An Impedance Cardiographic Study of the Mechanism of Blood Pressure Fall after Moderate Dietary Sodium Restriction

Abstract

Impedance cardiography was performed on 13 free-living subjects to determine the mechanism which ties modest sodium restriction to a reduction in blood pressure. During salt restriction intervention, significant decreases in systolic and diastolic blood pressure (6 and 7mmHg) were observed associated with mild reduction in urinary sodium excretion from 176 to 85mmol/day. The impedance cardiogram demonstrated a significant decrease in stroke volume (12ml), which was related to a fall in diastolic pressure (r=0.59, p<0.05). In the further analysis of individual parameters in Kubicek's formula calculating stroke volume, thoracic impedance (Zo/L) showed a significant increase during salt restriction and a change (Δ) in In L/Zo related significantly to Δln diastolic pressure in linear multiple regression analysis. As thoracic impedance has been reported to reflect intrathoracic fluid content, a decrease in extracellular fluid volume was suggested as a possible mechanism of the fall in blood pressure even with modest sodium restriction.