title: Is low VO2max/kg in obese heart failure patients indicative of cardiac dysfunction?
abstract: OBJECTIVE
  Low peak O2 consumption (VO2max/kg) has been widely used as an indirect indicator of poor cardiac fitness, and often guides management of patients with severe heart failure (HF). We hypothesized that it should be as good an indicator of cardiac dysfunction in obese and non-obese HF patients.
  
  
  METHODS
  We compared the cardiopulmonary exercise performance and non-invasive hemodynamics of 152 obese (BMI>34 kg.m(-2)) and 173 non-obese (BMI≤32) male HF patients in NYHA classes II and III, with reference to 101 healthy male controls. Their physical and cardiac functional reserves were measured during treadmill exercise testing with standard respiratory gas analyses and CO2 rebreathing to measure cardiac output non-invasively during peak exercise. Data are given as mean ± SD.
  
  
  RESULTS
  Obese HF patients with BMI 40.9 ± 7.5 kg·m(-2) (age 56.1 ± 14.0 years, NYHA 2.5 ± 0.5) exercised to acceptable cardiopulmonary limits (peak RER=1.07 ± 0.12), and achieved a mean VO2max/kg of 18.6 ± 5.2 ml·kg(-1)·min(-1), significantly lower than in non-obese HF counterparts (19.9 ± 5.6 ml·kg(-1)·min(-1), P=0.02, age 55.8 ± 10.6 years, BMI 26.6 ± 3.1, NYHA 2.4 ± 0.5, peak RER=1.07 ± 0.09), with both lower than controls (38.5 ± 9.7 ml·kg(-1)·min(-1), P<10(-6)). In contrast, the uncorrected VO2max was higher in obese (2.31 ± 0.69 ml·min(-1)) than non-obese HF patients (1.61 ± 0.49 ml·min(-1), P<10(-6)). When cardiac dysfunction was evaluated directly, peak cardiac power was significantly greater in obese than non-obese HF patients (4.11 ± 1.21 W vs 2.73 ± 0.82 W, P<10(-6)), with both lower than controls (5.42 ± 1.04 W, P<10(-6)).
  
  
  CONCLUSIONS
  These results demonstrate that VO2max/kg is not a generally reliable indicator of cardiac fitness in all patients. Instead, we found that despite having lower VO2max/kg, obese HF patients had stronger hearts capable of generating greater cardiac power than non-obese HF patients of equivalent clinical HF status.
authors.affiliation: Department of Cardiovascular Sciences; Physiological Laboratory, University of Cambridge, UK; Department of Biochemistry, University of Cambridge, UK.
authors.forename: S S
authors.initials: SS
authors.lastname: Hothi
authors.affiliation: Newcastle Medical School, Newcastle, UK.
authors.forename: D K
authors.initials: DK
authors.lastname: Tan
authors.affiliation: Leeds Institute of Biomedical and Clinical Sciences, University of Leeds and Leeds General Infirmary, Leeds, UK.
authors.forename: G
authors.initials: G
authors.lastname: Partridge
authors.affiliation: Leeds Institute of Biomedical and Clinical Sciences, University of Leeds and Leeds General Infirmary, Leeds, UK. Electronic address: ssh26@cam.ac.uk.
authors.forename: L B
authors.initials: LB
authors.lastname: Tan
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D005080:Exercise Test / Q000379:methods; D005260:Female; D006333:Heart Failure / Q000175:diagnosis* / Q000453:epidemiology / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000175:diagnosis* / Q000453:epidemiology / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*
keywords: Cardiac function; Cardiopulmonary exercise testing; Heart failure; Obesity; Oxygen consumption