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PubMed2004

Sites of symptomatic gas retention during intestinal lipid perfusion in healthy subjects.

BACKGROUND: Gas pooling within the gut may produce abdominal symptoms but the segment of the intestine responsible for gas retention is unknown. Our aim was to determine the role of the proximal and distal bowel in symptomatic gas accumulation using an experimental model of gas retention triggered by intraluminal lipids. SUBJECTS: Sixteen healthy subjects. METHODS: A gas mixture (N2, O2, and CO2 in venous proportions) was infused into the intestine at12 ml/min for three hours and gas evacuation was continuously measured via an anal cannula connected to a barostat. Abdominal perception and girth changes were measured at 10 minute intervals. Lipids (1 kcal/min) were simultaneously perfused either into the duodenum (n = 8) or into the ileum (n = 8). Each subject was studied twice on separate days, with gas infused into the jejunum or ileum. RESULTS: Duodenal lipids produced retention of gas infused into the jejunum (646 (62) ml) but the volume retained was much smaller when gas was infused directly into the ileum (262 (90) ml; p<0.05). The effects on gas retention were even more pronounced during ileal perfusion of lipids (1546 (184) ml during jejunal gas infusion and 847 (142) ml during ileal gas infusion; p<0.05). Abdominal distension correlated with the volume of gas retained (r = 0.87; p<0.001). Healthy subjects tolerated gas retention, and significant symptoms (score 3.7 (0.8)) developed only during jejunal gas infusion plus ileal lipid perfusion when gas retention was very large. CONCLUSION: Intraluminal lipids induce intestinal gas retention, predominantly acting on the proximal small bowel.

Abdomen↗
PubMed1998

Intestinal gas dynamics and tolerance in humans.

BACKGROUND & AIMS: Abdominal symptoms are often attributed to intestinal gas. In humans, gas production and composition have been previously investigated, but intestinal gas dynamics and tolerance remain virtually unknown. The aim of this study was to establish the relationship between intestinal gas loads, evacuation, perception of symptoms, and objective abdominal distention in healthy humans. METHODS: A dose-response study was performed in 46 healthy subjects; intestinal gas was infused for 3 hours (0, 1, 4, 12, and 30 mL/min), and anal gas evacuation, symptom perception, and abdominal distention were measured. A mixture of gases was infused in venous proportions to minimize diffusion. Anal gas recovery and calculations of gas retention were validated using sulfur hexafluoride as a nonabsorbable gaseous marker. RESULTS: At all of the infusion rates, gas evacuation rapidly equilibrated and paralleled gas infusion without significant differences in perception. Only 6 subjects retained >400 mL gas, and 5 of them developed abdominal distention and symptoms. By contrast, all but 4 of the 41 subjects without retention tolerated the gas loads without discomfort. CONCLUSIONS: Intestinal gas tolerance is normally high, because expeditious gas transit and evacuation prevent gas pooling and symptoms. When this protective mechanism is insufficient, gas retention occurs, and it causes abdominal symptoms and distention.

Abdomen↗
PubMed1990

Gas-forming infection of the urinary tract: an investigation of fermentation as a mechanism.

Most gas-forming infections occur in patients with diabetes. Carbon dioxide formation, resulting from fermentation of the high concentration of sugar in the urine and tissue by infecting organisms, was regarded as the key factor of gas formation in previous reports. Gas from an emphysematous infection of a polycystic kidney was analyzed to understand better the mechanisms involved in gas-forming infections of the urinary tract. The term emphysematous renal polycystic infection is proposed for this particular condition. Gas from the cysts contained 4.1% carbon dioxide, 10.5% oxygen, 67.3% nitrogen and 18.1% unknown gas. This finding is astonishingly similar to that of Wheeler in 1954 and cannot be fully explained by the sugar fermentation theory. Therefore, we propose a new hypothesis. Impaired transportation of gas produced by rapid catabolism leads to gas accumulation in the tissue, which will gradually expand and create chambers to form gas bubbles. Gas of adjacent tissues will attempt to come into equilibrium with the gas bubbles. Positive equilibrium will lead to continuous expansion of the lesion bubble. However, if the chamber is unable to withstand the increasing pressure then rupture or spontaneous drainage of the gas bubble may occur. During negative equilibrium gas in the bubble gradually simulates tissue gas with eventual shrinkage of the bubble. If the chamber is unable to sustain the pressure it collapses and the bubble disappears. However, if the chamber is capable of sustaining the pressure the bubble still may persist even when the gas content is equivalent to tissue gas. This hypothesis may lead to better understanding of emphysematous infections of the urinary tract and also may cast light on emphysematous infections of other organ systems.

