Muscle Displacement Research Articles

Ultra-fast in vivo x-ray microtomography of blowfly wingbeat

Ultra-fast in vivo x-ray microtomography of blowfly wingbeat

Einseitiger Exophthalmus mit Orbitaeinblutung

A 46-year-old woman presented with a sudden onset of non-traumatic periorbital hemorrhage, painless proptosis, conjunctival chemosis and injection as well as motility restriction of the right eye with double vision. Magnetic resonance imaging (MRI) revealed an extraconal mass in the medial orbit with lateral displacement of the medial rectus muscle and the eyeball without optic nerve involvement. A biopsy led to the diagnosis of non-specific inflammation. This case shows that sudden periorbital hemorrhages can be a sign for idiopathic orbital inflammation.

The Effects of a Three-Dimensional, Saddle-Shaped Annulus on Anterior and Posterior Leaflet Stretch and Regurgitation of the Tricuspid Valve

Tricuspid regurgitation (TR) is present in trace amounts or more in 82-86% of the population and is greater than mild in 14% of the population. In severe cases, it can contribute to right heart failure and adversely affect mitral valve repair durability. One major cause of TR is the dilation of the tricuspid annulus, which alters the geometry of the annulus from a saddle-shape to a more planar profile. Another cause of TR is the displacement of the papillary muscles (PMs), which results from right ventricular dilation. The objective of this study was to identify the effect of a saddle-shaped annulus on native tricuspid leaflet stretch mechanics and TR. In addition, the effects of geometric alterations, including annular dilatation and PM displacement, on leaflet stretch was investigated. Fresh porcine tricuspid valves (TVs) (n = 8) were excised and sutured to an adjustable three-dimensional annulus plate (allowing for dilatation and saddle-shape) and three PM attachment rods. The valve was then placed in the in vitro Georgia Tech right heart simulator. Dual-camera photogrammetry, was used to quantify the stretch ratio experienced by the valve leaflets at peak systole for the following conditions: physiologically normal, 100% annular dilatation, displaced PMs, and a combination of annular dilatation and PM displacement. In addition, a saddle and flat annulus were implemented for each of the four conditions. PM displacement was simulated by displacing all PMs by 10 mm in all directions (laterally, apically, posteriorly/anteriorly). The physiologically normal condition-normal annulus area, saddle-shaped annulus with PMs in a normal position, was used as a control. The results showed that the posterior leaflet exhibited significantly (p ≤ 0.05) higher major and areal stretch ratios as compared to the anterior leaflet at peak systole for all conditions tested. No significant difference was seen in stretch when a flat annulus was compared to saddle for the anterior or posterior leaflet for normal or disease conditions. Investigation of the impact of disease found a significant increase (p ≤ 0.10) in stretch in the posterior leaflet with a combination of annular dilatation and PM displacement (2.01 ± 0.68) as compared to the normal condition with a saddle annulus (1.43 ± 0.20). In addition displacement of the PMs resulted in a significant (p ≤ 0.01) reduction in TR, although the actual volume reduced was minimal (1.2 mL). Stretch values were measured for the anterior and posterior leaflet under both physiologic and pathologic conditions for the first time. Further, these results provide an understanding of the effects of geometric parameters on valve mechanics and function, which may lead to improved TV repairs.

Abstract 9177: Mitral Valve Adaptation in Chronic Aortic Regurgitation with Preserved Systolic Function: A Three-Dimensional Echocardiographic Study

