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Journal of Biomedicine and Biotechnology
Volume 2011 (2011), Article ID 294204, 6 pages
http://dx.doi.org/10.1155/2011/294204
Research Article

Contractile Strength during Variable Heart Duration Is Species and Preload Dependent

1Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH 43210, USA
2Department of Emergency Medicine, The Ohio State University, Columbus, OH 43210, USA

Received 1 July 2011; Accepted 15 August 2011

Academic Editor: Henk Granzier

Copyright © 2011 Carlos A. A. Torres and Paul M. L. Janssen. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We investigate the effect of beat-to-beat variability on cardiac contractility. Cardiac trabeculae were isolated from the right ventricle of rabbits and beagle dogs and stimulated to isometrically contract, alternating between fixed steady state versus variable interbeat intervals. Trabeculae were stimulated at physiologically relevant frequencies for each species (dog 1 and 4 Hz; rabbit 2 and 4 Hz) intercalating fixed periods with 40% variability. A subset of the trabeculae (at 90% of optimal length) was stretched prior to stimulation between 5 and 13% and stimulated at the same frequencies with a fixed versus 40% variation. Fixed rate response at the same base frequency was measured before and after each variable period and the average force reported. In canine preparations no change in force was observed as a result of the imposed variability in beat-to-beat duration. In the rabbit, we observed a nonsignificant decrease in force between fixed and variable pacing at both 2 and 4 Hz (n = 8) when 40% variability was introduced. When a 5% and 13% stretch was applied, the correlation coefficient sharply increased, indicating a more prominent impact of the prebeat duration on the following cycle with higher preload.