Blood pressure readings have a top number and a bottom number. The top number is the systolic blood pressure. It indicates the pressure placed on the artery walls with every heartbeat. Systolic blood pressure gets a lot of attention, but the bottom number — diastolic pressure — is important, too. Diastolic blood pressure is the pressure placed on the artery walls when the heart is resting between every heartbeat.
Medical practitioners obtain diastolic pressure readings by listening to Korotkoff sounds using a sphygmomanometer and a stethoscope. A sphygmomanometer is an inflatable cuff with a gauge. The practitioner inflates the cuff to block arterial blood flow, then listens to the brachial artery while allowing the cuff to deflate slowly. Systolic blood pressure is read at the point on the gauge where tapping sounds called Korotkoff sounds begin. Diastolic pressure is read at the point on the gauge where these sounds stop.
Pulse pressure is the difference between systolic and diastolic pressure. Sometimes, wide or narrow pulse pressure is a sign of an underlying condition, but not always. For example, a well-conditioned athlete has elevated systolic pressure as the cardiac output increases during exercise, while the diastolic pressure decreases due to a change in peripheral resistance.
A wide or narrow pulse pressure can also indicate the presence of several diseases and shows the close link between systolic and diastolic blood pressure. A widened pulse pressure can indicate heart valve conditions, anemia, hyperthyroidism, or aortic regurgitation. A narrow or smaller pulse pressure can mean heart failure, significant blood loss, or cardiac tamponade, which is when fluid builds around the heart, preventing it from filling.
Normal diastolic pressure is 80 mm Hg. Physicians usually use systolic blood pressure to determine hypertension, but diastolic pressure also plays a role. Stage 1 hypertension is a diastolic pressure of 80 to 89, while Stage 2 is a diastolic pressure of 90 or higher. A diastolic pressure higher than 120 can indicate a hypertensive crisis.
High diastolic pressure or hypertension typically happens in conjunction with systolic hypertension. Many things can cause high blood pressure. These include factors that cannot be controlled, like age, sex, race, and genetics. Other factors that cause high blood pressure are manageable, including diabetes, an unhealthy diet or a diet high in salt, a sedentary lifestyle, obesity, smoking, and excessive alcohol use.
The best way to prevent or manage high systolic and diastolic pressure is to make healthy lifestyle choices. Eating a healthy diet, limiting alcohol and salt intake, and maintaining a healthy weight are all helpful in managing hypertension. Getting at least 150 minutes of exercise every week also benefits heart health and can help lower elevated blood pressure.
Diastolic hypotension or low diastolic pressure is typically caused by severe hypotension or stiff arteries. Many factors can contribute to low blood pressure, including bradycardia, heart failure, and heart valve problems. Other conditions can cause hypotension, too, such as an over or underactive thyroid, adrenal insufficiency, dehydration, and hypoglycemia. Very stiff arteries can also cause low diastolic pressure, which can happen because of diabetes, vascular disease, or as a side effect of normal aging.
When treating systolic hypertension, there is a risk that diastolic pressure can be too low. At a certain point, low diastolic pressure can cause damage. One study measuring troponin, a protein that increases in the blood when the heart is damaged, indicated that people with a diastolic pressure below 60 were twice as likely to have heart damage as those with a diastolic pressure of 80 to 89.
Some patients may require modifications to their anti-hypertensive medication to prevent diastolic hypotension from treatment for hypertension. Driving the systolic pressure down or overtreating high blood pressure at the expense of lowering the diastolic pressure too much is something to consider as studies suggest this can cause further heart damage.
Although diastolic pressure is occasionally considered in isolation, it is important to remember that systolic and diastolic pressures are closely linked. This idea is apparent when assessing for overall hypertension, but this is also why changes in pulse pressure are used to show dissonance between the two. When considered in conjunction, systolic and diastolic pressure reveal a lot about heart health.
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