Andrew J Taberner

University of Auckland, Окленд, Auckland, New Zealand

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Publications (86)109.96 Total impact

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    ABSTRACT: Isolated ventricular trabeculae are the most common experimental preparations used in the study of cardiac energetics. However, the experiments have been conducted at sub-physiological temperatures. We have overcome this limitation by designing and constructing a novel calorimeter with sufficiently high thermal resolution for simultaneously measuring the heat output and force production of isolated, contracting, ventricular trabeculae at body temperature. This development was largely motivated by the need to better understand cardiac energetics by performing such measurements at body temperature to relate tissue performance to whole heart behavior in vivo. Our approach uses solid-state thermoelectric modules, tailored for both temperature sensing and temperature control. The thermoelectric modules have high sensitivity and low noise which, when coupled with a multi-level temperature control system, enable an exceptionally high temperature resolution with a noise-equivalent power an order of magnitude greater than those of other existing muscle calorimeters. Our system allows us to rapidly and easily change the experimental temperature without disturbing the state of the muscle. Our calorimeter is useful in many experiments that explore the energetics of normal physiology as well as pathophysiology of cardiac muscle. Copyright © 2015, American Journal of Physiology - Heart and Circulatory Physiology.
    AJP Heart and Circulatory Physiology 05/2015; DOI:10.1152/ajpheart.00194.2015 · 4.01 Impact Factor
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    ABSTRACT: Elevated systemic blood pressure, and the attendant development of pathologic left ventricular (LV) hypertrophy, ultimately culminates in heart failure and death. In clinical studies, a reduction of myocardial efficiency has been implicated in systemic hypertensive-hypertrophy. However, it is uncertain whether reduced efficiency correlates with LV wall thickness. Hence, we performed experiments on isolated working hearts of spontaneously hypertensive rats (SHRs)-a widely-used experimental model of human hypertensive-hypertrophy. We contrasted their mechanoenergetic performance with that of Wistar controls at two ages: Adult (9 months) and Aged (post-18 months). The use of animal hearts allowed us to perform experiments over a wide range of afterloads. We found that mechanoenergetic performance (coronary and aortic flows, work output and oxygen consumption) declined with age. The peak efficiency of the Adult SHR was essentially similar to that of Control, but that for the Aged SHR was lower, compared with that of age-matched Wistar rats. All variables, including peak efficiency, obtained from the failing Aged SHR hearts (which also developed right ventricular hypertrophy), were greatly reduced. Our data reveal that peak efficiency of the Aged SHR, upon transitioning from compensated hypertrophy to failure, diminishes sharply, arising from compromised flows-both aortic and coronary. We further show that the reduction of myocardial efficiency in hypertensive-hypertrophy does not correlate with LV wall thickness, but instead is inversely correlated with whole-heart mass. The latter relation may serve as a prognostic and diagnostic tool in the clinical setting.Hypertension Research advance online publication, 19 March 2015; doi:10.1038/hr.2015.37.
    Hypertension Research 03/2015; DOI:10.1038/hr.2015.37 · 2.94 Impact Factor
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    ABSTRACT: Design and develop an automated, hand-held instrument (elastometer) to assess in vivo passive stiffness of the pelvic floor muscle. The elastometer system consisted of a hand piece, real-time controller, and laptop computer. A cable connected the hand-piece to the controller, which communicated with a laptop computer via an ethernet connection. Force sensitivity calibration and displacement accuracy were determined experimentally using a spring load and an Instron mechanical tester. A test re-test series quantified the in vivo repeatability (within a procedure) and reproducibility (between procedures after a 5 min delay) of passive stiffness in volunteers (n = 20). Stiffness was determined from the gradient of the force-displacement curve for each cycle. The force-aperture spring measurements from the elastometer showed consistent (r(2) = 1.0000) agreement with those measured by the Instron. The difference between spring stiffness as measured by the elastometer and the Instron (388.1 N/m cf. 388.5 N/m, respectively) was negligible. The intra-class correlation coefficient for repeatability within procedures was 0.986 95% CI (0.964-0.994) n = 20, and reproducibility between procedures ICC 0.934 (95% CI 0.779-0.981) n = 12. Bland-Altman analysis determined a bias of 0.3 and 18.5 N/m, for repeatability and reproducibility respectively. Neither bias is likely to be clinically significance. The elastometer demonstrated very good repeatability and accuracy in the measurement of force/displacement during in vitro testing. There was a high degree of repeatability and reproducibility in stiffness measurements in a test re-test series. Our results demonstrate the elastometer is accurate and reliable and thereby suitable for larger clinical trials. Neurourol. Urodynam. © 2013 Wiley Periodicals, Inc.
