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PubMed1991

Optimizing fresh gas flow and circuit design for the delivery of continuous positive airway pressure.

OBJECTIVE: To examine the effect of varying circuit design and the fresh gas flow rate on the circuit work imposed by a continuous positive airway pressure (CPAP) circuit. DESIGN: Circuit work was measured during simulated inspiration (500 mL) with a lung model at inspiratory flow rates (V) of 40, 60, and 80 L/min during the administration of 10 cm H2O CPAP through either a modified Mapleson-A or modified Mapleson-D circuit, both alone and when connected to a face mask (i.e., simulating an intubated and nonintubated patient). Fresh gas flow was varied from 10 to 250 L/min. RESULTS: The minimum circuit work occurred at a fresh gas flow rate approximating V; however, circuit work was consistently lower for the modified Mapleson-A circuit compared with the modified Mapleson-D circuit. As the fresh gas flow rate was increased sequentially to 250 L/min, circuit work remained close to the minimum value for the modified Mapleson-A, but increased gradually with the modified Mapleson-D, e.g., from 0.017 kg.m/L at a fresh gas flow rate and V of 80 L/min to 0.035 kg.m/L at a fresh gas flow rate of 250 L/min and a V of 80 L/min. Rotation of the fresh gas flow inlet did not change the circuit work vs. fresh gas flow rate relationship. Addition of a face mask resulted in a smaller increase in circuit work for the modified Mapleson-D with increasing fresh gas flow rate. However, unlike the modified Mapleson-A circuit alone, the addition of a mask caused circuit work to increase with increasing fresh gas flow rate. CONCLUSIONS: The modified Mapleson-A circuit at a fresh gas flow rate equal to V minimizes circuit work, and hence represents an optimal CPAP circuit. The increases in circuit work at fresh gas flow rates above V that were found with the modified Mapleson-D circuit are not due to inertial differences, and are likely due to turbulent gas flow.

Humans↗
PubMed1991

Estimation of vulnerable zones due to accidental release of toxic materials resulting in dense gas clouds.

Heavy gas dispersion models have been developed at IIT (hereinafter referred as IIT heavy gas models I and II) with a view to estimate vulnerable zones due to accidental (both instantaneous and continuous, respectively) release of dense toxic material in the atmosphere. The results obtained from IIT heavy gas models have been compared with those obtained from the DEGADIS model [Dense Gas Dispersion Model, developed by Havens and Spicer (1985) for the U.S. Coast Guard] as well as with the observed data collected during the Burro Series, Maplin Sands, and Thorney Island field trials. Both of these models include relevant features of dense gas dispersion, viz., gravity slumping, air entrainment, cloud heating, and transition to the passive phase, etc. The DEGADIS model has been considered for comparing the performance of IIT heavy gas models in this study because it incorporates most of the physical processes of dense gas dispersion in an elaborate manner, and has also been satisfactorily tested against field observations. The predictions from IIT heavy gas models indicate a fairly similar trend to the observed values from Thorney Island, Burro Series, and Maplin experiments with a tendency toward overprediction. There is a good agreement between the prediction of IIT Heavy Gas models I and II with those from DEGADIS, except for the simulations of IIT heavy gas model-I pertaining to very large release quantities under highly stable atmospheric conditions. In summary, the performance of IIT heavy gas models have been found to be reasonably good both with respect to the limited field data available and various simulations (selected on the basis of relevant storages in the industries and prevalent meteorological conditions performed with DEGADIS). However, there is a scope of improvement in the IIT heavy gas models (viz., better formulation for entrainment, modification of coefficients, transition criteria, etc.). Further, isotons (nomograms) have been prepared by using IIT heavy gas models for chlorine, which provide safe distance for various storage amounts for 24 meteorological scenarios prevalent in the entire year. These nomograms are prepared such that a nonspecialist can use them easily for control and management in case of an emergency requiring the evacuation of people in the affected region. These results can also be useful for siting and limiting the storage quantities.

Accidents, Occupational↗
PubMed2006

Nutrient modulation of intestinal gas dynamics in healthy humans: dependence on caloric content and meal consistency.

