Oxygen Equivalent Research Articles

Independence of ventilation and blood lactate responses during graded exercise.

The effect of power output increment, based on an increase in pedal rate, on blood lactate accumulation during graded exercise is unknown. Therefore, in the present study, we examined the effect of two different rates of power output increments employing two pedal rates on pulmonary ventilation and blood lactate responses during graded cycle ergometry in young men. Males (n = 8) with an mean (SD) peak oxygen uptake of 4.2 (0.1) l.min-1 served as subjects. Each subject performed two graded cycle ergometer tests. The first test, conducted at 60 rev.min-1, employed 4 min of unloaded pedaling followed by a standard power output step increment (SI) of 60 W every 3rd min. The second test, conducted at 90 rev.min-1, employed 4 min of unloaded pedaling followed by a high power output step increment (HI) of 90 W every 3rd min. Venous blood was sampled from a forearm vein after 5 min of seated rest, 4 min of unloaded pedaling, and every 3rd min of graded exercise. Peak exercise values for heart rate, oxygen uptake (VO2), and ventilation (VE) were similar (P > 0.05) for SI and HI exercise, as was the relationship between VE and VO2, and between VE and carbon dioxide production (VCO2). However, the relationship between blood lactate concentration and VO2 was dissimilar between SI and HI exercise with blood lactate accumulation beyond the lowest ventilatory equivalent of oxygen, and peak exercise blood lactate concentration values significantly higher (P < 0.05) for SI [12.8 (2.6) mmol.l-1] compared to HI [8.0 (1.9) mmol.l-1] exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Metallkomplexe mit funktionalisierten Schwefelliganden, VIII [1]. 4-Phenyl-1,2-dithiolan-1-oxid, ein stabiles, fünfgliedriges cyclisches Thiosulfinat / Metal Complexes of Funetionalized Sulfur Containing Ligands, VIII [1]. 4-Phenyl-1,2-dithiolane-1-oxide, a Stable, Five-Membered Cyclic Thiosulfinate

Sensitized photooxidation of 4-phenyl-1,2-dithiolane 1 has been studied. Reacting it with 0.5 mole equivalents o f singlet oxygen, a mixture of 1, 4-phenyl-1,2-dithiolane-1-oxide 2, and 4-phenyl-1,2-dithiolane-2-dioxide 3 is produced. Using one mole equivalent of singlet oxygen, 3 is obtained in high yields. The chemical oxidation of 1 using H2O2/HOAc yields pure 2. With 2 a diastereoselectivity of 10:1 is observed. The oxidative addition of 1 to L2Pt(η2-C2H4)[L=PPh3 (4), 1/2 dppe (5)] leads to the 3-phenyl-propane dithiolato complexes 6a,b. The platinum(O) com pound 4 reacts with 2 to give the bimetallic compound 7 and the monometallic species . These complexes contain the 3-sulfido-l-(2-phenyl)-propanesulfenato ligand. All com pounds have been characterized by their spec­ troscopic data.

Metalimnetic Oxygen Depletion: Organic Carbon Flux and Crustacean Zooplankton Distribution in a Quarry Embayment

Metalimnetic Oxygen Depletion: Organic Carbon Flux and Crustacean Zooplankton Distribution in a Quarry Embayment

