Try free for 5 days Evidence-based content, created and peer-reviewed by physicians. Read the disclaimer. Cardiac physiology.
Summary The heart pumps blood through the circulatory system and supplies the body with blood. Overview The main function of the heart is to maintain blood circulation and ensure blood supply to the body through its continuous pumping action. Measurement Via Fick principle Cardiac output is proportional to the quotient of the total body oxygen consumption and the difference in oxygen content of arterial blood and mixed venous blood. The increased HR shortens the filling time diastole , which limits the increase in SV.
During exercise, a healthy young adult can increase their CO by a factor of approx. Systole 1. Isovolumetric contraction Main function: ventricular contraction Follows ventricular filling Occurs in early systole , directly after the atrioventricular valves AV valves close and before the semilunar valves open all valves are closed Ventricle contracts i. Systolic ejection Main function: Blood is pumped from the ventricles into the circulation and lungs. Follows isovolumetric contraction Occurs between the opening and closing of the aortic valve and pulmonary valve Ventricles contract i.
Isovolumetric relaxation Main function: ventricular relaxation Follows systolic ejection Occurs between aortic valve closing and mitral valve opening All valves closed volume remains constant Dicrotic notch : slight increase of aortic pressure in the early diastole that corresponds to closure of the aortic valve The ventricles relax i. The coronary arteries fill with blood during diastole because they are compressed during ventricular systole.
Ventricular filling Main function: ventricles fill with blood Rapid filling Follows isovolumetric relaxation Occurs in early diastole ; immediately after mitral valve opening Blood flows passively from the atria to the ventricles.
The largest volume of ventricular filling occurs during this phase. Features of valvular diseases Overview Valvular disease Pressure-volume loop Time-pressure curves Mitral regurgitation Rounder and flatter pressure-volume loop than normal. Overview of the conduction system of the heart Name Anatomic localization Characteristics Frequency Sinoatrial node Upper wall of the right atrium at the junction where the SVC enters Natural pacemaker center of the heart with specialized pacemaker cells Spontaneously generates electrical impulses that initiate a heartbeat Influenced by autonomic nervous system Supplied by sinus node artery branch of the right coronary artery ca.
Form functional syncytium : forward incoming stimuli very quickly via gap junctions to allow coordinated contraction ca. TMP is maintained at a plateau just below 0 mV. Assessment of right ventricular volumes and ejection fraction by echocardiography: from geometric approximations to realistic shapes..
Echo research and practice. Reference right ventricular systolic and diastolic function normalized to age, gender and body surface area from steady-state free precession cardiovascular magnetic resonance..
Eur Heart J. Open in Read by QxMD. Rounder and flatter pressure-volume loop than normal. Tall V-wave. The pressure-volume loop is narrower and flatter than the normal pressure-volume loop. The pressure-volume loop is rounder and taller than the normal pressure-volume loop. The pressure-volume loop is narrower and taller than the normal pressure-volume loop. Upper wall of the right atrium at the junction where the SVC enters.
Natural pacemaker center of the heart with specialized pacemaker cells Spontaneously generates electrical impulses that initiate a heartbeat Influenced by autonomic nervous system Supplied by sinus node artery branch of the right coronary artery. Within the AV septum superior and medial to the opening of the coronary sinus in the right atrium.
Receives impulses from the SA node and passes these impulses to the bundle of His Has the slowest conduction velocity Delays conduction for 60— ms allowing the ventricles to fill with blood; without this delay, the atria and ventricles would contract at the same time Supplied by the AV nodal artery posterior descending artery of right coronary artery. Directly below the cardiac skeleton , within the membranous part of the interventricular septum.
Conduct cardiac AP faster than any other cardiac cells Ensure synchronized contraction of the ventricles Purkinje fibers have a long refractory period. Form functional syncytium : forward incoming stimuli very quickly via gap junctions to allow coordinated contraction.
Cell membrane of cardiomyocytes. Plateau phase myocardium Upstroke phase SA node. A voltage-gated calcium channel that is opened by low-voltage depolarization potentials. Cell membrane of cardiac pacemaker cells. During the middle of phase 4 in pacemaker cells SA node.
Membrane of SR. Plateau phase myocardium. Nonselective cation channels e. Upstroke phase sinus node. Depolarization myocardium. Resting potential primarily myocardium ; sinus node. Repolarization sinus node and myocardium. Atria and ventricles. Fibers from the sympathetic cervical trunk superior, middle, and inferior cardiac nerve.