    Neurourology and Urodynamics 02/2015; 34(2). DOI:10.1002/nau.22537 · 2.46 Impact Factor
  • Biophysical Journal 01/2015; 108(2):294a. DOI:10.1016/j.bpj.2014.11.1601 · 3.83 Impact Factor
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    ABC9, University of Wollongong, NSW, Australia; 11/2014
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    ABSTRACT: Long-term systemic arterial hypertension, and its associated compensatory response of left-ventricular hypertrophy, is fatal. This disease leads to cardiac failure and culminates in death. The spontaneously hypertensive rat (SHR) is an excellent animal model for studying this pathology, suffering from ventricular failure beginning at about 18 months of age. In this study, we isolated left-ventricular trabeculae from SHR-F hearts and contrasted their mechanoenergetic performance with those from nonfailing SHR (SHR-NF) and normotensive Wistar rats. Our results show that, whereas the performance of the SHR-F differed little from that of the SHR-NF, both SHR groups performed less stress-length work than that of Wistar trabeculae. Their lower work output arose from reduced ability to produce sufficient force and shortening. Neither their heat production nor their enthalpy output (the sum of work and heat), particularly the energy cost of Ca2+ cycling, differed from that of the Wistar controls. Consequently, mechanical efficiency (the ratio of work to change of enthalpy) of both SHR groups was lower than that of the Wistar trabeculae. Our data suggest that in hypertension-induced left-ventricular hypertrophy, the mechanical performance of the tissue is compromised such that myocardial efficiency is reduced.
    11/2014; 2(11). DOI:10.14814/phy2.12211
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    ABSTRACT: Determining heat losses in power transfer components operating at high frequencies for implantable inductive power transfer systems is important for assessing whether the heat dissipated by the component is acceptable for implantation and medical use. However, this is a challenge at high frequencies and voltages due to limitations in electronic instrumentation. Calorimetric methods of power measurement are immune to the effects of high frequencies and voltages; hence, the measurement is independent of the electrical characteristics of the system. Calorimeters have been widely used to measure the losses of high power electrical components (>50 W), however it is more difficult to perform on low power components. This paper presents a novel power measurement method for components dissipating anywhere between 0.2 W and 1 W of power based on a heat balance calorimeter that uses a Peltier device as a balance sensor. The proposed balance calorimeter has a single test accuracy of ±0.042 W. The experimental results revealed that there was up to 35% difference between the power measurements obtained with electrical methods and the proposed calorimeter.
    Measurement Science and Technology 08/2014; 25(9):095010. DOI:10.1088/0957-0233/25/9/095010 · 1.35 Impact Factor
  • Bryan P Ruddy, Ian W Hunter, Andrew J Taberner
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    ABSTRACT: We present a scaling model for electrically-actuated needle free jet injectors, establishing the relationship between injection volume and motor size. Using an analytical electromagnetic model for the motor, we derive an optimal motor design, and show that this design is approximately scale-invariant. To illustrate the utility of this model, we then describe the design of a motor for use with 300μL disposable injection ampoules with a mass of just 300g, including a light-weight support structure. Experimental verification of the motor performance shows close agreement to model predictions, with a peak force of 1000 N/kg and a 150 m/s water jet delivered.
