Pulse Pressure is most easily defined as being the amount of pressure required to create the feeling of a pulse. Measured in millimeters of mercury (mmHg), the pressure difference between the systolic and diastolic pressures give you the amount of pressure change to create the pulse, which is the pulse pressure. If your resting blood pressure is (systolic/diastolic) 120/80 millimeters of mercury (mmHg), your pulse pressure is 40 — which is considered a normal and healthy pulse pressure
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 dampening 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.
- Systemic pulse pressure = Psystolic - Pdiastolic = 120mmHg - 80mmHg = 40mmHg
- Pulmonary pulse pressure = Psystolic - Pdiastolic = 25mmHg - 10mmHg = 15mmHg
Low (Narrow) Pulse Pressure
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.