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PubMed2002

The effect of heat and moisture exchanger and gas flow on humidity and temperature in a circle anaesthetic system.

OBJECTIVE: The aim of the study was to measure the humidity and temperature of the inspired gas in a circle absorber system at fresh gas flows of 11/min and 31/min and assess the need of a heat and moisture exchanger (HME). METHODS: This prospective randomised controlled study received the Hospital Ethics Committee approval and informed consent. Forty adult ASA 1 and 11 patients were randomised into four groups to receive with or without HME fresh gas flow of 1L/min or 3L/min. Temperature and the relative humidity readings were taken at the start and every 10 minutes for the first hour of anaesthesia. RESULTS: There was a significantly higher relative humidity, absolute humidity and temperatures of the inspired gases at fresh gas flow of 1L/min and 3L/min with a HME compared to 3L/min without HME. Patients receiving fresh gas flows of lL/min had higher relative and absolute humidity than patients with fresh gas flows of 3L/min. However, the addition of the HME improved the absolute and relative humidity of the inspired gas in patients receiving fresh gas flow of 3l/min to a comparable level. However, the addition of a HME to a fresh gas flow of 1L/min did not significantly improve the humidity of the inspired gas. CONCLUSION: This suggests that the inherent humidifying property of the circle system at low fresh gas flow of 1L/min was sufficient in short surgeries lasting less than one hour and that the addition of a HME may not be necessary.

Adult↗
PubMed1999

Theoretical study of inspiratory flow waveforms during mechanical ventilation on pulmonary blood flow and gas exchange.

A lumped two-compartment mathematical model of respiratory mechanics incorporating gas exchange and pulmonary circulation is utilized to analyze the effects of square, descending and ascending inspiratory flow waveforms during mechanical ventilation. The effects on alveolar volume variation, alveolar pressure, airway pressure, gas exchange rate, and expired gas species concentration are evaluated. Advantages in ventilation employing a certain inspiratory flow profile are offset by corresponding reduction in perfusion rates, leading to marginal effects on net gas exchange rates. The descending profile provides better CO2 exchange, whereas the ascending profile is more advantageous for O2 exchange. Regional disparities in airway/lung properties create maldistribution of ventilation and a concomitant inequality in regional alveolar gas composition and gas exchange rates. When minute ventilation is maintained constant, for identical time constant disparities, inequalities in compliance yield pronounced effects on net gas exchange rates at low frequencies, whereas the adverse effects of inequalities in resistance are more pronounced at higher frequencies. Reduction in expiratory air flow (via increased airway resistance) reduces the magnitude of upstroke slope of capnogram and oxigram time courses without significantly affecting end-tidal expired gas compositions, whereas alterations in mechanical factors that result in increased gas exchanges rates yield increases in CO2 and decreases in O2 end-tidal composition values. The model provides a template for assessing the dynamics of cardiopulmonary interactions during mechanical ventilation by combining concurrent descriptions of ventilation, capillary perfusion, and gas exchange.

Computer Simulation↗
PubMed2006

Wrong gas/liquid partition data by gas chromatography.

