Here are some commonly used cardiac POCUS formulae that can be useful when learning advanced Doppler techniques, whether you’re a nephrologist or an intensivist.

A few quick notes before we begin:

Start with the basics. Advanced POCUS depends on strong foundational skills. If you’re unable to consistently obtain good cardiac views, Doppler measurements will likely be inaccurate and could lead to poor clinical decisions.

If you’re just getting started with Doppler, my introductory posts on the Renal Fellow Network provide a helpful overview. You can find them here – Doppler 1, Doppler 2.

Pay attention to the angle. Always aim for a near-parallel angle to blood flow when acquiring Doppler waveforms. Use continuous wave Doppler (CWD) when estimating pressure gradients across valves or septal defects. Use pulsed wave Doppler (PWD) when assessing velocity at a specific site, such as the LV outflow tract or the mitral valve for diastology.

The Simplified Bernoulli Equation (ΔP = 4V²) is central to evaluating transvalvular pressure gradients.

When tracing waveform borders, such as for measuring VTI, it helps to increase the Doppler sweep speed so the envelopes appear wider and easier to trace. For assessing respiratory variation, like in tamponade, a slower sweep speed is better since it shows more envelopes across one or more breathing cycles.

Always take the average of multiple measurements before reporting a value – at least three in sinus rhythm and more if the patient has atrial fibrillation. Patience is essential in hemodynamic assessment – you’re obviously not trying to get these numbers while the patient is actively crashing.

Don’t put too much weight on a single number. Doppler relies on physiologic assumptions that may not hold under all clinical conditions, especially in the presence of significant valvular disease or changes in preload and afterload.

Except for the continuity equation, I have excluded detailed valvular assessment formulae here. They’re not all that useful in most bedside POCUS situations unless you’re working in a perioperative cardiac surgery setting.

LVOT Doppler

Left sided filling pressures

Right sided pressures