Cough frequency in health and disease

To the Editor: Chronic cough is a difficult clinical problem, partly because there is an absence of well-validated means to assess cough [1, 2]. We have previously reported that the semi-automated computerised Leicester Cough Monitor detects cough accurately over 6 h and that cough frequency is increased in patients with chronic cough compared to controls [3, 4]. There remains uncertainty on the performance of the system over 24 h and across the range of expected cough frequency in larger populations. We set out to address these questions in healthy adult volunteers and adult volunteers with respiratory disease. 44 healthy volunteers were recruited from those responding to a poster advertisement. All reported no current respiratory symptoms, were nonsmokers with a <5 pack-yr past smoking history and had normal spirometric values, methacholine airway responsiveness and induced sputum inflammatory cell counts. 78 patients with respiratory disease were recruited from respiratory clinics. The diagnostic criteria for the conditions have been described previously [5]. Six current smokers and four males taking angiotensin converting enzyme inhibitors (ACEi) were also recruited. The study was approved by the Leicestershire, Northampton and Rutland Research Ethics Committee. All volunteers underwent spirometry and those with normal spirometry had a methacholine inhalation test using the tidal breathing method. The Leicester Cough Monitor (iRiver iFP-799 mp3 device; iRiver Europe GmbH, Eschborn, Germany and Sennheiser MKE 2–5 field microphone; Sennheiser electronic GmbH & Co. KG, Wedemark, Germany) was attached and recordings obtained and analysed as …