A simple model to demonstrate perfusion and diffusion limitation of gases.

TRANSFER OF GASES across the respiratory membrane is limited by either perfusion or diffusion (1). This concept is usually explained in terms of whether a gas reaches its partial pressure equilibrium in the pulmonary capillaries. If it does, the gas is considered to be “perfusion limited,” and if it does not, it is considered to be “diffusion limited.” To facilitate the understanding of this concept, we designed an analogical model using paper cups and water to simulate the physiological principles behind gas transport.