In a paper published in 1992 [K.S. Reddy, J.-Cl. Dutoit, E.sz. Kováts, Pair-wise interactions by gas chromatography. I. Interaction free enthalpies of solutes with non-associated primary alcohol groups, J. Chromatogr. 609 (1992) 229] retention indices and standard chemical potential differences (SPOT-s) are given for about 160 solutes on a liquid branched paraffin hydrocarbon of the carbon number, z = 78. For the temperature dependence of the SPOT-s the proposal of Kirchhoff was accepted i.e. that at higher temperatures the molar heat capacity difference of the solute between the gas phase and the solution is nearly constant in a broad temperature range. The data were determined under conditions where the effect of adsorption could be neglected. By comparing the published data with those determined on another branched paraffin of the carbon number, z = 87 [F. Riedo, D. Fritz, G. Tarján, E.sz. Kováts, A tailor-made C87 hydrocarbon as a possible non-polar standard stationary phase for gas chromatography, J. Chromatogr. 126 (1976) 63] it is shown that the reported thermodynamic constants of solutes determined experimentally at higher temperatures (the group "H") are wrong on C78. In the present paper, the method of correction and the resulting corrected data are given. In later papers retention data are given on eight polar derivatives of the hydrocarbon C78 relative to those measured on the nonpolar standard [R. Cloux, G. Défayes, K. Fóti, J.-Cl. Dutoit, E.sz. Kováts, Pair-wise interactions by gas chromatography. III. Synthesis of isosteric stationary phases for gas chromatography, Synthesis (1993) 909; G. Défayes, K.S. Reddy, A. Dallos, E.sz. Kováts, Pair-wise interactions by gas chromatography. V. Interaction free enthalpies of solutes with primary chloro- and bromo-alkanes, J. Chromatogr. A 699 (1995) 131; K.S. Reddy, E.sz. Kováts, Pair-wise interactions by gas chromatography. II. Sociation free enthalpies of some hydrogen bonding solutes with non-associated primary alcohol groups, Chromatographia 34 (1992) 249; K.S. Reddy, R. Cloux, E.sz. Kováts, Pair-wise interactions by gas chromatography. IV. Interaction free enthalpies of solutes with trifluoromethyl-substituted alkanes, J. Chromatogr. A 673 (1994) 181; K.S. Reddy, R. Cloux, E.sz. Kováts, Pair-wise interactions by gas chromatography. VI. Interaction free enthalpies of solutes with primary methoxyalkane, cyanoalkane and alkanethiol groups, J. Chromatogr. A 704 (1995) 387; A. Dallos, A. Sisak, Z. Kulcsár, E.sz. Kováts, Pair-wise interactions by gas chromatography. VII. Interaction free enthalpies of solutes with secondary alcohol groups, J. Chromatogr. A 904 (2000) 211]. Obviously, the same data which are wrong in the nonpolar standard are also wrong in these solvents. The corrected data in the polar solvents are given in supplementary tables.

Chromatography, Gas↗
PubMed1999

Column performance and stability for high-speed vacuum-outlet GC of volatile organic compounds using atmospheric pressure air as carrier gas.

The development of lightweight, portable GC instrumentation is handicapped by the need for compressed carrier gas to drive the separation. The use of air as carrier gas eliminates the need for compressed gas tanks. If a vacuum pump is used to pull carrier gas and injected samples through the column, atmospheric pressure air can be used as carrier gas. Vacuum outlet operation also improves performance for high-speed separations by reducing detector dead time and by shifting optimal carrier gas velocity to higher values. Under vacuum outlet conditions using atmospheric pressure air as carrier gas, a 6-m-long, 0.25-mm-i.d. capillary column can generate approximately 12,500 theoretical plates, and a 12-m-long column can generate approximately 44,000 plates but with a 3-4-fold increase in separation time. The principal issues in column selection for high-speed GC with air as a carrier gas are efficiency and stability. Several bonded and nonbonded stationary phases were evaluated for use with air as carrier gas in the analysis of volatile organic compounds of interest in airmonitoring applications. These include dimethylpolysiloxane, 50% phenyl-50% methyl polysiloxane, 50% cycanopropylphenyl-50% methyl polysiloxane, trifluoropropyl polysiloxane, poly(ethylene glycol), and dicyanoallyl polysiloxane (nonbonded). The dimethyl polysiloxane and the trifluoropropyl polysiloxane columns showed good efficiency and no significant deterioration after 5 days of continuous operation with air as carrier gas. The 50% phenyl-50% methyl polysiloxane and the 50% cycanopropylphenyl-50% methyl polysiloxane columns showed poorer efficiency, and the poly(ethylene glycol) and dicyanoallyl polysiloxane columns showed excessive deterioration in air.

Air↗
PubMedDate not supplied

Small intrapulmonary artery lung prototypes. Mathematical modeling of gas transfer.

