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

Evidence for Alpha7 Nicotinic Receptor Activation During the Cough Suppressing Effects Induced by Nicotine and Identification of ATA-101 as a Potential Novel Therapy for the Treatment of Chronic Cough

Studies performed in healthy smokers have documented a diminished responsiveness to tussive challenges, and several lines of experimental evidence implicate nicotine as an antitussive component in both cigarette smoke and the vapors generated by electronic cigarettes (eCigs). We set out to identify the nicotinic receptor subtype involved in the antitussive actions of nicotine and to further evaluate the potential of nicotinic receptor-selective agonists as cough-suppressing therapeutics. We confirmed an antitussive effect of nicotine in guinea pigs. We additionally observed that the alpha-4 beta-2 (α ₄ β ₂)-selective agonist Tc-6683 was without effect on evoked cough responses in guinea pigs, while the α ₇-selective agonist PHA 543613 dose-dependently inhibited evoked coughing. We subsequently describe the preclinical evidence in support of ATA-101, a potent and highly selective (α ₇) selective nicotinic receptor agonist, as a potential candidate for antitussive therapy in humans. ATA-101, formerly known as Tc-5619, was orally bioavailable and moderately central nervous system (CNS) penetrant and dose-dependently inhibited coughing in guinea pigs evoked by citric acid and bradykinin. Comparing the effects of airway targeted administration versus systemic dosing and the effects of repeated dosing at various times prior to tussive challenge, our data suggest that the antitussive actions of ATA-101 require continued engagement of α ₇ nicotinic receptors, likely in the CNS. Collectively, the data provide the preclinical rationale for α ₇ nicotinic receptor engagement as a novel therapeutic strategy for cough suppression. The data also suggest that α ₇ nicotinic acetylcholine receptor (nAChR) activation by nicotine may be permissive to nicotine delivery in a way that may promote addiction. SIGNIFICANCE STATEMENT: This study documents the antitussive actions of nicotine and identifies the α₇ nicotinic receptor subtype as the target for nicotine during cough suppression described in humans. We additionally present evidence suggesting that ATA-101 and other α₇ nicotinic receptor-selective agonists may be promising candidates for the treatment of chronic refractory cough.

Impact of Tussigenic Stimuli on Perceived Upper Airway Sensation and Motor Cough Response Following Total Laryngectomy

Background

Total laryngectomy (TL) is standard intervention for carcinoma of the head and neck or, in cases of non-functional larynx, as a result of disease or radiation exposure. Laryngeal extirpation serves as a unique human model of both recurrent and superior laryngeal nerve section and offers insight into motor and sensory aspects of cough: both volitional and in response to tussigenic stimuli. While motor changes in cough function are expected among those status post-TL due to postoperative reconstruction of the upper airway, motor cough parameters have not been well described and sensory aspects of cough are unknown in this population, which provides insight into a vagal denervation model in humans.

Methods

Data were collected from three groups totaling 80 adults (39 male), including 25 healthy younger adults (HYA), 27 healthy older adults (HOA), and 28 adults post-TL. Cough was elicited both upon command and in response to nebulized capsaicin. Outcome measures included urge to cough and cough airflows.

Results

Kruskal–Wallis test showed that two of the three groups differed significantly by urge to cough χ²(2, N = 244) = 8.974, p = 0.011. Post hoc analysis showed that post-TL subjects had reduced perceived urge to cough at all concentrations of capsaicin (p < 0.05). Cough airflows were significantly reduced for post-TL subjects compared to healthy controls in all metrics except post-peak phase integral (PPPI) for which HOA and TLs were comparable under both volitional and capsaicin-induced conditions.

Conclusions

These findings support the hypothesis that both cough airflow and sensations are significantly reduced in post-TL subjects when compared with HOA. Interestingly, HOA and post-TL subjects have comparably reduced UTC and cough airflows when compared to HYA. The only metric of cough airflow for which these groups differ is the PPPI, which may be a compensatory adaptation for reduced cough airflows and/or sensation.

A systematic review of methods of citric acid cough reflex testing

INTRODUCTION

This systematic review summarises and appraises methods of citric acid cough reflex testing (CRT) documented in published literature.

METHODS

Electronic databases, MEDLINE, EMBASE, CINAHL, PsychINFO, Scopus were searched up to and including 11th February 2018. Studies reporting a method of citric acid CRT, published in peer-reviewed journals in English or Spanish, were assessed for the inclusion criteria. Of the selected studies, information on the instrumentation and CRT protocol was extracted.

RESULTS

A total of 129 studies were included. Instrumentation and protocols differed widely across studies. Reporting of methods of citric acid CRT was sub-standard, with many crucial methodological components omitted from published manuscripts, preventing their full replication.

