Cardiovascular physiology Flashcards
What determines cardiac output?
Cardiac output = heart rate x stroke volume
What is Darcy’s equation?
Flow = pressure / resistance
(cf Ohm’s law, i=v/r)
therefore,
Ventricular volume = BP / SVR
Define stroke volume
Stroke volume = ventricular volume - residual volume (SV=EDV-ESV)
How does hypoxia affect peripheral resistance?
It is a potent vasodilator
What causes peripheral vasodilatation?
- hypoxia
- acidosis
(therefore, tissue need for O2 → ↓PVR → ↑CO)
What causes increased ventricular volume (blood flow back to heart)?
Hypoxia, acidosis, venostriction (sympathetic fight or flight response)
How is ventricular residual volume decreased?
↑contractility
- Frank-Starling curve
- +ve inotropic agents
What is Starling’s law of the heart?
Stroke volume increases in response to increase in volume of blood filling the heart (the end diastolic volume) when all other factors remain constant
How does filling of ventricle increase contractility?
The stretching increases the affinity of troponin C for calcium, causing a greater number of actin-myosin cross-bridges to form within the muscle fibres
What are the 3 effects of the sypathetic / adrenergic system on the heart?
- inotropic (contractility)
- chronotropic (heart rate via SA node ↑Na influx)
- dromotropic (↑AV nodal conduction)
What is the parasympathetic effect on the heart?
↓heart rate via SA node, can be profound (→vasovagal)
What are the 3 determinants of stroke volume?
Preload, afterload, inotropy
Give 6 mechanisms of increased ventricular preload
- ↑CVP [↓venous compliance (sympathetic), ↑volume (i.v., respiration, muscle pump, gravity)]
- ↑ventricular compliance
- ↑atrial force contraction (sympathetic, frank-Starling)
- ↑ventricular filling time (↓HR)
- ↑aortic afterload (secondary effect)
- Pathological (poor LV, AS, AR)
Give 6 mechanisms of reduced ventricular preload
- ↓CVP (blood loss, gravity)
- impaired atrial contraction (e.g. AFib)
- ↑heart rate (↓filling time)
- ↓afterload
- ↓ventricular compliance (e.g. LVH, ↓relaxation)
- inflow valve obstruction