Acetoxylation of toluene catalyzed by supported Pd-Sn catalysts

The toluene acetoxylation run in the presence of Pd(OAc) 2, Sn(OH) 2 and KOAc was found to proceed through three characteristic stages of the oxygen absorption. In the first stage, the system produces a Pd(II) [Sn(II)] 2(OAc) 6 complex which remains homogeneous until the end of that phase. In the second region of the oxygen uptake curve there is an absorption of one equivalent of oxygen after which a heterogeneous palladium-tin species precipitates on the surface of the silica carrier present in the system. In the third region the oxygen adsorption is related only to the oxidation of the toluene to benzyl acetate and benzylidene diacetate which are formed in a 6.7/1 ratio. The turnover frequencies determined on the basis of the reaction rates were 3–4 times higher than observed with the reference system which used Sn(OAc) 2 as the tin precursor. An additional triple increase in the rate was observed for the same optimized system when the oxidation was begun in the presence of ICN 60 silica. The activity of these in-situ supported Pd/Sn species depends strongly on the porosity of the silica carriers. The optimal average pore diameter was found to be near 20–30 Å. The samples with variable Sn/Pd ratios and with variable loading exhibit strongly suppressed hydrogen chemisorption and single turnover (STO) surface reactivity which is thought to result from an SMSI state of the metallic palladium caused by the co-adsorbed tin.

Studies of the hydroxylase component of soluble methane monooxygenase from Methylococcus capsulatus (Bath)

Methane monooxygenase catalyses NAD(P)H2- and C>2-dependent oxidation of methane to methanol and this reaction initiates the metabolic pathway that supplies the total carbon and energy needs of methanotrophic bacteria. The soluble methane monooxygenase isolated from Methylococcus capsulatus (Bath) is comprised of three proteins: a hydroxylase (Afr. 250 kDa), a reductase {Mr. 38.6 kDa) and a regulator protein (named protein B, Mr. 16 kDa), all three of which are required for enzymatic activity. The hydroxylase is comprised of three polypeptides (a, 60.6 kDa; P, 45.0 kDa; y, 19.8 kDa) of a2P2Y2 stoichiometry and contains a non-heme binuclear iron active centre responsible for methane hydroxylation and a wide variorty of hydrocarbon oxidations. The reductase transfers electrons from NADH to the hydroxylase, and protein B appears to have several regulatory activity. Characterisation of oxygen donor for soluble methane monooxygenase has shown that oxygen is necessary for sMMO-catalysed oxygenation but the high oxygen concentrations result in a decrease of sMMO activity since toxic oxygen species, superoxide anion or peroxide ion, appeared in the reaction system under high oxygen concentration conditions. Characterisation of alternative donors, NO and N2O, demonstrated that they are not suitable for sMMO. Also, the designed experiments to encourage sMMO to catalyse radical recombination reactions were not successful either using non-natural donors or mimicing the conditions used for chemical oxidative coupling. These studies may indicated that upgrading of methane by the native sMMO complex would be impossible. Hydrogen peroxide can replace protein B, the reductase, oxygen and NADH in activation of the hydroxylase of sMMO from Methylococcus capsulatus (Bath) during catalysis of the oxidation of hydrocarbons. Hydrogen peroxide activation of the hydroxylase occurs at the active site iron atoms. The O atom derived from H2O2 is transferred to the substrates and decomposition of peroxide to O2 does not occur in the reaction. The homolytic cleavage of Fe bound O-O- pathway is favoured in the H202-driven system and hydroxyl radicals may be involved in the reaction cycle. Protein B may not only be in controlling electron flow in the sMMO system, but may also be connected with O2 binding to the active site. Proteolysis of the hydroxylase showed that the hydroxylase could be degraded by chymotrypsin and trypsin, but chymotrypsin could greatly degrads the protein resulting in a loss of protein activity. However, even when using a high concentration of trypsin to cleave the hydroxylase, a high percentage of the catalytic activity was still observed. Proteolysis of the hydroxylase by chymotrypsin or trypsin demonstrated that the iron atoms in the hydroxylase active site played an important role in the oxidation of hydrocarbons and that the certain structure of the hydroxylase protein were all necessary for enzyme activity. Chemical modification of the hydroxylase was also studied and the results showed that the hydroxylase protein thermostability could be raised by using crosslinking reagent, polyoxyethylene bis(imidazolyl carbonyl) and that the the PEG-modified hydroxylase could show activity in several organic solvents when H2O2 was used to provide oxygen and electron equivalents.

Increased physiological dead space during exercise after bronchodilation in cystic fibrosis.

