Introduction
Cystic fibrosis (CF) is the most common genetically inherited disease in the Caucasian population. It is a progressive life-shortening disease that affects several organs and is caused by mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene [
1]. However, the life expectancy of people with CF (pwCF) has increased continuously over the last few years, which has resulted in a growing population of adult pwCF [
2].
Pulmonary involvement continues to be the major cause of morbidity and mortality, with women experiencing a worse course of CF lung disease [
3]. Therapy for CF lung disease requires adherence to a strict daily and lifelong treatment regimen. A crucial part of daily CF management is airway clearance techniques (ACTs) to prevent progression of CF lung disease by coughing and expectorating sputum. However, pwCF frequent coughs as a bothersome and stressful symptom. They report being embarrassed by coughing in public situations and having concerns that they might disturb people around them [
4]. Furthermore, pwCF feelings of annoyance, irritation, frustration, and worry by frequent coughing [
5]. Nonetheless, only a very limited number of studies have reported on cough suppression (CS) in pwCF. In two detailed studies with adolescent pwCF, embarrassment about coughing was used as an indicator of CS [
6,
7]. Sex differences were found in a way that girls were more embarrassed about coughing than boys, with the consequence that girls suppressed coughing in public to avoid negative attention. CS has also been discussed as one of the factors contributing to the increased morbidity of female pwCF by affecting therapy adherence. Low adherence to the complex treatment regimens not only influences clinical variables related to pulmonary morbidity, including ppFEV
1 and BMI. Additionally, it has also been associated with a reduced quality of life [
8].
Health-related quality of life (HRQoL) is a multidimensional construct used as a health outcome and covers physical, psychological, and social functioning in daily life as seen from the patient's perspective [
9]. Determinants of HRQoL in pwCF include lung function and BMI [
10], treatment burden [
11], lack of hope for the future [
9], and sex. Consistent with sex differences regarding CS, female pwCF show lower HRQoL on several domains of generic and disease-specific scales, including global and mental health, than male pwCF [
9]. Male and female pwCF perceive their health status differently, with females having a more accurate perception of their objective clinical health status. Additionally, women respond differently to poor health by reporting higher levels of physical or emotional symptoms than men [
10].
Against this background, we report on explicitly captured CS in an adult cohort of pwCF and its relation to HRQoL, future health-related perspectives, and important clinical outcomes (ppFEV1 and BMI), also accounting for sex.
Discussion
With this cross-sectional study, we present for the first time that CS exists in adult pwCF, is more prevalent in women, and relates to reduced HRQoL. In contrast to previous studies in adolescents, which found that CS negatively correlated with ppFEV
1 and BMI [
6,
7], these findings could not be confirmed in adult pwCF. Furthermore, no relationship between CS and health-related perspectives of the future was observed. Despite the relationship between CS and HRQoL and a higher prevalence of CS in females, there was no significant sex difference regarding HRQoL or any other outcome measure, that is, ppFEV
1, BMI, or perspectives.
The existence of CS in adult pwCF illustrates that this behavior persists into later stages of life. Eighty-five percent of the participating pwCF reported CS, of which 20% reported CS frequently and 6% reported CS consistently. Even in adulthood, women exhibit CS more frequently than men. In the present study, 98% of female subjects suppressed coughing, and 40% did so 'frequently' or 'always'. This finding is consistent with previous studies in adolescent pwCF, indicating that females of either age are more self-conscious about the impact of their coughing on others and show a tendency to suppress coughing to avoid negative public attention [
6,
7]. From a social-cognitive perspective [
17], CS undergoes stabilization as development progresses by reinforcement that may include avoiding negative public attention, thus avoiding cough-related negative emotions. Accordingly, in adults with CF avoiding cough, there was an uncorrected significant impairment of social life as assessed by the CFQ-R. Thus, negative emotions related to coughing may help preserve this behavior and negatively affect psychological well-being beyond adolescence.
Adolescent female patients with CS showed worse physiological outcomes [
6,
7], but no such relationship was found in the adult cohort of pwCF in either sex regarding ppFEV
1 and BMI in the present study. Thus, although CS is still more common in adult women with CF, the effects on physical outcomes are dissipating. As mentioned above, female adolescents appear to be more sensitive to cultural and social norms and are more concerned with socially conforming behavior. One possible explanation might be that female pwCF have become more self-accepting concerning their disease in adulthood. However, using disclosure of the CF diagnosis as a proxy for self-acceptance, there was no difference in this regard between female and male pwCF in the present study. Thus, the negative effect of CS on physical health could be offset by mechanisms other than those assessed in the present study in more detail. Moreover, these mechanisms might also partially be maladaptive, resulting in psychological distress. As mentioned above, there is suggestive evidence that adult female pwCF avoiding coughing may limit their social life to avoid the negative psychological impact of CS, which may also extend to other areas of life. However, this explanation warrants further well-powered studies addressing avoiding strategies in adult pwCF exhibiting CS.
In the present study, we did not find a relationship between CS and therapy adherence, a hypothesized mechanism linking CS to worse clinical outcomes as an indicator of non-adherence. Interestingly, despite the observation that subjects prone to CS are not less adherent, these subjects experienced a (uncorrected) significantly higher subjective treatment burden, again implying that CS may represent a proxy for increased psychological strain. Importantly, comparing findings regarding the relationship between CS and clinical outcomes with previous studies, it must be considered that formerly CS was operationalized by recording embarrassment about coughing and not CS itself, as in the present study.
Analysis of our data indicated that CS is associated with HRQoL. This effect was independent of physical health status investigated by lung function, BMI, or the presence of CFRD. This indicates that HRQoL in pwCF with CS cannot be explained by clinical indicators of disease status but instead seems to be associated with other variables at a subjectively experienced level. Since CF also influences psychological well-being, it is likely that mental health indicators have an impact on CS and possibly HRQoL. Unfortunately, this information as well as data on psychological morbidities, such as depressive symptoms, were not collected in the present observational study. Nonetheless, our results corroborate previous studies showing that quality of life is more strongly associated with mental health factors than physical health indicators [
9,
18] and highlight the importance of screening patients’ mental health [
8].
A weakness of the present study is the sample size and a potential bias through the inpatient testing procedure. Although the sample size was relatively large for a single-center CF study, it may not have been large enough to detect the complexities in the relationship of CS and the physiological and psychological outcomes. For example, the analyses regarding the relationship between CS and the CFQ-R + 14 subscales did not survive corrections for multiple comparisons.
Ninety-six percent of the participating subjects took part during an inpatient hospital stay and suffered from advanced disease status. Therefore, it was a relatively homogeneous group of participants. The inclusion of more outpatient pwCF experiencing different clinical conditions might have resulted in a more heterogeneous group; it would be quite interesting if this would have had an impact on the results. Nonetheless, this study is the first to examine CS regarding clinical parameters of disease severity and HRQoL in adult pwCF.
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