Influence of Smoking Status on Cough Reflex Sensitivity in Subjects with COPD

Cough hypersensitivity and suppression in COPD

Cough reflex hypersensitivity and impaired cough suppression are features of chronic refractory cough (CRC). Little is known about cough suppression and cough reflex hypersensitivity in cough associated with chronic obstructive pulmonary disease (COPD). This study investigated the ability of patients with COPD to suppress cough during a cough challenge test in comparison to patients with CRC and healthy subjects. This study also investigated whether cough reflex hypersensitivity is associated with chronic cough in COPD.Participants with COPD (n=27) and CRC (n=11) and healthy subjects (n=13) underwent capsaicin challenge tests with and without attempts to self-suppress cough in a randomised order over two visits, 5 days apart. For patients with COPD, the presence of self-reported chronic cough was documented, and objective 24-h cough frequency was measured.Amongst patients with COPD, those with chronic cough (n=16) demonstrated heightened cough reflex sensitivity compared to those without chronic cough (n=11): geometric mean±sd capsaicin dose thresholds for five coughs (C5) 3.36±6.88 µmol·L^-1 versus 44.50±5.90 µmol·L^-1, respectively (p=0.003). Participants with CRC also had heightened cough reflex sensitivity compared to healthy participants: geometric mean±sd C5 3.86±5.13 µmol·L^-1 versus 45.89±3.95 µmol·L^-1, respectively (p<0.001). Participants with COPD were able to suppress capsaicin-evoked cough, regardless of the presence or absence of chronic cough: geometric mean±sd capsaicin dose thresholds for 5 coughs without self-suppression attempts (C5) and with (CS5) were 3.36±6.88 µmol·L^-1 versus 12.80±8.33 µmol·L^-1 (p<0.001) and 44.50±5.90 µmol·L^-1 versus 183.2±6.37 µmol·L^-1 (p=0.006), respectively. This was also the case for healthy participants (C5 versus CS5: 45.89±3.95 µmol·L^-1 versus 254.40±3.78 µmol·L^-1, p=0.033), but not those with CRC, who were unable to suppress capsaicin-evoked cough (C5 versus CS5: 3.86±5.13 µmol·L^-1 versus 3.34±5.04 µmol·L^-1, p=0.922). C5 and CS5 were associated with objective 24-h cough frequency in patients with COPD: ρ= -0.430, p=0.036 and ρ= -0.420, p=0.041, respectively.Patients with COPD-chronic cough and CRC both had heightened cough reflex sensitivity but only patients with CRC were unable to suppress capsaicin-evoked cough. This suggests differing mechanisms of cough between patients with COPD and CRC, and the need for disease-specific approaches to its management.

Effect of cigarette smoking on cough reflex induced by TRPV1 and TRPA1 stimulations

BACKGROUND

Recent studies have shown that neurogenic inflammation induced by cigarette smoke is inhibited by TRPA1 antagonist, but not by TRPV1 antagonist. Since cough reflex sensitivity is known to be modified by smoking status, we investigated the effects of cigarette smoking on TRPA1- and TRPV1-induced cough and urge-to-cough in healthy males.

METHODS

Twenty-six healthy never-smokers and 30 healthy current smokers were recruited via public postings. Cough reflex thresholds and urge-to-cough were evaluated by inhalation of capsaicin, a TRPV1 agonist, and cinnamaldehyde, a TRPA1 agonist. The cough reflex thresholds were defined as the lowest concentrations of capsaicin and cinnamaldehyde that elicited two or more coughs (C(2)) and five or more coughs (C(5)), respectively. The urge-to-cough was evaluated using the modified Borg scale.

RESULTS

In capsaicin-induced cough, the cough reflex thresholds, as expressed by C(2) and C(5), in current smokers were significantly higher than those in never-smokers (p<0.01 and p<0.001, respectively). The urge-to-cough log-log slopes in current smokers were significantly lower than those of never-smokers (p<0.001). There were no significant differences in the thresholds of the urge-to-cough between never-smokers and current smokers. In cinnamaldehyde-induced cough, there were no significant differences in cough reflex thresholds in C(2) and C(5) between never-smokers and current smokers, nor were there any significant differences in urge-to-cough log-log slope between never-smokers and current smokers. There were no significant differences in the thresholds of the urge-to-cough between never-smokers and current smokers.

CONCLUSION

The study suggests that smoking has a differential effect on cough responses between TRPV1 and TRPA1 stimulations.

