What should bottom blood pressure number be

Ask the doctor

A. This question comes up often, perhaps because doctors and patients alike tend to pay more attention to the top (first) number, known as systolic pressure. It reflects the amount of pressure inside the arteries as the heart contracts. The bottom (second) number, diastolic pressure, is always lower since it reflects the pressure inside the arteries during the resting phase between heartbeats.

As it turns out, both systolic and diastolic blood pressure are important. Per the most recent guidelines, you have what's called elevated blood pressure if your systolic blood pressure reading is 120 to 129 mm Hg (which stands for millimeters of mercury). Once your systolic reading reaches 130 or higher or your diastolic reading is 80 or higher, you're considered to have high blood pressure, or hypertension.

Most people have what's known as essential or primary hypertension, which means it's not caused by a medical condition, medication, or substance. Primary hypertension can affect both systolic and diastolic pressure to a similar degree. But sometimes, especially in older people, it affects mainly the systolic pressure; this is called isolated systolic hypertension.

Why does this happen? As you age, your arteries tend to become less elastic and less able to accommodate surges of blood. Blood flowing through your arteries at high pressure can damage the inner lining of these vessels, accelerating the buildup of cholesterol-laden plaque. This further stiffens and narrows the arteries, a condition known as atherosclerosis. Because the same volume of blood has to pass through a smaller area, the systolic pressure tends to rise, while the diastolic pressure remains the same or gradually falls over time. In some people with isolated systolic hypertension, the diastolic pressure reading may drop into the 50s or even the 40s.

Most studies show a greater risk of cardiovascular disease (especially strokes) related to high systolic pressure as opposed to elevated diastolic pressure. But in 2019, an eight-year-long study involving more than 1.3 million adults found that while elevated systolic pressure had a greater effect on cardiac outcomes, high diastolic readings also affected a person's risk, regardless of the systolic reading.

To ensure accurate readings when you're checking your blood pressure at home, be sure to sit comfortably with your back supported, your feet flat on the floor, and your arm resting on a table with your palm facing up. If needed, support your arm with a pillow so that your elbow is at the level of your heart.

— Deepak L. Bhatt, M.D., M.P.H.
Editor in Chief, Harvard Heart Letter

Image: © Vadim Zhakupov/Getty Images

• Diastolic Blood Pressure
  • What is diastolic blood pressure?
• Causes
  • What causes low diastolic blood pressure?
• Dangerous of Low Diastolic Blood Pressure
  • Is low diastolic blood pressure dangerous?
• Is 64 mmHg Too Low
  • Is a diastolic blood pressure of 64 mmHg too low?
• Related Resources
  • Related Resources - What Does it Mean When the Bottom Number of Your Blood Pressure is Over 100?

Diastolic blood pressure (DBP) is the pressure exerted on the walls of the arteries when the heart muscle relaxes between beats. When the bottom number of blood pressure (diastole) is over 100 mmHg, it may be called diastolic hypertension (DHT).

When the bottom number of blood pressure (diastole) is over 100 mmHg, it may be called diastolic hypertension (DHT). The normal range of diastolic pressure should be 60 to 80 mmHg in adults. Anything above this is considered abnormal (hypertension). However, when blood pressure readings are above 180/120 mmHg, they are dangerous and require immediate medical attention.

• Diastolic blood pressure (DBP) is the pressure exerted on the walls of the arteries when the heart muscle relaxes between beats.
• A high diastolic reading has been linked to a higher risk of diseases involving the large artery called the aorta that carries blood and oxygen from the heart to the abdomen and chest.
• People with an elevated diastolic reading were more prone to developing an abdominal aortic aneurysm, an enlargement of the aorta that may have serious consequences.
• The problem with such an enlargement is that it can lead to rupture and a high risk of death.
• Few studies and researchers have reported that elevated DBP appears to be associated with cognitive impairment (memory deficit) in people who are 45 years and older. Each 10-point increase over 90 mmHg was associated with a 7 percent higher risk of problems with cognition as per studies conducted at the University of Alabama at Birmingham. Although a causal relationship could not be established, it's possible that by preventing or treating high blood pressure, we could potentially prevent cognitive impairment.
• Diastolic pressure of more than 100 mmHg (DHT) is associated with a significant incidence of strokes.

Causes of DHT

DHT is most commonly associated with

• Increased body mass index (obesity)
• Increased glucose level
• Increased alcohol consumption
• High triglyceride levels
• Family history of hypertension
• Previous cardiovascular events
• Certain factors such as the male gender may put you at a slightly higher risk.

Treatment options for DHT

• Because the risk of cardiovascular events is low in young people, no treatment is required. However, treatment in elderly people should be individualized in such a way that the underlying cardiovascular disease is addressed and the target DBP does not fall below 70 mmHg.
• Lifestyle measures and weight loss must be initiated.
• A study on DHT reported that calcium channel blockers are frequently used with success. Other drugs of choice are angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and diuretics.

What is diastolic blood pressure?

