Physiological Principles of Blood Pressure Regulation
Blood pressure in the human body is a tightly regulated physiological constant. Complex mechanisms are involved in maintaining this vital indicator within normal limits. Hemodynamics is based on three main parameters:
- Cardiac output — the volume of blood pumped by the heart per unit of time.
- Total peripheral resistance (TPR) — the factor determining the tone of the vascular beds.
- Circulating blood volume (CBV) — the total amount of fluid within the vessels.
In addition to this fundamental triad, auxiliary factors influence hemodynamics to a lesser extent, including blood viscosity and electrolyte composition.
A crucial property of the circulatory system is the compensatory mechanism, which operates on the principle of homeostasis: whenever one of the three main parameters changes, the others immediately begin to shift in the strictly opposite direction. The sympathetic nervous system and the renin-angiotensin-aldosterone system coordinate these complex hemodynamic changes.
Normative Criteria and Etiological Classification
Clear boundaries for normal blood pressure are established in medical practice. The ideal reading is a systolic pressure of 120 mmHg and a diastolic pressure of 80 mmHg. A pathological state begins when these figures rise. Arterial hypertension (HTN) refers not to a single transient spike, but to a persistent elevation of blood pressure above threshold values: systolic exceeding 140 mmHg and diastolic exceeding 90 mmHg.
Depending on the primary underlying cause, the pathology is divided into two major categories:
- Primary (essential) hypertension. Its defining feature is that the elevated blood pressure itself acts as the primary and leading symptom. It is an extremely common problem, affecting 15–30% of the population in industrialized regions.
- Secondary (symptomatic) hypertension. In this case, high blood pressure readings are a direct consequence of other distinct underlying diseases. Major causes include severe renal pathologies, endocrine disorders, and specific tumors (such as pheochromocytoma).
Pathogenesis of Complications and Target Organ Damage
Long-standing and uncontrolled arterial hypertension is extremely dangerous because it inevitably triggers a cascade of severe pathological changes in the body. The so-called target organs suffer first.
In the heart, compensatory mechanisms lead to marked left ventricular hypertrophy, as the heart is forced to constantly overcome high vascular resistance. Within the blood vessels themselves, concentric cholesterol deposition occurs, thickening and stiffening their walls.
Favorite localizations for such vascular lesions include 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 dramatic: patients with prolonged hypertension face a significantly increased risk of life-threatening events, such as myocardial infarction and stroke.
Principles of Pharmacotherapy
The fundamental goal of prescribing any antihypertensive drugs is to reliably lower and long-term maintain blood pressure at a normal level, thereby protecting target organs and preventing vascular catastrophes.
The modern classification of these drugs is based exclusively on their antihypertensive mechanism of action. This means that medications are grouped according to how they influence basic hemodynamic factors: whether they decrease cardiac output, reduce total peripheral resistance, or decrease circulating blood volume.