Cough sensitivity in atopic dermatitis

Pathophysiology of Airway Afferent Nerves

Vagal afferent nerves provide an airway defense mechanism which is ensured by their activation. These nerves can be activated mechanically mainly through mechanosensitive Aβ fibers which are divided into slowly adapting (SARs) and rapidly adapting stretch receptors (RARs). Chemical activation is provided by an interaction of chemical substances with specific receptors. C-fibers are highly sensitive to a direct chemical stimulation accomplished by an activation of ligand-gated ion channels. According to the large influence and mechanisms of vagal afferent nerves, there is a probability that an inappropriate activity of these nerves can cause the symptoms of the respiratory diseases, e.g. cough, dyspnoea, or airway hyperreactivity. The aim of this review is to summarize the physiology of airway afferent nerves and point out the role of vagal sensory nerves dysfunction in the pathogenesis of some respiratory diseases. The understanding of its mechanism could lead to new therapeutic strategies in patients with airway-related pathology.

Changes in Cough Reflex Sensitivity in Children After Removal of Hypertrophied Adenoid Tissue

Purpose

The co-occurrence of adenoids and chronic cough is common in children. The goal of this research was to specify changes in cough reflex sensitivity as a result of adenoid tissue removal.

Patients and Methods

The sample group consisted of 17 children (six boys and 11 girls, aged 4–12 years, mean age 6.24 years), all of them possessing symptoms of chronic cough and adenoids, confirmed by nasal fiberoptic endoscopy. This sample group underwent cough reflex sensitivity assessment, which took place both prior to and after endoscopic adenoidectomy. The definition of the cough reflex sensitivity is the lowest capsaicin concentration that caused two (C2) or five (C5) coughs. Capsaicin aerosol in ascending concentrations (from 0.61 to 1250 µmol/L) was inhaled by a single-breath method (KoKo DigiDoser), with the addition of an inspiratory flow regulator valve (RIFR).

Results

Concentrations of capsaicin causing two (C2) and five coughs (C5) were reported. Cough sensitivity (geometric mean with 95% CI) for C2 was 31.86 (12.98–78.18) µmol/L preoperatively and 11.97 (6.16–23.26) µmol/L postoperatively (P=0.064). Cough sensitivity for C5 was 234.91 (97.19–567.77) µmol/L preoperatively and 69.13 (29.08–164.35) µmol/L postoperatively (P=0.022). The children’s pulmonary function was within the normal range.

Conclusion

In our study, adenoidectomy significantly increased cough reflex sensitivity in non-atopic children suffering from chronic cough.

A Cold Environment Aggravates Cough Hyperreactivity in Guinea Pigs With Cough by Activating the TRPA1 Signaling Pathway in Skin

Cough exacerbation in cold environments is a characteristic feature of patients with chronic cough. There is consensus that inhalation of cold air stimulates cough receptors but this idea is not consistent with the fact that cold air is usually unable to directly enter the lower airway. To elucidate the effects of cold environments and transient receptor potential ankyrin 1 (TRPA1) on cough, we compared cough reactivity, airway inflammation, and TRPA1 expression in guinea pigs with chronic cough induced by the repeated inhalation of citric acid for 15 days. The guinea pigs were exposed to cold environments for three consecutive days from day 13 to 15. Repeated inhalation of citric acid increased cough reactivity to inhaled cinnamaldehyde. We found that exposure to cold environments further aggravated cough hyperreactivity in guinea pigs with chronic cough, but not in normal guinea pigs. Cough hyperreactivity was promoted when the whole body and trunk-limbs, but not the heads, of the guinea pigs were exposed to cold environments, and abolished by pretreating the skin through immersion in the TRPA1 antagonist, HC-030031. Substance P levels in bronchoalveolar lavage fluid, and TRPA1 expression in the trachea and skin, were increased in guinea pigs when the whole body and trunk-limbs, rather than the head, were exposed to cold environments. However, this trend was also abolished by pretreatment of the skin via immersion in HC-030031. Similar changes in TRPA1 expression were also detected in the sensory fibers of the trachea and skin, as identified by immunofluorescence and laser-scanning confocal microscopy analysis. These results suggest that exaggerated cough hyperreactivity induced by cold environments may be related to activation of the cold-sensing TRPA1 signaling pathway in the skin, rather than the inhalation of cold air.

