Competing mechanisms of stress-assisted diffusivity and stretch-activated currents in cardiac electromechanics

We numerically investigate the role of mechanical stress in modifying the conductivity properties of the cardiac tissue and its impact in computational models for cardiac electromechanics. We follow a theoretical framework recently proposed in [Cherubini, Filippi, Gizzi, Ruiz-Baier, JTB 2017], in the context of general reaction-diffusion-mechanics systems using multiphysics continuum mechanics and finite elasticity. In the present study, the adapted models are compared against preliminary experimental data of pig right ventricle fluorescence optical mapping. These data contribute to the characterization of the observed inhomogeneity and anisotropy properties that result from mechanical deformation. Our novel approach simultaneously incorporates two mechanisms for mechano-electric feedback (MEF): stretch-activated currents (SAC) and stress-assisted diffusion (SAD); and we also identify their influence into the nonlinear spatiotemporal dynamics. It is found that i) only specific combinations of the two MEF effects allow proper conduction velocity measurement; ii) expected heterogeneities and anisotropies are obtained via the novel stress-assisted diffusion mechanisms; iii) spiral wave meandering and drifting is highly mediated by the applied mechanical loading. We provide an analysis of the intrinsic structure of the nonlinear coupling using computational tests, conducted using a finite element method. In particular, we compare static and dynamic deformation regimes in the onset of cardiac arrhythmias and address other potential biomedical applications

Nonlinear diffusion & thermo-electric coupling in a two-variable model of cardiac action potential

This work reports the results of the theoretical investigation of nonlinear dynamics and spiral wave breakup in a generalized two-variable model of cardiac action potential accounting for thermo-electric coupling and diffusion nonlinearities. As customary in excitable media, the common Q10 and Moore factors are used to describe thermo-electric feedback in a 10-degrees range. Motivated by the porous nature of the cardiac tissue, in this study we also propose a nonlinear Fickian flux formulated by Taylor expanding the voltage dependent diffusion coefficient up to quadratic terms. A fine tuning of the diffusive parameters is performed a priori to match the conduction velocity of the equivalent cable model. The resulting combined effects are then studied by numerically simulating different stimulation protocols on a one-dimensional cable. Model features are compared in terms of action potential morphology, restitution curves, frequency spectra and spatio-temporal phase differences. Two-dimensional long-run simulations are finally performed to characterize spiral breakup during sustained fibrillation at different thermal states. Temperature and nonlinear diffusion effects are found to impact the repolarization phase of the action potential wave with non-monotone patterns and to increase the propensity of arrhythmogenesis

Ipsilateral free semitendinosus tendon graft with interference screw fixation for minimally invasive reconstruction of chronic tears of the Achilles tendon.

OBJECTIVE: Minimally invasive ipsilateral semitendinosus reconstruction of large chronic tears aims to be advantageous for the patient in terms of plantar flexion recovery, anthropometric measures, fast return to daily and sport activity, is safe, with low donor site co-morbidities, low risks of wound complications and neurovascular injuries. INDICATIONS: Tendon gaps greater than 6 cm and in cases of revision surgery (rerupture). CONTRAINDICATIONS: Diabetes, vascular diseases, previous anterior cruciate ligament (ACL) reconstruction using ipsilateral semitendinosus tendon graft. SURGICAL TECHNIQUE: The semitendinosus tendon is harvested through an incision in the medial aspect of the popliteal fossa, and the proximal stump is exposed and mobilized through an incision performed 2 cm proximal and medial to the palpable tendon gap. We repeat the same steps distally, approaching the distal stump of the tendon through a 2.5 cm longitudinal incision made 2 cm distal and just anterior to the lateral margin of the distal stump. Through the distal incision, we expose the Kager's space and the postero-superior corner of the osteotomized calcaneum. We drill a bone tunnel into the calcaneum from dorsal to plantar using a cannulated headed reamer. The semitendinosus tendon graft is passed into the proximal stump through a medial-to-lateral small incision, its two ends are moved distally, and finally it is pulled down and shuttled through the bone tunnel. The construct is fixed to the calcaneum using an interference screw. POSTOPERATIVE MANAGEMENT: Immobilization in a below the knee plaster cast with the foot in plantar flexion for 2 weeks, weight bearing on the metatarsal heads as tolerated, use elbow crutches, and keep the knee flexed. At 2 weeks, plaster removed, and rehabilitative exercises started, walker cast allowed. RESULTS: Between 2008 and 2010, the procedure was performed on 28 consecutive patients (21 men and 7 women, median age 46 years). At the 2-year follow-up, average ATRS scores significantly improved (p < 0.0001) compared to average preoperative scores with good to excellent outcomes for 26 out of 28 patients (93 %); the maximum calf circumference also improved considerably whereby no clinical or functional relevance compared to the contralateral side observed. Of the 28 patients 16 (57 %) could practice sport at the same preinjury level, whereby 1 patient experienced persistent pain over the distal wound, which ameliorated after desensitization therapy