CONCLUSIONS

Considerable methodological variability exists for citric acid CRT in published literature. The findings suggest that caution is warranted in comparing citric acid cough thresholds across studies. Full replication of previously published methods of citric acid CRT is limited due to crucial elements of the citric acid CRT protocol being omitted from published manuscripts. These findings have implications on the use of citric acid CRT in clinical and pharmaceutical studies to evaluate the effects of antitussive medications and cough therapies.

Cough physiology in elderly women with nontuberculous mycobacterial lung infections

Elderly white, thin, nonsmoking women appear to be more susceptible to lung infections with Mycobacterium avium complex and other nontuberculous mycobacteria (NTM). It has been postulated that such disease in women is related to suppression of their cough. We hypothesized that patients with pulmonary NTM (pNTM) infections may have altered cough physiology compared with unaffected control subjects. We used capsaicin-induced cough to assess the cough reflex in pNTM subjects. Eight elderly white women with stable chronic pNTM infections and six unaffected age-matched control subjects were recruited. There was no significant difference between groups in capsaicin-elicited cough motor response, airflow pattern, or cough frequency. The urge-to-cough (UTC) score at the lowest capsaicin concentration was significantly lower in pNTM than control subjects (P < 0.05). There were no significant differences in the UTC score between pNTM and control subjects at >50 μM capsaicin. These results suggest lower UTC sensitivity to the lowest concentration of capsaicin in pNTM than control subjects. In other words, the pNTM subjects do not sense a UTC when the stimulus is relatively small.NEW & NOTEWORTHY This study investigates the cough motor response and cough sensitivity in patients with nontuberculous mycobacteria (NTM) infection. In elderly white female pulmonary NTM subjects, we demonstrated a capacity to produce coughs similar to that of age-matched control subjects but decreased cough sensitivity in response to a low dose of capsaicin compared with control subjects. These findings are important to understand the pathophysiological mechanisms resulting in NTM disease in elderly white women and/or the syndrome developing in elderly white female NTM patients.

Characterization of urge to cough and cough symptoms associated with the common cold: results of a US internet survey

OBJECTIVES

Our knowledge of cough physiology is limited despite years of study. Even less is known about the sensation of urge to cough. Given that limited clinical data are available about urge to cough and cough attributes during a common cold, we sought to gain insights into experiences and perceptions related to these symptoms.

METHODS

An internet survey consisting of 51 questions was fielded in the United States. Eligible survey participants included men and women aged 18 years and older who had suffered from a cold with cough within the three months preceding the survey. Participants who confirmed suffering from recurrent cough, asthma, chronic bronchitis, chronic obstructive pulmonary disease, cystic fibrosis, or gastrointestinal reflux were excluded.

RESULTS

Of 19,530 initial respondents, 8011 had a cold in the past three months. Of these, 6484 (81%) had experienced cough symptoms; 2708 respondents with cough due to cold and no exclusionary condition made up the analysis sample. Most respondents (62%) reported that cough developed one to two days after the onset of cold symptoms, and 45% felt that cough worsened their other cold symptoms. In 69% of respondents, cough outlasted other cold symptoms. Urge to cough was reported by 98% of respondents, and among these respondents, 64% described it as uncontrollable and 65% rated severity as moderate. More than half of respondents (57%) considered the sensation of urge to cough and the act of coughing as equally bothersome. Although urge to cough and inability to control cough were the most bothersome aspects of cough due to cold, few (<20%) respondents asked healthcare providers for treatment recommendations.

CONCLUSION

Symptoms of urge to cough and cough are common and have a significant impact on cold sufferers. Understanding attributes of these symptoms may provide insights for effective management and the development of novel treatment strategies.

Effect of transient receptor potential vanilloid-1 on cough hypersensitivity induced by particulate matter 2.5

AIMS

The mechanism of cough hypersensitivity induced by particulate matter 2.5 (PM2.5) remains elusive. The current study was designed to explore the effect of transient receptor potential vanilloid-1 (TRPV1) on cough hypersensitivity in airway and central nervous system.

MAIN METHODS

The PM2.5-induced chronic cough model of guinea pig was established by exposure to different doses of PM2.5 for three weeks. After exposure, the animals were microinjected with TRPV1 agonist capsaicine, antagonist capsazepine in the dorsal vagal complex respectively. Cough sensitivity was measured by determining the provocative concentration of citric acid inducing 5 or more coughs (C5). Airway inflammation was detected by hematoxylin eosin (HE) staining and Evans blue fluorescence, and substance P (SP) and TRPV1 expressions in airway were observed by immunohistochemical staining. TRPV1 expressions in the dorsal vagal complex were observed by immunofluorescence. Retrograde tracing by pseudorabies virus-Bartha (PRV-Bartha) was conducted to confirm the regulatory pathway between airway and central nervous system.

