Hydralazine is a medication prescribed to manage high blood pressure. It functions as a vasodilator, relaxing and widening blood vessels throughout the body. This action allows blood to flow more easily, reducing pressure against arterial walls. While primarily used for blood pressure control, hydralazine is also employed in specific situations, such as certain cases of heart failure.
Understanding Blood Pressure Readings
Blood pressure is measured as two numbers: systolic and diastolic. The systolic pressure, the top number, indicates the force of blood against artery walls when the heart contracts and pumps blood out. This is the highest pressure recorded during the heart’s pumping cycle.
The diastolic pressure, the bottom number, represents the pressure in the arteries when the heart relaxes between beats and refills with blood. Both readings provide important information regarding cardiovascular health, with the diastolic measurement reflecting the resistance in the blood vessels when the heart is at rest.
How Hydralazine Works
Hydralazine functions as a direct-acting vasodilator, relaxing the smooth muscle in blood vessel walls. This causes the blood vessels to widen. By expanding the vessels, hydralazine reduces the overall resistance blood encounters as it flows through the circulatory system.
This reduction in peripheral vascular resistance makes it easier for the heart to pump blood throughout the body. The exact molecular mechanism by which hydralazine achieves this effect is not fully understood, but it is believed to involve interfering with calcium movement within vascular smooth muscle cells.
Hydralazine’s Distinct Effect on Diastolic Blood Pressure
Hydralazine exhibits a more pronounced effect on lowering diastolic blood pressure compared to systolic blood pressure. This distinct action stems from its preferential dilation of arterioles, which are the small arteries that primarily determine peripheral vascular resistance. By directly relaxing these resistance vessels, hydralazine reduces the pressure within the arterial system during the heart’s resting phase.
The reduction in peripheral resistance directly impacts diastolic pressure, as this pressure reflects the force on arterial walls when the heart is not actively pumping. Relaxed and widened arterioles lead to less resistance and a notable decrease in the “resting” pressure within the arteries. This selective action on arterioles contributes to its specific influence on the diastolic reading.
Hydralazine in Hypertension Treatment
Hydralazine is utilized in the management of hypertension, often when other medications have not adequately controlled blood pressure. It is not a first-line treatment for essential hypertension due to its side effects and the availability of newer, better-tolerated antihypertensive drugs. A common side effect is reflex tachycardia, an increase in heart rate, which often necessitates its use in combination with a beta-blocker to counteract this effect.
The medication finds a role in treating resistant hypertension, which is high blood pressure uncontrolled by other agents. It is also used in hypertensive emergencies, where rapid blood pressure reduction is necessary, and is considered safe for use in hypertension during pregnancy. Hydralazine can be part of combination therapy, especially in specific populations or for conditions like heart failure.