Blood Pressure

Basic Concepts
Blood Pressure – the force exerted by the blood against a unit of area of the vessel wall (in mmHg)

During each heartbeat, the blood pressure changes between two values:
 * a maximum – SYSTOLIC PRESSURE – the pressure when the heart releases the blood in the vessels - about 120 mmHg
 * a minimum – DIASTOLIC PRESSURE – pressure in the blood vessels between each heartbeat (when the heart is resting) - about 80 mmHg

Pulse Pressure – the difference between systolic and diastolic pressures (40 mmHg)

Mean Arterial Pressure (MAP) – the average pressure within an artery over a complete cycle of one heartbeat MAP = Diastolic Pressure + 1/3 Pulse Pressure

Total Peripheral Resistance - the sum of the resistance of all peripheral vasculature in the systemic circulation.

A healthy adult's pressure should not be higher than 140/90 mmHg. High pressure is called hypertension and low pressure is called hypotension.


 * Blood pressure in selected parts of the circulation:

Measurement of Blood Pressure
Blood pressure can be measured in several ways: directly (invasively), indirectly, and automatically. For automatic measurement, we can use the auscultation method and the oscillometric method.

Regulation of Blood Pressure
There are 2 main mechanisms that regulate blood pressure:
 * Short/Fast Term Mechanism - Neurally mediated baroreceptor mechanism that regulate blood vessel diameter, heart rate and contractility
 * Slower/Long Term Mechanism - Hormonally regulated renin-angiotensin-aldosterone mechanism that regulate blood volume

Fast Term Mechanism

 * Is a negative feedback system that is responsible for the minute to minute regulation of arterial blood flow
 * The sensor for MAP is provided by baroreceptors (stretch receptors) located in the carotid sinus and aortic arch
 * Sensitive between 80 – 150 mmHg

Long Term Mechanism

 * Slow hormonal mechanism by adjustment of blood volume
 * Renin – angiotensin – aldosterone System



Summary

 * BP: FORCE EXERTED BY BLOOD AGAINST ANY UNIT AREA OF THE VESSEL WALL
 * BP HAS DIFFERENT VALUE THROUGH THE CIRCULATORY SYSTEM
 * ARTERIAL PRESSURE PULSATION: 120/80 mmHg
 * REGULATION VIA AUTONOMIC AND HORMONAL SYSTEM
 * BP IS CONTINUALLY CHANGING DEPENDING ON ACTIVITY, TEMPERATURE, DIET, PHYSICAL OR EMOTIONAL STATE, MEDICATION…