Biological factors in the pathogenesis of rotator cuff tears.

Rotator cuff tears are common, and lead to shoulder pain and functional impairment. Despite their frequency and related disability, etiology and pathogenesis are still debated. Multiple factors contribute to tears of the rotator cuff. Extrinsic factors are anatomic variables, such as acromial morphologic characteristics, os acromiale, and acromial spurs that compress the rotator cuff by bony impingement or direct pressure from the surrounding soft tissue. Intrinsic factors arise from the tendon itself, because of tensile overload, aging, microvascular supply, traumatisms, or degeneration. Little information is available from a cellular and molecular point of view. We reviewed the biological factors involved in the pathogenesis of rotator cuff tears. Understanding the mechanism of rotator cuff pathology would facilitate the rationale for therapeutic interventions, by guiding the design, selection, and implementation of treatment strategies such as biologic modulation and preventive measures

Ipsilateral hamstring tendon graft reconstruction for chronic patellar tendon ruptures: average 5.8-year follow-up.

BACKGROUND: Patellar tendon reconstruction is technically demanding and is indicated in patients with chronic ruptures (i.e., still present more than six weeks after injury). The purpose of this study was to assess the effectiveness of this procedure in patients with impaired function following patellar tendon rupture. METHODS: Nineteen patients underwent autologous ipsilateral hamstring tendon graft reconstruction for management of a chronic patellar tendon rupture. The clinical diagnosis was supported by imaging radiographs and magnetic resonance imaging. The modified Cincinnati rating system questionnaire and the Kujala scoring questionnaire were administered preoperatively and at the last examination, an average follow-up of 5.8 years (range, four to 7.8 years) postoperatively. Thigh volume, cross-sectional area of the thigh (muscle and bone), and the maximum isometric voluntary contraction strength of the extensor apparatus of the knee were measured bilaterally in all nineteen patients. RESULTS: At the last follow-up visit, knee flexion had increased from a mean of 110° preoperatively to a mean of 132° and extension lag had significantly decreased from 20° preoperatively to 3°; the mean modified Cincinnati and Kujala scores were notably improved. All patients had returned to ordinary daily activities. Fourteen of nineteen patients were very satisfied with the procedure, three were satisfied, one was moderately satisfied, and one was unsatisfied. CONCLUSIONS: On the basis of our review of nineteen patients, hamstring tendon reconstruction of chronic patellar tendon rupture provided good functional recovery and return to preinjury daily activitie

Modelling thermo-electro-mechanical effects in orthotropic cardiac tissue

In this paper we introduce a new mathematical model for the active contraction of cardiac muscle, featuring different thermo-electric and nonlinear conductivity properties. The passive hyperelastic response of the tissue is described by an orthotropic exponential model, whereas the ionic activity dictates active contraction incorporated through the concept of orthotropic active strain. We use a fully incompressible formulation, and the generated strain modifies directly the conductivity mechanisms in the medium through the pull-back transformation. We also investigate the influence of thermo-electric effects in the onset of multiphysics emergent spatiotemporal dynamics, using nonlinear diffusion. It turns out that these ingredients have a key role in reproducing pathological chaotic dynamics such as ventricular fibrillation during inflammatory events, for instance. The specific structure of the governing equations suggests to cast the problem in mixed-primal form and we write it in terms of Kirchhoff stress, displacements, solid pressure, dimensionless electric potential, activation generation, and ionic variables. We also advance a new mixed-primal finite element method for its numerical approximation, and we use it to explore the properties of the model and to assess the importance of coupling terms, by means of a few computational experiments in 3D

The FIFA 11+ program is effective in preventing injuries in elite male basketball players: a cluster randomized controlled trial.

