Blood pressure measures the force exerted by circulating blood against artery walls. It is expressed as two numbers: the higher systolic pressure and the lower diastolic pressure. These readings reflect the heart’s pumping and resting phases. A diastolic reading consistently below the normal range can signal a condition requiring attention. This article examines the implications of a low diastolic reading for overall health.
Understanding Diastolic Pressure and Thresholds
Diastolic blood pressure (DBP) represents the minimum pressure exerted within the arteries during diastole, the heart’s resting phase when it refills with blood. This pressure must remain adequate to continue pushing blood into the body’s tissues and organs. A normal diastolic reading for most adults is below 80 millimeters of mercury (mmHg).
A reading that falls below 60 mmHg is considered low. While overall hypotension is defined as below 90/60 mmHg, a low diastolic number can occur even if the systolic number is normal or high. This condition is known as Isolated Diastolic Hypotension (IDH). Maintaining acceptable diastolic pressure is important because it reflects the baseline pressure needed to perfuse all organs, especially the heart muscle.
Causes of a Low Diastolic Reading
Transient and Medication Causes
A low diastolic reading can stem from several underlying mechanisms, ranging from transient issues to more serious chronic conditions. A common transient cause is volume depletion, such as dehydration, which reduces the total fluid circulating in the blood vessels. This decrease in blood volume causes pressure in the arteries to drop, often presenting as a lower overall blood pressure reading.
Certain medications used for high blood pressure can also disproportionately lower the diastolic reading. Drugs like alpha-blockers or powerful vasodilators widen blood vessels, reducing peripheral resistance and causing an isolated drop in pressure. A physician may find that low diastolic pressure is a sign of overtreatment in a patient receiving medication for hypertension.
Cardiovascular and Systemic Issues
More serious causes often relate to underlying cardiovascular or systemic issues. Aortic regurgitation, where the aortic valve does not close completely, allows blood to flow backward into the heart during diastole. This “diastolic runoff” rapidly decreases aortic pressure, resulting in a significantly low reading and a characteristic widening of the pulse pressure.
Systemic inflammation, such as that seen in severe infection or sepsis, also leads to low diastolic pressure. The widespread inflammatory response causes blood vessels to dilate excessively and lose their tone, reducing the resistance needed to maintain proper diastolic pressure.
Aging
The natural process of aging can also contribute to a lower diastolic reading. As a person ages, major arteries become stiffer. This stiffness increases systolic pressure while simultaneously reducing the elasticity needed to maintain diastolic pressure, leading to a naturally widened pulse pressure.
How Low Diastolic Pressure Affects the Body
The primary concern with a low diastolic reading is insufficient perfusion, meaning vital organs are not receiving enough blood and oxygen. The brain is particularly sensitive to this reduced flow, which can cause acute symptoms like lightheadedness, dizziness, and fatigue. In more pronounced cases of hypoperfusion, a person may experience blurred vision, nausea, or syncope (temporary loss of consciousness).
The heart is uniquely vulnerable when diastolic pressure is low. Unlike other organs, the coronary arteries supplying the heart muscle are perfused mainly during the diastolic phase when the heart is at rest. If the diastolic pressure is too low, the pressure gradient driving blood into the coronary arteries is reduced. This inadequate flow can lead to myocardial ischemia, manifesting as chest pain or angina, especially during physical exertion. Chronically low diastolic pressure can weaken the heart muscle due to a consistent lack of oxygen, which is why isolated diastolic hypotension is associated with an increased risk of developing heart failure.
Medical Management and When to Seek Help
Diagnosis and Management
Evaluation of a low diastolic reading begins with identifying the underlying cause through a comprehensive medical history and physical examination. Diagnostic tests may include an electrocardiogram (ECG) to check electrical activity or an echocardiogram to visualize heart structure and function, especially the aortic valve. Blood and urine tests help rule out systemic issues like infection or dehydration. Management strategies are tailored to the source of the low reading.
For fluid loss, treatment involves increasing fluid intake and sometimes dietary salt to boost blood volume. If medication is the cause, the physician will adjust the dosage or switch to a different class of antihypertensive drug. For patients with low diastolic pressure due to stiff arteries or isolated diastolic hypotension, the treatment goal is often to maintain the pressure at or above 70 mmHg. This may require accepting a systolic pressure slightly higher than ideal to protect the heart’s coronary circulation. Medications to actively raise blood pressure, such as midodrine, are reserved for severe, symptomatic cases involving orthostatic hypotension.
When to Seek Emergency Help
Prompt medical attention is necessary if a low diastolic reading is accompanied by severe symptoms. These signs include chest pain, suggesting poor coronary perfusion, or sudden difficulty breathing. Immediate care is also required for severe confusion, a rapid and weak pulse, or cold, clammy skin, as these indicate shock and a dangerous level of organ hypoperfusion.