Denis S. Loiselle
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View article: Resolving an inconsistency in the estimation of the energy for excitation of cardiac muscle contraction
Resolving an inconsistency in the estimation of the energy for excitation of cardiac muscle contraction Open
In the excitation of muscle contraction, calcium ions interact with transmembrane transporters. This process is accompanied by energy consumption and heat liberation. To quantify this activation energy or heat in the heart or cardiac muscl…
View article: Letter to the Editor
Letter to the Editor Open
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View article: Uncovering cross-bridge properties that underlie the cardiac active complex modulus using model linearisation techniques
Uncovering cross-bridge properties that underlie the cardiac active complex modulus using model linearisation techniques Open
The properties underlying cardiac cross-bridge kinetics can be characterised by a muscle's active complex modulus. While the complex modulus can be described by a series of linear transfer functions, the biophysical mechanisms underlying t…
View article: Cardiac efficiency and Starling's Law of the Heart
Cardiac efficiency and Starling's Law of the Heart Open
The formulation by Starling of The Law of the Heart states that ‘the [mechanical] energy of contraction, however measured, is a function of the length of the muscle fibre’. Starling later also stated that ‘the oxygen consumption of the iso…
View article: Cross-bridge thermodynamics in pulmonary arterial hypertensive right-ventricular failure
Cross-bridge thermodynamics in pulmonary arterial hypertensive right-ventricular failure Open
This study characterizes cross-bridge mechano-energetics and dynamic stiffness of right-ventricular trabeculae isolated from a rat model of pulmonary hypertensive right-ventricular failure. Failing trabeculae showed increased passive force…
View article: Cardiac mechanical efficiency is preserved in primary cardiac hypertrophy despite impaired mechanical function
Cardiac mechanical efficiency is preserved in primary cardiac hypertrophy despite impaired mechanical function Open
Increased heart size is a major risk factor for heart failure and premature mortality. Although abnormal heart growth subsequent to hypertension often accompanies disturbances in mechano-energetics and cardiac efficiency, it remains uncert…
View article: Insights From Computational Modeling Into the Contribution of Mechano-Calcium Feedback on the Cardiac End-Systolic Force-Length Relationship
Insights From Computational Modeling Into the Contribution of Mechano-Calcium Feedback on the Cardiac End-Systolic Force-Length Relationship Open
In experimental studies on cardiac tissue, the end-systolic force-length relation (ESFLR) has been shown to depend on the mode of contraction: isometric or isotonic. The isometric ESFLR is derived from isometric contractions spanning a ran…
View article: Re-visiting the Frank-Starling nexus
Re-visiting the Frank-Starling nexus Open
Well over a century ago, Otto Frank, working at Carl Ludwig's Institute of Physiology in Munich, studying the isolated, blood-perfused, frog heart preparation, demonstrated that there are two distinct pressure-volume relations in the heart…
View article: An Equivocal Final Link – Quantitative Determination of the Thermodynamic Efficiency of ATP Hydrolysis – Sullies the Chain of Electric, Ionic, Mechanical and Metabolic Steps Underlying Cardiac Contraction
An Equivocal Final Link – Quantitative Determination of the Thermodynamic Efficiency of ATP Hydrolysis – Sullies the Chain of Electric, Ionic, Mechanical and Metabolic Steps Underlying Cardiac Contraction Open
Each beat of the heart completes the final step in a sequence of events commencing with electrical excitation-triggered release of Ca2+ from the sarcoplasmic reticulum which, in turn, triggers ATP-hydrolysis-dependent mechanical contractio…
View article: Energetics Equivalent of the Cardiac Force-Length End-Systolic Zone: Implications for Contractility and Economy of Contraction
Energetics Equivalent of the Cardiac Force-Length End-Systolic Zone: Implications for Contractility and Economy of Contraction Open
We have recently demonstrated the existence of a region on the cardiac mechanics stress-length plane, which we have designated "The cardiac end-systolic zone." The zone is defined as the area on the pressure-volume (or stress-length) plane…
View article: Mechanical loading of isolated cardiac muscle with a real‐time computed Windkessel model of the vasculature impedance
Mechanical loading of isolated cardiac muscle with a real‐time computed Windkessel model of the vasculature impedance Open
To date, the mechanical loads imposed on isolated cardiac muscle tissue in vitro have been oversimplified. Researchers typically applied loads that are time-invariant, resulting in either isometric and auxotonic contractions, or flat-toppe…
View article: Energy expenditure for isometric contractions of right and left ventricular trabeculae over a wide range of frequencies at body temperature
Energy expenditure for isometric contractions of right and left ventricular trabeculae over a wide range of frequencies at body temperature Open
We studied the energy expenditure of isometric contractions using both right-ventricular (RV) and left-ventricular (LV) trabeculae isolated from the rat heart. The energy expenditure under isometric contraction presents entirely as heat li…
View article: Solving a century-old conundrum underlying cardiac force-length relations
Solving a century-old conundrum underlying cardiac force-length relations Open
In the late 19th century, Otto Frank presented a diagram (Frank O. Z Biol 37: 483–526, 1899) showing that cardiac end-systolic pressure-volume relations are dependent on the mode of contraction: one for isovolumic contractions that locate …
View article: Computational Modelling of Cardiac Trabecula Mechanics
Computational Modelling of Cardiac Trabecula Mechanics Open
Cardiac trabeculae are thin strips of muscle within the ventricles that can be readily excised and used to investigate contractile mechanics of cardiac muscle. Recently, the Auckland Bioengineering Institute has developed a novel cardiac m…
View article: Pulmonary arterial hypertension reduces energy efficiency of right, but not left, rat ventricular trabeculae
Pulmonary arterial hypertension reduces energy efficiency of right, but not left, rat ventricular trabeculae Open
Key points Pulmonary arterial hypertension (PAH) triggers right ventricle (RV) hypertrophy and left ventricle (LV) atrophy, which progressively leads to heart failure. We designed experiments under conditions mimicking those encountered by…
View article: Left-Ventricular Energetics in Pulmonary Arterial Hypertension-Induced Right-Ventricular Hypertrophic Failure
Left-Ventricular Energetics in Pulmonary Arterial Hypertension-Induced Right-Ventricular Hypertrophic Failure Open
Pulmonary arterial hypertension (PAH) alters the geometries of both ventricles of the heart. While the right ventricle (RV) hypertrophies, the left ventricle (LV) atrophies. Multiple lines of clinical and experimental evidence lead us to h…
View article: Do right‐ventricular trabeculae gain energetic advantage from having a greater velocity of shortening?