The actions of nutrients on gut transit of liquids and solids have been extensively studied, but the effects of meal ingestion on intestinal gas flow are unexplored. We hypothesized that meals of varying caloric content and consistency modulate gas transit to different degrees. Nine healthy volunteers underwent jejunal perfusion of physiological gas mixtures at 12 ml.min(-1).3 h, with ingestion of nothing (control), water (240 ml), 240-kcal liquid meals, and 240-kcal solid meals at the end of the second hour in separate studies. Gas was quantified from an intrarectal catheter. After an initial lag phase, gas evacuation approached steady state by the end of the fasting period. Solid and liquid caloric meals increased total gas volumes evacuated from 5-40 min after ingestion vs. control studies (P < 0.05). These increases resulted from increased numbers of bolus gas evacuations (P < 0.05), whereas bolus volumes, pressures, and flow rates were similar for all test conditions. Solid and liquid caloric meals elicited similar effects on bolus gas dynamic parameters, whereas water did not affect these measures vs. control (NS, not significant). Both caloric meals and the noncaloric liquid meal increased continuous gas flow, which represented <2% of total gas expulsion. In conclusion, caloric meals promote bolus gas transit in healthy humans, whereas noncaloric liquids have no effect. Solids stimulate early postprandial gas dynamics to the same extent as liquid meals of similar caloric content. Thus modulatory effects of meals on intestinal gas transit depend on their caloric content but not their consistency.

Adaptation, Physiological↗
PubMedDate not supplied

Venous gas embolism associated with argon-enhanced coagulation of the liver.

Argon-enhanced coagulation (AEC) is a method for operative coagulation of tissues that utilizes a jet of argon gas encompassing an electrofulguration arc. Concern has been raised that the argon jet may produce harmful venous gas embolization. Two questions were addressed by this study. First, does AEC result in generation of venous gas emboli, and if so, what is the influence of gas flow rate and coagulation power on the amount of gas emboli generated? Second, does the amount of venous gas emboli generated by AEC produce harmful hemodynamic effects? Two AEC units were evaluated during coagulation of cut sections of the liver in pigs. The number of gas emboli generated was measured by an ultrasonic Doppler flow cuff placed around the caudal vena cava. Hemodynamic variables measured following AEC included systemic and pulmonary arterial pressure, pulmonary wedge pressure, and cardiac output by thermodilution. Venous gas emboli were produced during AEC of the liver. The number of gas emboli generated increased with increasing gas flow rates, but was not affected by coagulation power. No change in any of the measured hemodynamic variables was observed following AEC of the liver. The following recommendations were made: (1) Surgeons using AEC should select an argon flow rate as low as feasible to clear a bleeding tissue surface of blood and debris. (2) Although AEC seems to be associated with tolerable amounts of venous gas embolism, surgeons and anesthesiologists should be aware that the potential for harmful venous gas embolism exists. (3) In patients where extensive use of AEC is planned, appropriate monitoring and precautions for gas embolism should be undertaken.

Animals↗
PubMed1999

Frequency and clinical course of acute carbon monoxide poisoning in relation to the kind of emission gas.

The conversion of domestic supply from illuminating to natural gas in 1975 in Kraków was expected to diminish, or even eliminate the threat of CO intoxication. The aim of the study was to compare the frequency and clinical course of CO poisonings (early or delayed medical complication or death) regarding the source of CO (illuminating or natural gas). Under analysis there were adult inhabitants of Kraków treated at the Department of Clinical Toxicology from 1972 to 1974 when the main source of CO was illuminating gas and those treated from 1994 to 1996 i.e. after the conversion of domestic gas supply from illuminating to natural gas. All the cases of people who died at the scene of the accident prior to any treatment were also included. The frequency of acute poisonings among the inhabitants of Kraków was expressed by the incidence rate per 10,000 inhabitants with regard to age and sex. The severity of CO poisoning was estimated considering age, duration of exposure, carboxyhemoglobin (COHb) level, and the neurological state of patients on admission to the Clinic. Significantly higher frequency of suicidal poisonings was noted in the group of patients poisoned with illuminating gas compared to those poisoned with CO produced by incomplete combustion of natural gas (p < 0.001). No significant differences were noted considering the age of patients hospitalised in both periods. Duration of exposure was significantly longer and carboxyhemoglobin level was significantly higher in the group of patients poisoned with illuminating compared to natural gas. Significantly higher frequency of severe poisonings was noted in the group of patients intoxicated with illuminating gas compared to those intoxicated with natural gas. The frequency of acute CO poisonings in the population of Kraków determined by the incidence rate per 10,000 inhabitants was approximated to 2.4 in all the years analysed. The conversion of domestic supply from illuminating to natural gas significantly decreased the mortality rate. No differences in the number of patients suffering from medical complications were found between the two study periods. A higher incidence of late sequalae (psychoorganic and depressive syndromes) was found in the group of patients poisoned with CO produced by incomplete combustion of natural gas compared to illuminating gas.

