Arterial Blood Pressure

ARTERIAL BLOOD PRESSURE It is the pressure exerted by blood on the wall of a blood vessel, especially pressure in arteries. It is determined by the rate and force of heart beat and resistance to the flow of blood through vessels. MEASUREMENT OF BLOOD PRESSURE Blood pressure is measured by sphygmomanometer. Sphygmomanometer consists of a rubber cuff attached by a rubber tube to a compressible hand pump or bulb. Another tube attaches to the cuff and to a column of mercury or pressure dial. The cuff is wrapped around the power part of the upper arm and inflated by squeezing the bulb. The bulb is squeezed until the blood pressure is raised up to 200 mm Hg till pulse drops. The pulse is felt in two ways (1) by placing the stethoscope and/ or (2) by placing the fingers over the radial artery at the wrist. The pressure is slowly lowered by unscrewing the bulb till the reappearance of the radial pulse. The pressure at which radial pulse restarts or first sound is heard corresponds to the systolic pressure. The pressure is lowered further, when the sound becomes faint or disappears; the pressure recorded on the mercury column corresponds to the diastolic pressure.

FACTORS AFFECTING ARTERIAL BLOOD PRESSURE 1. AGE - BP increases with age. 2. SEX – In females before menopause, SBP is 5 mm Hg less than that in males. 3. EXERCISE – BP increases after exercise. 4. GRAVITY – The pressure in any blood vessel below heart level is increased and that in any blood vessel above heart level is decreased by the effect of gravity. 5. HEREDITARY – More prone in individuals with family history of hypertension. 6. POSTURE – Upon sudden standing, DBP increases. It corrects after 1 min. to normal. 7. MEALS – SBP rises after meals.

DETERMINANTS OF ARTERIAL BLOOD PRESSURE Arterial Blood Pressure – Cardiac output x Peripheral Resistance Any factor altering the cardiac output or peripheral resistance will cause a change in arterial blood pressure.

REGULATION OF BLOOD PRESSURE There are various mechanisms that exist in human body which regulate the systemic arterial blood pressure. 1. Rapidly acting regulatory mechanisms 2. Intermediate acting regulatory mechanisms 3. Long acting regulatory mechanisms 1. RAPIDLY ACTING REGULATORY MECHANISMS They help to maintain blood pressure within normal range and prevents from fluctuating to extreme high or low. They act within seconds of BP becoming abnormal. VARIOUS REFLEXES INVOLVED 1. Baroreceptor reflexes 2. Chemoreceptor reflexes 3. CNS Ischaemic response 2. INTERMEDIATE ACTING REGULATORY MECHANISMS They begin to act within minutes of BP becoming abnormal. They alter the blood volume and correct any change in BP. MECHANISMS 1. Capillary fluid shift mechanisms 2. Stress relaxation mechanisms 3. LONG ACTING REGULATORY MECHANISMS They are slow acting. Act over a period of days to years. a. Direct mechanisms

b. Indirect mechanisms -

Involve Renin- Angiotensin system Aldosterone system