 This is a randomized cross-over unblinded study in 15 subjects with COPD. All subjects will cross-over at four weeks of oPEP therapy or four weeks of no therapy. Each subject will visit the centre on five occasions baseline, 2 weeks, 4 weeks cross-over, 6 weeks and 8 weeks for one hour each and will perform: 1 spirometry and plethysmography, 2 six-minute walk test 6MWT, and 3 health status evaluation using a self-administered St. Georges Respiratory Questionnaire SGRQ. Subjects will first provide written informed consent and will complete: 1 SGRQ after inhaling 2-4 puffs 200-400μg of the short-acting bronchodilator eg. Salbutamol, 2 plethysmography and spirometry 355 minutes post-salbutamol. Vital signs will be documented and subjects will rest for approximately 15 minutes before completing the six-minute walk test 6MWT post-salbutamol. Subjects will be given an oPEP therapy system Aerobika to use at home, four times per day. Instruction and training on the use of the device will be given at the baseline visit. Subjects will be required to return the device upon completion of the study. 