Mechanical Events of the Cardiac Cycle
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
The cardiac cycle comprises two phases defined by ventricular muscle mechanical activity: systole (contraction) and diastole (relaxation). The sequence of events in the cardiac cycle can be described by beginning from before the onset of atrial contraction, in mid-diastole, through late diastole, isovolumetric contraction, ventricular ejection, to isovolumetric ventricular relaxation and rapid ventricular filling in early diastole. Three main factors, such as preload, afterload and myocardial contractility of the heart, determine the volume of blood ejected by the ventricles during systole and the ejection pressure. Sympathetic activity increases the rate and force of ventricular contraction at any given fibre length. Preload and afterload are intrinsic factors influencing the muscle of the heart, whereas sympathetic nervous activity is an extrinsic factor. Studies of isometric and isotonic contractions demonstrate that both the force and the velocity of contraction of cardiac muscle cells are influenced by the intrinsic factors of preload and afterload and the extrinsic factor of sympathetic autonomic activity.
Ventricular function
Burt B. Hamrell in Cardiovascular Physiology, 2018
Ventricular function is best understood after studying heart muscle function. Preload, contractility, and afterload are the major determinants of ventricular function and are functional parameters based on ventricular myocyte mechanical properties. The volume of ventricular ejection, the stroke volume, is partly determined by the amount of preceding diastolic filling. Ventricular pressure and volume during the cardiac cycle can be plotted to create a pressure-volume loop. Pressure-volume loops are useful to evaluate ventricular function and the area of the loop is a measure of ventricular work. The afterload is the load on a ventricle during contraction. It is called "afterload" because it is the load on the ventricles after contraction begins. A precise measure of ventricular afterload involves measuring ventricular wall stress or force, since wall force is what myocytes must work with during pressure development and shortening. Normal left ventricular afterload increases with increases in aortic systolic blood pressure.
Fetal hydrops
David M. Luesley, Mark D. Kilby in Obstetrics & Gynaecology, 2016
This chapter describes the accumulation of fluid in two or more serous cavities, example pericardium, pleura, abdomen or subcutaneously, and may also be associated with polyhydramnios. Fetal hydrops can be better understood by first dividing it into its traditional classification of immune hydrops, red cell alloimmunisation involving fetal haemolysis, or nonimmune hydrops. Fetal hydrops affects approximately one in 3000 pregnancies. Rhesus disease may occur when fetal red cells enter the maternal circulation via a fetomaternal haemorrhage, known as maternal sensitisation or alloimmunisation. Cardiac dysrhythmias, both tachyarrhythmias, supraventricular tachycardia, and bradyarrhythmias, complete heart block, are associated with fetal hydrops through disturbance of the cardiac diastolic function but also by the effect of hypoxia directly on the myocardium. Placental anomalies such as chorioangioma, sacrococ-cygeal teratomas and vein of Galen aneurysms can act as a large peripheral arteriovenous shunt and induce hydrops by decreasing peripheral vascular resistance and therefore cardiac afterload.
Eisenmenger syndrome and other types of pulmonary arterial hypertension related to adult congenital heart disease
Published in Expert Review of Cardiovascular Therapy, 2019
Carla Favoccia, Andrew H Constantine, Stephen J Wort, Konstantinos Dimopoulos
Introduction: Eisenmenger syndrome (ES) is the most advanced form of pulmonary arterial hypertension (PAH) in patients with congenital heart disease (CHD). It is characterised by a severe rise in pulmonary vascular resistance resulting in shunt reversal and cyanosis. Areas covered: In this paper, an overview of ES and other types of PAH related to CHD (PAH-CHD) in adults is provided. The modern management of PAH-CHD in tertiary centers is described, with an emphasis on co-morbidities and complications. Expert opinion: PAH-CHD describes a wide spectrum of conditions, of which ES is the archetype. The size and location of the shunt, the degree of adaptation of the right ventricle to the increased afterload and other compensatory mechanisms, such as secondary erythrocytosis, define the clinical presentation and natural history of these patients. PAH therapies have improved the quality of life and outcome of many patients with PAH-CHD, but expert multidisciplinary management remains essential in optimising the care of this rare and complex group of patients.
Combination therapy in pulmonary arterial hypertension: do we have the right strategy?
Published in Expert Review of Respiratory Medicine, 2011
Bhashkar Mukherjee, Luke Howard
The management of pulmonary hypertension has already incorporated the use of multiple therapies into routine practice. Available therapies act principally through vasodilatation of the pulmonary arterial circulation through well-delineated mechanisms, although right ventricular function determines function and prognosis. Therefore, the goal of these therapies is effectively to preserve right ventricular function through reducing right ventricular afterload. The clinical trial experience of combination therapy is limited and the optimal combinations and administration strategies have yet to be clarified.
Cardiac function during resuscitation from hemorrhagic shock with polymerized bovine hemoglobin-based oxygen therapeutic
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2017
Eilleen S. Y. Ao-ieong, Alexander Williams, Vivek Jani, Pedro Cabrales
Hemorrhage impairs myocardial contractile function and decreases oxygen delivery. This study investigates how polymerized bovine hemoglobin (PolyHb) solutions affect cardiac function after resuscitation from hemorrhagic shock (HS). Hamsters were hemorrhaged and resuscitated with PolyHb at 8.5 g/dL and 11.5 g/dL. Left ventricle (LV) function was assessed during shock and resuscitation using a miniaturize conductance catheter. PolyHb resuscitation had no beneficial effects in cardiac function; it increased cardiac afterload and systemic vascular resistance (SVR) of 46 and 116% for 8.5 and 11.5 g/dL, respectively. Study findings indicate that preclinical evaluation of cardiac function is essential to develop safe and efficacious alternatives to blood transfusion.