Bicycle ergospirometry was performed on 14 patients with cystic fibrosis (CF), for evaluating the effects of salbutamol and theophylline on the ventilatory response to exercise. After 1 week without bronchodilator therapy the patients cycled at 1/3 and 2/3 of their individual maximal working capacity (Wmax). The test was repeated three times after treatment with salbutamol, theophylline, or both drugs, respectively. After the combined therapy, physiological deadspace, ventilation, ventilatory equivalent of oxygen, and end-expiratory oxygen pressure increased significantly during steady state exercise at 1/3 Wmax. Similar, although not statistically significant changes, were observed after monotherapy with salbutamol or theophylline and during exercise at 2/3 Wmax. These effects could not be predicted by any lung function tests at rest or by the Shwachman-Kulczycki score. The results indicate that in some patients with CF bronchodilators can impair lung function during exercise. In conclusion, the effects of medication on exercise performance of patients with CF have to be considered. Especially, the use of bronchodilators requires a careful evaluation of their real benefit in each individual patient.

A new method for the evaluation of anaerobic running power in athletes.

A new maximal anaerobic running power (MARP) test was developed. It consisted of n.20-s runs on a treadmill with a 100-s recovery between the runs. During the first run the treadmill speed was 3.97 m.s-1 and the gradient 5 degrees. The speed of the treadmill was increased by 0.35 m.s-1 for each consecutive run until exhaustion. The height of counter-movement jumps and blood lactate concentration ([la-]b) were measured after each run. Submaximal ([la-]b = 3 mmol.l-1 and 10 mmol.l-1) and maximal speed and power (W3mmol, W10mmol and Wmax, respectively) were calculated and W was expressed in oxygen equivalents according to the American College of Sports Medicine equation. Thirteen male athletes whose times over 400 m ranged from 47.98 s to 54.70 s served as subjects. In the MARP-test the speed at exhaustion was 6.89 (SD 0.28) m.s-1 corresponding to a Wmax of 118 (SD 5) ml.kg-1 x min-1. The peak [la-]b after exhaustion was 17.0 (SD 1.6) mmol.l-1. A significant correlation (r = 0.89, P < 0.001) was observed between the Wmax and the average speed in the 400-m sprint. The maximal 20-m sprinting speed on a track and W10mmol correlated with both the Wmax and the 400-m speed. It was concluded that the new method allows the evaluation of several determinants of maximal anaerobic performance including changes in the force-generating capacity of leg muscles and [la-]b relative to the speed of the sprint running. the [la-]b at submaximal sprinting speed was suggested as describing the anaerobic sprinting economy.

Heat equivalents of noxious substances: a pollution indicator for environmental accounting

The energy requirements of pollution control in coal and nuclear power plants and the resulting heat emissions are computed in first-order waste heat analysis. Pollution control reduces injection of noxious substances into the biosphere to values below limits determined by risk assessment and social consensus. The heat emissions associated with pollution control are still a relatively benign environmental burden. They can be considered as a thermodynamic indicator of the (least troublesome) pollution potential of a given energy carrier and its appropriate energy conversion process. In this sense, environmental accounting with respect to a reference state can be done with the help of the heat equivalents of noxious substances (HEONS). They are defined as the waste heat generated by pollution control in a production process of given utility output divided by the primary energy input into a non-pollution-controlled production process of the same utility output. In the discussed scenarios the HEONS are about 0.7% for 80% NO x reduction, 1–4.4% for 60–95% desulfuration, 38% for 66% cryogenic CO 2 removal and deep ocean storage, and 0.08%–3%; for the disposal of radioactive nuclear fuel rods in interstellar space via electromagnetic launchers. The relative primary energy required for the indicated processes of pollution control is equal to the HEONS with the exception of the nuclear fuel rods where 0.02–0.9% have to be added for the energy lost in space. Similar to the oxygen equivalents of organic waste water pollutants in the German sewage levy law, the heat or energy equivalents of noxious substances may serve as one criterion for charging taxes and levies to energy carriers.