Adolescent↗
PubMedDate not supplied

Carbon dioxide gas heating inside laparoscopic insufflators has no effect.

BACKGROUND AND OBJECTIVES: Within recent years, the insufflation technique for laparoscopy has become more important with high flow insufflators (> or = 30 L/min) and high gas turn over (> or = 800 L/procedure). Increased amounts of carbon dioxide (CO2) gas used can lead to laparoscopic hypothermia. We studied the insufflator with versus insufflators without internal gas heating (inside insufflator) as a sufficient method of hypothermia prevention at different flow rates. METHODS: With a computer-based data acquisition model, different standard insufflators with internal gas heating (Snowden Pencer) vs. without (Storz Endoflator, Storz Laparoflator, Richard Wolf, and BEI Medical) were compared regarding CO2 gas temperature at different points in the insufflation system (insufflator exit, insufflation hose end). RESULTS: Gas temperature of the Snowden Pencer insufflator, which is flow-rate dependent, increases at the exit (max. 35.4 degrees C). However, gas temperature is back to room temperature (-0.22 to +1.10 degrees C) at the end of the insufflation hose (10 ft or 3 m) for all 5 insufflators studied. Even at high gas flow rates (< or = 20 L/min), CO2 gas is at room temperature when it reaches the patient. DISCUSSION: No difference was noted regarding gas temperature between the insufflators compared. Insufflator internal gas heating, such as the Snowden Pencer insufflator, can not have a clinically significant effect because it is too far away from the patient to raise the gas temperature in the abdomen. Purchasers are misled because the gas-heating device has no measurable benefit for the patient.

Carbon Dioxide↗
PubMed2001

Isoflurane and sevoflurane anesthesia in pigs with a preexistent gas exchange defect.

BACKGROUND: Decreased arterial partial pressure of oxygen (PaO2) during volatile anesthesia is well-known. Halothane has been examined with the multiple inert gas elimination technique and has been shown to alter the distribution of pulmonary blood flow and thus PaO2. The effects of isoflurane and sevoflurane on pulmonary gas exchange remain unknown. The authors hypothesized that sevoflurane with a relatively high minimum alveolar concentration (MAC) would result in significantly more gas exchange disturbances in comparison with isoflurane or control. METHODS: This study was performed in a porcine model with an air pneumoperitoneum that generates a reproducible gas exchange defect. After a baseline measurement of pulmonary gas exchange (multiple inert gas elimination technique) during propofol anesthesia, 21 pigs were randomly assigned to three groups of seven animals each. One group received isoflurane anesthesia, one group received sevoflurane anesthesia, and one group was continued on propofol anesthesia (control). After 30 min of volatile anesthesia at 1 MAC or propofol anesthesia, a second measurement (multiple inert gas elimination technique) was performed. RESULTS: At the second measurement, inert gas shunt was 15 +/- 3% (mean +/- SD) during sevoflurane anesthesia versus 9 +/- 1% during propofol anesthesia (P = 0.02). Blood flow to normal ventilation/perfusion (V(A)/Q) lung areas was 83 +/- 5% during sevoflurane anesthesia versus 89 +/- 1% during propofol anesthesia (P = 0.04). This resulted in a PaO2 of 88 +/- 11 mmHg during sevoflurane anesthesia versus 102 +/- 15 mmHg during propofol anesthesia (P = 0.04). Inert gas and blood gas variables during isoflurane anesthesia did not differ significantly from those obtained during propofol anesthesia. CONCLUSIONS: In pigs with an already existent gas exchange defect, sevoflurane anesthesia but not isoflurane anesthesia causes significantly more gas exchange disturbances than propofol anesthesia does.

