Hemodynamics and Salt-and-Water Balance Link Sodium Storage and Vascular Dysfunction in Salt-Sensitive Subjects

We investigated 24-hour hemodynamic changes produced by salt loading and depletion in 8 salt-sensitive (SS) and 13 salt-resistant (SR) normotensive volunteers. After salt loading, mean arterial pressure was higher in SS (96.5 +/- 2.8) than in SR (84.2 +/- 2.7 mm Hg), P<0.01, owing to higher total peripheral resistance in SS (1791 +/- 148) than in SR (1549 +/- 66 dyn*cm-5*s), P=0.05, whereas cardiac output was not different between groups (SS 4.5 +/- 0.3 versus SR 4.4 +/- 0.2 L/min, not significant). Following salt depletion, cardiac output was equally reduced in both groups. Total peripheral resistance increased 24 +/- 6% (P<0.001) in SR, whose mean arterial pressure remained unchanged. In contrast, total peripheral resistance did not change in SS (1 +/- 6%, not significant). Thus, their mean arterial pressure was reduced, abolishing the mean arterial pressure difference between groups. SS had higher E/e' ratios than SR in both phases of the protocol. In these 21 subjects and in 32 hypertensive patients, Na+ balance was similar in SR and SS during salt loading or depletion. However, SR did not gain weight during salt retention (-158 +/- 250 g), whereas SS did (819 +/- 204), commensurate to iso-osmolar water retention. During salt depletion, SR lost the expected amount of weight for iso-osmolar Na+ excretion, whereas SS lost a greater amount that failed to fully correct the fluid retention from the previous day. We conclude that SS are unable to modulate total peripheral resistance in response to salt depletion, mirroring their inability to vasodilate in response to salt loading. We suggest that differences in water balance between SS and SR indicate differences in salt-and-water storage in the interstitial compartment that may relate to vascular dysfunction in SS.