Comparison of obese patients and patients with normal body weight who have equal hypertension levels shows that obese patients have higher cardiac output, more expressed hypervolemia. Increase of arterial blood pressure during body weight increment in the beginning is associated with cardiac output increase and relatively normal peripheral resistance of blood vessels. However, if talking about pathogenetic hypertension mechanisms as an integral part of the chain, later at long-term obesity, insulin resistance syndrome (also later pancreatic diabetes of II type), dyslipidemia and sleep apnea come into view. In 1947 Jean Vague was the first to describe the relation of obesity, arterial hypertension, diabetes and dyslipidemia. In literature these pathologic states were often called "the lethal quartet", later X syndrome or insulin resistance syndrome. Despite the fact that all these pathophysiological chains are not fully clear until now, attempts are being made to find their correlation.
Arterial blood pressure has a direct relation to:
- Cardiac output;
- General peripheral resistance of blood vessels.
Cardiac output is ensured by:
- Amount of circulating blood;
- Myocardium inotropic function.
General peripheral resistance of blood vessels or tonus of blood vessels wall is regulated by biologically active substances that are causing:
- Vasodilatation: acetylcholine, a2 (alpha2) receptor agonists, bradykinin, prostaglandins, nitric oxide.
- vasoconstriction: a1 (alpha1) receptor agonists, calcium ions, aldosterone, angiotensin II, endothelin, thromboxane A2, serotonin.
Remodeling and fibrosis taking place in the blood vessel wall also cause irreversible vasoconstriction.
Obesity type
Distribution of fat in an organism is important for pathogenesis of arterial hypertension. It has been determined that abdominal obesity (also known as obesity of upper body part, masculine type, android or visceral obesity) is more connected with arterial hypertension in comparison to feminine type or gynoid obesity, when fat mainly accumulates in hip, seminal and thigh areas. Abdominal obesity is determined by calculation of waist / thigh correlation, which standard for men is > or equal to 0.95 and > or equal to 0.85 for women. Arterial hypertension in combination with this type of obesity by several times increases the risk of coronary heart disease.
Hyperinsulinemia
Increased insulin amount encourages activity of sympathetic nervous system. Hyperinsulinemia stimulates thermogenesis, which theoretically should decrease excess weight or at least keep it stable, however practical benefit is hardly noticeable. However, hyper - adrenergic state causes vasoconstriction. It is known that insulin causes vasodilatation partially working though nitric oxide in blood vessel walls. Though, at obesity and arterial hypertension its effect decreases. Increased insulin level raises the amount of intracellular calcium, delays synthesis of vasodilatation prostaglandins, stimulates the growth factor in small muscles.
Sodium exchange disorder
One of causes for sodium reabsorption disorder is increased activity of sympathetic nervous system, which excites constriction of kidney blood vessels. At obesity, changes in medullar part of kidneys also disturb sodium exchange. It has been determined that hyperinsulinemia disturbs sodium and water reabsorption in kidneys, increases filtration of glomerulas. Long - term glomerula hyperfiltration and perfusion disorders are connected with albuminuria.
Sleep apnea syndrome
The majority of patients having obesity are diagnosed with the sleep apnea syndrome which activates the sympathetic nervous system. Repetitive episodes of oxygen starvation disturb activity of blood vessels autoregulation system in the brain.
Dyslipidemia
Increased amount of free fatty acids in blood causes lipase resistance to insulin, thus blocking utilization of these acids in skeleton muscles. Increased amount of free fatty acids delays relaxation of blood vessels endothelium, which noticeably improves after dyslipidemia decrease.
Altered vasodilatation
Altered ability of insulin to cause dilatation especially in peripheral minor blood vessels complicates adequate supply of blood to the major body mass part.
Changes in leptin synthesis
Leptin is a recently discovered biologically active substance which is also known as "anti-obesity hormone". It is synthesized in visceral adipose tissue, its shortage is connected with sodium retention in kidneys.
