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 7 mmHg) were observed associated with mild reduction in urinary sodium excretion from 176 to 85 mmol/day. The impedance cardiogram demonstrated a significant decrease in stroke volume (12 ml), 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 ln 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.