Comparison and reproducibility of transthoracic bioimpedance and dual beam Doppler ultrasound measurement of cardiac function in healthy volunteers.

1. We compared the ease of use and reproducibility of two noninvasive methods, transthoracic electrical bioimpedance (TEB) (BoMed NCCOM3-R7) and non-imaging dual beam Doppler ultrasound (Quantascope--Vital Science), in cardiac output (CO) and stroke volume (SV) measurement in healthy volunteers at rest and during physiological stress, both short term and from day to day. 2. The TEB method was easier to use and not dependent on the operator. The TEB method was more reproducible both in the short term and from day to day. Both devices were able to detect CO and SV changes under physiological stress, but were less reproducible day to day during exercise. 3. At supine rest, the within subject coefficient of variation between time point for TEB was 4.6% for CO and 6.1% for SV, and 7.9% for CO and 7.4% for SV with Doppler. 4. The results from each device showed a linear correlation coefficient (r) of 0.69 for CO (P less than 0.0005) and 0.64 for SV (P less than 0.0005). The correlation coefficient improved to 0.76 (P less than 0.0005) when only changes in CO and SV were considered. There was no systematic difference in the changes detected by the two methods, but the individual variation was wide.