Acetylene Method Research Articles

Measurement of cardiac output by open-circuit acetylene uptake: a computer model to quantify error caused by ventilation–perfusion inequality

The ability to assess cardiac output noninvasively has been the focus of interest for many researchers. While the open-circuit acetylene (C2H2) method seems promising, it is prone to error due to ventilation–perfusion inequality. Measurements during exercise, at high altitude or in patients with chronic obstructive pulmonary disease (COPD) could be unreliable and further validation studies under these circumstances may be needed. We used a computer model based on formulae derived from the multiple inert gas elimination technique to quantify error in measurements resulting from inequality at rest, during exercise or at high altitude. Moreover, potential errors encountered in patients with COPD were quantified. In healthy subjects, inequality related measurement error seems negligible, under both normoxic and hypoxic conditions and especially during exercise. In COPD, errors up to 20% at rest and up to 15% during exercise are expected. It is therefore concluded from our model that the open-circuit C2H2 uptake method is expected to be accurate in normal subjects. Its validity in COPD needs further study.

Compared effects of long-term pig slurry applications and mineral fertilization on soil denitrification and its end products (N2O, N2)

The long-term (9 years) effect of pig slurry applications vs mineral fertilization on denitrifying activity, N2O production and soil organic carbon (C) (extractable C, microbial biomass C and total organic C) was compared at three soil depths of adjacent plots. The denitrifying activities were measured on undisturbed soil cores and on sieved soil samples with acetylene method to estimate denitrification rates under field or potential conditions. Pig slurry applications had a moderate impact on the C pools. Total organic C was increased by +6.5% and microbial biomass C by ≥25%. The potential denitrifying activity on soil suspension was stimulated (×1.8, P<0.05) 12 days after the last slurry application. This stimulation was still apparent, but not significant, 10 months later and, according to both methods of denitrifying activity measurement (r 2=0.916, P<0.01 on sieved soil; r 2=0.845, P<0.001 on soil cores), was associated with an increase in microbial biomass C above a threshold of about 105 mg kg−1. The effect of pig slurry on denitrification and N2O reduction rates was detected on the surface layer (0–20 cm) only. However, no pig slurry effect could be detected on soil cores at field conditions or after NO3 − enrichments at 20°C. Although the potential denitrifying activity in sieved soil samples was stimulated, the N2O production was lower (P<0.03) in the plot fertilized with pig slurry, indicating a lower N2O/(N2O + N2) ratio of the released gases. The pig-slurry-fertilized plot also showed a higher N2O reduction activity, which is coherent with the lower N2O production in anaerobiosis.

Physiologic and Pharmacologic Factors Influencing GlyceroneogenicContribution to Triacylglyceride Glycerol Measured by Mass IsotopomerDistribution Analysis

An imbalance between triacylglycerol synthesis and breakdown is necessary for the development of obesity. The direct precursor for triacylglycerol biosynthesis is alpha-glycerol phosphate, which can have glycolytic and glyceroneogenic origins. We present a technique for determining the relative glyceroneogenic contribution to triacylglyceride glycerol by labeling the glycerol moiety with 2H2O. The number of hydrogen atoms (n) incorporated from H2O into C-H bonds reflects the metabolic source of alpha-glycerol phosphate and can be calculated by combinatorial analysis of the distribution of mass isotopomers in triacylglyceride glycerol. Three physiological settings with potential effects on glyceroneogenesis and glycolysis were studied in rodents. Adipose tissue acylglyceride glycerol in mice fed a low carbohydrate diet had significantly higher values of n than in mice fed a high carbohydrate diet, suggesting an increased contribution from glyceroneogenesis of from 17 to 50% on the low carbohydrate diet. Similarly, mice administered rosiglitazone had a significant relative increase in glyceroneogenesis (from 17 to 53%), indicated by an increase in adipose acylglyceride glycerol n. Fructose infusion in overnight fasted rats rapidly lowered plasma triacylglyceride glycerol n, reflecting a decreased contribution from glyceroneogenesis (from 66 to 34%) presumably because of increased glycolytic input. In conclusion, we demonstrate that the number of C-H atoms derived from cellular H2O in triacylglyceride glycerol is an informative indicator of alpha-glycerol phosphate origin and, ultimately, triacylglycerol metabolism. Under certain physiological conditions, glyceroneogenesis can be up-regulated in adipose (e.g. low carbohydrate diet) or down-regulated in liver (e.g. fructose infusion). Additionally, stimulation of glyceroneogenesis by rosiglitazone in adipose tissue may be an important factor in the antilipolytic actions of thiazolidinediones.

