Pulmonary arterial hypertension (PAH) is a rare but serious complication of systemic lupus erythematosus (SLE). Chronic hypoxia is known to cause PAH resulting from pulmonary vascular remodeling. We investigated the association between anemic hypoxia and PAH in SLE patients.
Systolic pulmonary artery pressure (PAP) was measured in 132 SLE patients by echocardiography. Increased PAP was defined as resting PAP > 40 mm Hg. Oxygen delivery (DO2) was estimated as the product of cardiac output and arterial oxygen content.
Of 132 patients, 17 (12.9%) had increased PAP, and these patients had significantly lower DO2 values than patients with normal PAP (P = 0.002). The DO2 values inversely correlated with PAP values (γ = -0.308, P < 0.001) and plasma N-terminal pro-brain natriuretic peptide levels (γ = -0.323, P = 0.001), but positively correlated with hemoglobin levels (γ = 0.402, P < 0.001). Compared to those with normal PAP, patients with increased PAP had significantly longer durations of anemia over the preceding 6-24 months. Patients with anemia of longer durations (≥3 months) in the preceding 6 months had a higher risk of increased PAP compared to those with shorter durations (P < 0.001). When SLE patients were divided into 3 groups according to hemoglobin and PAP, serum interleukin-6 (IL-6) levels increased across groups with higher PAP (P = 0.001 for trend), but decreased across tertiles of hemoglobin levels (P = 0.008 for trend).
Our data indicate an association between chronic anemic hypoxia and increased PAP in SLE patients and suggest that increased IL-6 might participate in this process.