Which pulmonary function test involves measuring oxygen saturation using a probe on the patient's finger?

Pulse oximetry is the correct choice because it is specifically designed to measure the oxygen saturation of hemoglobin in the blood, typically using a sensor placed on a patient's fingertip. This non-invasive test provides real-time information about the patient's oxygen levels, helping healthcare providers assess respiratory function without the need for blood draws.

The other options relate to pulmonary function tests but do not directly measure oxygen saturation in the same way:

• Spirometry is used to assess lung function by measuring the volume and flow of air that can be inhaled and exhaled. It focuses on airflow characteristics rather than oxygen saturation.

• A peak flow meter also measures lung function, specifically the maximum speed of expiration, which can help manage conditions like asthma but does not indicate oxygen saturation levels.

• Bronchodilator responsiveness testing evaluates how well a patient's airways respond to bronchodilator medications to improve airflow and is relevant in diagnosing conditions like asthma or COPD, but it does not measure oxygen saturation.

Understanding the specific role of pulse oximetry in assessing oxygen saturation helps distinguish it from these other pulmonary assessments.