Use of an inhaled acetylene method to estimate changes in lung-to-lung circulation time during exercise in heart failure patients

Use of an inhaled acetylene method to estimate changes in lung-to-lung circulation time during exercise in heart failure patients

Influence of expiratory loading and hyperinflation on cardiac output during exercise.

Patients with obstructive lung disease are exposed to expiratory loads (ELs) and dynamic hyperinflation as a consequence of expiratory flow limitation. To understand how these alterations in lung mechanics might affect cardiac function, we examined the influence of a 10-cm H2O EL, alone and in combination with voluntary hyperinflation (ELH), on pulmonary pressures [esophageal (Pes) and gastric (Pg)] and cardiac output (CO) in seven healthy subjects. CO was determined by using an acetylene method at rest and at 40 and 70% of peak work. At rest and during exercise, EL resulted in an increase in Pes and Pg (7-18 cm H2O; P < 0.05) and a decrease in CO (from 5.3 +/- 1.8 to 4.5 +/- 1.4, 12.2 +/- 2.2 to 11.2 +/- 2.2, and 16.3 +/- 3.3 to 15.2 +/- 3.2 l/min for rest, 40% peak work, and 70% peak work, respectively; P < 0.05), which remained depressed after an additional 2 min of EL. With ELH, CO increased at rest and both exercise loads (relative to EL only) but remained below control values. The changes in CO were due to a reduction in stroke volume with a tendency for stroke volume to fall further with prolonged EL. There was a negative correlation between CO and the increase in expiratory Pes and Pg with EL (R = -0.58 and -0.60; P < 0.01), whereas the rise in CO with subsequent hyperinflation was related to a more negative Pes (R = 0.72; P < 0.01). In conclusion, EL leads to a reduction in CO, which appears to be primarily related to increases in expiratory abdominal and intrathoracic pressure, whereas ELH resulted in an improved CO, suggesting that lung inflation has little impact on cardiac function.

Denitrification and total fertilizer-N losses from an irrigated cotton field

In a 2-year field study, denitrification loss was measured from an irrigated sandy-clay loam under cotton receiving urea-N at 158–173 kg ha–1. An acetylene inhibition-soil core method was employed for the direct measurement of denitrification, considering also the N2O entrapped in the soil. Taking into account the N2O evolved from soil cores and that entrapped in the soil, a total of 65.7 kg N ha–1 and 64.4 kg N ha–1 was lost due to denitrification during the 1995 and 1996 cotton-growing seasons, respectively. Most (>70%) of the denitrification loss occurred during June–August, a period characterized by high soil temperatures and heavy monsoon rains. On average, 35% of the denitrification-N2O was found entrapped in the soil and the amount of entrapped N2O was significantly correlated with head space N2O concentration and with water-filled pore space. 15N-balance during the 1996 growing season revealed a loss of 71.8 kg N ha–1. It was concluded that a substantial proportion of the fertilizer-N applied to irrigated cotton is lost under the semiarid subtropical climatic conditions prevailing in the Central Punjab region of Pakistan and that denitrification is the major N loss process under irrigated cotton in this region.

