Comparison of impedance cardiography with indirect fick (CO2) method of measuring cardiac output in healthy children during exercise

Electric bioimpedance has been used to measure cardiac output for decades. Improvements in modeling and microprocessor technology have spawned newer generations of such devices. This method would be especially useful in children, in whom the use of invasive methods is limited. We tested a device (ICG-M401, ASK Ltd.) in 30 healthy children at 2 levels of exercise (0.5 and 1.5 W/kg), and compared impedance measurements of cardiac output (QICG) with carbon dioxide (CO2) rebreathing measurements of cardiac output (qrb). The QICG-oxygen uptake (VO2) relation was expressed by qicg = 3.8 + 4.6 VO2; r2 = 0.68. Mean ± SD bias (qicg-qrb) was 0.14 ± 1.05 L/min, not significantly different from zero (95% confidence interval −0.12 to + 0.44 L/ min). All qicg results were within ±15% of the hypothetical mean value (Bland and Altman analysis). The largest deviation of qicg from QRB was +30%, found in 1 of 57 paired determinations. Eighty percent of qicg values were within ±20% of the QRB result. We conclude that impedance cardiography with the ICG-M401 provided realistic and reliable estimates of cardiac output in healthy children during exercise. This, along with its ease of operation and utility at rest and during exercise, make it both useful and attractive for clinic and research purposes.