Mechanism of pathological changes includes the nature of disease and its transmitting principles.
The occurrence of disease results from the struggle between pathogenic factors and healthy qi which exists in the whole course of disease. In the struggle between pathogenic factors and healthy qi, various general or local pathological changes will be caused if healthy qi is impaired, the balance between yin and yang is damaged, the functions of meridians are in disorder and the flow of qi and blood is disturbed. Though complicated, pathological changes generally can be classified into such categories as predomination and decline of pathogenic factors and healthy qi, imbalance of yin and yang as well as disorder of qi, blood and body fluid.
Predomination and decline of pathogenic factorsand healthy qi
Predomination and decline of pathogenic factors and healthy qi refer to changes of pathogenic factors and healthy qi due to struggle between them. The result of predomination and decline of pathogenic factors and healthy qi affects the nature and transmission of disease.
1. Predomination and decline of pathogenic factors and healthy qi and the changes of deficiency and excess
The occurrence of disease is due to two factors, deficiency of healthy qi and attack of pathogenic factors. However, these two factors play different roles in a specific disease. Sometimes disease is caused by deficiency of healthy qi, and sometimes by attack of pathogenic factors, resulting in either deficiency syndrome or excess syndrome. Huangdi Neijing says: "Excess means predomination of pathogenic factors while deficiency means exhaustion of essence. " That is to say that "excess" is related to pathogenic factors while "deficiency" is related to healthy qi.
① Excess syndrome
Excess syndrome is characterized by predomination of pathogenic factors and abundance or certain degree impairment of healthy qi. Violent struggle between pathogenic factors and healthy qi leads to a series of excess symptoms. That is why it is a syndrome of excess nature. Excess syndrome is often seen at the early and medium stages of diseases caused by six abnormal climatic factors or diseases caused by phlegm, rheum, stagnant blood, retention of food and accumulation of dampness and water in the body. Clinically excess syndrome includes superabundance of phlegm, internal blockage of stagnant blood, indigestion and abnormal flow of water and dampness as well as the manifestations of high fever, mania, sonorous voice and hoarse breath, unpalpable abdominal pain, constipation, anuria and powerful pulse, etc.
② Deficiency syndrome
Deficiency syndrome is marked by deficiency of healthy qi. Though pathogenic factors are not totally eliminated, they are not strong enough to damage healthy qi. So the struggle between pathogenic factors and healthy qi is mild with symptoms of deficiency of healthy qi and hypofunction of the viscera. That is why this kind of syndrome is termed deficiency syndrome. Deficiency syndrome is often seen at the advanced stage of exogenous diseases. It usually results from non-restoration of healthy qi, or frequent weakness of the body, or exhaustion of essence due to serious disease, protracted disease and chronic disease, or damage of qi, blood and body fluid due to profuse sweating, violent vomiting and diarrhea and massive hemorrhage, etc. Clinically the manifestations of deficiency syndrome include dispiritedness, sallow complexion, palpitation and shortness of breath, spontaneous sweating, night sweating, or feverish sensation in the five centers (palms, soles and chest), or aversion to cold and cold limbs as well as weak pulse, etc.
③ Mixture of deficiency syndrome and excess syndrome
During the course of a disease, the predomination and decline of pathogenic factors and healthy qi may lead to either simple deficiency syndrome and excess syndrome or mixture of deficiency syndrome and excess syndrome. Mixture of deficiency syndrome and excess syndrome may be caused by delayed or improper treatment of excess syndrome that leads to prolonged retention of pathogenic factors in the body and impairment of healthy qi, or by coagulation of pathological substances like dampness, water and stagnant blood due to deficiency of healthy qi.
Mixture of deficiency syndrome and excess syndrome is characterized by either deficiency complicated by excess or excess complicated by deficiency. The former is marked by domination of deficiency syndrome accompanied by excess of pathogenic factors, such as edema due to inactivation of spleen-yang. The latter is marked by domination of excess syndrome accompanied by deficiency manifestations, such as excess-heat consuming yin-fluid at the medium stage of febrile diseases.
