypertension. [Copyright &y& Elsevier]

The baroreflex regulation of total peripheral resistance was quantified in closed-loop conditions. To vary arterial pressure cardiac output was reduced by graded inferior caval vein occlusion or by arterial bleeding. In eight lightly anaesthetised cats the static relation between mean arteriovenous pressure gradient and mean flow could be described by a curve that was convex to the pressure axis and had zero intercept. The ratio of the change in resistance to a given change in arterial pressure was taken as resistance gain (GR). The value of this gain was estimated with the aid of a model which predicts pressure from flow when the right parameter value for gain is filled in. It consists of a non-linear negative-feedback control system with control pressure as reference point and with a constant gain. The estimation was carried out with the aid of an automatic identification procedure. GR varied from 0.002 to 0.010 min·ml−1 in different animals under light anaesthesia. With deeper anaesthesia gain decreased by 35 to 50% and became zero with very deep anaesthesia or barodenervation.Assuming that the reflex is a linear system about control pressure and flow we linearised our model and computed the static overall open-loop gain (Go). Within this narrow range Go varied from 0.64 to 2.30 for different cats under light anaesthesia and decreased by the same percentage as GR with deeper anaesthesia. [ABSTRACT FROM PUBLISHER]