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.