On the psychology of cough

Provision, cough efficacy and treatment satisfaction of mechanical insufflation-exsufflation in a large multicenter cohort of patients with amyotrophic lateral sclerosis

In patients with amyotrophic lateral sclerosis (ALS), mechanical insufflation-exsufflation (MI-E) addresses cough deficiency to achieve major therapeutic goals: improving costal muscle and joint function, reducing atelectasis through insufflation, and clearing bronchial secretions via exsufflation. Despite its perceived benefits, there is limited systematic research on MI-E provision, symptom alleviation, or patient satisfaction. The research platform Ambulanzpartner coordinated this longitudinal observational study conducted in 12 German ALS centers from July 2018 to September 2023. Patients were enrolled based on ALS-related cough deficiency requiring MI-E therapy. The study recorded provision, reasons for withholding MI-E, clinical parameters, therapy frequency, subjective cough deficiency, and symptomatic relief. Satisfaction with MI-E therapy was determined by the likelihood of recommendation. Out of 694 ALS patients indicated for MI-E, 527 (75.9%) received the therapy. The primary reason for non-provision was that the patient had died before provision (n = 66 of 167; 39.5%). These patients were significantly more affected as represented by higher progression rates and lower cough peak flows (CPF) at the time of MI-E indication (p < 0.05). Most patients who received MI-E used it daily (n = 290 of 370; 78.4%). Self-assessed cough deficiency correlated with clinical measurements, especially for patients with higher deficits. At follow-up visits, patients reported reduced cough deficiency (p < 0.001). Frequent MI-E use was linked to greater symptom relief and higher likelihood of recommending the therapy. This study highlights the symptomatic and palliative potential of MI-E therapy for ALS patients.

Reframing Refractory Chronic Cough: The Role of Interoception

Refractory chronic cough (RCC) remains a persistent clinical challenge, often resistant to traditional treatments. Emerging evidence now positions RCC as a disorder rooted in hypersensitivity, driven primarily by central neural processes rather than external physiological causes. Central to this understanding is the concept of interoception-the brain's ability to perceive and interpret internal bodily signals. Neuroimaging research has identified abnormalities in brain regions associated with interoception and inhibitory control among RCC patients. Interestingly, RCC shares neurophysiological characteristics with other disorders like overactive bladder and urinary urge incontinence (OAB/UUI), which also involve dysregulated interoceptive and inhibitory mechanisms. Behavioral treatments for OAB/UUI are highly effective and are regarded as the first-line treatment in many consensus guidelines. OAB/UUI behavioral treatments have been shown to induce central neuroplastic changes, further underscoring their efficacy and potential parallel for RCC interventions. Behavioral cough suppression therapy (BCST), an efficacious treatment for RCC, may leverage similar neuroplastic adaptations, enhancing interoceptive processing and inhibitory control. Given the multi-dimensional nature of interoception, which encompasses sensory perception shaped by learning, memory, and emotional context, BCST's engagement of multiple neural pathways offers an alternative therapeutic option compared to single-mechanism pharmacological treatments. Future research should prioritize exploring the mechanistic underpinnings of BCST and other interoception-based therapies for developing more comprehensive and effective treatment options. Such research holds promise for improving patient outcomes, alleviating the significant healthcare burden associated with RCC, and advancing our understanding of central hypersensitivity disorders.

Regulation of vagally-evoked respiratory responses by the lateral parabrachial nucleus in the mouse

Vagal sensory inputs to the brainstem can alter breathing through the modulation of pontomedullary respiratory circuits. In this study, we set out to investigate the localised effects of modulating lateral parabrachial nucleus (LPB) activity on vagally-evoked changes in breathing pattern. In isoflurane-anaesthetised and instrumented mice, electrical stimulation of the vagus nerve (eVNS) produced stimulation frequency-dependent changes in diaphragm electromyograph (dEMG) activity with an evoked tachypnoea and apnoea at low and high stimulation frequencies, respectively. Muscimol microinjections into the LPB significantly attenuated eVNS-evoked respiratory rate responses. Notably, muscimol injections reaching the caudal LPB, previously unrecognised for respiratory modulation, potently modulated eVNS-evoked apnoea, whilst muscimol injections reaching the intermediate LPB selectively modulated the eVNS-evoked tachypnoea. The effects of muscimol on eVNS-evoked breathing rate changes occurred without altering basal eupneic breathing. These results highlight novel roles for the LPB in regulating vagally-evoked respiratory reflexes.

