Vascular narrowing in pulmonary arterial hypertension is heterogeneous: rethinking resistance

• Published in: Physiological reports Vol. 5; no. 6; pp. np - n/a
• Main Authors: Rol, Nina, Timmer, Esther M., Faes, Theo J.C., Vonk Noordegraaf, Anton, Grünberg, Katrien, Bogaard, Harm‐Jan, Westerhof, Nico
• Format: Journal Article
• Language: English
• Published: United States John Wiley & Sons, Inc 01.03.2017; John Wiley and Sons Inc
• Subjects: Adult; Aged; Blood Pressure; Constriction, Pathologic - pathology; Constriction, Pathologic - physiopathology; External diameters; Humans; Hypertension; Hypertension, Pulmonary - pathology; Hypertension, Pulmonary - physiopathology; internal diameters; Lung - pathology; Lung - physiopathology; Male; Middle Aged; Nitric oxide; Original Research; Physiology; Pulmonary Artery - pathology; Pulmonary Artery - physiopathology; Pulmonary hypertension; pulmonary vascular resistance; resistance vessels; Respiratory Conditions Disorder and Diseases; Vascular Remodeling - physiology; Vascular Resistance - physiology; Vasculature; wall thickness; Young Adult; resistance vessels; pulmonary vascular resistance; internal diameters; wall thickness; External diameters
• ISSN: 2051-817X; 2051-817X
• DOI: 10.14814/phy2.13159

In idiopathic pulmonary arterial hypertension (PAH), increased pulmonary vascular resistance is associated with structural narrowing of small (resistance) vessels and increased vascular tone. Current information on pulmonary vascular remodeling is mostly limited to averaged increases in wall thickness, but information on number of vessels affected and internal diameter decreases for vessels of different sizes is limited. Our aim was to quantify numbers of affected vessels and their internal diameter decrease for differently sized vessels in PAH in comparison with non‐PAH patients. Internal and external diameters of transversally cut vessels were measured in five control subjects and six PAH patients. Resistance vessels were classified in Strahler orders, internal diameters 13 μm (order 1) to 500 μm (order 8). The number fraction, that is, percentage of affected vessels, and the internal diameter fraction, that is, percentage diameter of normal diameter, were calculated. In PAH, not all resistance vessels are affected. The number fraction is about 30%, that is, 70% of vessels have diameters not different from vessels of control subjects. Within each order, the decrease in diameter of affected vessels is variable with an averaged diameter fraction of 50–70%. Narrowing of resistance vessels is heterogeneous: not all vessels are narrowed, and the decrease in internal diameters, even within a single order, vary largely. This heterogeneous narrowing alone cannot explain the large resistance increase in PAH. We suggest that rarefaction could be an important contributor to the hemodynamic changes. Current information on pulmonary vascular remodeling in Pulmonary Arterial Hypertension (PAH) is mostly limited to averaged increases in wall thickness, but quantitative information is limited on number of vessels affected and internal diameter decreases for vessels of different sizes. Our aim was to quantify numbers of affected vessels and their internal diameter decrease for differently sized vessels in PAH. We found that narrowing of resistance vessels is heterogeneous: not all vessels are narrowed, and decreased internal diameters, even within a single order, vary largely. Heterogeneous narrowing alone cannot explain the large resistance increase in PAH.