Cardiac cycle

About: Cardiac cycle is a research topic. Over the lifetime, 3290 publications have been published within this topic receiving 96159 citations.

Heart rate variability analysis: a tool to assess cardiac autonomic function.

Abstract: Heart rate monitoring is commonly used to provide an acute indicator of an individual's cardiovascular status and responsiveness. An increasingly popular technique involves quantifying the very small amounts by which the heart rate changes from one cardiac cycle to the next. This "heart rate variability (HRV) analysis" provides a substantial amount of additional information about the cardiovascular system and enables quantification of cardiac regulatory influences on the autonomic nervous system. The autonomic nervous system consists of two main components: the sympathetic system and the parasympathetic system. The relative influence of these two components on the sino-atrial node of the heart determines the heart rate. A number of physiological factors, including blood pressure and respiratory rate, can have a profound effect on this autonomic "balance." HRV analysis therefore provides a noninvasive method for investigating the dynamic influence of changing physiological parameters on cardiac regulation.

Shunt dynamics in experimental atrial septal defects.

Abstract: Inorder to study the hemodynamic variables involving the magnitude, direction, and timing of phasic shunt flow, both the interatrial pressure gradient and blood flow along with other pertinent hemodynamic variables were measured instantaneously across a surgically created atrial septal defect (ASD) in seven awake dogs. Atrial and ventricular pacing and infusion of phenylephrine and isoproterenol were used to alter hemodynamic conditions. The wave form of phasic ASD flow was similar both in configuration and timing to the interatrial pressure gradient. During the cardiac cycle, both left-to-right (L-R) and right-to-left (R-L) shunting occurred: atrial contraction augmented L-R flow; the onset of ventricular contraction was associated with R-L flow; during the latter part of ventricular contraction, flow returned to L-R with the maximum L-R shunting occurring in early diastole. Tachycardia, infusion of phenylephrine and isoproterenol did not alter the phasic flow pattern. Both spontaneous and positive pressure respiration decreased net L-R shunting.

The bigeminal pulse in atrioventricular rhythm

Abstract: Bigeminal pulsation in atrioventricular rhythm is extremely rare. In 1915, the electrocardiograms of an unique case seen at the Massachusetts General Hospital were published.1During the past year, a second case showing the same condition has been examined, also at the Massachusetts General Hospital. No other cases have been reported in the literature, so far as I am aware.2 Atrioventricular rhythm, once called "nodal rhythm," is that cardiac rhythm arising from the atrioventricular node (of Tawara) which lies in the connective tissue below the endocardium of the right auricle just above the septal edge of the tricuspid valve ring. Impulses arising in this node travel in both directions, upward to produce an upside-down contraction of the auricles, and downward to produce ventricular systole. If thea-vnode stimulates the ventricles alone while the sino-auricular node (the normal "pacemaker" of the heart) stimulates the auricles, auriculo-ventricular dissociation occurs either of the

A model of blood flow in the mesenteric arterial system.

Abstract: There are some early clinical indicators of cardiac ischemia, most notably a change in a person's electrocardiogram. Less well understood, but potentially just as dangerous, is ischemia that develops in the gastrointestinal system. Such ischemia is difficult to diagnose without angiography (an invasive and time-consuming procedure) mainly due to the highly unspecific nature of the disease. Understanding how perfusion is affected during ischemic conditions can be a useful clinical tool which can help clinicians during the diagnosis process. As a first step towards this final goal, a computational model of the gastrointestinal system has been developed and used to simulate realistic blood flow during normal conditions. An anatomically and biophysically based model of the major mesenteric arteries has been developed to be used to simulate normal blood flows. The computational mesh used for the simulations has been generated using data from the Visible Human project. The 3D Navier-Stokes equations that govern flow within this mesh have been simplified to an efficient 1D scheme. This scheme, together with a constitutive pressure-radius relationship, has been solved numerically for pressure, vessel radius and velocity for the entire mesenteric arterial network. The computational model developed shows close agreement with physiologically realistic geometries other researchers have recorded in vivo. Using this model as a framework, results were analyzed for the four distinct phases of the cardiac cycle – diastole, isovolumic contraction, ejection and isovolumic relaxation. Profiles showing the temporally varying pressure and velocity for a periodic input varying between 10.2 kPa (77 mmHg) and 14.6 kPa (110 mmHg) at the abdominal aorta are presented. An analytical solution has been developed to model blood flow in tapering vessels and when compared with the numerical solution, showed excellent agreement. An anatomically and physiologically realistic computational model of the major mesenteric arteries has been developed for the gastrointestinal system. Using this model, blood flow has been simulated which show physiologically realistic flow profiles.