Physiologically, two aspects are involved in the relationship between the lung and the spleen. One is the production of the pectoral qi. The lung is responsible for inhaling fresh air and the spleen for absorbing food nutrients through transportation and transformation. The accumulation of the fresh air and food nutrients in the chest eventually transforms into the pectoral qi. Thus the normal functions of the lung and the spleen are prerequisite to sufficient production of the pectoral qi. 

The other is the metabolism of fluid. The spleen absorbs and transports water and the lung distributes water to all parts of the body, both of which are important to the metabolism of water. If deficiency of spleen-qi or insufficiency of lung-qi affects the production of the pectoral qi, it will lead to shortness of breath, no desire to speak, chest oppression, poor appetite and loose stool. If it affects the metabolism of fluid, it will bring on cough, asthma, profuse phlegm, edema and oliguria.