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  • 1
    Digitale Medien
    Digitale Medien
    Perioperative Hemodynamics in Patients Undergoing Partial Left Ventriculectomy (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiac surgery 16 (2001), S. 0 
    Details
    ISSN: 1540-8191
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Objectives: Effects of partial left ventriculectomy (PLV) were studied by analyzing porioperative hemodynamics with measurements of left ventricular (LV) pressure-volume (PV) relationships and thermodilution catheter measurements in the pulmonary artery. Methods: Between July and October 1996, 43 consecutive patients underwent PLV with and without mitral valvuloplasty with a thermodilution catheter and PV loop analysis immediately before and after surgery. Patients were 52 ± 13 years and 67 ± 13 kg, with reduced functional capacity (New York Heart Association 3.3 ± 0.3) due to cardiomyopathy (24), ischomic disease (13), valvular disease (3), and Chagas' disease (3). Results: PLV required cardiopulmonary bypass for 44 ± 24 minutes, with the heart arrested in 10 patients for 26 ± 22 minutes for coronary artery bypass grafting (8), aortic valve replacement (2), and autotransplantation (2). Two patients failed to come off bypass, six died in the hospital and 35 (35 [81.4%] of 43) were discharged. Changes in PV loops included decreased end-diastolic and end-systolic volume, resulting in no change in stroke volume. Pulmonary artery wedge pressure decreased despite elevated end-diastolic pressure. Ejection fraction, end-systolic elastance (E-max), afterload recruitable stroke work, and volume intercepts all improved and resulted in similar stroke work with less energy expenditure (less PV area), thus improving myocardial energetic efficiency. Conclusion: Results suggest that PLV improves systolic function but decreases diastolic compliance, which results in reduced net ventricular function immediately after surgery. Thus, immediate hemodynamic improvements appeared to derive from reduced severity in mitral regurgitation and perioperative load manipulation. Improved myocardial energetics may ameliorate LV function and improve the course of underlying myocardial disease.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1540-8191.2001.tb00483.x
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  • 2
    Digitale Medien
    Digitale Medien
    Improved Left Ventricular Contraction and Energetics in a Patient with Chagas' Disease Undergoing Partial Left Ventriculectomy (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiac surgery 16 (2001), S. 0 
    Details
    ISSN: 1540-8191
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: A 43-year-old patient with heart failure, precluded from heart transplantation or dynamic cardiomyoplasty because of Chagas' disease cardiomyopathy, mitral regurgitation, and ventricular mural thrombi, underwent mitral valvuloplasty and partial left ventriculectomy (PLV) between the papillary muscles. Intraoperative pressure-volume relationship analyses suggested improvement in left ventricular contraction, energetics, isovolumic relaxation, and mitral valve competency. These improvements allowed prompt, short-term recovery despite unchanged myocardial pathology, which suggests that a surgical approach can after anatomic-geometric factors and achieve clinical improvement in a dilated failing ventricle.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1540-8191.2001.tb00480.x
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  • 3
    Digitale Medien
    Digitale Medien
    Electroporation in a Model of Cardiac Defibrillation (2001)
    Oxford, UK : Blackwell Science Inc
    Journal of cardiovascular electrophysiology 12 (2001), S. 0 
    Details
    ISSN: 1540-8167
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Electroporation in a Model of Cardiac Defibrillation. Introduction: It is known that highstrength shock disrupts the lipid matrix of the myocardial cell membrane and forms reversible aqueous pores across the membrane. This process is known as “electroporation.” However, it remains unclear whether electroporation contributes to the mechanism of ventricular defibrillation. The aim of this computer simulation study was to examine the possible role of electroporation in the success of defibrillation shock. Methods and Results: Using a modified Luo-Rudy-1 model, we simulated two-dimensional myocardial tissue with a homogeneous bidomain nature and unequal anisotropy ratios. Spiral waves were induced by the S1-S2 method. Next, monophasic defibrillation shocks were delivered externally via two line electrodes. For nonelectroporating tissue, termination of ongoing fibrillation succeeded; however, new spiral waves were initiated, even with high-strength shock (24 V/cm). For electroporating tissue, high-strength shock (24 V/cm) was sufficient to extinguish ongoing fibrillation and did not initiate any new spiral waves. Weak shock (16 to 20 V/cm) also extinguished ongoing fibrillation; however, in contrast to the highstrength shock, new spiral waves were initiated. Success in defibrillation depended on the occurrence of electroporation-mediated anodal-break excitation from the physical anode and the virtual anode. Some excitation wavefronts following electrical shock used a deexcited area with recovered excitability as a pass-through point; therefore, electroporation-mediated anodal-break excitation is necessary to block out the pass-through point, resulting in successful defibrillation. Conclusion: The electroporation-mediated anodal-break excitation mechanism may play an important role in electrical defibrillation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1540-8167.2001.01393.x
