The respirometer allows medical personnel to assess a patient's respiratory capacity. In order to use the respirometer, wipe the permanent mouthpiece with alcohol and then place a disposable mouthpiece over the permanent one. Set the dial for zero, then you are ready to begin.

Take a deep breath and exhale without using the device. Repeat several times.

Then practice exhaling through a disposable mouthpiece that is not attached to the device. Repeat several times.

Attach the disposable mouthpiece to the permanent mouthpiece, take a normal breath, and exhale at a normal rate into the mouthpiece.

Read the meter and record your results on a sheet of paper. The tidal_volume is the volume of air exhaled and inhaled during normal quiet respirations. Normal tidal volume is approximately 500 ml.

Now inhale normally, but exhale as hard as possible into the mouthpiece.

Record your result as the expiratory_reserve_volume (ERV). Normal ERV ranges between 1,000 and 1,200 ml.

Patients with COPD (chronic_obstructive_pulmonary_disease) have a  drastically reduced ERV.