Electric-field-induced phase transitions in bent-core mesogens determined by x-ray diffraction.

The changes in the x-ray diffraction diagram induced by an electric field have been studied in four bent-core liquid crystals. Two of the compounds present columnar B1 phases and the other two show dark conglomerate (DC) structures. In the B1 materials the electric field gives rise to switchable phases whose diffraction pattern is that of the smectic C polar (SmCP) phase. In the DC structures the positions of the Bragg reflections remain essentially unaltered, but in one of the compounds the peaks become narrower under field, indicating that the correlation length of the smectic order increases. A slight enhancement of the smectic spacing is found in the DC phases upon field application.

Polarization periodicity in the B(1) columnar phase determined by resonant x-ray scattering.

We report structural results that evidence the polarization distribution of the blocks in the columnar phase of an achiral bent-core liquid crystal. The study was performed using resonant x-ray diffraction at the sulfur K edge on oriented samples aligned on substrates. The extra periodicity is revealed through the violation of the systematic extinction rule of the structural symmetry group along the experimentally accessible diffraction direction. Further data obtained from the polarization analysis of a resonant reflection give information concerning the transition mechanism between B(1) and B(2) phases.

Pseudolayered structure of the columnar B1 phase of bent-core liquid crystals.

Three bent-core liquid-crystal compounds presenting the unusual columnar B1 to tilted polar smectic (Sm-CP or B2) phase transition are studied through small-angle x-ray diffraction on aligned samples. The well-established character of the smectic phase helps to characterize the structural changes during the transition. A mechanism for this transition is proposed, which accounts for the low enthalpy usually observed in this process. The B1 phase is found to possess a great degree of lamellarization, with pseudosmectic ferroelectric layers along the crystallographic (11) planes. As a consequence of these observations a distribution of the block polarizations in the columnar structure is proposed.

Réplica a "consideraciones sobre la conversión de tubo nasotraqueal a orotraqueal" / Author's reply to "on conversion from nasotracheal to orotracheal intubation

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[Exchanging and maintaining the airway in hyoid surgery: using a flexible exchanger during new surgical treatments for obstructive sleep apnea syndrome]. / Modificación y mantenimiento de la vía aérea en la cirugía del hioides. Empleo de un intercambiador flexible en las nuevas técnicas quirúrgicas del síndrome de apnea obstructiva del sueño.

OBJECTIVE: To assess the level of intubation difficulty and anatomical changes after hyoid surgery. To evaluate the difficulty of switching from nasotracheal to orotracheal intubation after hyoid and palatopharyngeal surgery using an exchanger. MATERIAL AND METHODS: Prospective study enrolling 30 patients undergoing surgery for obstructive sleep apnea syndrome (OSAS) in 2 consecutive phases. Anatomical features suggesting risk of difficult intubation, anatomical changes caused by surgery, the incidence of failure to intubate upon first attempt during the first surgical session, and upon switching from nasal to oral intubation, and the time required to intubate were recorded. The rate of complications during and after surgery was also noted. RESULTS: The incidence of difficult intubation was 15% and no complications developed in the switch from nasotracheal to orotracheal intubation (100% success rate). CONCLUSION: New surgical treatments for the OSAS patient require new anesthetic maneuvers such as nasotracheal-orotracheal intubation exchange after hyoid surgery. The exchanger used in the present study offers a valid way to achieve airway management in this situation.

Modificación y mantenimiento de la vía aérea en la cirugía del hioides. Empleo de un intercambiador flexible en las nuevas técnicas quirúrgicas del síndrome de apnea obstructiva del sueño / Exchanging and maintaining the airway in hyoid surgery: using a flexible exchanger during new surgical treatments for obstructive sleep apnea syndrome

OBJETIVO: Establecer el grado de dificultad de intubación así como las alteraciones anatómicas tras la cirugía hioidea. Valorar la dificultad que plantea el cambio de intubación nasotraqueal a orotraqueal tras la cirugía hioidea y palatofaríngea empleando un intercambiador. MATERIALES Y MÉTODOS: Estudio prospectivo en el que se incluyeron 30 pacientes intervenidos de cirugía del Síndrome de Apnea Obstructiva del Sueño (SAOS) en dos tiempos quirúrgicos consecutivos. Se recogieron variables anatómicas predictivas de intubación difícil, los cambios anatómicos producidos por la cirugía, la incidencia de intubaciones fallidas en el primer tiempo quirúrgico y en el cambio de intubación nasal a oral, recogiéndose el tiempo empleado en dicho cambio. También se recogieron las complicaciones intra y postoperatorias. RESULTADOS: La incidencia de intubación difícil fue de un 15%, ninguno de los cambios de intubación nasotraqueal a orotraqueal presentó complicaciones, obteniéndose un 100% de intubaciones exitosas. CONCLUSIÓN: Las nuevas técnicas quirúrgicas en el paciente con SAOS, implican nuevas actuaciones anestésicas, como el cambio de intubación nasotraqueal a orotraqueal necesario tras la cirugía hioidea. El intercambiador empleado en el presente trabajo plantea una alternativa valida para el manejo de la vía aérea en esa situación

OBJECTIVE: To assess the level of intubation difficulty and anatomical changes after hyoid surgery. To evaluate the difficulty of switching from nasotracheal to orotracheal intubation after hyoid and palatopharyngeal surgery using an exchanger. MATERIAL AND METHODS: Prospective study enrolling 30 patients undergoing surgery for obstructive sleep apnea syndrome (OSAS) in 2 consecutive phases. Anatomical features suggesting risk of difficult intubation, anatomical changes caused by surgery, the incidence of failure to intubate upon first attempt during the first surgical session, and upon switching from nasal to oral intubation, and the time required to intubate were recorded. The rate of complications during and after surgery was also noted. RESULTS: The incidence of difficult intubation was 15% and no complications developed in the switch from nasotracheal to orotracheal intubation (100% success rate). CONCLUSION: New surgical treatments for the OSAS patient require new anesthetic maneuvers such as nasotracheal- orotracheal intubation exchange after hyoid surgery. The exchanger used in the present study offers a valid way to achieve airway management in this situation

Electric-field-induced B1-B2 transition in bent-core mesogens.

We report experimental results on two bent-shaped mesogens showing the B1 phase. Contrary to the conventional B1 structures, we have found that our compounds display a clear electro-optic effect in this phase. Under the influence of a 100-Hz square-wave electric field of moderate amplitude, an increase of the birefringence is observed. However, no switching current is detected, indicating that the materials remain antiferroelectric. For high enough fields, a drastic change in the texture occurs. This change is a phase transition to a B2 phase, and shows the typical antiferroelectric switching of this phase. The induced B2 phase has been identified to be homochiral. Upon removal of the field, the B1 structure is recovered. Our study is based on differential scanning calorimetry, x-ray, electro-optics, polarization reversal, and dielectric measurements.

Interpretation of unusual textures in the B2 phase of a liquid crystal composed of bent-core molecules.

A liquid crystal material of bent-core molecules is investigated by means of optical texture observations, x-ray measurements, and miscibility studies. While the x-ray and miscibility data point towards a B2 phase, the texture is however unusual, showing optical isotropy and segregation in two domains with opposite gyrations. It is shown that the texture can be interpreted successfully in terms of a smectic-C(A)P(A) structure in small domains with random orientations. The optical activity data are also explained semiquantitatively.

Anestesia subaracnoidea en un caso de miopatía mitocondrial / Anesthesia in a case of mitochondrial myopathy

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Anestesia en un paciente con déficit congénito de antitrombina III / anesthesia in a patient with congenital antithromin III deficit

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