KEY FINDINGS

PM2.5 induced TRPV1 expressions in both of airway and dorsal vagal complex and airway neurogenic inflammation. Airway vascular permeability increased after being exposed to PM2.5. The expressions of SP in the airway and airway inflammation was increased after microinjecting TRPV1 agonist, and decreased after microinjecting TRPV1 antagonist. PRV infected neurons in medulla oblongata mainly located in the dorsal vagal complex.

SIGNIFICANCE

These findings show that TRPV1 in the dorsal vagal complex could promote airway neurogenic inflammation and cough reflex sensitivity through neural pathways of vagal complex-airways, which indicate the therapeutic potential of specific inhibition of TRPV1 for chronic cough induced by PM2.5.

Effect of viral upper respiratory tract infection on cough reflex sensitivity

Acute viral upper respiratory tract infection (URI; common cold) is among the most common medical conditions affecting man, with cough being a typical feature of the associated syndrome. Studies employing capsaicin inhalation challenge to measure cough reflex sensitivity have demonstrated a transient tussive hyperresponsiveness induced by URI that reverts to normal by 4-8 weeks post infection. Mechanisms proposed to explain the induction of cough by URI include a number of infection-associated airway effects, such as enhanced release of cytokines, neurotransmitters, and leukotrienes; increased neural receptor levels; reduced activity of neutral endopeptidases; transient modulation of afferent neural activity; mucus hypersecretion; and, possibly, effects on cholinergic motor pathways. Recent studies evaluating urge-to-cough (UTC), the sensation of irritation preceding the motor act of coughing, have demonstrated that URI induces a transient enhancement of UTC analogous to the effect observed on cough reflex sensitivity. The recently introduced concept of the Cough Hypersensitivity Syndrome may provide an explanation for the commonly observed clinical phenomenon of acute viral URI triggering what will develop into chronic, refractory cough in a subgroup of patients.

Gender differences in the effect of urge-to-cough and dyspnea on perception of pain in healthy adults

Previous studies have reported that respiratory sensations, such as urge‐to‐cough and dyspnea, have an inhibitory effect on pain. Considering the existence of gender differences in both urge‐to‐cough and pain, it is conceivable that a gender difference also exists in the analgesia induced by urge‐to‐cough. In this study, we evaluated gender differences in the pain perception response to urge‐to‐cough, as well as to dyspnea. Twenty‐seven male and 26 female healthy nonsmokers were originally enrolled. Citric acid challenge was used to induce the urge‐to‐cough sensation, and dyspnea was elicited by inspiratory loaded breathing. Before and during inductions of these two respiratory sensations, perception of pain was assessed by the thermal pain threshold, and differences between men and women were compared. The thermal pain threshold in women (43.83 ± 0.17°C) was significantly lower than that in men (44.75 ± 0.28°C; P < 0.05) during the baseline period. Accompanying increases in both citric acid concentration and inspiratory resistive load, thermal pain threshold values significantly increased in both men and women. The average thermal pain threshold changes for comparable increases in the urge‐to‐cough Borg score were parallel between men and women. Furthermore, the mean value of the thermal pain threshold plotted against the dyspnea Borg score also showed no significant gender difference. These results demonstrate that although gender differences exist in respiratory sensations, that is, urge‐to‐cough and dyspnea, the inhibitory effects of these respiratory sensations on the perception of pain are not significantly different between the sexes.

The relationships between citric acid dose and urge‐to‐cough rating or thermal pain threshold in each subject grouped by sex.

Inhibitory effect of cervical trachea and chest wall vibrations on cough reflex sensitivity and perception of urge-to-cough in healthy male never-smokers

BACKGROUND

Non-pharmacological options for symptomatic management of cough are desired. Although chest wall mechanical vibration is known to ameliorate cough reflex sensitivity, the effect of mechanical vibrations on perceptions of urge-to-cough has not been studied. Therefore, we investigated the effect of mechanical vibration of cervical trachea, chest wall and femoral muscle on cough reflex sensitivity, perceptions of urge-to-cough as well as dyspnea.

METHODS

Twenty-four healthy male never-smokers were investigated for cough reflex sensitivity, perceptions of the urge-to-cough and dyspnea with or without mechanical vibration. Cough reflex sensitivity and 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. Mechanical vibration was applied by placing a vibrating tuning fork on the skin surface of cervical trachea, chest wall and femoral muscle.

RESULTS

Cervical trachea vibration significantly increased cough reflex threshold, as expressed by the lowest concentration of citric acid that elicited five or more coughs (C5), and urge-to-cough threshold, as expressed by the lowest concentration of citric acid that elicited urge-to-cough (Cu), but did not significantly affect dypnea sensation during inspiratory resistive loading. On the other hand, the chest wall vibration not only significantly increased C5 and Cu but also significantly ameliorated the load-response curve of dyspnea sensation.