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  • 4
    Digitale Medien
    Digitale Medien
    Effects of Partial Left Ventriculectomy on Left Ventricular Pump Function Studied by Theoretical Analyses (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiac surgery 16 (2001), S. 0 
    Details
    ISSN: 1540-8191
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Although partial left ventriculectomy (PLV) was devised to reduce myocardial wall stress in patients with severe heart failure, whether the operation acutely improves cardiac pump function has not been determined either clinically or experimentally. Because precise control of preload, afterload, and heart rate is virtually impossible in animal experiments as well as clinically before and after surgery, we took advantage of the theoretical analysis to study quantitatively the changes in pump function by PLV. We reconstructed the end-systolic and end-diastolic pressure-volume relationships based on two different geometric conditions (i.e., before and after volume reduction) but from the same myocardial stress-strain relationship. The effect of volume reduction surgery on left ventricular pump function depended on preoperative conditions. We found that the improvement in pump function was achieved only if elastance (Ees) was low and if the end-systolic strain-axis scaling parameter (k) value was low. The presence of hypertrophy amplified the improved function, but again with low Ees and low end-systolic k. We conclude that the favorable hemodynamics are expected only in limited cases during the acute phase. Candidates for favorable preoperative factors include low end-systolic Ees, an end-systolic pressure-volume relationship being less convexed toward the volume axis (low k), and large left ventricular mass.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1540-8191.2001.tb00479.x
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  • 5
    Digitale Medien
    Digitale Medien
    Development of a servo-controller of heart rate using a cycle ergometer (1999)
    Springer
    Heart and vessels 14 (1999), S. 177-184 
    Details
    ISSN: 1615-2573
    Schlagwort(e): Negative feedback ; Transfer function ; Exercise
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary In exercise training, precise control of exercise intensity would maximize the training efficacy while minimizing risks. To adjust work rate, heart rate (HR) has been used as a measure of exercise intensity. Thus, we developed a servo-controller of HR using a cycle ergometer. After estimating the transfer function from work rate to HR, we optimized feedback parameters for achieving a quick and stable HR response by means of a computer simulation. We then examined the performance of the servo-controller of HR in 55 healthy volunteers. We set the target HR at 60% and 75% of the age-predicted maximum HR. Times required for HR to reach 90% of the target HR were 136 ± 33 and 137 ± 22s in the respective protocols. Standard deviations of the steady-state difference between the target and measured HRs were 2.5 ± 0.6 and 3.8 ± 1.1 beats/min. We conclude that the developed servo-controller makes it possible to precisely regulate HR and, thereby, exercise intensity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02482304
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  • 6
    Digitale Medien
    Digitale Medien
    Transient oxygen uptake response to exercise characterizes functional capacity of the cardiocirculatory system in patients with chronic heart failure: a random stimulus approach (1998)
    Springer
    European journal of applied physiology 78 (1998), S. 333-339 
    Details
    ISSN: 1439-6327
    Schlagwort(e): Key words: Exercise ; Heart failure ; Oxygen uptake ; Transient response
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The transient response of oxygen uptake (V˙O2) to submaximal exercise, known to be abnormal in patients with cardiovascular disorders, can be useful in assessing the functional status of the cardiocirculatory system, however, a method for evaluating it accurately has not yet been established. As an alternative approach to the conventional test at constant exercise intensity, we applied a random stimulus technique that has been shown to provide relatively noise immune responses of system being investigated. In 27 patients with heart failure and 24 age-matched control subjects, we imposed cycle exercise at 50 W intermittently according to a pseudo-random binary (exercise-rest) sequence, while measuring breath-by-breath V˙O2. After determining the transfer function relating exercise intensity (W˙) to V˙O2 and attenuating the high frequency ranges (〉6 exercise-rest cycles · min−1), we computed the high resolution band-limited (0–6 cycles · min−1) V˙O2 response (0–120 s) to a hypothetical step exercise. The V˙O2 response showed a longer time constant in the patients than in the control subjects [47 (SD 37) and 31 (SD 8) s, respectively, P 〈 0.05]. Furthermore, the amplitude of the V˙O2 response after the initial response was shown to be significantly smaller in the patients than in the control subjects [176 (SD 50) and 267 (SD 54) ml · min−1 at 120 s]. The average amplitude over 120 s correlated well with peak V˙O2 (r = 0.73) and ΔV˙O2/ΔW˙ (r = 0.70), both of which are well-established indexes of exercise tolerance. The data indicated that our band-limited V˙O2 step response using random exercise was more markedly attenuated and delayed in the patients with heart failure than in the normal controls and that it could be useful in quantifying the overall functional status of the cardiocirculatory system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004210050428
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