Extensions and improvements of the electrical conductance method

Continuous monitoring of cardiac output is important in patients who are undergoing intensive care, thoracic surgery or a catheterization for diagnostic reasons. In these patients arterial pressure is routinely determined. In the patients, who are undergoing a catheterization for diagnostic reasons, aortic pressure is detennined. During intensive care and thoracic surgery arterial pressure is determined in both the pulmonary artery and the artery femoralis or radialis. The radial or femoral catheter is a replacement of the pressure catheter in the aorta. To detennine cardiac output continuously from an arterial pressure signal, the aortic pressure was reconstructed from the peripheral pressure [Wesseling et al. 1976, Gratz et al. 1992]. For this continuous cardiac output monitoring from aortic pressure, a model of the circulation is used. A parameter of this model is the compliance of the arterial system, which is the change in volume per unit of length (i.e. segmental volume) over a change in pressure. The compliance is derived from in vitro measurements using a selected group of human aorta's [Langewouters 1984]. Cardiac output can also be detelmined from the pulmonary arterial pressure signal, which is directly measured in this artery. Thus, a reconstruction of this pressure signal is not needed. To calculate right ventricular output, i.e. cardiac output, according to a pulse contour method, we detennined the pulmonary arterial compliance. To determine arterial volume, which was needed to determine compliance we modified the conductance method. We studied the relationship between arterial volume and pressure at a large range of pulmonary arterial pressure. To outline the context in which the research presented in this thesis has been carried out, the function of blood vessels and of large arteries in particular will be described. Next, the anatomy of arteries will be considered. Subsequently, the terms concerning mechanics of blood vessels are explained and fmally the method to determine blood volume in large arteries; the conductance method, will be described

Determination of the mean cross-sectional area of the thoracic aorta using a double indicator dilution technique

A double indicator dilution technique for determining the mean cross-sectional area (CSA) of a blood vessel in vivo is presented. Analogous to the thermodilution method, dilution of hypertonic saline was measured by an electrical conductance technique. Because the change in conductance rather than absolute conductance was used to calculate CSA, pulsatile changes in shear rate of blood and conductance of surrounding tissues had no effect on the data. To calculate CSA from an ion mass balance, cardiac output was needed and estimated from the thermodilution curve using the same 'cold' (hypertonic) saline injection. The mean CSA, obtained from this double indicator dilution method (CSA(GD)), was compared with the CSA obtained from the intravascular ultrasound method (IVUS) in 44 paired observations in six piglets. The regression line is close to the line of identity (CSA(GD) = -1.83 + 1.06 · CSA(IVUS), r = 0.96). The difference between both CSAs was independent of the diameter of the vessel, on average -0.99 mm2 ± 2.64 mm2 (mean CSA(GD) = 46.84 ± 8.21 mm2, mean CSA(IVUS) = 47.82 ± 9.08 mm2) and not significant. The results show that the double indicator dilution method is a reliable technique for estimating the CSA of blood vessels in vivo

Моделирование магнетронной распылительной системы методом конечных элементов

В работе проведено моделирование магнетронной распылительной системы методом конечных элементов и методом Галеркина. Получены распределения концентрации и скоростей носителей заряда, распределение электрического потенциала и магнитного поля, рассмотрены временные зависимости физических величин. Разработано программное обеспечение для моделирования сложных физических задач. Проведена верификация расчетного алгоритма на примере решения модельных задач. Отличительной особенностью исследуемой модели от существующих является учет нестационарного и конвективного слагаемых в уравнении для переноса скорости электрона и максимально точная реализация всех слагаемых в дифференциальном уравнении (в рамках метода Галеркина).The dissertation examines the modeling of a magnetron sputtering system by finite element analysis and Galerkin method. The model makes it possible to calculate the concentration, velocity, temperature, electrical potential and magnetic field. The methods and the code developed according to the model are usable for modeling complex physical tasks. The work also includes analysis and verification of results

Electrical modalities beyond pacing for the treatment of heart failure

In this review, we report on electrical modalities, which do not fit the definition of pacemaker, but increase cardiac performance either by direct application to the heart (e.g., post-extrasystolic potentiation or non-excitatory stimulation) or indirectly through activation of the nervous system (e.g., vagal or sympathetic activation). The physiological background of the possible mechanisms of these electrical modalities and their potential application to treat heart failure are discussed

Mapping for acute transvenous phrenic nerve stimulation study (MAPS Study)

Background: Central sleep apnea syndrome, correlated with the occurrence of heart failure, is characterized by periods of insufficient ventilation during sleep. This acute study in 15 patients aims to map the venous system and determine if diaphragmatic movement can be achieved by phrenic nerve stimulation at various locations within the venous system. Methods: Subjects underwent a scheduled catheter ablation procedure. During the procedural waiting time, one multielectrode electrophysiology catheter was subsequently placed at the superior and inferior vena cava and the junctions of the left jugular and left brachiocephalic vein and right jugular and right brachiocephalic vein, for phrenic nerve stimulation (1–2 seconds ON/2–3 seconds OFF, 40 Hz, pulse width 210 μs). Diaphragmatic movement was assessed manually and by a breathing mask. During a follow-up assessment between 2 and 4 weeks postprocedure, occurrence of adverse events was assessed. Results: In all patients diaphragmatic movement was induced at one or more locations using a median threshold of at least 2 V and maximally 7.5 V (i.e., e 3.3 mA, 14.2 mA). The lowest median current to obtain diaphragmatic stimulation without discomfort was found for the right brachiocephalic vein (4.7 mA). In 12/15 patients diaphragmatic movement could be induced without any discomfort, but in three patients hiccups occurred. Conclusion: Diaphragmatic stimulation from the brachiocephalic and caval veins is feasible. Potential side effects should be eliminated by adapting the stimulation pattern. This information could be used to design a catheter, combining cardiac pacing with enhancing diaphragm movement during a sleep apnea episode

An indirect component in the evoked compound action potential of the vagal nerve \ud

The vagal nerve plays a vital role in the regulation of the cardiovascular system. It not only regulates the heart but also sends sensory information from the heart back to the brain. We hypothesize that the evoked vagal nerve compound action potential contains components that are indirect via the brain stem or coming via the neural network on the heart. In an experimental study of 15 pigs, we identified four components in the evoked compound action potentials. The fourth component was found to be an indirect component, which came from the periphery. The latency of the indirect component increased when heart rate and contractility were decreased by burst stimulation (P = 0.01; n = 7). When heart rate and contractility were increased by dobutamine administration, the latency of the indirect component decreased (P = 0.01; n = 9). This showed that the latency of the indirect component of the evoked compound action potentials may relate to the state of the cardiovascular system.\u