Pulse pressure

Pulse pressure is the difference between the systolic and diastolic pressure readings. It is measured in millimeters of mercury (mmHg). It represents the force that the heart generates each time it contracts. If resting blood pressure is (systolic-diastolic) 120-80 millimeters of mercury (mmHg), pulse pressure is 40.

Formally it is the systolic pressure minus the diastolic pressure.

Theoretically, the systemic pulse pressure can be conceptualized as being proportional to stroke volume, or the amount of blood ejected from the left ventricle during systole and inversely proportional to the compliance of the aorta.

The aorta has the highest compliance in the arterial system due in part to a relatively greater proportion of elastin fibers versus smooth muscle and collagen. This serves the important function of damping the pulsatile output of the left ventricle, thereby reducing the pulse pressure. If the aorta becomes rigid in conditions such as arteriosclerosis or atherosclerosis, the pulse pressure would be very high.

A pulse pressure is considered abnormally low if it is less than 25% of the systolic value. The most common cause of a low (narrow) pulse pressure is a drop in left ventricular stroke volume. In trauma a low or narrow pulse pressure suggests significant blood loss (insufficient preload leading to reduced cardiac output).

If the pulse pressure is extremely low, i.e. 25 mmHg or less, the cause may be low stroke volume, as in Congestive Heart Failure and/or shock.

A narrow pulse pressure is also caused by aortic valve stenosis and cardiac tamponade.

Usually, the resting pulse pressure in healthy adults, sitting position, is about 30–40 mmHg. The pulse pressure increases with exercise due to increased stroke volume, healthy values being up to pulse pressures of about 100 mmHg, simultaneously as total peripheral resistance drops during exercise. In healthy individuals the pulse pressure will typically return to normal within about 10 minutes.

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