Fei is located in the chest, occupying the highest position among the viscera, like a brilliant roof covered by a fine mist of slightly white, radiant light. It is delicate, vulnerable, and easily attacked by pathogens of Heat or Cold. Fei correlates with Metal in the Five Elements Theory and belongs to Yin within Yang. It is externally–internally related to the Large Intestine by meridians. The Fei complex consists of the Lung system, including its meridian and aura; it is related to the Large Intestine, skin, hair, and nose.
Fei 
depends on the propelling and securing functions of Lung-Qi to moisten, govern Qi and respiration, control circulation channels and Blood vessels, and control dispersing and descending.
The Basic Questions says, “The Fei is like a Minister from whom policies are issued” . Since Fei assists Xin 
to promote Blood circulation, it is the “Prime Minister” of Xin .
The physiological and mental functions of Fei (, Lung, with its aura and meridian as one union)
(1) Fei dominates Qi and respiration
Most importantly, Fei extracts “clean Qi” from inhaled air and exhales stale air; it combines clean Qi with food Qi from Pi (Spleen-related system), and produces Pectoral Qi (Zong Qi). Pectoral Qi regulates the generation and flow of Qi by ascending, descending, exiting, and entering the whole body to maintain all vital activities. The Basic Questions says, “The whole body’s Qi originates from the Fei ” . This means that it involves Pectoral Qi generation in the chest, the “Sea of Qi,” created through a combination of Fei-inhaled fresh air and Essential Qi from food and water digested and absorbed by the Pi and Stomach. Pectoral Qi rises to stimulate respiration, and then returns to Xin and vessels with Blood to distribute warmth and nourishment to the entire body. Fei also spreads Qi throughout the body, and regulates the flow. Fei’s respiratory movement makes Qi flow. The Miraculous Pivot says, “The Pectoral Qi gathers together without moving to accumulate in the chest, the Sea of Qi, which comes out of the Fei, goes to the throat and facilitates inhalation and exhalation”. Fei’s rhythmic inhalation and exhalation coordinate the Qi motion of the whole body. Pectoral Qi, residing in the chest, aids Fei and Xin in promoting good circulation. If the Qi motion is disturbed, it will present as tiredness, weak voice, cough, asthmatic respiration, breathlessness, listlessness, and asthenia.
(2) Fei is in regulation of the activities of dispersing and descending
Fei, as the uppermost organ, disperses body fluid and Essence from food and water transported by the Pi to the whole body, hair, and skin; distributes Defensive (Wei) Qi to warm the skin and muscles, and protects the body from pathogens; exhales the waste gas by its respiratory movement; regulates the closing and opening of the pores for sweat.
Fei’s Qi must descend. Fei’s purifying and descending actions transmit body fluid and nature’s fresh air down to Shen (
, Kidney, with its aura and meridian as one union).
Fei’s dispersing and descending functions complement each other. The Basic Questions says, “Obstruction of Qi flow marked by dyspnea and stuffiness of the chest is mostly ascribed to Fei disorder” . If the ascending and descending actions are not coordinated, i.e. “failure of the dispersing (
, Xuan) of the Fei,” it will present as a runny nose, a dry throat, and obstructed breathing. “Failure of the purifying–descending (
, Su Jiang) of the Fei” may affect the Large Intestine, which will not have the power to control defecation, suffering from constipation, or urine retention.
(3) Fei regulates water circulation
Fei treats water through the dispersing and descending process. Assisted by scattering body fluid and Essence to nourish every part of the body, Fei discharges waste by exhaling and sweating. Fei receives Pi 
’s refined fluid, reforms it to a fine mist, and “sprays” it under the skin as part of the dispersing process. Fei’s descending action constantly transmits body fluid down to Shen 
; otherwise, Fei cannot disperse and descend, and it will present as phlegm, edema, and rheum. The Basic Questions says, “When the fluid enters the Stomach, the refined part is transmitted up to the Fei by Pi –Qi, regulated by the Fei and sent down to the Bladder”.
(4) Fei controls the channels and blood vessels
Fei regulates Qi. Qi guides Blood, and Blood vessels converge in Fei. Blood circulates in vessels, and Qi circulates along the channels. Without Fei-Qi assisting Xin , blood circulation weakness will cause chest distress and palpitations.
Fei assists Xin’s administration and regulation of the body’s vital activity of Qi actions, driving and regulating Blood circulation, and maintaining water metabolism equilibrium. Therefore, Fei is in charge of coordinating the vital activity of the body.
(5) Fei controls the skin and hair
The skin protects the body, excretes sweat, and adjusts body temperature. When exogenous pathogens invade the body, they usually attack the skin first, and then Fei, causing stagnation of Fei-Qi. The Basic Questions says, “The Fei control the skin and manifest on the hair” .
(6) Fei opens into the nose
The nose senses odors, and opens a vantage of air to Fei. Fei-Qi regulates the smelling and ventilating functions of Fei. The Miraculous Pivot says, “The Fei opens into the nose; if the Fei is harmonious, the nose can smell”. Other organs, such as Gan 
and the Gall Bladder, also affect the sense of smell.
Since the Fei Meridian runs across the throat, Fei regulates respiration, ventilation, and vocalization. If Fei-Qi is insufficient or fails to disperse, it will present as a rough, sore, or bleeding throat.
(7) Fei is responsible for the emotion of sadness
In TCM, Fei houses the Corporeal Soul (Po) and deals with the makeup of mind and body.
Fei relates to sorrow or sadness, and possibly to anxiety. It is stimulated by internally generated reactions to real, imagined, or remembered events or information. Because the relationship is reciprocal, sorrow, sadness, and anxiety can damage Fei.
For example, chronic obstructive pulmonary disease (COPD) is a chronic respiratory, irreversible lung disease. Because of its slow sexual development, it seriously affects the patient’s ability to work and the quality of life. Due to its complex syndrome with high mortality, we suggest that the Lung-Yangming meridian–Zang Xiang system be used and a differential treatment be followed.