Nitrogen Washout Make an Appointment Ask a Question Refer Patient Reviewed by George Zeman, RRT, CPFT, BS and Amy Olson, MD, MSPH (August 01, 2013) This test measures lung volumes of patients unable to tolerate plethysmography. Nitrogen Washout is used to calculate Total Lung Capacity (TLC) and Residual Volume (RV). The patient may be asked to repeat the procedure after a short rest period. This test may be done with or without a bronchodilator. This information has been approved by George Zeman, RRT, CPFT, BS and Amy Olson, MD, MSPH (August 2013).