Topic
Cardiac cycle
About: Cardiac cycle is a research topic. Over the lifetime, 3290 publications have been published within this topic receiving 96159 citations.
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TL;DR: Experiments are presented which show that changes in impedance occur during the cardiac cycle but do not result from the actual volume changes of the heart, as has been suggested in the literature.
Abstract: If the trunk is placed between two electrodes of a high frequency circuit, changes in impedance occur during the cardiac cycle. Experiments are presented which show that these variations do not result from the actual volume changes of the heart, as has been suggested in the literature. The changes in impedance are caused by the rhythmic variations in blood content of the vessels.
63 citations
TL;DR: It is shown that measuring torsion is an extremely sensitive indicator of the existence of ectopic excitation and the effects of different pacing protocols on left ventricular (LV) torsions were evaluated over the full cardiac cycle.
Abstract: The effects of different pacing protocols on left ventricular (LV) torsion were evaluated over the full cardiac cycle. A systolic and diastolic series of magnetic resonance imaging (MRI) scans were combined and used to calculate the torsion of the LV in a canine model. The asynchronous activation resulting from ventricular pacing interferes with the temporal evolution of LV torsion. The torsion of the left ventricle was investigated under three different protocols: 1) right atrial pacing, 2) right ventricular pacing, and 3) simultaneous pacing from the right ventricular apex and LV base. The temporal evolution of torsion was determined from tagged MRI and evaluated over the cardiac cycle. The peak rotation for the atrially paced hearts was 11.1 degrees (+/- 3.5 degrees) compared to 6.1 degrees (+/- 1.7 degrees) and 6.1 degrees (+/- 0.7 degree) for those hearts paced from the right ventricle and from both ventricles, respectively. While biventricular pacing increases the synchrony of contraction, it significantly alters the pattern of LV torsion. From these experiments we have shown that measuring torsion is an extremely sensitive indicator of the existence of ectopic excitation.
63 citations
TL;DR: A computational model that accounts for blood-tissue interaction under physiological flow conditions was developed and applied to a thin-walled model of the left heart, showing that dysfunction can be modeled by changing the relationships for fiber resting-length and/or stiffness.
Abstract: A computational model that accounts for blood-tissue interaction under physiological flow conditions was developed and applied to a thin-walled model of the left heart. This model consisted of the left ventricle, left atrium, and pulmonary vein flow. The input functions for the model included the pulmonary vein driving pressure and time-dependent relationship for changes in chamber tissue properties during the simulation. The Immersed Boundary Method was used for the interaction of the tissue and blood in response to fluid forces and changes in tissue pathophysiology, and the fluid mass and momentum conservation equations were solved using Patankar's Semi-Implicit Method for Pressure Linked Equations (SIMPLE). This model was used to examine the flow fields in the left heart under abnormal diastolic conditions of delayed ventricular relaxation, delayed ventricular relaxation with increased ventricular stiffness, and delayed ventricular relaxation with an increased atrial contraction. The results obtained from the left heart model were compared to clinically observed diastolic flow conditions, and to the results from simulations of normal diastolic function in this model [1]. Cases involving impairment of diastolic function were modeled with changes to the input functions for fiber relaxation/ contraction of the chambers. The three cases of diastolic dysfunction investigated agreed with the changes in diastolic flow fields seen clinically. The effect of delayed relaxation was to decrease the early filling magnitude, and this decrease was larger when the stiffness of the ventricle was increased. Also, increasing the contraction of the atrium during atrial systole resulted in a higher late filling velocity and atrial pressure. The results show that dysfunction can he modeled by changing the relationships for fiber resting-length and/or stiffness. This provides confidence in future modeling of disease, especially changes to chamber properties to examine the effect of local dysfunction on global flow fields.
63 citations
TL;DR: The major variations in the cardiac cycle occurred during the periods of ventricular ejection and isovolumic relaxation, which are primarily affected by the changing relationships of the size of the defect, ratio of pulmonary to systemic resistance, and magnitude of net shunts.
Abstract: This study was conducted to determine the nature of intracardiac shunting in 50 patients between the ages of 3 and 15 years with isolated ventricular septal defects. Simultaneous right and left ventricular pressures and biplane cineangiocardiography were utilized to study the timing and the direction of flow across the defect. Patients with low to moderately elevated right ventricular pressures demonstrated left-to-right shunting across the defect throughout the cardiac cycle. When pressure in the right ventricle approximated that of the left, right-to-left shunting occurred across the defect into the left ventricle during isovolumic relaxation. All patients shared in common the following: (1) a predominant left-to-right gradient and shunt across the defect into the body of the right ventricle during diastole; and, (2) augmentation of the left-to-right gradient with resultant increase of the shunt into the right ventricle during isovolumic contraction immediately preceding opening of the aortic valve. In comparing patients with and without pulmonary hypertension, the major variations in the cardiac cycle occurred during the periods of ventricular ejection and isovolumic relaxation. These two periods are primarily affected by the changing relationships of the size of the defect, ratio of pulmonary to systemic resistance, and magnitude of net shunts.
63 citations
TL;DR: Using diastolic rather than systolic data for device sizing resulted in a change of the recommended valve size in nearly half of patients for both annular area and perimeter, suggesting device sizing with potential for valve under-sizing if diastsolic annular dimensions are employed.
63 citations