Cardiac Output and Cardiopulmonary Responses to Exercise in Heart Failure: Application of a New Bio-Reactance Device

Abstract 

Background

Cardiopulmonary exercise testing (CPX) is widely used to evaluate heart failure (HF) patients, but lacks information about ventricular performance. There is a need for a noninvasive cardiac output (CO) measurement.

Methods and Results

Twenty-three HF patients and 13 normals underwent CPX and CO measurements with a new, noninvasive, bioreactance technology based on assessment of relative phase shifts (dΦ/dt) of electric currents injected across the thorax, heart rate, and ventricular ejection time. CO and oxygen uptake (VO₂) closely paralleled each another during exercise, and peak CO was strongly correlated with peak VO₂ (r = 0.73, P < .001). The relationships between peak VO₂ and peak cardiac index (CI) were similar for directly measured CI (r = 0.61) and noninvasive CI (r = 0.61). The CO-VO₂ relationship was also similar between the current study and previous studies from the literature, as evidenced by a similar line of best fit and 95% confidence limits. Maximal CO was significantly related to indices of ventilatory efficiency, including the VE/VCO₂ slope (r = −0.47, P < .01), and the oxygen uptake efficiency slope (r = 0.67, P < .01).

Conclusion

Noninvasive measurement of CO during exercise using a novel bioreactance-based device has potentially important applications as a simple, inexpensive tool to supplement the clinical evaluation of patients with HF.

Key Words: Heart failure, cardiac index, oxygen uptake, exercise testing