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Circulatory volume in essential hypertension. Relationships with age, blood pressure, exchangeable sodium, renin,
Insights
In essential hypertension, blood volume and exchangeable sodium are typically normal, challenging hypervolemia theories. Certain young hypertensive males may even have decreased body sodium levels.
Area of Science:
- Cardiovascular Physiology
- Renal Physiology and Hypertension
Background:
- Essential hypertension is a complex condition with debated underlying mechanisms.
- The role of circulatory volume and sodium balance in hypertension pathogenesis requires clarification.
Purpose of the Study:
- To investigate circulatory volume and exchangeable sodium in normal subjects versus patients with benign essential hypertension.
- To determine the relationship between blood volume, exchangeable sodium, age, and blood pressure.
Main Methods:
- Measurement of circulatory volume and exchangeable sodium in 110 normal subjects and 120 patients with essential hypertension.
- Analysis of correlations between these parameters, age, blood pressure, and plasma hormone levels.
- Normalization of body constituents to body surface area for comparison.
Main Results:
- Circulatory volume and exchangeable sodium were generally normal in hypertensive patients when adjusted for body surface area.
- Exchangeable sodium correlated positively with age and blood pressure in essential hypertension.
- Younger hypertensive males (<35 years) showed a slight decrease in exchangeable sodium compared to controls.
Conclusions:
- Hypervolemia is unlikely to be the primary cause of benign essential hypertension.
- Changes in blood volume appear to be a consequence, not a cause, of elevated blood pressure.
- Body sodium levels can be normal or even decreased in certain hypertensive individuals, particularly younger males.
Abstract:
The circulatory volume and exchangeable sodium were measured in 110 normal subjects and 120 patients with benign untreated essential hypertension. The two study groups did not differ in age, sodium and potassium metabolism, and plasma levels of renin, aldosterone and norepinephrine, while plasma epinephrine was slightly higher in essential hypertension. Total plasma and blood volume correlated with total exchangeable sodium (r = 0.64-0.75; p less than 0.001); these correlations were similar in normal and hypertensive subjects. Body surface area was found to be the most appropriate frame of reference for judging individual values of plasma and blood volume or exchangeable sodium; using this approach these body constituents were on average normal in the hypertensive population. Blood volume was unrelated to age or blood pressure in normal and hypertensive subjects. Exchangeable sodium tended to increase with age (r = 0.25; p less than 0.02) and correlated positively with blood pressure (r = 0.25; p less than 0.02) in essential hypertension but not in normal subjects. The latter body constituent was slightly but significantly decreased in hypertensive males aged less than 35 years as compared with appropriate normal controls (96.1 +/- 6.8% versus 99.6 +/- 6.7%; p less than 0.05). These findings confirm that blood volume and exchangeable sodium are on average normal in patients with benign essential hypertension. Body sodium may even be decreased in certain young hypertensive patients. These observations do not support the concept that hypervolemia may represent the initial event leading to high blood pressure in essential hypertension; in contrast, changes in blood volume appear to reflect variations in blood pressure.