Atypical Activation of Laryngeal Somatosensory-Motor Cortex During Vocalization in People With Unexplained Chronic Cough

Importance

Unexplained chronic cough is common and has substantial negative quality-of-life implications, yet its causes are not well understood. A better understanding of how peripheral and central neural processes contribute to chronic cough is essential for treatment design.

Objective

To determine if people with chronic cough exhibit signs of abnormal neural processing over laryngeal sensorimotor cortex during voluntary laryngeal motor activity such as vocalization.

Design, Setting, and Participants

This was a cross-sectional study of a convenience sample of participants with chronic cough and healthy participants. Testing was performed in an acoustically and electromagnetically shielded chamber. In a single visit, electroencephalographic (EEG) signals were recorded from participants with chronic cough and healthy participants during voice production. The chronic cough group participants presented with unexplained cough of 8 weeks or longer duration with prior medical evaluation including negative results of chest imaging. None of the participants had a history of any neurologic disease known to impair vocalization or swallowing. Data collection for the healthy control group occurred from February 2 to June 28, 2018, and for the chronic cough group, from November 22, 2021, to June 21, 2022. Data analysis was performed from May 1 to October 30, 2022.

Exposure

Participants with or without chronic cough.

Main Outcome Measures

Event-related spectral perturbation over the laryngeal area of somatosensory-motor cortex from 0 to 30 Hz (ie, θ, α, and β bands) and event-related coherence as a measure of synchronous activity between somatosensory and motor cortical regions.

Results

The chronic cough group comprised 13 participants with chronic cough (mean [SD] age, 63.5 [7.8] years; 9 women and 4 men) and the control group, 10 healthy age-matched individuals (mean [SD] age, 60.3 [13.9] years; 6 women and 4 men). In the chronic cough group, the typical movement-related desynchronization over somatosensory-motor cortex during vocalization was significantly reduced across θ, α, and β frequency bands when compared with the control group.

Conclusions and Relevance

This cross-sectional study found that the typical movement-related suppression of brain oscillatory activity during vocalization is weak or absent in people with chronic cough. Thus, chronic cough affects sensorimotor cortical activity during the asymptomatic voluntary activation of laryngeal muscles.

Examining the Influence of Chemosensation on Laryngeal Health and Disorders

Inhaled airborne stimuli are associated with laryngeal disorders affecting respiration. Clinically, several themes emerged from the literature that point to specific gaps in the understanding and management of these disorders. There is wide variation in the types of airborne stimuli that trigger symptoms, lack of standardization in provocation challenge testing using airborne stimuli, and vague reporting of laryngeal symptoms. Scientifically, evidence exists outside the field of voice science that could prove useful to implement among patients with impaired laryngeal-respiration. To expand this area of expertise, here we provide a thematic overview of relevant evidence and methodological tools from the discipline of chemosensory sciences. This review provides distinctions across the three chemosensory systems of olfaction, trigeminal chemesthesis, and gustation, guidance on selecting and delivering common chemosensory stimuli for clinical testing, and methods of quantifying sensory experiences using principles of human psychophysics. Investigating the science of chemosensation reveals that laryngeal responses to inhaled airborne stimuli have explanations involving physiological mechanisms as well as higher cognitive processing. Fortunately, these findings are consistent with current pharmacological and nonpharmacological interventions for impaired laryngeal-respiration. Based on the close relationships among inhaled airborne stimuli, respiration, and laryngeal function, we propose that new perspectives from chemosensory sciences offer opportunities to improve patient care and target areas of future research.

The interrelationship of chronic cough and depression: a prospective population-based study

Background

Chronic cough is a debilitating medical condition that is often complicated by psychomorbidities such as depressive symptoms. Nevertheless, little is known about the impact of chronic cough on the risk of developing depression. Therefore, we investigated the association between chronic cough and prevalent, incident and recurrent depression in a population-based sample of middle-aged and older persons.

Methods

Within the Rotterdam Study, a population-based cohort, we defined chronic cough as reporting daily coughing for ⩾3 months. Depression was assessed using the Center for Epidemiologic Studies Depression scale, clinical interviews and medical records. Associations between chronic cough and depression were determined with linear, logistic and Cox regression analyses.

