 [ Symptoms ] my mother is left lung had collapsed but doctors do not know why [ Disease ] hi lung collapse or pnemothorax is usually caused by injury or rib fracture but with your mum it would be of no cause due to aging or just secondary complication to chronic obstructive pulmonary disease my advice start teaching her breathing exercises to expand the lung buy her a spirometer by which you can do biofeedback inspiration exercise to promote lung expansion a physiotherapist may help her walk better and breath better… regards