Hyperoxia test: 1  Administer 100 % oxygen for > 10 min. 2  PaO2 > 100 mmHg: pulmonary disease likely. 3  PaO2 < 70 mmHg, rise by < 30 mmHg or SaO2 unchanged: cardiac cause (R-L shunt) likely. 4  Total anomalous pulmonary venous return may respond. 5  Pulmonary disease with a massive intrapulmonary shunt may not respond.