Etiology and pathogenesis of hypertension: Six major theories of Western medicine and the theory of liver and kidney in traditional Chinese medicine

Etiology and pathogenesis of hypertension

1. Vascular central nervous system theory

The vascular central nervous system theory posits that dysfunction of the cerebral cortex, with its imbalanced excitation and inhibition processes, leads to the formation of excitatory foci dominated by vasomotor nerve impulses in the subcortical vasomotor centers. This causes spasm of small arteries throughout the body, increasing peripheral resistance and resulting in elevated blood pressure. Therefore, it is difficult to explain the correlation between hypertension and increased secretion of catecholamines and adrenocortical hormones. Rather, it is more likely that the patient's sympathetic nervous system function differs from that of normal individuals, with small arteries exhibiting a strong response to increased secretion from a few tiny catecholamines.

2. Neurogenic Theory

The neurogenic theory posits that peripheral arterioles are target organs of the reflex arc of the autonomic nervous system that regulates blood pressure. When this reflex arc malfunctions, it can cause spasm of the arterioles surrounding the target organ, leading to elevated blood pressure.

3. The Renin-Angiotensin-Aldosterone Theory

The nephrogenic theory posits that during renal ischemia, the juxtaglomerular cells in the juxtaglomerular apparatus decrease and/or serum sodium increases. Simultaneously, the macula densa cells increase renin secretion (a protein-hydrolyzing enzyme), which enters the bloodstream. Activated by chloride-activated enzymes, renin combines with angiotensinogen (α-globulin) synthesized in the liver to form angiotensin I (10-peptide). Angiotensin I then circulates through the lungs and kidneys, where it is converted to angiotensin II (8-peptide) by converting enzymes. Angiotensin II is further converted to angiotensin III (7-peptide) by the removal of aspartic acid through enzymatic action.

4. The Theory of Spirit

The psychogenic theory posits that adverse stimuli from the internal and external environment cause repeated mental stress and trauma, leading to an imbalance in the excitation and inhibition processes of the cerebral cortex. This results in the formation of an excitatory focus in the subcortical vasomotor center dominated by vasoconstrictive nerve impulses, causing spasm of small arteries throughout the body and increased peripheral resistance, thus leading to elevated blood pressure.

5. The excessive sodium intake theory

The excessive sodium intake theory posits that sodium retention increases extracellular fluid, leading to increased cardiac output and increased water content in the walls of small arteries, resulting in increased peripheral resistance. Changes in the ratio of intracellular to extracellular sodium concentration increase arterial tension, all contributing to elevated blood pressure. Others believe that the role of sodium in the pathogenesis of this disease is conditional, affecting only individuals with genetic defects.

6. Traditional Chinese Medicine

Traditional Chinese medicine believes this disease is related to the liver and kidneys. An imbalance of Yin and Yang in the body, or a deficiency of either, and dysfunction of Qi and blood are the internal factors contributing to the onset of the disease. Its pathogenesis involves an excess in the upper body and a deficiency in the lower body. The excess in the upper body is due to stagnation of liver Qi, with liver fire and liver wind rising upwards, causing Qi and blood to flow upwards. The deficiency in the lower body is due to kidney Yin deficiency, where water fails to nourish wood, resulting in liver Yang excess. Over time, Yin damage affects Yang, leading to a deficiency of both Yin and Yang, resulting in corresponding symptoms. Generally, the early stage is characterized by liver Yang excess, the middle stage by liver and kidney Yin deficiency, and the late stage by a deficiency of both Yin and Yang.

Extensive evidence suggests that hyperactivity of the sympathetic nervous system is a major factor in the formation and maintenance of hypertension. Increased sympathetic activity elevates plasma renin and norepinephrine levels in these patients, as well as enhancing vascular stress responses, leading to increased myocardial contractility, heart rate, venous return, and peripheral resistance arteriolar constriction and spasm, resulting in elevated blood pressure. Patients with essential hypertension exhibit excessive blood pressure-raising and lowering responses under stress and relaxation. The degree to which blood pressure decreases during periods of quiet contemplation or other relaxation, and the degree to which it rises during mental arithmetic or emotional excitement, both exceed the normal range of blood pressure changes. These phenomena explain why tragedies frequently occur among hypertensive patients at the mahjong table and why hypertensive patients are more irritable than normal individuals. Large-scale surveys have found that the incidence of hypertension is significantly higher in urban areas than in rural areas. During the World Cup, the rate of hypertension patients seeking medical attention was significantly higher than usual, indicating that adverse environmental factors and stress responses can also raise blood pressure. Stress exerts its effects through the sympathetic nervous system. Some antihypertensive drugs work by inhibiting the excitation of the sympathetic nervous system to lower blood pressure.

Occupation and Hypertension

The incidence of hypertension is clearly related to occupation. People who engage in work that requires a high degree of concentration, experience prolonged mental stress, or are exposed to environmental noise for extended periods are more prone to hypertension. For example, the incidence of hypertension is generally higher among drivers, accountants, and similar professions.

The psychogenic theory posits that when patients experience prolonged or repeated significant emotional changes such as mental stress, anxiety, and irritability under external stimuli, the balance between excitation and inhibition in the cerebral cortex becomes imbalanced. This leads to an increase in the release of catecholamines (mainly norepinephrine and epinephrine) from the sympathetic nerve endings, which in turn causes arteriolar constriction, increased peripheral vascular resistance, and elevated blood pressure.

Therefore, while undergoing medication, patients with hypertension need to emphasize appropriate physiological and psychological adjustments and adequate rest. Approximately 60% of hypertension patients experience a reduction in blood pressure of more than 10% after resting for two weeks by avoiding a stressful work environment.

Blood lipids and blood pressure

Human blood contains many lipids, among which cholesterol, triglycerides, phospholipids, and free fatty acids are of greatest concern to patients with hypertension, as they are most closely related to atherosclerosis and coronary heart disease. Lipids are insoluble in water and must bind with different apolipoproteins to form hydrophilic lipoproteins. Lipoproteins can be classified according to their molecular size and density into high-density lipoproteins, low-density lipoproteins, and very low-density lipoproteins, etc. Healthy human serum contains a certain concentration of various lipoproteins.

Blood lipid levels are low at birth and increase with age, with men generally having higher levels than women. Women experience a significant increase in blood lipid levels after menopause. Blood lipid levels begin to decline in old age, and then become similar in men and women. High-density lipoprotein cholesterol (HDL-C) levels are higher in childhood, rising slowly and stabilizing in adulthood. Hyperlipidemia or hyperlipoproteinemia is defined as blood lipid or lipoprotein levels consistently exceeding normal limits. Hyperlipidemia is the basis of atherosclerosis, while HDL-C transports cholesterol to the liver for breakdown, thus having an anti-atherosclerotic effect. Atherosclerosis easily leads to isolated systolic hypertension. Conversely, in patients with hypertension and hyperlipidemia, damage to the vascular endothelium allows lipids to easily enter the arterial media, leading to atherosclerosis. Therefore, the medical community has consistently listed hypertension and hyperlipidemia as risk factors for atherosclerosis and coronary heart disease.

Blood lipid levels are affected by a variety of factors, including diet, lifestyle, and various diseases or medications. Some antihypertensive drugs have side effects that affect lipid metabolism, so medication should be used with caution in patients with hyperlipidemia.