Final answer:
Infection or edema in the lung can lead to a physiological shunt, which decreases ventilation and changes the V/Q ratio, affecting gas exchange.
Step-by-step explanation:
A physiological shunt can develop if there is infection or edema in the lung that obstructs an area. This will decrease ventilation but not affect perfusion; therefore, the V/Q ratio changes and gas exchange is affected.
A physiological shunt refers to the portion of the blood flow in the circulatory system that bypasses the lungs or doesn't participate in gas exchange due to certain anatomical or physiological factors. In a healthy individual, blood that passes through the lungs should be adequately oxygenated, but a physiological shunt results in blood that remains poorly oxygenated.