MethodsA Multicenter Study of Noninvasive Cardiac Output by Bioreactance During Symptom-limited Exercise
Section snippets
Methods
Basic demographic data and medical history were obtained from 232 subjects referred for stress testing at 4 institutions. The medical history included the primary clinician's assessment of New York Heart Association (NYHA) functional classification. This study was approved by each Institutional Review Board and all subjects gave written informed consent to participate. The only inclusion criterion was that each subject was already referred for a stress test; a small group of patients (n = 22)
Results
Typical NICOM signals obtained at rest, approximately halfway to peak exercise, and at peak exercise from a test performed during treadmill testing are shown in Fig. 1. All tracings, including 3 leads of an electrocardiogram, the NICOM phase signal (Φ(t)), and the first derivative of phase (dΦ(t)/dt)) represent signals that were averaged over a 1-minute period. With increasing amounts of exercise, heart rate increases, the peak-to-peak amplitude of the Φ(t) signal increases (indicating increase
Discussion
The present study, performed in a relatively large number of patients, demonstrates that CO can readily be measured at rest and throughout symptom limited treadmill or bicycle exercise using the bioreactance technique in patients with heart failure spanning a wide range of NYHA classes recruited from multiple centers. The physiologic information obtained about heart failure conforms well with data from several prior studies in which CO was measured invasively and reinforces the concept that
Summary and Conclusions
In summary, using the bioreactance-based noninvasive measurements of CO at rest and at peak exertion, we identified NYHA class-dependent pathophysiologic abnormalities of cardiovascular function consistent with those identified in prior studies using invasive methods of CO measurement.4, 5 These consisted of NYHA class-dependent limitations in ability to increase CO because of both chronotropic incompetence and inability in increase SV during symptom-limited exercise as well as class-dependent
Acknowledgments
The authors are grateful for the superb administrative assistance of Amanda Milgram.
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Supported by a grant from Cheetah Medical. D. Burkhoff and J. Myers are consultants to Cheetah Medical.