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CARDIOVASCULAR ANESTHESIA

Starling-Effect-Independent Lusitropism Index in Canine Left Ventricle: Logistic Time Constant

Ju Mizuno, MD, PhD^*, Satoshi Mohri, MD, PhD^*, Juichiro Shimizu, MD, PhD^*, Shunsuke Suzuki, MD, PhD, Takeshi Mikane, MD, PhD, Junichi Araki, MD, PhD, Hiromi Matsubara, MD, PhD, Terumasa Morita, MD, PhD, Kazuo Hanaoka, MD, PhD^#, and Hiroyuki Suga, MD, PhD^*¶

*Departments of Cardiovascular Physiology, Anesthesiology and Resuscitology, Cardiovascular Internal Medicine, and Cardiovascular Surgery, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan; #Department of Anesthesiology, Faculty of Medicine, The University of Tokyo, Tokyo, Japan; ¶National Cardiovascular Center Research Institute, Suita, Osaka, Japan

Address correspondence and reprint requests to Ju Mizuno, Assistant Professor Department of Anesthesiology, Faculty of Medicine, The University of Tokyo 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8655, Japan Fax +81-3-5800-8938 Tel +81-3-5800-8668; Email: mizuno_ju{at}yahoo.co.jp

The logistic time constant (_L) has been proposed as a better index of the rate of left ventricular (LV) relaxation or lusitropism than the conventional monoexponential time constant (_E). However, whether and how the Frank-Starling effect influences _L remains to be elucidated. We compared the effect of LV volume (LVV) loading on both logistic and monoexponential fittings. The isovolumic LV relaxation pressure curves from the maximum negative time derivative of pressure (-dP/dt_max) were analyzed at 3 different end-points at 4 LVVs of 10, 12, 14, and 16 mL in 8 excised, cross-circulated canine hearts. We found that the logistic fitting was superior to the monoexponential fitting at all LVVs and end-points. LVV loading did not affect _L but affected _E slightly. Although the advancing end-point increased both _L and _E, the increases were significantly smaller for _L than for _E at all LVVs. Moreover, the changes in both the amplitude constants and nonzero asymptotes with the advancing end-point were significantly smaller for the logistic fitting than for the monoexponential fitting. We conclude that _L served as a more reliable index of lusitropism that is independent of the change in LVV loading or the Frank-Starling effect.

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