CONCLUSIONS

Both cervical and trachea vibrations significantly inhibited cough reflex sensitivity and perception of urge-to-cough. These vibration techniques might be options for symptomatic cough management.

Prospective description of coughing, hemodynamic changes, and oxygen desaturation during endoscopic sedation

BACKGROUND

Deep sedation is increasingly used for endoscopy. The impact of sedation level on hemodynamic status, oxygenation, and aspiration risk is incompletely described.

AIMS

To describe the incidence of intraprocedural cough, hemodynamic changes, oxygen desaturation, and their relationship to clinical factors and sedation level.

METHODS

Detailed prospective recordings of hemodynamic changes, oxygen desaturation, and cough during 757 nonemergent endoscopic procedures done under sedation using propofol, midazolam, and/or fentanyl.

RESULTS

Thirteen percent of patients had at least one cough and 3% had prolonged cough. Cough was more common in nonsmokers (P = 0.05), upper endoscopy (P < 0.0001), with propofol (P = 0.0008), longer procedures (P = 0.0001), and hiccups (P = 0.01). The association between supine positioning during colonoscopy and cough approached significance (P = 0.06). Oxygen desaturation was rare (4%) and associated only with deep sedation (P = 0.02). Mean systolic and diastolic blood pressure (BP) dropped by 7.3 and 5.6% respectively. Decreases in systolic BP were more common in whites (P = 0.03), males (P = 0.004), nonsmokers (P = 0.04), during colonoscopy (P < 0.0001), and in patients receiving midazolam and fentanyl (P = 0.01). Heart rate (HR) dropped >20% from baseline in 15% of patients and was more common during colonoscopy (P = 0.002). HR increased >20% in 20% of patients and was more common with coughing (P < 0.0001) and in younger patients (P = 0.0002). No patient required pharmacologic treatment of BP or HR.

CONCLUSIONS

We have described procedural predictors of cough that may help clinicians reduce the risk of aspiration during endoscopy. Hemodynamic changes during endoscopy are common but largely clinically insignificant.

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.

Aging deteriorated perception of urge-to-cough without changing cough reflex threshold to citric acid in female never-smokers

Background

The effect of aging on the cognitive aspect of cough has not been studied yet. The purpose of this study is to investigate the aging effect on the perception of urge-to-cough in healthy individuals.

Methods

Fourteen young, female, healthy never-smokers were recruited via public postings. Twelve elderly female healthy never-smokers were recruited from a nursing home residence. The cough reflex threshold and the urge-to-cough were evaluated by inhalation of citric acid. The cough reflex sensitivities were defined as the lowest concentration of citric acid that elicited two or more coughs (C₂) and five or more coughs (C₅). The urge-to-cough was evaluated using a modified the Borg scale.

Results

There was no significant difference in the cough reflex threshold to citric acid between young and elderly subjects. The urge-to-cough scores at the concentration of C₂ and C₅ were significantly smaller in the elderly than young subjects. The urge-to-cough log-log slope in elderly subjects (0.73 ± 0.71 point · L/g) was significantly gentler than those of young subjects (1.35 ± 0.53 point · L/g, p < 0.01). There were no significant differences in the urge-to-cough threshold estimated between young and elderly subjects.

Conclusions

The cough reflex threshold did not differ between young and elderly subjects whereas cognition of urge-to-cough was significantly decreased in elderly subjects in female never-smokers. Objective monitoring of cough might be important in the elderly people.

Gender differences in perceptions of urge to cough and dyspnea induced by citric acid in healthy never smokers

BACKGROUND

The mechanism of the gender difference in cough reflex threshold has not been clearly elucidated. In the present study, we evaluated gender differences in the cough reflex threshold along with the perceptions of respiratory sensations, urge to cough, and dyspnea.

METHODS

Nineteen male and 20 female healthy never smokers were recruited through public postings. The cough reflex threshold and the urge to cough were evaluated by 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 and suprathreshold to citric acid in women, as expressed by the log transformation of the lowest concentration of citric acid that elicited two or more and five or more coughs, was significantly lower than that in men. The urge-to-cough log-log slope in women (1.47 ± 0.81 point × L/g) was significantly steeper than in men (0.96 ± 0.28 point × L/g; P < .03). There were no significant differences in the urge-to-cough threshold estimated between men and women. The slope of the dyspnea Borg score change during the external inspiratory resistive loads is steeper in women (0.17 ± 0.04 point/cm H₂O/L/s) than that in men (0.13 ± 0.05 point/cm H₂O/L/s; P < .01). The urge-to-cough slope significantly correlated with the perception of dyspnea slope (r = 0.537; P < .01).

CONCLUSIONS

The gender difference in cough reflex threshold accompanied the gender difference in amplification rate of respiratory sensations in the same direction. The higher central gain for common pathways for respiratory sensations may play a role in lower cough reflex threshold in women. Further studies are needed to elucidate this issue.