Desensitization of the cough reflex by exercise and voluntary isocapnic hyperpnea

Abstract

Little is known about the effects of exercise on the sensory and cognitive aspects of coughing evoked by inhalation of tussigenic agents. The threshold for the cough reflex induced by inhalation of increasing nebulizer outputs of ultrasonically nebulized distilled water (fog), an index of cough reflex sensitivity, was assessed in twelve healthy humans in control conditions, during exercise and during voluntary isocapnic hyperpnea (VIH) at the same ventilatory level as the exercise. The intensity of the urge to cough (UTC), a cognitive component of coughing, was recorded throughout the trials on a linear scale. The relationships between inhaled fog nebulizer outputs and the correspondingly evoked UTC values, an index of the perceptual magnitude of the UTC sensitivity, were also calculated. Cough appearance was always assessed audiovisually. At an exercise level of 80% of anaerobic threshold, the median cough threshold was increased from a control value of 0.73 to 2.22 ml/min (P<0.01), i.e., cough sensitivity was downregulated. With VIH, the threshold increased from 0.73 to 2.22 ml/min (P<0.01), a similar downregulation. With exercise and VIH compared with control, mean UTC values at cough threshold were unchanged, i.e., control, 3.83 cm; exercise, 3.12 cm; VIH, 4.08 cm. The relationship of the fog nebulizer output/UTC value was linear in control conditions and logarithmic during both exercise and VIH. The perception of the magnitude of the UTC seems to be influenced by signals or sensations arising from exercising limb and thoracic muscles and/or by higher nervous (cortical) mechanisms. The results indicate that the adjustments brought into action by exercise-induced or voluntary hyperpnea exert inhibitory influences on the sensory and cognitive components of fog-induced cough.

Coordination of Breathing with Nonrespiratory Activities

“…The urge to cough is associated with widespread activation of cortical and subcortical structures (179). Hypoxia, exercise, and voluntary hyperventilation also suppress coughing (72,165). It is clear from this description that the cough CPG integrates inputs from a variety of reflex and nonreflex sources and adapts or captures neurons involved in eupnea for use in an augmented inspiratory and expiratory effort aimed at cleansing the airways.…”

Brainstem mechanisms underlying the cough reflex and its regulation

“…Pharyngeal afferents can activate not only the gag reflex (Bassi et al, 2004), but also coughing or the "urge-to-cough"; the receptors implicated are probably innervated by vagal and glossopharyngeal nerves or by trigeminal branches . Central and peripheral mechanisms involved in exercise and voluntary isocapnic hyperventilation may downregulate the cough response (Lavorini et al, 2010;Poussel et al, 2014). However, exercise (electrically induced hindlimb muscular contractions) in ovalbumin-sensitized rabbits fails to produce similar effects (Tiotiu et al, 2017).…”

Cough and exhaled nitric oxide levels: what happens with exercise?

“…(2, 3) However, some clinicians have observed that exercise can exacerbate cough in any child with a pre-existing cough, irrespective of diagnosis. Yet, in adult studies on cough sensitivity to fog (which is dependent on minute volume), desensitization of the cough reflex occurs post-exercise (4). Increased cough is usually associated with increased cough reflex sensitivity.…”