Why there is a need to discuss pulmonary hypertension other than pulmonary arterial hypertension?

Abstract

Pulmonary hypertension (PH) is a condition characterized by the elevation of the mean pulmonary artery pressure above 25 mmHg and the pulmonary vascular resistance above 3 wood units. Pulmonary arterial hypertension (PAH) is an uncommon condition with severe morbidity and mortality, needing early recognition and appropriate and specific treatment. PH is frequently associated with hypoxemia, mainly chronic obstructive pulmonary disease and DPLD and/or left heart diseases (LHD), mainly heart failure with reduced or preserved ejection fraction. Although in the majority of patients with PH the cause is not PAH, a significant number of published studies are still in regard to group I PH, leading to a logical assumption that PH due to other causes is not such an important issue. So, is there a reason to discuss PH other than PAH? Chronic lung diseases, mainly chronic obstructive lung disease and DPLD, are associated with a high incidence of PH which is linked to exercise limitations and a worse prognosis. Although pathophysiological studies suggest that specific PAH therapy may benefit such patients, the results presented from small studies in regard to the safety and effectiveness of the specific PAH therapy are discouraging. PH is a common complication of left heart disease and is related to disease severity, especially in patients with reduced ejection fraction. There are two types of PH related to LHD based on diastolic pressure difference (DPD, defined as diastolic pulmonary artery pressure - mean PAWP): Isolated post-capillary PH, defined as PAWP > 15 mmHg and DPD < 7 mmHg, and combined post-capillary PH and pre-capillary PH, defined as PAWP > 15 mmHg and DPD ≥ 7 mmHg. The potential use of PAH therapies in patients with PH related to left heart disease is based on a logical pathobiological rationale. In patients with heart failure, endothelial dysfunction has been proposed as a cause of PH and hence as a target for treatment, supported by the presence of increased endothelin-1 activity and impaired nitric oxide-dependent vasodilation. Unfortunately, so far, there is no evidence supporting the use of specific PAH therapies in patients with PH related to left heart disease. In conclusion, the presence of PH in patients with conditions other than PAH contributes to the severity of the disease, affecting the outcome and quality of life. The disappointing results regarding the effectiveness of specific PAH therapies in patients with chronic lung diseases and LHD underline the need for seeking new underlying mechanisms and thus novel therapies targeting PH due to left heart disease and/or lung diseases.

Keywords: Pulmonary hypertension; Pulmonary arterial hypertension; Chronic obstructive pulmonary disease; Heart failure; Treatment

Core tip: Pulmonary arterial hypertension (PAH) is a rare disease that concerns a small population of patients. Recently, there has been a significant number of research, publications and novel therapies concerning PAH. However, pulmonary hypertension (PH), that concerns a much larger population of patients with common diseases such as lung and left heart diseases (LHD), is generally overlooked despite the fact that it significantly affects the prognosis of these patients. This editorial underlines the need for further research in regard to the pathogenesis and novel therapies for PH related to lung and LHD.