Pulmonary hypertension is defined as a resting mean pulmonary artery pressure of 25 mm Hg or above. This review deals with pulmonary arterial hypertension (PAH), a type of pulmonary hypertension that primarily affects the pulmonary vasculature. In PAH, the pulmonary vasculature is dynamically obstructed by vasoconstriction, structurally obstructed by adverse vascular remodeling, and pathologically non-compliant as a result of vascular fibrosis and stiffening. Many cell types are abnormal in PAH, including vascular cells (endothelial cells, smooth muscle cells, and fibroblasts) and inflammatory cells. Progress has been made in identifying the causes of PAH and approving new drug therapies. A cancer-like increase in cell proliferation and resistance to apoptosis reflects acquired abnormalities of mitochondrial metabolism and dynamics. Mutations in the type II bone morphogenetic protein receptor (BMPR2) gene dramatically increase the risk of developing heritable PAH. Epigenetic dysregulation of DNA methylation, histone acetylation, and microRNAs also contributes to disease pathogenesis. Aberrant bone morphogenetic protein signaling and epigenetic dysregulation in PAH promote cell proliferation in part through induction of a Warburg mitochondrial-metabolic state of uncoupled glycolysis. Complex changes in cytokines (interleukins and tumor necrosis factor), cellular immunity (T lymphocytes, natural killer cells, macrophages), and autoantibodies suggest that PAH is, in part, an autoimmune, inflammatory disease. Obstructive pulmonary vascular remodeling in PAH increases right ventricular afterload causing right ventricular hypertrophy. In some patients, maladaptive changes in the right ventricle, including ischemia and fibrosis, reduce right ventricular function and cause right ventricular failure. Patients with PAH have dyspnea, reduced exercise capacity, exertional syncope, and premature death from right ventricular failure. PAH targeted therapies (prostaglandins, phosphodiesterase-5 inhibitors, endothelin receptor antagonists, and soluble guanylate cyclase stimulators), used alone or in combination, improve functional capacity and hemodynamics and reduce hospital admissions. However, these vasodilators do not target key features of PAH pathogenesis and have not been shown to reduce mortality, which remains about 50% at five years. This review summarizes the epidemiology, pathogenesis, diagnosis, and treatment of PAH.

Rationale:: Pulmonary arterial hypertension (PAH) is a lethal syndrome characterized by pulmonary vascular obstruction caused, in part, by pulmonary artery smooth muscle cell (PASMC) hyperproliferation. Mitochondrial fragmentation and normoxic activation of hypoxia-inducible factor-1α (HIF-1α) have been observed in PAH PASMCs; however, their relationship and relevance to the development of PAH are unknown. Dynamin-related protein-1 (DRP1) is a GTPase that, when activated by kinases that phosphorylate serine 616, causes mitochondrial fission. It is, however, unknown whether mitochondrial fission is a prerequisite for proliferation. Objective:: We hypothesize that DRP1 activation is responsible for increased mitochondrial fission in PAH PASMCs and that DRP1 inhibition may slow proliferation and have therapeutic potential. Methods and Results:: Experiments were conducted using human control and PAH lungs (n=5) and PASMCs in culture. Parallel experiments were performed in rat lung sections and PASMCs and in rodent PAH models induced by the HIF-1α activator, cobalt, chronic hypoxia, and monocrotaline. HIF-1α activation in human PAH leads to mitochondrial fission by cyclin B1/CDK1–dependent phosphorylation of DRP1 at serine 616. In normal PASMCs, HIF-1α activation by CoCl ₂ or desferrioxamine causes DRP1-mediated fission. HIF-1α inhibition reduces DRP1 activation, prevents fission, and reduces PASMC proliferation. Both the DRP1 inhibitor Mdivi-1 and siDRP1 prevent mitotic fission and arrest PAH PASMCs at the G2/M interphase. Mdivi-1 is antiproliferative in human PAH PASMCs and in rodent models. Mdivi-1 improves exercise capacity, right ventricular function, and hemodynamics in experimental PAH. Conclusions:: DRP-1–mediated mitotic fission is a cell-cycle checkpoint that can be therapeutically targeted in hyperproliferative disorders such as PAH.

