The isolated working mouse heart: methodological considerations |
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Authors: | T S Larsen Darrell D Belke Rozsa Sas Wayne R Giles David L Severson Gary D Lopaschuk John V Tyberg |
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Institution: | (1) Department of Physiology and Biophysics, University of Calgary, Faculty of Medicine, Calgary, Alberta, Canada T2N 4N1 e-mail: terjel@fagmed.uit.no Tel.: +47-77644694, Fax: +47-77645440, CA;(2) Department of Pharmacology and Therapeutics, University of Calgary, Faculty of Medicine, Calgary, Alberta, Canada T2N 4N1, CA;(3) Departments of Pediatrics and Pharmacology, University of Alberta, Edmonton, Alberta, Canada T6G 2S2, CA |
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Abstract: | Our aim was to develop a working isolated murine heart model, as the extensive use of genetically engineered mice in cardiovascular
research requires development of new miniaturized technology. Left ventricular (LV) function was assessed in the isolated
working mouse heart perfused with recirculated oxygenated Krebs-Henseleit bicarbonate buffer (37 °C pH 7.4) containing 11.1
mM glucose and 0.4 mM palmitate bound to 3% albumin. The hearts worked against an afterload reservoir at a height equivalent
to 50 mmHg, and heart rate was controlled by electrical pacing of the right atrium. LV pressure was measured with a micromanometer
connected to a small steel cannula inserted through the apex of the heart. The experimental protocol consisted of two interventions.
First, following instrumentation and stabilization, the preload reservoir was raised from a pressure equivalent of 7 to 22.5
mmHg, while pacing at 390 beats·min–1. Thereafter the height of the preload reservoir was set to 10 mmHg, and the pacing rate was varied from 260 to 600 beats·min–1. Aortic and coronary flows were measured by timed collections of effluent from the afterload line and that dripping from
the heart, respectively aortic+coronary flow=cardiac output (CO)]. Elevation of LV end-diastolic pressure (LVEDP) from approximately
5 to 10 mmHg resulted in a twofold increase in average cardiac power product of LV developed pressure (LVDevP) and CO], whereas
myocardial contractility (first derivative of LV pressure, dP/dt) and LVDevP (LV systolic pressure–LVEDP) increased only minimally (5–10%). Measured LVEDP was lower than the equivalent height
of the preload reservoir by an amount that was related to the heart rate. Cardiac power, LVDevP and dP/dt were stable at heart rates up to 400 beats·min–1, but declined markedly with higher rates, consistent with the decrease in LVEDP. Thus, cardiac power was reduced to 50% of
its maximum value when stimulated at approximately 500 beats·min–1, and at even higher rates there was little ejection. By systematic manipulation of the height of the preload reservoir and
heart rate, we conclude that LV afterload and preload can be assessed only by high-fidelity measurement of intraventricular
pressures. The heights of the afterload column and the preload reservoir are unreliable and potentially misleading indicators
of LV afterload and preload.
Received: 28 September 1998 / Accepted: 25 January 1999 |
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Keywords: | Mouse heart Cardiac power Preload Afterload |
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