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The impact of surgery on pelvic floor muscle (PFM) function remains uncertain. There is a pressure differential along the length of the vagina, influenced by surrounding active and passive tissue structures, giving rise to a pressure profile. The aim of this study is to determine if an intravaginal pressure sensor, femfit®, can measure differences in pressure profiles before and after surgery for pelvic organ prolapse (POP). This pilot study includes 22 women undergoing POP surgery. Intravaginal pressure profiles were measured with femfit® pre- and post-surgery and differences tested using paired Student’s t-tests. Patients completed validated questionnaires for vaginal, bowel, and urinary incontinence symptoms pre- and post-POP surgery and a femfit® usability questionnaire. Sixteen sets of vaginal pressure data were analysed. The highest pressure generated was identified as the peak PFM pressure, whilst all sensor measurements provided a pressure profile. Intra-abdominal pressure (IAP) was measured by the most distal sensor, 8. On average, the difference between peak PFM pressure and IAP was significantly greater post-surgery (p

Current techniques for tracking the displacement and strain patterns within contracting cardiac specimens often require ‘invasive’ markers to be fixed on the sample, offer only modest spatial resolution, and are computationally inefficient. We present a new technique for determining, without requiring the addition of markers, the dynamic displacement and strain distribution within isolated cardiac muscle samples. We use an accurate and robust new digital image correlation algorithm to measure deformations from a stitched-together time-series of images of a contracting trabecula, and a video recording of a contracting myocyte, captured by an optical transmission microscope. This technique yielded a 2D map of local deformation and strain throughout each specimen, over the time-course of a twitch, at a spatial resolution far exceeding that of previous techniques. In the trabecula we examined, our method enabled us to quantify its non-uniform strain and sarcomere length dynamics even when it was contracting with its length fixed. We noted the non-uniform relaxation of the specimen, where part of the trabecula appeared to be in contraction while the rest was in extension. The images of the myocyte revealed a strain distribution that ranged from −7% to −18%. By applying this method, it is now possible to accurately quantify internal deformation in isolated muscle samples to subpixel resolution, which is essential for interpreting any motion-dependent measurements such as sarcomere length and change in cross-sectional area, all of which are preparation-specific.

Introduction and hypothesis Vaginal childbirth is associated with pelvic floor muscle (PFM) damage in a third of women. The biomechanics prediction, detection and management of PFM damage remain poorly understood. We sought in this pilot study to determine whether quantifying PFM stiffness postnatally by vaginal elastometry, in women attending a perineal trauma clinic (PTC) within 6 months of obstetric anal sphincter injury, correlates with their antecedent labour characteristics, pelvic floor muscle damage, or urinary/bowel/sexual symptoms, to inform future definitive prospective studies. Methods In this pilot study, we measured postnatal PFM stiffness by vaginal elastometry in 54 women. A subset of participants (n = 14) underwent magnetic resonance imaging (MRI) to define any levator ani (LA) muscle defects from vaginal childbirth. We investigated the association of PFM stiffness with demographics, labour and delivery characteristics, clinical features and MRI evidence of LA damage. Results Raised maternal BMI was associated with reduced pelvic floor stiffness (r = −0.4; p n = 14) vs non-forceps vaginal delivery (n = 40; 630 ± 40 N/m vs 500 ± 30 N/m; p n = 37) demonstrated higher pelvic floor stiffness values than those without (570 ± 30 N/m vs 450 ± 40 N/m; p Conclusions A history of delayed second stage of labour and forceps delivery was associated with higher PFM stiffness values in the postnatal period. Whether high pelvic muscle stiffness antenatally is a risk factor for instrumental vaginal delivery and LA avulsion is unknown.

