Volume homeostasis, renal function and hypertension

Area of Science:

• Nephrology
• Cardiovascular Physiology
• Hypertension Pathophysiology

Background:

• Generalized vasoconstriction was historically considered the primary cause of human hypertension.
• Recent hemodynamic studies have challenged this long-held belief.
• Understanding early hemodynamic changes in renal disease is crucial for hypertension research.

Purpose of the Study:

• To investigate the initial hemodynamic abnormalities in patients with chronic renal disease who are normotensive but at high risk for developing hypertension.
• To elucidate the pathophysiological mechanisms underlying the transition from normal blood pressure to hypertension in this cohort.

Main Methods:

• Hemodynamic studies were conducted on subjects with chronic parenchymatous non-uraemic, non-anaemic renal disease.
• Analysis focused on identifying abnormalities while blood pressure was still within the normal range.
• Assessment included evaluation of blood volume, cardiac output, and renal salt excretion.

Main Results:

• The earliest abnormality identified was hypervolemia (excess blood volume) and high cardiac output (hyperkinesis) with tissue hyperperfusion in normotensive subjects.
• This hypervolemia stems from impaired renal excretion of isotonic saline.
• Chronic hypervolemia leads to increased sodium and calcium in vascular smooth muscle, reducing compliance and increasing vascular resistance.

Conclusions:

• The primary driver of hypertension in this renal disease model is not vasoconstriction, but rather a renal inability to balance sodium intake and output, leading to hypervolemia.
• This pathophysiological mechanism, initiated by renal salt handling abnormalities, is likely applicable to various forms of human hypertension.
• Vascular adjustments to hypervolemia and high cardiac output eventually lead to elevated blood pressure, with renin playing a role in later stages.