Pulmonary function tests
To check how and if the condition of myasthenia gravis is affecting the breathing, the doctor might order pulmonary function tests such as plethysmography and spirometry. In case of spirometry, the doctor asks patient to take deep breaths and then blow into a mouthpiece while for plethysmography, the patient sits in an airtight room and starts breathing in a mouthpiece to detect the breathing.