This stroke volume calculator determines SV based on cardiac output or Doppler VTI determinations such as LVOT. Below the form there is in depth information on the two methods to calculate stroke volume.
How does this stroke volume calculator work?
This health tool estimates stroke volume based on two different methods, one invasive and one non-invasive. The first tab in the stroke volume calculator employs cardiac output calculations and registered heart rate while the second tab uses the results from the Doppler VTI method.
■ First method of calculation through hemodynamic monitoring:
Stroke volume = Cardiac output in mL/min / Heart rate in bpm
Where cardiac output respects the Fick principle:
CO = VO2 / (Ca - Cv)
■ Second method of calculation:
Since the least variable position to measure cardiac output is the left ventricular outflow tract, this diameter measurement that changes very little during systole and diastole is used to provide information about blood flow and volume alongside the LVOT subvalvular velocity time:
- Left ventricle outflow tract in mm (LVOT);
- LVOT subvalvular velocity time integral in cm (LVOT VTI).
SV = π x (LVOT/2)2 x LVOT VTI x 0.01
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.
Stroke volume guidelines
SV is the volume of blood pumped by the heart (left ventricle) during each heart beat. Stroke volume variation is defined as: End-diastolic volume – End systolic volume during the left ventricular angiogram.
SV normal range is between 60 and 120mL and both ventricles have similar volumes.
For example in a healthy person with an EDV of 120mL and ESV of 50mL, the SV is 70mL.
As a determinant of cardiac output, it reflects the pump function of the heart and decreases in heart failure and other circulatory conditions.
SV varies with heart condition, contractility, preload and afterload.
■ Factors that increase stroke volume:
- Increased venous return;
- Increased vascular resistance;
- Sympathetic stimulation;
- Epinephrine and norepinephrine stimulation;
- Thyroid hormones.
■ Factors that decrease stroke volume:
- Decreased vascular resistence;
- Sodium and potassium concentrations;
- Calcium channel blockers;
- Parasympathetic stimulation.
Another example of SV variation is during exercise when it’s only normal that due to the increased cardiovascular requirements, heart rate and stroke volume increase, therefore increasing the rate at which the heart circulates the entire blood in the body.
At maximal exercise intensity in normal training activities SV can increase up to 120mL while in athletes, the increase is more poignant: up to 200mL. However, there is also a plateau limit to which SV can increase during exercise and when this is reached, SV remains steady.
Stroke volume determinations are also useful in anesthesiology where most anesthetics will decrease stroke volume.
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