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    ABSTRACT: An integrated instrument is being developed to study live cardiac trabeculae, which is capable of stimulating the muscle under controlled conditions while measuring the heat production, force, and sarcomere length distribution. To improve the accuracy of estimation of stress, strain, and volumetric heat production, the geometry of the muscle must be known. A spectral domain optical coherence tomography system (SD-OCT) has been constructed and calibrated to image the trabecula mounted inside the instrument. This system was mounted above the muscle chamber and a series of equally-spaced cross-sectional images were obtained. These were processed using a workflow developed to extract cross-sectional area and volume. The initial results have demonstrated the feasibility of using OCT to capture the overall geometry of cardiac trabecula mounted in the instrument. Further work will be directed to improve the image quality for larger samples and apply meshing algorithms to the acquired data.
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    ABSTRACT: Vascularized biological tissue has been shown to increase in stiffness with increased perfusion pressure. The interaction between blood in the vasculature and other tissue components can be modeled with a poroelastic, biphasic approach. The ability of this model to reproduce the pressure-driven stiffening behavior exhibited by some tissues depends on the choice of the mechanical constitutive relation, defined by the Helmholtz free energy density of the skeleton. We analyzed the behavior of a number of isotropic poroelastic constitutive relations by applying a swelling pressure, followed by homogeneous uniaxial or simple-shear deformation. Our results demonstrate that a strain-stiffening constitutive relation is required for a material to show pressure-driven stiffening, and that the strain-stiffening terms must be volume-dependent.
    Journal of Biomechanical Engineering 05/2014; 136(8). DOI:10.1115/1.4027666 · 1.75 Impact Factor
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    ABSTRACT: Diabetes induces numerous electrical, ionic and biochemical defects in the heart. A general feature of diabetic myocardium is its low rate of activity, commonly characterised by prolonged twitch duration. This diabetes-induced mechanical change, however, seems to have no effect on contractile performance (i.e., force production) at the tissue level. Hence, we hypothesise that diabetes has no effect on either myocardial work output or heat production and, consequently, the dependence of myocardial efficiency on afterload of diabetic tissue is the same as that of healthy tissue. We used isolated left ventricular trabeculae (streptozotocin-induced diabetes versus control) as our experimental tissue preparations. We measured a number of indices of mechanical (stress production, twitch duration, extent of shortening, shortening velocity, shortening power, stiffness, and work output) and energetic (heat production, change of enthalpy, and efficiency) performance. We calculated efficiency as the ratio of work output to change of enthalpy (the sum of work and heat). Consistent with literature results, we showed that peak twitch stress of diabetic tissue was normal despite suffering prolonged duration. We report, for the first time, the effect of diabetes on mechanoenergetic performance. We found that the indices of performance listed above were unaffected by diabetes. Hence, since neither work output nor change of enthalpy was affected, the efficiency-afterload relation of diabetic tissue was unaffected, as hypothesised. Diabetes prolongs twitch duration without having an effect on work output or heat production, and hence efficiency, of isolated ventricular trabeculae. Collectively, our results, arising from isolated trabeculae, reconcile the discrepancy between the mechanical performance of the whole heart and its tissues.
    Cardiovascular Diabetology 04/2014; 13(1):79. DOI:10.1186/1475-2840-13-79 · 3.71 Impact Factor
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    ABSTRACT: It is generally recognized that increased consumption of polyunsaturated fatty acids, fish oil (FO) in particular, is beneficial to cardiac and cardiovascular health, whereas equivalent consumption of saturated fats is deleterious. In this study, we explore this divergence, adopting a limited purview: The effect of dietary fatty acids on the mechanoenergetics of the isolated heart per se. Mechanical indices of interest include left-ventricular (LV) developed pressure, stroke work, cardiac output, coronary perfusion, and LV power. The principal energetic index is whole-heart oxygen consumption, which we subdivide into its active and basal moieties. The primary mechanoenergetic index of interest is cardiac efficiency, the ratio of work performance to metabolic energy expenditure. Wistar rats were divided into three Diet groups and fed, ad libitum, reference (REF), fish oil-supplemented (FO), or saturated fatty acid-supplemented (SFA) food for 6 weeks. At the end of the dietary period, hearts were excised, mounted in a working-heart rig, and their mechanoenergetic performance quantified over a range of preloads and afterloads. Analyses of Variance revealed no difference in any of the individual mechanoenergetic indices among the three Diet groups. In particular, we found no effect of prior dietary supplementation with either saturated or unsaturated fatty acids on the global efficiency of the heart.