Two diffusion models have been developed to analyze gas transfer data previously measured in an intravascular artificial lung consisting of a central gas supply catheter from which are tethered a large number of blind-ended microporous fibers of equal length. A convective-diffusion model (CD) describes the countercurrent transfer of a binary gas pair when gas is supplied at constant pressure conditions, and a well mixed (WM) cycled pressure model predicts transfer when the gas supply pressure is time cycled between compression and vacuum conditions. Regression of gas to gas and liquid to gas excretion data with the CD model resulted in estimates of the liquid phase mass transfer coefficient kAI. Because these values were intermediate between the kAI expected for flow parallel to a cylinder and for flow normal to a cylinder, gas transfer was influenced by both the tethered region of the fiber that was nearly perpendicular to the axis of the test section and the free end of the fiber that rested along the wall of the test section. With a time cycled gas supply pressure, the enhanced carbon dioxide and oxygen excretion predicted by the WM model was similar to the data, but a loss in transfer efficiency with fiber length was not accounted for by the theory.

Algorithms↗
PubMed1994

Measuring oxygen uptake and carbon dioxide production in critically ill patients using a standard blood gas analyzer.

OBJECTIVE: The measurement of oxygen uptake and CO2 production in critically ill patients requires invasive monitoring or complex analysis equipment. This study investigates the hypothesis that oxygen uptake and CO2 production can be accurately determined by measuring oxygen and CO2 concentrations in samples from inspiratory and expiratory ventilator circuitry, using a standard blood gas analyzer. DESIGN: Prospective comparison of CO2 production and oxygen uptake measurements determined by use of a blood gas analyzer vs. a mass spectrometer. SETTING: University teaching hospital medical and surgical intensive care units (ICUs). PATIENTS: Critically ill patients (n = 46) receiving mechanical ventilation in the ICUs. INTERVENTIONS: PO2 and PCO2 were obtained with two new techniques and compared simultaneously with measurements on a mass spectrometer in critically ill, mechanically ventilated patients. Two methods were evaluated: a) arterial blood gas analyzer measurements of PO2 and PCO2 from fluid collected in traps on the inspiratory and expiratory limbs of the ventilator circuitry; b) PO2 and PCO2 measurements of inspiratory and expiratory gas samples collected in bags and injected directly into an arterial blood gas analyzer. Oxygen consumption and CO2 production were compared, using both methods of gas measurements. MEASUREMENTS AND MAIN RESULTS: Direct injection of gas samples collected in a bag from inspiratory and expiratory limbs of a breathing circuit into the arterial blood gas analyzer correlated very closely with mass spectrometer measurements for all variables (n = 32 sample measurements in 25 patients): fractional oxygen (r2 = .99, slope = 1.02, bias = 0.37%, precision = 0.54), fractional expired CO2 (r2 = .90, slope = 0.86, bias = -0.10%, precision = 0.15), oxygen uptake (r2 = .87, slope = 0.99, bias = 21.6 mL/min, precision = 38.0), and CO2 production (r2 = .98, slope = 0.95, bias = 7.90 mL/min, precision = 15.3). In contrast, although fractional oxygen and CO2 concentrations were approximated by analysis of fluid collected from inspiratory and expiratory traps, the values did not correlate well enough with mass spectrometer values to yield reasonable oxygen uptake or CO2 production results. CONCLUSION: We have demonstrated that direct Fick oxygen uptake and CO2 production can be accurately determined in mechanically ventilated patients, using direct injection of collected gas samples into standard blood gas analyzers. This simple, inexpensive technique can be performed using equipment readily available in any hospital.

Bias↗
PubMed1997

Continuous assessment of gastric intramucosal PCO2 and pH in hemorrhagic shock using capnometric recirculating gas tonometry.

