title: A structure-function analysis of the left ventricle.
abstract: This study presents a structure-function analysis of the mammalian left ventricle and examines the performance of the cardiac capillary network, mitochondria, and myofibrils at rest and during simulated heavy exercise. 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 then extended to heavy exercise by increasing cardiac work according to published hemodynamics of sheep and goats performing sustained treadmill exercise. Left ventricular work rate averaged 0.017 W/cm3of tissue at rest and was estimated to increase to ∼0.060 W/cm3during heavy exercise. According to an oxygen transport model we applied to the left ventricular tissue, we predicted that oxygen consumption increases from 195 nmol O2·s-1·cm-3of tissue at rest to ∼600 nmol O2·s-1·cm-3during heavy exercise, which is within 90% of the oxygen demand rate and consistent with work remaining predominantly aerobic. Mitochondria represent 21-22% of cardiomyocyte volume and consume oxygen at a rate of 1,150 nmol O2·s-1·cm-3of mitochondria at rest and ∼3,600 nmol O2·s-1·cm-3during 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 in the range of 50 to 70 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.
authors: Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa; edward.snelling@wits.ac.za.
authors: Edward P
authors: 0000-0002-8985-8737
authors: EP
authors: Snelling
authors: School of Biological Sciences, University of Adelaide, Adelaide, South Australia, Australia.
authors: Roger S
authors: 0000-0002-3395-0059
authors: RS
authors: Seymour
authors: School of Mathematical Sciences, University of Adelaide, Adelaide, South Australia, Australia.
authors: J E F
authors: 0000-0001-5061-9563
authors: JE
authors: Green
authors: Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa; Department of Paraclinical Sciences, University of Pretoria, Pretoria, South Africa.
authors: Leith C R
authors: LC
authors: Meyer
authors: Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa; Department of Paraclinical Sciences, University of Pretoria, Pretoria, South Africa.
authors: Andrea
authors: A
authors: Fuller
authors: Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa.
authors: Anna
authors: A
authors: Haw
authors: Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa; School of Anatomy, Physiology and Human Biology, University of Western Australia, Crawley, Western Australia, Australia.
authors: Duncan
authors: D
authors: Mitchell
authors: Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada; Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia, Canada.
authors: Anthony P
authors: AP
authors: Farrell
authors: Central Animal Service, University of the Witwatersrand, Johannesburg, South Africa; and.
authors: Mary-Ann
authors: MA
authors: Costello
authors: School of Anatomy, Physiology and Human Biology, University of Western Australia, Crawley, Western Australia, Australia.
authors: Adian
authors: A
authors: Izwan
authors: School of Physiology, University of the Witwatersrand, Johannesburg, South Africa.
authors: Margaret
authors: M
authors: Badenhorst
authors: Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa; School of Anatomy, Physiology and Human Biology, University of Western Australia, Crawley, Western Australia, Australia.
authors: Shane K
authors: SK
authors: Maloney
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology*; D003198:Computer Simulation; D005260:Female; D006041:Goats; D006352:Heart Ventricles / Q000033:anatomy & histology*; D008297:Male; D008929:Mitochondria, Heart / Q000502:physiology*; D008953:Models, Anatomic; D008955:Models, Cardiovascular; D009929:Organ Size / Q000502:physiology; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology*; D012756:Sheep; D016277:Ventricular Function, Left / Q000502:physiology*
chemical_list: D010100:Oxygen
keywords: capillary; heart; mitochondria; myofibril; work