Acid-Base Equilibrium↗
PubMed1984

Toxicological and chemical characterization of the process stream materials and gas combustion products of an experimental low-btu coal gasifier.

The process gas stream of an experimental pressurized McDowell-Wellman stirred-bed low-Btu coal gasifier, and combustion products of the clean gas were characterized as to their mutagenic properties and chemical composition. Samples of aerosol droplets condensed from the gas were obtained at selected positions along the process stream using a condenser train. Mutagenicity was assessed using the Ames Salmonella mammalian microsome mutagenicity assay (TA98, with and without rat liver S9). All materials required metabolic activation to be mutagenic. Droplets condensed from gas had a specific mutagenicity of 6.7 revertants/microgram (50,000 revertants/liter of raw gas). Methylnaphthalene, phenanthrene, chrysene, and nitrogen-containing compounds were positively identified in a highly mutagenic fraction of raw gas condensate. While gas cleanup by the humidifier-tar trap system and Venturi scrubber led to only a small reduction in specific mutagenicity of the cooled process stream material (4.1 revertants/microgram), a significant overall reduction in mutagenicity was achieved (to 2200 revertants/liter) due to a substantial reduction in the concentration of material in the gas. By the end of gas cleanup, gas condensates had no detectable mutagenic activity. Condensates of combustion product gas, which contained several polycyclic aromatic compounds, had a specific mutagenicity of 1.1 revertants/microgram (4.0 revertants/liter). Results indicate that the process stream material is potentially toxic and that care should be taken to limit exposure of workers to the condensed tars during gasifier maintenance and repair and to the aerosolized tars emitted in fugitive emissions. Health risks to the general population resulting from exposure to gas combustion products are expected to be minimal.

Air Pollutants↗
PubMed1993

Clinical performance of a blood gas monitor: a prospective, multicenter trial.

OBJECTIVE: To prospectively assess the clinical performance of a fluorescent optode-based blood gas monitoring system that is designed to perform arterial pH, PCO2, and PO2 measurements as frequently as clinically required without violating the integrity of the arterial catheter tubing system or permanently removing blood from the patient. DESIGN: A prospective, multicenter study to compare modern blood gas analyzer measurements with the coinciding measurements of the blood gas monitoring system. SETTING: Four intensive care units (ICUs) in academic centers with varying patient populations, blood gas measurement routines, and blood gas laboratory facilities. PATIENTS: Adult ICU patients (n = 117), with appropriately functioning radial arterial catheters in place, who were assessed as likely to require multiple arterial blood gas measurements for > or = 2 days. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: A total of 117 patients had 1,341 concurrent blood gas analyzer and monitor measurements of arterial pH, PCO2, and PO2 over a 1- to 4-day period. The range of values were 7.14 to 7.64 for arterial pH, 19 to 98 torr (2.5 to 13.0 kPa) for PaCO2, and 38 to 413 torr (5.1 to 54.9 kPa) for PaO2. Linear regression analysis of the optode-based monitor compared with the electrode-based blood gas analyzer demonstrated r2 values of .85 for pH, .92 for PCO2, and .94 for PO2. Comparative statistical analyses for bias (mean difference between analyzer and monitor) and precision (standard deviation of the mean difference [+/- SD] between analyzer and monitor) were respectively:-0.004 and +/- 0.027 for pH; -0.8 torr (-0.11 kPa) and +/- 2.4 torr (0.32 kPa) for PCO2; -2.2 torr (-0.31 kPa) and +/- 8.7 torr (1.2 kPa) for PO2. CONCLUSIONS: Clinical performance of this fluorescent, optode-based blood gas monitoring system demonstrates stability, consistency, and accuracy comparable to modern blood gas analyzers. This system withstood the normal abuse and rigors of clinical conditions common to the ICU while reliably performing in critically ill patients for up to 80 hrs. Use of the device did not significantly alter the function or longevity normally expected from a 20-gauge radial artery catheter. We submit that this blood gas monitoring system can replace the use of blood gas analyzers for ICU patients with indwelling arterial catheters.

