Blood pressure is a measurement represented by two numbers, where the top number is the systolic pressure and the bottom number is the diastolic pressure. This measurement reflects the force exerted by circulating blood against the walls of the body’s arteries. The systolic reading captures the peak pressure when the heart muscle contracts and pumps blood out. This article focuses specifically on the lower number, the diastolic pressure, and examines what it means when that measurement consistently falls below the expected normal range.
Defining Low Diastolic Pressure
The diastolic pressure represents the pressure remaining in the arteries when the heart is resting and refilling with blood between beats (diastole). This phase is significant because it is when the coronary arteries receive the majority of their blood supply. A healthy blood pressure reading is typically considered to be less than 120 millimeters of mercury (mmHg) over 80 mmHg.
Low blood pressure, or hypotension, is generally defined as a reading below 90/60 mmHg. An isolated low diastolic reading is usually defined as a measurement persistently below 60 mmHg. This condition is formally known as Isolated Diastolic Hypotension (IDH) when the systolic pressure remains within a normal range. This low pressure can compromise the flow of oxygen and nutrients to the heart muscle itself during the relaxation phase. Research indicates that a persistent diastolic pressure below 60 mmHg is linked to an increased risk of cardiovascular damage over time.
Common and Temporary Causes of Low Diastolic Readings
A transient drop in the diastolic number can often be traced back to easily corrected lifestyle or environmental factors. One of the most frequent causes is dehydration, which reduces the total volume of blood circulating in the body, decreasing pressure within the arteries.
Certain medications prescribed for common conditions are also known to selectively lower diastolic pressure. Blood pressure-lowering drugs like diuretics and alpha-blockers can cause significant dips in the lower number. Additionally, drugs used for Parkinson’s disease, erectile dysfunction, and some antidepressants may induce a temporary hypotensive effect.
Positional changes can also result in a temporary drop, a phenomenon known as orthostatic hypotension. When a person stands up quickly, the diastolic pressure may briefly decrease as gravity pools blood in the lower extremities. Recent strenuous exercise similarly causes widespread vasodilation, which temporarily lowers peripheral resistance and results in a lower diastolic reading.
Underlying Medical Conditions Indicated by Low Diastolic Pressure
A persistently low diastolic reading, especially IDH, can be a marker for more serious, underlying chronic health issues. A prominent example is Aortic Regurgitation, a condition where the heart’s aortic valve does not close tightly.
During diastole, this faulty valve allows blood to leak backward from the aorta into the heart’s left ventricle. This back-flow causes the pressure in the aorta to drop rapidly, resulting in the characteristic low diastolic reading. This reduces the pressure that drives blood into the coronary arteries, potentially starving the heart muscle of oxygen. Over time, this chronic lack of perfusion can weaken the heart and contribute to heart failure.
Other systemic conditions can also cause a significant drop in diastolic pressure by inducing widespread vasodilation (the relaxation of blood vessel walls). Sepsis, a severe response to infection, is one such condition where the body’s inflammatory response causes blood vessels to dilate excessively. This drastically reduces circulatory resistance, leading to a dangerously low diastolic pressure. Endocrine disorders, such as hormone deficiencies, can also disrupt the body’s fluid and vascular regulation, contributing to chronic low pressure.
Recognizing Symptoms and Knowing When to Seek Care
While some individuals naturally have a lower diastolic pressure without experiencing any issues, a drop that causes symptoms warrants attention. Common symptoms associated with inadequate blood flow include lightheadedness and dizziness, especially when moving to a standing position. Other signs may include general fatigue, nausea, or a feeling of weakness.
In cases where the pressure is significantly low, fainting (syncope) may occur due to insufficient blood flow to the brain. If you notice a low reading on a home monitor without symptoms, schedule a routine appointment with your healthcare provider for evaluation.
Immediate medical attention is necessary if a low diastolic reading is accompanied by severe or acute symptoms. These urgent warning signs can indicate a state of shock or severely compromised organ perfusion, requiring emergency care to restore adequate blood pressure and circulation:
- Confusion or disorientation
- Rapid and shallow breathing
- A fast or irregular pulse
- Chest pain