    03/2014; 2(3). DOI:10.1002/phy2.272
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    ABSTRACT: Numerous epidemiological studies, supported by clinical and experimental findings, have suggested beneficial effects of dietary fish- or fish oil- supplementation on cardiovascular health. One such experimental study showed a profound (100%) increase in myocardial efficiency (i.e., the ratio of work output to metabolic energy input) of the isolated whole-heart, achieved by a corresponding decrease in the rate of myocardial oxygen consumption. However, a number of other investigations have returned null results on the latter energetic index. Such conflicting findings have motivated us to undertake a re-examination. To that effect, we investigated the effects of dietary fatty acid supplementation on myocardial mechano energetics, with our primary focus on cardiac efficiency. We used both isolated hearts and isolated left ventricular trabeculae of rats fed with one of three distinct diets: Reference (REF), Fish Oil-supplemented (FO) or Saturated Fat-supplemented (SFA). For all three groups, and at both spatial levels, we supplied 10 mM glucose as the exogenous metabolic substrate. In the working-heart experiments, we found no difference in the average mechanical efficiency among the three dietary groups: 14.8 ± 1.1% (REF), 13.9 ± 0.6% (FO) and 13.6 ± 0.7% (SFA). Likewise, we observed no difference in peak mechanical efficiency of LV trabeculae: 13.3 ± 1.4%, 11.2 ± 2.2% and 12.5 ± 1.5% among the REF, FO and SFA groups, respectively. We conclude that there is no effect of a period of pre-exposure to a diet supplemented with either fish oil or saturated fatty-acids on the efficiency of the myocardium at either spatial level: tissue or whole-heart.
    The Journal of Physiology 02/2014; 592(8). DOI:10.1113/jphysiol.2013.269977 · 4.54 Impact Factor
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    ABSTRACT: Diabetes is known to alter the energy metabolism of the heart. Thus, it may be expected to affect the efficiency of contraction (i.e., the ratio of mechanical work output to metabolic energy input). The literature on the subject is conflicting. The majority of studies have reported a reduction of myocardial efficiency of the diabetic heart, yet a number of studies have returned a null effect. We propose that these discrepant findings can be reconciled by examining the dependence of myocardial efficiency on afterload. We performed experiments on streptozotocin (STZ)-induced diabetic rats (7-8 weeks post-induction), subjecting their (isolated) hearts to a wide range of afterloads (40 mmHg to maximal, where aortic flow approached zero). We measured work output and oxygen consumption, and their suitably scaled ratio (i.e., myocardial efficiency). We found that myocardial efficiency is a complex function of afterload: its value peaks in the mid-range and decreases on either side. Diabetes reduced the maximal afterload to which the hearts could pump (105 mmHg versus 150 mmHg). Thus, at high afterloads (for example, 90 mmHg), the efficiency of the STZ heart was lower than that of the healthy heart (10.4% versus 14.5%) due to its decreased work output. Diabetes also reduced the afterload at which peak efficiency occurred (optimal afterload: 63 mmHg versus 83 mmHg). Despite these negative effects, the peak value of myocardial efficiency (14.7%) was unaffected by diabetes. Diabetes reduces the ability of the heart to pump at high afterloads and, consequently, reduces the afterload at which peak efficiency occurs. However, the peak efficiency of the isolated working rat heart remains unaffected by STZ-induced diabetes.