Myocardial Oxygen Consumption and Lactate Release by the Hypoxic Hagfish Heart

ABSTRACT Myocardial oxygen consumption and lactic acid release were measured in the isolated heart of a hagfish (Eptatretus cirrhatus Forster) perfused in vitro. Two different ranges of partial pressures of oxygen were employed ( 3.87–5.87 and 1.60–2.67kPa). All hearts released lactate into the perfusate, but the rate of release was greater and was depressed at the lower . When energy production through the glycolytic pathway to lactate is converted to oxygen equivalents and added to measured oxygen consumption rates, over a wide range of power outputs and different values of , the data can be fitted to a single linear regression line. The rate of oxygen consumption of the hagfish myocardium, so obtained, is similar to values reported for teleost fish. The unusual ability of the hagfish myocardium to support perhaps up to 50% of its maximal power output through anaerobic metabolism is related to its extremely low cardiac energy demand.

The Relationship between Specific Dynamic Action (SDA) and Protein Synthesis Rates in the Channel Catfish

The purpose of the study was to investigate the relationship between specific dynamic action (SDA) and the rate of protein synthesis following a simulated meal consisting of an essential amino acid infusion. After such an infusion, the O₂ consumption rates of catfish approximately doubled, and the rate of protein synthesis in white muscle rose from 1.3 to 2.86 mg g⁻¹ d⁻¹. After pretreatment with the protein synthesis inhibitor cycloheximide, there was no significant SDA (defined as the increase in oxygen consumption) and the rate of protein synthesis fell to 0.34 mg g⁻¹ d⁻¹. There was good agreement between the magnitude of the SDA observed, the magnitude of the increase in protein synthesis, and theoretical calculations of the expected metabolic costs of protein synthesis based on oxygen equivalents for ATP production and ATP requirements for protein formation. The results support the idea that SDA may be directly attributable to the cost of protein synthesis, and therefore to the metabolic cost of growth.

Fluxes of Oxygen Equivalents and Nutrients across the Sediment-Water Interface after Combined Sewer Overflows

The fluxes of oxygen into sediments and the release rate of COD, methane and nitrogen after deposition of fresh sewage sludge were measured in an experimental laboratory apparatus. Effects of the initial surface loading revealed a progressive contribution of COD release to the flux of oxygen equivalent to increased loading. Lower oxygen concentrations had the same effect. The actual conversion rate of the organics in the sediments was lower than the potential maximal aerobic degradation rate and higher than the anaerobic rate of hydrolysis. Preferential oxidation of soluble organics at the sediment interface over particulate material limits the release of COD except for high-loaded systems or at low DO concentrations.

Reappraisal of the Weir equation for calculation of metabolic rate

In 1949 Weir (3) demonstrated that the metabolic rate calculated from respiratory gas exchange measurements is to a close approximation proportional to the difference in percentage oxygen content between inspired and expired air. Although values for the energy equivalent of oxygen consumed and for the respiratory quotient for the oxidation of various nutrients have been revised since 1949, we show that the error in the calculation remains generally below 0.5% for the oxidation of dietary carbohydrate, fat, and protein. Where the original equation is uncritically applied to situations in which other nutrients are being oxidized, the error may reach 3%, although alternative methods for calculating the metabolic rate may be similarly in error. We give the derivation from first principles of the general mathematical solution to the calculation of the metabolic rate following Weir's method. Examples are provided of the subsequent derivation of specific equations for the more precise calculation of the metabolic rate where different combinations of nutrients are being oxidized.

Validation of [1-11C]acetate as a tracer for noninvasive assessment of oxidative metabolism with positron emission tomography in normal, ischemic, postischemic, and hyperemic canine myocardium.

