Calibration of seven ICU ventilators for mechanical ventilation with helium-oxygen mixtures

The study evaluated seven intensive care unit (ICU) ventilators (Veolar FT, Galileo, Evita 2, Evita 4, Servo 900C, Servo 300, Nellcor Puritan Bennett 7200 Series) with helium-oxygen (HeO2), using a lung model, to develop correction factors for the safe use of HeO2. A 70:28 helium-O-2 mixture (heliox) replaced air and combined with O-2 (HeO2). Theoretical impact of HeO2 on inspiratory valves and gas mixing was computed. True fraction of inspired oxygen (Ro,del) was compared with fraction of inspired oxygen (FIo2) set on the ventilator (FI(o2)set). True tidal volume (VTdel) was compared with VT set on the ventilator (VTset) in volume control and with control VTdel at FIo2 1.0 in pressure control. FI(o2)del minimally exceeded FI(o2)set (less than or equal to 5%) except with the 7200 Series (FI(o2)del > FI(o2)set by 125%). In volume control, with the Veolar FT, Galileo, Evita 2, and Servo 900C, VTdel > VTset, with the 7200 Series VTdel VTset (nonlinear relationship), whereas with the Servo 300 VTdel = VTset. In pressure control, VTdel was identical to control measurements, except with the 7200 Series (ventilator malfunction). Correction factors were developed that can be applied to most ventilators

Palaeoenvironment reconstruction, volcanic evolution and geochronology of the Cerro Blanco subcomplex, Nevados de Chillan volcanic complex, Central Chile

Nevados de Chillán Volcanic Complex, central Chile, has been active for at least 640 ka—a period spanning a number of glacial and interglacial periods. Geologic mapping, radiometric dating and geochemical analysis have identified six new volcanic units and produced four new 40Ar/39Ar ages for Cerro Blanco, the northern subcomplex of Nevados de Chillán volcano. Compositions range from dacite to basaltic-andesite and a new geologic map is presented. Examination of lava fracture structures on both newly mapped lavas and those mapped during previous studies has enabled interpretations of former eruptive environments. Palaeoenvironment reconstructions, combined with 40Ar/39Ar ages and comparison with the marine oxygen isotope record, show that at least three phases of volcanic activity have occurred during the evolution of Cerro Blanco: (1) a constructive, pre-caldera collapse period; (2) a period of caldera formation and collapse; and (3) a constructive period of dome growth forming the modern day volcanic centre. This style of volcanic evolution, whereby large-scale caldera collapse is followed by growth of a new stratocone is common at Andean volcanoes

Recent Eruptive Activity At El-misti Volcano (south Peru) - Implications for Hazard Assessment in Arequipa Area

About 1 million people live at risk in Arequipa city which lies 15 km from the vent of the active El Misti stratovolcano (5,825 m), in the Pliocene to Holocene Central Andean Volcanic Zone. Built on volcaniclastic bedrock, El Misti encompasses a stratovolcano of Pleistocene age and a modern stratocone. The bulk of the modern strato-cone consists of a series of stubby lava flows and pyroclastic debris reaching 2,800 m in thickness. The interpretation of eighteen tephra profiles situated in gorges of the western to southeastern foot of the El Misti volcano shows that the volcano has erupted repeatedly during the upper Pleistocene, the more recent products corresponding to repeated plinian eruptions. The uppermost huge tephra sequence lies on a poorly developed palaeosol containing charcoal that was dated by C-14 method at 1,920 +/- 200 yrs BP. Historical data refer to some volcanic activity at AD 1440-1470. Based on the tephrostratigraphic study, the most important volcanic hazards for the 900,000 inhabitants of Arequipa are four-fold: tephra fallout as thick as 50 cm falling from high plinian columns, pyroclastic flows expected in any valley towards the northern suburbs, lahars during the wet season (December to March), and uncommon debris avalanches

Ice-melt collapse pits and associated features in the 1991 lahar deposits of Volcán Hudson, Chile: criteria to distinguish eruption-induced glacier melt.

In subaerial volcaniclastic sequences, structures formed by ice blocks can provide information about a volcano's history of lahar generation by glacier melt. At Volcán Hudson in Chile, catastrophic lahars were initiated by eruption-induced melting of glacier ice in August and October 1991. They transported large ice blocks 50?km down the Rio de los Huemules valley to the sea. Large current crescents with lee-side lenses were formed where ice blocks were deposited during waning stages of the flood. When stranded blocks of ice melted, they left cone-shaped and ring-shaped heaps of ice-rafted debris on the sediment surface. Several hundred ice blocks were completely buried within the aggrading lahar sediment, and when these melted circular collapse pits formed in the sediment. Collapse types included subsided coherent blocks of sediment bounded by an outward-dipping ring-fracture, trapdoor structures with horseshoe-shaped fractures, downsag pits with centroclinal dips locally up to 60°, pits with peripheral graben and crevasses, piecemeal (highly fragmented) collapse structures and funnel-shaped pits containing disaggregated sediment. A sequence of progressive collapse is inferred in which initial downsag and subsidence on an outward-dipping ring fracture produces a small diameter pit. This is followed by widening of the pit by progressive development of concentric ring fractures and downsag outside the early formed pit, and by collapse of overhanging pit walls to produce vertical to inward-dipping walls and aprons of collapse debris on the pit floor. The various structures have potential for preservation even in regions prone to high rainfall and flooding, and they can be used to indicate that former lahars contained abundant blocks of ice