Physiological principles of blood pressure regulation
The level of arterial blood pressure in the human body is an extremely strict physiological constant. Complex mechanisms are involved in maintaining this vital indicator within the normal range. Hemodynamics is based on three main parameters:
- Cardiac output — the volume of blood pumped by the heart per unit of time.
- Total peripheral vascular resistance (TPVR) — the factor determining the tone of the vascular beds.
- Circulating blood volume (CBV) — the total amount of fluid in the vessels.
In addition to this fundamental triad, there are additional factors that influence hemodynamics to a somewhat lesser extent. These include blood viscosity itself and its electrolyte composition.
The most important property of the circulatory system is the compensation mechanism. It operates on the principle of maintaining homeostasis: whenever one of the three main parameters changes, the others immediately begin to change in the strictly opposite direction. The coordination of all these complex hemodynamic shifts is carried out by two key regulatory systems of the body: the sympathoadrenal and renin-angiotensin systems.
Norm criteria and etiological classification
Clear limits of normal blood pressure have been established in medical practice. The ideal indicator is considered to be a systolic pressure of 120 mmHg and a diastolic pressure of 80 mmHg. A pathological condition begins when these figures rise. Arterial hypertension (AH) is understood not as a single-time spike, but specifically as a sustained increase in blood pressure above threshold values: systolic — above 140 mmHg, diastolic — above 90 mmHg.
Depending on the root cause, the pathology is divided into two major categories:
- Primary (essential) hypertension. Its main distinguishing feature is that the rise in blood pressure itself acts as the primary and leading symptom. This is an extremely common problem, covering 15–30% of the population in industrially developed regions.
- Secondary (symptomatic) hypertension. In this case, high readings on the blood pressure monitor are merely a direct consequence of developing entirely different diseases. Among the main causes are severe renal pathologies, endocrine disorders, and specific tumors (e.g., pheochromocytoma).
Pathogenesis of complications and target organ damage
Long-standing and uncontrolled arterial hypertension is extremely dangerous because it inevitably triggers a whole cascade of severe pathological changes in the body. First and foremost, the so-called target organs suffer.
In the heart, pronounced left ventricular hypertrophy develops compensatorily, as the ventricle is forced to constantly overcome high vascular resistance. In the blood vessels themselves, concentric cholesterol deposition occurs, thickening and hardening their walls.
The preferred localization of such vascular lesions includes the coronary arteries supplying the myocardium, renal and cerebral vessels, and the small vessels of the retina. The clinical outcomes of these pathological processes are quite dramatic: patients with long-term hypertension have a significantly increased risk of developing life-threatening conditions — myocardial infarction and strokes.
Principles of pharmacotherapy
The fundamental goal of prescribing any antihypertensive drugs is to reliably reduce and long-term maintain blood pressure at a normal level, which protects target organs and prevents vascular catastrophes.
The modern classification of these drugs is based exclusively on the principle of their antihypertensive action. This means that drugs are grouped depending on their mechanism of influence on basic hemodynamic factors: whether they decrease cardiac output, reduce total peripheral vascular resistance, or decrease circulating blood volume.
Briefly: answers to topical questions
On what principle are antihypertensive drugs classified, and what are the main pharmacological groups included in this classification?
Antihypertensive agents are classified based on the principle of their antihypertensive action, i.e., the mechanism of influence on hemodynamic factors. Sources indicate that groups used for arterial hypertension include: ACE inhibitors or ARBs, beta-blockers, calcium channel blockers, and diuretics. Drugs that block adrenoceptors include three groups: $\alpha$-blockers, $\beta$-blockers, and $\alpha, \beta$-blockers. Myotropic agents that reduce vascular tone through a direct effect on smooth muscle are divided into calcium channel blockers, potassium channel openers, nitric oxide (NO) donors, and other agents.
What is the mechanism of the antihypertensive action of thiazide diuretics?
The antihypertensive action of thiazide diuretics is due to a dual mechanism: a decrease in circulating blood volume and a vasodilating effect, which is of decisive importance. The excretion of excess sodium leads to a decrease in its concentration in the vessel wall and a reduction in transmembrane transport of calcium ions into the cell. This decreases the hyperreactivity of the vascular wall, dilates blood vessels, reduces total peripheral vascular resistance, and leads to a sustained decrease in blood pressure.
Which drugs belong to the group of angiotensin-converting enzyme (ACE) inhibitors?
Angiotensin-converting enzyme inhibitors include short-acting and long-acting drugs. A short-acting representative is captopril. Long-acting drugs include enalapril, lisinopril, fosinopril, perindopril, ramipril, and trandolapril.
What are the absolute contraindications to the prescription of non-selective beta-blockers?
An absolute contraindication has been confirmed for non-selective $\beta$-blockers in bronchial asthma, since the blockade of $\beta_2$-adrenoceptors in the bronchi provokes bronchospasm. For propranolol, contraindications are also indicated: conduction disorders including AV block, severe bradycardia, acute and severe chronic heart failure, arterial hypotension, vasospastic angina pectoris, obliterating peripheral vascular diseases, and pregnancy due to the risk of premature labor and negative impact on the fetus.
Which antihypertensive drugs belong to the dihydropyridine class of slow calcium channel blockers?
Sources indicate that amlodipine belongs to slow calcium channel blockers, and lercanidipine is mentioned among third-generation calcium antagonists. Dihydropyridine derivatives are also separately named as selective calcium channel blockers, but whether amlodipine or lercanidipine specifically belongs to the dihydropyridine class is not explicitly stated in the cited sources.
For quick memorization of the three main hemodynamic factors, use the abbreviation COS: Cardiac output, Outflow (circulating blood volume), Systemic vascular resistance (TPVR).
Class and exam questions
What hemodynamic factors determine the level of blood pressure?
The level of blood pressure depends on three main parameters: cardiac output, total peripheral vascular resistance (TPVR), and circulating blood volume (CBV). Additionally, blood viscosity and its electrolyte composition influence hemodynamics.
What is the compensation mechanism during hemodynamic changes?
The compensation mechanism aims to preserve homeostasis. If one of the main hemodynamic parameters changes, the remaining parameters automatically begin to change in the opposite direction to keep the pressure within a strict constant range.
Which organs are considered target organs in prolonged arterial hypertension?
With prolonged pressure elevation, the main burden is borne by the heart (left ventricular hypertrophy develops) and blood vessels (concentric cholesterol deposition occurs). The coronary, renal, cerebral, and retinal vessels are the most vulnerable.
What is the basis for the classification of antihypertensive drugs?
Drugs are grouped based on the principle of their antihypertensive action. The classification takes into account the specific mechanism of the drug's effect on key hemodynamic factors, such as SVR, BCC, or cardiac output.
What else to study on this topic
- The role of the sympathoadrenal system in the regulation of vascular tone
- Mechanisms of action of the renin-angiotensin system
- Pathogenesis of left ventricular hypertrophy
- Influence of electrolyte composition on blood viscosity
- Pheochromocytoma as a cause of secondary hypertension
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