Extraction and clearance kinetics of [1-11C]acetate were examined in 65 experiments in 30 open-chest dogs. Twenty-nine studies were performed at control, 13 during ischemia, eight after reperfusion, 13 during dipyridamole-induced hyperemia, and two during alteration of cardiac workload. [1-11C]Acetate was injected directly into the left anterior descending coronary artery, and myocardial tissue-time activity curves were recorded with a gamma probe. The single-pass extraction fraction averaged 64.2 +/- 9.7% in control, 65.3 +/- 9.1% in ischemia, 70.0 +/- 4.4% in reperfusion, and 46.5 +/- 7.4% in dipyridamole-induced hyperemia groups. 11C clearance was biexponential in all cases. The rate constant k1 for the first rapid clearance phase correlated closely with myocardial oxygen consumption (r = 0.94) in control, ischemia, reperfusion, and dipyridamole-induced hyperemia groups. Monoexponential fitting of only the first linear part of the clearance curve yielded the rate constant kmono, which also correlated with myocardial oxygen consumption (r = 0.96). Arterial lactate concentrations and the amount of free fatty acid oxygen equivalents consumed by the myocardium were shown to have a small but statistically significant impact on the relation between [1-11C]acetate clearance rate constants and myocardial oxygen consumption. The fraction of 14CO2 activity contributing to overall 14C activity leaving the myocardium after simultaneous injection of [1-14C]acetate (n = 24) was relatively high in all cases (97.4 +/- 2.5% in control, 89 +/- 2.6% in ischemia, 94.1 +/- 3.5% in reperfusion, and greater than 99% in dipyridamole groups), indicating that externally measured 11C clearance corresponds to CO2 production and thus to tricarboxylic acid cycle activity. In conclusion, the results validate the use of [1-11C]acetate as a tracer of oxidative myocardial metabolism for use with positron emission tomography.

Physiological effects of inspiratory resistance on progressive aerobic work

The purpose of this study was to determine the potential effects on progressive aerobic work while breathing through a new military type chemical and biological (CB) respirator loaded with three different types of purifying canisters. Twelve healthy well-motivated male subjects (mean age 23 +/- 3 years) participated in the study. Results indicated that mean maximal oxygen uptake (VO2max), time to exhaustion, respiratory exchange ratio, rate of perceived exertion, respiratory rate and tidal volume at exhaustion, maximal lactate and the 2-min post-exercise lactate were not significantly influenced when breathing with the respirator and the canisters in comparison to a laboratory valve. Mean pulmonary ventilation, however, was reduced by 21% while oxygen and carbon dioxide ventilatory equivalents were significantly lower by 9% and 8% respectively. Review of the stage-by-stage responses to the treadmill test between the laboratory valve and respirator/canister conditions indicated no significant differences (NS) in oxygen uptake but slightly lower heart rates (NS). Ventilation was not influenced by the canisters until 80% of VO2max at which time the mean oxygen ventilatory equivalent became significantly lower. Blood lactate was significantly depressed between 60% and 90% VO2max under the respirator/canister conditions. It was concluded that, although physiological adaptation occurred, breathing with the new CB respirator and each of the three purifying canisters had no detrimental effect on progressive aerobic work to exhaustion. However, prolonged work at intensities greater than 80-85% of VO2max would in all probability be impaired when breathing with the CB mask and the canisters.

Lactate, oxygen uptake, and cycling performance in triathletes.