Introduction: Chronic aortic regurgitation (AR) causes left ventricular (LV) remodeling and ultimately heart failure. This creates the potential for functional mitral regurgitation (MR) caused by papillary muscle displacement and mitral valve tethering. However, MR is typically absent during the compensated stage of AR despite substantial LV dilatation. Increased mitral leaflet area has been identified in ischemic and non-ischemic heart failure. It is unknown whether increased mitral valve size could represent a compensatory mechanism capable of preventing MR in patients with LV dilatation due to chronic AR. Hypothesis: Chronic AR is associated with mitral valve enlargement and this can prevent functional MR in patients with LV dilatation. Our objective is to compare mitral valve leaflet area in patients with chronic AR and preserved systolic function to that of normal patients using 3D-echocardiography. Methods: From January to April 2011, we prospectively enrolled 44 patients (22 with at least moderate aortic regurgitation and 22 controls). 3D echocardiograms were performed to assess mitral valve geometry including total diastolic leaflet area measured by a previously validated method. Results: Both groups had normal ejection fraction (60 ± 7 % in AR vs 63 ± 7 % in normals, p=0.17). Only 1 AR patient had significant (more than mild) functional MR. LV volume by 3D echocardiography was significantly larger in the AR group (LV end-diastolic volume index: 80 ± 23 cm3/m2 vs 49 ± 12 cm3/m2, p<0.01). The mitral valve leaflet area indexed for body surface area was significantly increased in the AR group (8.9 ± 1.7 cm2/m2 vs 7.4 ± 1.2 cm2/m2, p<0.01). Patients with AR also had increased mitral leaflet thickness (2.3 ± 0.3 mm vs 2.0 ± 0.3 mm, p<0.01) regardless of AR jet impact on the valve. Mitral valve leaflet area significantly correlated with LV end-diastolic LV volume (p<0.01). Conclusion: Mitral valve leaflet area and thickness are significantly increased in patients with chronic AR and preserved ejection fraction. Area enlargement is proportional to LV volume, and can potentially explain why functional MR is uncommon in this population. Understanding the mechanisms underlying this adaptation could lead to new therapeutic interventions for functional MR.

Correlates of Tricuspid Regurgitation as Determined by 3D Echocardiography: Pulmonary Arterial Pressure, Ventricle Geometry, Annular Dilatation, and Papillary Muscle Displacement

While it is understood that annular dilatation contributes to tricuspid regurgitation (TR), other factors are less clear. The geometry of the right ventricle (RV) and left ventricle (LV) may alter tricuspid annulus size and papillary muscle (PM) positions leading to TR. Three-dimensional echocardiographic images were obtained at Emory University Hospital using a GE Vivid 7 ultrasound system. End-diastolic area was used to classify ventricle geometry: control (n=21), isolated RV dilatation (n=17), isolated LV dilatation (n=13), and both RV and LV dilatation (n=13). GE EchoPAC was used to measure annulus area and position of the PM tips. Patients with RV dilatation had significant (P≤ 0.05) displacement of all PMs apically and the septal PM and posterior PM away from the center of the RV toward the LV. Patients with LV dilatation had significant (P≤0.05) apical displacement of the anterior PM. Pulmonary arterial pressure (r=0.66), annulus area (r=0.51), apical displacement of the anterior PM (r=0.26), posterior PM (r=0.49), and septal PM (r=0.40), lateral displacement of the septal PM (r=0.37) and posterior PM (r=0.40), and tenting area and height (r=0.54, 0.49), were significantly (P≤0.05) correlated to the grade of TR. Ventricle classification (r=0.46) and RV end-diastolic area (r=0.48) also were correlated with the grade of TR. A regression analysis found ventricle classification (P=0.001), pulmonary arterial pressure (P≤0.001) annulus area (P=0.027), and apical displacement of the anterior PM (P=0.061) to be associated with the grade of TR. Alterations in ventricular geometry can lead to TR by altering both tricuspid annulus size and PM position. Understanding these geometric interactions with the aim of correcting pathological alterations of the tricuspid valve apparatus may lead to more robust repairs.

In Vitro Characterization of the Mechanisms Responsible for Functional Tricuspid Regurgitation

Functional tricuspid regurgitation (TR) is increasingly recognized as a source of morbidity. Current repair strategies focus on annular remodeling because annular dilatation is common in patients with TR. Although papillary muscle (PM) displacement is recognized in functional mitral regurgitation, its role in TR is less well characterized. The objective of this in vitro study was to further clarify the mechanisms by which TR occurs as an effect of annular dilatation and PM displacement. Porcine tricuspid valves (n=16) were studied in an in vitro right heart simulator. The valve dynamics were quantified with isolated annular dilatation starting with a normal annular size (6 cm(2)) and incrementally dilated up to 100%, isolated PM displacement, and a combination of the 2. All valves lost competence at 40% dilatation, resulting in a TR of 7.9 ± 3.4 mL (P ≤ 0.05) compared with baseline and central residual leaflet length of 0.5 ± 0.2 cm. Multidirectional displacement of the anterior and posterior/septal PMs and all PMs significantly (P ≤ 0.05) increased TR, with normal annular area. Malcoaptation was observed where the 3 leaflets joined with all significant levels of TR. The anterior leaflet had the greatest percent change in residual leaflet length, whereas PM displacement caused a reduction in residual leaflet length for the septal leaflet for all conditions. This study shows that although annular dilatation alone leads to TR, isolated PM displacement can also cause TR; annular remodeling strategies should be tailored in the setting of severe PM displacement.