Results

The study included 5877 participants (mean±sd age 72±8 years, 59% female) who contributed 37 287 person-years of follow-up. At baseline, participants with chronic cough reported more depressive symptoms (adjusted standardised mean difference 0.15, 95% CI 0.07–0.22) compared to those without chronic cough. Over time, chronic cough was associated with an increased risk of depression in participants with a history of depression (hazard ratio (HR) 1.45, 95% CI 1.13–1.84), but not in those without a history of depression (HR 0.91, 95% CI 0.68–1.22).

Conclusions

Adults with chronic cough have a disproportionate burden of depressive symptoms and an increased risk of recurrent depression. This highlights the importance of screening for depression in patients with chronic cough.

Adults with chronic cough have a disproportionate burden of depressive symptoms and are more likely to suffer recurrent depression, highlighting the need for screening for depression in individuals with chronic coughhttps://bit.ly/3sPvYTd

Reflexive Airway Sensorimotor Responses in Individuals with Amyotrophic Lateral Sclerosis

BACKGROUND

Progressive motor denervation in amyotrophic lateral sclerosis (ALS) leads to reduced expiratory cough flow and diminished airway clearance physiologic capacity. Although ALS is thought to primarily impact motor systems, preliminary data from our laboratory suggest degradation of afferent pathways that regulate reflexive cough responses to radiographically confirmed aspiration. We, therefore, aimed to delineate both sensory and motor responses to a tussigenic airway irritant in individuals with ALS compared to healthy controls.

METHODS

Thirty-two individuals with ALS and 34 healthy age and gender-matched controls completed reflex cough testing. Capsaicin stimuli (0, 50, 100, 150, 200 μM) were presented in a randomized three-block design and motor (cough spirometry metrics) and sensory (patient-rated urge to cough, UtC) ratings collected. ALS patients underwent videofluoroscopy with penetration-aspiration ratings completed. Descriptives, Mann-Whitney U, and mixed models ANOVAs were performed.

RESULTS

Sensory: Individuals with ALS demonstrated greater UtC sensitivity slopes (i.e., increased stimulus sensitivity) vs. healthy controls (p = 0.036). Within the ALS group, however, silent aspirators (PAS = 8) demonstrated blunted UtC sensitivity slopes compared to ALS patients who did not (PAS ≤ 7, p = 0.0001). Motor: Compared to healthy controls, ALS individuals demonstrated reduced peak expiratory flow rates (p = 0.004), longer peak expiratory rise time (p = 0.017), and lower cough volume acceleration (p = 0.000).

CONCLUSIONS

ALS individuals demonstrated increased sensitivity to an upper airway irritant; however, they demonstrated slower and weaker expiratory cough motor output compared to healthy controls. In ALS silent aspirators, blunted sensorimotor responses were observed, suggesting that sensory degradation may occur at the final or most severe stage of bulbar disease progression.

Dual Tasking Influences Cough Sensorimotor Outcomes in Healthy Young Adults

Purpose Reflex cough is an essential airway protective mechanism that often occurs in the context of divided attention. The effect of divided attention on measures of reflexive cough airflow and sensitivity remains unknown. We present findings from a study testing the effects of divided attention (via a dual-task paradigm) on measures of reflex cough in healthy young adults. Method Volunteers (N = 20, age = 20-40 years) underwent 4 blocks of capsaicin-induced cough challenges. Within each block, capsaicin ranging from 0 to 200 μM was presented in a randomized order. Two blocks consisted of cough testing only (single task). During the other 2 blocks, participants counted tones while simultaneously undergoing cough testing (dual task). Measures of cough motor response, self-reported urge-to-cough, cough frequency, and cough airflow were collected. Results Participants coughed more in the single-task condition compared to the dual-task condition (p ≤ .001). Participants' urge-to-cough ratings were lower in the dual-task condition (x̅ = 2, "slight") compared to the single-task condition (x̅ = 3, "moderate"; p = .007). Participants' cough reflex sensitivity thresholds were significantly increased in the dual-task condition (p = .002). Cough peak expiratory flow rates did not change between the 2 conditions (p = .34). Conclusions Somatosensation of tussive stimuli changes during dual tasking. Abnormal cortical resource allocation may be a mechanism involved in silent aspiration.