OBJECTIVES: To test a novel device for continuous monitoring of gut intramucosal PCO2 and pH and to compare its use with conventional intermittent saline balloon-tonometry in a model of hemorrhagic shock. DESIGN: A prospective animal study. SETTINGS: A university research laboratory. SUBJECTS: Eight anesthetized, mechanically ventilated mongrel dogs. INTERVENTIONS: Two balloon-tip tonometry catheters, one conventional and one modified for continuous recirculating gas tonometry, were inserted into each animal's stomach by the oral route. Gastric intramucosal PCO2 was recorded continuously by capnometric recirculating gas tonometry throughout the experiment. After a baseline period of 90 mins, vital signs, arterial and mixed venous blood gases, and intramucosal PCO2 values were obtained by recirculating gas tonometry and by the conventional method. Using a modified Wiggers' model, the animals were then subjected to hemorrhage of up to 45 mL/kg, or the volume required to effect a decrease in mean arterial pressure to < 30 mm Hg. After 30 mins, the shed blood was reinfused and the experiment continued for an additional 30 mins. Vital signs, arterial and mixed venous blood samples, saline tonometry samples, and recirculating gas tonometry readings were obtained immediately before and 30 mins after reinfusion of blood. MEASUREMENTS AND MAIN RESULTS: Mean +/- SD baseline intramucosal PCO2 was 47.6 +/- 9.5 torr (6.3 +/- 1.3 kPa) by capnometric recirculating gas tonometry and 45.8 +/- 3.4 torr (6.1 +/- 0.5 kPa) by conventional saline tonometry (p = NS). By 5 mins after inducing hemorrhage, intramucosal PCO2 by recirculating gas tonometry had increased significantly (49.3 +/- 9.7 torr [6.6 +/- 1.3 kPa]; p < .05), and by 30 mins, it had increased to 59.7 +/- 11.3 torr (8.0 +/- 1.5 kPa; p < .001 compared with baseline). After 30 mins of hemorrhage, the conventional method showed an increase in intramucosal PCO2 to 63.0 +/- 20.9 torr (8.4 kPa +/- 2.8 kPa; p = NS vs. baseline by conventional method; p = NS vs. corresponding recirculating gas tonometry values). Gastric intramucosal pH, as determined by recirculating gas tonometry, decreased significantly at 5 mins after starting hemorrhage (7.13 +/- 0.10 to 7.10 +/- 0.10, p < .02). After 30 mins of hemorrhage, intramucosal pH decreased to 6.88 +/- 0.14 (from 7.10 +/- 0.10) by the conventional saline tonometry technique (p < .01) and to 6.89 +/- 0.10 by recirculating gas tonometry (p < .001 vs. baseline). Intramucosal PCO2 by both techniques remained significantly increased above baseline values 30 mins after reinfusion of the shed blood. CONCLUSIONS: Capnometric recirculating gas tonometry allows continuous and automated assessment of gastrointestinal tract perfusion by providing on-line measurements of intramucosal PCO2, which can also be used to derive intramucosal pH. The technique is able to detect changes in intramucosal PCO2 in response to an induced insult over intervals as short as 5 mins.

Animals↗
PubMedDate not supplied

Development of ambulatory arterio-venous carbon dioxide removal (AVCO2R): the downsized gas exchanger prototype for ambulation removes enough CO2 with low blood resistance.

We are developing an ultra compact gas exchanger to allow ambulation during arterial-venous CO2 removal (AVCO2R). The ambulatory AVCO2R gas exchanger (135 ml prime volume and 1.3 M2 gas exchange surface area) is made of polymethylpentene hollow fibers. The gas exchanger was attached to sheep carotid artery (12F) and jugular vein (14F) by percutaneous cannulae for 6 hours (n = 5). Device CO2 removal was measured and calculated at a constant blood flow rate of 1 L/min coupled with varying sweep gas from 1 to 15 L/min, and at constant sweep gas flow of 2 L/min coupled with varying blood flow from 0.5 to 1.25 L/min to determine capacity of CO2 removal at Pa CO2 = 40-50 mm Hg. Blood gases, CO2 removal and hemodynamics were recorded at 0, 3, and 6 hours. CO2 removal increased with sweep gas flow rate and with increase of device blood flow. Hemodynamics remained unchanged throughout study. Gas exchanger resistance remained stable at 2.3 +/- 0.53 mm Hg/L/min. CO2 removal with 1 L/min blood flow and 2 L/min sweep gas was 110 +/- 12 then stabilized at 85 +/- 14 mL/min to 6 hours. The compact ambulatory AVCO2R gas exchanger achieves stable, near total CO2 removal for at least 6 hours with a simple arteriovenous shunt.

Animals↗
PubMed1993

Construction and uses of a concentric catheter for gas sampling in lung airways.

