Background

Several studies have shown microvascular changes in patients with hypertension, but the question is still open as to whether these alterations are functional or structural. In particular, it is unknown whether the microcirculation adapts to changes in sodium intake or remains relatively fixed.

Methods

We examined bulbar conjunctival microvascular densities after 1 week of low (55 mmol Na+/24 h) and high (220 mmol Na+/24 h) sodium diet, in untreated patients with essential hypertension and in normotensive control subjects.

Results

On a low sodium diet, venular density was lower in essential hypertension (EH) compared with controls [median and interquartile ranges: 4.77 (4.01–5.71) versus 6.43 (6.02–7.20) mm/mm 2, P= 0.001], while arteriolar density was higher [3.80 (2.41–4.46) versus 2.06 (1.74–2.23) mm/mm 2, P= 0.03]. In the whole group (patients and controls), venular density correlated inversely and arteriolar density correlated positively with mean arterial pressure (MAP). Switching to a high sodium intake resulted in opposite responses in the two groups with respect to venular density (P= 0.0001): a 33%(3–80) increase in EH, but a 28%(− 3 to 34) decrease in controls. Changes in venular density with increased sodium intake correlated positively with MAP on a low sodium diet in the whole group. Arteriolar density did not change significantly in either group. Also, capillary density was similar on both diets.

Conclusion

Functional microvascular density in EH patients differs from that in normotensive subjects in a way that is dependent upon sodium intake.