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?
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)
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?
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 ?
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?