Aged↗
PubMed2001

Gas production and migration in landfills and geological materials.

Landfill gas, originating from the anaerobic biodegradation of the organic content of waste, consists mainly of methane and carbon dioxide, with traces of volatile organic compounds. Pressure, concentration and temperature gradients that develop within the landfill result in gas emissions to the atmosphere and in lateral migration through the surrounding soils. Environmental and safety issues associated with the landfill gas require control of off-site gas migration. The numerical model TOUGH2-LGM (Transport of Unsaturated Groundwater and Heat-Landfill Gas Migration) has been developed to simulate landfill gas production and migration processes within and beyond landfill boundaries. The model is derived from the general non-isothermal multiphase flow simulator TOUGH2, to which a new equation of state module is added. It simulates the migration of five components in partially saturated media: four fluid components (water, atmospheric air, methane and carbon dioxide) and one energy component (heat). The four fluid components are present in both the gas and liquid phases. The model incorporates gas-liquid partitioning of all fluid components by means of dissolution and volatilization. In addition to advection in the gas and liquid phase, multi-component diffusion is simulated in the gas phase. The landfill gas production rate is proportional to the organic substrate and is modeled as an exponentially decreasing function of time. The model is applied to the Montreal's CESM landfill site, which is located in a former limestone rock quarry. Existing data were used to characterize hydraulic properties of the waste and the limestone. Gas recovery data at the site were used to define the gas production model. Simulations in one and two dimensions are presented to investigate gas production and migration in the landfill, and in the surrounding limestone. The effects of a gas recovery well and landfill cover on gas migration are also discussed.

Biodegradation, Environmental↗
PubMed2004

Gas in stems: abundance and potential consequences for tree biomechanics.

Secondary xylem of woody plants has a large volumetric proportion of gas occupying spaces that would otherwise be filled with water. We examined whether these gas-filled voids have a mechanical role by either decreasing the fresh mass the tree must support (by replacing some of the water with gas) or by providing inexpensive filler to increase stem diameter (thereby increasing the second moment of area at the expense of the modulus of elasticity and modulus of rupture). Calculations from published data show that temperate softwood species (n = 26) average 18 and 50% gas by volume for sapwood and heartwood, respectively; temperate hardwood species (n = 31) average 26% gas by volume in both the sapwood and heartwood; and tropical species (n = 52) with mixed sapwood and heartwood have 18% gas by volume. In this paper, we develop equations to show how gas affects the mechanical behavior of tree stems, and describe model results to show how gas affects mechanical stability, based on mass and stem diameters for six 34-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees. For the same applied load, modeled stems in which the gas space was filled with water differed in their surface stresses by < 2% from modeled stems in the native state (partially gas-filled), indicating no practical benefit from a reduction in stem mass due to gas. A second modeling scenario compared the native state to stems in which gas was removed and stem diameters decreased (and material properties adjusted to concur with the increased wood density) to conserve mass. Removal of the gas-filled voids resulted in up to 41% higher surface stress for the same applied load, caused by a decrease in the second moment of area greater than the increase in modulus of elasticity. Trees with gas removed had higher modulus of rupture, but could withstand up to 14% lower maximum wind forces than trees in their native state, suggesting a biomechanical role for the gas if the model assumptions are valid. The gas content may, however, have evolved in response to pressures unrelated to biomechanics. We discuss some of its potential effects on sapwood physiology.

Biomechanical Phenomena↗
PubMed1993

Perfluorocarbon-associated gas exchange (partial liquid ventilation) in respiratory distress syndrome: a prospective, randomized, controlled study.

