title: Biomechanical efficiency is decreased in heart failure during low-level steady state and maximal ramp exercise.
abstract: BACKGROUND
  Previous studies of biomechanical efficiency (external work/energy input--Watt/O(2) consumed) in heart failure (HF) using cardiopulmonary exercise testing (CPET) and magnetic resonance spectroscopy (MRS) have had discordant results with increased efficiency by CPET and decreased efficiency by MRS.
  
  
  OBJECTIVE
  Compare biomechanical efficiency of HF subjects and normal controls during steady state (SS=35 W for 6 min) and ramp cycle ergometer exercise. The hypothesis was that HF subjects would have impaired biomechanical efficiency that correlated with HF symptoms.
  
  
  METHODS
  Biomechanical efficiency used the actual Vo(2) during exercise and recovery. Gross (Vo(2) above zero), Net (Vo(2) above the resting Vo(2)) and Work (Vo(2) above the unloaded pedaling Vo(2)) efficiencies were calculated.
  
  
  RESULTS
  HF subjects had an 18% higher Vo(2) during SS exercise (P=0.029). Biomechanical efficiency was reduced during SS exercise (gross -15%, P=0.019, net -15%, P=0.062, and work -35%, P=0.002). Gross Efficiency during SS exercise had the strongest correlation with HF symptoms (r=0.55). During ramp exercise gross (-26%), net (-10%) and work (-8%) biomechanical efficiency were all reduced (all P<0.05). The slope of the Vo(2)/Watt relationship during ramp exercise had the best correlation with HF symptoms (r=0.46).
  
  
  CONCLUSIONS
  HF subjects have an increased O(2) cost/Watt during SS and ramp exercise that correlates with HF symptoms of fatigue and breathlessness. Methods to improve biomechanical efficiency in HF subjects by exercise training or medications may improve the symptoms and the impaired exercise capacity associated with HF.
authors.affiliation: University of Washington, Box 356422, 1959 NE Pacific Street, Seattle, WA 98195, USA. levywc@u.washingon.edu
authors.forename: Wayne C
authors.initials: WC
authors.lastname: Levy
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Maichel
authors.forename: Natalie P
authors.initials: NP
authors.lastname: Steele
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Leclerc
authors.forename: John R
authors.initials: JR
authors.lastname: Stratton
mesh_terms: D001794:Blood Pressure; D016022:Case-Control Studies; D015444:Exercise; D005080:Exercise Test; D017079:Exercise Tolerance; D005260:Female; D006333:Heart Failure / Q000503:physiopathology*; D006339:Heart Rate; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D011237:Predictive Value of Tests; D013318:Stroke Volume; D014861:Washington