Denitrification and total N losses from an irrigated sandy-clay loam under maize-wheat cropping system

Denitrification and total N losses were quantified from an irrigated field cropped to maize and wheat, each receiving urea at 100 kg N ha-1. During the maize growing season (60 days), the denitrification loss measured directly by acetylene inhibition-soil cover method amounted 2.72 kg N ha-1 whereas total N loss measured by 15N balance was 39 kg ha-1. Most (87%) of the denitrification loss under maize occurred during the first two irrigation cycles. During the wheat growing season (150 days), the denitrification loss directly measured by acetylene inhibition-soil cover and acetylene inhibition-soil core methods was 1.14 and 3.39 kg N ha-1, respectively in contrast to 33 kg N ha-1 loss measured by 15N balance. Most (70-88%) of the denitrification loss under wheat occurred during the first three irrigation cycles. Soil moisture and NO 3 - -N were the major factors limiting denitrification under both crops. Higher N losses measured by 15N balance than C2H2 inhibition method were perhaps due to underestimation of denitrification by C2H2 inhibition method and losses other than denitrification, most probably NH3 volatilization.

Electrochemical behaviour of molybdenum coated with flame CVD polycrystalline diamond film

Although natural diamond is a complete chemically-inert material for a wide range of aggressive environments, its comparative scarcity and problems for coating design have hampered its utility as a corrosion protective coating. The recent discovery and development of chemical vapour deposition methods for growing diamond crystals and polycrystalline diamond films has opened up a wide range of applications thanks to their excellent tribological, electronic and optical properties. Various applications are in progress for corrosion and combined wear and corrosion protection. This paper presents the first study of the corrosion behaviour of continuous polycrystalline diamond films using electrochemical impedance electroscopy. Diamond films have been deposited on molybdenum substrates by means of the acetylene flame combustion method (FCVD). Electrochemical behaviour has been studied in a 0.6 M NaCl solution, it being seen that despite the inert character and apparent continuity of the film, there are areas of the base material which are exposed to the electrolyte. This behaviour has been modelled by means of an equivalent circuit which allows for the corroboration of the proposed mechanism.

Denitrification in gravel-pit lakes

By constructing a budget of nitrate inputs and outputs in several gravel-pit lakes and directly measuring denitrification through the emission of N2O (using acetylene method), it was possible to evaluate the depolluting activity in the lakes in relation to groundwaters. Seasonal monitoring of the denitrification process allowed us to appraise the influence of various factors such as nitrate concentration, the bioavailability of carbon compounds and the temperature. The application of denitrification towards an improvement of the quality of the water pumped in the wellfields is discussed.

Nitrate removal by denitrification in alluvial ground water: Role of a former channel

Chemical variations of ground water in an ancient meander of the Garonne river (southern France) were compared with that of ground water located under the intensively cultivated fields of the surrounding alluvial plain. Nitrate, Mn[II] and Fe [II] concentrations were found to be very different in the two situations. The denitrification process in the former channel was identified through the natural 15N isotope enrichment on residual nitrate induced by isotope fractionation and by the in situ measurement of gaseous nitrogen losses using the acetylene method. A recent embankment leads to the progressive drying of the waterlogged soils thereby decreasing the capacity of this natural riparian wetland to regulate nitrate transfers from the agricultural plain to the river.

Perspectives on measurement of denitrification in the field including recommended protocols for acetylene based methods

Of the biogeochemical processes, denitrification has perhaps been the most difficult to study in the field because of the inability to measure the product of the process. The last decade of research, however, has provided both acetylene and 15N based methods as well as undisturbed soil core and in situ soil cover sampling approaches to implementing these methods. All of these methods, if used appropriately, give comparable results. Thus, we now have several methods, each with advantages for particular sites or objectives, that accurately measure denitrification in nature. Because of the general usefulness of the acetylene methods, updated protocols for the following three methods are given: gas-phase recirculation soil cores; static soil cores; and the denitrifying enzyme assay also known as the phase 1 assay. Despite the availability of these and other methods, denitrification budgets remain difficult to accurately establish in most environments because of the high spatial and temporal variability inherent in denitrification. Appropriate analysis of those data includes a distribution analysis of the data, and if highly skewed as is typically the case, the most accurate method to estimate the mean and the population variance is the UMVUE method (uniformly minimum variance unbiased estimator). Geostatistical methods have also been employed to improve spatial and temporal estimates of denitrification. These have occasionally been successful for spatial analysis but in the attempt described here for temporal analysis the approach was not useful.

