Cardio Equations * Flashcards
CO =
SV x HR
- also: (MAP - Right atrial P) / TPR
- R atrial P = preload
Ficke equation; CO =
rate of O2 consumption/ (arterial O2 cont. - venous O2 cont)
MAP = (#1)
CO x TPR
MAP = (#2)
2/3 diastolic pressure + 1/3 systolic pressure
what does MAP give a measure of
afterload!
pulse pressure =
systolic pressure - diastolic pressure
what is pulse pressure proportional to?
stroke volume
SV = (2 equations)
CO/ HR = EDV - ESV
what two factors maintain HR in early exercise? Late exercise?
HR and SV increase initially, but SV can only increase so much, so eventually only HR is increasing to ↑ HR
what happens to CO if HR gets too high
as HR ↑ diastolic filling is incomplete, so CO ↓
two conditions that ↑ HR leads to ↓ CO
Ventricular tachycardia and atrial fibrillation
What three variables affect SV
- Contractility
- Preload
- Afterload
- ” SV CAP”
Contractility (and SV) increase in what 3 changes?
- Catecholamines (β1 agonism = ↑[Ca] intracell by stimulating SR release)
- ↓ extracell Na+
- Digitalis⇒ (blocks Na/K pump, leading to ↑ [Na] intracell; this ↓ action of Ca/Na pump that pumps Ca out of cell = ↑ intracell Ca
Contractility (and SV) decrease in what 5 ways
- β1 blockade (↓cAMP)
- Heart failure (systolic dysfunction)
- Acidosis
- Hypoxemia/ Hypercapnia
- Non-DHP CCB (verapamil)
* also MI ( loss of myocardium)
mycocardial O2 demand is increased when what 4 variables increase?
- ↑ afterload (proportional to arterial pressure)
- ↑ contractility
- ↑ HR
- ↑ heart size (↑ wall tension)
Preload is roughly equal to what 3 other measures?
- ventricular EDV
- Right atrial pressure
- Central venous pressure
Afterload is equal to what
MAP (proportional to TPR)
Venodilators decrease what? example of one
Preload (vEno = prEload)
- nitroglycerin is venodilator
vasodilators (arterial) decrease what? example
afterload (vAso = Afterload)
- hydralazine is vasodilator
preload increases in what 3 conditions
- exercise (slightly)
- ↑ blood volume (pregnancy, overtransfusion over hydration)
- excitement (↑ sympathetic activity)
what usually happens to CO or SV as preload (ventricular EDV) increases? (Starling curve)
usually increases in healthy individuals⇒ force of contraction is proportional to end-diastolic length of cardiac muscle fiber
why can CO or SV increase even more during exercise with increasing preload than under normal conditions
sympathetic nerve stimulation⇒ β1 stimulation, which increase contractility and thus SV, leading to increased CO
why does the CO or SV actually fall in CHF once preload gets past a certain point (starling curve rises, then begins to dip)
fluid overload⇒ overloads capacity of SV to increase anymore and past a certain point is actually counter-productive (drop in CO)
*CHF already have high preload to begin with (starling curve shifted to the right)
what drug can be helpful in maintaining CO in CHF
digoxin ⇒ ↑ contractility, increasing SV
