Diastole vs. Systole: A Guide to Blood Pressure
When you visit your doctor, the first thing they often do is check your blood pressure. This is an important step because your blood pressure is a measure of how hard your heart’s working.
Your heart is a muscle about the size of your fist. It’s made up of four chambers and contains four valves. The valves open and close to let blood move through the chambers and into and out of your heart. According to the American Heart Association, your heart beats 60 to 100 times per minute or about 100,000 times per day. As it beats, blood is forced against your artery walls.
Your systolic blood pressure is the top number on your reading. It measures the force of blood against your artery walls while your ventricles — the lower two chambers of your heart — squeeze, pushing blood out to the rest of your body.
Your diastolic blood pressure is the bottom number on your reading. It measures the force of blood against your artery walls as your heart relaxes and the ventricles are allowed to refill with blood. Diastole — this period of time when your heart relaxes between beats — is also the time that your coronary artery is able to supply blood to your heart.
Blood pressure ranges
Your blood pressure may be normal, high, or low. High blood pressure is also referred to as hypertension, and low blood pressure is called hypotension. The American Heart Association describes the different blood pressure ranges for adults as:
- Normal: less than 120 systolic and 80 diastolic
- Elevated: 120–129 systolic and less than 80 diastolic
- Stage 1 hypertension: 130–139 systolic or 80–89 diastolic
- Stage 2 hypertension: at least 140 systolic or at least 90 diastolic
- Hypertensive crisis: higher than 180 systolic and/or higher than 120 diastolic
- Hypotension: can be 90 or less systolic, or 60 or less diastolic, but these numbers can vary because symptoms help determine when blood pressure is too low
Your doctor may diagnose high blood pressure if either your systolic or diastolic is high, or if both numbers are high. They may diagnose low blood pressure by checking systolic and diastolic numbers, along with evaluating your symptoms and age, and what medications you’re taking.
High and low blood pressure risk factors
Both high blood pressure and low blood pressure need to be managed. Overall, it’s much more common to have high blood pressure. According to the American College of Cardiology, almost half of the adults in the United States now fit the new definition of high blood pressure. Not surprisingly, the risk factors for these two conditions are very different.
Risk factors for high blood pressure
Your gender affects your risk of high blood pressure. The American Heart Association states that men are at a higher risk of high blood pressure than women are until age 64. But at 65 years and older, women are at higher risk than men. Your risk is also higher if:
- you have a close relative with high blood pressure
- you’re African-American
- you’re overweight or obese
- you have diabetes
- you have high cholesterol
- you have kidney disease
Your lifestyle also affects your risk level. Your risk is higher if:
- you don’t get much physical activity
- you experience chronic stress
- you drink too much alcohol
- you smoke
- your diet is high in salt, sugar, and fat
Sleep apnea is a risk factor for high blood pressure that’s often overlooked. It’s a condition that causes you to stop breathing or have ineffective breathing one or more times during sleep.
When your breathing is inadequate, your oxygen levels fall and your blood vessels constrict. This increases your blood pressure. When sleep apnea is persistent, this increased blood pressure may continue during the day when breathing is normal. Properly treating sleep apnea will help lower blood pressure.
Risk factors for low blood pressure
If you’re older than 65, you may be at risk of orthostatic hypotension, a condition in which your blood pressure drops when you move from sitting to standing. Endocrine problems, neurological diseases, heart problems, heart failure, and anemia may also cause the condition.
You may also be at risk for low blood pressure if you become dehydrated or take certain prescription drugs such as:
- high blood pressure medications
- anxiety or depression medications
- erectile dysfunction medications
Low blood pressure can also be caused by a variety of heart, hormonal, or nervous system problems. These include:
- thyroid problems
- abnormal heart rhythms
- abnormal heart valves
- postural orthostatic tachycardia syndrome (POTS)
- spinal cord injury
- multiple sclerosis (MS)
- Parkinson’s disease
Treating high or low blood pressure
A range of treatments is available for high or low blood pressure.
