Response of diastolic blood pressure to long-term sodium restriction is posture related

Eighty-five subjects, aged 31-55 years, suffering from uncomplicated essential hypertension and receiving no regular medication were randomized to sodium restriction and control groups. Systolic (SBP) and diastolic (DBP) blood pressure were measured during an orthostatic test at baseline and after 6 months sodium restriction. The mean daily sodium excretion of 43 treated subjects decreased from 193 +/- 91 mmol to 95 +/- 70 mmol (p less than 0.001). Treated patients were divided on the basis of their mean overall out-patient clinic (OC) DBP decrease in the sitting position during the 6 months (monthly measurements) into sodium-sensitive (DBP decrease greater than 10 mmHg, n = 17), indeterminate (DBP decrease 5-10 mmHg, n = 18) and sodium-resistant (DBP decrease less than 5 mmHg, n = 8) subgroups. At 6 months the level of DBP in the supine position was lower than at baseline in both sensitive and resistant subgroups, whereas in the standing position a lower DBP than at baseline was seen only in the sodium-sensitive subgroup. The magnitude of the subsequent OC DBP decrease was significantly associated with a high baseline seated OC DBP (p less than 0.001) and a high, for baseline OC DBP adjusted orthostatic DBP increase (p = 0.014). Our data suggest that posture should be included in the concept of sodium sensitivity and that an orthostatic test is useful in the prediction of seated and standing DBP decrease produced by moderate, long-term sodium restriction.