Blood to interstitial fluid volume ratio in chronic hypokalaemic states

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Abstract
The distribution of extracellular fluid over the intra- and extravascular spaces was determined in hypokalaemic and normokalaemic patients. In six patients with Bartter''s syndrome, four with pseudoBartter''s syndrome, and twenty with essential hypertension (EH) chronically treated with chlorthalidone, serum (ECFV) were decreased, while plasma volume (PV) and blood volume (BV) were normal (see Table 1 for means, standard deviations, and levels of significance). Consequently, the ratio of BV to interstitial fluid volume (IFV) was increased. In ten patients with EH on long-term combined enalapril/chlorthalidone therapy, eight EH patients on long-term spironolactone treatment, and twenty-three EH patients treated by short-term sodium restriction, PV, BV, and ECFV were decreased, but serum K+ and BV/IFV were normal. In six patients with primary hyperaldosteronism (PHA) serum K+ was decreased, while PV, BV, and BV/IFV were elevated. Significant negative correlations between sK and BV/IFV were found in the Bartter patients (r = - 0.88) and the pooled data of all patients (r = -0.50). These findings suggest an association between chronic hypokalaemia and a fluid shift from the extra- into the intravascular space. The hypothesis that this phenomenon is due to a decreased venous resistance as a consequence of chronic hypokalaemia is discussed.