Wave propagation in physiological collapsible tubes and a proposal for a Shapiro number

In this Brief Communication, a few introductory comments are made first, regarding wave propagation in collapsible tubes and flow limitation, as well as what is commonly referred to as the “speed index”, namely the ratio of the flow velocity in the collapsible tube divided by the wave-propagation velocity. It is then proposed that it is fitting for this speed index to be henceforth named as the Shapiro number.