Cardio Equations

Question 1

Cardiac Output

Answer 1

CO = stroke volume (SV) ×heart rate (HR)

Fick principle:
CO = rate of O2 consumption/
arterial O2 content − venous O2 content

Question 2

Mean Arterial Pressure (MAP)

Answer 2

MAP = CO × total peripheral resistance (TPR)

MAP = 2 ⁄3 diastolic pressure + 1⁄3 systolic pressure

Question 3

Pulse Pressure

Answer 3

Pulse pressure = systolic pressure – diastolic pressure

Pulse pressure is proportional to SV, and inversely proportional to arterial compliance.

INC pulse pressure in hyperthyroidism, aortic regurgitation, aortic stiffening (isolated systolic hypertension in elderly), obstructive sleep apnea ( sympathetic tone), exercise (transient).

DEC pulse pressure in aortic stenosis, cariogenic shock, cardiac tamponade, advanced heart failure (HF).

Question 4

Preload

Answer 4

approximated by ventricular EDV

Question 5

Afterload

Answer 5

approximated by MAP

Question 6

Ejection fraction

Answer 6

EF = SV/EDV = (EDV − ESV)/ EDV