THE HEART

Blood Pressure

Within the cardiovascular system, there are many different levels of pressure exerted by the blood. The most commonly measured blood pressure is that of Systolic (ejection of blood into the aorta) and Diastole (when the heart is resting and receiving blood). For most people who do not have heart disease, this is generally around 100-140/60-80mmHg, with males having a slightly higher pressure. Blood pressure reduces as blood flows to the different areas of the body. When blood leaves the heart, it is under its highest pressure (systole approx 120mmHg). As it flows out of the arteries and into arterioles and capillaries, its pressure is very much lower (approx 25mmHg). This pressure reduces further when measured at the veins.

Systolic pressure is determined by the amount if blood being forced into the aorta and arteries with each ventricular contraction (heartbeat). If the volume of blood is increased, the systolic pressure is increased. Systolic pressure can also be affected buy the elasticity of the arteries. If the walls of the artery become stiff, a condition called arteriosclerosis, they are unable to compensate for the sudden increase in blood flow which occurs on ventricular contraction. Thus, systolic pressure increases, leading to hypertension.

Diastolic pressure provides valuable information regarding peripheral resistance. This is the resistance to blood flow through the vascular network of arteries and veins. If the body need to increase blood pressure e.g. during fainting, one of the ways it achieves this is by constricting the arterioles; a process known as arteriolar vasoconstriction. This constriction of the vessel impedes blood flow from the arterial network, thus increasing blood pressure. The diastolic pressure is also dependent on a number of other factors, such as systolic blood pressure, the thickness or viscosity of the blood, and presence or absence of arteriosclerosis.