Is the time constant of the pulmonary circulation truly constant?

I read with great interest the recent article by DELCROIX et al. [1] on vascular and right ventricular remodelling in chronic thromboembolic pulmonary hypertension (CTEPH). I found it very informative; however, I would like to comment on some of the statements that were made. In relation to pulmonary vascular remodelling, the authors have stated that in spite of there being proportionally more wave reflection in CTEPH, the RC (resistance6compliance) time constant of the pulmonary circulation is not different in CTEPH and pulmonary arterial hypertension. They invoked that the functional adaptation of the pulmonary circulation to vascular disease is monotonous (any change in pulmonary vascular resistance (PVR) determines proportional changes in pulmonary compliance (Cp)). Therefore, compliance and resistance are inseparably connected in health and disease, and after treatment [2]. The constant RC time also explains the proportional relationships between systolic and diastolic pulmonary arterial pressure (PAP) with mean pressure being linear relationships with a slope (Ksys and Kdias, respectively) and intercept [3, 4]. Moreover, a constant PVR6Cp product implies that right ventricular oscillatory power (Wosc) remains a constant fraction of total power (Wtot), irrespective of PAP [3]. As mean PAP (mPAP) is the geometric mean of systolic PAP (sPAP) and diastolic PAP (dPAP), the product of Ksys and Kdias is close to unity, so that mPAP5!(sPAP6dPAP). This relationship, however, is independent of a constant RC time [4].