    Cardiovascular Diabetology 01/2014; 13(1):4. DOI:10.1186/1475-2840-13-4 · 3.71 Impact Factor
  • Biophysical Journal 01/2014; 106(2):776a. DOI:10.1016/j.bpj.2013.11.4255 · 3.83 Impact Factor
  • Biophysical Journal 01/2014; 106(2):773a. DOI:10.1016/j.bpj.2013.11.4244 · 3.83 Impact Factor
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    ABSTRACT: 3D surface measurements are important for studying the biomechanical properties of deformable tissues. For 3D surface profiling and reconstruction, corresponding points on an object should be matched in different camera views. This process is traditionally performed in systems that use stereo camera pairs or multiple cameras with aligned optical axes. To measure the deformation in soft tissues, it may be more appropriate to arbitrarily position the cameras. For instance, cameras can be placed to overcome obstructions that may be caused by measurement apparatus, such as a surface indenter. A truly arbitrary placement system requires the development of a new algorithm for finding corresponding points during surface reconstruction, as existing methods cannot handle large incompatibilities due to the perspective effects between rotated camera views. In this study, we have proposed a procedure for feature matching that can be used with arbitrarily positioned cameras. This proposed method is then used to generate a 3D surface profile of a silicone gel phantom.
    2013 28th International Conference of Image and Vision Computing New Zealand (IVCNZ); 11/2013
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    ABSTRACT: 3D surface measurements have many industrial and medical applications. We have previously used 3D surface deformation and tracking to identify mechanical properties of the skin. To be able to detect dynamic changes in the surface of the skin we need to have a real-time 3D measurement system. A significant portion of the computation time for tracking the changes is spent during 2D cross-correlation of surface images. This study focuses on improving cross-correlation speed by taking advantage of parallel computation in field programmable gate arrays (FPGAs). We have implemented variable size 2D cross-correlation computations using the Xilinx System Generator tool in the Virtex-6 LX240T FPGA. We have also proposed a hierarchical approach for finding the cross-correlation peak in order to efficiently use our method for different image sizes. Furthermore, the use of RAM blocks instead of shift registers in our design has lowered the resource requirements compared with other FPGA implementations. Preliminary results for our special design indicate better than 200 times speed up compared with a PC with an Intel Xeon E5620 CPU (2.4 GHz clock speed, 4 cores and 8 threads) and 12 GB DDR3 RAM and also 190 times speed up in comparison to an NVidia GForce GT 525M as the graphics processing unit (GPU).
    2013 28th International Conference of Image and Vision Computing New Zealand (IVCNZ); 11/2013
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    ABSTRACT: The characterization of skin mechanics has many clinical implications and has been an active area of research for the past few decades. Biomechanical models have evolved from earlier empirical models to state-of-the-art structural models that provide linkage between tissue microstructure and macroscopic stress-strain response. To maximize the accuracy and predictive capabilities of such computational models, there is a need to reliably identify often a large number of unknown model parameters. This is critically dependent on the availability of experimental data that cover an extensive range of different deformation modes, and quantification of internal structural features, such as collagen orientation. To this end, future challenges should include the ongoing development of noninvasive instrumentation and imaging modalities for in vivo skin measurements. We highlight the important concept of tightly integrating computational models, instrumentation, and imaging modalities into a single platform to investigate skin biomechanics. WIREs Syst Biol Med 2013. doi: 10.1002/wsbm.1228 For further resources related to this article, please visit the WIREs website.
    Wiley Interdisciplinary Reviews Systems Biology and Medicine 09/2013; 5(5). DOI:10.1002/wsbm.1228 · 3.01 Impact Factor
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    ABSTRACT: We describe our laboratories' experimental methods for interrogating cardiac energetics - at the organ (whole-heart), tissue (trabecula) and perforated fibre (mitochondrial) levels. In whole-heart and trabecula experiments, we focus on measuring pressure-volume (force-length) work and oxygen consumption (heat production) from which mechanical efficiency is derived. In both preparations, i.e., across scales differing by three orders of magnitude, we find efficiency values of 10-15%. Mitochondrial experiments invoke a trio of titration protocols to yield information on oxygen consumption, ATP flux, membrane potential, electron leak and ROS production, the latter two of which index energy transfer inefficiencies. This article is protected by copyright. All rights reserved.
    Clinical and Experimental Pharmacology and Physiology 06/2013; DOI:10.1111/1440-1681.12139 · 2.41 Impact Factor