Stroke Volume Calculator

Variables and formula

Stroke volume can be measured or estimated through a series of formulas with different variables, obtained through non-invasive and invasive measurement methods.

As a determinant of cardiac output, it reflects the pump function of the cardiac muscle.

■ The first tab uses a method called hemodynamic monitoring:

Stroke volume = Cardiac output in mL/min / Heart rate in bpm

Cardiac output respects the Fick principle:

CO = VO₂ / (Ca - Cv)

■ The second tab uses the Doppler VTI method:

Stroke volume = π x (LVOT/2)² x LVOT VTI x 0.01

Where:

LVOT = Left ventricle outflow tract in mm;

LVOT VTI = LVOT subvalvular velocity time integral in cm.

The LVOT pulsed wave is registered through Doppler in apical long axis or 5 chamber view while the VTI is traced on the ultrasound machine. The LVOT diameter changes very little through the heart contraction and can be assumed as constant and in shape of a circle.

Unfortunately, the former measurement may not be accurate in cases with irregular rhythm or atrial fibrillation.

Stroke volume guidelines

SV is defined as the volume of blood pumped by the heart (from the left ventricle) in the systemic circulation) during one contraction or heart beat. Both ventricles pump similar volumes.

Stroke volume variation is defined as: End-diastolic volume – End systolic volume during the left ventricular angiogram. For example, at a healthy EDV of 120 mL and ESV of 50 mL, the SV is 70 mL which is in the normal range of 60 to 120mL.

Abnormal decreases can be seen in heart failure and other circulatory conditions.

Stroke volume varies with heart condition, contractility, preload and afterload. The table below summarizes the factors that increase or decrease SV:

A normal physiological variation of stroke volume is that during exercise, which is due to an increase in cardiovascular requirement.

The heart rate and SV increase, thus ensuring the heart pumps blood in circulation as required.

In normal maximal exercise intensity SV can increase up to 120mL while in the case of athletes, the increase can go up to 200mL.

SV cannot increase undetermined as there is a physiological individual plateau, that, when reached, SV remains steady.

References

1. Huntsman LL, Stewart DK, Barnes SR, Franklin SB, Colocousis JS, Hessel EA. Noninvasive Doppler determination of cardiac output in man. Clinical validation. Circulation. 1983; 67(3):593-602.

2. Stöhr EJ, González-Alonso J, Shave R. Left ventricular mechanical limitations to stroke volume in healthy humans during incremental exercise. Am J Physiol Heart Circ Physiol. 2011; 301(2):H478-87.

3. Vincent JL. Understanding cardiac output. Crit Care. 2008; 12(4): 174.