© 2004 European Society of Cardiology
Biomechanical efficiency is decreased in heart failure during low-level steady state and maximal ramp exercise
a University of Washington Box 356422, 1959 NE Pacific Street, Seattle, WA 98195, USA
b VA Puget Sound Health Care System USA
c Brooke Army Medical Center San Antonio, TX, USA
* Corresponding author. Tel.: +1-206-221-4507; Fax: +1-206-221-6835. E-mail address: levywc{at}u.washington.edu
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Abstract |
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Background: Previous studies of biomechanical efficiency (external work/energy input – Watt/O2 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.
Aims: 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 VO2 during exercise and recovery. Gross (VO2 above zero), Net (VO2 above the resting VO2) and Work (VO2 above the unloaded pedaling VO2) efficiencies were calculated.
Results: HF subjects had an 18% higher VO2 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 VO2/Watt relationship during ramp exercise had the best correlation with HF symptoms (r=0.46).
Conclusions: HF subjects have an increased O2 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.
Key Words: Abbreviations • HF, Heart failure • SS, Steady state • MLWHF, Minnesota living with HF questionnaire • VO2, oxygen consumption • CPET, cardiopulmonary exercise testing • MRS, magnetic resonance spectroscopy • VT, ventilatory threshold
Received August 20, 2003; Revised January 26, 2004; Accepted February 25, 2004
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