Does increased oxygen extraction contribute to the improvement of VO2peak observed in patients who exercise with increased LVAD speed?: reply

We are grateful for the excellent comments from Dr Loyaga-Rendon on our work. We agree that several factors, beyond cardiac output, potentially can contribute to enhanced peak oxygen uptake during maximal exercise with increased pump speed in continuous flow left ventricular assist device (CF-LVAD) patients, including peripheral factors such as oxygen extraction. In the work of Brassard et al.,1 cardiac output during maximal exercise did not differ between

exercise at fixed vs. incremental pump speed. Thus we agree that the increased peak oxygen uptake with increased pump speed in the current study2 cannot automatically be credited to increased cardiac output as we did not measure this parameter directly in our study. The obvious limitations of the small sample sizes in both studies (n = 8 and n = 14) should be mentioned. It is possible that the variability of Swan–Ganz measurements of cardiac output increases with increasing levels of exercise, thus increasing the likelihood of a type II error at peak exercise. Thus larger randomized controlled trials are merited to confirm the relationship between pump speed and exercise capacity as well as to clarify the relative importance of central and peripheral components in exercise physiology in CF-LVAD patients.

References

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doi:10.1002/ejhf.175 Online publish-ahead-of-print 15 October 2014

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LETTER TO THE EDITOR

1. Brassard P, Jensen AS, Nordsborg N, Gustafsson F, Moller JE, Hassager C, Boesgaard S, Hansen

© 2014 The Authors European Journal of Heart Failure © 2014 European Society of Cardiology

PB, Olsen PS, Sander K, Secher NH, Madsen PL. Central and peripheral blood flow during exercise with a continuous-flow left ventricular assist device: constant versus increasing pump speed: a pilot study. Circ Heart Fail 2011;4: 554–560. 2. Jung MH, Hansen PB, Sander K, Olsen PS, Rossing K, Boesgaard S, Russell D, Gustafsson F. Effect of increasing pump speed during exercise on peak oxygen uptake in heart failure patients supported with a continuous-flow left ventricular assist device. A double-blind randomized study. Eur J Heart Fail 2014;16:403–408.

Mette Holme Jung Department of Cardiology University Hospital Rigshospitalet Blegdamsvej 9 Copenhagen 2100 Denmark Tel: + 45 23 48 47 34 Fax: +45 35 45 77 05 Email: [email protected]

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Does increased oxygen extraction contribute to the improvement of VO2peak observed in patients who exercise with increased LVAD speed?: reply.

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