Ideally, ejection fraction should be assessed during normal, with regards to the patient, loading conditions. If repeated echocardiograms yield pronounced variations in ejection fraction, then it is likely that variations in preload and afterload, rather than changes in contractile function, explains the varying ejection fraction.
Ejection fraction is also affected by left ventricular volume size. For example, athletes have large ventricular dimensions and often lower ejection fraction, as compared with non-athletes. In general, individuals with small ventricular volumes tend to have high ejection fractions.
This inverse relationship appears to be a compensatory mechanism, such that small ventricular volumes are compensated with greater ejection fractions. Individuals with hypertrophic cardiomyopathy may display normal, or supranormal ejection fraction , despite manifest heart failure and severe symptoms.
These individuals exhibit pronounced hypertrophy, resulting in a reduction of ventricular volume and subsequently an increase in ejection fraction. Stroke volumes are generally reduced in hypertrophic cardiomyopathy. Numerous conditions can lead to reduced ejection fraction. Cardiomyopathy , valvular heart disease, diabetes, hypertension , renal failure, ischemic heart disease coronary heart disease are among the common causes.
The mechanisms leading to deterioration in ejection fraction vary for these conditions. Two examples follow. This results in ventricular volume overload, which the ventricle attempts to counteract by dilating and developing hypertrophy. The dilatation prevents the volume overload from causing pressure overload, and the development of hypertrophy enables the ventricle to eject larger volumes of blood.
Thus, dilatation and hypertrophy mitigate the consequences of volume overload. Unfortunately, the long-term effects of dilatation and hypertrophy are remodeling of the myocardium and neurohormonal disturbances that gradually impair contractility and lead to the development of myocardial fibrosis.
Ultimately, contractility of individual muscle fibers worsen and ejection fraction deteriorates. As evident from these examples, the mechanisms leading to reduced ejection fraction may vary substantially.
However, once ejection fraction has been reduced, the natural course is strikingly similar across all etiologies. Impaired ejection fraction triggers neurohormonal mechanisms see below that are initially beneficial, but in the long run cause deterioration of the condition. Symptoms of heart failure eg, dyspnea, impaired performance, edema, etc. Reduced ejection fraction leads to reduced cardiac output.
High-pressure baroceptors in the left ventricle, aortic arch, and carotid sinus detect reductions in cardiac output and respond by increasing their afferent signaling to vasomotorcenter in the central nervous system CNS. Activation of the vasomotorcenter results in increased activity in efferent sympathetic pathways that innervate the heart, skeletal muscle, kidney and peripheral vasculature.
Activation of the vasomotorcenter also lead to increased secretion of vasopressin from the posterior pituitary gland Figure 2. As evident in Figure 2, a range of neurohormonal mechanisms is triggered when ejection fraction is reduced. These mechanisms and their consequences include:. Ejection fraction can be estimated visually. This means that the ejection fraction is estimated by means of eyeballing the two-dimensional video clips.
This method is obviously subjective and requires a substantial amount of experience. However, studies Gudmundsson et al indicate that eyeballed ejection fraction correlates well with quantitative assessments of ejection fraction.
Objective estimation of ejection fraction requires measurements in M-mode or two-dimensional 2D echocardiography. Measurements in M-mode are based on two brave assumptions: 1 ventricular geometry must be perfectly normal and 2 there must not be regional differences in contractile function. These assumptions are frequently violated, such that M-mode is inferior to 2D echocardiography.
Thus, 2D methods are preferred for the calculation of ejection fraction. This method is less dependent on the geometry of the ventricle, as compared with M-mode. The entire endocardium, from mitral annulus to mitral annulus must be traced Figure 3.
The ultrasound system then divides the area into a number of equal disks and reconstructs these so that volumes can be calculated. The term biplane means that the measurements are made in two planes, namely A4C and A2C. As mentioned above, the formula used to calculate ejection fraction is as follows:. When visualizing the left ventricle from apical windows, small angle errors may lead to large differences in ventricular dimensions.
Actually, all angle errors lead to underestimation of ventricular volumes. This is evident in Figure 4, which illustrates how angle errors lead to foreshortening. Hartupee et al : Neurohormonal activation in heart failure with reduced ejection fraction. Nature Reviews Cardiology No products in the cart.
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Hemodynamic principles and calculations.
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