A look at diastolic blood pressure

When it comes to managing blood pressure, doctors tend to focus on lowering the top (systolic) number, and for good reason: aggressively treating high systolic pressure can help lower the risk of heart attack or stroke.

But what about the bottom (diastolic) number? It also plays an essential role in heart health, although it tends to get overlooked.

Tale of two numbers

The two blood pressure numbers measure the heart at work and at rest. Systolic pressure is the pressure in the arteries when the heart contracts to pump blood throughout the body. The higher the number, the harder the heart works to pump blood.

Diastolic pressure is the pressure during the heart's resting phase between heartbeats. A healthy diastolic pressure is critical for the coronary vessels to adequately supply oxygen to the heart muscle.

According to current guidelines, normal blood pressure is a systolic number less than 120 millimeters of mercury (mm Hg) and a diastolic number less than 80 mm Hg. A systolic number of 120 to 129, with the diastolic measurement less than 80, is considered "elevated" blood pressure.

When it comes to diagnosing high blood pressure (hypertension), either number can be an indicator if persistently elevated. For instance, you're said to have Stage 1 hypertension if your systolic pressure is 130 to 139 or your diastolic pressure is 80 to 89 - or both. Stage 2 hypertension is defined as either 140 or higher for systolic or 90 or higher for diastolic – or both.

In many cases, if one number is high, so is the other, so it's important to monitor both systolic and diastolic pressures.

Exceptions to the rules

However, there are exceptions. While systolic pressure tends to increase with age as blood vessels weaken and narrow, diastolic pressure often declines after age 50.

Why? Arteries become less elastic with age. If they become too stiff, arteries that expand with the systolic push of blood have a harder time springing back between heartbeats, which causes diastolic blood pressure to drop.

Another possible cause of declining diastolic pressure is endothelial dysfunction, a condition where the coronary arteries on the heart's surface constrict instead of opening.

It also is possible to have only a high systolic number, a condition known as isolated systolic hypertension. This is a common type of high blood pressure among older adults. Isolated systolic hypertension happens because less elastic arteries have trouble accommodating surges of blood. Blood flowing at high pressure through these arteries can damage their inner lining, accelerating the buildup of cholesterol-laden plaque. This further stiffens and narrows the arteries, which elevates systolic blood pressure while diastolic pressure remains within a normal range.

Lower but not too low

Is diastolic pressure ever a serious concern? While lower is better for overall blood pressure, you don't want either number to drop too low. A very low systolic blood pressure increases the likelihood for weakness, lightheadedness, and fainting.

For most older adults, the goal should be to keep the systolic blood pressure close to 120 mm Hg, and perhaps a bit lower, as long as the diastolic pressure stays at 60 mm Hg or higher.

Lifestyle changes like reducing dietary sodium, increasing potassium, exercising more, and maintaining a healthy weight are always the cornerstones of treatment, even if you also need medication to control your blood pressure.

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