Effects of the transition time between muscle-tendon stretch and shortening on mechanical efficiency

The net mechanical efficiency of positive work (ηpos) has been shown to increase if it is immediately preceded by negative work. This phenomenon is explained by the storage of elastic energy during the negative phase and its release during the subsequent positive phase. If a transition time (T) takes place, the elastic energy is dissipated into heat. The aim of the present study was to investigate the relationship between ηpos and T, and to determine the minimal T required so that ηpos reached its minimal value. Seven healthy male subjects were tested during four series of lowering-raising of the body mass. In the first series (S 0), the negative and positive phases were executed without any transition time. In the three other series, T was varied by a timer (0.12, 0.24 and 0.56s for series S 1, S 2 and S 3, respectively). These exercises were performed on a force platform sensitive to vertical forces to measure the mechanical work and a gas analyser was used to determine the energy expenditure. The results indicated that ηpos was the highest (31.1%) for the series without any transition time (S 0). The efficiencies observed with transition times (S 1, S 2 and S 3) were 27.7, 26.0 and 23.8%, respectively, demonstrating that T plays an important role for mechanical efficiency. The investigation of the relationship between ηpos and T revealed that the minimal T required so that ηpos reached its minimal value is 0.59

Surgical treatment of subaortic stenosis after biventricular repair of double-outlet right ventricle

AbstractOut of 180 patients who underwent biventricular repair of double-outlet right ventricle between 1980 and 1995, 9 (5%) required reoperation because of subaortic stenosis. Two other patients who initially underwent operation elsewhere underwent reoperation at our institution because of subaortic stenosis. The median age at biventricular repair was 4 months. Repair consisted of tunnel construction from the left ventricle to the aorta in nine patients; the remaining two patients received an arterial switch operation with ventricular septal defect closure. Subaortic stenosis developed with time: the mean postoperative left ventricle–to–aorta gradient after repair was 10 ± 19 mm Hg (range, 0 to 50 mm Hg) and became 84 ± 27 mm Hg (range, 40 to 124 mm Hg) in a mean delay of 45 ± 66 months (range, 1 to 213 months). At reoperation, the obstruction was caused by the protrusion of the inferior rim of the ventricular septal defect into the left ventricular outflow tract associated with subaortic hypertrophied muscle and membrane. The 11 patients underwent 15 reoperations. Surgical technique consisted of an extended septoplasty in 6 reoperations. In this technique an incision was made in the septal patch and was extended into the muscle toward the apex until a large opening of the left ventricular outflow pathway was obtained. A new patch was then secured to streamline the left ventricular outflow tract. None of the patients who underwent extended septoplasty had to undergo reoperation. There were no early or late deaths. At 115 ± 85 months after biventricular repair, all patients were in New York Heart Association functional class I or II and the mean postoperative left ventricle–to–aorta gradient was 20 ± 24 mm Hg (range, 0 to 60 mm Hg). We conclude that after biventricular repair of double-outlet right ventricle, the subaortic region is at risk for the development of stenosis. Surgical treatment adapted to the anatomy of the obstruction can offer good early and midterm results. It seems that an aggressive approach by an extended septoplasty avoids multiple reoperations. (J Thorac Cardiovasc Surg 1996;112:1570-80

Aortic arch reconstruction with pulmonary autograft patch aortoplasty

AbstractObjective: The optimal technique for aortic arch reconstruction through median sternotomy is still under debate. We have introduced the technique of pulmonary autograft patch aortoplasty as a reliable alternative. Methods: The outcomes of 51 infants who underwent neonatal repair of interrupted aortic arch (n = 28) or coarctation associated with ventricular septal defect (n = 23) since 1992 were analyzed. The patients were reviewed in three groups according to the aortic arch reconstruction technique: group I underwent direct anastomosis (n = 23), group II underwent homograft or pericardial patch aortoplasty (n = 8), and group III underwent pulmonary autograft patch aortoplasty (n = 20). The pulmonary autograft patch consisted in the anterior wall of the main pulmonary artery, between the supracommissural level and the divided ductus arteriosus. The created defect was replaced with fresh autologous pericardium. Results: All patients except 1 were discharged without significant residual gradient at the level of the aortic arch. At a median delay of 7 months (range 2-51 months), 11 patients (22%) had recurrence of arch obstruction and underwent balloon angioplasty (n = 8) or surgical correction (n = 3). One patient who had undergone direct anastomosis required reoperation for bronchial compression. At a median follow-up of 29 months, the actuarial freedoms from recurrent arch obstruction were 81% for direct anastomosis, 28% for homograft or pericardial patch aortoplasty, and 100% for pulmonary autograft aortoplasty (P =.03 for group III vs group I and P <.0001 for group III vs group II). Conclusions: The aortic arch repair associated with pulmonary autograft patch augmentation resulted in superior midterm outcomes and therefore constitutes a reliable alternative to the direct anastomosis technique. It allowed complete relief of anatomic afterload and diminished the anastomotic tension, thus reducing the risk of restenosis and tracheobronchial compression. We observed a significantly higher rate of recurrence after patch aortoplasty with other materials.J Thorac Cardiovasc Surg 2002;123:443-5

Preoperative and postoperative evaluation of airways compression in pediatric patients with 3-dimensional multislice computed tomographic scanning: Effect on surgical management

