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Ventricular pressure is the measure of blood pressure in the ventricles of the heart. Measured in Torr, or the gravitic pressure of a 1 millimeter column of mercury at a defined density, the right ventricle can normally register as much as 30 Torr. The left ventricle, responsible for pumping blood out to the entire body, will normally exert 100-140 Torr during its contraction. At rest, both ventricles will register hardly 2-3 Torr. When pressure is continuously measured, not just for the ventricles but for all of the heart’s parts, the graph becomes a medical diagnostic tool of surprisingly high fidelity for cardiac functioning.
The anatomy of the human heart consists of four chambers — left and right atriums and ventricles — each contracting or relaxing in coordinated rhythm. The two atria receive blood, the right ventricle pumps blood out to the lungs, and the left ventricle simultaneously pumps blood out through the massive aorta blood vessel to circulate oxygen and nutrients to the entire body. The term "cardiac cycle" is used to describe the sequential contraction of the chambers, the opening and closing of the one-way valves that separate the chambers as well as their respective incoming or outgoing blood vessels and the resulting flow path and fluid characteristics of the blood.
On the uptick of the familiar iambic heartbeat, several valves popping shut indicate that the two atria have contracted and their contents have flowed into the ventricles. On the downbeat, about 0.1 seconds later, necessarily strong ventricular pressure from their contraction ejects the contents to remote parts of the body. The task would not be possible without the heart’s pulsing action — the propelling wave created by alternating pressure changes within blood vessels from the heart’s systolic contraction and diastolic relaxation. The same principle of pressure changes within the heart’s four chambers and connecting vessels automatically drives the well-synchronized cardiac cycle itself.
Over the years, cardiologists studying the heart have attached sensitive transducers to measure the precise pressure of each of its anatomical parts undergoing a normal cardiac cycle. When plotted, the X-axis measuring the duration of a cycle and the Y-axis measuring pressure, it is clear to see, for example, that ventricular pressure quickly climbs and peaks for blood ejection at systole. Also evident is that the left ventricular pressure is about 4.7 times greater than its lateral counterpart, which needs only to pump blood to the nearby lungs for respiratory gas exchange. When all of the graphs are color-coded and overlaid, the resulting chart is called a Wiggers diagram.
Even a glance of the Wiggers diagram is medically diagnostic. The intersections of ventricular pressure and atrial pressure curves — that is, when their respective pressures equalize — define the exact point when their connecting valves open and close. The aortic graph shows a brief dip in pressure when, shortly following the left ventricle’s contraction, its large valve closes, unable to prevent a small amount of backwash. Additional overlays to the diagram, such as the electrical signals from an electrocardiogram or rate of change in each heart chamber’s blood volume, yield further diagnostic information.
Given the well-known baselines, discrepancies in the Wiggers diagram are indicators of various heart conditions and illnesses. Weakened and regurgitating valves can be identified by “hiccups” in the pressure curves, or a constricted blood vessel will have an elevated pressure difference with its connected chamber. Unusually high diastolic pressure of the left ventricle is considered a risk factor when considering cardiac surgery. A left ventricular pressure-volume loop that combines the two respective curves reveals overall cardiac efficiency and circulatory health.