You would expect a larger decrease in the PaO 2 in a patient with a q,bilateral…

➤ Why does pneumothorax lower arterial oxygen tension (PaO2)?
Pneumothorax lowers PaO2 mainly by producing V/Q mismatch and a physiologic shunt. Air in the pleural space collapses alveoli while pulmonary blood flow often continues, so perfused regions receive little ventilation. Diffusion limitation is less important. The result is reduced oxygen transfer into arterial blood.