Physiology of Blood Pressure

Question 1

Two Ways to Increase BP

Answer 1

• increase CO (increase HR or stroke volume)

- increase SVR (reduce diameter of vessel

Question 2

Resistance - Radius Relationship

Answer 2

Resitance = 1/radius to the 4th power

Question 3

Patient Extremities When Vasodilated

Answer 3

Vasodilation = Bigger Diameter = Lower SVR = More Blood Flow = Extremities are warm and pink

Question 4

Patient Extremities When Vasoconstricted

Answer 4

Vasoconstriction = Lower Diameter = Higher SVR = Less Blood Flow = Extremities are cold and pale

Question 5

Measuring SVR

Answer 5

• PA (Swan Ganz) catheter -> uses thermodilution
• physical exam of extremities
• vasodilation = low SVR = warm extremities
• vasoconstriction = high SVR = cold extremities

Question 6

Cardiac Output Equation

Answer 6

CO = HR x SV

Question 7

Baroreceptors

Answer 7

• baroreceptors found in arch of aorta and carotid sinus

- send afferent info to brain in a tonic manner

Question 8

Cascade of Baroreceptors

Answer 8

• baroreceptors send info to medulla of brain
• medulla affects 3 pathways directly
  
  • PSNS
  • SNS
  • AVP
• medulla activates PSNS, which in turn lowers HR, resulting in lower CO
• medulla inhibits SNS, which results in lower HR and SV resulting in lower CO, lower SVR, and reduced Renin-AII release
• reduced Renin-AII release results in lower SVR, lower aldosterone release, no effect on blood volume
• medulla inhibits AVP release, which therefore cannot increase blood volume

Question 9

Cascade of Baroreceptors in Hypotension

Answer 9

• reduced stretch of baroreceptors produces reduced activity of baroreceptors, reduced activity in medulla
• reduced activity in medulla produces reduced activity in PSNS, increased activity in SNS, increased AVP release
• reduced activity in PSNS results in increased HR, increasing CO
• increased activity in SNS results in increased SV and SVR, increasing CO and BP
• increased activity in SNS results in increased Renin-AII release, increasing SVR, and increasing aldosterone release, which increases blood volume
• reduced activity in medulla produces increased AVP release which increases blood volume
• increased SV and SVR return BP to normal, long term increase in blood volume

Question 10

SNS receptors

Answer 10

• beta 1 in heart
• alpha 1 in blood vessels
• acted on by noradrenaline

Question 11

PSNS receptors

Answer 11

-acetylcholine binds muscarinic receptors

Question 12

Angiotensin II

Answer 12

-increases SVR

Question 13

Aldosterone

Answer 13

-increases BV

Question 14

AVP

Answer 14

-increases BV

Question 15

Noradrenaline binding alpha 1

Vasopressin and AII binding receptors

Answer 15

-increased MLCK activity, producing vasoconstriction and venoconstriction

Question 16

Orthostatic Hypotension

Answer 16

-failure to increase HR and SVR in response to postural changes to compensate for gravity

Question 17

Local Regulators of Vasoconstrictiong/Dilation

Answer 17

Endothelin

Nitric Oxide

Question 18

Endothelin

Answer 18

• produced by endothelial cells
• powerful vasoconstrictor
• activates MLCK producing contraction
• important in hypoxia in lungs - shift blood away from hypoxic areas to ensure oxygenation

Question 19

Nitric Oxide

Answer 19

• produced from arginine by nitric oxide synthase
• diffuses into cells and results in phosphorylation of MLCK, reducing contraction and producing vasodilation
• synthesized in endothelial cells

Question 20

NO Treatment of chest pain

Answer 20

• produces vasodilation of coronary arteries, increases oxygen supply to myocardium
• produces venodilation, reduces blood return to heart, reduces preload, reduces oxygen demand of myocardium