Almitrine: A respiratory stimulant that enhances respiration by acting as an agonist of peripheral chemoreceptors located on the carotid bodies. The drug increases arterial oxygen tension while decreasing arterial carbon dioxide tension in patients with chronic obstructive pulmonary disease. It may also prove useful in the treatment of nocturnal oxygen desaturation without impairing the quality of sleep.Respiratory System Agents: Drugs used for their effects on the respiratory system.Pulmonary Heart Disease: Hypertrophy and dilation of the RIGHT VENTRICLE of the heart that is caused by PULMONARY HYPERTENSION. This condition is often associated with pulmonary parenchymal or vascular diseases, such as CHRONIC OBSTRUCTIVE PULMONARY DISEASE and PULMONARY EMBOLISM.Doxapram: A central respiratory stimulant with a brief duration of action. (From Martindale, The Extra Pharmocopoeia, 30th ed, p1225)Levorphanol: A narcotic analgesic that may be habit-forming. It is nearly as effective orally as by injection.