A catheter for intra-airway sampling of gas concentrations was constructed from concentric polyethylene tubes. The internal tube (0.58 mm ID, 0.91 mm OD) was connected to a gas analyzer while the external tube (1.20 mm ID, 1.75 mm OD) was constantly flushed by air or a calibration gas, except during sampling. Injection and sampling dead spaces were 0.35 and 0.28 ml, respectively. Delay at 4-ml/min sampling rate was 4.0 +/- 0.2 s. The 0-90% step response to a sudden change in gas composition was 0.24 s when connected to a mass spectrometer. This catheter was used to assess tracer gas dispersion during oscillatory flow (1-20 Hz) in a straight long tube. Local concentrations measured through the catheter, after a small bolus of tracer gas was injected through the external tube, compared favorably with direct measurements through needles inserted via the tube wall and with theoretical predictions. The catheter was also used to measure intra-airway gas concentrations in dog airways during spontaneous breathing, conventional mechanical ventilation, high-frequency ventilation, high-frequency vibration ventilation, and constant-flow ventilation. It ws placed by a fiber-optic bronchoscope and used to measure local quasi-steady concentrations of CO2 and local dispersion with the bolus method. The occurrence of catheter clogging with secretions was substantially reduced with flow through the external tube. Transmitting a calibration gas through the external tube facilitated in situ recalibration of the gas analyzer without removing the catheter. The use of this catheter improved the efficiency and accuracy of measurements of gas concentrations inside lung airways.

Animals↗
PubMed1993

Gas exchange in a three-compartment lung model analyzed by forcing sinusoids of N2O.

A mathematical gas exchange model, using sinusoidal forcing functions of inert inspired gas (A. Zwart, R. C. Seagrave, and A. Van Dieren. J. Appl. Physiol. 41: 419-424, 1976), has been extended by us to include dead space (VD), a single alveolar compartment (VA) perfused with blood flow (Qp), and a shunt (Qs). In this new work we use N2O as the indicator gas in the mathematical model and in the experimental studies, in low enough concentrations [<6% (vol/vol)] to avoid anesthetic effects. Mathematical relationships between the inspired and expired N2O gas partial pressures, the blood gas N2O partial pressures, and their variation with forcing frequency are derived for a continuous ventilation uptake and a conventional anesthetic gas distribution model. We show that these gas and blood gas N2O relationships give direct derivation of cardiorespiratory parameters such as VA, Qp, the dead space-to-total ventilation ratio (VD/VT), and the shunt-to-total blood flow ratio (Qs/QT) without altering the subject's oxygenation and that they are essentially free from recirculation effects at high forcing frequencies > or = 2 min-1. Theoretical results from the model are presented for a wide range of forcing frequencies between 2 x 10(-2) and 10 min-1 (sinusoid periods 30-0.1 min), and these show that VA, Qp, and VD/VT can all be measured by N2O forcing frequencies > or = 1 min-1. We also present results from five animal studies, with an experimental inspired gas forcing frequency range of 0.125 to 2 min-1, which show qualitative agreement with the predictions of the continuous ventilation model. During these animal studies both mass spectrometric N2O respiratory gas measurements and intravascular polarographic arterial and mixed venous blood N2O partial pressure measurements were made, and examples of these in vivo measurements are presented, together with examples of the calculations derived from them.

Animals↗
PubMed1998

Pulmonary gas-exchange analysis by using simultaneous deposition of aerosolized and injected microspheres.

Numerical methods for determining end-capillary gas contents for ventilation-to-perfusion ratios were first developed in the late 1960s. In the 1970s these methods were applied to validate distributions of ventilation-to-perfusion ratios measured by the multiple inert-gas-elimination technique. We combined numerical gas analysis and fluorescent-microsphere measurements of ventilation and perfusion to predict gas exchange at a resolution of approximately 2.0-cm3 lung volume in pigs. Oxygen, carbon dioxide, and inert gas exchange were calculated in 551-845 compartments/animal before and after pulmonary embolization with 780-micrometers beads. Whole lung gas exchange was estimated from the perfusion- and ventilation-weighted end-capillary gas contents. Before lung injury, no significant difference existed between microsphere-estimated arterial PO2 and PCO2 and measured values. After lung injury, the microsphere method predicted a decrease in arterial PO2 but consistently underestimated its magnitude. Correlation between predicted and measured inert gas retentions was 0.99. Overestimation of low-solubility inert gas retentions suggests underestimation of areas with low ventilation-to-perfusion ratios by microspheres after lung injury. Regional deposition of aerosolized and injected microspheres is a valid method for investigating regional gas exchange with high spatial resolution.