Do right‐ventricular trabeculae gain energetic advantage from having a greater velocity of shortening? Open
Key points We designed a study to test whether velocity of shortening in right‐ventricular tissue preparations is greater than that of the left side under conditions mimicking those encountered by the heart in vivo . Our experiments allowe…
View article: Experimental and modelling evidence of shortening heat in cardiac muscle
Experimental and modelling evidence of shortening heat in cardiac muscle Open
Key points Heat associated with muscle shortening has been repeatedly demonstrated in skeletal muscle, but its existence in cardiac muscle remains contentious after five decades of study. By iterating between experiments and computational …
View article: Does the intercept of the heat–stress relation provide an accurate estimate of cardiac activation heat?
Does the intercept of the heat–stress relation provide an accurate estimate of cardiac activation heat? Open
Key points The heat of activation of cardiac muscle reflects the metabolic cost of restoring ionic homeostasis following a contraction. The accuracy of its measurement depends critically on the abolition of crossbridge cycling. We abolishe…
View article: A Comparison of Discretization Methods for the Inverse Problem of Electrocardiography
A Comparison of Discretization Methods for the Inverse Problem of Electrocardiography Open
Epicardial electrical activity reconstructed non-invasively from body surface potentials is currently used clinically to map electrical activity. Here, two methods for solving this problem are evaluated using in-vivo experimental data: A c…
View article: Thermodynamic analysis questions claims of improved cardiac efficiency by dietary fish oil
Thermodynamic analysis questions claims of improved cardiac efficiency by dietary fish oil Open
Studies in the literature describe the ability of dietary supplementation by omega-3 fish oil to increase the pumping efficiency of the left ventricle. Here we attempt to reconcile such studies with our own null results. We undertake a qua…
View article: Myocardial energetics is not compromised during compensated hypertrophy in the Dahl salt-sensitive rat model of hypertension
Myocardial energetics is not compromised during compensated hypertrophy in the Dahl salt-sensitive rat model of hypertension Open
Salt-induced hypertension leads to development of left ventricular hypertrophy in the Dahl salt-sensitive (Dahl/SS) rat. Before progression to left ventricular failure, the heart initially undergoes a compensated hypertrophic response. We …
View article: Impaired ADP channeling to mitochondria and elevated reactive oxygen species in hypertensive hearts
Impaired ADP channeling to mitochondria and elevated reactive oxygen species in hypertensive hearts Open
Systemic hypertension initially promotes a compensatory cardiac hypertrophy, yet it progresses to heart failure (HF), and energetic deficits appear to be central to this failure. However, the transfer of energy between the mitochondria and…
View article: Thermodynamics and kinetics of the F<sub>o</sub>F<sub>1</sub>-ATPase: application of the probability isotherm
Thermodynamics and kinetics of the F<sub>o</sub>F<sub>1</sub>-ATPase: application of the probability isotherm Open
We use the results of recent publications as vehicles with which to discuss the thermodynamics of the proton-driven mitochondrial F o F 1 -ATP synthase, focusing particularly on the possibility that there may be dissociation between rotato…
View article: Muscle heat: a window into the thermodynamics of a molecular machine
Muscle heat: a window into the thermodynamics of a molecular machine Open
The contraction of muscle is characterized by the development of force and movement (mechanics) together with the generation of heat (metabolism). Heat represents that component of the enthalpy of ATP hydrolysis that is not captured by the…
View article: A counterview of ‘An investigation of the false discovery rate and the misinterpretation of <i>p</i> -values’ by Colquhoun (2014)
A counterview of ‘An investigation of the false discovery rate and the misinterpretation of <i>p</i> -values’ by Colquhoun (2014) Open
In commenting on the instructive, comprehensive and entertainingly written article by Prof. Colquhoun (hereinafter referred to as 'the author'), we state unequivocally that we have no truck with its motivation.Indeed, we too often find the…
View article: Regulation of cardiac cellular bioenergetics: mechanisms and consequences
Regulation of cardiac cellular bioenergetics: mechanisms and consequences Open
The regulation of cardiac cellular bioenergetics is critical for maintaining normal cell function, yet the nature of this regulation is not fully understood. Different mechanisms have been proposed to explain how mitochondrial ATP producti…