ObjectivesSurgical management of airway compression of vascular origin requires an accurate analysis of anatomy and various mechanisms of compression. This study assessed the usefulness of 3-dimensional computed tomographic scanning in the preoperative and postoperative evaluation of airways compression in a pediatric population.MethodsThirty-seven consecutive patients (median age, 4 months) were examined with multislice 3-dimensional computed tomographic scanning: 18 patients before surgical treatment of anomalies of vascular rings, 2 patients because of respiratory symptoms after repair of esophageal atresia, and 17 patients because of persisting respiratory symptoms or prolonged mechanical ventilation after cardiac surgery for congenital heart disease.ResultsThe procedure was successful, with high-quality diagnostic imaging obtained in all cases without any complications. The anatomy and relationship between the vascular arches and airways was analyzed in all referred patients with vascular arch anomalies confirmed on the basis of the surgical findings, and this helped the surgeon to plan the procedure and choose the best approach. After cardiac surgery, the airway and vascular structures involved and the mechanism of compression were specified in all but one case, and the 3-dimensional computed tomographic scan serves as an important tool for deciding whether to perform reoperation on patients requiring prolonged mechanical ventilation.ConclusionThree-dimensional computed tomographic scanning is a safe, fast, and noninvasive method useful for accurately analyzing the mechanisms of airway compression of vascular origin and thus possible improving the surgical management of pediatric patients

Left-sided lesions after anatomic repair of transposition of the great arteries, ventricular septal defect, and coarctation: Surgical factors

AbstractObjectiveThis study was undertaken to identify potential anatomic and surgical factors creating left-sided lesions, namely recoarctation of the aorta and neoaortic regurgitation, after anatomic repair of transposition of the great arteries with ventricular septal defect and aortic coarctation.MethodsFrom 1983 to September 2002, 109 survivors out of 120 patients were studied. Two-stage repair was performed in 42 patients (group A), and single-stage repair was performed in 67 (groups B and C). Before repair, the diameters of the ascending aorta and main pulmonary artery were measured. In the patients with single-stage repair, coarctation was repaired by extended end-to-end anastomosis in 35 patients (group B) and by pulmonary homograft patch augmentation in 32 patients (group C). The ventricular septal defect was closed through the pulmonary artery in 70 patients and through the right ventricle or atrium in 39 patients. The neoaorto-aortic discrepancy was treated by V-shaped resection of the posterior sinus of Valsalva in 7 cases, pulmonary homograft patch in 32 cases, and anterior splitting of the ascending aorta in all cases. Before discharge from the hospital, neoaortic root and ascending aorta diameters and aortic regurgitation grade were recorded. Neoaortic regurgitation progression and reintervention were the end points of follow-up (97.2 ± 61.2 months).ResultsEarly and late survivals were significantly better in group C (P < .001). Risk factors for neoaortic regurgitation at discharge by univariate analysis were single-stage repair (P < .05) and ventricular septal defect closure through the pulmonary artery (P = .0076). On multivariate analysis, the latter was the only risk factor for neoaortic regurgitation at discharge and at last follow-up. Multivariate analysis showed that higher neoaortic root/ascending aorta ratio and ventricular septal defect closure through the pulmonary artery were risk factors for neoaortic regurgitation evolution at last follow-up. There were 29 reinterventions, 19 for recoarctation of the aorta and 10 for neoaortic regurgitation with or without aortic root dilatation. Group B (P < .05), high neoaortic root/ascending aorta ratio (P < .01), and progressive neoaortic regurgitation (P < .05) were risk factors for recoarctation of the aorta. Group A was a risk factor for aortic valve replacement at 10 years (P < .05).ConclusionNeonatal single-stage repair with pulmonary homograft aortic augmentation remains the optimal approach to transposition of the great arteries with ventricular septal defect and aortic coarctation. It provides better early and late survivals and freedoms from left-sided lesions. Avoidance of late recoarctation of the aorta and progressive neoaortic regurgitation requires meticulous closure of the ventricular septal defect and evenly sized reconstruction of the aorta from root to distal arch

Machine detector interface for the e+e−e^+e^- future circular collider

The international Future Circular Collider (FCC) study aims at a design of $pp$, $e^+e^-$, $ep$ colliders to be built in a new 100 km tunnel in the Geneva region. The $e^+e^-$ collider (FCC-ee) has a centre of mass energy range between 90 (Z-pole) and 375 GeV (tt_bar). To reach such unprecedented energies and luminosities, the design of the interaction region is crucial. The crab-waist collision scheme has been chosen for the design and it will be compatible with all beam energies. In this paper we will describe the machine detector interface layout including the solenoid compensation scheme. We will describe how this layout fulfills all the requirements set by the parameters table and by the physical constraints. We will summarize the studies of the impact of the synchrotron radiation, the analysis of trapped modes and of the backgrounds induced by single beam and luminosity effects giving an estimate of the losses in the interaction region and in the detector.Comment: 6 pages, 7 figures, 62th ICFA ABDW on High Luminosity Circular $e^+e^-$ Colliders, eeFACT2018, Hong Kong, Chin

A simple method for measurement of maximal downstroke power on friction-loaded cycle ergometer

International audienceThe aim of this study was to propose and validate a post-hoc correction method to obtain maximal power values taking into account inertia of the flywheel during sprints on friction-loaded cycle ergometers. This correction method was obtained from a basic postulate of linear deceleration-time evolution during the initial phase (until maximal power) of a sprint and included simple parameters as flywheel inertia, maximal velocity, time to reach maximal velocity and friction force. The validity of this model was tested by comparing measured and calculated maximal power values for 19 sprint bouts performed by five subjects against 0.6-1 N kg(-1) friction loads. Non-significant differences between measured and calculated maximal power (1151+/-169 vs. 1148+/-170 W) and a mean error index of 1.31+/-1.20% (ranging from 0.09% to 4.20%) showed the validity of this method. Furthermore, the differences between measured maximal power and power neglecting inertia (20.4+/-7.6%, ranging from 9.5% to 33.2%) emphasized the usefulness of power correcting in studies about anaerobic power which do not include inertia, and also the interest of this simple post-hoc method