Voluntary upregulation of reflex cough is possible in healthy older adults and Parkinson's disease

Cough is an airway-protective mechanism that serves to detect and forcefully eject aspirate material. Existing research has identified the ability of healthy young adults to suppress or modify cough motor output based on external cueing. However, no study has evaluated the ability of people with Parkinson's disease (PD) and healthy older adults (HOAs) to upregulate cough motor output. The goal of this study was to evaluate the ability of people with PD and healthy age-matched controls (HOAs) to upregulate reflex and voluntary cough function volitionally with verbal instruction and visual biofeedback of airflow targets. Sixteen participants with PD and twenty-eight HOAs (56-83 yr old) were recruited for this study. Experimental procedures used spirometry to evaluate 1) baseline reflex cough (evoked with capsaicin) and voluntary sequential cough and 2) reflex and voluntary cough with upregulation biofeedback. Cough airflow was recorded and repeated-measures ANOVA was used to analyze differences in cough airflow parameters. Cough peak expiratory airflow rate and cough expired volume were significantly greater in the cueing condition for both induced reflex (P < 0.001) and voluntary cough (P < 0.001) compared with baseline measures. This is the first study to demonstrate the ability of people with PD and HOAs to upregulate induced reflex and voluntary cough motor output volitionally. These results support the development of studies targeting improved cough effectiveness in patients with airway-protective deficits.NEW & NOTEWORTHY Aspiration pneumonia is a leading cause of death in Parkinson's disease (PD) and results from concurrent dysphagia and dystussia (cough dysfunction). This is the first study to demonstrate that people with PD and healthy age-matched controls can volitionally upregulate induced reflex and voluntary cough effectiveness when presented with novel cueing strategies. Thus targeting upregulation of cough effectiveness via biofeedback may be a viable way to enhance airway protection in people with PD.

Psychological profile of individuals presenting with chronic cough

Chronic refractory cough (CRC) is a common problem in respiratory clinics. Adverse effects on quality of life are documented in the literature, but relatively little is known about the underlying psychological factors in this patient population. We aimed to investigate the association of psychological factors with chronic cough, comparing CRC to explained cough and non-cough groups. 67 patients attending a specialist cough clinic (CRC, n=25; explained cough, n=42) and 22 non-cough individuals participated. All participants completed the Hospital Anxiety & Depression Scale, Big Five Inventory (Personality), Chalder Fatigue Scale and Patient Health Questionnaire-15. Cough patients also completed the Illness Perception Questionnaire-Revised. Appropriate statistical analyses were used to compare participant groups. Chronic refractory coughers displayed significantly higher levels of anxiety, depression, fatigue and somatic physical symptoms than non-cough participants. Compared to explained coughers, there were higher depression and fatigue scores and significantly more negative illness representations (specifically, strong beliefs regarding negative consequences, lower illness coherence and higher emotional representations). "Explained" coughers reported significantly increased fatigue and somatic symptoms in comparison to non-coughers. The prevalence of fatigue, low mood, negative illness beliefs and increased physical symptom reporting should be considered in consultations and in developing novel interventions for CRC patients.

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.

'Chronic cough, cause unknown': A qualitative study of patient perspectives of chronic refractory cough

Chronic refractory cough patients have persistent, unexplained, treatment-resistant symptoms. Very little is known about non-physiological processes underlying chronic refractory cough or patients' experience of the condition. In all, 14 patients participated in semi-structured interviews. Interviews were based on the comprehensive cognitive behavioural model and analysed thematically. Eight key themes emerged illustrating that the experience of the onset and persistence of chronic refractory cough is complex, often involving multiple interlinking factors. Themes highlighted the involvement of biological and psychological factors, and the prominent role of the social dimension in how the cough is experienced, perceived and managed. Implications for intervention development are discussed.

Preliminary Evidence of Reduced Urge to Cough and Cough Response in Four Individuals following Remote Traumatic Brain Injury with Tracheostomy

Cough and swallow protect the lungs and are frequently impaired following traumatic brain injury (TBI). This project examined cough response to inhaled capsaicin solution challenge in a cohort of four young adults with a history of TBI within the preceding five years. All participants had a history of tracheostomy with subsequent decannulation and dysphagia after their injuries (resolved for all but one participant). Urge to cough (UTC) and cough response were measured and compared to an existing database of normative cough response data obtained from 32 healthy controls (HCs). Participants displayed decreased UTC and cough responses compared to HCs. It is unknown if these preliminary results manifest as a consequence of disrupted sensory (afferent) projections, an inability to perceive or discriminate cough stimuli, disrupted motor (efferent) response, peripheral weakness, or any combination of these factors. Future work should attempt to clarify if the observed phenomena are borne out in a larger sample of individuals with TBI, determine the relative contributions of central versus peripheral nervous system structures to cough sensory perceptual changes following TBI (should they exist), and formulate recommendations for systematic screening and assessment of cough sensory perception in order to facilitate rehabilitative efforts. This project is identified with the National Clinical Trials NCT02240329.

