CHAPTER 12 VASODILATORS IN ANGINA Flashcards
Which structure as the highest vascular tone?
Arteriolar tone- major areas of smooth muscle contraction
Venous tone - some but less tone.
What keeps veins flow since they have lower tone?
Series of one way valves keeps blood flowing the correct direction.
Muscle pumps
What percentage of the blood is in the venous system?
70%
What is the pathway of blood vessel contraction?
How does it contract?
- Ca2+ comes causes CICR.
- Ca2+ is released from SR and binds to Calmoudulin.
- Ca2+ Calmouldulin complex activates MLCK
- MLCK adds phosphate group to myosin causing an interaction with actin resulting in contraction.
cAMP will inhibit MLCK, relaxing SM
What are the 3 AHA Angina Classification
Causes and Precipitating Factors?
Stable (Angina of Effort): Caused by plaque, precipitating factor: exercise/stress, can be relieved with rest.
Unstable (Acute coronary syndrome): Caused by plaque, precipitating factor: resting, this is an emergency.
Variant (Prinzmetal): Caused by hyperreactive vessels, precipitating factor: resting, rare: 2% of angina
What is oxygen debt?
Balance of oxygen availability and the oxygen requirement of the heart.
What affects O2 availability?
Arterial O2 concentration (Hgb concentration): Anemic patients will have less O2 carry capacity in the blood.
Coronary Flow and Distribution: Plaque and Shunts
O2 extraction and coronary circulation: Small amount of plaques elsewhere
What contributes to O2 requirement?
HR- Increase HR, Increase O2
Wall Tension- amount of pressure b/w heart and walls of the heart, blood in the heart at any given time.
Contractile State- Increase in systole
How is coronary blood flow related to perfusion pressure, duration of diastole, and to coronary vascular bed resistance?
Directly related to perfusion pressure
Directly related to duration of diastole (coronary blood flow is perfused during diastole)
Inversely proportional to coronary vascular bed resistance (more plaque, less coronary blood flow)
What are the targets to relax vascular tone?
Blocking Ca2+ Channels
Increasing cGMP (removes the phosphate group from MLC causing relaxation)
Target Beta-2 agonist (increase in cAMP to phosphorylate MLCK, inactivating the enzyme), but can have systemic effects.
Actions of NO, Nitrates, Nitrites
Activates GC
Increase cGMP
Relaxation
Actions of Beta-2 Agonist
GPCR
cAMP
Relaxation (mainly respiratory)
Actions of Beta Blockers
Decrease demand by decrease HR
Actions of CCB
Less Ca2+ influx
Relaxation
Actions of Sidenafil
Blocks PDE5
increase cGMP
Relaxation