Aerosols↗
PubMed1991

[Impairment of gas exchange in acute lung injury].

To demonstrate the characteristics of impaired gas exchange in acute respiratory distress syndrome (ARDS), an experimental model of lung injury was produced in 24 mongrel dogs by intravenously injecting 0.07 ml/kg of oleic acid. While allowing the animal to breathe a mixture of 0.1% CO in air, normal saline, which contained appropriate amounts of six inert gases such as SF6, ethane, cyclopropane, halothane, ether and acetone, was infused at a constant rate through a peripheral vein. After a steady state was established, the expired gas was collected and the samples of both arterial and mixed venous blood were taken simultaneously. The concentrations of the nine indicator gases (O2, CO2, CO and six inert gases) in the samples were measured in terms of a gas chromatograph, permitting analysis of the distribution of ventilation to perfusion (VA/Q) as well as the diffusing capacity to perfusion (G/Q) in injured lungs. To determine the role of hypoxic pulmonary vasoconstriction (HPV) in maintaining gas exchange in ARDS, hemodynamic and gas-exchange parameters were investigated at inspired O2 concentrations (FIO2) of either 21 or 60%. The impairment of gas exchange was examined by measuring the fractional retention (R) of the inert gases in arterial blood. Furthermore, to assess the possible contribution of vasoactive prostanoids in regulating vascular reactivity in ARDS, observations at FIO2 of 60% were repeated after administered indomethacin at a dose of 5 mg/kg. Analytical results revealed that shunt flow in experimental dogs with lung damage caused by oleic acid averaged 17%. Furthermore, widening of VA/Q distribution was found accompanied with significant contribution of extremely low VA/Q areas. In addition, most of the lung was operating in G/Q units with values ranging from 10(-3) to 10(-2) but 9.8% of total Q(QT) was received by the area with G/Q less than 10(-3), which might limit O2 exchange between the alveolar gas phase and capillary blood. Although pulmonary vascular resistance (PVR) in injured lungs observed at FIO2 of 60% was significantly smaller than the value obtained at FIO2 of 21%, QT as well as extravascular lung water did not differ in the two conditions. The R value for the indicator gas was consistently lower at FIO2 of irrespective of gas species. Administration of indomethacin caused a considerable diminution of the R value for inert gas but a rise in PVR without an appreciable change of either QT or extravascular lung water. This was followed by a significant rise in arterial PO2 from 84 to 99 Torr.(ABSTRACT TRUNCATED AT 400 WORDS)

Acute Disease↗
PubMed1987

CNS oxygen toxicity in oxygen-inert gas mixtures.

Central nervous system oxygen toxicity in hyperbaric oxygen-inert gas mixtures was studied by exposing male rats to various gas mixtures having the same oxygen partial pressure and varying pressures of inert gases. The duration of the latent period until the appearance of electrical discharges in the electroencephalogram was used as the criterion for the sensitivity to CNS oxygen toxicity. Two hundred and twenty rats with chronically implanted cortical electrodes were subjected to a single exposure to 1 of 11 different gas mixtures at ambient pressures ranging from 5 to 10 ATA. All gas mixtures had a constant oxygen partial pressure of 5 ATA and varying pressures of inert gas (helium or nitrogen). The duration of the latent period was found to be significantly different in the 11 experimental groups (P less than 0.001). While increasing the inert gas pressure, the latency gradually shortened, reaching the lowest values in mixtures of 5 ATA oxygen and 3 ATA of either inert gas. On further increase in the inert gas pressure up to a total ambient pressure of 10 ATA, the latency returned to control (pure 5 ATA oxygen) values. No difference was found between nitrogen and helium of equal partial pressures. These findings suggest that the risk of CNS oxygen toxicity in gas mixtures is not determined solely by the PO2, and even a relatively low pressure of inert gas can contribute to the imminence of hyperbaric-oxygen-induced seizures.

