Blood pressure is measured using two numbers: systolic and diastolic. Systolic pressure (the top number) reflects the pressure in your arteries when your heart contracts and pumps blood out. Diastolic pressure (the lower number) measures the pressure in your arteries when the heart rests and fills with blood between beats. A reading that consistently shows a low diastolic number can be a source of concern because this pressure plays a direct role in ensuring adequate blood flow to the heart muscle itself. For some, a low reading may be normal, but for others, it indicates a physiological issue requiring attention from a healthcare provider.
What a Low Diastolic Reading Means
A diastolic blood pressure reading of 60 millimeters of mercury (mm Hg) or lower is considered low. When evaluating this reading, it is important to distinguish between general hypotension and isolated diastolic hypotension (IDH). General hypotension occurs when both systolic and diastolic numbers are low, usually below 90/60 mm Hg. IDH is a specific condition where the diastolic pressure is below 60 mm Hg, but the systolic pressure remains in a normal or elevated range. This distinction is significant because IDH is often associated with distinct underlying physiological changes, particularly in older adults.
Situations That Can Lower Diastolic Pressure
Several factors can temporarily cause a drop in diastolic pressure without indicating a chronic disease. Medications prescribed for high blood pressure, such as alpha-blockers or diuretics, can cause a disproportionate reduction in the diastolic number. Drugs used for Parkinson’s disease and depression may also contribute to lower readings. Adjusting the dosage or changing the type of medication often resolves this issue.
Dehydration due to insufficient fluid intake, excessive sweating, or acute illness can reduce the total volume of blood circulating in the body. This decrease in fluid naturally lowers the pressure exerted on artery walls, leading to a temporary drop in both systolic and diastolic measurements. Pregnancy can also cause the diastolic pressure to drop, particularly during the first and second trimesters, as the circulatory system adapts.
When Low Diastolic Pressure Is a Concern
Low diastolic pressure poses a risk because the coronary arteries receive oxygenated blood primarily during the diastolic phase, when the heart is relaxed. If the pressure in the arteries is too low during this period, the heart muscle may not receive enough blood and oxygen, a condition known as ischemia. Over time, this chronic lack of adequate perfusion can weaken the heart and potentially contribute to the development of heart failure.
This situation is often seen in conjunction with a wide pulse pressure, which is the large numerical gap between the systolic and diastolic readings. A wide pulse pressure is frequently linked to the stiffening of the arteries that occurs with age, where the vessels lose their elasticity. Underlying serious health conditions, such as severe aortic valve problems or structural heart issues, can also cause the diastolic number to drop significantly.
Symptoms that accompany a consistently low diastolic reading are important indicators of whether the heart and brain are receiving sufficient blood flow. Common signs include feeling tired, lightheadedness, or dizziness, especially when standing up quickly. More serious symptoms, such as confusion, chest pain, or sudden fainting, require urgent medical assessment.
Monitoring and Seeking Professional Advice
If you notice persistently low diastolic readings, monitoring your blood pressure accurately at home is a helpful step before consulting a healthcare provider. Use a validated cuff and ensure you are seated quietly with your back supported and feet flat on the floor, avoiding caffeine or exercise for at least 30 minutes prior to measurement. Taking readings at the same time each day and logging them provides your doctor with a clear picture of your pressure trends. If you are experiencing mild symptoms like occasional fatigue or lightheadedness, schedule an appointment to discuss your readings. However, certain symptoms signal a medical emergency and require immediate care, such as sudden confusion, acute chest pain, rapid and shallow breathing, or signs of shock like cold, clammy skin. A medical professional will evaluate your overall health, review your medications, and may perform tests like an electrocardiogram.