The Systemic Arterial Blood Pressure

Question 1

What can the arterial pulse be described as?

Answer 1

reflected pressure wave

pumping blood out the heart with resistance to this blood flow

Question 2

What does the lowest pulse pressure correspond to?

Answer 2

diastolic BP

around 70mmHg

Question 3

What causes the increase in pulse pressure?

Answer 3

ejection phase

Question 4

What does the peak pulse pressure correspond to?

Answer 4

systolic BP

around 120 mmHg

Question 5

What causes a slight second notch/peak in pressure after systole?

Answer 5

closure of aortic valve

Question 6

What can be calculated if diastolic and systolic BPs are known?

Answer 6

Mean Arterial Pressure

Question 7

How to calculate the mean blood pressure

Answer 7

mean BP = (DBP + 1/3PP)

Question 8

What is the pulse pressure?

Answer 8

difference between SBP and DBP

Question 9

What is SBP determined by?

Answer 9

stroke volume

aortic elasticity

Question 10

How is SBP affected when stroke volume is increased?

Answer 10

increase in SBP

Question 11

How is SBP affected when aortic elasticity is decreased?

Answer 11

increase in SBP

Question 12

Why does aortic elasticity affect SBP?

Answer 12

elastic aorta takes up kinetic energy from the blood during systole and dampens the rise in pressure

Question 13

Clinical relevance of aortic elasticity and SBP

Answer 13

aortic elasticity reduces as age increases

therefore inelastic aortas may cause systolic hypertension in the elderly

Question 14

What is DBP determined by?

Answer 14

mainly peripheral resistance
aortic elasticity
heart rate

Question 15

How is DBP affected if total peripheral resistance is increased?

Answer 15

increased DBP

Question 16

How is DBP affected when aortic elasticity is decreased?

Answer 16

decreased DBP

Question 17

Why is does aortic elasticity affect DBP?

Answer 17

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

Question 18

How is DBP affected when heart rate decreases?

Answer 18

decreased DBP

Question 19

Clinical relevance of aortic elasticity and DBP

Answer 19

less taken up, less to give back

causes wide pulse pressure in elderly

Question 20

How to calculate mean arterial blood pressure

Answer 20

cardiac output x total peripheral resistance

Question 21

How does systemic and pulmonary circulation compare?

and why?

Answer 21

systemic resistance around 20 au, pulmonary is 2 au

due to much lower mean pulmonary arterial pressure (cardiac output is the same)

Question 22

Why is control of arterial blood pressure important?

Answer 22

provides a pressure head to drive blood flow

permits activity, postural changes - protects against effects of gravity

Question 23

How is control of arterial BP achieved?

Answer 23

feedback system:
pressure sensors in circulation to brain (afferent)
integration centres in CNS - output (efferent)
effector mechanisms via autonomic nervous system

Question 24

What are the pressure sensors?

and where are they located?

Answer 24

arterial (high pressure) baroreceptors - walls of carotid sinus and aortic arch
cardiopulmonary (low pressure) baroreceptors - pulmonary vasculature, atrial-vena caval junctions, ventricular walls

Question 25

How do the arterial baroreceptors work?

Answer 25

increase in transmural pressure increases afferent nerve discharge and vice versa carotid sinus/aortic nerves, glossopharyngeal and vagus (IX and X cranial nerves)

Question 26

What are effector mechanisms?

Answer 26

autonomic control of the circulation

Question 27

What do effector mechanisms affect?

Answer 27

Heart and total peripheral resistance

Question 28

How do effector mechanisms affect the heart?

Answer 28

activation of: parasympathetic - acetylcholine, muscarinic receptors, decrease HR sympathetic - noradrenaline, β1-adrenoceptors, increase HR and force

Question 29

How do effector mechanisms affect total peripheral resistance?

Answer 29

sympathetic activated release of NA, bind onto α1-adrenoceptors on smooth muscle cells causing vasoconstriction which increases total peripheral resistance

Question 30

How do the cardiopulmonary baroreceptors work?

Answer 30

'volume receptors' - reflection of volume as blood returned to the heart increase in transmural pressure - oncrease in afferent nerve discharge (vagus)

Question 31

Where are the integration centres?

Answer 31

medulla

Question 32

What occurs to the afferent nerve activity in the integration centres?

Answer 32

``` 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 ```

Question 33

What effect does a nerve activity in the caudal ventrolateral medulla have?

Answer 33

it is a depressor decreases sympathetic efferent activity decrease total peripheral resistance and BP

Question 34

What effect does a nerve activity in the rostral ventrolateral medulla have?

Answer 34

it is a pressor increases sympathetic efferent activity increases total peripheral resistance and BP

Question 35

What effect does a nerve activity in the cardiac vagal nuclei have?

Answer 35

sends signal to nucleus ambiguus control cardiac vagal efferent activity switched on - increase parasympathetic activity

Question 36

How are pressor areas activated?

Answer 36

tonically active | baroreceptors tonically inhibit it

Question 37

How are depressor areas activated?

Answer 37

not tonically active | activated by an increase in baroreceptor afferent nerve discharge

Question 38

What happens when arterial BP decreases?

Answer 38

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

Question 39

What occurs when someone goes from a supine position to standing?

Answer 39

gravity causes blood to pool in legs and abdomen decreases venous return (immediate) decreases cardiac output and MAP (F-S law) blood pressure fallen

Question 40

What is the body's postural reflex to standing from supine?

Answer 40

unload cardiopulmonary and arterial baroreceptors decrease afferent discharge via NTS/medulla decrease vagal efferent, increase sympathetic efferent increased HR, StV and vasoconstriction BP restored

Question 41

How does the steady state of someone just gone from supine position to standing differ to normal?

Answer 41

``` 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 ```