Adolescent↗
PubMed1995

Perfluorocarbon-associated gas exchange improves pulmonary mechanics, oxygenation, ventilation, and allows nitric oxide delivery in the hypoplastic lung congenital diaphragmatic hernia lamb model.

OBJECTIVES: To determine the efficacy of perfluorocarbon-associated gas exchange and the effects of inhaled nitric oxide during perfluorocarbon-associated gas exchange in the congenital diaphragmatic hernia lamb model. DESIGN: Prospective, nonrandomized, controlled, nonhuman trial. SETTING: Animal research facility. SUBJECTS: Fetal lambs of 16 time-dated pregnant ewes, at 80 days gestation (term 140 to 145 days). MEASUREMENTS AND MAIN RESULTS: The congenital diaphragmatic hernia lamb model was created in 16 animals. Twelve animals survived to be studied. All animals were mechanically ventilated for 4 hrs with a time-cycled, pressure-limited ventilator. Perfluorocarbon-associated gas exchange was started after 15 mins of ventilation (n = 6). Blood gases were analyzed at 30 mins and then hourly. The perfluorocarbon-associated gas exchange animals had dynamic compliance and tidal volumes measured. After 1 hr, inhaled nitric oxide (80 parts per million) was delivered to the perfluorocarbon-associated gas exchange animals for 10 mins. All blood gas parameters, including pH (6.72 +/- 0.06 vs. 7.14 +/- 0.07), PCO2 (186 +/- 12 vs. 70.5 +/- 16.7 torr [24.8 +/- 1.6 vs. 9.5 +/- 2.1 kPa]), and PO2 (48 +/- 17 vs. 156 +/- 48 torr [6.4 +/- 2.3 vs. 20.8 +/- 6.4 kPa]) were significantly improved in the perfluorocarbon-associated gas exchange-treated group at 4 hrs (p < .005). Dynamic compliance (0.13 +/- 0.02 vs. 0.32 +/- 0.06 mL/cm H2O/kg) and tidal volume (3.5 +/- 0.35 vs. 7.22 +/- 0.61 mL/kg) were also significantly (p < .001) increased in the perfluorocarbon-associated gas exchange group. In the perfluorocarbon-associated gas exchange animals, nitric oxide caused a significant (p < .05) increase in oxygenation and a reduction in pulmonary hypertension. This effect was reversed by stopping the inhaled nitric oxide. CONCLUSIONS: Perfluorocarbon-associated gas exchange significantly improved gas exchange, dynamic compliance, and tidal volumes. Furthermore, inhaled nitric oxide can be effectively delivered during perfluorocarbon-associated gas exchange to reduce pulmonary hypertension and enhance oxygenation.

Animals↗
PubMed1989

Effect of inert gas switching at depth on decompression outcome in rats.

The present investigation was performed to determine whether inert gas sequencing at depth would affect decompression outcome in rats via the phenomenon of counterdiffusion. Unanesthetized rats (Rattus norvegicus) were subjected to simulated dives in either air, 79% He-21% O2, or 79% Ar-21% O2; depths ranged from 125 to 175 feet of seawater (4.8-6.3 atmospheres absolute). After 1 h at depth, the dive chamber was vented (with depth held constant) over a 5-min period with the same gas as in the chamber (controls) or one of the other two inert gas-O2 mixtures. After the gas switch, a 5- to 35-min period was allowed for gas exchange between the animals and chamber atmosphere before rapid decompression to the surface. Substantial changes in the risk of decompression sickness (DCS) were observed after the gas switch because of differences in potencies (He less than N2 less than Ar) for causing DCS and gas exchange rates (He greater than Ar greater than N2) among the three gases. Based on the predicted gas exchange rates, transient increases or decreases in total inert gas pressure would be expected to occur during these experimental conditions. Because of differences in gas potencies, DCS risk may not directly follow the changes in total inert gas pressure. In fact, a decline in predicted DCS risk may occur even as total inert gas pressure in increasing.