Desensitization of the Cough Reflex Induced by Corticosteroids in Ovalbumin-Sensitized Rabbits During Artificial Limb Exercise

Introduction

Cough is a major symptom frequently experienced during exercise, mainly in asthmatic patients. Inhaled glucocorticoids represent the keystone treatment in the management of asthma, but little is known about interactions between cough and exercise, especially in controlled patients. During exercise, cough reflex (CR) appears downregulated in healthy animal models whereas a lack of desensitization of CR has been shown in ovalbumin-sensitized animal models, mimicking asthmatic disease.

Aims and Objectives

The goal of our study was to clarify the potential modulation of the CR induced by inhaled corticosteroids (CS) in ovalbumin (OVA) sensitized rabbits during artificial limb exercise.

Materials and Methods

Seventeen OVA sensitized rabbits were studied. Among them, 9 were treated with CS delivered intravenously (OVA-Corticoids). The ventilatory response to direct tracheal stimulation, performed at rest and during exercise, was determined to assess the incidence and the sensitivity of the CR. Broncho-alveolar lavage (BAL) and cell counts were performed to determine the level of airway inflammation. Exercise was mimicked by electrically induced hindlimb muscular contractions (EMC).

Results

Compared to rest values, EMC increased minute ventilation by 28% without any decrease in respiratory resistance (Rsr). Among 322 tracheal stimulations, 172 (53%) were performed at rest and 150 (47%) during exercise. The sensitivity of CR decreased during artificial limb exercise compared to baseline in OVA-Corticoids rabbits (p = 0.0313) while it remained unchanged in OVA rabbits (p = NS).

Conclusion

Corticosteroids appear to restore the desensitization of the CR in OVA sensitized rabbits during artificial limb exercise, suggesting the potential role of airway inflammation in the pathophysiology of cough during exercise in asthmatics.

Legacy of Prof. Juraj Korpáš: International Impact of Slovak School of Experimental Respirology

Human health is the main role of medical research. Scientists were always intrigued by disease prevention, their diagnostics and proper treatment. In fact, research in medicine is always directed towards the improvement of the health care and improvement of the quality of life of the target population. Nowadays, physiological research, which is the base stone for clinical research, progresses fast forward, providing new information about body functions in health and diseases. This obvious progress is associated with modern methods, such as neuronal tracing, patch-clamp methods, electrophysiology, molecular biology and many more, which supported by comprehensive information technology guarantees high quality and complex data. Our younger colleagues, young scientists, post-docs or PhD students are well-trained and qualified in utilizing these new methods.

The effect of adenoidectomy on cough reflex sensitivity in atopic children

The aim of this study was to determine whether cough sensitivity is changed after adenoidectomy in atopic children with chronic cough. 21 Children having symptoms of chronic cough and adenoid hypertrophy verified by nasal fiberoptic endoscopy were submitted to cough sensitivity measurement before and after adenoidectomy. Their pulmonary function was within normal range. Concentrations of capsaicin causing two (C2) and five coughs (C5) were reported. Children' (14 boys and 7 girls, mean age 6,52 yrs) cough sensitivity (geometric mean, with 95% CI) for C2 was preoperatively (before adenoidectomy) 19.95 (9.95-39.98) micromol/l vs. children' C2 postoperatively 14.04 (7.16-27.55) (P = .083 for Wilcoxon paired two sample test). Children' C5 was preoperatively 86.26 (39.25-189.57) micromol/l vs. C5 postoperatively 95.23 (46.33-195.75) micromol/l (P = .794 for Wilcoxon paired two sample test). We conclude that cough sensitivity for C2 and C5 was not significantly changed after adenoidectomy in atopic children with chronic cough.

Cough reflex sensitivity after exercise challenge testing in children with asthma

Bronchial challenge tests are commonly used in clinical medicine and research. The aim of this study was to clarify changes of cough reflex sensitivity before and after exercise challenge testing in asthma children. 42 asthmatic children were submitted to cough reflex sensitivity measurement - capsaicin aerosol in doubling concentrations (from 0.61 to 1250 micromol/l) was inhaled by a single breath method - before and after exercise challenge testing. Concentrations of capsaicin causing two (C2) and five coughs (C5) were reported. Children' (31 boys and 11 girls, mean age 14.05 ± 2.08 yrs) cough reflex sensitivity (median, with the 95% CI) for C2 was before exercise challenge testing 9.77 (6.10-10.99) micromol/l vs. children' C2 after it 7.32 (6.10-14.65) (P = 0.58 for the Wilcoxon two sample paired test). Children' C5 was before exercise challenge testing 19.53 (14.65-80.57) micromol/l vs. C5 after it 39.06 (24.42-58.59) micromol/l (P = 0.09 for the Wilcoxon two sample paired test). We conclude that cough reflex sensitivity was not significantly changed after exercise challenge testing in children with asthma.

