Sunday, November 10, 2019

How to calculate SVR and PVR using Ohm's law

Hi!

Ohms law: Current (I) equals the voltage difference (ΔV) divided by resistance (R)
Simplified, V=IR

In hemodynamics, what is voltage difference? The pressure difference or pressure gradient! (ΔP)


Okay, what is resistance? The resistance to blood flow offered by the blood vessels (R).

What is the current? What makes the blood flow? The cardiac output (CO).

Okay, so let's calculate the resistances!

What is the pressure difference (voltage) for the systemic vasculature?
Arterial pressure - Venous pressure! That is, Mean Arterial Pressure (MAP) and Central Venous Pressure (CVP).

What is the pressure difference (voltage) for the pulmonary vasculature?
Again, arterial pressure - venous pressure. That is,  Mean Pulmonary Arterial Pressure (mPAP)- Pulmonary Capillary Wedge Pressure (PCWP).

Therefore,

SVR = MAP - CVP / CO

PVR = mPAP - PCWP / CO

That's all!

Isn't it cool how physics applies to medicine? :)

-IkaN

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