OBJECTIVE: To determine the efficacy of perfluorocarbon-associated gas exchange (partial liquid ventilation) in respiratory distress syndrome. DESIGN: Prospective, randomized, controlled study. SETTING: State University of New York at Buffalo, School of Medicine and Biomedical Sciences. SUBJECTS: Eleven premature lambs with respiratory distress syndrome, delivered by cesarean section. INTERVENTIONS: Five lambs were supported by conventional mechanical ventilation alone. Six lambs were switched to perfluorocarbon-associated gas exchange after 60 to 90 mins of conventional mechanical ventilation. Perfluorocarbon-associated gas exchange was accomplished by instilling a volume of liquid perfluorocarbon equivalent to normal functional residual capacity (30 mL/kg) into the trachea, performing 3 to 4 mins of tidal liquid ventilation, and, at end-expiration, with liquid functional residual capacity of 30 mL/kg remaining in the lung, reconnecting the animal to the volume ventilator for gas tidal volumes. MEASUREMENTS AND MAIN RESULTS: Serial arterial blood gases and lung mechanics were measured. While receiving conventional ventilation, all animals developed progressive hypoxemia, hypercarbia, and acidosis. However, in the perfluorocarbon-associated gas exchange group, within 5 mins of the initiation of perfluorocarbon-associated gas exchange, mean PaO2 increased four-fold, from 59 +/- 6 torr (7.9 +/- 0.8 kPa) during conventional ventilation to 250 +/- 28 torr (33.3 +/- 3.7 kPa; p < .05) during perfluorocarbon-associated gas exchange, and this increase was sustained at 60 mins of perfluorocarbon-associated gas exchange (268 +/- 38 torr; 35.7 +/- 5.1 kPa; p < .05). Mean PaCO2 decreased progressively from 62 +/- 4 torr (8.3 +/- 0.5 kPa) during conventional ventilation to 38 +/- 3.3 torr (5.1 +/- 0.4 kPa) at 60 mins of perfluorocarbon-associated gas exchange (p < .05). Mean pH concomitantly increased. Dynamic compliance increased three-fold within 15 mins of instituting perfluorocarbon-associated gas exchange, from 0.31 +/- 0.02 mL/cm H2O during conventional ventilation to 0.90 +/- 0.11 mL/cm H2O during perfluorocarbon-associated gas exchange, and this increase was sustained at 60 mins of perfluorocarbon-associated gas exchange (p < .05). Mean peak expiratory flow and mean expiratory resistance were essentially unchanged during perfluorocarbon-associated gas exchange as compared with conventional ventilation in the same group. CONCLUSIONS: We conclude that perfluorocarbon-associated gas exchange, which employs liquid functional residual capacity and gas tidal volumes delivered by a conventional ventilator, can facilitate oxygenation and CO2 removal, and dramatically improve lung mechanics in the premature lamb with respiratory distress syndrome.

Airway Resistance↗
PubMed2000

Enantioselective stopped-flow multidimensional gas chromatography. Determination of the inversion barrier of 1-chloro-2,2-dimethylaziridine.

Enantioselective stopped-flow multidimensional gas chromatography (stopped-flow MDGC) is a fast and simple technique to determine enantiomerization (inversion) barriers in the gas phase in a range of delta G#gas(T)=70-200 kJ mol(-1). After complete gas-chromatographic separation of the enantiomers in the first column, gas phase enantiomerization of the heart-cut fraction of one single enantiomer is performed in the second (reactor) column at increased temperature and afterwards this fraction is separated into the enantiomers in the third column. From the observed de novo enantiomeric peak areas a(j), the enantiomerization time t and the enantiomerization temperature T, the enantiomerization (inversion) barrier delta G#gas(T) is determined and from temperature-dependent experiments, the activation enthalpy delta H#gas and the activation entropy delta S#gas are obtained. Enantiomerization studies on chiral 1-chloro-2,2-dimethylaziridine by stopped-flow MDGC yielded activation parameters of nitrogen inversion in the gas phase, i.e., delta G#gas(353 K)=110.5+/-0.5 kJ mol(-1), delta H#gas=71.0+/-3.8 kJ mol(-1) and delta S#gas=-109+/-11 J mol(-1) K(-1). By the complementary method of dynamic gas chromatography (GC), the apparent enantiomerization (inversion) barrier of 1-chloro-2,2-dimethylaziridine in the gas-liquid biphase system was found delta G#app(353 K)=108 kJ mol(-1). The values obtained by stopped-flow MDGC in the gas phase were used to calculate the activation parameters of nitrogen inversion of 1-chloro-2,2-dimethylaziridine in the liquid phase in the presence of the chiral selector Chirasil-nickel(II), i.e.. deltaG#liq(353 K)=106.0+/-0.4 kJ mol(-1), delta H#liq=68.3+/-1.4 kJ mol(-1) and deltaS#liq=-106+/-3.0 J mol(-1) K(-1).

