- Blood Pressure refers to the physical force which blood exerts on the vascular wall
- The absolute pressure of blood in the vasculature can never be measured and thus any reference to a "Blood Pressure" will always be relative to the pressure of blood in some standard, accessible context. In the clinical setting, the standard physical context is assumed to be blood sitting outside at atmospheric pressure. This value is by notation 0 mm Hg. For example, any reference to an arterial blood pressure of, say, 100 mm Hg in actuality means that there is 100 mm Hg more pressure in the arterial blood compared to blood sitting outside the body.
- The average blood pressure in the systemic and pulmonary arteries is of significant physiological consequence for homeostasis. Therefore, throughout the text you will see references to systemic arterial pressure and the pulmonary arterial pressure.
- When referring to these pressures we are indicating their "Mean Arterial Pressure" (MAP) which is the average pressure seen by the respective systemic or pulmonary arteries. The value of the MAP is weighted toward the diastolic pressure because two-thirds of the cardiac cycle is spent in diastole whereas one-third is spent in systole.
- Mean Arterial Pressure = 1/3 x Systemic Arterial Pressure + 2/3 x Diastolic Arterial Pressure