Continuous measurement of heart rate variability following carbon dioxide pneumoperitoneum during nitrous oxide/sevoflurane anaesthesia

Background: Previous studies of autonomic nervous system activity through analysis of heart rate variability (HRV) have demonstrated increased sympathetic activity during positive-pressure pneumoperitoneum. We employed an online, continuous method for rapid HRV analysis (MemCalc™, Tarawa, Suwa Trust, Tokyo, Japan) to demonstrate rapid changes in autonomic nervous system during pneumoperitoneum for laparoscopy. Method: The powers of low-frequency (LF) (0.04-0.15 Hz) and high-frequency (HF) (0.15-0.4 Hz) components of HRV in 20 healthy adult patients were monitored under sevoflurane anaesthesia for 10 minutes after the initiation of carbon dioxide pneumoperitoneum at 10 mmHg. Results: Heart rate increased promptly, but transiently, just after peritoneal insufflation. At that time, the ratio between the LF and HF components increased on HRV. Similar, but small, changes occurred following head-up positioning. Conclusion: By monitoring HRV continuously, we have demonstrated that the change in autonomic nervous system balance induced by peritoneal insufflation was prompt and transient. The change in autonomic nervous system activity could have been due to increased sympathetic activity, reduced vagal activity, or both.Keywords: heart rate variability; positive pressure pneumoperitoneum; continuous monitorin

Local Ferromagnetism in Microporous Carbon with the Structural Regularity of Zeolite Y

Magnetization M(H,T) measurements have been performed on microporous carbon (MC) with a three-dimensional nano-array structure corresponding to that of a zeolite Y supercage. The obtained results unambiguously demonstrate the occurrence of high-temperature ferromagnetism in MC, probably originating from a topological disorder associated with curved graphene sheets. The results provide evidence that the ferromagnetic behavior of MC is governed by isolated clusters in a broad temperature range, and suggest the occurrence of percolative-type transition with the temperature lowering. A comparative analysis of the results obtained on MC and related materials is given.Comment: To be published in Physical Review B (2003

Ferromagnetism in Oriented Graphite Samples

We have studied the magnetization of various, well characterized samples of highly oriented pyrolitic graphite (HOPG), Kish graphite and natural graphite to investigate the recently reported ferromagnetic-like signal and its possible relation to ferromagnetic impurities. The magnetization results obtained for HOPG samples for applied fields parallel to the graphene layers - to minimize the diamagnetic background - show no correlation with the magnetic impurity concentration. Our overall results suggest an intrinsic origin for the ferromagnetism found in graphite. We discuss possible origins of the ferromagnetic signal.Comment: 11 figure

ELECTRICAL AND STRUCTURAL PROPERTIES OF A NEW CONDUCTING POLYMER : PYROLYTIC POLY (p-PHENYLENE-1,3,4-OXADIAZOLE)

Des films de poly (p-phénylène-1,3,4-oxadiazole) ont été pyrolisés à diverses températures et leurs propriétés électriques et structurales étudiées. Les films pyrolisés présentaient des états électroniques étendus contribuant à une conductivité métallique indépendante de la température (jusqu'à 510 S/cm) et des états localisés entraînant un mouvement des électrons par sauts. La structure est supposée du type graphite ayant des couches condensées d'aromatiques avec des noyaux hétérocycliques contenant des azotes.Poly(p-phenylene-1,3,4-oxadiazole) films were pyrolyzed at various temperatures and their electrical and structural properties were investigated. The pyrolyzed films were composed of both extended electronic states which contribute to a temperature-independenent metallic conductivity (up to 510 S/cm) and localized states giving rise to a variable range hopping motion of electrons. The structure was thought to be a graphite-like crystal having condensed aromatic layers with nitrogen-containing heterocyclic rings