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The biomechanical environment to which cells are exposed is important to their normal growth, development, interaction, and function. Accordingly, there has been much interest in studying the role of biomechanical forces in cell biology and pathophysiology. This has led to the introduction and even commercialization of many experimental devices. Many of the early devices were limited by the heterogeneity of deformation of cells cultivated in different locations of the culture plate membranes and were also attached with complicated technical/electronic efforts resulting in a restriction of the reproducibility of these devices. The objective of this study was to design and build a simple device to allow the application of dose-dependent homogeneous equibiaxial static stretch to cells cultured on flexible silicone membranes to investigate biological and biomedical questions. In addition, cultured neonatal rat atrial cardiomyocytes were stretched with the proposed device with different strain gradients. For the first time with this study we could demonstrate that stretch up to 21% caused dose-dependent changes in biological markers such as the calcineurin activity, modulatory calcineurin-interacting protein-l, voltage-gated potassium channel isoform 4.2, and voltage-gated [K.sup.+] channel-interacting proteins-2 gene expression and transient outward potassium current densities but not the protein-to-DNA ratio and atrial natriuretic peptide mRNA. With both markers mentioned last, dose-dependent stretch alterations could only be achieved with stretch up to 13%. The simple and low-cost device presented here might be applied to a wide range of experimental settings in different fields of research. equibiaxial stretch; hypertrophy; calcineurin

Cardiac resynchronization therapy provides a treatment option for patients with congestive heart failure. Electrodes are usually advanced via the cardiac venous system (CVS). Placement is often hampered by small vessel diameter or tortuosity. The aim of this study was to develop and test a magnetized stimulation wire (MSW) capable of being navigated into small and tortuous CVS branches. Therefore, a conventional guide wire with a permanent magnet and a single stimulation electrode at its tip was coated with iridium oxide at the distal end and insulated except for the very tip (coating thickness: 500 nm, active uncoated area: 10 mm(2)). The MSW was designed to allow for a remote magnetic steering using a magnetic navigation system (MN) (Stereotaxis™). After in vitro testing of the electrical properties, the MSW was tested in an animal model (n=6 sheep): the MSW was placed in a CVS side branch and navigation characteristics of the MSW were determined. The effective (unipolar) pacing threshold was 4.9±2.4 V (at 2 ms pulse width). The rheobase was 1.89±0.44 V and the chronaxie time was 0.75±0.7 ms. The MSW could be navigated into small CVS branches with reasonable MN properties. This could allow stimulation at CVS sites currently not accessible for conventional stimulation catheters or electrodes.

Background: Exercise intensity in coronary patients is controlled by heart rate measurements. Very few investigations have compared the maximum heart rate in cardiac outpatient groups, in leisure-time sport activities, and especially in swimming., Patients and Methods: Within different exercise conditions 21 coronary patients, nine in well-compensated cardiac condition joining a training group and twelve joining the exercise group with lower intensity, without signs of heart failure, engaged in an incremental bicycle ergometry. A six-lead ECG was derived at the same time with a 24-h ECG. The performance tolerance was measured by the pulse limit derived in 20 patients; one patient failed to show signs of subjective or objective ischemia. During a 24-h ECG monitoring, the patients took part in a 1-h standardized cardiac outpatient program, a standardized swimming program 4 x 25 m, and a typical self-selected leisure-time activity., Results: The patients showed a peak work capacity of 2.2 W/kg and a symptom-free work capacity of 1.3 W/kg. The derived upper heart rate limit was passed during swimming by 19, during leisure-time activity by 16, and during cardiac outpatient program by two patients. The maximum of the mean overriding the limit occurred in leisure-time activity. Signs of ischemia occurred during ergometry in 15, during swimming training in ten patients, during leisure-time activity in eight, and during cardiac outpatient therapy in one. Arrhythmia < Lown IVa was documented on the ergometer in 15, during leisure-time sport activity in 15, during cardiac outpatient therapy in 17, and during swimming in eight patients. Arrhythmia Lown IVa occurred in one patient each during ergometry, leisure sports, and during the night., Conclusion: Coronary patients are in danger to exercise beyond the pulse limit during swimming and other leisure-time sports and not during cardiac outpatient therapy. The upper heart rate limit should be observed during swimming and other endurance leisure-time activities, and is of little importance during cardiac outpatient therapy.