International Journal of Cardiology 189 (2015) 234
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Letter to the Editor
VO2max/kg is expected to be lower in obese individuals! Benno Krachler a,b,⁎, Kai Savonen a,c, Pirjo Komulainen a, Maija Hassinen a, Timo A. Lakka a,d, Rainer Rauramaa a,c a
Kuopio Research Institute of Exercise Medicine, Kuopio, Finland Occupational and Environmental Medicine, Department of Public Health and Clinical Medicine, Umeå University, Sweden c Department of Clinical Physiology and Nuclear Medicine, Kuopio University Hospital, Kuopio, Finland d Institute of Biomedicine/Physiology, University of Eastern Finland, Kuopio, Finland b
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Article history: Received 10 April 2015 Accepted 14 April 2015 Available online 15 April 2015 Keywords: Heart failure Maximal oxygen uptake Exercise capacity Cardiopulmonary ﬁtness Obesity Body composition
VO2max follows a linear function of lean mass . Moreover, VO2max divided by lean mass has been shown to be a better prognostic factor in HF-patients compared to VO2max divided by total body mass . Anthropometric-based formulas have been shown to estimate body composition with an acceptable degree of bias . In retrospective studies without measurements of body composition, values for lean mass based on these estimates may be a preferable base for scaling VO2max compared to using the ﬂawed total-weight standard. With that addition, the study by Hothi and coworkers might even contribute to resolving the obesityparadox  in HF-patients: If both CPOmax and lean-mass-scaled VO2max show that obese HF-patients have better cardiac ﬁtness, the “paradox” that obese HF-patients have a better prognosis might simply reﬂect the fact that the clinical instruments used to diagnose and classify HF systematically underestimate cardiac function in obese patients. Conﬂict of interest
To the Editor We have read with interest the article of Hothi and coworkers recently published in the International Journal of Cardiology . The authors found that despite having lower peak oxygen uptake divided by body weight (VO2max/kg), obese patients with severe heart failure (HF) had stronger hearts with a higher functional reserve (CPOmax) than non-obese HF patients of equivalent clinical HF status. We agree with the authors that body composition data should form an essential part of future prospective studies in order to ﬁnd better scaling methods than division by body mass. However, we would even go a step further and claim that meaningful comparisons of VO2max between obese and non-obese individuals require scaling for body composition: The contribution of fat mass to oxygen consumption is negligible and independent of exercise performance . Therefore, dividing VO2max uptake by total body weight (i.e., lean mass + fat mass) systematically underestimates cardiorespiratory ﬁtness in obese individuals. Our research group has demonstrated both, the introduction of a substantial body-composition bias if VO2max is divided by total body weight  and the elimination of body-composition bias if VO2max is divided by lean mass . These results agree with the previous ﬁnding of others that ⁎ Corresponding author at: Department of Public Health and Clinical Medicine, Umeå University Hospital, 90185 Umeå, Sweden. E-mail address: [email protected]
http://dx.doi.org/10.1016/j.ijcard.2015.04.100 0167-5273/© 2015 Elsevier Ireland Ltd. All rights reserved.
The authors report no relationships that could be construed as a conﬂict of interest. References  S.S. Hothi, D.K. Tan, G. Partridge, L.B. Tan, Is low VO2max/kg in obese heart failure patients indicative of cardiac dysfunction?, Int. J. Cardiol. 184 (2015) 755–762.  M. Goran, D.A. Fields, G.R. Hunter, S.L. Herd, R.L. Weinsier, Total body fat does not inﬂuence maximal aerobic capacity, Int. J. Obes. Relat. Metab. Disord. 24 (2000) 841–848.  K. Savonen, B. Krachler, M. Hassinen, P. Komulainen, V. Kiviniemi, T.A. Lakka, et al., The current standard measure of cardiorespiratory ﬁtness introduces confounding by body mass: the DR's EXTRA study, Int. J. Obes. (Lond.) 36 (2012) 1135–1140.  B. Krachler, K. Savonen, P. Komulainen, M. Hassinen, T.A. Lakka, R. Rauramaa, Cardiopulmonary ﬁtness is a function of lean mass, not total body weight: the DR's EXTRA study, Eur. J. Prev. Cardiol. (Nov 7, 2014) http://dx.doi.org/10.1177/204787314557962.  A.M. Batterham, P.M. Vanderburgh, M.T. Mahar, A.S. Jackson, Modeling the inﬂuence of body size on V(O2) peak: effects of model choice and body composition, J. Appl. Physiol. 87 (1999) 1317–1325.  A.F. Osman, M.R. Mehra, C.J. Lavie, E. Nunez, R.V. Milani, The incremental prognostic importance of body fat adjusted peak oxygen consumption in chronic heart failure, J. Am. Coll. Cardiol. 36 (2000) 2126–2131.  B. Krachler, E. Volgyi, K. Savonen, F.A. Tylavsky, M. Alen, S. Cheng, BMI and an anthropometry-based estimate of fat mass percentage are both valid discriminators of cardiometabolic risk: a comparison with DXA and bioimpedance, J. Obes. 2013 (2013) 862514.  A.L. Clark, G.C. Fonarow, T.B. Horwich, Obesity and the obesity paradox in heart failure, Prog. Cardiovasc. Dis. 56 (2014) 409–414.