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.
Heart Valve Dynamics
Joseph D. Bronzino, Donald R. Peterson in Biomedical Engineering Fundamentals, 2006
The heart has four valves that control the direction of blood flow through the heart, permitting forward flow and preventing back flow. On the right side of the heart, the tricuspid and pulmonic valves regulate the flow of blood that is returned from the body to the lungs for oxygenation. The mitral and aortic valves control the flow of oxygenated blood from the left side of the heart to the body. The aortic and pulmonic valves allow blood to be pumped from the ventricles into arteries on the left and right side of the heart, respectively. Similarly, the mitral and tricuspid valves lie between the atria and ventricles of the left and right sides of the heart, respectively. The aortic and pulmonic valves open during systole when the ventricles are contracting, and close during diastole when the ventricles are filling through the open mitral and tricuspid valves. During isovolumic contraction and relaxation, all four valves are closed (Figure 55.1).
The aortic valve
Andrew R Houghton in Making Sense of Echocardiography, 2009
The parasternal long axis view (Fig. 6.2, p. 56) bisects the aortic valve, showing the right coronary cusp anterior to the non-coronary cusp. 2-D imaging shows the structure of the aortic valve and allows an assessment of cusp mobility. An M-mode study of the valve, at the level of the cusp tips, shows the cusps opening at the start of systole (Fig. 13.1). The aortic root as a whole moves anteriorly during systole, being pushed forwards by the expanding left atrium (LA) as it fills during diastole. Conditions that enhance LA filling, such as mitral regurgitation, exaggerate this anterior motion of the aortic root. The aortic valve cusps close at the end of systole to make a single thin closure line. This M-mode pattern of normal aortic valve cusp motion is described as ‘box-shaped’. While in this view, use colour Doppler to assess valvular flow.
Normal Left Ventricular Wall Motion Measured with Two-Dimensional Myocardial Tagging
Published in Acta Radiologica, 1993
P. Qi, Carsten Thomsen, F. Ståhlberg, O. Henriksen
Using a myocardial tagging technique, normal left ventricular wall motion was studied in 3 true short axis views and a double oblique 4-chamber view in 14 and 11 volunteers, respectively. Three orthogonal directions of left ventricular motion were observed throughout the systole; a concentric contraction towards the center of the left ventricle, a motion of the base of the heart towards the apex, and a rotation of the left ventricle around its long axis. the direction of left ventricular rotation changed from early systole to late systole. the base and middle levels of the left ventricle rotated counterclockwise (CCW) at early systole and clockwise (CW) at late systole, whereas the apex of the heart rotated CW at early systole and CCW at late systole. the different directions of the rotation of base and apex resulted in a myocardial twisting that changed direction from early to late systole. We conclude that MR imaging with myocardial tagging is a method that can be used to study normal left ventricular wall motion, and that is promising for future use in patient groups.
Orthogonal Factors of Cardiac Intervals and Their Response to Stress
Published in Research Quarterly. American Association for Health, Physical Education and Recreation, 1968
Left ventricular intervals were determined on 61 middle-aged men in basal condition, during and after mental concentration and after submaximal exercise. Four orthogonal factors were determined from a factor analysis, using varimax rotation. The tests with the highest loadings for the four factors were mechanical systole, diastole, isovolumetric contraction period, and electromechanical lag. The effects of mental arithmetic and a submaximal ergometer ride on these intervals were determined by an analysis of variance and Duncan's multiple range. The mental arithmetic caused significant reductions in diastole (23 standard scores), mechanical systole (17 SS), electromechanical lag (11 SS), and isovolumetric contraction period (4 SS). Exercise caused significant reductions in mechanical systole (46 SS), isovolumetric contraction period (33 SS), diastole (20 SS), and electromechanical lag (8 SS).
Heart synchronized gamma — camera gating: Displaying two heart cycles on one screen
Published in Journal of Medical Engineering & Technology, 1979
N. G. Holmer, J. Lessem, K. Lindström
A method for the evaluation of the haemodynamic status of a patient with acute myocardial infarction is presented. Left ventricular ejection fraction has been considered to be an accurate indicator of haemodynamic status before and after therapy. A device for synchronising the R-wave, and controlling the recording oscilloscope during systole and diastole is described. The intention is to display both systole and diastole on one oscilloscope.