Atelectasis is a condition of the lung that decreases the deep breathing capability of a person. The entire lung, or a part of it, becomes airless and collapses. Atelectasis is not life-threatening to adults, because normally, only a small part of the lung is affected by it. But in children below 10 years of age, the condition may be critical as their bronchial tubes are already very narrow. A large part of the lung affected by atelectasis, may even result in lung damage.