Aziridines↗
PubMed2006

Duodenal infusion of different nutrients and the site of gaseous stimulation influence intestinal gas dynamics.

OBJECTIVE: Excessive intestinal gas can be involved in postprandial abdominal symptom generation, but whether the small bowel influences intestinal gas dynamics, depending on the ingested meal, remains to be demonstrated. We compare the intestinal response to a proximal and distal small intestinal gas challenge during different duodenal nutrient components. MATERIAL AND METHODS: We randomly studied 32 healthy subjects, twice, on different days with a gas mixture infused at 12 ml/min either directly into the proximal jejunum or into the ileum; during duodenal lipids, amino acids, glucose, at 1 kcal/min each, or saline (n=8 for each group). Gas evacuation was monitored continuously and abdominal perception and girth changes were assessed. RESULTS: In response to the jejunal gas challenge, duodenal lipids delayed intestinal gas clearance more potently than amino acids (733+/-26 ml and 541+/-108 ml final gas retention; p<0.001), but when gas was directly infused into the ileum the retained volumes were much smaller (271+/-78 ml and 96+/-51 ml; p<0.001). During duodenal glucose, intestinal gas clearance following jejunal or ileal gas infusion was not significantly influenced. Abdominal perception in response to the jejunal and ileal gas challenge only increased slightly during duodenal lipids (2.0+/-0.3 score and 2.3+/-0.6 score; p<0.05 versus control). CONCLUSION: Postprandial intestinal gas clearance is hampered by duodenal lipids and amino acids but not by glucose. Specific inhibitory effects are more pronounced when gas is infused into the jejunum, which underlines the importance of the small intestine in postprandial gas retention.

Adult↗
PubMed1992

Comparison of gas and liquid ventilation: clinical, physiological, and histological correlates.

To differentiate the effects of gas and liquid ventilation on cardiopulmonary function during early development, we compared the clinical, physiological, and histological profiles of gas- and liquid-ventilated preterm lambs (n = 16; 108-116 days gestation). Immediately after cesarean section delivery, ventilation commenced using gas delivered by a volume ventilator (n = 9) or liquid perfluorochemical (n = 7) delivered by a mechanically assisted liquid ventilation system. Pulmonary gas exchange, acid-base status, vital signs, and respiratory compliance were assessed during the 3-h protocol; sections of the lungs were obtained for histological analyses when the animals were killed. Six of nine gas-ventilated lambs expired from respiratory failure before 3 h, with the remaining animals experiencing severe respiratory insufficiency, pneumothoraces, and cardiovascular deterioration. Six of seven liquid-ventilated lambs survived with good gas exchange and cardiovascular stability and without fluorothorax; one experienced ventricular fibrillation before 1 h and expired despite pulmonary stability. Respiratory compliance was significantly greater in the liquid- than in the gas-ventilated lambs. Histological analyses of gas-ventilated lungs demonstrated nonhomogeneous lung expansion, with thick-walled gas exchange spaces containing proteinaceous exudate, hemorrhage, and hyaline membranes. In contrast, liquid-ventilated lungs appeared clear, with thin-walled and uniformly expanded gas exchange spaces that were free of hyaline membranes and luminal debris. Morphometric analyses demonstrated that surface area and gas exchange index were greater in the liquid- than in the gas-ventilated lambs. These results indicate that elimination of surface active forces by liquid ventilation during early development provides more effective gas exchange with less barotrauma compared with gas ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2002

The effect of inlet gas temperatures on heated humidifier performance.

The aim of the current study was to determine the temperature range of gas at the point at which it passes into a heated humidifier within an intensive care unit and to experimentally examine the effect of different inlet gas temperatures on the performance of a heated humidifier. Various gas and ambient temperatures were measured in an intensive care unit and within ventilator circuits. Ventilator oxygen and air inlet temperatures, ventilator gas outlet temperatures, and humidifier gas inlet temperatures were measured in conjunction with the use of a number of ventilators. Ambient temperatures within the ward ranged from 22.8 degrees C to 28.9 degrees C, while typical ward humidifier gas inlet temperatures ranged from 24.3 degrees C to 28.8 degrees C. Humidity output from a heated humidifier was then determined in an experimental setup at controlled levels of inlet gas temperature using a constant gas flow. A decrease in humidity production, from approximately 36 mg/L at a humidifier inlet gas temperature of 18 degrees C, to 26 mg/L at a humidifier inlet gas temperature of 32 degrees C, was observed with increasing gas inlet temperature. We conclude that humidity output from a heated humidifier varies with inlet gas temperature, decreasing as inlet gas temperature increases. Inlet gas temperatures above 26 degrees C may result in inadequate humidification.

