Comparison of Nocturnal Cough Analysis in Healthy Subjects and in Patients with Cystic Fibrosis and Primary Ciliary Dyskinesia: A Prospective Observational Study.

Radine A, Werner C, Raidt J, Dougherty GW, Kerschke L, Omran H, Grosse-Onnebrink J.

This study set out to see if there is a difference in cough frequency between healthy subjects (HS), cystic fibrosis (CF) and primary ciliary dyskinesia (PCD) patients. Some studies currently use cough frequency as the successful measure of the study outcome, or endpoint. This study tested the feasibility of using a cough monitor to see if there is a difference in cough rate and cough patterns between the three subject groups. It also looked at whether cough is related to disease severity in CF and PCD patients and whether it could be used in clinical trials.

The study enrolled 75 total subjects with 25 subjects in each of the three groups: HS, CF and PCD. The three groups did not differ by age, sex or body mass index (BMI). The PCD and CF group did not differ by lung function or oral antibiotic courses a year. The CF group had a higher use of IV and nebulized antibiotics and higher rates of inflammation and infections.

A battery-operated device that electronically records breath and lung sounds using four microphones was used by subjects over two consecutive nights. The subjects were shown how to attach the microphones and use the equipment at home.

The recordings were listened to for cough impulse and cough epoch. They defined a cough impulse by the characteristic cough sound and a cough epoch as a succession of coughs with less than 2 seconds between individual coughs. They required a minimum of 5 hours of recordings for each subject per night. The software used for the study did not reliably record the number of coughs so the researchers manually marked coughs sounds.

Sleep studies have shown that there is a “first-night” effect. This is where the subjects adjust themselves to the new environment or equipment. The assumption was that the subjects would adjust to the new equipment on the first night and sleep more naturally on the second night.

Out of the 75 subjects, 66 had their coughs successfully recorded for the 5 hour minimum for both nights. There was almost no coughing in the HS. The researchers noted that coughs “varied significantly” between the CF and PCD patients, as CF patients coughed more than PCD patients both in the total cough count and cough epic count.

There was a significant association between forced expired volume in 1 second (FEV1) and cough frequency in both PCD and CF. There was also an association between the age and BMI of the PCD patient and the amount of coughing with older and higher BMI patients coughing more. CF patients had higher cough frequencies with increased inflammation and infections.

The study was done at one center and does not adequately represent the PCD and CF populations. The authors noted they found the results unexpected as their clinical observations were that PCD patients coughed more frequently than CF patients.