Ischemic mitral regurgitation

Secondary or 'functional' mitral regurgitation (MR) is often due to ischemic heart disease that results in disordered left ventricle and mitral valve geometry. In patients with coronary disease, concomitant MR results in worse morbidity and mortality. Coronary artery disease may result in annular dilation due to left ventricle cavity dilation, excessive leaflet motion, impaired leaflet motion due to leaflet tethering and papillary muscle displacement, and/or decreased mitral valve closing forces due to systolic dysfunction. Although transthoracic echocardiography is the first step in the diagnosis of ischemic MR, transesophageal and three-dimensional echocardiography are often useful adjuncts to better understand the mechanism(s) of disease and planning repair. Furthermore, noninvasive evaluation of ischemia and viability may provide important prognostic information. Medical therapy for ischemic MR is directed at the underlying ischemic substrate and concomitant systolic dysfunction, and consists of β-blockers and vasodilators. Percutaneous strategies for repair are currently under investigation, and have shown promising results. Surgical repair is favored over replacement, and is generally recommended for patients with moderate or severe MR undergoing coronary artery bypass. Unfortunately, long-term freedom from MR is elusive even with surgical repair, and trials are currently underway to determine the best approach to treatment in patients with moderate disease.

The Mitral Valve in Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) has evoked both fascination and controversy since its first modern description >50 years ago.1 Originally described as “functional aortic subvalvar stenosis” by Brock, the majority of articles about HCM in the ensuing first decade emanated from observations made in the operating room or in the cardiac catheterization laboratory.1 The actual cause of left ventricular outflow tract (LVOT) obstruction in patients with this condition had not yet been clarified. Ironically, the mechanisms of LVOT obstruction in HCM were only elucidated several years after surgery was first performed in these patients. In fact, an early report by Morrow described the septal myotomy procedure as surgical treatment for HCM and proposed that the myotomy interfered with the sphincter-like muscular contraction ring in the LVOT.1 Article see p 40 Noninvasive cardiovascular imaging studies have greatly advanced our knowledge about HCM.2 Hypertrophic cardiomyopathy is now felt to have tremendous genetic,3 clinical, morphological, and hemodynamic heterogeneity.1 Nevertheless, the presence of LVOT obstruction in patients with HCM has continued to inspire interest. The often contentious debates surrounding LVOT obstruction have centered on its very existence, its causes, its clinical impact and prognosis, and its optimal management.1 These issues have inextricably included the mitral valve, which has long been felt to play a pivotal role in the pathophysiology of LVOT obstruction in patients with HCM. In the present issue of Circulation , Maron et al use cardiovascular magnetic resonance (CMR) imaging to characterize mitral valve leaflets in patients with HCM.4 This study assessed the lengths of the anterior mitral leaflet (AML) and posterior mitral leaflet in 172 consecutive patients with HCM. Their findings were compared with 172 normal control subjects matched for age, sex, and body surface area. In addition, the study included a small cohort of …

Comparative Effects of Two Oral Appliances on Upper Airway Structure in Obstructive Sleep Apnea

Oral appliances are increasingly being used for treatment of obstructive sleep apnea (OSA). Mandibular advancement splint (MAS) mechanically protrudes the mandible, while the tongue stabilizing device (TSD) protrudes and holds the tongue using suction. Although both appliances can significantly improve or ameliorate OSA, their comparative effects on upper airway structure have not been investigated. Cohort study. Sleep Investigation Unit. 39 patients undergoing oral appliance treatment for OSA. OSA patients underwent magnetic resonance imaging (MRI) of the upper airway during wakefulness at baseline and with MAS and TSD in randomized order. Treatment efficacy was determined by polysomnography in a subset of 18 patients. Upper airway lumen and surrounding soft tissue structures were segmented using image analysis software. Upper airway dimensions and soft tissue centroid movements were determined. Both appliances altered upper airway geometry, associated with movement of the parapharyngeal fat pads away from the airway. TSD increased velopharyngeal lateral diameter to a greater extent (+0.35 ± 0.07 vs. +0.18 ± 0.05 cm; P<0.001) and also increased antero-posterior diameter with anterior displacement of the tongue (0.68 ± 0.04 cm; P<0.001) and soft palate (0.12 ± 0.03 cm; P<0.001). MAS resulted in significant anterior displacement of the tongue base muscles (0.35 ± 0.04 cm). TSD responders (AHI reduction ≥50%) increased velopharyngeal volume more than non-responders (+2.65 ± 0.9 vs. -0.44 ± 0.8 cm(3); P < 0.05). Airway structures did not differ between MAS responders and non-responders. These results indicate that the patterns and magnitude of changes in upper airway structure differ between appliances. Further studies are warranted to evaluate the clinical relevance of these changes, and whether they can be used to predict treatment outcome.

