Vascular narrowing in pulmonary arterial hypertension is heterogeneous: rethinking resistance.
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 13μm (order 1) to 500μm (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.
Department of Pulmonary Diseases, VU University Medical Center, Amsterdam, the Netherlands n.rol@vumc.nl.|Laboratory for Physiology, Institute for Cardiovascular Research ICaR-VU VU University Medical Center, Amsterdam, the Netherlands.
Nina
N
Rol
Department of Physics and Medical Technology, VU University Medical Center, Amsterdam, the Netherlands.
Esther M
EM
Timmer
Department of Physics and Medical Technology, VU University Medical Center, Amsterdam, the Netherlands.
Theo J C
TJ
Faes
Department of Pulmonary Diseases, VU University Medical Center, Amsterdam, the Netherlands.
Anton
A
Vonk Noordegraaf
Department of Pathology, Radboud UMC, Nijmegen, the Netherlands.
Katrien
K
Grünberg
Department of Pulmonary Diseases, VU University Medical Center, Amsterdam, the Netherlands.
Harm-Jan
HJ
Bogaard
Department of Pulmonary Diseases, VU University Medical Center, Amsterdam, the Netherlands.|Laboratory for Physiology, Institute for Cardiovascular Research ICaR-VU VU University Medical Center, Amsterdam, the Netherlands.
Nico
N
Westerhof
D000328:Adult; D000368:Aged; D003251:Constriction, Pathologic / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D006976:Hypertension, Pulmonary / Q000473:pathology* / Q000503:physiopathology; D008168:Lung / Q000473:pathology* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D011651:Pulmonary Artery / Q000473:pathology* / Q000503:physiopathology; D066253:Vascular Remodeling / Q000502:physiology*; D014655:Vascular Resistance / Q000502:physiology*; D055815:Young Adult
External diameters; internal diameters; pulmonary vascular resistance; resistance vessels; wall thickness