Dear editor
We read the study by Hee Jin Park et alCitation1 with great interest. The authors have investigated the prevalence of comorbidities in Korean chronic obstructive pulmonary disease (COPD) population. We raise our concern regarding the definition of COPD in this study. The study defines COPD as airflow limitation (only pre-spirometry forced expiratory volume in 1 second/forced vital capacity [FEV1/FVC] <70%) in subjects aged ≥40 years. To differentiate, between asthma and COPD, it is essential to do a post bronchodilator spirometry. It would have been wise to report the findings as prevalence of comorbidities in obstructive airway diseases rather than specifically calling it as COPD.
In this study, the authors have compared the prevalence of comorbidities between three groups: normal, restrictive, and obstructive. There is a discrepancy in defining restriction on the basis of spirometry values. Here, restriction is defined as FEV1/FVC normal and FEV1 <80%, but the actual criteria is FVC <80% predicted. However, it is important to note that restriction should be confirmed with static lung volumes rather than just relying on spirometry indices. Aaron et al have reported that out of the total number of subjects with low FVC on spirometry, only 41% had restriction when confirmed with lung volume measurements.Citation2
It is likely that in this study restriction is overestimated due to the lack of static lung volume measurements. We assume that most of the subjects showing restriction on spirometry but otherwise having normal static lung volumes would have been then added to the normal group. Probably, this may have resulted in no significant differences in the comorbidities between the two groups (normal and obstructive). It would have been interesting to know the mean FVC and FEV1 values in the restrictive group. Apart from restriction, there are several reasons for reduced FVC. One of the reasons for reduced FVC in the restrictive group is obesityCitation3 because 52.1% of the subjects in this group have body mass index (BMI) ≥23.0 kg/m2.
The study concludes that hypertension is a common comorbidity in COPD compared to the normal group. However, this finding is confounded by factors such as age and sex. There is a significant difference in the mean age between normal and obstructive group. Anderson et al have reported that increased age is associated with significant increase in the prevalence of hypertension after 60 years of age.Citation4 The male:female ratio is different in both the groups. There are more number of males in the obstructive group (68%) as compared to normal (38.4%). It is known that the incidence of hypertension is greater in men than that in women.Citation5,Citation6 A proper grouping, sex-, and age-matched analysis would have given a true estimate of the prevalence of comorbidities in different groups.
Disclosure
The authors report no conflicts of interest in this communication.
Reference
- ParkHJLeemAYLeeSHComorbidities in obstructive lung disease in Korea: data from the fourth and fifth Korean National Health and Nutrition Examination SurveyInt J Chron Obstruct Pulmon Dis2015101571158226300636
- AaronSDDalesRECardinalPHow accurate is spirometry at predicting restrictive pulmonary impairment?Chest1999115386987310084506
- ZammitCLiddicoatHMoonsieIMakkerHObesity and respiratory diseasesInt J Gen Med2010333534321116339
- AndersonGHEffect of age on hypertension: analysis of over 4,800 referred hypertensive patientsSaudi J Kidney Dis Transpl199910328629718212439
- AnastosKCharneyPCharonRAHypertension in women: what is really known? The Women’s Caucus, Working Group on Women’s Health of the Society of General Internal MedicineAnn Intern Med199111542872931854113
- BurtVLWheltonPRoccellaEJPrevalence of hypertension in the US adult population. Results from the Third National Health and Nutrition Examination Survey, 1988–1991Hypertension19952533053137875754