Many computer vision algorithms have been presented to track surface deformations, but few have provided a direct comparison of measurements with other stereoscopic approaches and physics-based models. We have previously developed a phase-based cross-correlation algorithm to track dense distributions of displacements over three-dimensional surfaces. In the present work, we compare this algorithm with one that uses an independent tracking system, derived from an array of fluorescent microspheres. A smooth bicubic Hermite mesh was fitted to deformations obtained from the phase-based cross-correlation data. This mesh was then used to estimate the microsphere locations, which were compared to stereo reconstructions of the microsphere positions. The method was applied to a 35 mm × 35 mm × 35 mm soft silicone gel cube under indentation, with three square bands of microspheres placed around the indenter tip. At an indentation depth of 4.5 mm, the root-mean-square (RMS) differences between the reconstructed positions of the microspheres and their identified positions for the inner, middle, and outer bands were 60 µm, 20 µm, and 19 µm, respectively. The usefulness of the strain-tracking data for physics-based finite element modelling of large deformation mechanics was then demonstrated by estimating a neo-Hookean stiffness parameter for the gel. At the optimal constitutive parameter estimate, the RMS difference between the measured microsphere positions and their finite element model-predicted locations was 143 µm.

Estimating the accuracy of subpixel image registration algorithms in practical experiments is important, yet challenging in many applications. The accuracy of these algorithms in camera-based systems is influenced not only by image content, but also camera noise. In this study, five experiments were designed to quantify the effect of changing camera settings on the image noise level, and consequently on the accuracy of subpixel displacement measurements. The systematic errors of the algorithms were measured separately to provide estimates of their contributions to the total measurement error. Experiments were conducted to measure the effects of random noise on the accuracy of displacement measurements. The results showed that the camera parameters directly influenced the image noise level, but the accuracy of algorithms in measuring displacements was not proportional to the image noise level. These results provide information on the quantitative relationship between camera settings and the registration error for a camera-based measurement system.

A wireless intravaginal pressure sensor (IVPS) has been developed to quantify abdominal pressure (Pabd) changes during exercise and activities of daily living to guide post-operative advice given to women. In this pilot study, we aimed to compare IVPS performance, comfort, retention, and acceptability to a standard fluid-filled intrarectal pressure catheter currently used to measure Pabd during routine urodynamics. A Life-Tech 3-mm urodynamic intrarectal catheter and IVPS were inserted concurrently in volunteers attending a urodynamics clinic. The IVPS was positioned above the levator plate and the intrarectal catheter positioned in routine fashion well above the anal sphincter. Routine urodynamics was undertaken, with women asked to perform star jumps if coughing or Valsalva did not invoke leakage. Subjects rated device comfort using a visual analogue scale (0–10). Repeated measures Bland-Altman analysis determined level of agreement (LOA) between the two devices for peak pressures for each activity. Twenty-seven women were recruited, 67 % of the participants preferred the IVPS, 18 % the intrarectal catheter, while 15 % had no preference. Mean comfort score was 0.9 ± 1.7 and 2.1 ± 2.6 (p = 0.049) for the IVPS and intrarectal catheter respectively. Bland-Altman analysis demonstrated minimal bias for cough and Valsalva, however LOA were wide. Differences were more prominent during star jumps where rapid dynamic pressure changes occurred. The IVPS had a higher comfort score and was well retained. The LOA between the two systems was moderate, but the high sampling rate and lower susceptibility to motion artefacts of the IVPS may provide more accurate information that will be important clinically.

Detailed knowledge of the lymphatic drainage of the breast is limited. Lymphoscintigraphy is a technique used during breast cancer treatment to accurately map patterns of lymphatic drainage from the primary tumour to the draining lymph nodes. This study aimed to create a statistical model to analyse the spread of breast cancer and primary tumour location using a large lymphoscintigraphy database, and visualise the results with a novel computational model. This study was based on lymphoscintigraphy data from 2,304 breast cancer patients treated at the Royal Prince Alfred Hospital Medical Centre in Sydney, Australia. Bayesian inferential techniques were implemented to estimate the probabilities of lymphatic drainage from each region of the breast to each draining node field, to multiple node fields, and to determine probabilities of tumour prevalence in each breast region. A finite element model of the torso and discrete model of the draining node fields were created to visualise these data and a software tool was developed to display the results ( www.abi.auckland.ac.nz/breast-cancer ). Results confirmed that lymphatic drainage is most likely to occur to the axillary node field, and that there is significant likelihood of drainage to the internal mammary node field. The likelihood of lymphatic drainage from the whole breast to the axillary, internal mammary, infraclavicular, supraclavicular and interpectoral node fields were 98.2, 35.3, 1.7, 3.1, and 0.7%, respectively; whilst the probability of lymphatic drainage to multiple node fields was estimated to be 36.4%. Additionally, primary tumours are most likely to develop in the upper regions of the breast. The models developed provide quantitative estimates of lymphatic drainage of the breast, giving important insights into understanding breast cancer metastasis and have the potential to benefit both clinicians and patients during breast cancer diagnosis and treatment.

