Prone position: Does it help with acute respiratory distress syndrome (ARDS) requiring extracorporeal membrane oxygenation (ECMO)?

Introduction: Lung protective ventilation therapy with low tidal volume-high PEEP is the standard treatment for the patients with acute respiratory distress syndrome (ARDS). Oscillators are occasionally used for salvage ventilation in cases where poor compliance restricts the use of traditional ventilation with ARDS. In addition to ventilator therapy, prone positioning has been used to improve oxygenation. We presented a challenging case of ARDS, which failed medical management extracorporeal membrane oxygenation (ECMO) support and oscillatory ventilation. Prone positioning was initiated which improved oxygenation, respiratory compliance and posterior atelectasis. Case presentation: A 41-year-old morbid obese female developed ARDS due to influenza pneumonia. The patient remained hypoxic despite optimum medical and ventilator management and required veno-venous extracorporeal membrane oxygenation (VV ECMO). CT scan of the chest showed ARDS with posterior consolidation. Despite ARDSnet ventilation support, antiviral therapy and ECMO support, there was no clinical improvement. High frequency oscillatory ventilation was initiated on ECMO day #13, which resulted in no respiratory improvement over the next 5 days. On ECMO day #18, the patient was placed on a Rotaprone? bed Therapy, utilizing a proning strategy of 16 hours a day. The clinical improvements observed were resolving of the consolidation on CXR, improvements in ventilatory parameters and decreased oxygen requirements. The patient was successfully weaned off ECMO on POD#25 (8 days post prone bed). Conclusions: Prone position improved oxygen saturation and pulmonary compliance in severe ARDS requiring ECMO and it might facilitate early weaning

Light Stimulation of Sensory Hair Cells

Hair cells are the mechanosensory detectors that underlie our senses of audition and balance. Their mechanosensitivity arises from direct gating of force-sensitive ion channels by the tension in tip links located at the tops of the stereocilia. The study of hair cells and their mechanically gated channels has heretofore required physical displacement of a hair bundle to open its mechanotransduction channels. The work presented here describes a novel method of hair-bundle stimulation: irradiation with light. The original aim of this study was to elucidate the role of Ca2+ in fast adaptation, a process thought to underlie a hair bundle’s ability to amplify stimuli. I aimed to do this by generating intracellular surges in Ca2+ concentration without altering the state of the mechanotransduction channel or its associated elements. This procedure would permit me to study the mechanical correlates of fast adaptation independently from those associated with transduction. I used a light-sensitive, Ca2+-loaded cage compound to release Ca2+ in hair cells by ultraviolet irradiation. To my surprise, irradiation both in the presence and absence of the caged compound caused rapid motion of hair bundles towards their tall edge, a motion typically associated with excitatory stimulation. Tight-seal, whole-cell recording disclosed that the motion was associated with rapid opening of mechanotransduction channels. Both the light-evoked movement and the channel gating disappeared when tip links were ruptured, indicating that the mechanotransduction apparatus is involved in a hair cell’s response to light. Blockage of the mechanotransduction channels in their open state with gentamicin abolished the light-evoked electrical response but incompletely reduced the light-evoked displacement, suggesting that channel gating is only partially responsible for light-evoked hair-bundle motion. I sought to identify the cellular components underlying light-evoked hair-bundle motion. Using an illumination system containing a digital micromirror device, I localized the absorptive element responsible for hair-bundle motion to the region directly below the bundle. The absorbers appeared to be mitochondrial chromophores that release the absorbed energy as heat. In experiments combining ultraviolet and infrared irradiation, I found that heat pulses of 0.5 K are sufficient to elicit hair-bundle motion. These heat pulses may alter the mechanical properties of tip links, leading to hair-bundle motion and mechanotransduction-channel gating. Thus the hair bundle confers thermal sensitivity upon a hair cell. The ability to stimulate hair cells using light will benefit physiological investigations of hair-cell function, and may have a role in non0invasively boosting hair-cell function in patients with hearing loss

Incorporation Of Certification Revocation And Time Concept Into A Trust Model For Information Security System

In large open networks, handling trust and authenticity adequately is an important prerequisite for security policy. Trust issues influence not only the specification of security policies but also the techniques needed to manage and implement security policies for systems. Certification is one of the main components of trust models and is known as a common mechanism for authentic public key distribution. In order to obtain a public key, verifiers need to extract a certificate path from a network of certificates, which is called the public key infrastructure (PKI). There are two classifications of PKI; namely the centralized and decentralized PKIs. In this thesis, attention is paid the decentralized PKIs, such as Maurer’s model. This model is comprised of two parts; the deterministic and probabilistic models. An important limitation in this model is that certification revocation is not considered. Revocation happens in cases, among others, such as the loss of private key. Another limitation of Maurer’s model is that it lacks time consideration, which is important as trust changes over time. In this thesis, a novel trust model is developed, addressing the limitations of other models. Negative values such as revocation of certification have been incorporated, making a complete trust model that includes both positive and negative evidences. Particularly, certification is considered as positive evidence while certification revocation is considered negative. The time concept is then added to the model in order to address the change of trusts status over time. Hence, the complete trust model is able to incorporate certification revocation and time concept into both deterministic and probabilistic parts of a model. Incorporating two new concepts into Maurer’s model increases the generality and expressive power of the model. Novel extension of the trust model enabling it to capture all aspects of public key certification which includes trust, recommendations, confidence values for trust metric and authenticity of public keys, multiple certification paths, certification revocation and the time concept. Experimental results show that after incorporating the new concept, a decrease in confidence value in comparison to Maurer’s model was observed, resulting to a more realistic model

Impulse Control in Finance: Numerical Methods and Viscosity Solutions

The goal of this thesis is to provide efficient and provably convergent numerical methods for solving partial differential equations (PDEs) coming from impulse control problems motivated by finance. Impulses, which are controlled jumps in a stochastic process, are used to model realistic features in financial problems which cannot be captured by ordinary stochastic controls. The dynamic programming equations associated with impulse control problems are Hamilton-Jacobi-Bellman quasi-variational inequalities (HJBQVIs) Other than in certain special cases, the numerical schemes that come from the discretization of HJBQVIs take the form of complicated nonlinear matrix equations also known as Bellman problems. We prove that a policy iteration algorithm can be used to compute their solutions. In order to do so, we employ the theory of weakly chained diagonally dominant (w.c.d.d.) matrices. As a byproduct of our analysis, we obtain some new results regarding a particular family of Markov decision processes which can be thought of as impulse control problems on a discrete state space and the relationship between w.c.d.d. matrices and M-matrices. Since HJBQVIs are nonlocal PDEs, we are unable to directly use the seminal result of Barles and Souganidis (concerning the convergence of monotone, stable, and consistent numerical schemes to the viscosity solution) to prove the convergence of our schemes. We address this issue by extending the work of Barles and Souganidis to nonlocal PDEs in a manner general enough to apply to HJBQVIs. We apply our schemes to compute the solutions of various classical problems from finance concerning optimal control of the exchange rate, optimal consumption with fixed and proportional transaction costs, and guaranteed minimum withdrawal benefits in variable annuities