Blood pressure is measured by two numbers: systolic (top) and diastolic (bottom). The systolic reading registers the pressure in the arteries when the heart contracts and pushes blood out to the body. The diastolic reading measures the pressure in the arteries while the heart is at rest between beats. Understanding the bottom number is important for assessing overall cardiovascular well-being, as a consistently low reading can signal an underlying health issue that may require medical attention.
The Role of Diastolic Pressure in Heart Health
The diastolic blood pressure reflects the minimum pressure exerted on the artery walls during diastole, the heart’s relaxation phase. This period of rest is when the heart chambers refill with blood in preparation for the next beat. The diastolic reading is significant because it determines the level of perfusion, or blood flow, to the heart muscle itself. The coronary arteries, which supply oxygen and nutrients to the heart tissue, receive most of their blood flow during this resting phase. If the diastolic pressure drops too low, there may be insufficient force to push blood through the coronary arteries effectively. This reduced pressure can deprive the heart muscle of necessary oxygen, a condition known as ischemia. Chronic ischemia can weaken the heart and potentially lead to heart failure.
Identifying the Critical Diastolic Thresholds
Hypotension, or low blood pressure, is generally defined as a reading below 90/60 millimeters of mercury (mmHg). While a healthy blood pressure is typically below 120/80 mmHg, the specific concern for low diastolic pressure begins when the bottom number is consistently below 60 mmHg. This threshold is particularly relevant for older adults and individuals with existing cardiovascular disease. A persistent diastolic reading below 60 mmHg, especially when the systolic pressure remains within a normal range (above 100 mmHg), is often termed “isolated diastolic hypotension.” This condition carries an increased risk for adverse cardiovascular events, including heart attack and heart failure. Monitoring this lower number is therefore an important part of managing blood pressure, even when the top number appears acceptable.
Recognizing Symptoms of Acute Hypotension
When blood pressure drops rapidly or remains too low, the body may not receive adequate blood flow to the brain and other organs. Common symptoms of acute hypotension include lightheadedness or dizziness, particularly when moving from a sitting or lying position to standing. Individuals may also experience unsteadiness, weakness, or fatigue. Other acute signs can include blurred vision, nausea, and difficulty concentrating. In severe cases of acute hypotension, a person may faint, which is medically referred to as syncope. Immediate medical attention is necessary if a sudden drop in pressure causes signs of shock, such as cold, clammy skin, a rapid and weak pulse, or rapid, shallow breathing. These symptoms indicate a life-threatening lack of oxygen delivery to the body’s tissues.
Common Causes of Chronically Low Diastolic Pressure
A variety of underlying factors can contribute to a consistently low diastolic reading, ranging from pharmacological effects to chronic medical conditions. Medications are a frequent cause, particularly those prescribed to manage high blood pressure, such as certain alpha-blockers or central-acting anti-hypertensive agents. Diuretics can also lower blood pressure by reducing fluid volume, as can other medications like tricyclic antidepressants or drugs used to treat erectile dysfunction.
Heart and Volume Issues
Dehydration is another common cause, as a reduced blood volume directly lowers the pressure within the arteries. Persistent low diastolic pressure can also be linked to heart conditions, such as severe heart failure or problems with the heart valves, like aortic regurgitation. These issues can impair the heart’s ability to fill properly or maintain sufficient vascular resistance during the resting phase.
Systemic Conditions
Endocrine disorders, like Addison’s disease, or autonomic nervous system dysfunction, often seen in conditions like diabetic neuropathy, can also disrupt the body’s normal blood pressure regulation.