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Preventing hemodilution abolishes natriuresis of water immersion in humans

1998; American Physiological Society; Volume: 275; Issue: 3 Linguagem: Inglês

10.1152/ajpregu.1998.275.3.r879

1522-1490

Lars Johansen, Bettina Pump, Jørgen Warberg, Niels Juel Christensen, Peter Norsk,

Hemodynamic Monitoring and Therapy

The hypothesis was tested that hemodilution is one of the determinants of the water immersion (WI)-induced natriuresis. Eight males were subjected to 3 h of 1) WI to the midchest (Chest), 2) WI to the neck combined with thigh cuff-induced (80 mmHg) venous stasis (Neck + stasis), and 3) a seated time control ( n = 6). Central venous pressure and left atrial diameter increased to the same extent during Chest and Neck + stasis ( P < 0.05), whereas renal sodium excretion only increased during Chest from 77 ± 7 to 225 ± 13 μmol/min ( P < 0.05). During Chest, plasma colloid osmotic pressure (COP) decreased from 27.7 ± 0.7 to 25.1 ± 0.7 mmHg ( P< 0.05), and plasma volume (PV) increased from 3,263 ± 129 to 3,581 ± 159 ml ( P < 0.05), whereas these variables remained unchanged during Neck + stasis. Plasma norepinephrine concentration decreased similarly during Chest and Neck + stasis by 45 ± 7 and 34 ± 4%, respectively ( P < 0.05), whereas plasma renin activity decreased only during Chest ( P < 0.05). In conclusion, during WI in humans 1) hemodilution (decrease in COP and increase in PV) is a pivotal stimulus for the natriuresis and 2) central blood volume expansion without hemodilution does not augment renal sodium output.