Impedance cardiography the reproducibility of stroke volume measurements under conditions of mass examination.

The stroke volume at rest of 81 test subjects with no evident cardiac or circulatory dysfunction was determined by impedance cardiography and the measurements were repeated after 11 weeks. In order to attain comparable and reproducible conditions, 44 test subjects were chosen who showed heart rates at rest not higher than 83 beats per min, and whose changes in heart rate between the two tests were not greater than 11 beats per min. The stroke volumes determined by impedance cardiography are greater than those measured with the invasive methods reported by other authors. If the electrodes are removed between the tests sufficient reproducibility is not obtained. It is concluded that determinations of stroke volume by impedance cardiography as described in the literature are only suitable for detecting directional changes when the electrodes are left in place. It is impossible to obtain comparable data with electrodes once removed and replaced for the second measurement. Impedance cardiography is based on theoretical assumptions which do not permit estimation of errors affecting the measurement.