Animals↗
PubMed2004

Fermentation of biomass-generated producer gas to ethanol.

The development of low-cost, sustainable, and renewable energy sources has been a major focus since the 1970s. Fuel-grade ethanol is one energy source that has great potential for being generated from biomass. The demonstration of the fermentation of biomass-generated producer gas to ethanol is the major focus of this article in addition to assessing the effects of producer gas on the fermentation process. In this work, producer gas (primarily CO, CO(2), CH(4), H(2), and N(2)) was generated from switchgrass via gasification. The fluidized-bed gasifier generated gas with a composition of 56.8% N(2), 14.7% CO, 16.5% CO(2), 4.4% H(2), and 4.2% CH(4). The producer gas was utilized in a 4-L bioreactor to generate ethanol and other products via fermentation using a novel clostridial bacterium. The effects of biomass-generated producer gas on cell concentration, hydrogen uptake, and acid/alcohol production are shown in comparison with "clean" bottled gases of similar compositions for CO, CO(2), and H(2). The successful implementation of generating producer gas from biomass and then fermenting the producer gas to ethanol was demonstrated. Several key findings following the introduction of producer gas included: (1) the cells stopped growing but were still viable, (2) ethanol was primarily produced once the cells stopped growing (ethanol is nongrowth associated), (3) H(2) utilization stopped, and (4) cells began growing again if "clean" bottled gases were introduced following exposure to the producer gas.

Bioreactors↗
PubMed2004

Solvation effects on alanine dipeptide: A MP2/cc-pVTZ//MP2/6-31G** study of (Phi, Psi) energy maps and conformers in the gas phase, ether, and water.

The effects of solvation on the conformations and energies of alanine dipeptide (AD) have been studied by ab initio calculations up to MP2/cc-pVTZ//MP2/6-31G**, utilizing the polarizable continuum model (PCM) to mimic solvation effects. The energy surfaces in the gas phase, ether, and water bear similar topological features carved by the steric hindrance, but the details differ significantly due to the solvent effects. The gas-phase energy map is qualitatively consistent with the Ramachandran plot showing seven energy minima. With respect to the gas-phase map, the significant changes of the aqueous map include (1) the expanded low-energy regions, (2) the emergence of an energy barrier between C5-beta and alpha(R)-beta(2) regions, (3) a clearly pronounced alpha(R) minimum, a new beta-conformer, and the disappearance of the gas-phase global minimum, and (4) the shift of the dominant region in LEII from the gas-phase C7(ax) region to the alpha(L) region. These changes bring the map in water to be much closer to the Ramachandran plot than the gas-phase map. The solvent effects on the geometries include the elongation of the exposed N-H and C=O bonds, the shortening of the buried HN--CO peptide bonds, and the enhanced planarity of the peptide bonds. The energy surface in ether has features similar to those both in the gas phase and in water. The free energy order computed in the gas phase and in ether is in good agreement with experimental studies that concluded that C5 and C7(eq) are the dominant species in both the gas phase and nonpolar solvents. The free energy order in water is consistent with the experimental observation that the dominant C7(eq) in the nonpolar solvent was largely replaced by P(II)-like (i.e., beta) and alpha(R) in the strong polar solvents. Based on calculations on AD + 4H(2)O and other AD-water clusters, we suggest that explicit water-AD interactions may distort C5 and beta (or alpha(R) and beta) to an intermediate conformation. Our analysis also shows that the PCM calculations at the MP2/cc-pVTZ//MP2/6-31G** level give good descriptions to the bulk solvent polarization effect. The results presented in this article should be of sufficient quality to characterize the peptide bonds in the gas phase and solvents. The energy surfaces may serve as the basis for developing of strategies enabling the inclusion of solvent polarization in the force field.

