The Systemic Arterial Blood Pressure Flashcards
What can the arterial pulse be described as?
reflected pressure wave
pumping blood out the heart with resistance to this blood flow
What does the lowest pulse pressure correspond to?
diastolic BP
around 70mmHg
What causes the increase in pulse pressure?
ejection phase
What does the peak pulse pressure correspond to?
systolic BP
around 120 mmHg
What causes a slight second notch/peak in pressure after systole?
closure of aortic valve
What can be calculated if diastolic and systolic BPs are known?
Mean Arterial Pressure
How to calculate the mean blood pressure
mean BP = (DBP + 1/3PP)
What is the pulse pressure?
difference between SBP and DBP
What is SBP determined by?
stroke volume
aortic elasticity
How is SBP affected when stroke volume is increased?
increase in SBP
How is SBP affected when aortic elasticity is decreased?
increase in SBP
Why does aortic elasticity affect SBP?
elastic aorta takes up kinetic energy from the blood during systole and dampens the rise in pressure
Clinical relevance of aortic elasticity and SBP
aortic elasticity reduces as age increases
therefore inelastic aortas may cause systolic hypertension in the elderly
What is DBP determined by?
mainly peripheral resistance
aortic elasticity
heart rate
How is DBP affected if total peripheral resistance is increased?
increased DBP
How is DBP affected when aortic elasticity is decreased?
decreased DBP
Why is does aortic elasticity affect DBP?
kinetic energy taken up during systole is given back in diastole, adding to the pressure
if less is taken up, there is less to give back
How is DBP affected when heart rate decreases?
decreased DBP
Clinical relevance of aortic elasticity and DBP
less taken up, less to give back
causes wide pulse pressure in elderly
How to calculate mean arterial blood pressure
cardiac output x total peripheral resistance
How does systemic and pulmonary circulation compare?
and why?
systemic resistance around 20 au, pulmonary is 2 au
due to much lower mean pulmonary arterial pressure (cardiac output is the same)
Why is control of arterial blood pressure important?
provides a pressure head to drive blood flow
permits activity, postural changes - protects against effects of gravity
How is control of arterial BP achieved?
feedback system:
pressure sensors in circulation to brain (afferent)
integration centres in CNS - output (efferent)
effector mechanisms via autonomic nervous system
What are the pressure sensors?
and where are they located?
arterial (high pressure) baroreceptors - walls of carotid sinus and aortic arch
cardiopulmonary (low pressure) baroreceptors - pulmonary vasculature, atrial-vena caval junctions, ventricular walls
How do the arterial baroreceptors work?
increase in transmural pressure increases afferent nerve discharge and vice versa
carotid sinus/aortic nerves, glossopharyngeal and vagus (IX and X cranial nerves)
What are effector mechanisms?
autonomic control of the circulation
What do effector mechanisms affect?
Heart and total peripheral resistance
How do effector mechanisms affect the heart?
activation of:
parasympathetic - acetylcholine, muscarinic receptors, decrease HR
sympathetic - noradrenaline, β1-adrenoceptors, increase HR and force
How do effector mechanisms affect total peripheral resistance?
sympathetic activated
release of NA, bind onto α1-adrenoceptors on smooth muscle cells
causing vasoconstriction which increases total peripheral resistance
How do the cardiopulmonary baroreceptors work?
‘volume receptors’ - reflection of volume as blood returned to the heart
increase in transmural pressure - oncrease in afferent nerve discharge (vagus)
Where are the integration centres?
medulla
What occurs to the afferent nerve activity in the integration centres?
goes to nucleus of the tractus solitarius (NTS) passed to 3 subsets of the medulla: 1. caudal ventrolateral medulla 2. rostral ventrolateral medulla 3. cardiac vagal nuclei
What effect does a nerve activity in the caudal ventrolateral medulla have?
it is a depressor
decreases sympathetic efferent activity
decrease total peripheral resistance and BP
What effect does a nerve activity in the rostral ventrolateral medulla have?
it is a pressor
increases sympathetic efferent activity
increases total peripheral resistance and BP
What effect does a nerve activity in the cardiac vagal nuclei have?
sends signal to nucleus ambiguus
control cardiac vagal efferent activity
switched on - increase parasympathetic activity
How are pressor areas activated?
tonically active
baroreceptors tonically inhibit it
How are depressor areas activated?
not tonically active
activated by an increase in baroreceptor afferent nerve discharge
What happens when arterial BP decreases?
unload arterial baroreceptors
decreases afferent nerve discharge (decreased vagal nerve activity)
decreases tonic inhibition at pressor area
increase in sympathetic nerve activity
increased HR + force (=StV) and therefore cardiac output
increase in peripheral resistance (α1)
returns BP towards normal
What occurs when someone goes from a supine position to standing?
gravity causes blood to pool in legs and abdomen
decreases venous return (immediate)
decreases cardiac output and MAP (F-S law)
blood pressure fallen
What is the body’s postural reflex to standing from supine?
unload cardiopulmonary and arterial baroreceptors
decrease afferent discharge via NTS/medulla
decrease vagal efferent, increase sympathetic efferent
increased HR, StV and vasoconstriction
BP restored
How does the steady state of someone just gone from supine position to standing differ to normal?
lower StV - decreases SBP lower than normal cardiac output, higher HR - increases DBP higher than normal TPR (due to acticated sympathetic NS) - increases DBP same BP