Humans↗
PubMed2004

Inhibitory actions of a high fibre diet on intestinal gas transit in healthy volunteers.

BACKGROUND: Fibre treatment often produces gaseous symptoms which have been attributed to fermentation by colonic bacteria with increased gas production. Effects of fibre ingestion on intestinal gas flow are unexplored. AIMS: We aimed to test the hypothesis that consumption of a high fibre diet retards gas transit. SUBJECTS: Ten healthy volunteers participated. METHODS: To investigate the effects of fibre on gas dynamics, physiological gas mixtures were jejunally perfused at 12 ml/min x 2 hours after a standard diet for seven days with and without psyllium 30 g/day in a crossover fashion. Gas was collected from an intrarectal catheter to bypass the anus and evacuation was quantified in real time using a barostat. RESULTS: On initiating gas perfusion under control conditions, an initial lag phase with no gas expulsion was observed (1129 (274) seconds). Thereafter, gas evacuation from the rectum proceeded with cumulative volumes of 1429 (108) ml by the end of the second hour. Evacuation was pulsatile with passage of 20.9 (2.5) boluses, with mean volumes of 68.2 (5.0) ml. Fibre prolonged the lag time (2265 (304) seconds; p<0.05) and reduced cumulative gas evacuation volumes (1022 (80) ml; p<0.05). Decreased gas evacuation resulted from reductions in the numbers of bolus passages (14.2 (1.1); p<0.05) but not bolus volumes (70.7 (3.4) ml; p = 0.66). CONCLUSIONS: Consumption of a high fibre diet retards intestinal gas transit by decreasing bolus propulsion to the rectum. Thus, in addition to increasing gas production by colonic flora, fibre ingestion may elicit gaseous symptoms by promoting gas retention.

Adult↗
PubMed2005

Radiofrequency ablation of liver tumors: a new cause of benign portal venous gas.

PURPOSE: To retrospectively describe and categorize the presence of portal venous gas (PVG) from radiofrequency (RF) ablation of hepatic tumors. MATERIALS AND METHODS: The study was HIPAA compliant, and informed consent was waived. Thirty-four consecutive computed tomography (CT)-guided percutaneous RF ablations of liver tumors in 26 patients (13 men, 13 women; mean age, 69 years) with five hepatocellular carcinomas and 21 metastatic liver tumors (13 colon, five other, and three unknown primary tumors) were performed with an institutional review board-approved protocol. Two treatment modalities were used: RF ablation alone (13 procedures) and combined RF ablation and ethanol injection (21 procedures). Presence of PVG was quantified with three parameters: maximum length of a portal venous branch with gas, number of Couinaud segments in which PVG was seen, and total number of portal venous branch points with gas. Then an overall PVG score from 0 to 5 was determined. Also, when tumoral gas was seen on CT scans, the largest cross-sectional area of gas was measured. The two ablation methods were compared for quantities of PVG and tumoral gas. The role of N(2)O anesthetic in PVG and tumoral gas formation during ablation also was studied. Statistical analyses were performed with Wilcoxon rank sum and Student t tests. RESULTS: In 25 procedures (74%), gas was found in portal vein branches; in 30 procedures (88%), gas was also found in tumoral and peritumoral tissues. There was no significant difference in frequency of PVG between the ablation methods. Combined therapy yielded significantly greater lengths of PVG (P < .002) and more portal venous branch points (P < .001) than did RF ablation alone. Mean PVG score was 2.4 +/- 0.4 (standard error of the mean) for combined therapy and 0.9 +/- 0.2 for RF ablation alone (P < .004). N(2)O anesthetic was associated with greater amounts of tumoral gas (P < .008) and PVG (P < .03). Tumoral gas, peritumoral gas, and PVG dissipated within 20 minutes after ablation in all patients. No morbidity or mortality was associated with PVG. CONCLUSION: RF ablation is a common yet benign cause of transient PVG, tumoral gas, and peritumoral gas. Combined RF and ethanol ablation was associated with more PVG than was RF ablation alone.

