Haemodynamics and post-exercise recovery response in chronic obstructive pulmonary disease-pulmonary hypertension and interstitial lung disease-pulmonary hypertension: An appraisal

Dear Editor, We read with great interest the article titled ‘Haemodynamics and post-exercise recovery response in chronic obstructive pulmonary disease-pulmonary hypertension and interstitial lung disease-pulmonary hypertension: An appraisal’. We have the following comments to offer: The role of age as a potential confounding factor appears to be underappreciated in interpreting the results in this article. The demographic comparison of the two groups shows that chronic obstructive pulmonary disease-pulmonary hypertension (COPD-PH) has a significantly higher age (P value 0.002). Age is independently associated with parameters such as right ventricular function (Tricuspid annular plane systolic excursion [TAPSE]), pulmonary artery pressures, pulse rate variability, desaturation trends and comorbidity burden. Systolic pulmonary artery pressure increases with age approximately 1 mmHg per decade and should be considered when comparing populations of different ages.[1] Age-stratified subgroup analysis and propensity score matching would improve the validity of conclusions. Pulmonary function in chronic lung disease correlates with disease severity. Significantly different baseline pre-bronchodilator forced expiratory volume in 1 s (FEV1) values between the groups reflect a substantial difference in ventilatory capacity (P value < 0.0001). The observed higher decline in peak expiratory flow rate (PERR) in the interstitial lung disease (ILD) group can be due to the initial higher ventilatory capacity (higher FEV1). Thus, it is a confounding variable. This also suggests that the study groups may have been in different stages of disease, therefore influencing the results. The study lacks a detailed assessment of comorbidities and does not appear to have systematically ruled out other potential causes of pulmonary artery hypertension, such as left heart disease (Group 2) or chronic thromboembolic PH (Group 4). This limitation is particularly important given the likelihood of multi-factorial PH in older adults, which could impact the results.[2] The study does not mention the World Health Organization (WHO) functional classification, which limits the clinical interpretation of post-exercise recovery response. Functional classification provides essential context regarding patients’ symptom burden and exercise capacity, and its inclusion would have provided great clarity on the severity and functional impairment of PH in each group. The study does not mention smoking status, which is an independent risk factor for PH. Tobacco exposure promotes endothelial dysfunction, smooth muscle proliferation and vascular remodelling even in the absence of airflow obstruction.[3] It may confound the observed haemodynamic differences between COPD-PH and ILD-PH cohorts. The study relies on the two-chair test as a method for post-exercise recovery. This test lacks widespread validity and makes cross-study comparison difficult.[4] Standard tests like the 6-min walk test (6MWT) and the 1-min sit-to-stand (STS) are internationally accepted and better validated, and provide stronger prognostic insight into chronic lung disease.[5] The study provides important comparative data on ILD-PH and COPD-PH; however, a key limitation is the absence of follow-up evaluation. Given the progressive nature of both interstitial and obstructive lung disease with associated PH, follow-up is essential to assess the changes in right ventricular function. The absence of follow-up data restricts the ability to evaluate disease progression, the stability of haemodynamic parameters and long-term outcomes in either group. Financial support and sponsorship Nil. Conflict of interest There are no conflicts of interest.