Arterial blood pressure

The outwards (hydrostatic) pressure exerted by the blood on blood vessel walls.

The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts.

Should not normally reach or exceed 140 mmHg under resting conditions

The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes- during diastole.

Should not normally reach or exceed 90 mm Hg under resting conditions

Clinical presentation of blood pressure of 140/90 mmHg or higher and daytime average of 135/85 mmHg or higher.

The difference between systolic and diastolic blood pressures

Normally between 30 and 50 mm Hg

Flow in the artery is blocked and no sound can be heard through the stethoscope.

Flow is turbulent when blood pressure (blood pressure exceeds cuff pressure)- audible through the stethoscope.

No sound is heard because of uninterrupted laminar flow

There are 5 phases of the Korotkoff sounds which correspond to different phases of the cycle:-

1. 1. First sound heard – peak systolic pressure
2. Intermittent sounds due to turbulent flow exceeding cuff pressure- becomes more intense and swishing
3. Becomes more crisp and distinct.
4. Last sound heard at minimum diastolic pressure (muted/muffled).
5. No sound heard- this corresponds to the diastolic blood pressure, the pressure in the arteries when the heart is at rest between beats.

The ventricular contraction and thus, the pressure gradient between the aorta and the right atrium drives the blood during the systemic circulation.

Pressure gradient= Mean arterial pressure (MAP)- Central venous (right atrial) pressure (CVP)

The average arterial blood pressure during a single cardiac cycle, which involves contraction and relaxation of the heart.

Normal range is about 70 - 105 mmHg

Inadequate perfusion of tissues (must be 60+ mmHg)

Can damage blood vessels and create extra strain

1. MAP = [(2x diastolic pressure) + systolic pressure]/3
2. DBP + 1/3 pulse pressure

The volume of blood pumped by each ventricle per minute

The volume of blood pumped by each ventricle per heartbeat

The sum of resistance of all vasculature in the systemic circulation. The arterioles are the main vessels providing resistance.

1. MAP = [(2x diastolic pressure) + systolic pressure]/3
2. MAP = DBP + 1/3 pulse pressure
3. MAP = CO x SVR = HR x SV x SVR

The baroreceptor reflex is a negative feedback mechanism to regulate blood pressure. It consists of three components:-

1. Pressure sensor- baroreceptors
2. Control centre- medulla
3. Effectors- Heart (HR, SV) and blood vessels (SVR).

Arch of aorta and the carotid sinus

Baroreceptors cannot regulate blood pressure long-term because firing decreases if high blood pressure is sustained.

1. Increased arterial pressure stretches the wall of the blood vessel, triggering the baroreceptors.
2. These baroreceptors then feedback to the autonomic nervous system. 3)The ANS then acts to reduce the heart rate and cardiac contractility via the efferent parasympathetic fibres (vagus nerve), and decrease sympathetic constrictor tone (decreasing SVR), thus reducing blood pressure.

1. Decreased arterial pressure is detected by baroreceptors, which then trigger a sympathetic response.
2. This stimulates an increase in heart rate and cardiac contractility, and increased sympathetic constrictor tone (increasing SVR), leading to an increased blood pressure.

The postural hypotension results from a failure of the baroreceptor responses to gravitational shifts in blood, when moving from horizonal to vertical position.

1. Decreased baroreceptor firing then triggers a sympathetic response
2. This stimulates an increase in heart rate and cardiac contractility, and increased sympathetic constrictor tone (increasing SVR), leading to an increased blood pressure.

A positive result is indicated by a drop, within 3 minutes of standing from lying position:

1. In systolic blood pressure of at least 20 mmHg (with or without symptoms).
2. A drop in diastolic blood pressure of at least 10 mm Hg (with symptoms).