To assess the relationship of exercise test variables to each other and to bike race times in an ultra-distance triathlon, we studied 24 participants (14 men, 10 women) in the 1985 Hawaii Ironman Triathlon, using a graded, maximal cycle ergometer test with gas exchange and blood lactate (LA) measurements at each work load. Exercise test variables were oxygen uptake (VO2) and heart rate (HR) at the lactate and ventilatory thresholds. Lactate threshold (LT-1) was defined as the exercise intensity that elicited a 1 mM increase in blood lactate concentration above the value measured during the first work load for each subject. Variables were also examined at the lactate thresholds of 2 mM and 4 mM. Ventilatory thresholds (VT) were identified as the points at which the ventilatory equivalent of oxygen (VE/VO2) increased without a corresponding increase in the ventilatory equivalent of carbon dioxide (VE/VCO2). Mean peak oxygen uptake (peak VO2) for this sample of Ironman triathletes was 57.4 ml.kg-1.min-1. Cycle peak VO2 was inversely correlated, r = 0.68 (P less than 0.0002) with bike finish time. VO2 and HR as well as the respective percentages of maximum were higher at all lactate thresholds than at VT (P less than 0.0001). Therefore VT should not be used to identify a lactate threshold in ultra-endurance triathletes. VO2 values at the lactate and ventilatory thresholds were not highly related to bike finish time (r = -0.26 to -0.58). Fractional utilization of peak VO2 (% peak VO2), HR, and % peak HR at thresholds were not related to bike finish time (r = -0.01 to 0.06).(ABSTRACT TRUNCATED AT 250 WORDS)

A study of ionization electrons drifting over large distances in liquid argon

We have measured the lifetime of electrons drifting in liquid argon using a gridded ionization chamber with a drift gap of 153 mm. The electrons were produced by the passage of cosmic rays through the chamber. We find a best fit for the electron lifetime τ at 5 V/cm of 9.2 ms (with 13.2 > τ > 7.1 ms at 95% CL). This value is consistent with all the data below 15 V/cm. This corresponds to an impurity concentration ρ = 0.03 ppb oxygen equivalent. The attenuation length calculated from the above lifetime is 18 m for a field of 1 kV/cm. The liquid remained in the chamber for 14 weeks with no recirculation system and suffered no noticeable deterioration with respect to the lifetime or the pulse height. The low field mobility μ 0 has been measured for fields up to 150 V/cm and we find a value of 545 ± 4 cm 2 V −1 s −1 which is consistent with measurements by other authors. The electron yield as a function of the electric field strength has been measured down to 3 V/cm. The results seem to indicate the need for a modification of the geminate recombination theory.

N-Hydroxy-N-arylacetamides. V. Differences in the Mechanism of Haemoglobin Oxidationin Vitro, byN-hydroxy-4-Chloroacetanilide andN-Hydroxy-4-Chloroaniline

1. Autoxidation of N-hydroxy-4-chloroaniline(I) in buffer pH 7.4 was rapid and yielded 4,4'-azoxybischlorobenzene, 4-chloronitrosobenzene, 4-chloronitrobenzene, and 4-chlorophenyl nitroxide. In contrast, autoxidation of N-hydroxy-4-chloroacetanilide(II) was very slow, since in ether and water 78 and 92%, respectively, had decomposed in six months. 2. Haemoglobin(HbO2)-catalysed autoxidation of (I) occurred at a molar ratio of haemoglobin-Fe2+ to (I) of less than 0.25 and was accompanied by ferrihaemoglobin(HbFe3+)-formation and oxygen consumption. Coupled oxidation of HbO2 with (I) occurred at a molar ratio of greater than 0.2 and was accompanied by liberation of oxygen and the formation of HbFe3+, haemoglobin-4-chloronitrosobenzene complex, HbO2, desoxyhaemoglobin, 4-chloronitrosobenzene, 4-chloronitrobenzene, 4-chloroaniline, 4,4'-azoxybischlorobenzene, and 4-chlorophenyl nitroxide. At an equimolar ratio of 10(-3) M haemoglobin-Fe2+ to (I), 96% HbO2 was converted into HbFe3+ (50%) and haemoglobin-4-chloronitrosobenzene complex in the initial fast phase of the reaction, but only 34% of the bound oxygen was liberated, the rest was sequentially reduced to water. (I) completely disappeared, and 4-chloronitrosobenzene was the major metabolite, mainly bound to haemoglobin. 3. Chemical oxidation of (II) by PbO2 in benzene produced acetyl 4-chlorophenyl nitroxide, whose spontaneous decomposition gave 38% 4-chloronitrosobenzene, 33% N-acetoxy-4-chloroacetanilide, 10% 4-chloroacetanilide, and 8% 4-chloronitrobenzene. Its spontaneous decomposition in water also followed second order kinetics, K = 350 l mol-1 sec-1 and yielded N-(2-acetylamino-5-chlorophenyl)-p-benzo-quinoneimine-N-oxide in addition. 4. In the coupled oxidation of 10(-3) M haemoglobin-Fe2+ with 10(-3) M (II), 75% HbFe3+ was formed after 1 h, but only one third of the equivalent of oxygen was released, and two thirds were reduced to water. Concentration of (II) decreased by 5% only, indicating that one mol of (II) had catalysed the oxidation of 15 equivalents of haemoglobin-Fe2+. The identity of the product pattern formed with HbO2 with that produced by chemical one-electron oxidation indicated that oxygen bound to haemoglobin also functions as an acceptor for electrons from (II) as from (I), but the different redox potentials can explain why the secondary aromatic nitroxide was catalytically active and the primary nitroxide was not.