Do sex and atopy influence cough outcome measurements in children?

BACKGROUND

Despite the commonality of cough and its burden, there are no published data on the relationship between atopy or sex on objectively measured cough frequency or subjective cough scores in children. In 202 children with and without cough, we determined the effect of sex and atopy on validated cough outcome measurements (cough receptor sensitivity [CRS], objective cough counts, and cough scores). We hypothesized that in contrast to adult data, sex does not influence cough outcome measures, and atopy is not a determinant of these cough measurements.

METHODS

We combined data from four previous studies. Atopy (skin prick test), the concentration of capsaicin causing two and five or more coughs (C2 and C5, respectively), objectively measured cough frequency, and cough scores were determined and their relationship explored. The children's (93 girls, 109 boys) mean age was 10.6 years (SD 2.9), and 56% had atopy.

RESULTS

In multivariate analysis, CRS was influenced by age (C2 coefficient, 5.9; P = .034; C5 coefficient, 29.1; P = .0001). Atopy and sex did not significantly influence any of the cough outcomes (cough counts, C2, C5, cough score) in control subjects and children with cough.

CONCLUSIONS

Atopy does not influence important cough outcome measures in children with and without chronic cough. However, age, but not sex, influences CRS in children. Unlike adult data, sex does not affect objective counts or cough score in children with and without chronic cough. Studies on cough in children should be age matched, but matching for atopic status and sex is less important.

Workshop: tuning the 'cough center'

The Workshop considered the mechanisms whereby the 'cough center' could be tuned by various afferent inputs. There were particular presentations on the effects of inputs from the nose, mouth, respiratory tract and lungs, cerebral cortex, somatic tissues and the pharynx. From all these sites cough induced from the lungs could be increased or decreased in its strength or modified in its pattern. Thus 'tuning' of cough could be due to the interaction of afferent inputs, or to the sensitization or desensitization of brainstem neural pathways. The pattern of response depended on the 'type' of cough being studied and, in some instances, on the timing of the sensory input into the brainstem. Cough inputs could also affect various 'non-cough' motor outputs from the brain, although this was not the main theme of the Workshop. The main conclusion was that cough is not a stereotyped output from the medullary 'cough center', but that its pattern and strength depend on many afferent inputs acting on the 'cough center'.

Mechanisms of the cough associated with rhinosinusitis

The diseases of the nose and paranasal sinuses (rhinosinusitis) often in combination with asthma and gastroesophageal reflux are common causes of chronic cough in patients with normal chest radiograph. The relationships between rhinosinusitis and cough are incompletely understood. We investigated modulation of the cough reflex by the inputs from the nose. We demonstrate that the cough reflex is sensitized by the intranasal administration of sensory nerve activators in animal models and in humans. Cough reflex is also sensitized in the guinea pig model of allergic nasal inflammation and in patients with allergic rhinitis. In patients with allergic rhinitis the cough sensitization is augmented during the allergen season. We conclude that the cough reflex can be sensitized from the nose. Our data indicate that this sensitization is mediated by nasal sensory nerves. We speculate that by inducing the cough reflex sensitization rhinosinusitis contributes to chronic cough. If combined with environmental or endogenous cough triggers, the cough reflex sensitization is predicted to cause excessive coughing. The potential endogenous cough triggers may be associated with rhinosinusitis (postnasal drip, aspiration of nasal secrets) or secondary to a coexistent disease such as asthma or gastroesophageal reflux.

