Comparison of band and spot electrodes for the measurement of stroke volume by the bioelectric impedance technique.

OBJECTIVES

Conventional impedance cardiography uses a tetrapolar band electrode configuration to determine thoracic bioelectrical impedance changes and to quantify cardiovascular variables. The present study evaluated the effect of electrode type, band or electrocardiograph (spot), placed in the same anatomical location, on both the absolute value of cardiovascular variables and the percent change in the variable when the patient changed position from supine to standing.

DESIGN

Prospective, randomized studies using repeated-measures design.

SETTING

Research laboratory.

PATIENTS

Twenty-one adult volunteer subjects.

INTERVENTIONS

Subjects were studied while supine and again when standing, in random order as to first position.

MEASUREMENTS AND MAIN RESULTS

Stroke volume and impedance-derived variables were measured. Values for stroke volume measured by the band electrode array were 85 +/- 7 and 49 +/- 3 mL for supine and standing, respectively. In contrast, stroke volume measured through the spot electrodes was 110 +/- 8 and 59 +/- 3 mL, respectively. These differences were due to a lower baseline thoracic bioelectrical impedance value measured through the spot electrodes. However, the percent changes for stroke volume with standing subjects were the same when measured through band (-41 +/- 3%) or spot (-44 +/- 3%) electrodes.

CONCLUSIONS

The comparison of cardiovascular values obtained by impedance cardiography should be accomplished only when the values are obtained using similar electrode configuration and type. While there may be a variation in the absolute value of the variable, the direction and magnitude of the change in the variable is relatively unaffected by the electrode types as used in this study.