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Type: Journal article
Title: A structure-function analysis of the left ventricle
Author: Snelling, E.
Seymour, R.
Green, J.
Meyer, L.
Fuller, A.
Haw, A.
Mitchell, D.
Farrell, A.
Costello, M.
Izwan, A.
Badenhorst, M.
Maloney, S.
Citation: Journal of Applied Physiology, 2016; 121(4):900-909
Publisher: American Physiological Society
Issue Date: 2016
ISSN: 8750-7587
Statement of
Edward P. Snelling, Roger S. Seymour, J. E. F. Green, Leith C. R. Meyer, Andrea Fuller, Anna Haw, Duncan Mitchell, Anthony P. Farrell, Mary-Ann Costello, Adian Izwan, Margaret Badenhorst, Shane K. Maloney
Abstract: Left ventricular external mechanical work rate was calculated from cardiac output and systemic mean arterial blood pressure in resting sheep (Ovis aries; N = 4) and goats (Capra hircus; N = 4) under mild sedation, followed by perfusion-fixation of the left ventricle, and quantification of the cardiac capillary-tissue geometry and cardiomyocyte ultrastructure. The investigation was extended to heavy exercise by increasing cardiac work according to published hemodynamics during sustained treadmill exercise. Left ventricular work rate averaged 0.017 W cm(-3) of tissue at rest, and was estimated to increase to ~0.060 W cm(-3) during heavy exercise. We predicted that oxygen consumption increases from 195 nmol O2 s(-1) cm(-3) at rest, to ~600 nmol O2 s(-1) cm(-3) during heavy exercise, which is within 90% of the demand rate and consistent with work remaining predominantly aerobic. Mitochondria represent 21 - 22% of cardiomyocyte volume and consume oxygen at a rate of 1150 nmol O2 s(-1) cm(-3) of mitochondria at rest, and ~3600 nmol O2 s(-1) cm(-3) during heavy exercise, which is within 80% of maximum in vitro rates and consistent with mitochondria operating near their functional limits. Myofibrils represent 65 - 66% of cardiomyocyte volume, and according to a Laplacian model of the left ventricular chamber, generate peak fiber tensions between ~54 and 62 kPa at rest and during heavy exercise, which is less than maximum tension of isolated cardiac tissue (120 - 140 kPa), and is explained by an apparent reserve capacity for tension development built into the left ventricle.
Keywords: Capillary
Rights: Copyright © 2016 the American Physiological Society
DOI: 10.1152/japplphysiol.00435.2016
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