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In this work, the thermo-acoustic instabilities of a gas turbine model combustor, the so-called SFB606 combustor, are numerically investigated using Large Eddy Simulation (LES) combined with tabulated chemistry and Artificial Thickened Flame (ATF) approach. The main focus is a detailed analysis of the thermo-acoustic cycle and the accompanied equivalence ratio oscillations and their associated convective time delay. In particular, the variations of the thermo-chemical state and flame characteristics over the thermo-acoustic cycle are investigated. For the operating point flame B (Pth = 25kW, Φ = 0.7), the burner exhibits thermo-acoustic instabilities with a dominant frequency of 392 Hz, the acoustic eigenmode of the inner air inlet duct. These oscillations are accompanied by an equivalence ratio oscillation, which exhibits a convective time delay between the injection in the inner swirler and the flame zone. Two LES, one adiabatic and one accounting for heat losses at the walls by prescribing the wall temperatures from experimental data and Conjugated Heat Transfer (CHT) simulations, are conducted. Results with the enthalpy-dependent table are found to predict the time-averaged flow field in terms of velocity, major species, and temperature with higher accuracy than in the adiabatic case. Further, they indicate, that heat losses should be accounted for to correctly predict the flame position. Subsequently, the thermo-chemical state variations over the thermo-acoustic cycle for the enthalpy-dependant case are analyzed in detail and compared with experimental data in terms of phase-conditioned averaged profiles and conditional averages. An overall good prediction is observed, although an overestimation of the oscillation amplitude yields a slight over-prediction of the velocity field in the low-pressure phases. The results provide a detailed quantitative analysis of the thermo-acoustic feedback mechanism of this burner.

Aims: Phrenic nerve palsy (PNP) is still a cause for concern in Cryoballoon ablation (CBA) procedures. New surveillance techniques, such as invasive registration of the compound motor action potential (CMAP), have been thought to prevent the occurrence of PNP. The present study investigates the impact of CMAP surveillance via an alternative and non-invasive ECG-conduction technique during CBA. Methods: PVI with CBA was performed in 166 patients suffering from AF. Diaphragmal contraction was monitored by abdominal hands-on observation in Observation Group I; Observation Group II was treated using additional ECG-conduction, as a means of modified CMAP surveillance method. During the ablation of the right superior and inferior pulmonary veins, the upper extremities lead I was newly adjusted between the inferior sternum and the right chest, thereby recording the maximum CMAP. The CMAP in the above-mentioned ECG leads was continuously observed in a semi-quantitative manner. Results: PNP was observed in 10 (6%) patients in total. In Observation Group I, 6 out of 61 (9.8%) demonstrated PNP. In Observation Group II a significant decrease of PNP could be demonstrated (p

Background: Pulmonary Vein Isolation (PVI) is evolving as an established treatment option in atrial fibrillation (AF). Different fluoroscopy-guided ablation devices exist either on the basis of expandable circumferential and mesh designs with mapping and ablation of pulmonary vein potentials, or of a balloon technology, a “single shot” device with a purely anatomical approach. Systematic comparisons between procedure duration (PD), fluoroscopy time (FT) and clinical outcome in using different ablation tools are lacking in the literature. Methods: In a single center retrospective analysis, 119 PVI procedures were performed between August 2008 and March 2011 in paroxysmal AF (PAF, 59.7%) and persistent AF (persAF, 40.3%) patients with mean age of 59.4±10.3 years and history of AF since 8.1±9.7 months. The PVI procedures were evaluated by comparing PD and FT using I) the High Density Mesh Mapper (HDMM), II) the High Density Mesh Ablator (HDMA), and III) the Arctic Front® Cryoballoon. The primary endpoints were FT and PD, the secondary endpoint was procedural safety and efficacy in short- and longterm follow-up. Results: The procedures performed for 119 patients (63.0 % male) included 42 PVIs with the HDMM (35.3 %), 47 with the HDMA (39.5 %) and 30 with the cryoballoon (25.2 %). Comparing the 30 first procedures in groups of 10 in the HDMM and HDMA group, PD and FT fell in the HDMM group (PD from 257.5 to 220.9 min and FT from 80.5 to 67.3 min, both p < 0.05) as well as in the HDMA group (PD from 182.9 to 147.2 min and FT from 41.02 to 29.1 min, both p < 0.05). In the cryoballoon group, there was a steep learning curve with a steady state after the first 10 procedures (PD and FT decreased significantly from 189.5 to 138.1 min and 36.9 to 27.3 min, p values 0.005 and 0.05 respectively). With respect to recurrence of AF in a 24 months follow up, the HDMM and cryoballoon group showed comparable results with ~72% of patients free of arrhythmias. None of the patients died due to severe complications, or suffered a hemodynamic relevant pericardial effusion and/or stroke. Impairment of the phrenic nerve was observed in three patients. Conclusion: Use of the cryoballoon technology was associated with a steep learning curve and a reduced PD and FT; the long-term outcome was similar compared with the HDMM group. The efficacy and safety of the devices but also PD and FT should be respected as the strongest indicators of the quality of ablation. Further studies with long time follow-ups will show if the time for correct mapping of the PV potentials is a price we should be willing to pay or if we should adopt a “wait-and-see” attitude referring the AF recurrence.