Dear Editor,

Chronic cough (CC) is a common and widespread clinical condition and one of main reasons for seeking medical attention globally [1]. Defined by clinical guidelines as lasting for ≥8 weeks [2], it has a noteworthy impact on quality of life [3]. Limited data are available about the relationship between airway and lung structural changes in CC. Previous studies revealed features of airway remodeling [4, 5] and the presence of increased airway wall thickness [4, 6]. We previously reported no specific airway changes in CC using advanced computer tomographic imaging [7]. To further explore the structure-function relationship in CC, impedance measurements by applying forced oscillation technique (FOT) are analyzed as part of a prospective, population-based study.

Oscillometry is assumed to be a sensitive measurement for detection of small airway disease and allows identifying potential alterations in the impedance of the respiratory system. Impedance data using FOT have not been assessed within a large sample size of individuals with CC. Our analysis included cross-sectional data from 5,698 adults aged ≥18 years from the Austrian general population.

We compared FOT parameters among 3 groups comprising (i) individuals without respiratory symptoms or pathologies, (ii) those with only CC, and (iii) those with CC and other respiratory symptoms (wheezing and/or breathlessness). CC was defined as a cough lasting more than 8 weeks. We analyzed resistance (R) and reactance (X) at 5 Hz, as well as the area of X (AX) and frequency dependence of R (R5–R19).

As summarized in Table 1, no changes in impedance characteristics could be demonstrated in CC subjects. Our impedance findings confirm previous CT data suggesting the absence of structural airway changes in subjects with CC.

Table 1.

Comparison of baseline characteristics and oscillometry parameters

No respiratory symptoms or pathologies (n = 5,389)CC only (n = 175)CC + symptoms (n = 134)
Age 45.9 (29.7; 60.7) 51.6 (30.7; 65.0) 53.3 (34.6; 63.1)* 
Females (%) 2,757 (51) 88 (50) 68 (51) 
BMI 24.7 (22.2; 27.8) 26.5 (22.9; 29.3)* 27.1 (23.9; 30.8)* 
Weight, kg 72.8 (62.9; 83.8) 75.1 (66.7; 86.3) 79.1 (68.5; 91.8)* 
Height, cm 170 (164; 178) 170 (164; 175) 170 (162; 177) 
R5 %pred 83.2 (69.3; 101.1) 85.7 (72.9; 108.9) 86.6 (71.3; 107.6) 
X5 %pred 81.4 (60.2; 108.1) 81.8 (60.7; 106.3) 83.9 (59.4; 124.7) 
AX %pred 132.1 (78.1; 219.2) 137.7 (76.4; 245.3) 160.2 (76.9; 278.6) 
R5–R19 %pred 63.1 (−90.8; 222.5) 83.8 (−64.2; 211.9) 102.0 (−9.2; 244.9) 
No respiratory symptoms or pathologies (n = 5,389)CC only (n = 175)CC + symptoms (n = 134)
Age 45.9 (29.7; 60.7) 51.6 (30.7; 65.0) 53.3 (34.6; 63.1)* 
Females (%) 2,757 (51) 88 (50) 68 (51) 
BMI 24.7 (22.2; 27.8) 26.5 (22.9; 29.3)* 27.1 (23.9; 30.8)* 
Weight, kg 72.8 (62.9; 83.8) 75.1 (66.7; 86.3) 79.1 (68.5; 91.8)* 
Height, cm 170 (164; 178) 170 (164; 175) 170 (162; 177) 
R5 %pred 83.2 (69.3; 101.1) 85.7 (72.9; 108.9) 86.6 (71.3; 107.6) 
X5 %pred 81.4 (60.2; 108.1) 81.8 (60.7; 106.3) 83.9 (59.4; 124.7) 
AX %pred 132.1 (78.1; 219.2) 137.7 (76.4; 245.3) 160.2 (76.9; 278.6) 
R5–R19 %pred 63.1 (−90.8; 222.5) 83.8 (−64.2; 211.9) 102.0 (−9.2; 244.9) 

BMI, body mass index; R5, resistance at 5Hz; X5, reactance at 5Hz; AX, area of reactance; R5–19, difference between inspiratory resistance at 5 and 19 Hz.

*p < 0.05 with “no respiratory symptoms or pathologies”.

The authors have no conflicts of interest to declare.

The Austrian LEAD Study is supported by Ludwig Boltzmann Gesellschaft, the Municipal Department of Health and Environment of Vienna, the Federal State Governmental Department of Health of Lower Austria, and unrestricted scientific grants from AstraZeneca, Chiesi Farmaceutici, GlaxoSmithKline, and Menarini Pharma. The supporting parties had no participation in data collection or interpretation, nor did they contribute to the design or the content of the letter. The LEAD study (ClinicalTrials.gov: NCT01727518) is being conducted in accordance with the International Conference on Harmonization notes for guidance on Good Clinical Practice and the principles of the Declaration of Helsinki and has been approved by the Ethics Committee of Vienna (EK-11-117-0711). All participants gave written informed consent, and no new consent was needed for the current analysis which includes data from the 4-year follow-up phase II between 2017 and 2021.

Under the supervision of E.F.M.W. and M.K.B., H.A. prepared the initial draft. All authors provided critical revision of the letter, as well as read and approved the final version. All authors had full access to the data and accepted responsibility for the decision to submit for publication.

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