Cardiac A&P Flashcards
What determines the intrinsic heart rate?
- rate of phase 4 depolarization of the SA node
We can alter the HR by manipulating what 3 variables?
- rate of spontaneous 4 depolarization
- threshold potential
- resting membrane potential
What are the 3 conditions that increase HR? (each causes the threshold to be reached faster)
- rate of spontaneous phase 4 depolarization increases
- rate of phase 4 remains constant but threshold becomes more negative
- rate of phase 4 remains constant, but RMP becomes less negative
What causes increased contractility?
- SNS stimulation
- Catecholamines
- Calcium
- Digitalis
- Phosphodiasterase inhibitors
What causes decreased contractility?
- Myocardial ischemia
- Severe hypoxia
- Acidosis
- Hypercapnia
- Hyperkalemia
- Hypocalcemia
- Volatile anesthetics
- Propofol
- Beta-blockers
- Calcium Channel Blockers
What can set afterload proximal to the systemic circulation?
- aortic stenosis
- hypertrophic cardiomyopathy
- coarctation of the aorta
What reduces wall stress?
- dec. intraventricular pressure
- dec. radius
- inc. wall thickness
LV dysfunction is present when EF is less than what?
- 40%
What is coronary blood flow autoregulation?
MAP 60-140 mmHg
What vasodilators dose the coronary endothelium release as MVO2 increases?
- nitric oxide
- prostaglandins
- hydrogen
- potassium
- carbon dioxide
What causes coronary artery constriction?
- alpha (epidcardial)
- histamine-1
- both inc. IP3 –> inc. intracellular Ca+2
What causes coronary artery dilation?
- Beta-2 (epicardial) - inc. cAMP –> dec. intracellular Ca+2
- Histamine-2 - inc. cAMP –> dec. intracellular Ca+2
- Muscarinic –> NO
When is LV subendocardium best perfused?
- diastole
Is the right heart coronary perfusion affected during the cardiac cycle?
- no, it is well perfused throughout the cardiac cycle
What percent of CO is coronary blood flow?
4-7%