Decreased cough sensitivity and aspiration in Parkinson disease

BACKGROUND

Aspiration pneumonia is a leading cause of death in people with Parkinson disease (PD). The pathogenesis of these infections is largely attributed to the presence of dysphagia with silent aspiration or aspiration without an appropriate cough response. The goal of this study was to test reflex cough thresholds and associated urge-to-cough (UTC) ratings in participants with PD with and without dysphagia.

METHODS

Twenty participants with PD were recruited for this study. They completed a capsaicin challenge with three randomized blocks of 0, 50, 100, and 200 μM capsaicin and rated their UTC by modified Borg scale. The concentration of capsaicin that elicited a two-cough response, total number of coughs, and sensitivity of the participant to the cough stimulus (UTC) were measured. The dysphagia severity of participants with PD was identified with the penetration-aspiration scale.

RESULTS

Most participants with PD did not have a consistent two-cough response to 200 μM capsaicin. UTC ratings and total number of coughs produced at 200 μM capsaicin were significantly influenced by dysphagia severity but not by general PD severity, age, or disease duration. Increasing levels of dysphagia severity resulted in significantly blunted cough sensitivity (UTC).

CONCLUSIONS

UTC ratings may be important in understanding the mechanism underlying morbidity related to aspiration pneumonia in people with PD and dysphagia. Further understanding of decreased UTC in people with PD and dysphagia will be essential for the development of strategies and treatments to address airway protection deficits in this population.

A framework for understanding shared substrates of airway protection

Deficits of airway protection can have deleterious effects to health and quality of life. Effective airway protection requires a continuum of behaviors including swallowing and cough. Swallowing prevents material from entering the airway and coughing ejects endogenous material from the airway. There is significant overlap between the control mechanisms for swallowing and cough. In this review we will present the existing literature to support a novel framework for understanding shared substrates of airway protection. This framework was originally adapted from Eccles' model of cough²⁸ (2009) by Hegland, et al.⁴² (2012). It will serve to provide a basis from which to develop future studies and test specific hypotheses that advance our field and ultimately improve outcomes for people with airway protective deficits.

Attentional modulation of reflex cough

OBJECTIVE

Reflex cough is a defensive response generated in the brainstem in response to chemical and mechanical stimulation of the airways. However, converging evidence shows that reflex cough is also influenced by central neural control processes. In this study, we investigate whether reflex cough can be modulated by attentional focus on either external stimuli or internal cough-related stimuli.

METHODS

Healthy volunteers (N = 24; seven men; age range, 18-25 years) completed four blocks of citric acid-induced cough challenges while, simultaneously, auditory stimuli were presented. Within each block, four concentrations were administered (30, 100, 300 and 1,000 mM, randomized). During two subsequent blocks, participants focused their attention externally (counting tones). During the other two blocks, participants focused their attention internally (counting coughs). The order of attentional focus was counterbalanced across participants. Ratings of the urge to cough were collected after each challenge. Cough frequency was determined by audio recording.

RESULTS

Cough frequency was higher when participants focused their attention internally vs externally (P < .05). Also urge to cough was greater during internal vs external focus (P < .05), but the effect was smaller in later blocks of trials.

CONCLUSIONS

Reflex cough can be modulated by attentional focus. Internally focused attention may be a mechanism involved in excessive (idiopathic) cough, while an external focus may be introduced as part of treatments targeting excessive cough.

The larynx in cough

About 40% of the population will experience chronic cough at some point during their lives and it tends to be more common in women (Thorax 58:901-7, 2003). Post-nasal drip (or upper airway cough syndrome), gastro-esophageal reflux disease and asthma are considered the most common causes. Yet only a small percentage of patients with these common conditions experience chronic cough. Also there is no agreed measure of post-nasal drip and controversy exists about the diagnosis of reflux above the upper esophageal sphincter (laryngopharyngeal reflux) based on observable changes to the larynx. The approach of the otolaryngologist is to consider the upper and lower airways as a continuum and that a common pathology can have an impact on all these anatomical sites.A multidisciplinary approach is advocated, utilising the skills of the respiratory physician, otolaryngologist, gastroenterologist and speech pathologist.

