Blood pressure and sodium balance in hypertensive patients in hospital

Ninety-one subjects with uncomplicated essential hypertension were admitted to hospital. They received a diet with a fixed amount of sodium (55 mmol/day), without calorie restriction. Blood pressure was measured at 2-hr intervals and averaged for each day. In patients who apparently adhered to a low salt diet before admission (group I), BP dropped 5 mmHg during the first 24 hr and then remained stable. In patients who previously ingested more salt (group II) a similar drop in pressure occurred during the first day, but pressure declined another 6 mmHg during the second day, to stabilize thereafter. Both neurovegetative and sodium-dependent factors appear to contribute to the decrease in BP while the patient is in hospital.