Mitral-Valve Surgery in the Elderly: Comparative Results of Mitral Repair and Replacement

Evaluation of: Chikwe J, Goldstone AB, Passage J et al.: A propensity score-adjusted retrospective comparison of early- and mid-term results of mitral-valve repair versus replacement in octogenarians. Eur. Heart J. 32(5), 618–626 (2011). Mitral regurgitation (MR) is common in the elderly, increasing in prevalence with age. Common causes of MR include: degenerative disease of the valve and subvalvular apparatus; ischemic MR due to annular dilatation, papillary muscle displacement and left ventricular remodeling; rheumatic mitral valve disease and infectious endocarditis. The optimal treatment of severe mitral insufficiency in the elderly remains unknown. Mitral-valve repair or replacement have historically been considered high risk in older patients and, for this reason, many elderly patients are not offered surgery. Yet with recent advances in surgical techniques and outcomes, mitral-valve surgery is being increasingly utilized in elderly patients. A recent study by Chikwe et al. in the European Heart Journal examines overall and comparative outcomes of mitral-valve repair and mitral-valve replacement in an elderly cohort. This study finds that mitral-valve repair confers a survival benefit relative to mitral-valve replacement in octogenarians, particularly in patients undergoing surgery for degenerative disease.

Effect of vertical transposition of the medial rectus muscle on primary position alignment in infantile esotropia with A- or V-pattern strabismus

To determine the effect of vertical displacement of muscle insertions on the surgical dose-response relationship in patients undergoing bilateral medial rectus recessions. Retrospective chart review of patients undergoing bilateral medial rectus recessions for correction of congenital esotropia with or without vertical displacement for A or V patterns. Patients were clustered into A pattern, V pattern, and "simple" (no pattern) groups. Strabismus angle at distance and near before and after surgery was recorded. Surgical dose-response relationships (in prism diopters/mm) were determined at the 6-month follow-up visit and compared. A total of 55 patients (28 male and 27 female patients; mean age, 6.9 years; range, 2-17 years) were included. Of these, 28 had either A pattern (18) or V pattern (10), and 27 were in the simple group. Mean preoperative angle of deviation was 34Δ at distance and 40Δ at near. The surgical dose-response relationship was significantly greater (at both distance and near) in the A pattern group (2.43Δ/mm, distance [p=0.005]; 2.76Δ/mm, near [p=0.04]) than in the simple group (1.56Δ/mm, distance; 2.03Δ/mm, near). The surgical response in the V pattern group (1.96Δ/mm, distance [p=0.34]; 2.03Δ/mm, near [p=0.94]) was not significantly different from the simple group. Upward displacement of the medial rectus muscles increased the surgical dose/response relationship in patients with A-pattern esotropia. A similar effect was not observed with downward displacement in patients with V-pattern strabismus. Surgeons should be aware of this enhanced response when planning surgery for A-pattern esotropia.

The Role of Mecahnical Dyssynchrony on Functional Mitral Regurgitation in Patients with Dilated Cardiomyopathy

