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

https://doi.org/10.1016/j.cardfail.2007.05.009Get rights and content

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.

Section snippets

Subjects

This was a retrospective analysis of clinical data obtained from 36 consecutive subjects referred to a private cardiology clinic for CPX testing for evaluation of dyspnea. All patients provided consent for the use of their data in the analysis. Twenty-three of the subjects had heart failure (18 with low ejection fraction [EF], 5 with normal EF) and 13 were ultimately diagnosed as normal (normal EF, dyspnea based on noncardiac factors). Demographic and clinical characteristics of the subjects

Exercise Test Responses

Exercise test responses are summarized in Table 2. For the overall group, the mean maximal perceived exertion was 7.8 ± 1.7 (range 5–10), and the mean peak respiratory exchange ratio was 1.12 ± 0.09 (range 0.87–1.28), suggesting that maximal effort was achieved by most patients. Among CHF patients, the mean maximal heart rate of 103 ± 24 beats/min (range 76–140) was lower than that expected for age (61% of predicted), reflecting the fact that many patients were limited by symptoms associated

Discussion

Cardiac output is a fundamental measure for the assessment of cardiac performance; its measurement has been widely used to quantify the presence and degree of cardiovascular disease and response to various interventions. CHF, in particular, is characterized by a reduction in cardiac output at rest and an impaired cardiac output response to exercise; measures of both resting and exercise cardiac output have been shown to be important prognostic markers in CHF.2, 25, 26, 27 Clinically, the

Summary

The present findings provide face validity to the noninvasive measurement of cardiac output in response to exercise using a novel device based on bioreactance technology. Estimates of cardiac output and ventricular performance concurred with previous studies using direct Fick measures in patients with CHF. We also explored the interactions between CPX and cardiac output responses to exercise in patients with CHF, and observed that the noninvasive device provided insight on interactions between

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    Supported in part by a grant from Cheetah Medical Inc, Wilmington, DE.

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