Aged↗
PubMed1993

Inhaled nitric oxide reverses hypoxic pulmonary vasoconstriction without impairing gas exchange.

Nitric oxide (NO) is an endogenous endothelium-derived relaxing factor that participates in the regulation of vascular tone. We studied the effects of inhaled NO gas on transient hypoxic pulmonary vasoconstriction and normal lungs in mechanically ventilated sheep. We measured hemodynamics and pulmonary gas exchange. For gas exchange measurements we used conventional blood gas analysis and the multiple inert gas elimination technique to estimate ventilation-perfusion heterogeneity. Our hypotheses were 1) inhaled NO reverses hypoxic pulmonary vasoconstriction, 2) the hemodynamic effects of inhaled NO are limited to the pulmonary circulation, and 3) inhaled NO does not impair pulmonary gas exchange and may redistribute blood flow to better ventilated areas of the lungs. Hypoxic pulmonary vasoconstriction was induced by using a hypoxic inspiratory gas mixture. The addition of 20 ppm NO to the hypoxic inspiratory gases returned pulmonary arterial pressure to baseline values. Systemic hemodynamics and gas exchange indexes derived from conventional blood gas analysis remained constant. Gas exchange indexes for ventilation-perfusion ratios and gas dispersions improved. The addition of 20 ppm NO to medical air (21% O2) had no such significant effects on hemodynamics or pulmonary gas exchange. Our findings show that inhaled NO reverses transient hypoxic pulmonary vasoconstriction. The hemodynamic effects of NO are limited to the pulmonary circulation; it does not impair pulmonary gas exchange. Moreover, it redistributes blood flow to better ventilated alveoli. As such, NO has potential in the treatment of lung diseases associated with pulmonary hypertension.

Administration, Inhalation↗
PubMed1995

Cardiorespiratory effects of perfluorocarbon-associated gas exchange at reduced oxygen concentrations.

OBJECTIVE: To determine whether reducing FIO2 during perfluorocarbon-associated gas exchange would cause deterioration of hemodynamics, lung mechanics, or gas exchange in normal piglets. DESIGN: A prospective, controlled animal trial. SETTING: Experimental animal laboratory in a university setting. SUBJECTS: Twelve normal, anesthetized piglets, 7 to 14 days old, and weighing 3.31 +/- 0.75 kg. INTERVENTIONS: After the induction of anesthesia, tracheostomy and catheterization, piglets were stabilized. They were mechanically ventilated with a tidal volume of 15 mL/kg, inspiratory time of 25%, positive end-expiratory pressure of 4 cm H2O, and a respiratory rate of 20 to 28 breaths/min to obtain a baseline PaCO2 between 34 and 45 torr (4.7 and 6.0 kPa). Each animal was studied during continuous positive-pressure breathing, and during perfluorocarbon-associated gas exchange. They were ventilated at an FIO2 of 1.0 for 15 mins. FIO2 was randomly varied among 0.75, 0.5, and 0.3 every 15 mins, then returned to 1.0. At each FIO2, measurements of gas exchange, lung mechanics, and hemodynamics were made. After continuous positive-pressure breathing, perfluorocarbon-associated gas exchange was instituted by replacing the gaseous functional residual capacity of the lungs with perfluorooctylbromide. Animals were then ventilated and measurements were taken. MEASUREMENTS AND MAIN RESULTS: At each FIO2, measurements of gas exchange (arterial blood gases and saturation), lung mechanics (mean airway pressure, static end-inspiratory pressure, and peak inspiratory pressure), and hemodynamics (heart rate, and mean arterial, right atrial, pulmonary artery occlusion, and pulmonary arterial pressures) were recorded. In six piglets, cardiac output was measured at each FIO2 by thermodilution. Cardiac index, indexed oxygen delivery and consumption, and indexed pulmonary vascular resistance were derived using standard formulas. Piglets were well saturated at all FIO2 settings during continuous positive-pressure breathing. However, during perfluorocarbon-associated gas exchange, arterial saturation decreased to 72% at an FIO2 of 0.3. Cardiac index and oxygen consumption were not affected by reducing FIO2 during perfluorocarbon-associated gas exchange, and were not significantly different than during continuous positive-pressure breathing. Oxygen delivery was reduced at an FIO2 of 0.3 during perfluorocarbon-associated gas exchange, but oxygen consumption remained in the flow independent portion of the curve despite arterial desaturation. Pulmonary arterial pressure was higher during perfluorocarbon-associated gas exchange than during continuous positive-pressure breathing. Pulmonary arterial pressure and indexed pulmonary vascular resistance were significantly higher during perfluorocarbon-associated gas exchange at an FIO2 of 0.3 than at any other FIO2 settings. CONCLUSIONS: Piglets showed no adverse effects on lung mechanics during perfluorocarbon-associated gas exchange. Hemodynamics were well supported at all FIO2 settings, and arterial blood was fully oxygenated during perfluorocarbon-associated gas exchange at an FIO2 of > or = 0.5.