REFER TO THE PAGE 69-75 Functional mitral regurgitation (FMR) occurs despite a structurally normal mitral valve (MV) as a consequence of global or regional left ventricular (LV) dysfunction. It is a common complication and predicts poor outcome in patients with dilated cardiomyopathy.1) The pathophysiology of FMR is closely related to several factors such as systolic MV tenting as a result of LV geometric changes, a reduced closing force, dilatation of the mitral annulus and LV dyssynchrony.2) Of these, mechanical dyssynchrony of the LV may play a potential role in determining the degree of FMR as a result of uncoordinated contraction of the papillary muscles and reduced closing force.3) This hypothesis support the ability of cardiac resynchronization therapy (CRT) to decrease the severity of FMR due to improved coordinated timing of the papillary muscles and reverse remodeling of the LV, which tends to recur when CRT is withdrawn.4) However, a mechanistic study has suggested that mechanical dyssynchrony is less important than LV remodeling and MV tethering.5) The role of mechanical dissynchrony in the pathophysiology of FMR remains unclear. In this issue of the journal, Choi et al.6) reported the role of mechanical dyssynchrony on FMR in patients with dilated cardiomyopathy using real time 3D echocardiography. The dyssynchrony index was significant higher in the patients with FMR than that in the patients with non-FMR and the dyssynchrony index was well correlated with the effective regurgitation orifice area (ERO) of the FMR. However, the dyssynchrony index was not a significant determinant of ERO on the multivariate model. Displacement of the anterior papillary muscle and consequent MV tenting remained the strongest determinants of the degree of ERO. These findings suggested that the distorted geometric change of the LV with MV tenting is a necessary condition for the development of FMR, whereas mechanical dyssynchrony could have a minor role. There are several limitations of the study by Choi et al.6) First, the study had a relatively small sample size (n = 53), a mild degree (ERO = 0.17 ± 0.10 cm2) of FMR and a small percentage of left bundle branch block (18%) as compared to the previous studies. These factors might affect the results between mechanical dyssynchrony and the degree of FMR. Second, they measured the geometric parameters using 3D echocardiography and the multi-planar reconstruction (MPR) mode of a 3D image analysis program. This method is ideal to measure the mitral apparatus at a specific angle compared with that of 2D echocardiography. But the reproducibility is modest (the intra-observer correlation coefficients were 0.69-0.73 for the measurement of the mitral apparatus). This might also have affected the results. Despite the limitations, Choi et al's study is the first trial to estimate the distances of both papillary muscles using MPR by 3D echocardiography. This method is promising to evaluate the mechanism of FMRs if the technical issues related to the image resolution of 3D echocardiography and the learning curve can be resolved.

Development of a Rubber Artificial Muscle with Inner Diameter Sensor and Its Control

Due to the ageing and the decreasing birth rate in Japanese society, an important problem of providing nursing care for the elderly has occurred. Therefore, it is strongly desired to develop a wearable actuator to use in nursing care or rehabilitation. The purpose of this study is to develop a high-power flexible actuator which can be used in supporting a bathing. We proposed and tested a rubber artificial muscle with the inner diameter sensor which consisted of two photo reflectors. This inner diameter sensor can be expected to estimate the axial-direction displacement of the rubber artificial muscle. The position control was carried out using the actuator with the built-in inner diameter sensor and the quasi-servo valve. As a result, the axial-direction displacement of the actuator could be estimated well by the tested inner diameter sensor, and a good position control performance was obtained even when a load mass of 29.4N existed. As an application of the tested actuator, the large-scale bending actuator was also proposed and tested. As a result, its maximum bending angle is about 90 degrees. The bending angle of the actuator could be also estimated well using the tested inner diameter sensor.

Ischaemic mitral regurgitation: pathophysiology, outcomes and the conundrum of treatment

Ischaemic mitral regurgitation is a frequent complication of left ventricular global or regional pathological remodelling due to chronic coronary artery disease. It is not a valve disease but represents the valvular consequences of increased tethering forces (papillary muscles displacement leading to a more apical position of the leaflets and their coaptation point) and reduced closing forces (reduced contractility, dyssynchrony of the papillary muscles, intra-left ventricular dyssynchrony). Although mitral regurgitation has an unloading effect and reduces impedance, the volume overload begets further left ventricular dilatation, increases ventricular wall stress leading to worsened performance. Ischaemic mitral regurgitation is characteristically dynamic: its severity may vary with haemodynamic conditions. Both the severity of ischaemic mitral regurgitation and its dynamic component worsen prognosis. There are numerous possible treatment modalities, but the management of the individual patient remains difficult. Medical therapy is mandatory; revascularization procedures are frequently not sufficient to reduce mitral regurgitation; the role of combined surgical therapy by mitral valve repair is not yet defined in the absence of large randomized trial. Some patients are good candidates for cardiac resynchronization therapy that may reduce the amount of regurgitation. New therapeutic targets are under investigation.

