Blood Pressure Definition

Covering systolic and diastolic blood pressure definition as well as high, low, arterial, normal and orthostatic blood pressure definitions

Definition of Blood Pressure

Blood pressure refers to the pressure that is exerted by blood on the walls of the blood vessels as it flows. The heart beats about 60-70 times a minute and in each of these times pumps blood into the arteries. Per each beat the heart pumps 70ml of blood. Altogether an adult heart pumps 6000 to 7000 liters per day which is equivalent to 1500 to 2000 gallons per day. This however does not mean there are 7000 liters of blood in a human being. This simply refers to the repeated action of pumping about five liters of total blood in a human being.

Blood pressure definition may also be understood in the context of the actual mechanical work of the heart. During each heartbeat, the heart muscles contract forcing blood through arteries under a wave of pressure which is known as pulse. Each single heartbeat has one pulsation which can be felt under the skin on the back of the knee, wrist, neck and groin amongst other strategic places on a person's body.

When at rest your blood pressure is less and raises with activity to 20 liters of blood flow under pressure from the heart up from 5 liters when you are resting. Blood flow follows a circadian rhythm in a normal person. The circadian rhythm refers to an 'internal body clock" that regulates the 24-hour cycle of biological processes in animals and plants.

Blood pressure for human beings falls at bedtime and spikes just before waking. This is the time when morning hypertension occurs. Many people who try to understand blood pressure definition generally have a mistaken view that blood pressure in itself is harmful. Blood pressure is not harmful. In fact it is essential as it is the necessary force driving blood through vessels to supply oxygen and nutrients to body organs and tissues and carries away waste materials such as carbon dioxide.

Systolic and diastolic blood pressure definition

The definition for blood pressure is best understood in the context of systolic and diastolic blood pressures. Systolic and diastolic measurements are also an important part of understanding the context in which blood flows under pressure. During heartbeats blood pressure oscillates between maximum which is systolic and minimum which is diastolic.

The two readings together form the standard and complete interpretation and written values of blood pressure readings for example 120/80mmHg. 120 mmHg in this case is the systolic readings whilst 80mmHg is the diastolic blood pressure reading. Systolic blood pressure is when the ventricles of the heart contracts pushing out blood from the heart into the arteries. This happens at greater force than diastolic hence the greater number of 120.

Put in other words, the systolic blood pressure represents a period of greatest pressure in the arterial vascular system. Systolic pressure which is exerted on the walls of the arteries during ventricular contraction will vary according to age, gender, size and a person's physical condition. Due to heart disease and other underlying medical condition, the systolic blood pressure can be excessively elevated above the high normal blood pressure range of 139. This will be called isolated systolic hypertension or high systolic blood pressure.

The diastolic blood pressure definition refers to the least or lowest pressure exerted on artery walls. This occurs in between heartbeats hence the blood pressure reading is smaller i.e 80 compared to that of the systolic blood pressure reading of 120. Diastolic blood pressure occurs when blood pressure is rushing back to fill the heart ventricles which is the diastole phase of the cardiac cycle.

In much the same way as systolic blood pressure, diastolic blood pressure will vary with size, age, gender and the subject's physical condition. When diastolic blood pressure is abnormally elevated whilst systolic blood pressure remains within the normal blood pressure range this is medically known as isolated diastolic hypertension or high diastolic blood pressure. For various reasons, the diastolic pressure can be abnormally low giving severely low blood pressure readings and this is known as low diastolic blood pressure.

Normal, high and low blood pressure definition

Understanding blood pressure definition of normal, high and low blood pressure is best achieved with the help of the blood pressure chart below.

blood pressure chart

High blood pressure guidelines also known as hypertension guidelines issued by reputable institutions generally categorize blood pressure into optimal, normal and high normal ranges. As shown above in the blood pressure chart, beyond high normal blood pressure range, stage 4 hypertension also known as mild hypertension sets in. This goes up all the way to severe hypertension which is stage 3 and isolated systolic hypertension.

By definition normal blood pressure is blood pressure in the systolic range of 120-129 and diastolic range of 80-84mmHg i.e 120/80mmHg to 129/84mmHg. High blood pressure is defined as blood pressure in the systolic range of 140-159 and diastolic range of 90-99mmHg i.e 140/90mmHg - 159/99mmHg.

On the other hand there is no agreed definition of low blood pressure even though doctors agree that a blood pressure reading of 90/60mmHg for someone with usually higher blood pressure measurements warrants medical observation of signs of low blood pressure. This is because low blood pressure readings in them self are not adequate for an abnormally low blood pressure diagnosis without presenting known symptoms of low blood pressure.

Arterial and orthostatic blood pressure definition

Arterial blood pressure refers to pressure of the blood in the arterial system. Arterial blood pressure depends on other factors such as the heart's pumping pressure, elasticity of blood vessels, blood viscosity, blood volume and the resistance of the arterial walls.

Orthostatic blood pressure definition refers to a temporary lowering of blood pressure in most cases as a result of suddenly standing up. It occurs in all types of people but is more outspoken in older members of society above the age of 60. Also known as postural hypotension it causes temporary disorientation due to a shortage of blood to the brain depriving it of much needed oxygen.

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