Left Ventricular Pressure & Volume Changes (Wigger's Diagram)

A Wigger's diagram shows multiple parameters of cardiac flow and volume simultaneously. We'll focus on the events of the left side of the heart, but know that the right side is similar, but with reduced pressures. We recommend that you review our more detailed tutorials on the ECG and cardiac cycle prior to viewing this tutorial. Systemic venous blood enters the right atrium via the vena cavae openings, and passes through the right atrioventricular valve to the right ventricle (the right AV valve is also called the tricuspid valve). When the right ventricle contracts, blood is pushed past the pulmonary valve, through the pulmonary trunk to the lungs. Oxygenated blood returns to the left atrium via the pulmonary veins, then passes through the mitral valve to the left ventricle. When the left ventricle contracts, blood is pushed past the aortic valve, into the aorta, and is then distributed to the body tissues. Notice that we've presented the pathway as if only one chamber contracts at a time, for simplicity, but, in fact, the atria contract in unison, as do the ventricles. At the top of the graph, show that we'll track events of the left atrium and left ventricle, as follows: The left atrium is in systole from time 0 – 0.1, then enters diastole. The left ventricle is in diastole during atrial systole; at 0.1 seconds, systole begins; at 0.4 seconds, re-entry into diastole begins. Notice that atrial diastole overlaps with ventricular systole and early diastole. X-axis is time in seconds from 0 to 0.8, which is the duration of a typical healthy cardiac cycle. Y-axis: Five Key Parameters of the Cardiac Cycle: 1. ECG, which reflects the electrical events of the heart. 2. Changes in Ventricular Volume from 65-130 millimeters. 3. Heart Sounds, as recorded by a phonocardiograph, which reflect closure of the valves. 4. Pressure changes from 0-120 millimeters of mercury; we'll trace aortic, ventricular, and atrial pressures. 5. Mechanical Events of the left ventricle. Our ECG starts approximately halfway through the P wave, which reflects depolarization of the atria. The QRS complex peaks at 0.1 seconds. Recall that this large wave reflects ventricular depolarization, so it corresponds with entry into ventricular systole. The T wave lasts from approximately 0.3-0.4 seconds. It reflects ventricular repolarization, so it corresponds with entry into ventricular diastole. The next P wave, which initiates the next cardiac cycle, occurs at ~ 0.8 seconds. Three phases of ventricular systole: isovolumetric contraction, rapid ejection, reduced ejection. Three phases of ventricular diastole: isovolumetric relaxation, rapid filling, reduced filling (aka, diastasis). Recall that "isovolumetric" refers to events that change ventricular muscle tension without changing blood volume (details regarding the mechanical events of the cardiac cycle are discussed elsewhere). Relatively steady at approximately 75-80 mmHg until the end of ventricular isovolumetric contraction, when the aortic valve is pushed open and blood enters the aorta. Rises to ~120 mmHg, then falls. Changes in aortic pressure mirror that of left ventricular pressure throughout ventricular systole. At the end of systolic contraction, ventricular pressure falls, and the aortic valve closes. Immediately after valve closure, aortic pressure dips, reflected by the dicrotic notch (aka, incisura), then briefly rises. The positive pressure wave reflects the sudden backward movement of blood against the closed aortic valve. For the remainder of ventricular diastole, aortic pressure slowly declines to approximately 80 mmHg. Can be measured via catheterization. During the final period of diastole, forceful atria contraction pushes blood into the left ventricle, raising its pressure slightly. The "atrial kick" moves only a small amount of blood into the ventricle, but serves as a priming mechanism to increase ventricular preload prior to ejection. The mitral valve (aka, left atrioventricular valve) is forced closed by high ventricular pressure. Consequently, pressure in the left ventricle mounts as isovolumetric contraction produces muscular tension against a fixed blood volume. When ventricular pressure reaches approximately 75-80 mmHg, it surpasses aortic pressure. The aortic valve is forced open, and blood is rapidly ejected from the ventricle. Ventricular pressure peaks at approximately 120 mmHg, then begins to fall during the reduced ejection phase; notice that this corresponds with the T wave and ventricular repolarization. Due to blood ejection, left ventricular pressure eventually falls below aortic pressure. This allows closure of the aortic valve (there is a slight delay due to the momentum of ejected blood). Because both the aortic and mitral valves are closed, isovolumetric relaxation occurs: there is a drastic reduction of pressure, but no change in blood volume, yet. Ultimately, ventricular pressure falls below atrial pressure, and the mitral valve opens and allows passive ventricular filling to begin during diastole. Recall that 90% of ventricular filling occurs during this passive period; only the last 10% is added by the "atrial kick" during atrial systole. During the final period of ventricular diastole, volume rises slightly as the atrium contracts and forces the last bit of blood into the ventricle. Ventricular filling ends when the mitral valve closes, and volume plateaus at approximately 120-130 mL. This is End diastolic volume, EDV. When the aortic valve opens, contraction and ejection reduces ventricular blood volume to 60-70 mL. This is End systolic volume, ESV. Stroke volume is the volume of blood ejected during systole. It's approximately 70 mL. During the isovolumetric relaxation phase of diastole, ventricular volume remains low because the closed mitral valve prohibits passive filling. When the mitral valve opens and filling begins, volume increases rapidly at first, then less rapidly, as the pressure gradient between the atria and ventricle falls. It its often measured indirectly by use of a Swan-Ganz catheter to obtain the pulmonary capillary wedge pressure (direct methods have also been proposed). Corresponds to cardiac events and venous return. a wave: produced by atrial contraction. c wave: produced during isovolumetric ventricular contraction, when rising ventricular pressure pushes the mitral valve into the left atrium. v wave: produced when atrial pressure peaks during ventricular systole due to venous return from the pulmonary circulation. Appear on a phonocardiograph. S1: The first heart sound ("lub") is produced when the mitral and tricuspid valves close at the beginning of ventricular systole. The mitral valve closes slightly before the tricuspid valve. S1 is best heard at heart apex. S2: The second heart sound ("dub") is produced when the aortic and pulmonary valves close at the end of ventricular systole. S2 is best heard at the left sternal edge. Audible physiological splitting of S2 occurs because the aortic valve closes before the pulmonary valve (the left ventricle contracts slightly before the right ventricle). Splitting is most apparent at end-inspiration, because increased venous filling causes a delay in pulmonary valve closure (sounds like "lub d/dub" at inspiration). S3: The third heart sound can be heard in children during rapid ventricular filling. It may also be present some very fit adults, but, in unhealthy adults, may signify volume overload and congestive heart failure. S4: The fourth heart sound may be heard during the aortic "kick" in individuals with noncompliant left ventricles. This is heard in aortic stenosis, systemic hypertension, hypertrophic cardiomyopathy, and ischemia. If present, it is loudest at the heart apex. Valve Stenosis & Regurgitation alter these heart sounds.