Diastolic blood pressure means the blood pressure reading during the phase when your heart relaxes (diastole). Force of the blood against the walls of the arteries (the blood vessels carrying blood from the heart to other sites) in the body is called blood pressure. The heart pumps the blood into the arteries as it contracts (systole). This blood pressure reading when the heart is actively contracting to push out blood is called systolic blood pressure. When the heart is relaxing (diastole), some pressure is still exerted on the arterial walls by the blood they contain because of the elastic recoil of the blood vessels. This blood pressure is lower than systolic blood pressure and is called diastolic blood pressure.

Blood pressure is expressed in mmHg. This is because mercury (or Hg) was used in the first accurate pressure gauges and is still being used in medicine today as the standard unit of measurement for pressure. Whenever blood pressure is mentioned, systolic pressure generally precedes diastolic pressure.

• Thus, a blood pressure of 130/80 mmHg means systolic pressure is 130, whereas diastolic blood pressure is 80.
• A systolic blood pressure of less than 120 mmHg and diastolic blood pressure of lower than 80 mmHg is generally regarded as normal.
• A blood pressure reading lower than 90/60 mmHg is generally considered low blood pressure (hypotension).

Both diastolic blood pressure and systolic blood pressure determine the risk of cardiovascular diseases including ischemic heart disease (IHD) such as myocardial infarction or heart attack. According to recent studies, the risk of death from IHD and stroke doubles with every 20 mmHg systolic or 10 mmHg diastolic increase among people who are 40-89 years of age.

SLIDESHOW

What causes low diastolic blood pressure?

The decrease in your diastolic blood pressure (DBP) probably represents age-related stiffening of your arteries. Because diastole is a time when the heart receives blood, low diastolic pressure may compromise the blood flow to the heart. Causes of low diastolic blood pressure are as follows.

• Prolonged bed rest causes a reduction in the tone of the arteries.
• Dehydration due to excess sweating.
• Reduced water intake.
• Loss of water in stools due to diarrhea.
• Loss of water in urine due to medications such as diuretics, antihypertensive medications, medications for Parkinson’s disease, and narcotics tricyclic antidepressants.
• Alcohol can cause dilation of the blood vessels, which may lead to lower diastolic blood pressure, lower heart rate, malfunctioning of the heart valves, and heart attack. These are serious disorders that require care and treatment.
• Hormonal deficiencies and other types of endocrine dysfunction such as hypothyroidism or excessive blood loss during menstruation.
• Allergic reactions due to drugs, food, or insect bites.
• Nutritional deficiency of B vitamins and iron leads to anemia.
• Prolonged standing may lead to blood pooling in the legs.

Common signs and symptoms of low DBP may include

• Unusual thirst
• Breathlessness
• Light-headedness
• Fainting
• Dizziness, which may increase with walking or position change
• Confusion
• Dullness
• Sweating
• Nausea

Studies have shown that very low DBP is associated with an increased risk of heart disease. More importantly, a study found that low DBP was associated with an increased likelihood of coronary heart disease events and mortality. Studies explained that if individuals have DBP that is too low, they might not receive enough blood flow to the heart muscle itself, and this could lead to elevations in troponin (cardiac enzyme). Over time, it’s not just elevations in troponin but low DBP that cause actual damage to the heart muscle. Research, however, shows that high systolic readings are the most predictive of a harmful cardiovascular outcome. As a result, they were given more weight in cardiology guidelines and estimating risk. Having both numbers within a healthy range is good for you and your heart.

Health News

Is low diastolic blood pressure dangerous?

Low diastolic blood pressure may cause serious consequences. Diastole is the phase when your heart is relaxing. During this phase, the blood flows through the blood vessels supplying the heart (coronary arteries) to deliver oxygen and nutrients to the heart.

• Low diastolic pressure may reduce the flow of blood through the coronary arteries thereby increasing the risk of lowered oxygen and nutrient supply to the heart. There is an especially higher risk of reduced oxygen and nutrient delivery to the endocardium or the innermost layers of the heart (endocardial ischemia).
• Low diastolic blood pressure is also a marker for widened pulse pressure. Pulse pressure is defined as the difference between your systolic blood pressure and diastolic blood pressure. Widened pulse pressure is considered an indicator of increased arterial stiffness and hardening of the arteries caused by fat deposition (atherosclerosis).
• Furthermore, low blood pressure may increase the risk of falls or accidents because it may cause dizziness or fainting. Thus, it is important to consult a doctor if your blood pressure (diastolic or systolic or both) is low or you have any symptoms of low blood pressure such as light-headedness, cold and clammy skin, difficulty in breathing, or fainting.

QUESTION

Is a diastolic blood pressure of 64 mmHg too low?

Diastolic pressure lower than 60 mmHg is generally regarded as serious. Thus, a diastolic pressure of 64 mmHg is not too low. There may, however, be individual variations. Hence, if you have any symptoms of low blood pressure such as dizziness, confusion, sweating, blurred vision, or unusual thirst, you must seek medical help.

Low diastolic pressure in the absence of low systolic pressure is called isolated diastolic hypotension. It is defined as a diastolic blood pressure of less than 60 mmHg along with a systolic blood pressure of more than or equal to 100 mmHg.

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Medically Reviewed on 3/2/2022

References

Medscape Medical Reference

American Journal of Hypertension

NEJM

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