Animals↗
PubMed1994

Expression of a growth arrest specific gene (gas-6) during liver regeneration: molecular mechanisms and signalling pathways.

A set of growth arrest-specific (gas) genes negatively regulated by serum has been identified. To define the role of gas genes in a model of cell proliferation in vivo we analyzed the expression of one of these genes (gas-6) during liver regeneration after partial hepatectomy (PH). We found that gas-6 mRNA was down-regulated 4 hours after PH, within the G0 to G1 transition. Later on, gas-6 mRNA increased over the level found in normal liver with a peak at 16 hours, before the onset of DNA synthesis. This surge was probably triggered by an inflammatory response caused by the surgical trauma, because an increase of similar extent occurring with the same time course was present in livers of sham-operated and turpentine-treated rats. Comparison of mRNA steady state levels with nuclear transcription rates indicated that gas-6 expression is post-transcriptionally regulated. As we found that down-regulation of gas-6 expression was prevented by treatment with Actinomycin D, a labile protein might be involved in the determination of gas-6 mRNA stability. To investigate the mitogenic signals controlling gas-6 expression during liver regeneration we treated hepatectomized rats with a specific alpha-1-adrenoceptor blocker (prazosin) as well as with drugs which modify intracellular calcium levels. The decrease of gas-6 mRNA 4 hours after PH was prevented by prazosin and by neomycin, an inhibitor of calcium release from endogenous stores. These findings suggest that down-regulation of gas-6 expression during hepatic regeneration is triggered by catecholamines interaction with alpha-1-adrenergic receptors and by subsequent calcium release. In addition we found that the rise of gas-6 gene expression occurring at 16 hours after PH was not affected by prazosin but was inhibited by trifluoperazine. Therefore, we suggest that up-regulation of gas-6 gene expression is mediated by the interaction of calcium with calmodulin, independently of catecholamines.

Animals↗
PubMed2001

An assessment of intraocular pressure rise in patients with gas-filled eyes during simulated air flight.

PURPOSE: To investigate the safety of aircraft flight for patients with small volumes of residual postoperative intraocular gas. DESIGN: Nonrandomized comparative trial. PARTICIPANTS: Seventeen eyes (nine gas filled and eight control eyes) of nine patients and one eye of one control subject were tested. METHODS: Patients with postoperative intraocular gas and the control subject were tested in the controlled environment of a hypobaric chamber to simulate the cabin depressurization associated with a typical commercial aircraft flight. Before, during, and after a simulated flight, the intraocular pressure (IOP) in the gas-containing and contralateral eyes was tested using the Perkins (Edinburgh, UK) and Tono-Pen XL (Jacksonville, FL) tonometers. MAIN OUTCOME MEASURES: The absolute and percentage change in IOP with varied cabin pressurization. RESULTS: Of the nine patients with intraocular gas, seven had 10% to 15% gas volume and two had 20% gas volume. In the 10% to 15% gas volume group, the IOP rose by an average of 109% from baseline during ascent to an average cabin altitude of 7429 feet above sea level. The IOP dropped to an average of 30% above baseline IOP during the cruise phase and further decreased to an average of 38% below baseline IOP on return to baseline altitude. In the 20% gas volume group, the IOP rose by an average of 84% from baseline during ascent to an average cabin altitude of 3400 feet above sea level. The IOP dropped to an average of 42% below baseline IOP on return to baseline altitude. The IOP in the contralateral control eyes did not vary with altitude changes. No patient experienced pain or visual loss during the experiments. CONCLUSIONS: Our results demonstrate that IOP may rise significantly in gas-filled eyes during simulated air flight, supporting the current conservative recommendation against air travel for most patients with intraocular gas bubbles. Further testing is warranted to develop a more objective measure of intraocular gas volume estimation and to define better the tolerability of aircraft flight for patients with intraocular gas.

