The partial pressure of oxygen in the alveolar gas is affected by certain situations. Classify each of the following conditions as causing an increase, decrease, or no change in alveolar PO_2. Solution Increase in pO2 will occur due to Increased alveolar ventilation and unchanged metabolism Decreased metabolism and unchanged alveolar ventilation. Decreased pO2 will occur due to Decreased alveolar ventilation and unchanged metabolism Increased metabolism and unchanged alveolar ventilation Breathing air with low pO2 No change in pO2 will occur due to Proportional increase in metabolism and alveolar ventilation Remember that, metabolism requires oxygen so it lowers partial pressure of oxygen whereas alveolar ventilation always increase pO2..