Arterial blood pressure Flashcards
Blood pressure
the force exerted by blood pushing against the walls of the arteries as he heart pumps blood
Systolic BP
The max pressure in artery generated following ventricular contraction
~120 mm Hg
Diastolic BP
Lowest pressure in artery which occurs during diastole
~80 Hg
Pulse pressure
measure of amplitude of pulse pressure wave
~40 mm Hg
Mean aortic pressure
Average pressure
estimate of average effective pressure forcing blood through the circulatory system
~100 mm Hg
Hypotension
<105/60 mm Hg
blood flow to tissues reduced
cause dizziness etc
Hypertension
> 140/90 mmHg
cause excessive capillary pressures and damage to organs
can cause strokes
relationship between pressure gradient and flow
delta P = flow X resistance
Flow is proportional to the pressure gradient
Resistance is determined by the properties of vessels and of the fluid
Baroreceptors
in carotid sinus and aortic arch respond to changes of blood pressure
only capable of regulating BP over a short time scale
Baroreceptor reflex
Short term regulation of arterial blood pressure
Negative feedback mechanism
Variable -> Baroreceptors -> Sinus nerve -> medullary cardiovascular centres -> Arterioles & Heart
Used eg correction of postural hypotension
Long term control of BP
An increase of volume (hypervolaemia) will raise BP
Decrease (hypovolaemia) will reduce BP
Effective circulating volume ECV
the volume perfusing the tissues
kidneys respond to changes of ECV
e.g. when ECV reduced, Na secretion causes water retention
Autoregulation
for some tissues, blood flow is almost independent of arterial pressure
= AUTOREGULATION
e.g. brain and kidney circulations
Action of adrenaline
Adrenaline released from adrenal medulla under action of preganglionic sympathetic fibres
Acts on B receptors to increase heart rate and force contraction
net effect is to increase cardiac output
Korotkoff sounds
Used with stethoscopes to measure heart rate
