title: Non-invasive estimate of cardiac output during exercise based on impedance cardiography and oxygen uptake in the elderly.
abstract: OBJECTIVE
  This study assessed the agreement between cardiac output (Q) measurements generated by two indirect methods and their applicability in 54 men and 77 women (aged 60-90).
  
  
  METHODS
  The subjects performed a cardiopulmonary test with incremental to maximal exercise on a cycle-ergometer. "Q" was estimated based on oxygen uptake and on impedance cardiography at 50% and 100% of the maximal workload (Wmax) reached during the test. The limits of agreement and mean differences (biases) were estimated using the methodology proposed by Bland-Altman, whereas the relationship between the methods was analyzed by linear regression and intra-class correlation (ICC).
  
  
  RESULTS
  For the load equivalent do 50% of Wmax, the bias between the means of the two methods was -0.58 L x min-1 (6.3% smaller for the impedance measurement) and the limit of agreement was +/- 2.54 L x min-1 (24.7%). At 100% of Wmax, the bias was 1.03 L x min-1 (8.5% greater for the impedance measurement) with a limit of agreement of +/- 3.35 L x min-1 (27.6%). ICC values and the regression curves obtained between the methods were: Qimp=1.82+0.75Q VO2 (r(2)=0.765, p<0.001; ICC=0.727, p<0.01) at 50% Wmax; and Qimp=0.93+1.00Q VO2 (r(2)=0.755, p<0.001; ICC=0.796, p<0.01) at 100% Wmax.
  
  
  CONCLUSIONS
  These results suggest that there is a good agreement between the two methods for the measurement of Q during exercise in the elderly, which is compatible with the findings of similar studies with young subjects.
authors.affiliation: Universidade do Estado do Rio de Janeiro, Rio de Janeiro, RJ, Brazil. rodriguesm@ig.com.br
authors.forename: Maurício Nunes
authors.initials: MN
authors.lastname: Rodrigues
authors.forename: Jacques Henri-Paul
authors.initials: JH
authors.lastname: Vanfraechem
authors.forename: Paulo de Tarso Veras
authors.initials: Pde T
authors.lastname: Farinatti
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002302:Cardiac Output / Q000502:physiology*; D002307:Cardiography, Impedance / Q000379:methods*; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology*; D015203:Reproducibility of Results