<prompt> Increase blood flow to lungs causeNo change in pulmonary vascular resistanceIncreased pulmonary vascular resistanceDecreases pulmonary vascular resistanceInitial increase followed by decrease in pulmonary vascular resistance  <response>: Other causes include obstructive sleep apnea, congenital hea disease, chronic hypoxemia, pulmonary thrombosis blood clots, or left ventricular failure. ... Hemodynamically, PAH can be caused by increased right ventricular output, increased pulmonary systemic vascular resistance, or increased pulmonary venous pressure Ref: guyton and hall textbook of medical physiology 12 edition page number:311,312,313 