Conditioned pain modulation mechanisms may reduce chronic cough, urge to cough

Endogenous inhibitor control mechanisms, particularly those active through pain, may reduce coughing and urge to cough, researchers reported in the European Respiratory Journal.

“The study of conditioned pain modulation mechanisms has been useful in quantifying an individual’s endogenous inhibitor of pain and has provided insights into disease mechanisms and treatment effects,” Emma Hilton, MD, from the division of infection, immunity and respiratory medicine at Manchester Academic Health Science Center at the University of Manchester, U.K., and colleagues wrote. “However, the effectiveness of conditioned pain modulation-like mechanisms in modulating airway sensations and reflexes ... has not been investigated either in healthy volunteers or in patients with refractory chronic cough.”

The randomized, controlled, crossover study enrolled 20 healthy volunteers (mean age, 50 years; 50% women) and 20 patients with refractory chronic cough (mean age, 60 years; 55% women) to investigate the effects of endogenous inhibitory control mechanisms on cough and urge to cough. Patients attended four randomized intervention visits on capsaicin-evoked coughing and urge to cough: immersing a hand in cold water, immersing a hand in warm water alone, immersing a hand in warm water while voluntarily suppressing coughing and no intervention. The researchers recorded urge to cough scores and cough numbers using an ambulatory cough monitor.

Researchers observed a reduction in capsaicin-evoked urge to cough scores (1.6 vs. 2.2; P < .001) and cough numbers (4.8 vs. 7.9; P < .001) with noxious cold water immersion compared with warm water immersion. There were similar reductions in urge to cough during noxious cold water immersion among both healthy volunteers and patients with refractory chronic cough.

Among patients with refractory chronic cough, noxious cold water immersion and voluntary cough suppression interventions were less effective at reducing capsaicin-evoked cough compared with healthy volunteers (P = .041).

According to the researchers, because these mechanisms were impaired in patients with refractory chronic cough compared with healthy volunteers, this implies that cough control failure mechanisms may be more extensive than previously thought.

“The inefficiency of this mechanism in refractory chronic cough patients compared with healthy controls implicates impairment of endogenous inhibitory control mechanisms in the pathophysiology of refractory chronic cough, which may be an important therapeutic target,” the researchers wrote.