Alanine↗
PubMed1977

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

In mongrel dogs weighing 15--25 kg and anesthetized with thiopental-gamma-hydroxybutyric acid the effects of venous gas infusion and injection on several respiratory variables were investigated. During spontaneous respiration pulmonary gas embolism caused an increase of the ventilatory minute volume depending on the degree of embolization. The contribution of breathing frequency and tidal volume to the increase of ventilatory minute volume varied from one animal to the other. During constant artificial ventilation pulmonary gas embolism impaired the pulmonary gas exchange depending on the degree of embolization. How far a steady-state phase in gas exchange can be reached during continuous venous gas infusion depended on the adaptation of the circulation. At severe degrees of embolization circulation as well as gas exchange became deficient. Increasing artificial ventilation during pulmonary gas embolism improved the wash-out of carbon dioxide, but hardly affected the uptake of oxygen. The most important origin of the disturbed gas exchange in pulmonary gas embolism seemed to be an increased inequality of the ventilation-perfusion ratio distribution.

Animals↗
PubMed1997

[Noise in intensive care units. Noise reduction by modification of gas humidification].

Today, noise pollution is an evident and ubiquitous problem even in intensive care units. Noise can disturb the physiological and psychological balance in patients and staff. Especially intubated patients and those breathing spontaneously through a T-piece are exposed to the noise emitted by the nebuliser used to humidity the respiratory gas. This may make patients feel uncomfortable. To reduce noise pollution in the ICU a modified T-piece has been developed and investigated. In order to heat and humidity the respiratory gas a Conchaterm III unit (Kendall company) and a thermo flow cylinder (De Vilbiss company) is necessary. While respiratory gas is flowing, water is sucked out of the heated thermoflow cylinder and nebulised according to the Venturi-Bernoulli principle. To adjust the oxygen concentration of the respiratory gas a plastic ring must be turned to either close (98% oxygen) or open a valve allowing room air to mix (40% oxygen). Noise pollution of the unit varies with admixture of room air. With a new device--a special oxygen-air mixing chamber--the oxygen concentration of the respiratory gas can be adjusted outside the thermoflow cylinder, hardly producing any noise pollution. Therefore the principle of nebulisation could be changed to humidification. A thermoflow cylinder without the nebulisation unit allows the respiratory gas to flow through the thermoflow cylinder over heated and evaporating water, hardly causing any noise pollution. In both types of T-pieces the temperature of the respiratory gas is controlled and corrected by the Conchaterm unit. As the result of these modifications, noise pollution has been reduced from 70 dB(A) to 55 dB(A). In the modified T-piece, the quality of humidification has been evaluated with a fresh gas flow of 22 l/min and at a gas temperature of 37 degrees C, not only collecting condensed water but also lost water. The modified T-piece allows a physiological humidification of the respiratory gas. The modified T-piece is a simple and efficacious substitute. Patients and staff are protected from adverse noise effects and patient well-being might be improved.

Humans↗
PubMed2000

The effect on sound generation of varying both gas flow rate and the viscosity of sputum-like gel in a simple tubular model.

Gas flows of 2, 3, and 4 L/min were directed through a sputum-like gel with viscosities of 100, 150, and 200 P and placed in a tube similar in diameter to a human segmental bronchus (4 mm), which was immersed in a bath of water. The sound produced by gas flow through the gel was recorded with a hydrophone. Sound data were subjected to time-expanded waveforms and fast Fourier transform (FFT) analysis. This study demonstrated that the number of crackles generated was directly related to the flow rate and inversely related to gel viscosity. The initial deflection width (IDW), two-cycle duration (2 CD), and peak-to-peak amplitude of crackles were significantly affected by the gas flow rate but not the viscosity of the gel. A lower gas flow rate generated crackles with longer IDW and 2 CD, but higher gas flow rates generated crackles with higher amplitude. Peak sound intensity measured from FFT increased as flow rate increased but decreased as the viscosity of the gel increased. At low gas flows, no gel-induced crackle sound was generated within the data capture window when the most viscous gel was examined. A digital video image of gas flow through the gel was captured, and this confirmed the absence of bubbles or slug formation at low flows through 200 P gel during the 3 seconds of data acquisition. This study describes some characteristics of crackles generated from different combinations of gas flow and gel viscosity and suggests that "coarse crackles" results from the explosion of gas bubbles in pulmonary secretions. Health care practitioners should consider the combined effect of rate of inspiratory gas flow and sputum viscosity during auscultation of patients' lungs.

Bronchi↗