Heart function measurement

Heart rate (HR)

Heart rates are measured in beats per minute (bpm). Normal heart rate is 60-100 bpm. 

Heart rate above 100 bpm is tachycardia. Under 60 bpm is bradycardia

Stroke volume (SV)

The stroke volume (SV) indicates the volume of blood pumped out of a heart's ventricles at the end per beat, a healthy heart ejects the same blood volume.

To calculate the stroke volume, first find the:

• end-diastolic volume (EDV) - volume of blood before a ventricular contraction/at the end of the filling stage, diastole. 

• end-systolic volumes (ESV) - volume of blood after a ventricular contraction/at the end of the contracting stage, systole.

Then: EDV (blood before contraction) - ESV (blood after contraction) = SV (blood injected during contraction) 

Cardiac output (CO)

Cardiac output is the volume of blood pumped by the heart per minute. Too high or low of cardiac output indicates a heart problem. 

HR x SV = CO

Mean/Average arterial pressure (MAP)

Mean/Average arterial pressure is the average arterial pressure in a complete cardiac cycle. It's a better indicator than SBP and DBP.

It's calculated by multiplying cardiac output (CO) by total peripheral resistance (TPR):

TPR x CO = MAP 

or by directly multiplying TPR, HR, and SV (recall that HR x SV = CO), together:

TPR x (HR x SV) = MAP

If increasing any of the used units to find MAP, MAP will increase as well.

Total peripheral resistance (TPR)

Total Peripheral Resistance (TPR) is the amount of resistance that blood describes how much resistance blood experiences as it flows through the body's vasculature, as it flows into smaller tubes, creating resistance. 

• vasculature: blood vessel network in an organ or body

When a blood vessel undergoes vasoconstriction, it shrinks, increasing the TPR. 

If vasodilation, it expands, decreasing the TPR.

Auscultation