A Multistable Linear Actuation Mechanism Based on Artificial Muscles

In this paper, we report on a multistable linear actuation mechanism articulated with electroactive polymer actuators, widely known as artificial muscles. These actuators, which can operate both in wet and dry media under as small as 1.0 V potential difference, are fundamentally cantilever beams made of two electroactive polymer layers (polypyrrole) and a passive polyvinylidene fluoride substrate in between the electroactive layers. The mechanism considered is kinematically analogous to a four-bar mechanism with revolute-prismatic-revolute-prismatic pairs, converting the bending displacement of a polymer actuator into a rectilinear movement of an output point. The topology of the mechanism resembles that of bistable mechanisms operating under the buckling effect. However, the mechanism proposed in this paper can have many stable positions depending on the input voltage. After demonstrating the feasibility of the actuation concept using kinematic and finite element analyses of the mechanism, experiments were conducted on a real mechanism articulated with a multiple number (2, 4, or 8) of electroactive polymer actuators, which had dimensions of 12×2×0.17 mm3. The numerical and experimental results demonstrate that the angular displacement of the artificial muscles is accurately transformed into a rectilinear motion by the proposed mechanism. The higher the input voltage, the larger the rectilinear displacement. This study suggests that this multistable linear actuation mechanism can be used as a programmable switch and/or a pump in microelectromechanical systems (MEMS) by adjusting the input voltage and scaling down the mechanism further.

Polymer Injection Therapy to Reverse Remodel the Papillary Muscles

Background— Ischemic mitral regurgitation (MR) results from displacement of the papillary muscles caused by ischemic ventricular distortion. Progressive left ventricular (LV) remodeling has challenged therapy. Our hypothesis is that repositioning of the papillary muscles can be achieved by injection of polyvinyl-alcohol (PVA) hydrogel polymer into the myocardium in chronic MR despite advanced LV remodeling. Methods and Results— Ten sheep underwent ligation of the circumflex branches to produce chronic ischemic MR over 8 weeks. PVA was injected into the myocardium underlying the infarcted papillary muscle. Two-dimensional and 3D echocardiograms and hemodynamic data were obtained before infarct (baseline), before PVA (chronic MR), and after PVA. PVA injection significantly decreased MR from moderate to severe to trace (MR vena contracta, 5.8±1.2 to1.8±1.3 mm; chronic MR to post-PVA stage; P =0.0003). This was associated with a decrease in infarcted papillary muscle–to–mitral annulus tethering distance (30.3±5.7 to 25.9±4.6 mm, P =0.02), tenting volume (1.8±0.7 to 1.4±0.5 mL, P =0.01), and leaflet closure area (8.8±1.3 cm 2 to 7.6±1.3 cm 2 , P =0.004) from chronic MR to post-PVA stages. PVA was not associated with significant decreases in LV ejection fraction (41±3% versus 40±3%, P =NS), end-systolic elastance, τ (82±36 ms to 72±26, P =NS), or LV stiffness coefficient (0.05±0.04 to 0.03±0.01). Conclusions— PVA hydrogel injections improve coaptation and reduce remodeling in chronic MR without impairing LV systolic and diastolic function. This new approach offers a potential alternative for relieving tethering and ischemic MR by correcting papillary muscle position.

Intermuscular force transmission between human plantarflexor muscles in vivo

The exact mechanical function of synergist muscles within a human limb in vivo is not well described. Recent studies indicate the existence of a mechanical interaction between muscle actuators that may have functional significance and further play a role for injury mechanisms. The purpose of the present study was to investigate if intermuscular force transmission occurs within and between human plantarflexor muscles in vivo. Seven subjects performed four types of either active contractile tasks or passive joint manipulations: passive knee extension, voluntary isometric plantarflexion, voluntary isometric hallux flexion, passive hallux extension, and selective percutaneous stimulation of the gastrocnemius medialis (MG). In each experiment plantar- and hallux flexion force and corresponding EMG activity were sampled. During all tasks ultrasonography was applied at proximal and distal sites to assess task-induced tissue displacement (which is assumed to represent loading) for the plantarflexor muscles [MG, soleus (SOL), and flexor hallucis longus (FHL)]. Selective MG stimulation and passive knee extension resulted in displacement of both the MG and SOL muscles. Minimal displacement of the triceps surae muscles was seen during passive hallux extension. Large interindividual differences with respect to deep plantarflexor activation during voluntary contractions were observed. The present results suggest that force may be transmitted between the triceps surae muscles in vivo, while only limited evidence was provided for the occurrence of force transfer between the triceps surae and the deeper-lying FHL.

