Second number in blood pressure is low

Understanding Low Blood Pressure -- the Basics

What Is Low Blood Pressure?

Hypotension is the medical term for low blood pressure (less than 90/60).

Table of Contents Show

Understanding Low Blood Pressure -- the Basics
What Is Low Blood Pressure?
What Causes Low Blood Pressure?
What causes the second number in blood pressure to be low?
What is a dangerously low bottom number for blood pressure?
What does the second reading on blood pressure mean?
Which of the 2 blood pressure number is more important?

A blood pressure reading appears as two numbers. The first and higher of the two is a measure of systolic pressure, or the pressure in the arteries when the heart beats and fills them with blood. The second number measures diastolic pressure, or the pressure in the arteries when the heart rests between beats.

Optimal blood pressure is less than 120/80 (systolic/diastolic). In healthy people, low blood pressure without any symptoms is not usually a concern and does not need to be treated. But low blood pressure can be a sign of an underlying problem -- especially in the elderly -- where it may cause inadequate blood flow to the heart, brain, and other vital organs.

Chronic low blood pressure with no symptoms is almost never serious. But health problems can occur when blood pressure drops suddenly and the brain is deprived of an adequate blood supply. This can lead to dizziness or lightheadedness. Sudden drops in blood pressure most commonly occur in someone who's rising from a lying down or sitting position to standing. This kind of low blood pressure is known as postural hypotension or orthostatic hypotension. Another type of low blood pressure can occur when someone stands for a long period of time. This is called neurally mediated hypotension.

Postural hypotension is considered a failure of the cardiovascular system or nervous system to react appropriately to sudden changes. Normally, when you stand up, some blood pools in your lower extremities. Uncorrected, this would cause your blood pressure to fall. But your body normally compensates by sending messages to your heart to beat faster and to your blood vessels to constrict. This offsets the drop in blood pressure. If this does not happen, or happens too slowly, postural hypotension results and can lead to fainting.

The risk of both low and high blood pressure normally increases with age due in part to normal changes during aging. In addition, blood flow to the heart muscle and the brain declines with age, often as a result of plaque buildup in blood vessels. An estimated 10% to 20% of people over age 65 have postural hypotension.

What Causes Low Blood Pressure?

The cause of low blood pressure isn't always clear. It may be associated with the following:

Pregnancy
Hormonal problems such as an underactive thyroid (hypothyroidism), diabetes, or low blood sugar (hypoglycemia)
Some over-the-counter medications
Some prescription medicines such as for high blood pressure, depression or Parkinson’s disease
Heart failure
Heart arrhythmias (abnormal heart rhythms)
Widening, or dilation, of the blood vessels
Heat exhaustion or heat stroke
Liver disease

What Causes a Sudden Drop in Blood Pressure?

Sudden drops in blood pressure can be life-threatening. Causes of this type of hypotension include:

Loss of blood from bleeding
Low body temperature
High body temperature
Heart muscle disease causing heart failure
Sepsis, a severe blood infection
Severe dehydration from vomiting, diarrhea, or fever
A reaction to medication or alcohol
A severe allergic reaction called anaphylaxis that causes an irregular heartbeat

Who Gets Postural Hypotension?

Postural hypotension, which is low blood pressure when standing up suddenly, can happen to anyone for a variety of reasons, such as dehydration, lack of food, or being overly fatigued. It can also be influenced by genetic make-up, aging, medication, dietary and psychological factors, and acute triggers, such as infection and allergy.

Postural hypotension occurs most frequently in people who are taking drugs to control high blood pressure (hypertension). It can also be related to pregnancy, strong emotions, hardening of the arteries (atherosclerosis), or diabetes. The elderly are particularly affected, especially those who have high blood pressure or autonomic nervous system dysfunction.

Hypotension after meals is a common cause of dizziness and falls after eating. This is most common after large meals containing a lot of carbohydrates. It’s believed to be caused by blood pooling into the vessels of the stomach and intestines.

Several drugs are commonly associated with postural hypotension. These medications can be divided into two major categories:

Drugs used to treat high blood pressure, such as diuretics, beta-blockers, calcium-channel blockers, and angiotensin-converting enzyme (ACE) inhibitors
Drugs that have hypotension as a side effect, including nitrates, erectile dysfunction medications, drugs for Parkinson's disease, antipsychotics, neuroleptics, anti-anxiety agents, sedative-hypnotics, and tricyclic antidepressants

Common causes of naturally occurring postural hypotension include:

Dehydration and electrolyte loss, which may result from diarrhea, vomiting, excessive blood loss during menstruation, or other conditions
Age-associated decline in blood pressure regulation, which may be worsened by certain health conditions or medications

Certain diseases can also cause postural hypotension. These include:

Central nervous system disorders, such as Shy-Drager syndrome or multiple system atrophy
Nerve problems, such as peripheral neuropathy or autonomic neuropathy
Cardiovascular disorders
Alcoholism
Nutritional diseases

What causes the second number in blood pressure to be low?

Cause of Low Diastolic Blood Pressure Pregnancy and heart conditions, such as low heart rate, heart valve disorders, and heart failure, can lead to low diastolic blood pressure. Aging is another risk factor, as well.

What is a dangerously low bottom number for blood pressure?

A 2016 study that lasted more than 3 decades and involved more than 11,000 people found that a diastolic blood pressure below 60 mm Hg is dangerous. People with this level are 50 percent more likely to have heart damage. This is compared with those who have a low diastolic pressure level between 80 and 89 mm Hg.

What does the second reading on blood pressure mean?

The second number is the diastolic number. For example, if your doctor says your blood pressure is “120 over 80,” the first number, 120, is the systolic number, and the second number of your blood pressure reading is the diastolic number (80 in this example).

Which of the 2 blood pressure number is more important?

Q. When I am monitoring my blood pressure, which number is most important — top, bottom, or both? A. While both numbers in a blood pressure reading are essential for diagnosing and treating high blood pressure, doctors primarily focus on the top number, also known as systolic pressure.