The Resmon Pro Forced Oscillation Technique is a non-invasive method of being able to measure the mechanical properties of the lung and airways during tidal breathing. It can be utilized to measure the expiratory flow limitations which will signal the presence of any respiratory obstruction. It also measures the total impedance which is the resistance and reactance. Patented technology was developed by Restech to determine the breath by breath presence and EFL severity during quiet breathing. Using the Resmon Pro, the presence, severity and reversibility of expiratory flow limitation (EFL) can be detected, leading to the evaluation of the degree of airflow obstruction and shortness of breath that is experienced by the patient.