Implications of the linear pressure–natriuresis relationship and importance of sodium sensitivity in hypertension

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Abstract
Although the concept of the pressure–natriuresis curve is very clear, considerable confusion concerning its importance and utility in understanding the pathophysiology of hypertension persists. We recently showed that the pressure–natriuresis curve could be considered linear. In this brief review, we would like to stress the advantages of treating it as a line. Its linear approximation simplifies understanding of the sodium sensitivity of the blood pressure and mechanisms of hypertension. The blood pressure can be expressed as the sum of two components: the non-sodium-sensitive component determined by the x intercept of the pressure–natriuresis curve and the sodium sensitive one determined by the product of the reciprocal of the slope and the amount of sodium intake. Theoretically, it can be affected in two different ways to cause hypertension; either a parallel shift along the blood pressure axis toward a higher blood pressure level due to the increase in the x intercept or a decrease in the slope. The parallel shift induces non-sodium-sensitive hypertension, whereas the decrease in slope induces sodium-sensitive hypertension. Thus, the linear approximation makes the definition of the sodium sensitivity of the blood pressure very clear and, furthermore, suggests that mechanisms of hypertension can be clarified if the determinants of the x intercept and the slope of the pressure–natriuresis curve are known. A clear definition of sodium sensitivity allows us to study its importance as a marker of a greater risk of renal and cardiovascular complications.