What is pulse pressure and why are people talking about it?

Pulse pressure refers to the difference between the systolic (top) and diastolic (bottom) blood pressure. If your blood pressure (BP) is 120/80, for instance, your pulse pressure is 120 - 80 = 40 mmHg. A pulse pressure of 40 mmHg is normal.  

Why does this matter? Does it add important information beyond knowing just your systolic and diastolic values?

Before we answer this question, let's consider what the two basic values mean in the first place.

Think of a piston that cyclically forces water into a pipe: It pushes forward, then rests; pushes forward, then rests. The pressure within the pipe when the piston pushes forward is systolic pressure; the pressure in the pipe when the piston is resting is the diastolic pressure.

As in the make-believe pipe, systolic blood pressure in the body is the pressure felt in the arteries (pipe) while the heart is contracting (like a pumping piston) and pushing blood rapidly forward. The heart squeezes most of its contents out, then relaxes. The pressure remaining after relaxation of the heart is the diastolic pressure.

As we age, systolic blood pressure (at least in Western societies) increases. Starting in our 20s and 30s, systolic pressure climbs higher and higher as we get older. Systolic pressure increases primarily due to increasing stiffness of the large arteries of the body, especially the aorta (the large artery that first receives the blood ejected by the heart) and its large tributaries. Increased blood volume within this enclosed space can also increase systolic pressure.

Diastolic pressure behaves differently. Up until age 50 or so, diastolic pressure increases in parallel with systolic pressure. After age 50, however, diastolic and systolic pressures part ways, and diastolic pressure trends downward while systolic pressure continues its climb upward. This occurs because the small, "downstream" vessels in muscles and organs become stiff, slowing "runoff" of blood into all the small blood vessel tributaries. There are also complex effects, such as "reflected waves" of pressure that can contribute to dropping diastolic pressure and increasing pulse pressure of aging. Because pulse pressure is the difference between the two values, pulse pressure increases as systolic and diastolic pressures diverge. Thus, BP of 120/80 at age 25 yields a pulse pressure of 40 mmHg, while a BP of 160/65 at age 75 yields a pulse pressure of 95 mmHg.

There are also unusual causes for a widened pulse pressure, such as a leaky aortic valve (aortic valve "insufficiency"), arteriovenous malformations (hidden connections between arteries and veins), and thyroid disease, issues best considered by your doctor.

Both systolic and diastolic hypertension have been associated with increased risk for stroke and heart attack, with risk beginning as low as a systolic pressure of 115 mmHg, diastolic pressure of 75 mmHg. Cardiovascular risk increases as either or both pressures increase, though systolic pressure is probably a better predictor than diastolic.