Pathogenesis of acute arterial hypotension
One of the most striking and dangerous manifestations of hypoaldosteronism is acute arterial hypotension. Its development is complex and associated with the exhaustion of the cardiovascular system's compensatory mechanisms.
The fundamental causes of blood pressure drop lie in a combination of hypovolemia with an acute deficiency of both mineralocorticoids and catecholamines. As a result of this combined deficiency, a cascade of hemodynamic disorders is triggered:
- Cardiac output drops sharply.
- The tone of smooth muscle cells (SMCs) of the vascular wall decreases.
- The circulating blood volume (CBV) decreases critically.
Hypohydration and electrolyte imbalance
A key link in the development of pathological changes is body hypohydration. It occurs primarily due to a lack of mineralocorticoids, which deprives the kidneys of the ability to adequately reabsorb sodium ($Na^+$) and water.
The process of fluid loss can be rapidly exacerbated by the onset of vomiting, which is especially typical for patients against the background of severe infectious processes or pronounced intoxications.
As a result of the loss of aldosterone's physiological effects, classical markers of the disease are formed:
- Hyponatremia (massive loss of sodium in the urine).
- Hyperkalemia (retention of potassium in the body).
Generalized circulatory failure
Progressive circulatory failure (CF) is generalized in nature and affects all levels of the vascular bed. It includes central, organ-tissue, and microcirculatory failure.
The mechanism of formation of this life-threatening condition is based on a triad of factors: the development of acute heart failure (HF), a pathological decrease in the tone of arteriolar smooth muscle cells, and a significant decrease in CBV (which entails a decrease in total peripheral vascular resistance).
Important: Acute severe circulatory failure is the main cause of death in patients experiencing a hypoadrenal crisis.
Main Clinical Manifestations
The symptoms of hypoaldosteronism directly stem from the pathogenetic mechanisms described above and are divided into three main groups:
- Electrolyte disturbances: manifest as hyponatremia and hyperkalemia.
- Hemodynamic disorders: include arterial hypotension and bradycardia. The slowing of the heart rate here is a direct consequence of the toxic effect of high potassium levels on the myocardium.
- Neuromuscular disorders: patients complain of severe muscle weakness and pathologically increased fatigue, which is also closely related to the disruption of the transmembrane ion gradient.
Briefly: answers to topical questions
What causes lead to the development of primary hypoaldosteronism?
Factors indicated in sources for hypoaldosteronism and adrenal insufficiency include:
- Addison's disease;
- withdrawal of mineralocorticoid therapy;
- administration of diuretics — aldosterone receptor blockers;
- inherited genetic adrenal defects: familial adrenal hypoplasia, adrenoleukodystrophy;
- congenital developmental anomalies: adrenal hypoplasia, low ACTH sensitivity;
- primary steroidogenesis disorders: inherited or congenital adrenocortical dysfunction, cholesterol metabolism enzyme deficiency;
- immune autoaggression leading to the destruction of adrenal cortex tissue.
How does the acid-base balance of the blood change in aldosterone deficiency?
In aldosterone deficiency, the acid-base balance shifts toward metabolic acidosis. According to sources, hypoaldosteronism is accompanied by $K^+$ retention and $Na+$ excretion, which is associated with hyperkalemia; the presence of metabolic acidosis is indicated for hyperkalemia.
What is the precise cellular mechanism of muscle weakness against the background of hyperkalemia?
Muscle weakness in hyperkalemia is caused by the disruption of electrophysiological processes in excitable tissues. The cellular mechanism includes disruption of the formation of the membrane potential, action potential, and neuromuscular transmission of excitation. In the neuromuscular system during hyperkalemia, there is a temporary increase followed by a drop in excitability; clinically, this manifests as muscle hypotonia, weakness, hyporeflexia, muscle paralysis, and muscle pain.
To avoid confusing electrolyte shifts, use the "seesaw rule": in aldosterone deficiency, Sodium and Pressure plummet (hyponatremia, hypotension), while Potassium rises (hyperkalemia).
Class and exam questions
Why does bradycardia develop in hypoaldosteronism?
Bradycardia is secondary and develops against the background of hyperkalemia, which disrupts the normal excitability and conductivity of the myocardium.
What leads to a decrease in vascular tone?
The drop in arteriolar wall tone is caused by an acute deficiency of catecholamines and mineralocorticoids, which impairs the contractile ability of smooth muscle cells.
What is the main cause of death in a hypoadrenal crisis?
The main cause of death for patients in this condition is acute, severe, generalized circulatory failure.
What else to study on this topic
- Mechanisms of formation of central and microcirculatory failure
- The role of catecholamine deficiency in the pathogenesis of vascular collapse
- Pathophysiology of neuromuscular weakness in hyperkalemia
- Features of the course of hypoadrenal crisis against the background of infections and intoxications
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