Obstructive sleep apnoea (OSA) - a silent killer in anaesthesia?

Sleep-disordered breathing (SDB) encompasses a wide range of disorders that afflict both adults and children. These disorders are often unrecognised preoperatively and the pathophysiological consequences may impact severely on the patient in the peri-operative period

Hypertension and Anaesthesia

The difficulty that anaesthetists face is that they often, when seeing a patient pre-operatively, do not have the benefit of seeing the patient’s “normal  average” blood pressure taken at different times over a period of weeks. The decision to cancel surgery based on the blood pressure found at the pre-operative visit must, therefore, take into account the urgency of the surgery, as well as the presence of end organ damage from chronic  hypertension. A detailed history and examination should be performed looking for evidence of coronary artery disease, cerebrovascular disease and renal dysfunction

Hypertension and Anaesthesia

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Acute subarachnoid haemorrhage and the mysterious electrocardiogram

 Subarachnoid haemorrhage (SAH) is a devastating neurological insult, and is increasingly understood as a multi-system condition initiated in the central nervous system. Perioperative investigation of patients presenting for aneurysm surgery often includes a routine electrocardiogram (ECG) which frequently reveals an abnormality. We describe a patient who presented with SAH and who was found to have significant Q waves on the ECG suggestive of a trans-mural myocardial infarction, despite a negative medical history for such an event. We brie­ y highlight the issues faced by the anaesthesiologist when dealing with the patient with SAH and ECG abnormality, and the implications for cardiovascular dysfunctio

Pressure-Induced Anomalous Phase Transitions and Colossal Enhancement of Piezoelectricity in PbTiO3_3

We find an unexpected tetragonal-to-monoclinic-to-rhombohedral-to-cubic phase transition sequence induced by pressure, and a morphotropic phase boundary in a pure compound using first-principles calculations. Huge dielectric and piezoelectric coupling constants occur in the transition regions, comparable to those observed in the new complex single-crystal solid-solution piezoelectrics such as Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$-PbTiO$_{3}$, which are expected to revolutionize electromechanical applications. Our results show that morphotropic phase boundaries and giant piezoelectric effects do not require intrinsic disorder, and open the possibility of studying this effect in simple systems.Comment: 4 pages, to appear in Phys. Rev. Let

Microscopic origin of Magnetic Ferroelectrics in Nonlinear Multiferroics

A simple but general microscopic mechanism to understand the interplay between the electric and magnetic degrees of freedom is developed. Within this mechanism, the magnetic structure generates an electric current which induce an counterbalance electric current from the spin orbital coupling. When the magnetic structure is described by a single order parameter, the electric polarization is determined by the single spin orbital coupling parameter, and the material is predicted to be a half insulator. This mechanism provides a simple estimation of the value of ferroelectricity and sets a physical limitation as well.Comment: 4 pages, 1 figur

First-principles study of epitaxial strain in perovskites

Using an extension of a first-principles method developed by King-Smith and Vanderbilt [Phys. Rev. B {\bf 49}, 5828 (1994)], we investigate the effects of in-plane epitaxial strain on the ground-state structure and polarization of eight perovskite oxides: BaTiO$_3$, SrTiO$_3$, CaTiO$_3$, KNbO$_3$, NaNbO$_3$, PbTiO$_3$, PbZrO$_3$, and BaZrO$_3$. In addition, we investigate the effects of a nonzero normal stress. The results are shown to be useful in predicting the structure and polarization of perovskite oxide thin films and superlattices.Comment: 10 page

Elastic effects of vacancies in strontium titanate: Short- and long-range strain fields, elastic dipole tensors, and chemical strain

We present a study of the local strain effects associated with vacancy defects in strontium titanate and report the first calculations of elastic dipole tensors and chemical strains for point defects in perovskites. The combination of local and long-range results will enable determination of x-ray scattering signatures that can be compared with experiments. We find that the oxygen vacancy possesses a special property -- a highly anisotropic elastic dipole tensor which almost vanishes upon averaging over all possible defect orientations. Moreover, through direct comparison with experimental measurements of chemical strain, we place constraints on the possible defects present in oxygen-poor strontium titanate and introduce a conjecture regarding the nature of the predominant defect in strontium-poor stoichiometries in samples grown via pulsed laser deposition. Finally, during the review process, we learned of recent experimental data, from strontium titanate films deposited via molecular-beam epitaxy, that show good agreement with our calculated value of the chemical strain associated with strontium vacancies.Comment: 14 pages, 11 figures, 4 table