Effect of changes in posture on circulatory homeostasis in patients with the nephrotic syndrome

To assess whether the upright posture causes circulatory hypovolaemia in patients with the nephrotic syndrome (NS), we studied 12 subjects with NS and 12 healthy subjects during recumbency, 110 min of standing, followed again by recumbency. Control blood-pressure was 134/88 +/- 4/3 mmHg in the patients and 113/75 +/- 2/3 mmHg in the normal subjects (P less than 0.01), and remained higher in the patients throughout the procedure. Heart rate was continuously higher in the patients (P less than 0.05), but acceleration on standing was normal. The blood volume, which was not different during recumbency, had fallen below that in normal subjects after 25 min of standing (P less than 0.05), due to excessive plasma volume reduction (-16.8 +/- 0.8% in the patients against -11.7 +/- 1.2% in the normals, P less than 0.02). Plasma renin activity (PRA) was higher in the patients while recumbent (P less than 0.001) but not during standing, due to a blunted response in some. No significant differences in plasma noradrenaline were found, but four patients reacted with an excessive rise in plasma noradrenaline and heart rate. This subset, which had high PRA levels as well, comprised the only subject who experienced orthostatic hypotension. It is concluded that during standing an excessive drop in plasma volume leads to a lowered blood volume in NS patients. This forms a paradox with the heart rate acceleration and noradrenaline levels, which were mostly normal, and with the blood-pressure, which remained slightly elevated. Even in a few patients with enhanced stimulation of heart rate and noradrenaline, blood-pressure was found to be high in the majority of cases. PRA was usually found to be increased but, in part, independent of posture.