THERMOGENESIS AND THE EFFECT OF INJECTED CATECHOLAMINES ON THE OXYGEN CONSUMPTION OF CAFETERIA‐FED RATS

1. The oxygen consumption (VO2) of unrestrained rats given a 'cafeteria' (high energy, high fat) or control diet was studied. The resting values of VO2 were the same in each dietary group, whether maintained at 26 degrees C or 6 degrees C. This negative finding suggests that cafeteria feeding is not an important cause of diet-induced thermogenesis (DIT). 2. The response of each group of rats to injected noradrenaline or dopamine was also studied. Each catecholamine could increase VO2 values but the response was much less in cold-adapted rats measured at 6 degrees C. In all experimental circumstances the dopamine response exceeded that of noradrenaline. There was no evidence that the cafeteria diet consistently increased the response to either catecholamine. 3. These results suggest that DIT cannot be equated with non-shivering thermogenesis (NST). Furthermore, it is suggested that dopamine would be a better agent for measuring the oxygen equivalent of NST, since it would stimulate the dopamine receptors as well as the alpha- and beta-adrenoreceptors of brown fat.

Theory and validity of indirect calorimetry during net lipid synthesis

A critical examination is made of the validity of indirect calorimetry when the nonprotein respiratory quotient is greater than 1. The different published stoichiometries for lipogenesis from glucose are excluded as a source of uncertainty in the interpretation of gaseous exchange measurements. The validity of indirect calorimetry is proved independently by an algebraic approach which, in contrast to previous attempts, makes minimal assumptions about stoichiometries. Although equations relating the respiratory quotient to the heat equivalent of oxygen are found valid, there is uncertainty in using these equations to predict accurately carbohydrate utilization and fat oxidized or synthesized. Reference tables interrelating respiratory data, the heat equivalent of oxygen, and net fuel utilization or synthesis for specified fuels are provided. A suggested framework for calculating energy expenditure in terms of ATP gain is given as an appendix.

Estimation of energy expenditure, net carbohydrate utilization, and net fat oxidation and synthesis by indirect calorimetry: evaluation of errors with special reference to the detailed composition of fuels

Sources of error in the interpretation of respiratory data are evaluated and reviewed with special reference to the detailed composition of foods. Estimates of fuel utilization or synthesis are 12-fold more sensitive to errors in the nonprotein respiratory quotient than is the heat equivalent of oxygen. Estimates of protein oxidation from nitrogen excretion can be in error from +14 to -39% of the true value. Heat equivalents of oxygen, respiratory quotients, and urinary nitrogen-to-oxygen conversion ratios are considered for 60 artificial and 101 conventional food proteins, 36 artificial and 125 conventional food fats, and the different carbohydrates contained in these foods. It is concluded that there is considerable uncertainty when the mix of fuels utilized is assessed accurately. Accuracy is best within 5% of the true values. This analysis is completed with descriptions of some physiological sources of error in an appendix.