Animals↗
PubMed1996

Continuous fiberoptic arterial and venous blood gas monitoring in hemorrhagic shock.

STUDY OBJECTIVE: To compare the performance of continuous fiberoptic blood gas monitoring with standard, intermittent blood gas sampling in the measurement of arterial and central venous blood gases during marked hemodynamic changes. DESIGN: Prospective, consecutive, enrollment, experimental study. SETTING: Research laboratory at a university medical center. PARTICIPANTS: Seven anesthetized, mechanically ventilated pigs. INTERVENTIONS: Severe shock was induced by hemorrhage in pigs monitored by a pulmonary artery catheter, an arterial line, and two fiberoptic blood gas sensors: one intra-arterial, and the other inserted into the superior vena cava via right internal jugular vein cutdown. Fiberoptic blood gas monitor measurements were compared with standard intermittent blood gas sampling. MEASUREMENTS AND RESULTS: A total of 184 blood gas samples were compared in seven animals at baseline, during shock, and after resuscitation. The baseline mean (+/- 1 SD) cardiac output decreased from 4.0 +/- 0.9 to 1.2 +/- 0.6 L/min during shock and returned to baseline after retransfusion (3.9 +/- 1.3 L/min). The comparison of continuous fiberoptic blood gas monitoring with intermittent blood gas sampling showed a bias+/-precision of 0.035 +/- 0.047 for arterial pH, 0.021 +/- 0.031 for central venous pH, -4.09 +/- 2.96 mm Hg (-0.55 +/- 0.39 kPa) for arterial Pco2, -3.67 +/- 2.44 mm Hg (-0.49 +/- 0.3 3 kPa) for central venous Pco2, -5.79 +/- 9.64 mm Hg (-0.77 +/- 1.29 kPa) for arterial Po2, and -7.85 +/- 8.52 mm Hg (-1.05 +/- 1.14 kPa) for central venous Po2. CONCLUSIONS: Continuous fiberoptic blood gas monitoring agrees closely with standard intermittent blood gas sampling during severe hemodynamic shifts and has a comparable accuracy for both arterial and venous blood gas measurements. Changes in venous Pco2 have recently been shown to correlate with changes in global tissue perfusion (eg, changes in cardiac output). Such data, available immediately via continuous venous blood gas monitoring, may be useful for monitoring shock and the response to resuscitation.

Animals↗
PubMed2002

Effects of nebulizing and drying gas flow on capillary electrophoresis/mass spectrometry.

This study was focused on examining the influence of gas flow parameters on capillary electrophoresis/mass spectrometry (CE /MS) performance using sheath-liquid CE /MS interfaces. The effects of nebulizing and drying gas velocity and drying gas temperature on CE separation and MS detection sensitivity were systematically determined. Nebulizing gas velocity was observed to be a critical parameter in the optimization of CE /MS method, since it affected both MS detection sensitivity, and also CE separation efficiency for one interface design tested. Better detection sensitivity was obtained when the nebulizing gas velocity was increased. However, high velocity of the nebulizing gas flow can cause a hydrodynamic bulk flow inside the CE capillary, thus clearly increasing the apparent mobility and decreasing the resolution obtained for the compounds studied. Increasing the drying gas velocity or temperature did not affect the apparent mobility or the separation efficiency and the temperature could be increased to achieve the optimal detection sensitivity in the CE /MS analysis. For comparison, the effects of nebulizing gas flow were studied using a different design of the coaxial sheath-liquid CE /MS interface, and in this case better detection sensitivity but no effect on CE separation efficiency was observed with increased nebulizing gas velocity. These different effects of nebulizing gas flow on the CE bulk flow were concluded to result from pressure differences at the tip of the CE capillaries for the different CE /MS interface arrangements. It is therefore recommended that the cross-sectional dimensions of the fused-silica and steel capillaries, and the gas streamlines, should be optimized when CE /MS interfaces are built. Moreover, the effect of gas flow on CE separation should be studied when optimizing the CE /MS operation parameters.

