PERIPHERAL MICROVASCULAR PARAMETERS IN THE NEPHROTIC SYNDROME

Background. Peripheral edema, in combination with severe proteinuria a nd low serum albumin levels, is pathognomonic of the nephrotic syndrom e, yet the exact mechanism of its formation is unknown. Two of the mos t important of the factors in Starling's forces controlling fluid filt ration across the capillary have hitherto not been studied in nephroti c subjects. Methods. The hydrostatic capillary pressure at the finger nailfold in actively nephrotic subjects and age and ses matched contro ls was studied, using direct puncture of the apex of the capillary und er video microscopy, and a servonulling apparatus to give a direct mea surement of capillary pressure. Capillary filtration capacity (CFC) at the calf was measured noninvasively by a modern derivative of the tec hnique of mercury strain gauge plethysmography. Fifteen nephrotic subj ects with a variety of underlying pathological lesions, and age matche d controls were studied. Results. Contrary to the assumption of the '' overflow'' hypothesis of edema formation, there was no evidence of cap illary hypertension. The capillary pressure showed no difference betwe en nephrotic subjects and controls: median (range) of 17.6 (12.0 to 24 .2) compared with 17.3 (9.0 to 21.6) mm Hg, P = NS. CFC was significan tly higher in nephrotic subjects than controls [5.23 (3.28 to 8.52) x 10(-3) versus 3.55 (2.43 to 5.28) x 10(-3) ml/min/100 g/mm Hg, P < 0.0 1].Conclusions. An increase in CFC provides a potentially novel mechan ism contributing at least in part to the formation of peripheral edema in the nephrotic syndrome.