An Oscillating Positive Expiratory Pressure Therapy System or OPEP device is designed to aid in the loosening and removal of mucus build-up in the lungs. You may need OPEP treatments if you have a lung disease such as cystic fibrosis or COPD where your lungs need help keeping up with the amount of mucus produced each day. OPEP therapy is done by inhaling and exhaling through the device several times, then ‘huff coughing’ to remove the loosened mucus.