Buprenorphine↗
PubMed1977

Effects of pulmonary gas embolism on circulation and respiration in the dog. I. Effects on circulation.

Mongrel dogs weighing 15-25 kg and anesthetized with thiopental-gamma-hydroxybutyric acid were used to investigate the effects of pulmonary gas embolism on pulmonary arterial pressure (Pap), systemic arterial pressure (Pa) and cardiac output (Q). Pulmonary gas embolism was produced either by venous injecton or by venous infusion. The most marked effect of pulmonary gas embolism on circulation was an increase in Pap which returned to the original level after stopping the gas administration. 1. After gas injection Pap rose to a maximum within 30--60 s. The extent of this rise in Pap showed a positive correlation with the volume of the injected gas. The kind of gas (oxygen, helium, neon, nitrogen, air), however, did not influence the extent of the rise in Pap, but did influence the time of return of Pap to the original level. Carbon dioxide showed an exceptional behavior in that it had almost no effect on Pap at all. P a hardly changed with the volume of the gas injections (20--60 ml injected within 1 s); Q was not measured after gas injection (the direct Fick method is not usable in this situation). 2. Gas infusion caused a slow rise of Pap, its steepness and extent depending on the rate of infusion and on the physical properties of the infused gas. When the right ventricle was able to maintain its output, a constant level of Pap was reached after 10--15 min. In this circulatory steady state Pap appeared to be a measure of the degree of embolization. However, this relationship no longer held when the right ventricle failed as evidenced by a fall in Pap, Pa and Q. It may be concluded that pulmonary gas embolism produces a transient partial obstruction in the pulmonary circulation and that the performance of the right ventricle determines the maximum degree of embolization compatible with a sufficient circulation.

Animals↗
PubMed1993

Sampled gas need not be returned during low-flow anesthesia.

OBJECTIVE: The purpose of this investigation was to study the N2 flux between the patient and the breathing circuit, and the excess gas during N2O anesthesia with the low, fresh gas flow technique. METHODS: Forty patients were studied. After a 6-minute high, fresh gas flow denitrogenation period, the O2 fresh gas flow was set at about 4 ml/kg/min and the N2O fresh gas flow was set to maintain an inspired O2 fraction of 0.30. The excess gas flow and N2 excretion were measured by a variant of the Douglas bag method. RESULTS: The mean inspired N2 concentration reached a peak of 5.9% at 40 minutes. The estimated mean N2 excretion was 39 ml/min at 10 minutes, declining to 18 ml/min at 60 minutes. A calculation of N2 homeostasis during closed-circuit anesthesia based on the results of the patient study indicated that sampling for gas analysis actually reduces the gas costs if the sampled gas is scavenged instead of returned to the circle system, since intermittent flushing with high, fresh gas flow for denitrogenation is unnecessary in the former situation. CONCLUSIONS: Regardless of the fresh gas flow used, sampled gas need not be returned during N2O anesthesia.

Adult↗
PubMed2006

Middle ear gas loss in inflammatory conditions: the role of mucosa thickness and blood flow.

Several middle ear (ME) pathologies are associated with ME gas deficit. These include in particular the chronic otitis media diseases that are associated with inflammation (hence, increased ME mucosal blood flow) and/or reduced Eustachian tube (ET) function. The present study models the trans-mucosal gas exchange in normal and inflamed middle ears of rats. The model evaluates the role of the gas diffusion path in the ME mucosa using mucosa thickness as its index and the role of the mucosal blood flow rate on ME gas economy in order to compare between normal and inflamed MEs. An experimental method employing ME gas volume changes at constant pressure due to trans-mucosal gas exchange, and blood gas values from the literature, was used in anaesthetized rats to corroborate the model. Mucosa thickness was measured as an index of the gas diffusion path between the ME space and the ME circulation. ME inner surface area was estimated from its measured gas volume. Inflammation was inflicted by applying lipopolysaccharide (LPS) into one ear. The contralateral ear served as control. ME gas volume decreased significantly faster with time (p=0.02) in inflamed ears (-0.107 microL min(-1) +/- 0.034 S.D., n=10) versus control ears (-0.067 microL min(-1) +/- 0.036 S.D., n=10). Mucosa thickness was significantly thicker in inflamed ears (48.4 microm +/- 11.0 S.D.) versus controls (20.5 microm +/- 10.1 S.D.). The mathematical model, the experimental results, and the blood gas values were used to estimate the relative effective mucosal blood flow rate. The model predicts that in spite of almost doubling mucosa thickness in LPS treated ears, the increased gas loss in inflamed ears may be explained by increased mucosal blood flow rate. We suggest that the ability to estimate ME blood flow as obtained by applying the model to the measurements, is relevant to medical management of inflamed ME.

