Cough provocation tests: their clinical value

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.

Diagnosis and treatment of chronic cough in China: an insight into the status quo

Chronic cough is a very common complaint in clinics throughout China. Clinical and basic science research on chronic cough started late, but in recent years the effort has yielded promising findings regarding the etiological diagnosis, treatment and pathogenesis. We found that inflammation in nonasthmatic eosinophilic bronchitis has some similarities to cough variant asthma but also a number of distinct differences. Recent evidence has also suggested a mechanistic link between airway neurogenic inflammation and and gastroesophageal reflux cough (GERC). Cough-related animal models have been developed, including models for esophageal reflux, nonasthmatic eosinophilic bronchitis and allergic rhinitis. Normal reference values for differential cell counts in induced sputum, cough sensitivity and esophageal 24-h pH monitoring in Chinese healthy subjects have been established. By using a modified algorithm for the etiological diagnosis of chronic cough, the causes of chronic cough have been investigated across a number of cities in China. The most common causes of chronic cough are cough variant asthma, eosinophilic bronchitis, upper airway cough symptoms, atopic cough and GERC, however, there are some regional variations. The Chinese National Guidelines on Diagnosis and Management of Chronic Cough were drafted in 2005, updated in 2009, and have been widely publicized and disseminated through many channels since their publication.

Acute sustained hypoxia suppresses the cough reflex in healthy subjects

RATIONALE

An intact cough reflex is important to protect the lung from injurious substances and to clear excess secretions. A blunted cough reflex may be harmful or even fatal in respiratory disease. Hypoxia is common in respiratory disorders and has been shown to have depressant effects on respiratory sensation and ventilation. We hypothesized that it might also suppress the cough reflex.

OBJECTIVES

To determine if acute hypoxia increases cough threshold and cough tachyphylaxis to inhaled capsaicin.

METHODS

On two occasions, 16 healthy subjects inhaled a saline control followed by doubling doses of capsaicin aerosol (range, 0.49-500 microM) every minute for 15 s during controlled ventilation (approximately 190% baseline) with isocapnic hypoxia (SpO2, approximately 80%) or isocapnic normoxia, in random order. When a subject responded to a dose with five or more coughs, the next doubling dose of capsaicin was administered continuously for 60 s to assess acute tachyphylaxis.

MAIN RESULTS

The capsaicin concentration required to elicit five coughs was significantly higher during isocapnic hypoxia compared with normoxia (29.6 +/- 16.0 vs. 23.4 +/- 15.6 microM, p = 0.01). During continuous capsaicin inhalation, significantly more coughs were evoked in the first 10 s compared with the last (2.3 +/- 0.3 vs. 1.3 +/- 0.3, p < 0.01), indicating cough tachyphylaxis. However, the decrease was the same during hypoxia and normoxia (-1.3 +/- 0.4 vs. -0.9 +/- 0.6, p = 0.54).

CONCLUSIONS

Acute isocapnic hypoxia suppresses cough reflex sensitivity to inhaled capsaicin. This finding raises the possibility that the cough reflex may be impaired during acute exacerbations of hypoxic-respiratory disorders.