The respiratory disability rating scale (RDRS) is a tool used by the VA to measure the severity of respiratory impairments. The scale consists of four levels, with Level I the mildest and Level IV the most severe. Level I: No impairment. This Level includes those who have no trouble with one or more activities of daily living. The disability rating given here is 0% and it is considered that the person has no lung damage. Level II: Mild impairment. This Level includes those who have a little difficulty with breathing and walking up and down stairs. The disability rating given is between 10%-20%. Level III: Moderate impairment. This Level includes those who have  difficulty walking for a moderate distance such as 100 yards. The disability score here lies between 30%-50% Level IV: Severe impairment. This Level includes those who have severe difficulty in walking, going up to major problems in even taking a few steps. The rating goes from 60% - 100% here, 100% being for people who are completely bedridden.