title: Normalization for peak oxygen uptake increases the prognostic power of the ventilatory response to exercise in patients with chronic heart failure.
abstract: BACKGROUND
  Peak exercise oxygen uptake (peak VO2) and ventilation to CO2 production (VE/VCO2) slope are established prognostic indicators in patients with chronic heart failure (CHF). A high VE/VCO2 slope, however, does not take into account the level of physical performance as expressed by peak VO2. We hypothesized that the prognostic value of a high VE/VCO2 slope may be improved by normalization for peak VO2 (VE/VCO2/VO2).
  
  
  METHODS
  One hundred patients with CHF underwent pulmonary function tests at rest (spirometry and lung diffusion capacity) and maximal cardiopulmonary exercise testing. The prognostic value of VE/VCO2 slope, peak VO2 and VE/VCO2/VO2 was probed prospectively.
  
  
  RESULTS
  Twenty-one patients died from cardiac reasons during a mean follow-up of 26 +/- 19 months. Nonsurvivors, compared to survivors, showed a lower peak VO2 (13.6 +/- 4.0 vs 17.5 +/- 4.1 mL x min(-1) x kg(-1), P <.01) and a steeper VE/VCO2 slope (43 +/- 11 vs 31.6 +/- 5.0, P <.01). Nonetheless, in patients whose VE/VCO2 slope exceeded 34 (upper normal limit), there was no correlation with peak VO2 (r = -35, P = not significant). Interestingly 35% of them showed a normal exercise performance (peak VO2 > or =18 mL x min(-1) x kg(-1)). At multivariate analysis, the VE/VCO2 slope showed a prognostic power stronger than that of peak VO2; however, the VE/VCO2/VO2 index retained a prognostic power greater than that of both VE/VCO2 slope and peak VO2. A VE/VCO2/VO2 > or =2.4 signaled cases at higher risk.
  
  
  CONCLUSIONS
  Discrepancies between VE/VCO2 slope and peak VO2 may generate uncertainty. Normalization of the former by the latter improves outcome prediction and may be considered a simple and effective way for maximizing the clinical applicability of these 2 indicators.
authors.affiliation: Istituto di Cardiologia, Università degli Studi di Milano, Milan, Italy. marco.guazzi@unimi.it
authors.forename: Marco
authors.initials: M
authors.lastname: Guazzi
authors.forename: Stefano
authors.initials: S
authors.lastname: De Vita
authors.forename: Paola
authors.initials: P
authors.lastname: Cardano
authors.forename: Simona
authors.initials: S
authors.lastname: Barlera
authors.forename: Maurizio D
authors.initials: MD
authors.lastname: Guazzi
mesh_terms: D000704:Analysis of Variance; D002245:Carbon Dioxide / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005260:Female; D006333:Heart Failure / Q000378:metabolism* / Q000401:mortality / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010101:Oxygen Consumption; D011379:Prognosis; D011659:Pulmonary Gas Exchange; D012372:ROC Curve; D012129:Respiratory Function Tests
chemical_list: D002245:Carbon Dioxide