Measurement of cardiac stroke volume by impedance cardiography in the last trimester of pregnancy

Abstract

Simultaneous determination of cardiac stroke volume by impedance cardiography and the dye dilution technique was compared in 10 women during the last trimester of pregnancy. Measurements were performed in different body positions to investigate the influence of body position on stroke volume; r = 0.87 for all measurements. Mean stroke volume determined by impedance cardiography was significantly (P < 001) lower than mean stroke volume calculated by the dye dilution technique. There was no significant difference between the mean change in stroke volume determined by the 2 techniques during serial measurements. The reproducibility of individual impedance-determined stroke volumes (6.1 ml) did not differ significantly from individual values obtained by dye dilution (9.3 ml). Maximum mean impedance-determined stroke volume was recorded in the left lateral position (83.8 .+-. 4.0 ml). Mean stroke volume was significantly (P < 0.01) reduced in the supine position (17.9%). A smaller (14.4%) reduction was registered in the right lateral position. These changes in stroke volume according to body position were equally evident by both methods. Impedance cardiography is a safe, reliable, non-invasive technique for the measurements of changes in stroke volume during late pregnancy. The ability to impedance cardiography to determine the changes in stroke volume was unaffected by changes in body position.