In Vivo Documentation of Stimulus Velocity Tuning of Mechanically Induced Reflex Cough.

In order to clear airways and lungs defensive reflexes are provoked rather by the dynamic phase of mechanical stimulus. It is speculated that provocation of defensive response depends not only on stimulus duration but also on stimulus velocity. Fourteen adult rabbits were anaesthetized and tracheotomized. Mechanical stimulus was provoked by a mechanical probe introduced through the tracheotomy and rotated by a small electrical motor using a rotational velocity of 40 rpm/s and 20 rpm/s. Threshold, incidence and intensity of cough reflex (CR) were analyzed for each animal. Statistical comparisons between two velocities were performed using Friedman nonparametric test for repeated measurements. Results are median (25-75 %). The threshold of CR was significantly increased (p=0.005) from 350 ms (300-500 ms) to 550 ms (350-1150 ms) and the incidence of cough reflex was significantly reduced (p=0.002) from 50 % (19 50 %) to 0 % (0-25 %) when the rotational velocity of the mechanical probe was reduced by half. The findings of this study are of interest as they show that protective reflex cough, an important mechanism that allows clearing airways even during sleep or anesthesia, is tuned by mechanical stimulus velocity.