Asymbiotic dinitrogen fixation by tundra in the Imnavait Creek drainage, Alaska, USA

N2 fixation by free-living microorganisms was investigated at an intensively studied low Arctic site near Toolik Lake in the northern foothills of the Brooks Range, Alaska, during July 1987. Four characteristic vegetation associations along an elevational gradient were assayed using minimally disruptive in situ acetylene reduction assay methods. The acetylene reduction rates did not differ significantly among vegetation associations. The mean rate for the site was 9.60 μmol m−2 h−1 or 90 μg N m−2 day−1, which is within the range of values given for other Arctic and alpine tundra studies. The complex microtopography and resulting patchy distribution of free-living and phycobiont diazotrophs is the most likely cause of the high spatial variability in acetylene reduction activity. Rates were most variable among samples from the lowest position, a riparian site. The potential contribution of heterotrophic diazotrophs was examined through a laboratory enrichment study. Soils from the two lower slope positions showed dramatic responses to added C, suggesting that heterotrophs may contribute fixed N2 to this system.

Field Denitrification Estimation by Nitrogen‐15 and Acetylene Inhibition Techniques

AbstractDirect quantification of denitrification N loss from N‐fertilized soils has been a long standing problem in soil N research. Recently 15N or acetylene inhibition methods have been used to make in‐field estimates of N loss from the soil resulting from denitrification. both methods have potential problems that may affect the validity of the data acquired. A field study was conducted to compare the acetylene inhibition approach with a 15N technique for measuring total N evolution (N2O + N2) from a N‐fertilized soil. Miniplots were established in an unplanted clay loam soil and fertilized with 15N‐labeled ammonium sulfate. Total N emissions were followed during three irrigation and subsequent drying events. The total N emissions measured by the acetylene method averaged 12 kg N ha−1 compared to 9 kg N ha−1 measured by the 15N technique from the nonacetylene‐treated plots. This difference between methods was small relative to the spatial variability observed in measuring gaseous N emissions in the field.

Cardiac output determined by the CO2 rebreathing method with correlation of lung-bag volume shrinkage.

The purpose of this study was to elucidate the effect of lung-bag volume shrinkage on P'VCO2 estimated by the CO2 rebreathing method and to correct its effect in calculation of cardiac output. The P'VCO2 was extrapolated with the linear relationship between dPACO2/dt and PACO2 during rebreathing. The P'VCO2 was higher than real mixed PCO2 by 0.82 mmHg at rest, by 1.35 mmHg at 50W, 1.57 mmHg at 100W, and 3.06 mmHg at 150W considering the effect of lung-bag volume shrinkage detected by argon concentration. The cardiac output obtained by the CO2 rebreathing method with correction of above differences was in good agreement with that determined by the acetylene method (r = 0.930, p less than 0.001). When the cardiac output was plotted against O2 uptake, our results and the regression line were fairly close to the reported regression lines.

The Acetylene Inhibition Method for Short‐term Measurement of Soil Denitrification and its Evaluation Using Nitrogen‐13

AbstractAcetylene was found to effectively inhibit the reduction of N2O by anaerobic soils. With concentrations of C2H2 above 0.1 atm, added NO3‐ was quantitatively converted to N2O, and added N2O was reduced at an insignificant rate. Experiments with 13N demonstrated that at low soil nitrate concentrations at least 0.1 atm C2H2 was required for effective inhibition. Denitrification rates determined by 13N and by C2H2 inhibition methods correlated well, as did determinations of N2O/(N2 + N2O). The methods also revealed that an acceleration in denitrification rate occurred within a few hours after soil was exposed to anaerobic conditions. The acetylene method was generally used to measure denitrification rates in soils incubated as anaerobic slurries, but was also used to determine rates for field moist aggregrates incubated anaerobically and aerobically. When assayed as anaerobic slurries, initial denitrification rates ranged from 0.1 to 0.7 nmoles N gas · soil−1 · min−1 for the mineral soils examined. The denitrification rate in aerobic aggregrates was approximately 1,000 times less, showing the strong inhibitory effect of O2 on the indigenous denitrifying enzymes.

