六经辨证

Six-channel pattern differentiation was created by the late-Han physician Zhang Zhongjing (張仲景) in his Treatise on Cold Damage (《傷寒論》), the earliest mature diagnostic system in Chinese medicine. It organizes the unfolding course of externally contracted febrile illness into six successive stages, each with its own location, nature, and treatment.

A word of caution: the "six channels" of this system are not identical to the six like-named meridians of channel theory, although they share the names. Here they are diagnostic categories — clinical syndromes — into which the unfolding illness can be sorted. The three yang stages (Tai Yang, Yang Ming, Shao Yang) are characteristically exterior, hot, and excess, with strong upright qi locked in struggle with the pathogen. The three yin stages (Tai Yin, Shao Yin, Jue Yin) are characteristically interior, vacuous, and cold, with the upright qi already exhausted. Movement through the six is in principle from yang to yin, from exterior to interior, from excess to vacuity, and from heat to cold — though Zhongjing repeatedly shows that real cases skip stages, retreat, or combine.

Tai Yang (太陽): the pathogen is at the surface, fighting against the defensive qi at the exterior. Characteristic signs are fever and aversion to cold, stiffness and pain in the head and neck, and a floating pulse. Tai Yang is further divided into "wind stroke" (with sweating and a floating-moderate pulse, treated with Cinnamon Twig Decoction, Guì Zhī Tāng) and "cold damage" (without sweating and with a floating-tight pulse, treated with Ephedra Decoction, Má Huáng Tāng).

Yang Ming (陽明): the pathogen has entered the Yang Ming and transformed into intense interior heat. There are two presentations. The Yang Ming channel pattern shows the "four greats" — great heat, great sweating, great thirst, and a great surging pulse — and is treated with White Tiger Decoction (Bái Hǔ Tāng). The Yang Ming organ pattern shows abdominal fullness with hard pain, constipation, tidal fever, and delirious speech — heat has bound with stool in the Large Intestine — and is treated with the Order-the-Qi (chéng qì) family of purgatives.

Shao Yang (少陽): the pathogen is half-exterior and half-interior, neither fully repelled nor yet fully internalized. The characteristic signs are alternating chills and fever, fullness and discomfort in the chest and hypochondria, irritability with frequent retching, a bitter taste, dry throat, dizziness, and a wiry pulse. The treatment principle is to harmonize the Shao Yang, paradigmatically with Minor Bupleurum Decoction (Xiǎo Chái Hú Tāng).

Tai Yin (太陰): the pathogen has entered the Tai Yin Spleen; Spleen yang is failing and the function of transportation and transformation is impaired. The characteristic signs are abdominal fullness with vomiting, inability to take food, spontaneous diarrhea, absence of thirst, and a moderate-weak pulse. Treatment warms the middle and disperses cold — the Regulate-the-Middle Decoction family (Lǐ Zhōng Tāng) is paradigmatic.

Shao Yin (少陰): the yang qi of the Heart and Kidney is severely exhausted. The characteristic signs are a faint and thready pulse, a constant desire only to sleep, cold extremities reaching to the elbows and knees, and undigested food in the stool. The most dangerous variant is yin flourishing with yang collapsing, which requires Frigid Extremities Decoction (Sì Nì Tāng) urgently to restore yang and rescue from collapse. There is also a Shao Yin heat-transformation pattern that arises in patients whose constitution converts the pathogen toward heat instead of cold.

Jue Yin (厥陰): the deepest stratum of the six. Cold and heat are tangled together, with heat above and cold below, and bouts of cold extremities alternating with febrile flushes. The classical signs are wasting thirst, qi rushing upward into the chest, painful heat over the heart, hunger without desire to eat, and vomiting of roundworms when food is taken. Treatment must be tailored to the precise configuration of cold and heat in each case.