74 years old Male COPD patient suffering with Orthopnea

My dad (aged 74) is a COPD patient and had quit smoking and consumption of alcohol 10 years ago. He started suffering with Orthopnea from past few weeks. His pulmonary and cardio test reports seem normal. His SpO2 reading is 92 when lay down, otherwise 96. He is having discomfort while sleeping on bed (side position)and siting in a chair throughout the night. Some medication is given by pulmonologist and it's not helping much.