Function of the Heart as a Pump Flashcards
What are the three primary determinants of cardiac pump function?
- Contractility
- Cardiac loads
- Heart rate
How is cardiac output calculated?
CO = HR x SV
Why does the length of cardiac muscles at rest determine the force of contraction?
At increased length there is increasing overlap of actin and myosin filaments at rest (without stimulation).
= good cross-bridge formation
(length-tension relationship)
What effect does filling have on stroke volume?
Increased filling = increased SV
Decreased filling = decreased SV
What inhibits SNS activity on the heart?
alpha-2 receptors modulate SNS
- inhibits VMC
- inhibits NA release from presynaptic terminal
What stimulates SNS activity on the heart?
PDEI = increased cAMP
What substances act as PDEIs?
- Caffeine
- Milrinone
- Amrinone
What is the end result of digitalis administration?
Increased inotropy
Which two mechanisms mediate apoptosis but play no role in necrosis?
- Activation of the RAAS (Angiotensin II)
2. Cytokines (TNF-alpha)
Which mechanisms mediate both apoptosis and necrosis?
- Activation of the SNS (NE excess)
- Calcium overload
- Decreased oxygen
- Oxygen free radicals (superoxides)
What 3 things determine stroke volume?
- Frank-Starling effects (cardiac preload)
- Contractility
- Afterload (wall stress)
What influences Frank-Starling effects (cardiac preload)?
- Venous return
- Blood volume
- Diastolic function
- HR
What influences contractility?
- SNS: beta-1 adrenergic agonists
- cAMP (PDEI)
- long acting calcium channels
- NA+-K+ ATPase pump / Na+-Ca2+ exchanger
- Adenosine type 1 receptors
- oxygen / ATP
- cell death (apoptosis / necrosis)
- pharmacological depressants
What influences afterload?
Afterload = wall stress:
- pressure
- radius
- wall thickness