The aim of the present study was to determine contemporary survival in pulmonary arterial hypertension (PAH), and to investigate whether or not the National Institutes of Health (NIH) equation remains an accurate predictor of survival.In 576 patients with PAH referred during 1991–2007, observed survival was described using the Kaplan–Meier method. In patients with idiopathic, familial and anorexigen-associated PAH (n = 247), observedversusNIH equation predicted survival was compared. A new survival prediction equation was developed using exponential regression analysis.The observed 1-, 3- and 5-yr survival in the total cohort were 86, 69 and 61%, respectively. In patients with idiopathic, familial and anorexigen-associated PAH, the observed 1-, 3- and 5-yr survival (92, 75 and 66%, respectively) were significantly higher than the predicted survival (65, 43 and 32%, respectively). The new equation (P(t) = e^-A(x,y,z)t, where P(t) is probability of survival,tthe time interval in years, A(x,y,z) = e^{(−1.270–0.0148x+0.0402y–0.361z)},xthe mean pulmonary artery pressure,ythe mean right atrial pressure andzthe cardiac index) performed well when applied to published contemporary studies of survival in PAH.Contemporary survival in the PAH cohort was better than that predicted by the NIH registry equation. The NIH equation underestimated survival in idiopathic, familial and anorexigen-associated PAH. Once prospectively validated, the new equation may be used to determine prognosis.

The aim of this study was to define the epidemiology of World Health Organization (WHO) Group I pulmonary arterial hypertension (PAH) in a large referral centre in the USA.The Pulmonary Hypertension Connection registry, initiated in 2004, evaluated all patients in a single USA practice from 1982–2006. For comparison, the authors divided the group by incidentversusprevalent cohorts, aetiology and by treatment era.In total, 578 patients (77% female) aged 48±14 yrs were entered. Of these, 80% had class III or IV symptoms. Over time, connective tissue disease-associated PAH increased, while referrals for HIV remained low. One-third of patients were referred on calcium channel blocker therapy even though only 4.6% had an acute response to vasodilator challenge. When compared by treatment era, there were no differences in the severity of PAH. However, survival had improved over time, with a 1-yr survival of 85% in the incident cohort.In the USA, pulmonary arterial hypertension patients are still referred to tertiary centres too late. Referral of connective tissue disease is increasing, while referral of HIV remains low. Inappropriate calcium channel blocker treatment is common. Survival rates have increased but remain low suggesting that prognosis is improving but PAH is still a progressive, fatal disease.

Background—: Pulmonary vascular disease associated with left-side heart failure and preserved ejection fraction (PH-HFpEF) is an increasingly common cause of pulmonary hypertension. The distinction between PH-HFpEF and pulmonary arterial hypertension (PAH) is important because therapies indicated for PAH can be detrimental in HFpEF. The characteristic features of PH-HFpEF are understudied. Methods and Results—: In a cross-sectional study, we compared the clinical, echocardiographic, and hemodynamic features of PH-HFpEF (n=100), with PAH (n=522), and HFpEF without pulmonary vascular disease (n=45). We determined the clinical characteristics that best differentiated PH-HFpEF from PAH. Compared with patients with PAH, patients with PH-HFpEF were older; had a higher prevalence of cardiovascular comorbidities; had worse exercise capacity and renal function; more frequently had left atrial enlargement; and less frequently had right atrial enlargement. PH was less severe in PH-HFpEF patients than in PAH patients (pulmonary vascular resistance 4.8 [interquartile range 3 to 8.4] versus 10.9 [interquartile range 7.4 to 15.7] Wood units; P <0.001). Old age, the presence of hypertension and coronary artery disease, the absence of right atrial enlargement, higher aortic systolic pressure, higher mean right atrial pressure, and higher cardiac output best differentiated PH-HFpEF from PAH (area under the receiver operating characteristics curve; curve 0.97). Compared with HFpEF patients without pulmonary hypertension, PH-HFpEF patients were often female and more symptomatic, more often had right ventricular hypertrophy and right atrial enlargement, and had higher right atrial pressure. Conclusions—: These data should help better identify PH-HFpEF, an entity that has become increasingly recognized and difficult to treat.

Pulmonary arterial hypertension (PAH) is characterized by remodeling of the extracellular matrix (ECM) of the pulmonary arteries with increased collagen deposition, cross-linkage of collagen, and breakdown of elastic laminae. Extracellular matrix remodeling occurs due to an imbalance in the proteolytic enzymes, such as matrix metalloproteinases, elastases, and lysyl oxidases, and tissue inhibitor of matrix metalloproteinases, which, in turn, results from endothelial cell dysfunction, endothelial-to-mesenchymal transition, and inflammation. ECM remodeling and pulmonary vascular stiffness occur early in the disease process, before the onset of the increase in the intimal and medial thickness and pulmonary artery pressure, suggesting that the ECM is a cause rather than a consequence of distal pulmonary vascular remodeling. ECM remodeling and increased pulmonary arterial stiffness promote proliferation of pulmonary vascular cells (endothelial cells, smooth muscle cells, and adventitial fibroblasts) through mechanoactivation of various signaling pathways, including transcriptional cofactors YAP/TAZ, transforming growth factor-β, transient receptor potential channels, Toll-like receptor, and NF-κB. Inhibition of ECM remodeling and mechanotransduction prevents and reverses experimental pulmonary hypertension. These data support a central role for ECM remodeling in the pathogenesis of the PAH, making it an attractive novel therapeutic target.