Pulmonary parenchymal tissue volume measurements in graded degrees of pulmonary edema in dogs.

We investigated the accuracy and the sensitivity of a modification of the acetylene inhalation technique for the determination of lung tissue volume (Vt) during various grades of hemodynamic pulmonary edema in 23 dogs. After base-line acetylene measurements were obtained, intravascular driving force (pulmonary wedge pressure minus intravascular colloid osmotic pressure) was varied between -8 and +71 mm Hg by the inflation of an intra-aortic ballon and the infusion of isotonic saline. After 30 minutes at this new driving force, four timed acetylene samples were again collected. Vt (when factored by alveolar volume, VA) increased from base line to 0.23 plus or minus 0.07 ml/ml between a driving force of 0 and + 17 mm Hg. This same change in Vt/VA was accompanied by an increase in the lung wet weight-dry weight ratio from 3.84 plus or minus 0.31 to 5.2 plus or minus 0.25. Vt was 271 plus or minus ml compared with an actual lung wet weight of 288 plus or minus 57 g; Vt tended to overestimate lung wet weight in severe pulmonary edema. Alloxan-induced pulmonary edema (6 dogs) tended to parallel these data. We conclude that the acetylene method may ve a relatively accurate noninvasive method for the determination of increasing lung water in pulmonary edema.

A modified acetylene method for the determination of cardiac output during muscular exercise.

A modified acetylene method of determining cardiac output during exercise is described, in which acetylene is absorbed by combustion in a combustion pipette fitted to a Lloyd gas analyser. The procedure is more sensitive than Christensen's (1931) and requires lower acetylene concentrations. It. is suitable for determination of cardiac output during maximum exercise. The standard deviation of a single result from the mean of a series of estimates at maximum work intensity was +− 06 1/min at outputs of 20—25 1/min. The results of cardiac output determined at various work rates agreed closely with published results obtained by direct methods.

Algal and bacterial non-symbiotic nitrogen fixation in paddy soils

The nitrogen fixing activity of three Ivory Coast soils was tested in the laboratory by the acetylene reduction assay and the Kjeldahl method. Nitrogen fixation due to algae was estimated to be of the order of 4 to 8 (acetylene method) and 7 μg N per g soil per day (Kjeldahl method). Nitrogen fixation due to bacterial activity in the rice rhizosphere was estimated to be of the order of 2 to 5 (acetylene method) and 1 to 3 μg N per g soil per day (Kjeldahl method). These results emphasize the importance of the bacterial nitrogen fixation in the rhizosphere which had been hitherto overlooked. Comparison of acetylene method and Kjeldahl method results shows discrepancies the origin of which has been discussed. Time course of acetylene reduction by rhizosphere soils exhibits a lag phase which may be attributed to Postgate's switch off — switch on process.

水圏における窒素固定に関する微生物学的研究-VI.

In various water environments, the rate of nitrogen fixation was estimated by the use of the acetylene method which was modified by the present authors in the previous paper. The rate ranged from 0.3 to 4.46mg N/hr/m3, depending on seasons, localities of the water regions, etc. Considerably high values were observed in the water of fish culture ponds and the rate estimated in the sea water of Maizuru Bay was similar to that in fresh water environments. Nitrogen fixation by microorganisms of size larger than 5 μ amounted to 30-50% of the total activity of the water in fresh water environments. In fresh water regions, nitrogen fixation proceeds actively in the bottom sediments rather than in the water.

Alveolar-arterial gas tension differences during graded exercise.

Alveolar-arterial gas tension differences during graded exercise.