BACKGROUND: Recently, structured training programs for sports injury prevention ("The 11" and "The 11+") have been validated in soccer. The FIFA 11+ program has not been evaluated in basketball. HYPOTHESIS: The FIFA 11+ program is effective in reducing the rates of injury in male basketball players. STUDY DESIGN: Randomized controlled trial; Level of evidence, 1. METHODS: The authors randomized 11 teams of the same club. Seven teams were allocated to the intervention group (80 players; mean [SD] age 13.5 [2.3] years), and 4 teams were allocated to the control group (41 players; mean [SD] age 15.2 [4.6] years). The authors conducted an injury surveillance program during a 9-month season. The primary outcome was any injury to the athletes. The secondary outcome was any injury to the lower extremity (foot, ankle, lower leg, knee, thigh, groin, and hip). They included an analysis of the type of exposure (match or training), injury location in the body, and type of injury (acute or overuse). RESULTS: During the 9-month season, 23 (19%) of the 121 players included in the study sustained a total of 31 injuries (14 in the intervention group and 17 in the control group). In the intervention group, injury rates per 1000 athlete-exposures were lower than those in the control group, with statistical significance, for overall injuries (0.95 vs 2.16; P = .0004), training injuries (0.14 vs 0.76; P = .007), lower extremity injuries (0.68 vs 1.4; P = .022), acute injuries (0.61 vs 1.91; P < .0001), and severe injuries (0 vs 0.51; P = .004). The intervention group also had statistically significant lower injury rates for trunk (0.07 vs 0.51; P = .013), leg (0 vs 0.38; P = .007), and hip and groin (0 vs 0.25; P = .023) compared with the control group. There was no statistically significant difference in match injuries, knee injuries, ankle injuries, and overuse injuries between 2 groups. The most frequent acute injury diagnoses were ligament sprains (0.41 and 0.38 in the intervention and control groups, respectively; P < .006) and contractures (0.76 and 0.07 in the control and intervention groups, respectively; P < .003). CONCLUSION: The FIFA 11+ warm-up program is effective in reducing the rates of injuries in elite male basketball players

Competing mechanisms of stress-assisted diffusivity and stretch-activated currents in cardiac electromechanics

We numerically investigate the role of mechanical stress in modifying the conductivity properties of cardiac tissue, and also assess the impact of these effects in the solutions generated by computational models for cardiac electromechanics. We follow the recent theoretical framework from Cherubini et al. (2017), proposed in the context of general reaction-diffusion-mechanics systems emerging from multiphysics continuum mechanics and finite elasticity. In the present study, the adapted models are compared against preliminary experimental data of pig right ventricle fluorescence optical mapping. These data contribute to the characterization of the observed inhomogeneity and anisotropy properties that result from mechanical deformation. Our novel approach simultaneously incorporates two mechanisms for mechano-electric feedback (MEF): stretch-activated currents (SAC) and stress-assisted diffusion (SAD); and we also identify their influence into the nonlinear spatiotemporal dynamics. It is found that (i) only specific combinations of the two MEF effects allow proper conduction velocity measurement; (ii) expected heterogeneities and anisotropies are obtained via the novel stress-assisted diffusion mechanisms; (iii) spiral wave meandering and drifting is highly mediated by the applied mechanical loading. We provide an analysis of the intrinsic structure of the nonlinear coupling mechanisms using computational tests conducted with finite element methods. In particular, we compare static and dynamic deformation regimes in the onset of cardiac arrhythmias and address other potential biomedical applications