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Yin-yang pattern differentiation refers to the categorization of patterns according to yin-yang theory, e.g. interior, cold, and deficiency patterns pertaining to yin, and exterior, heat, and excess patterns pertaining to yang.
Yin pattern is a collective term for interior, cold, deficiency patterns with inhibitory*, hypo-functional*, quiescent*, or dimmed* manifestations, or inward and downward symptoms, as well as morbid conditions caused by pathogenic factors of yin nature.
There are many yin patterns and their manifestations are various but there are some common symptoms and signs. The common symptoms and signs are pale or dull complexion, listlessness, heavy body, fatigue, cold limbs, low voice, shortness of breath, bland taste in the mouth without thirst, long voiding of clear urine, loose stool with fishy smell, pale and tender tongue, sunken, slow and weak pulse.
Yin decreases the body metabolism. Listlessness, fatigue, low voice and shortness of breath are signs of hypo-function of the body, and therefore pertain to yin. Pale or dull complexion, cold limbs, bland taste in the mouth without thirst, long voiding of clear urine and loose stool with fishy smell are symptoms and signs of internal cold which also pertains to yin. Pale tongue and slow pulse are caused by cold, because cold congeals and makes blood vessels contract and slows blood flow. Tender tongue is indicative of deficiency, sunken pulse is the pulse of interior pattern, and weak pulse is the pulse of deficiency pattern.
Yang pattern is a collective term for exterior, heat, excess patterns with excitatory*, hyper-functional*, restless, or bright manifestations, or outward and upward symptoms, as well as morbid conditions caused by pathogenic factors of yang nature.
There are many yang patterns as well, and their manifestations vary greatly. The usual symptoms are flushed complexion, high fever with preference for cold, scorching heat in the skin, high voice, restlessness, heavy breath, panting with phlegm rale, dry mouth with thirst and desire for drink, scanty yellow urine, and constipation with foul smell, red purple tongue with yellow and dry fur, floating rapid, surging, slippery and replete pulse.
Yang increases the body metabolism. Flushed complexion, fever with preference for cold and scorching heat are caused by yang heat. High voice, restlessness, heavy breath, and panting with phlegm rale are caused by excess pattern which pertains to yang. Dry mouth with thirst and desire to drink, scanty yellow urine, and constipation with foul smell are signs of exuberant heat. Yang heat gives rise to red purple tongue with yellow and dry fur. Floating rapid pulse is usually caused by exterior heat pattern. Surging, slippery, replete pulses are signs of excess pattern or heat pattern.
As mentioned, yin and yang pattern differentiation can be done through exterior (yang) and interior (yin), cold (yin) and heat (yang), and deficiency (yin) and excess (yang) patterns, and we can also differentiate yin and yang patterns from the four examinations.