Smoking status and anti-inflammatory macrophages in bronchoalveolar lavage and induced sputum in COPD

BACKGROUND

Macrophages have been implicated in the pathogenesis of COPD. M1 and M2 macrophages constitute subpopulations displaying pro- and anti-inflammatory properties. We hypothesized that smoking cessation affects macrophage heterogeneity in the lung of patients with COPD. Our aim was to study macrophage heterogeneity using the M2-marker CD163 and selected pro- and anti-inflammatory mediators in bronchoalveolar lavage (BAL) fluid and induced sputum from current smokers and ex-smokers with COPD.

METHODS

114 COPD patients (72 current smokers; 42 ex-smokers, median smoking cessation 3.5 years) were studied cross-sectionally and underwent sputum induction (M/F 99/15, age 62 ± 8 [mean ± SD] years, 42 (31-55) [median (range)] packyears, post-bronchodilator FEV1 63 ± 9% predicted, no steroids past 6 months). BAL was collected from 71 patients. CD163+ macrophages were quantified in BAL and sputum cytospins. Pro- and anti-inflammatory mediators were measured in BAL and sputum supernatants.

RESULTS

Ex-smokers with COPD had a higher percentage, but lower number of CD163+ macrophages in BAL than current smokers (83.5% and 68.0%, p = 0.04; 5.6 and 20.1 × 10(4)/ml, p = 0.001 respectively). The percentage CD163+ M2 macrophages was higher in BAL compared to sputum (74.0% and 30.3%, p < 0.001). BAL M-CSF levels were higher in smokers than ex-smokers (571 pg/ml and 150 pg/ml, p = 0.001) and correlated with the number of CD163+ BAL macrophages (Rs = 0.38, p = 0.003). No significant differences were found between smokers and ex-smokers in the levels of pro-inflammatory (IL-6 and IL-8), and anti-inflammatory (elafin, and Secretory Leukocyte Protease Inhibitor [SLPI]) mediators in BAL and sputum.

CONCLUSIONS

Our data suggest that smoking cessation partially changes the macrophage polarization in vivo in the periphery of the lung towards an anti-inflammatory phenotype, which is not accompanied by a decrease in inflammatory parameters.

Perception of urge-to-cough and dyspnea in healthy smokers with decreased cough reflex sensitivity

Background

Although cigarette smoking has been implicated as an important risk factor for the development of respiratory symptoms, the perceptional aspects of two symptoms in smokers have not been fully elucidated. Therefore, we simultaneously evaluated the cough reflex sensitivity, the cognition of urge-to-cough and perception of dyspnea in both healthy smokers and non-smokers.

Methods

Fourteen male healthy never-smokers and 14 age-matched male healthy current-smokers were recruited via public postings. The cough reflex sensitivity and the urge-to-cough were evaluated by the inhalation of citric acid. The perception of dyspnea was evaluated by Borg scores during applications of external inspiratory resistive loads.

Results

The cough reflex threshold to citric acid, as expressed by the lowest concentration of citric acid that elicited two or more coughs (C₂) and the lowest concentration of citric acid that elicited five or more coughs (C₅) in smokers was significantly higher than in non-smokers. The urge-to-cough log-log slope in smokers was significantly milder than that of non-smokers. There were no significant differences in the urge-to-cough threshold between non-smokers and smokers. There were no significant differences in perceptions of dyspnea between non-smokers and smokers.

Conclusions

The study showed that decreased cough reflex sensitivity in healthy smokers was accompanied by a decreased cognition of urge-to-cough whereas it was not accompanied by the alternation of perception of dyspnea. Physicians should pay attention to the perceptual alterations of cough in smokers.

Effect of smoking on cough reflex sensitivity in humans

Despite the importance of cigarette smoking as a cause of respiratory symptoms and disease, until recently there has been little attention on the effect of smoking on cough reflex sensitivity. Recent studies have shown that in otherwise healthy smokers, cough reflex sensitivity is diminished relative to that of nonsmokers. One proposed mechanism, chronic cigarette smoke-induced desensitization of airway cough receptors, is supported by the demonstration that smoking cessation leads to prompt enhancement of cough reflex sensitivity, even after many years of smoking. Furthermore, resumption of cigarette smoking promptly results in suppression of cough reflex sensitivity. These observations have introduced the concept that cough reflex sensitivity in humans is a dynamic phenomenon, able to be modulated by the presence or absence of stimuli such as cigarette smoke, even after prolonged exposure.