Final answer:
The causes of an increased A-a gradient include physiological shunt and V/Q mismatch. Physiological shunt occurs when infection or edema obstructs an area in the lungs, while V/Q mismatch arises from a mismatch between ventilation and perfusion. Both conditions lead to changes in the V/Q ratio and affect gas exchange.
Step-by-step explanation:
A physiological shunt can develop in the lungs due to infection or edema, which obstructs an area and decreases ventilation but does not affect perfusion. This leads to a change in the V/Q ratio and affects gas exchange. V/Q mismatch, which can arise from anatomical or physiological changes, is another cause of an increased A-a gradient. V/Q mismatch occurs when there is a mismatch between ventilation and perfusion in the lungs, resulting in regions of broken down or blocked lung tissue known as dead spaces.