Diurnal pattern of water and electrolyte excretion and body weight in idiopathic orthostatic hypotension. The effect of three treatments.

The diurnal pattern of water and solute excretion and body weight were examined in five control subjects and in a patient with idiopathic orthostatic hypotension before and during treatment. The patient had a reversed diurnal pattern of excretion of sodium, urea and water but not of potassium and creatinine, and there was an excessive diurnal variation in body weight. The effects of three treatments, high salt diet alone and then with the addition of head-up tilt, and later fludrocortisone, were studied. Fludrocortisone caused marked clinical improvement and retention of sodium and water. Once a steady state was achieved none of the treatments had any significant effect either on the diurnal variation in weight or on the water and solute xcretion pattern except for a small reduction in sodium excretion at night when the patient slept with a head-up tilt. In is concluded that these treatments cause symptomatic improvement in idiopathic orthostatic hypotension through an increase in extracellular fluid volume rather than through any change in the abnormal diurnal pattern of water and salt excretion.