What is the effect of the Valsalva maneuver on DLCO?

The Valsalva maneuver, which involves a forced exhalation against a closed airway (such as closing the mouth and pinching the nose while trying to exhale), can lead to physiological changes within the thoracic cavity and subsequently affect gas exchange.

During the maneuver, intrathoracic pressure increases, which can compress the pulmonary vasculature. This compression can reduce blood flow through the pulmonary capillaries where gas exchange occurs, thereby decreasing the amount of carbon monoxide that can be absorbed per unit of lung volume during the diffusion capacity test (DLCO). A decrease in blood flow effectively lowers the surface area available for gas exchange, making the transfer of gas between the alveoli and the bloodstream less efficient.

Consequently, the outcome of the Valsalva maneuver is a reduction in the DLCO, reflecting decreased gas exchange efficiency during this maneuver. This rationale supports the correct identification of the effect of the Valsalva maneuver on DLCO as a decrease.