ABSTRACT
In the paper, the researches on sleeves made out of maraging steel 1.2709 using selective laser melting (SLM) technology are presented. This additive technology is recognized as favorable for the environment, due to 100% use of material and durability of manufactured details. The fabricated sleeves underwent subsequent tests, in particular, microhardness, porosity and homogeneity of the material was examined before and after heat treatment and salt bath nitrocarburizing process. Two kinds of fatigue tests were performed. The first consisted of the typical sinusoidal alternating load, the other was the high pressure pulse load test close to the real work conditions. It is of high importance that the fatigue strength of the tested sleeves is considerably higher than that of the similarly produced details shaped as a standard samples for tensile stress. The Mössbauer spectrometry analysis of hyperfine magnetic field distributions proved that SLM did not change considerably the martensite structure at atomic level.
ABSTRACT
BACKGROUND: The aim of our research was to evaluate the influence of general anesthesia with controlled nitroglycerin-induced hypotension on splanchnic mucosal perfusion using gastric tonometry. MATERIAL/METHODS: In six patients (1 female, 5 males, median age 46 years, range 32-62) undergoing elective resection of meningiomas, measurements of gastric mucosal perfusion were taken by nasogastric tonometry. Controlled hypotension was initiated after craniotomy and terminated prior to hemostasis procedures. The mean arterial blood pressure (MAP) was maintained 25-30% below initial parameters during controlled hypotension. The adequacy of perfusion was defined by the intramucosal pH (pHi) and the difference between arterial and intramucosal pH (pHGAP). All parameters were analyzed before the induction of controlled hypotension, after the 1st, 2nd, and 3rd hour, and 1 hour after the termination of controlled hypotension. RESULTS: The MAP decreased during controlled hypotension by ca. 26.5% (min. 21.1%; max 31.6%). The lower MAP was accompanied by a statistically significant increase in heart rate. A significant increase from baseline in regional prCO2 was seen after the 1st, 2nd, and 3rd hour of controlled hypotension. Intramucosal pH values decreased significantly during the same period, from 7.428+/-0.032 to 7.372+/-0.015. Despite these statistically significant differences during controlled hypotension, the pHi values were always greater than 7.35, and the pHGAP values were lower than 0.05, which were recognized as being within the normal range. CONCLUSIONS: Controlled hypotension allows accurate evaluation of the blood flow quality at the level of microcirculation. Mild controlled hypotension slightly alters splanchnic mucosal perfusion, but does not lead to ischemia and hypoxia in tissues.