hronic congestive heart failure (CHF) is a complex metabolic syndrome resulting from global hypoperfusion and neurohumoral activation. Sympathoadrenergic hyperactivity and stimulation of the reninangiotensin -aldosterone cascade promote endothelial dysfunction in the macro-and microcirculation, and thus influence the distribution of the terminal blood flow. The increased total peripheral resistance, reduction of blood supply and impaired peripheral vascular dilatation in response to vasodilator stimuli result in atrophy of skeletal muscle and decreased oxidative activity. Physical training could reverse the pathologic changes in patients with CHF and there have been many reports during the past decade that clearly demonstrate the benefits of exercise on functional capacity, ventilation, metabolic status, autonomic control of heart rate (HR) variability and other parameCirculation Journal Vol. 70, January 2006 ters, 1-5 including skeletal muscle performance and impaired endothelial function. 6,7 However, most of the actual training protocols are based on systemic exercise requiring increased cardiac output, which cannot be achieved by all patients, and in general are only suitable for patients with a moderately advanced grade of CHF; less attention has been paid to the development of safe and efficient training programs for patients with severe grades of the disease. Background This study was designed to evaluate the effects of low-frequency electrical stimulation (LFES) on muscle strength and blood flow in patients with advanced chronic heart failure (CHF). Methods and ResultsPatients with CHF (n=15; age 56.5±5.2 years; New York Heart Association III -IV; ejection fraction 18.7±3.3%) were examined before and after 6 weeks of LFES (10 Hz) of the quadriceps and calf muscles of both legs (1 h/day, 7 days/week). Dynamometry was performed weekly to determine maximal muscle strength (Fmax; N) and isokinetic peak torque (PTmax; Nm); blood flow velocity (BFV) was measured at baseline and after 6 weeks of LFES using pulsed-wave Doppler velocimetry of the right femoral artery.

Abstract-The purpose of this study was to ultrasonically characterize infarcted human myocardial tissue at the microscopic level by scanning acoustic microscopy. Infarcted myocardial specimens from ten cases with acute myocardial infarction were studied. Specimens were formalin fixed, para& embedded and sectioned to lo-pm thickness. A specially developed scanning acoustic microscope system, operating in the lOO-to 200-MHz ultrasound frequency range, was used for the measurements.

The present study has proposed a new method for estimating the pressure head (P(t)[mm Hg]) and flow (Q(t)[L/min]) of a centrifugal pump on the basis of voltage (V(t)[V]), current (I(t)[A]), and rotational speed (N(t)[k(rpm)]) of the DC motor for a pump without any additional sensors. In the proposed estimation method, two auto-regressive exogenous (ARX) models are employed. One ARX model has an output, P(t) or Q(t), and three inputs, VI(t) = V(t)I(t) and N(t) and the steady state gain (K) of the system from VI(t) to N(t). It can be assumed that K may include the information on viscosity of blood. The coefficient parameters of this ARX model are identified in an off-line fashion before implantation of the pump. After implantation, P(t) or Q(t) is estimated by the same ARX model with the already identified parameters. The other ARX model is used to identify Kon the basis of VI(t) and N(t) in an on-line fashion every time the viscosity of blood may change. In the experiment, a mock circulatory system consisting of a centrifugal pump and a reservoir with 37% glycerin or water was employed. The root mean square error between measured Q(t) and its estimate obtained from the proposed method was 1.66L/min. On the other hand, a different method based on a single ARX model with inputs of VI(t) and N(t), but without the additional input of K, yielded the corresponding estimation error of 2.22L/min. This means that the proposed method can reduce its estimation error by about 25% in comparison with a method that cannot cope with the change in blood viscosity.

The present study showed that radial and brachial artery blood flow volume decreased immediately during acupuncture on LR-3 acupoint, but increased at 180 seconds after acupuncture. This reaction is attributed to the change in peripheral vascular resistance.

A mutual information (MI) method for assessment of the relationship between hemodynamic variables was proposed and applied to the analysis of heart rate (HR), arterial blood pressure (BP), and renal sympathetic nerve activity (RSNA) in artificial heart-implanted dogs to quantify correlation between these parameters. MI measures the nonlinear as well as linear dependence of two variables. Simulation studies revealed that this MI technique furnishes mathematical features well suited to the investigation of nonlinear dynamics such as the cardiovascular system and can quantify a relationship between two parameters. To constitute a model free of the natural heart, two pneumatically actuated ventricular assist devices were implanted as biventricular bypasses in acute canine experiments. RSNA was detected with the use of bipolar electrodes attached to the renal sympathetic nerve. Analysis of data during control revealed that correlation between HR and RSNA was higher than that between HR and BP and that between RSNA and BP ( P < 0.05). Although RSNA seemed to fluctuate noncorrelatedly with BP in higher pacing rates, the MI values between them disclosed their strong correlation. Surprisingly, correlation between RSNA and BP was stronger during a pacing rate of 60 beats/min than during higher pacing rates and control ( P < 0.05). It is suggested that the baroreflex system may be susceptible to pacing rates during the total artificial heart state. We calculated the time delay between HR and RSNA, between RSNA and BP, and between HR and BP by regarding a time delay at which the maximum MI value between each pair of parameters was given as a physiological delay. Our results indicate that RSNA leads BP, BP leads HR, and RSNA leads HR during control ( P < 0.05). We conclude that this method could provide a powerful means for measuring correlation of physiological variables.