Adult↗
PubMed2003

On-line analysis of the size distribution of fine and ultrafine aerosol particles in flue and stack gas of a municipal waste incineration plant: effects of dynamic process control measures and emission reduction devices.

The size distribution of particles in the waste gas of a municipal waste incineration plant (23 MW) was measured on-line at two sampling points in the flue-gas duct (700 and 300 degrees C) as well as in the stack gas (80 degrees C). The measurements were performed during both stable combustion conditions and transient operating conditions. The particle measurements were carried out by a mobile system consisting of a home-designed sampling system with dilution device and a scanning mobility particle sizer (SMPS) for the particle size range 17-600 nm as well as an aerodynamic particle sizer (APS) for the size range 500 nm-30 microm. The APS and SMPS data were combined using a special method and a home written software tool. The maximum of the particle-size distribution in the flue gas of the incinerator shifts from about 90 nm at the 700 degrees C sampling point to about 140 nm at the 300 degrees C point, showing the particle growth by coagulation processes and condensation of inorganic and organic gaseous species with decreasing temperature. This finding is consistent with the measured concentration profiles of gaseous organic chemical species in the flue gas. While at flue-gas temperatures of 600-800 degrees C a rich pattern of polycyclic aromatic hydrocarbon species (PAH) is observable, the PAH concentrations are considerably reduced further downstream of the flue-gas channel, where the temperature drops below 500 degrees C. Condensation and reactive bonding of gaseous chemicals onto particulate matter is, among other reasons, responsible for the depletion of gas-phase species. Process control measures, such as firing the backup burners or cleaning of the grate with pressurized air, can cause dynamic changes of the particle-size distribution. Furthermore the flue-gas cleaning measures have great impact onto both the particle concentration and the size distribution. For this reason the impact of one particular emission reduction device, the wet electrostatic dust precipitator (wet-ESP), is evaluated. The wet-ESP reduces considerably the particle concentration over the whole size range. Behind the flue-gas processing units a broad maximum in the particle-size distribution occurs at about 70 nm, but no pronounced particle-size distribution could be observed. The particle concentration level atthis maximum is about 3 magnitudes lower than in the raw flue gas. However, intermittent periods lasting for several minutes of high emissions of ultrafine particles with d < 40 nm were observed. These particles are most likely formed by nucleation processes behind the wet-ESP from gas-phase constituents of the stack gas.

Aerosols↗
PubMed1992

Expression of a growth arrest specific gene (gas-1) in transformed cells.

A set of growth arrest-specific (gas) genes negatively regulated by serum has been identified. We report the analysis of the expression of one of them (gas-1) in transformed cells. We found a down regulation of gas-1 expression in NIH 3T3 cells transfected in vitro with an activated Ha-ras oncogene. In five chemically-induced mouse tumours grown in vivo the amounts of gas-1 mRNA were largely different but not related to the proliferating activity (evaluated by both H3 histone expression and 3H-thymidine incorporation into DNA). The amount of gas-1 mRNA in the tumours was in general higher than in normal tissues. Expression of c-myc was also evaluated and found to be high in tumours which exhibited low gas-1 expression. Two fibrosarcomas, CA-2 and CB-20, with similar phenotype, similar growth rate, different expression of c-myc and 100-fold difference in gas-1 expression were further investigated and gas-1 expression was found to be correlated with the expression of a differentiated function (as judged from collagen expression). Cell lines derived from CA-2 and CB-20 and maintained under different culture conditions showed that the cell cycle regulation and serum response of gas-1 expression were lost in CA-2. The higher steady state level of gas-1 mRNA in spite of a shorter mRNA half life suggests that in CB-20 cells the gas-1 gene is transcribed faster than in CA-2 cells indicating that transcriptional regulation is the major determinant of gas-1 gene expression in tumour cells. The finding of gas-1 expression in tumour cells suggests that its expression is not sufficient to maintain cells into quiescence, however, as a marker specific for the G0 phase, it could be useful, in conjunction with other growth related genes, to define the cell cycle distribution of a cell population.

3T3 Cells↗