HIGH SODIUM SENSITIVITY IMPLICATES NOCTURNAL HYPERTENSION IN ESSENTIAL-HYPERTENSION

We investigated the relationship between sodium sensitivity and diurna l variation of blood pressure in patients with essential hypertension. Twenty-eight inpatients with essential hypertension were maintained o n high sodium (12 to 15 g NaCl per day) and low sodium (1 to 3 g NaCl per day) diets for 1 week each. Twenty-four-hour blood pressure and ur inary sodium excretion were measured at the end of each diet period, a nd the sodium sensitivity index was calculated as the ratio of the cha nge in mean arterial pressure to the change in urinary sodium excretio n rate by sodium restriction. Patients whose average mean arterial pre ssure was lowered more than 10% by sodium restriction were assigned to the sodium-sensitive group (n=16); the remaining patients, whose mean arterial pressure was lowered by less than 10%, were assigned to the non-sodium-sensitive group (n=12). In the non-sodium-sensitive group, mean arterial pressure and heart rate fell during the nighttime, and a verage values of systolic, diastolic, and mean arterial pressures duri ng the night were significantly lower than those during the day during both low and high sodium diets. On the other hand, in the sodium-sens itive group, there was no nocturnal fall in mean arterial pressure, an d none of the systolic, diastolic, and mean arterial pressure values d uring the nighttime was different from the respective pressure values during the daytime during either sodium diet. The sodium sensitivity i ndex was positively correlated with the fall in mean arterial pressure during the nighttime during a high sodium diet (r=.55, P<.01). These results indicate that in patients with sodium-sensitive essential hype rtension, blood pressure fails to fall during the night. High sodium s ensitivity may be a marker of greater risk of renal and cardiovascular complications, as has been found in nondippers, patients whose blood pressure fails to fall during the night.