Treating high blood pressure
Lifestyle changes are recommended as the first step in treating any stage of high blood pressure. These changes may include:
- eliminating unhealthy foods, such as excess sugars and saturated fats, from your diet
- eating more heart-healthy foods such as lean meats, fish, fruits and vegetables, and whole grains
- cutting back on sodium in your diet
- drinking more water
- getting daily physical activity
- quitting smoking
- maintaining a healthy weight
- reducing alcohol consumption (to one or fewer drinks per day for women, and two or fewer per day for men)
- managing stress
- monitoring your blood pressure regularly
In addition to these steps, consider whether you’re taking medications that could be increasing your blood pressure, such as cold medicines, diet pills, or medications for attention deficit hyperactivity disorder (ADHD). If you are, your doctor might recommend stopping that drug, changing medications, or adjusting your dosage.
However, lifestyle changes and medication adjustments may not be enough to bring your blood pressure numbers down. If that’s the case, or if you have stage 2 hypertension or have experienced hypertensive crisis, your doctor will likely prescribe one or more blood pressure medications.
Commonly prescribed medications include:
- calcium channel blockers
- angiotensin-converting enzyme (ACE) inhibitors
- angiotensin II receptor blockers (ARBs)
This medication will be prescribed in addition to continued lifestyle changes.
Treating low blood pressure
Treatment for low blood pressure depends on the cause of the condition.
If a medication is causing your low blood pressure, your doctor may change your dosage of that drug or stop your treatment with it.
If your low blood pressure is caused by an infection, your doctor might prescribe an antibiotic to treat the infection. Or if it’s caused by anemia, your doctor may prescribe iron or vitamin B-12 as a supplement.
If a medical condition or disease is causing your low blood pressure, it’s important for your doctor to identify the specific cause. Proper management of the problem can help improve or limit episodes of low blood pressure.
High or low blood pressure complications
High blood pressure doesn’t cause symptoms unless you’re in hypertensive crisis. It’s actually known as a “silent killer” because it quietly damages your blood vessels and organs, and you may not realize you have it until the damage is done. Unmanaged high blood pressure can lead to:
- heart failure
- heart attack
- vision problems
- vision loss
- kidney disease
- sexual dysfunction
On the other hand, blood pressure that’s too low will cause symptoms. Symptoms or complications that may occur from low blood pressure can include:
- chest pain
- loss of balance
- inability to concentrate
- blurred vision
- shallow breathing
- shortness of breath
- clammy skin
- bluish-tinged skin
Preventing blood pressure problems
The good news is that there are things you can do to help prevent blood pressure problems.
Preventing high blood pressure
You may head off blood pressure problems before they start, or limit your risk if you follow a healthy lifestyle. Following the steps listed above under “Treating high or low blood pressure” can help protect you from developing high blood pressure.
In addition, if you suspect you have sleep apnea symptoms, such as heavy snoring, daytime sleepiness, or restless sleep, talk to your doctor about a sleep study. Sleep apnea is believed to affect at least 25 million American adults. Research has shown that using a CPAP machine while sleeping can reduce blood pressure in people with sleep apnea.
Preventing low blood pressure
To help prevent low blood pressure, drink plenty of fluids, preferably water, to prevent dehydration. Stand up slowly from a sitting position to help prevent orthostatic hypotension.
Also, notify your doctor right away if you feel a medication is causing your blood pressure to drop. There may be another medication option that will have less impact on your blood pressure numbers.
In addition, if you’ve been diagnosed with any medical conditions known to be linked with low blood pressure, talk to your doctor. Discuss which symptoms you should look out for and how to best monitor your condition.
For many people, high or low blood pressure is manageable. For high blood pressure, your outlook is best if you take lifestyle steps that support overall heart health and follow your doctor’s recommendations about medications to manage your blood pressure. For low blood pressure, it’s important to identify the cause and follow through with any recommended treatment plans.
Because high blood pressure doesn’t cause symptoms, once you’ve been diagnosed with it, it’s critical to measure your blood pressure regularly. This is true even if you’re taking blood pressure medication. And whether you’ve got high or low blood pressure, tracking your systolic and diastolic numbers is a great way to gauge how well lifestyle changes or medications are working.