④ Mutual transformation between deficiency syndrome and excess syndrome
Deficiency syndrome ancl excess syndrome are not fixed, they often transform into each other due to struggle between pathogenic factors and healthy qi.
Such a mutual transformation is characterized by transformation either from excess into deficiency or from deficiency into excess. In excess syndrome, healthy qi is usually not deficient. However, delayed or improper treatment may prolong the course of duration, leading to impairment of healthy qi and the physiological functions of the viscera and resulting in transformation of excess into deficiency. In deficiency syndrome, there is no invasion of pathogenic factors. However, deficiency of healthy qi and hypofunction of the viscera may lead to abnormal flow of qi, blood and body fluid and bring on qi stagnation, stagnant blood, phlegm and rheum as well as water and dampness, eventually resulting in deficiency complicated by excess. Though there is excess of pathogenic factors, healthy qi is still insufficient. Thus this morbid state is termed "excess caused by deficiency".
2. The relationship between the prognosis of disease and the state of pathogenic factors and healthy qi
In the course of struggle between pathogenic factors and healthy qi, healthy qi can eliminate pathogenic factors and pathogenic factors are also able to impair healthy qi. Thus the struggle between pathogenic factors and healthy qi is marked by constant variation of both sides. Such a variation decides the development of disease that manifests in two ways: recovery or death. If healthy qi becomes dominant, pathogenic factors will be reduced and disease will be improved and gradually cured; if pathogenic factors become dominant, healthy qi will be weakened and disease will become worsened or death will be caused.
① Domination of healthy qi and decline of pathogenic factors
Domination of healthy qi and decline of pathogenic factors are the necessary conditions for improvement and cure of disease. If healthy qi is sufficient, it will be powerful in resisting pathogenic factors and pathogenic factors will gradually be eliminated. If timely treatment is resorted to, pathogenic factors will be eliminated or reduced and healthy qi will be gradually restored. In both cases the functions of the viscera are improved, pathogenic factors are eliminated and eventually disease is cured.
The course of domination of healthy qi and decline of pathogenic factors may be long or short, depending on individual conditions. Generally speaking, the duration of exogenous disease and excess syndrome is short because pathogenic factors have not penetrated deep into the body and healthy qi is not seriously impaired. So exogenous disease and excess syndrome are easy to improve and cure. However, the duration of endogenous disease and deficiency syndrome is long because pathogenic factors have penetrated deep into the body and healthy qi is seriously impaired. So endogenous disease and deficiency syndrome are difficult to improve and cure. Usually correct and timely treatment can shorten the course of domination of healthy qi and decline of pathogenic factors. Incorrect and delayed treatment will certainly prolong the course of such a development.
② Domination of pathogenic factors and decline of healthy qi
Domination of pathogenic factors and decline of healthy qi are the basic causes of aggravation of disease or death. Such a variation results either from frequent deficiency of healthy qi that fails to restrict the development of pathogenic factors, or from exuberance of pathogenic factors that go beyond the body resistance, or from wrong or delayed treatment that impairs healthy qi and strengthens pathogenic factors, resulting in declination of visceral functions and separation of yin and yang, and eventually leading to death.
In the course of the variation of healthy qi and pathogenic factors, if healthy qi is not strong enough to eliminate pathogenic factors and pathogenic factors are not strong enough to further develop, it will bring on such a condition in which healthy qi and pathogenic factors are at a stalemate or healthy qi is deficient and pathogenic factors are still lingering. In this case healthy qi is difficult to restore, disease may change from an acute one into a chronic one or become obstinate, or certain sequelae may be caused.
Imbalance between yin and yang is a summarization of all kinds of basic pathogenesis, including dysfunction of the viscera, disorder of the meridians and disharmony of qi and blood, etc.