Although mild pulmonary hypertension (PH) is a common feature of chronic obstructive pulmonary disease (COPD), there appears to be a subgroup of patients in whom a specific phenotype may develop that is characterized by moderate airflow limitation, severe precapillary PH, low partial pressure oxygen, impaired diffusion capacity of the lungs for carbon monoxide (DLCO), and progressive right heart failure — all of which leads to have very poor survival, according to an article published by the American Journal of Respiratory and Critical Care Medicine.
Gabor Kovacs of the Medical University of Graz and the Ludwig Boltzmann Institute for Lung Vascular Research in Graz, Austria, and colleagues reviewed the pulmonary vascular changes in COPD and explored the evidence gaps, unmet needs, and current research questions regarding a possible pulmonary vascular phenotype.
The authors reviewed factors underlying the pulmonary vascular changes seen in COPD, such as cigarette smoking, which can lead to pulmonary vascular remodeling, and the role of endothelial cells in regulating pulmonary vascular tone. The airway abnormalities that are common to COPD can cause hypoxic pulmonary vasoconstriction in poorly ventilated areas of the lung that reduces blood flow. If hypoxic pulmonary vasoconstriction persists in many areas of the lung, it can lead to PH with pulmonary vascular remodeling, characterized by thickening of the medial layer of the muscular arteries and neomuscularization of small vessels.
A cluster analysis indicated that the clinical profile of patients in whom severely elevated pulmonary arterial pressure and pulmonary vascular resistance develop differs from that of people with other COPD phenotypes. These patients have less severe airflow limitation but more severe arterial hypoxemia often accompanied by hypocapnia, very low DLCO, and severe dyspnea during exercise. During exercise, they show a clear cardiovascular limitation pattern in contrast to those with COPD with less severe PH who experience combined circulatory and ventilatory exercise limitation. Furthermore, in patients who might be characterized as having a pulmonary vascular COPD phenotype, progressive right heart failure often develops and these patients have significantly poorer survival compared with those with mild to moderate PH.
Based on their review of the issues involved, the authors proposed a tentative working definition of the pulmonary vascular phenotype of COPD: the presence of severe PH with moderate airflow limitation and no hypercapnia, very low DLCO, circulatory exercise limitation, and/or progressive right heart failure. They further suggested that based on these criteria, only 1% to 4% of patients with COPD would meet the definition.
The authors called for a prospective controlled study to determine whether patients with a pulmonary vascular COPD phenotype would benefit from early targeted pulmonary arterial hypertension therapy.
Kovacs G, Agusti A, Barberà JA, et al. Pulmonary vascular involvement in COPD – Is there a pulmonary vascular phenotype? [published online May 10, 2018]. Am J Respir Crit Care Med. doi: 10.1164/rccm.201801-0095PP