Final answer:
The DLCO test is the PFT least dependent on patient effort, as it assesses gas exchange efficiency in the lungs rather than relying on patient-performed maneuvers like in spirometry.
Step-by-step explanation:
The Pulmonary Function Test (PFT) that is least dependent on patient effort is the measurement of diffusing capacity of the lungs for carbon monoxide (DLCO). Unlike spirometry, which requires a patient to inhale and exhale forcefully, DLCO measures how well gases exchange between the blood and the air within the lungs. This particular test primarily depends on the physiologic process rather than patient effort, making it a useful and reliable tool for assessing conditions affecting the pulmonary vasculature or the alveolar-capillary membrane, such as pulmonary fibrosis or emphysema.