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Title: Objective measures of cough severity
Author: Lee, Kai Kong
Awarding Body: King's College London
Current Institution: King's College London (University of London)
Date of Award: 2014
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Cough is a common complaint that results in significant morbidity and impairment in quality of life. The assessment of cough severity is central to the diagnosis and clinical management of cough. The aim of this thesis was to evaluate objective measures of cough frequency and cough intensity in patients with acute and chronic cough. 24-hour cough frequency was investigated in a longitudinal observational study of 33 healthy subjects with acute cough. At baseline, 24-hour cough frequency was elevated and was associated with impaired health related quality of life. Cough frequency improved significantly over the 8-day study period. The minimal clinically important difference in cough frequency was determined as a 54% change from baseline. The sample sizes required for clinical trials to use cough frequency as a primary endpoint were calculated using this data. A second study of cough frequency was undertaken in 100 patients with chronic cough to investigate whether short duration recordings (1-6 hours) were comparable to 24-hours. Cough frequency obtained from short recordings were strongly correlated with 24-hour cough frequency (ρ=0.77 to 0.93), but those less than 4 hours were limited by weak relationships with subjective measures of cough. 4-hour cough frequency was found to be responsive to improvements in cough severity following trials of therapy, supporting its feasibility as a tool for assessing outcomes in chronic cough. The intensity of cough is an important determinant of global cough severity, but few studies have assessed cough intensity objectively in patients with chronic cough. The intensity of voluntary, induced and spontaneous cough was investigated in 28 patients with chronic cough and 21 healthy controls. Oesophageal pressure (Poes), gastric pressure (Pga) and peak cough flow rate (PCFR) during maximum voluntary cough were significantly greater in patients with chronic cough compared with controls when taking into account the preceding inspired volume. There was no difference in expiratory muscle strength or degree of abdominal muscle activation between patients and controls but the compression phase duration (CPD) was increased in female patients with cough compared to controls (mean ± SD CPD 0.50 ± 0.22 vs. 0.28 ± 0.17 seconds; p=0.007). Cough intensity during spontaneous cough was comparable to induced cough, but less than maximum voluntary cough intensity. Poes, Pga and PCFR were closely correlated with cough intensity visual analogue score (ρ=0.86 to 0.90), suggesting that these indices are important to subjective perception of cough intensity. Cough sound is a potential measure of cough intensity, but it has not been validated against physiological measures of cough intensity. The relationship between a range of cough sound parameters and PCFR and Poes were investigated in 17 patients with chronic cough and 15 healthy controls. Cough sound power and energy were found to correlate most strongly with PCFR (ρ=0.82 to 0.88) and Poes (ρ=0.85 to 0.89). The relationships between sound and PCFR or Poes were similar for sound analysed from a fixed 0.5-second time-window and from time-windows that were manually marked by cough phase, supporting the potential for future automated analysis. Sound power and energy were highly repeatable measures (ICC 0.93 to 0.94). Cough sound measurement has the advantage of being non-invasive and suitable for ambulatory monitoring and further studies should now assess its responsiveness as a measure of cough intensity.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (M.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available