Blood pressure measures the force exerted by circulating blood against artery walls. It is recorded as two numbers. The top number is systolic pressure, measured when the heart contracts to push blood out. The bottom number is diastolic pressure, which measures the pressure in the arteries when the heart is relaxed between beats. When diastolic pressure consistently measures 80 millimeters of mercury (mmHg) or higher, it indicates the arteries are not relaxing sufficiently during this resting phase.
The Role of Vascular Resistance
The physiological mechanism behind elevated diastolic pressure is an increase in peripheral vascular resistance (PVR). PVR is the resistance to blood flow created by the small arteries, or arterioles, which regulate blood flow and pressure. When the muscular walls of these arterioles constrict, they narrow the channel for blood flow, increasing resistance. This high resistance forces pressure to remain elevated even during the heart’s resting phase, preventing blood from easily flowing into the capillaries. Over time, this chronic constriction leads to stiffening of the vessel walls, cementing a higher baseline pressure.
Underlying Health Conditions
Various underlying medical issues can trigger arterial narrowing and stiffening, leading to increased vascular resistance. Kidney disease is a frequent contributor, as the kidneys regulate fluid volume and blood pressure hormones. Impaired kidney function causes fluid retention and overproduction of hormones like renin, which leads to widespread vasoconstriction and raises diastolic pressure.
Thyroid disorders, particularly hypothyroidism, are also linked to elevated diastolic readings by affecting heart function and vascular tone. Adrenal gland issues, such as tumors causing aldosterone overproduction, disrupt fluid balance. This hormonal imbalance causes the body to retain sodium and water, increasing blood volume and elevating pressure. Obstructive sleep apnea also raises diastolic pressure through chronic vascular stress. Repeated breathing interruptions cause drops in blood oxygen, triggering the fight-or-flight response and releasing stress hormones that promote vasoconstriction.
Daily Habits That Raise Diastolic Pressure
Everyday behaviors significantly influence peripheral vascular resistance. High sodium intake, often from processed foods, causes the body to retain water. This increased fluid volume raises arterial pressure and contributes to stiffness. Limiting sodium to less than 1,500 milligrams per day can help mitigate this effect.
Chronic, unmanaged stress elevates diastolic pressure by activating the sympathetic nervous system. This activation releases hormones like adrenaline and cortisol, which are powerful vasoconstrictors that temporarily tighten blood vessels. Repeated hormonal surges contribute to a consistently elevated baseline resistance over time. Physical inactivity also promotes higher diastolic readings by reducing the flexibility of arterial walls. Furthermore, excessive consumption of alcohol and caffeine acts as an acute vasoconstrictor. When these substances are consumed habitually, they compound the effects on vascular tone, leading to a higher resting pressure.
When Diastolic Pressure Is High Alone
Isolated Diastolic Hypertension (IDH) occurs when the bottom number is high (80 mmHg or higher) but the top number remains normal (below 130 mmHg). This scenario is most frequently observed in younger adults, typically those under age 55. IDH occurs because their large arteries remain elastic and accommodate the blood pumped by the heart, keeping the systolic pressure normal. However, the peripheral arterioles are already experiencing high resistance, which is reflected in the elevated diastolic reading. This high resistance is often linked to factors like obesity, high blood sugar levels, and chronic kidney disease. Recognizing IDH is important because it indicates a problem with vascular tone that requires intervention to prevent long-term damage.