Comparison of thoracic bioimpedance with acetylene uptake for measuring cardiac output

Cardiac output is shown to be a key determinant for oxygen transport, performance and health. Reliable and accurate non-invasive measurements of cardiac output, especially during exercise, are therefore of importance. The present study compared a new thoracic bioimpedance method with the established single-breath acetylene uptake method. We assessed cardiac output in 20 (24±4 years.) moderately trained males, at rest and during cycling. Both methods showed good test-retest reliabilities with ±2 SD limits of agreement of 3.67 and -4.50 L ∙ min(-1) (thoracic bioimpedance) and 4.46 and -5.69 L ∙ min(-1) (single breath), respectively. When thoracic bioimpedance was compared with single breath, the ±2 SD limits of agreement were poor (-6.05 and 9.57 L ∙ min(-1)). Thoracic bioimpedance displayed significantly lower (p<0.05) absolute cardiac output values than single breath, and the cardiac output-oxygen consumption slopes (y=5.7x+5.5 (single breath) and y=5.0x+5.0 (thoracic bioimpedance) tended (p=0.08) to show less increase for thoracic bioimpedance.

Results from the single-breath method are in line with previous findings, showing a good reliability. Although thoracic bioimpedance showed a similar reliability as the single-breath method, and is easier to use, the agreement with single breath was poor, and thoracic bioimpedance seems not to be able to replace it.