Relation between measurements of cough severity

Abstract

Background: In asthma, measurements of airway inflammation correlate poorly with clinical markers and airway hyperresponsiveness. While the relation between determinants of asthma severity is known, that for cough is unknown. We hypothesised that cough sensitivity changes relate to changes in cough scores and objectively measured cough frequency.

Aims: To examine the relation between commonly used outcome measurements of cough severity in children.

Methods: The concentration of capsaicin causing two and five or more coughs (C2 and C5 respectively), cough frequency objectively measured using an ambulatory cough meter, and parent and child recorded subjective cough scores were determined in 40 children with recurrent cough on two occasions.

Results: On occasion one, log cough frequency significantly correlated with parent and child recorded log cough score (r(s) = 0.32, p = 0.05; and r(s) = 0.32, p = 0.046 respectively) and significantly negatively correlated with log C2 (r(s)= -0.5, p = 0.005). Subjective cough scores did not relate to either C2 or C5. On occasion two, the relation between cough frequency and C2 and C5 measures was lost, but C2 had a weak but significant relation to parent recorded cough score (r(s) = -0.38, p = 0.047). When the changes in the log values were determined, C5 but not C2 significantly related to cough frequency.

Conclusion: In children, measures of cough sensitivity have a weak relation with cough frequency. Subjective cough scores have a stronger and consistent relation with cough frequency. These cough severity indices measure different aspects of cough. The choice of indices depends on the reason for performing the measurement.

Figure 1

Log cough frequency measured using an ambulatory cough meter significantly correlated with log C2 (concentration of capsaicin required to stimulate 2–4 coughs); r_s = -0.5 (95% CI -0.74 to -0.18), p = 0.005.

Figure 2

The change in measurements of the two occasions the tests were undertaken. (A) The correlation between the change in log cough frequency with change in log C2 was just outside statistical significance, r_s = -0.4 (95% CI -0.7 to 0.02), p = 0.06. (B) Change in log cough frequency significantly correlated with change in log C5, r_s = -0.38 (95% CI -0.63 to -0.07), p = 0.03.