All are causes of pulmonary hypeension except,

Hyperventilation [Ref Harrison 17th/e p. 1579; 161h/e p. 14041 There are three main causes of pulmonary hypeension:- i) Cardiac diseases ii) Respiratory disease iii) Pulmonary thromboembolic disease Cardiac diseases -Lead to pulmonary hypeension by increasing pulmonary blood flow (e.g., large left to right shunt) or by increasing pulmonary venous pressure (e.g., L V. failure). In Respiratory diseases, - The predominant mechanism for the pulmonary hypeension is an increase in resistance to pulmonary blood flow arising from perivascular parenchymal changes coupled with pulmonary vasoconstriction due to hypoxia. * In pulmonary thromboembolic disease, - Clots in pulmonary vessels increase resistance to blood flow causing pulmonary hypeension. Now about other options mentioned in the question. Alveolar hyperventilation Pulmonary hypeension is seen in Alveolar hypoventilation (not hyperventilation). In patients with alveolar hypoventilation the primary pathogenic mechanism responsible for pulmonary hypeension is alveolar hypoxia potentiated by respiratory acidosis. (alveolar hypoxia leads to constriction of pulmonary vessels). Regardless of the etiology, whether pulmonary hypeenstion will occur in patients with alveolar hypoventilation depends on whether there is sufficient alveolar and aerial hypoxia to raise pulmonary aerial pressure considerably. In sleep apnea syndrome seen in obese individuals - Severe aerial hypomexia occurs during sleep due to hypoventilation (apnea). This causes pulmonary hypeension during sleep. After some point of time, the pulmonary hypeension may continue even during the day time. Anorexiants Pulmonary hypeension has been associated with anorexiants. "A causal relationship has been established between exposure to several anorexigens including aminorex and fenfluramine and development of pulmonary aery hypeension."