Dynamic RING + STRING for ischemic mitral regurgitation: Papillary muscle repositioning and modification of the septal–lateral diameter in the loaded beating heart under echocardiographic guidance

Ischemic mitral regurgitation (MR) involves annular dilatation in all cases. Some patients, however, also exhibit severe leaflet tethering due to papillary muscle displacement. Leaflet tethering is the strongest predictor of repair failure in up to 30% of patients treated by undersized ring annuloplasty (RING). These failures emphasize the need for subvalvular strategies. Several adjunctive techniques have been proposed, but only 3 techniques have received clinical acceptance. Borger and associates reported initial results of cutting second-order chordae. The impact of this technique on left ventricular systolic function, however, has been discussed controversially. Leaflet extension has been performed successfully in a case series by de Varennes and associates. We have reported a technique (RING þ STRING) that allows repositioning of the posterior papillary muscle under transesophageal echocardiographic (TEE) guidance. Even though midterm results with this technique have been encouraging, we have been looking for further improvement. Reduction of the septal–lateral diameter has been the key to reduction of ischemic MR in the experimental setting. This observation has been the basis for the use of aggressively undersized complete rings used clinically. Recently, however, Magne and colleagues documented functional mitral stenosis with associated pulmonary hypertension and reduced functional capacity as result of aggressive undersizing, the equivalent of patient–prosthesis mismatch in mitral valve repair.

A New Transconjunctival Muscle Reinsertion Technique for Minimally Invasive Strabismus Surgery

To describe a novel, minimally invasive strabismus surgery (MISS) technique for horizontal rectus muscle recessions, plications, and advancements. Subjects for this prospective study were the first 20 consecutive patients who underwent unilateral horizontal rectus muscle surgery with a transconjunctival suturing (TRASU) technique for primary muscle displacements of 4.5 mm or greater or for repeat muscle displacements of 3.0 mm or greater. The TRASU technique was associated with no increase in complication rate and was accomplished through a conjunctival approach with an incision that was smaller by 31% ± 11% compared to incisions for previously described MISS approaches. Of the 19 patients (20 eyes) returning for follow-up, 11 (55%) had minimal redness as the only grossly visible sign of surgery on the first postoperative day. By 6 months postoperatively, visual acuity and refractive error were not significantly different from preoperative values (P > .10 for each). The TRASU technique is safe and can be accomplished through a conjunctival incision that averages two-thirds the size of incisions for previously reported MISS techniques.

Effect of lower limb muscle fatigue on anticipatory postural adjustments associated with bilateral-forward reach in the unipedal dominant and non-dominant stance

Voluntary arm movements are preceded by dynamical and electromyographical (EMG) phenomena in "postural segments" (i.e. body segments not directly involved in the voluntary movement) called "anticipatory postural adjustments" (APA). The present study examined how the central nervous system organizes APA under fatigued state of postural musculature elicited by series of high-level isometric contractions (HIC), i.e. corresponding to 60% of maximal voluntary contraction. Subjects (N=14) purposely performed series of bilateral-forward reach task (BFR) under unipodal stance (dominant and non-dominant) before ("no fatigue" condition, NF) and after ("fatigue" condition, F) a procedure designed to obtain major fatigue in hamstrings. Centre-of-gravity acceleration, centre-of-pressure displacement, and electrical activity of trunk and leg muscles were recorded and quantified within a time-window typical of APA. Results showed that there was no significant effect of fatigue on the level of muscle excitation and APA onset in any of the postural muscles recorded. Similarly, no change in APA onset could be detected from the biomechanical traces. In contrast, results showed that the amplitude of anticipatory centre-of-pressure displacement and centre-of-gravity acceleration reached lower value in F than in NF. Similar results were obtained whether dominant or non-dominant leg was considered. The changes in biomechanical APA features could not be ascribed to a different focal movement performance (maximal BFR velocity and acceleration) between F and NF. These results suggest that, when fatigue is induced by HIC, the capacity of the central nervous system to adapt APA programming to the fatigued state of the postural muscle system might be altered.