Noninvasive assessment of cardiac index in healthy volunteers: a comparison between thoracic impedance cardiography and Doppler echocardiography.

BACKGROUND: Thoracic bioimpedance cardiography (ICG) has been proposed as a noninvasive, continuous, operator-independent, and cost-effective method for cardiac output monitoring. In the present study, we compared cardiac index (CI) measurements with ICG (Niccomo device) and transthoracic Doppler echocardiography in resting healthy volunteers undergoing hemodynamic load challenge. METHODS: Twenty-five healthy volunteers (7 men and 18 women, mean age 36 +/- 6 yr, body surface area 1.75 +/- 0.17 m(2)) were investigated during three experimental conditions: baseline, positive end-expiratory pressure + 10 cm H(2)O and lower body positive pressure by means of medical antishock trousers inflated to 30 cm H(2)O in the abdominal compartment. RESULTS: ICG signal quality was >89% over all sets of measurements. A weak but significant relationship was observed between CI(TTE) and CI(ICG) (r = 0.36; P = 0.002). Agreement between both techniques was 0.94 L x min(-1) x m(-2) (95% CI: 0.77-1.11), limits of agreement were -0.47 to 2.35 L x min(-1) x m(-2), and percentage error was 53%. No statistically significant relationships were found between percent changes in CI(TTE) and CI(ICG) after applications of positive end-expiratory pressure + 10 cm H(2)O (r = 0.21; P = 0.31) and medical antishock trousers (r = 0.22; P = 0.30). CONCLUSIONS: Poor correlation and lack of agreement between absolute values of CI measured by ICG and transthoracic Doppler echocardiography were found in resting healthy volunteers. The Niccomo device was also unreliable for monitoring changes in CI during hemodynamic load challenge.