Determining the mechanical properties of an individual's skin is important in the fields of pathology, biomedical device design, and plastic surgery. To address this need, we present a finite element model that simulates the skin of the anterior forearm and posterior upper arm under a rich set of three-dimensional deformations. We investigated the suitability of the Ogden and Tong and Fung strain energy functions along with a quasi-linear viscoelastic law. Using non-linear optimization techniques, we found material parameters and in vivo pre-stresses for different volunteers. The model simulated the experiments with errors-of-fit ranging from 13.7 to 21.5%. Pre-stresses ranging from 28 to 92 kPa were estimated. We show that using only in-plane experimental data in the parameter optimization results in a poor prediction of the out-of-plane response. The identifiability of the model parameters, which are evaluated using different determinability criteria, improves by increasing the number of deformation orientations in the experiments.

Pelvic floor dysfunction and pelvic organ prolapse have been associated with damage to the levator ani (LA) muscle, but the exact mechanisms linking them remain unknown. It has been postulated that factors such as vaginal birth and ageing may contribute to long-term, irreversible LA muscle damage. To investigate the biomechanical significance of the LA muscle during childbirth, researchers and clinicians have used finite element models to simulate the second stage of labour. One of the challenges is to represent the anisotropic mechanical response of the LA muscle. In this study, we investigated the effects of anisotropy by varying the relative stiffness between the fibre and the matrix components, whilst maintaining the same overall stress-strain response in the fibre direction. A foetal skull was passed through two pelvic floor models, which incorporated the LA muscle with different anisotropy ratios. Results showed a substantial decrease in the magnitude of the force required for delivery as the fibre anisotropy was increased. The anisotropy ratio markedly affected the mechanical response of the LA muscle during a simulated vaginal delivery. It is apparent that we need to obtain experimental data on muscle mechanics in order to better approximate the LA muscle mechanical properties for quantitative analysis. These models may advance our understanding of the injury mechanisms of pelvic floor during childbirth.

This study presents a method for estimating the spatial variations in material properties of elastic membranes, such as biological tissue, which contain both inhomogeneous strain fields and inhomogeneous material properties. In order to validate the method, an inhomogeneous, isotropic rubber membrane was biaxially loaded to obtain a set of states. A neo-Hookean finite element model, together with the measured strains, was used to estimate the material parameters by minimizing the residuals between the measured and modelled residual on surface tractions.

FieldML is being developed as an XML standard for communicating computational field descriptions and data. Important principles in its design include building models from as few and as fundamental a set of concepts as necessary, supporting maximum reuse, and allowing the functional derivation of fields to be of unlimited complexity.This talk introduces concepts from the FieldML data model (at version 0.3), and demonstrates how they combine to describe rich field representations.

One of the main goals in Synthetic Biology is to assess the feasibility of building novel biological systems from interchangeable and standardized parts. In order to collect and share parts, a Registry of standardized DNA BioBricks[1] has been established at the MIT. BioBricks can be assembled to form devices and systems to operate in living cells. Design of reliable devices and systems would benefit from accurate models of system function. To predict the function of systems built from many parts, we need to have accurate models for the parts and mechanisms to easily compose those part models into a system model. Therefore, in parallel to increasing the number of parts available and characterising them experimentally, a logical extension to the Registry would be to build a Registry of BioBrick models to complement the physical parts.

Background 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. Methods 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). Results 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. Conclusions 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.