The difficult-to-treat, therapy-resistant cough: why are current cough treatments not working and what can we do?

Cough can persist despite exhaustive diagnostic and therapeutic effort and has been termed 'idiopathic' or 'unexplained' but perhaps 'difficult to treat' cough is a more appropriate description. In this article the reasons for poor treatment response are discussed. These include a lack of physician fidelity to management guidelines, patient non-adherence and the lack of effective medicines. A number of randomized controlled trials have been undertaken including low dose opiate therapy, the use of a speech pathology intervention, oral antibiotics and antidepressants. The success or otherwise of such interventions will be discussed. A number of approaches to deal with the problem of 'difficult to treat cough' will be considered.

Cough, sarcoidosis and idiopathic pulmonary fibrosis: raw nerves and bad vibrations

Cough is a common symptom in people who develop interstitial lung diseases (ILD). The pathological features of the ILDs are many and varied suggesting that the cause of cough may also vary with each disease. This article reviews what is currently known about cough in sarcoidosis and idiopathic pulmonary fibrosis; two of the commonest ILDs. It also outlines some of the theories which have been proposed to explain why cough develops in these conditions and describes what little is known about how to treat it.

Sensorimotor circuitry involved in the higher brain control of coughing

There is an overwhelming body of evidence to support the existence of higher brain circuitries involved in the sensory detection of airways irritation and the motor control of coughing. The concept that cough is purely a reflex response to airways irritation is now superseded by the recognition that perception of an urge-to-cough and altered behavioral modification of coughing are key elements of cough disorders associated with airways disease. Understanding the pathways by which airway sensory nerves ascend into the brain and the patterns of neural activation associated with airways irritation will undoubtedly provide new insights into disordered coughing. This brief review aims to explore our current understanding of higher order cough networks by summarizing data from recent neuroanatomical and functional studies in animals and humans. We provide evidence for the existence of distinct higher order network components involved in the discrimination of signals arising from the airways and the motor control of coughing. The identification of these network components provides a blueprint for future research and the development of targeted managements for cough and the urge-to-cough.

Antitussive effects of nasal thymol challenges in healthy volunteers

Eighteen healthy volunteers with normal lung function were tested for cough. Before and after nasal administration of thymol (0.025 ml, 10(-3) M) into both nostrils, urge-to-cough, cough threshold, cumulative and total count of coughs per provocation were estimated during standardized and validated capsaicin cough challenge. Nasal thymol challenges induced pleasant olfactory sensation and in 6 out of the 18 subjects also mild cooling sensation. Cough threshold was not influenced when compared with intranasal saline and vehicle challenges (12.5 vs. 13.2 vs. 10.2 μM of capsaicin to induce two or more coughs (C2), respectively), but the total count of coughs after nasal thymol challenge was significantly lower than that obtained after saline or vehicle (19 vs. 20 vs. 14 coughs/provocation, respectively; p<0.05). Importantly, subjects did not report the urge to cough, which appeared to correspond to C2. We conclude that the modulation of cough by thymol is mostly of olfactory origin.

Modulation of cough response by sensory inputs from the nose - role of trigeminal TRPA1 versus TRPM8 channels

Background

Cough, the most important airways defensive mechanism is modulated by many afferent inputs either from respiratory tussigenic areas, but also by afferent drive from other organs. In animal models, modulation of cough by nasal afferent inputs can either facilitate or inhibit the cough response, depending on the type of trigeminal afferents stimulated.

Methods

In this study we addressed the question of possible bidirectional modulation of cough response in human healthy volunteers by nasal challenges with TRPA1 and TRPM8 agonists respectively. After nasal challenges with isocyanate (AITC), cinnamaldehyde, (−) menthol and (+) menthol (all 10^-3 M) nasal symptom score, cough threshold (C2), urge to cough (Cu) and cumulative cough response were measured).

Results

Nasal challenges with TRPA1 relevant agonists induced considerable nasal symptoms, significantly enhanced urge to cough (p<0.05) but no statistically significant modulation of the C2 and cumulative cough response. In contrast, both TRPM8 agonists administered to the nose significantly modulated all parameters including C2 (p<0.05), Cu (p<0.01) and cumulative cough response (p <0.01) documenting strong anti irritating potential of menthol isomers.

Conclusions

In addition to trigeminal afferents expressing TRP channels, olfactory nerve endings, trigemino – olfactoric relationships, the smell perception process and other supramedullar influences should be considered as potential modulators of the cough response in humans.