The LVOT Diameter is measured in the parasternal long axis view in mid systole and is usually around 2cm. 

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The LVOT velocity time integral (VTI) provides information regarding blood velocity across the time period of systole and is in the units of cm. It is considered a stroke distance. Typical values are around 15 to 25cm.  One needs to use pulsed wave Doppler in either the apical long axis or 5 chamber view to obtain it. The VTI can be traced out on the ultrasound machine or using digital software offline.

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Recall that:

Cardiac output is = Heart Rate x Stroke Volume 

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and 

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Stroke Volume = LVOT area x LVOT VTI

 

so Stroke Volume= 3.14 (LVOT diameter/2)^2 x LVOT VTI.

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In this example:

 

LV stroke volume = 3.14 (2.0cm/2)^2 x 19cm = 60 cm^3 or 60 ml

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If the heart rate is 100 then 

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Cardiac Output = HR x SV = 100 beats/min x 60 ml/beat = 6000 ml/min or 6.0L/min

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