L42 – Generation and Control of Arterial Pressure Flashcards Preview

MBBS I CPRS > L42 – Generation and Control of Arterial Pressure > Flashcards

Flashcards in L42 – Generation and Control of Arterial Pressure Deck (45):

What causes arterial walls to stretch and store energy in systole?

Systole > increase blood volume in artery > blood cannot quickly pass through the peripheral resistance (arterioles) > elastic arteries stretch > energy required for stretching stored as potential energy in the stretched arterial wall


What maintains Maintain high pressure in arterial system during diastole?

arteries recoil elastically

Return potential energy to blood > Continues to drive blood through the peripheral resistance


How to calculated Cardiac output?

CO = Stroke volume x HR


Calculate mean arterial blood pressure?

Cardiac output x Total peripheral resistance

Diastolic P + 1/3 pulse pressure


What is pulse pressure?

(difference between systolic and diastolic pressure)


How does increase Cardiac output lead to higher pressure?

Increase CO > increase flow from heart into artery > increase volume in artery > increased stretch, more potential energy into arterial wall > higher pressure


How does increase TPR cause increase in pressure?

Increase TPR> less blood flow out of artery into capillary > increased volume in artery > increased stretch... etc > increase pressure


In diastole, artierial pressure is constant or not?

Flow is continuous even if heart pumping is discontinuous

But arterial pressure continues to drop as blood moves against TPR during diastole


What does arterial pressure depend on?

1. Volume added to artery by each heart beat: stroke volume

2. “run-off” (= volume flowing out of artery to periphery)


What is “run-off” (= volume flowing out of artery to periphery) determined by?

 Peripheral resistance
 Heart rate (inversely rated to time available for run-off)


What is normal BP?



What is prehypertension?



What is grade 1 hypertension?



What is grade 2 hypertension?



4 factors for BP variation between people?

1. Age (BP expected to increase with age):
 Changes in blood vessel structure (see above)
 Decrease in exercise level, endothelial function (secrete fewer vasodilators)

2. Gender (higher in men than women)

3. Race (higher in African, lower in Chinese)

4. Genetics (similar to parents), etc.


What physiological changes can change BP?

 Posture (see baroreceptor reflex)
 Activity level
 Mental activity (e.g. stress, excitement)
 Hormone levels > circadian rhythm


Target BP for adult without diabetes or chronic kidney disease under and over 60?

Under 60 = <140/90

Over 60 = <150/90


Target BP for adult with diabetes or chronic kidney disease?

18 or over = <140/90


Pressure in vessel is calculated by?

Volume of blood in vessel/ compliance of vessel wall


How does change in volume of blood in vessel change compliance?

Normal volume = mainly elastin fibres are stretched = relatively compliant

Larger volumes: collagen fibres (less distensible) are also stretched = less compliance


Shallow gradient on pressure volume curve shows high or low compliance?

Shallow = high compliance


How does aging affect vessel compliance?

elastin fibres in arterial wall tend to become broken into shorter lengths > arteries can easily expand to a volume where collagen fibres are stretched > decrease arterial compliance > larger pulse pressure


In what circulation does the sympathetic nervous system maintain autoregulation of blood flow?

cerebral circulation


How is HR and run-off related?

HR is inversely related to run-off

High HR = less time available = low run-off


How does increase in HR but no change in SV change the BP?

Increase HR > less time for blood to empty out of artery to peripheral vessel > incomplete run-off to peripheral vessels > volume in artery increases > Increase in both systolic and diastolic BP


Increase HR + same SV = increased CO

Why does the systolic pressure increase slightly more than the diastolic ?

Same increases in systolic and diastolic arterial volumes > but systolic pressure increases slightly more because the upper part of the pressure/ volume curve is steeper


How does increase in SV but no change in HR change the BP?

Each heartbeat adds larger volume to artery > increase systolic arterial volume

Insufficient time for this larger volume to run off completely to periphery > also increase diastolic arterial volume

Large SV = systolic increases much more than diastolic


What does larger pulse pressure indicate?

pulse pressure = systolic P – diastolic P > larger pulse pressure implies increased stroke volume


How does increase in TPR change the BP?

Increase TPR > less run-off > diastolic arterial volume increase > diastolic arterial pressure increase

Less run-off > less venous return > Stroke volume also decreases > Systolic volume basically unchanged


What does small pulse pressure indicate?

Smaller pulse pressure implies increase in peripheral resistance


Systolic pressure is strongly dependent on ?

Cardiac output


Diastolic pressure is strongly dependent on ?



What regulates short term change in BP? Long term change in BP?

Short-term = baroreceptors

Long-term = adjust blood volume by volume receptors


Where are baroreceptors for regulating systemic arterial pressure?

Carotid sinus, aortic arch


How does increase in BP cause baroreceptor firing?

High BP> increase transmural pressure > stretches arterial wall > distorts baroreceptor within the wall > receptors depolarize >firing of nerve impulses in proportion to BP within sensitive range


What are the carriages of afferent signals for cartoid sinus baroreceptor?

glossopharyngeal nerve (CN IX) > nucleus tractus solitaries in medulla > cardiovascular centre


What are the carriages of afferent signals for aortic arch baroreceptor?

vagus nerve (CN X) > nucleus tractus solitaries in medulla > cardiovascular centre


How do baroreceptors fire at exceptionally high and low BP?

V. High > reach maximum firing

V. Low > baroreceptors stop firing below threshold already > cannot signal lower than threshold BP drop > rely on chemoreceptors instead


What are the sensitive ranges for baroreceptors?

Carotid sinus= ~50 – 180 mmHg

Aortic arch= ~80 – 200 mmHg


When do baroreceptors show DYNAMIC response?

burst of firing during the rising (anacrotic) limb of arterial pressure wave (e.g. ventricle contracts)

always fire at the start of systole > tell HR


When do baroreceptors show STATIC response?

number of impulses produced (e.g. after dynamic stroke) is proportional to mean pressure > tell mean pressure


Baroreceptor firing due to increased in BP is coordianted at Cardiovascular centre by what mechanisms?

Decrease sympathetic tone in Heart, Arteriole and Veins:

1) Decrease sympathetic, increase parasympathetic (vagal) tone on heart> lower HR and contractility > lower CO

2) Decrease sympathetic tone on arterioles> vasodilation > lower TPR

3) Decrease sympathetic tone on veins (increase compliance) > lower venous pressure & venous return > lower CO


During exercise, how is cardiovascular center signaled?

hypothalamus takes control > signal CV center > physiological change > increase BP


Cardiovascular centre integrates information from which 3 centers/ receptors?

CVS receptors


Higher centres


Explain fainting in vasovagal syncope?

Higher centre > CV centre:

1) Sudden withdrawal of sympathetic noradrenergic tone on blood vessels
2) Sudden increase in vagal tone on heart > bradycardia

Sudden drop in TPR and BP

cerebral pressure drop below 40mmHg > low cerebral flow > faint

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