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

Abstract

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.

Evaluation methods and influencing factors of cough sensitivity

“… 18 , 30 An animal study shows that the introduction of a rotating mechanical probe to mechanically stimulate the airway of anesthetized rabbits induces the cough reflex. 11 …”

“…In an animal study, the incidence of cough reflex was related to the intensity, duration, and rate of mechanical stimulation. 11 But in human studies, these factors have not been explored. Also, like the study by Jones et al , 15 the effect difference caused by different vibration frequency and vibration position needs to be further studied.…”

“…9 The concentration of cough-inducing stimulant is used to determine cough reflex sensitivity, 9 which mainly reflects the cough reflex mediated by specific peripheral chemoreceptors. 10 In addition to chemical stimulation, mechanical stimulation can also induce cough directly, [11][12][13][14][15] reflecting the cough reflex mediated by mechanoreceptors. 10 Other indirect methods are also used to evaluate cough sensitivity, including different questionnaires, which subjectively and indirectly evaluate cough sensitivity, and brain functional magnetic resonance imaging (fMRI), which objectively and indirectly evaluates cough sensitivity, showing central nervous system activity related to cough reflex.…”

“…18,30 An animal study shows that the introduction of a rotating mechanical probe to mechanically stimulate the airway of anesthetized rabbits induces the cough reflex. 11 Studies of mechanical stimulation to evaluate cough sensitivity in humans have applied mechanical vibration, including laryngeal vibration and thoracic vibration, to different locations of the airway. For laryngeal vibration, mechanical stimulation is applied to the cervical trachea.…”

Chronic cough—the limitation and advances in assessment techniques

“…Cough can be elicited by the activation of mechanically sensitive vagal afferent nerves projecting to the large airways (some specialised Aδ fibres, commonly named cough receptors) and lungs [mechanoreceptors, including rapidly adapting receptors (RARs) and slowly adapting receptors (SARs)] (15). In preclinical animal studies, the invasive intratracheal mechanical stimulation was found to induce the cough reflex in anaesthetised rabbits/cats/dogs (16)(17)(18)(19)(20). For humans in clinical practice, the common area where the mechanical stimulation has been applied are the large airways level and the chest (8,9).…”