Regulation of cough by secondary sensory inputs

We have reviewed the role of afferent inputs and blood chemical changes to the central nervous system, and the way in which they modify the cough and expiration reflexes (CR and ER). Slowly adapting pulmonary stretch receptors (SARs) augment the CR, insofar as when their activity is abolished the CRs from the tracheobronchial (TB) tree and larynx are abolished or weakened. However, stimulation of SARs by lung inflation has an inconsistent effect on the CR. Activation of SARs strongly potentiates the ER from the vocal folds, by a reflex mechanism, and inhibition of SARs weakens the ER. Bronchopulmonary C-fibre receptors inhibit the CR, as do capsaicin-sensitive afferents from the heart and splanchnic bed, cutaneous cold receptors and those that respond to chest wall vibration. Nasal receptors responsive to the irritant agent capsaicin potentiate the reflex. Acute hypoxia also augments the CR, and the reflex is down-regulated by carotid body resection. On the other hand, the CR is inhibited by prolonged hypoxia and hyperoxia, and by hypercapnia. Thus different inputs to the cough-controlling mechanism in the brainstem have very varied effects on the CR. We conclude that the sensitivities of the CR and ER can be modified in a large variety of physiological and clinical conditions, and that there is no clear relationship between the reflexes and changes in breathing caused by the interventions.

The effects of nasal histamine challenge on cough reflex in healthy volunteers

The aim of the study was to investigate the effects of nasal histamine on the intensity of cough reflex and the effects of intensified nasal breathing following the nasal histamine challenge on cough sensitivity (CS) in humans. 20 volunteers (mean age 23, nonsmokers, no history of nasal or respiratory system diseases and atopy) were recruited to the study. Baseline CS was determined in all subjects. 2 days later the subjects (n = 20) were challenged with nasal histamine (8 mg/ml, 0.1 ml) and the number of coughs was determined after four consecutive single-breath inhalations of capsaicin C2 concentration during the period of the most intensive nasal symptoms (sneezing, itching of the nose). The same capsaicin C2 challenge was performed after nasal saline challenge two days later. One week later CS was determined after nasal histamine challenge with subsequent 10 min of intensified breathing (5-6 sniff-like aspirations to total lung capacity per minute) through the nose and mouth in randomized order in ten volunteers, and with a two-day interval between the challenges. The same manoeuvres after intranasal saline challenge were performed in volunteers of the control group (n = 10). The number of coughs after nasal histamine was significantly higher than that after intranasal saline challenge (8(6-10) vs 5(3-7); p = 0.038(. CS was not significantly different between the baseline challenge and challenges after nasal histamine followed by the intensified nasal and mouth breathing ((2.21 (1.8-2.62) vs 2.04 (1.57-2.51) vs 2.05 (1.6-2.5) log(10) of capsaicin concentration in mumol.l(-1); p = 0.09).

CONCLUSIONS

During the period of maximum nasal symptoms after nasal histamine challenge the cough response to inhaled capsaicin was enhanced. Capsaicin cough sensitivity measured after a 10-min. intensified nasal breathing after nasal histamine challenge, compared to a previous measurement of CS, remain unchanged.

A link between skin and airways regarding sensitivity to fragrance products?

BACKGROUND

Exposure to volatile fragrances is commonplace and may be related to various eye and airway symptoms. Skin exposure to fragrances is known to cause perfume contact allergy and eczema, but it is unknown whether eye or airway symptoms elicited by fragrance products are associated with contact allergy or eczema.

OBJECTIVES

To investigate if eye and airway symptoms elicited by fragrance products are associated with perfume contact allergy or hand eczema in a population-based sample.

METHODS

A questionnaire on eye and airway symptoms elicited by fragrance products was mailed to 1189 individuals who had recently participated in a Danish population-based study of allergic diseases. Results from the questionnaire about localization and character of the symptoms were compared with data on patch testing and 1-year prevalence of hand eczema collected during the health examination.

RESULTS

Positive, independent and significant (P < 0.05) associations were found between eye and airway symptoms elicited by fragrance products and perfume contact allergy (adjusted odds ratios 2.0-3.7) and hand eczema (adjusted odds ratios 1.6-2.6). In further analysis, similar and consistent results were found regarding severity of the symptoms. No associations were found between nickel contact allergy and the symptoms. Female sex and psychological vulnerability were independently associated with eye and airway symptoms elicited by fragrance products, but adjustment in multivariate analysis did not change the results regarding perfume contact allergy and hand eczema.

CONCLUSIONS

Individuals with perfume contact allergy and/or hand eczema, as opposed to those without, have more frequent and more severe eye or airway symptoms after exposure to volatile fragrance products. Having hand eczema has the greatest impact on reporting eye and airway symptoms elicited by fragrance products.