Animals↗
PubMed1999

Reactor Design Issues for Synthesis-Gas Fermentations.

Synthesis gas is readily obtained by gasifying coal, oil, biomass, or waste organics and represents an abundant, potentially inexpensive, feedstock for bioprocessing. The primary components of synthesis gas, carbon monoxide and hydrogen, can be converted into methane, organic acids, and alcohols via anaerobic fermentations. Bioconversion of synthesis gas is an attractive alternative to catalytic processing because the biological catalysts are highly specific and often more tolerant of sulfur contaminants than inorganic catalysts. However, because the aqueous solubilities of carbon monoxide and hydrogen are low, synthesis-gas fermentations are typically limited by the rate of gas-to-liquid mass transfer. Consequently, a major engineering challenge in commercial development of synthesis-gas fermentations is to provide sufficient gas mass transfer in an energy-efficient manner. This paper reviews recent progress in the development of synthesis-gas fermentations, with emphasis on efforts to increase the efficiency of gas mass transfer. Metabolic properties of several microbes able to ferment synthesis gas are described. Results of synthesis-gas fermentations conducted in various bioreactor configurations are summarized. Recent results showing enhancement of synthesis-gas fermentations using microbubble dispersions are presented, and studies of the mass-transfer and coalescence properties of microbubbles are described.

Journal Article↗
PubMed2002

Relative importance of gas-phase diffusive and advective tichloroethene (TCE) fluxes in the unsaturated zone under natural conditions.

It was hypothesized that atmospheric pressure changes can induce gas flow in the unsaturated zone to such an extent that the advective flux of organic vapors in unsaturated-zone soil gas can be significant relative to the gas-phase diffusion flux of these organic vapors. To test this hypothesis, a series of field measurements and computer simulations were conducted to simulate and compare diffusion and advection fluxes at a trichloroethene-contaminated field site at Picatinny Arsenal in north-central New Jersey. Moisture content temperature, and soil-gas pressure were measured at multiple depths (including at land surface) and times for three distinct sampling events in August 1996, October 1996, and August 1998. Gas pressures in the unsaturated zone changed significantly over time and followed changes measured in the atmosphere. Gas permeability of the unsaturated zone was estimated using data from a variety of sources, including laboratory gas permeability measurements made on intact soil cores from the site, a field air pump test, and calibration of a gas-flow model to the transient, one-dimensional gas pressure data. The final gas-flow model reproduced small pressure gradients as observed in the field during the three distinct sampling events. The velocities calculated from the gas-flow model were used in transient, one-dimensional transport simulations to quantify advective and diffusive fluxes of TCE vapor from the subsurface to the atmosphere as a function of time for each sampling event. Effective diffusion coefficients used for these simulations were determined from independent laboratory measurements made on intact soil cores collected from the field site. For two of the three sampling events (August 1996 and August 1998), the TCE gas-phase diffusion flux at land surface was significantly greater than the advection flux over the entire sampling period. For the second sampling event (October 1996), the advection flux was frequently larger than the diffusion flux. When averaged over the second sampling event, the advection and diffusion fluxes were comparable in magnitude. Sensitivity analyses indicate that diffusion fluxes increase significantly with increases in air-filled porosity near land surface, whereas advection fluxes do not. For October 1996, the comparable advection and diffusion fluxes were caused by high moisture content near land surface and a subsequent reduction in the diffusion flux relative to the advection flux. These results indicate that under certain environmental conditions, the organic vapor advection flux from the unsaturated zone to the atmosphere may be equal to or greater than the diffusion flux.

Air Movements↗