Blood pressure Flashcards
What is blood pressure
Hydrostatic pressure exerted by blood against walls of blood vessels
High BP in arteries & low BP in veins – must have pressure difference for blood to flow
What is systolic & diastolic pressure
Systolic – highest pressure reached during ejection phase (120)
Diastolic – lowest pressure reached during ventricular filling phase (80)
What is mean arterial pressure
Usual range: 70-110mmHg
Dependent upon where in body measured
Increased HR will move MAP closer to systolic as diastole will be shortened
Dependent on cardiac output, total peripheral resistance, blood volume & composition
How is mean arterial pressure measured
Arterial pressure measured using:
Sphygmomanometer (non-invasive)
Invasive method with fluid filled catheter
Factors that affect measurement of BP:
Emotional state (pain/fear)
Cuff size
Position/posture
Temperature
Full bladder
What is pulse pressure
Pulse pressure = systolic – diastolic
High pulse pressure ≠ high MAP & thus doesn’t mean good tissue perfusion
What receptors regulate BP in the short term
In short term, BP is monitored by baroreceptors (sensitive to stretch) & chemoreceptors (sensitive to pO2 & pCO2 changes) located in carotid sinus & aortic arch
Information is integrated in medulla oblongata
Autonomic nervous system then makes appropriate changes
What is autoregulation
Ability to maintain local pressure despite arterial pressure changes
Brain, kidney, heart
What factors affect blood pressure
Cardiac output:
Increased CO = increased BP
Sympathetic stimulation = increases heart rate & force of contraction
Parasympathetic stimulation: decreases heart rate & force of contraction
Total peripheral resistance:
Sympathetic stimulation increases BP
Blood volume & viscosity:
Loss of blood leads to decreased BP
Increased viscosity leads to increased BP
What is the response to haemorrhage
Autonomic effects on heart:
Increased heart rate & increased force of contraction sympathetic nervous tone increased – noradrenaline acts on B1 adrenoreceptors
Parasympathetic vagal tone decreased
Increased stroke volume –> increased cardiac output –> increased MAP
Neural effect on adrenal:
Sympathetic stimulation of adrenal glands
Releases adrenaline in blood
Acts on B1 adrenoreceptors
Neural effect on vasculature:
Increased sympathetic tone to vessels stimulates vasoconstriction
Increased systemic vascular resistance –> MAP back to normal
Increased ADH released pituitary in response to reduced blood volume causes vasoconstriction
Increased angiotensin II increases blood vessel tone
Increased EPO increases viscosity
How do kidneys control elevated BP in the long term
When renal artery BP is elevated there is increased perfusion pressure on kidney
Results in reduced Na+ & water re-absorption in proximal tubule which increases Na+ & water excretion
Causes ECF volume to decrease & elevated BP to be diminished
Difference between hypovolaemia & dehydration
Hypovolaemia is fluid loss from vasculature
Hypovolaemic shock is loss of enough vascular fluid to cause inadequate oxygen delivery to tissues
Dehydration is loss of fluid from extracellular fluid & intracellular fluid
How does hypovolaemia affect cardiac function
Preload decreased
Stroke volume decreased
MAP decreased
Tissue oxygen delivery decreased
