Topic
Cardiac cycle
About: Cardiac cycle is a research topic. Over the lifetime, 3290 publications have been published within this topic receiving 96159 citations.
Papers published on a yearly basis
Papers
More filters
TL;DR: The preliminary results demonstrate that parametric EIT has the potential to measure SV, and may be applicable for both clinical and home environment usage.
Abstract: The bio-impedance technique appears appropriate for non-invasive cardiac stroke volume (SV) measurement, as the thoracic conductivity distribution is altered during the cardiac cycle due to the heart contraction and blood perfusion. In the present work, the feasibility of a parametric electrical impedance tomography (EIT) for assessing the cardiac SV was studied. An impedance model of the thorax was constructed from segmented axial MRI images along 19 phases of the cardiac cycle. The heart was simulated as an ellipsoid, with its axes' lengths set as the reconstruction parameters, while all other tissues' geometry and conductivity values were kept fixed. A Newton?Raphson parametric optimization scheme was utilized, yielding a correlation between the reconstructed and anatomical left ventricular volumes of 0.97 (p = 2 ? 10?11). An analysis of noise sensitivity showed that the proposed algorithm requires an SNR greater than 65 dB. The simulation results were compared to physical data, collected with a portable EIT system (PulmoTrace?, CardioInspect). The validation study was employed for a group of N = 28 healthy patients, and a comparison with impedance cardiography measurements (BioZ?, Cardiodynamics) was made, showing a correlation of r = 0.86 (p = 4 ?10?9). The preliminary results demonstrate that parametric EIT has the potential to measure SV, and may be applicable for both clinical and home environment usage.
52 citations
TL;DR: A more satisfactory method of dependably maintaining the heart in ventricular fibrillation is needed before induced ventricularfibrillation can be safely employed to arrest cardiac contraction for prolonged periods during open cardiac operations.
Abstract: The effects of induced ventricular fibrillation on ventricular performance and cardiac metabolism were studied in dogs. When ventricular fibrillation was induced by a brief 7.5-v a-c stimulus and allowed to persist spontaneously for one hour, no significant effects on subsequent cardiac function were apparent. An increase in myocardial oxygen consumption and a decrease in coronary vascular resistance occurred during the period of fibrillation. When ventricular fibrillation was maintained by constant a-c stimulation, however, immediate and significantly deleterious effects on cardiac performance resulted. Coronary vascular resistance rose; myocardial oxygen consumption increased, but the increase was significantly less than in animals in which fibrillation persisted without electrical stimulation. Anerobic glycolysis ensued, leading to lactate accumulation in coronary venous blood. The small a-c current used to maintain ventricular fibrillation impairs oxygen utilization, interferes with oxygen availability, and has a markedly deleterious effect on cardiac performance. A more satisfactory method of dependably maintaining the heart in ventricular fibrillation is needed before induced ventricular fibrillation can be safely employed to arrest cardiac contraction for prolonged periods during open cardiac operations.
52 citations
TL;DR: Under certain conditions atrial contraction may contribute to an increase in cardiac output and may enhance over-all cardiac performance in man and particularly in patients with heart disease.
Abstract: Under certain conditions atrial contraction may contribute to an increase in cardiac output and may enhance over-all cardiac performance in man. The increase in flow and pressures resulting from atrial contraction is variable, depending on the functional capacity of the atria and ventricles and also on the basic pathologic condition. Atrial contribution in man appears to be more significant during exercise, during fast heart rates and particularly in patients with heart disease.
52 citations
TL;DR: In this paper, the authors describe the optimization of an implantable soft robotic system for heart failure whereby soft actuators wrapped around the ventricles are programmed to contract and relax in synchrony with the beating heart.
Abstract: Soft robotic devices have significant potential for medical device applications that warrant safe synergistic interaction with humans This article describes the optimization of an implantable soft robotic system for heart failure whereby soft actuators wrapped around the ventricles are programmed to contract and relax in synchrony with the beating heart Elastic elements integrated into the soft actuators provide recoiling function so as to aid refilling during the diastolic phase of the cardiac cycle Improved synchronization with the biological system is achieved by incorporating the native ventricular pressure into the control system to trigger assistance and synchronize the device with the heart A three-state electro-pneumatic valve configuration allows the actuators to contract at different rates to vary contraction patterns An in vivo study was performed to test three hypotheses relating to mechanical coupling and temporal synchronization of the actuators and heart First, that adhesion of the actuators to the ventricles improves cardiac output Second, that there is a contraction-relaxation ratio of the actuators which generates optimal cardiac output Third, that the rate of actuator contraction is a factor in cardiac output
52 citations
TL;DR: This investigation tested the hypothesis that pulsatile left ventricular assist synchronized to the cardiac cycle provides superiorleft ventricular unloading and circulatory support compared with continuous-flow left Ventricular assist devices at the same level of ventricular assistance device flow.
52 citations