What’s ventr. pressure?

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Ventricular pressure is the measure of blood pressure in the ventricles of the heart. Measured in Torr, or the gravitational pressure of a 1-millimeter column of mercury at a defined density, the right ventricle can normally register up to 30 Torr. The left ventricle, responsible for pumping blood throughout the body, will normally exert 100-140 Torr during its contraction. At rest, both ventricles will register just 2-3 Torr. When pressure is measured continuously, not just for the ventricles but for all parts of the heart, the graph becomes an astonishingly accurate medical diagnostic tool for heart function.

The anatomy of the human heart consists of four chambers – the left and right atria and ventricles – each contracting or relaxing in a coordinated rhythm. The two atria receive blood, the right ventricle pumps blood to the lungs, and the left ventricle simultaneously pumps blood through the huge blood vessel of the aorta to circulate oxygen and nutrients throughout the body. The term “cardiac cycle” is used to describe the sequential contraction of the chambers, the opening and closing of the one-way valves separating the chambers, as well as the respective incoming or outgoing blood vessels and the resulting flow path and characteristics of the blood fluid.

As the familiar iambic heartbeat increases, several valves closing indicate that the two atria have contracted and their contents have drained into the ventricles. On the beat, about 0.1 second later, a necessarily strong ventricular pressure from their contraction ejects the contents into remote parts of the body. The task would not be possible without the pulsing action of the heart, the propulsive wave created by the alternating pressure changes within the 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 who study the heart have attached sensitive transducers to measure the precise pressure of each of its anatomical parts as they go through a normal cardiac cycle. When plotted, the X-axis measuring the length of a cycle and the Y-axis measuring pressure, it is clear, for example, that ventricular pressure rises rapidly and peaks for blood ejection at systole. It is also apparent that left ventricular pressure is approximately 4.7 times greater than its lateral counterpart, which only needs to pump blood to nearby lungs for respiratory gas exchange. When all the graphs are color-coded and superimposed, the resulting graph is called a Wiggers diagram.

Even a look at the Wiggers diagram is medically diagnostic. The intersections of the ventricular pressure and atrial pressure curves, i.e. when their respective pressures equalize, define the exact point at which the connecting valves open and close. The aortic graph shows a brief drop in pressure when, shortly after the left ventricle contracts, its large valve closes, unable to prevent a small amount of backwashing. Additional overlays on the diagram, such as the electrical signals of an EKG or the rate of change of blood volume in each heart chamber, provide additional diagnostic information.

Given the well-known baselines, discrepancies in the Wiggers diagram are indicators of various heart conditions and diseases. Weakened and regurgitant valves can be identified by “hiccups” in the pressure curves, or a constricted blood vessel will have a large pressure difference with its connected chamber. Unusually high left ventricular diastolic pressure is considered a risk factor when considering cardiac surgery. A LV pressure-volume cycle combining the two respective curves reveals overall cardiac efficiency and circulatory health.

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