The ‘Q’ In “V/Q Mismatch”

You can’t read about pulmonary physiology without encountering the topic of V/Q mismatch, otherwise known as ventilation-perfusion mismatch. In fact, of the five major etiologies of hypoxemia, V/Q mismatch is the most common!

But that leaves one very important question – if the ‘V’ stands for “ventilation”, why does ‘Q’ stand for “perfusion?”

Without delving into too much history, ‘Q’ comes from “quantité“, the French word for quantity or amount. French scientists like Darcy and Poiseuille derived equations involving rate of flow represented by the variable ‘Q’, and till this day, we often use the same letter to represent flow rates in other branches of science. In this example, ‘Q’ refers to the effective arterial perfusion of alveolar segments. 🙂