title: 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.
  
  
  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 (d phi/d t) 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Cardiology Division, Veterans Affairs Palo Alto Health Care System and Stanford University, Palo Alto, California 94304, USA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Myers
authors.forename: Pradeep
authors.initials: P
authors.lastname: Gujja
authors.forename: Suresh
authors.initials: S
authors.lastname: Neelagaru
authors.forename: Daniel
authors.initials: D
authors.lastname: Burkhoff
mesh_terms: D000328:Adult; D000368:Aged; D002302:Cardiac Output / Q000502:physiology*; D005080:Exercise Test / Q000295:instrumentation* / Q000379:methods*; D005260:Female; D006333:Heart Failure / Q000175:diagnosis / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015656:Respiratory Mechanics / Q000502:physiology*; D012189:Retrospective Studies