Measurement Of O2 Uptake Research Articles

Benthic oxygen fluxes on the Washington shelf and slope: A comparison of in situ microelectrode and chamber flux measurements

Benthic oxygen fluxes calculated from in situ microclectrode profiles are compared with benthic flux chamber O2 uptake measurements on a transect of eight stations across the continental shelf and three stations on the slope of Washington State. Station depths ranged from 40 to 630 m and bottom‐water oxygen concentrations were 127–38 µM. The fluxes measured by the two methods were similar on the slope, but on the shelf, the chamber flux exceeded the microelectrode flux by as much as a factor of 3–4. We attribute this difference to pore‐water irrigation, a process which apparently accounts for the oxidation of a significant amount of organic C in the continental shelf sediments. Combining our diffusive flux data with other data demonstrates clearly that the bottom‐water oxygen concentration must play some significant role in determining the sedimentary oxygen consumption rate. Numerical simulation of the microelectrode O2 profiles suggests that roughly half the diffusive O2 flux must be consumed within ∼ 1 mm of the sediment surface. If this conclusion is correct, then the magnitude of the diffusive flux depends both on the bottom‐water oxygen concentration and on the supply rate of labile C to the sediment surface.

A Method for Increasing Confidence in Respiratory Gas Exchange Measurements in Mechanically Ventilated Patients

Measurement of O2 uptake (VO2) and CO2 output (VCO2) with automated instruments can be used to optimize nutritional management of critically ill patients. However, these measurements may be made infrequently because of calibration problems or suspected inaccuracies, especially when the patient is given supplemental oxygen. A simple method is described for periodic testing of automated gas exchange measurements. While a test lung is mechanically ventilated an accurately known mixture of CO2 and nitrogen is introduced into the inspired gas, simulating VO2 by dilution and VCO2 by addition of CO2. The ratio of VCO2:VO2 (respiratory gas exchange ratio, R) in the "expired gas" should be [FGCO2/(1-FGCO2)] x [(1-FIO2)/FIO2], where FGCO2 is the fraction of CO2 in the diluting gas and FIO2 is the fraction of O2 in the inspired gas. R is independent of the flow rate of the diluting gas or the rate of ventilation of the test lung. Using a mixing chamber-mass spectrometer, we found that R calculated from measurement of CO2 and O2 concentrations in the simulated mixed expired gas closely matched the predicted R for FIO2 = 0.21-0.50. On the other hand, when an automated gas exchange measurement device was tested, R was sometimes excessively high, especially for FIO2 greater than 0.35. This method, using a single diluting gas and without precision flowmeters, may be useful for periodic testing of respiratory gas exchange instruments in the intensive care unit. If a discrepancy is found between measured and predicted R, measurements should not be relied upon until further calibration or repairs can be effected.

How Reliable are Short-term Measurements of Oxygen Uptake in Polytraumatized and Long-term Ventilated Patients?

O2-uptake was measured continuously in 18 polytraumatized and 21 long-term ventilated patients. All patients were on assisted ventilation with sufficient sedation and analgesia. O2-uptake was measured every minute, the values were recorded over 24 h and the mean O2-uptake/min was calculated. At the same time, the O2-uptake of the last 15 min of every hour was measured separately (e.g. 7.45-8.00, 8.45-9.00, etc.). The mean O2-uptake/min measured continuously was compared and correlated with the mean O2-uptake per day, calculated on the basis of each of the short-term measurements. There were only slight differences between the mean values of the two procedures: In the group of long-term ventilated patients the mean O2-uptake was found to be 364 ml/min in continuous measurements and 363 ml/min in short-term measurements. This O2-uptake corresponded to an energy expenditure of 2360 kcal/day. The mean correlation coefficient was 0.89 (range: 0.79-0.96). If O2-uptake was measured over 2 periods of 15 min each, e.g. in the late morning and in the afternoon, the mean correlation coefficient improved to 0.94 and the standard deviation was reduced. Comparable results were obtained in the group of polytraumatized patients. This study shows that under certain preconditions short-term measurements of O2-uptake of 2 x 15 min allow sufficiently reliable predictions of the daily O2-uptake and energy expenditure in severely traumatized or critically ill patients.

A novel antioxidant role for hemoglobin. The comproportionation of ferrylhemoglobin with oxyhemoglobin.

Ferrylhemoglobin (X-FeIV-OH, where X denotes an amino acid residue in the globin moiety) has long been suspected as a cytotoxic agent produced by the interaction of oxyhemoglobin (X-FeIIO2) or methemoglobin (X-FeIII) with H2O2 in red blood cells. To date, however, technical difficulties have prevented the identification and quantification of X-FeIV-OH. Oxyhemoglobin exposed to a continuous flux of H2O2 (generated at a rate of 120 microM/min during the glucose oxidase-catalyzed oxidation of glucose) was oxidized to (a) X-FeIV-OH when [X-FeIIO2] less than 75 microM and (b) X-FeIII when [X-FeIIO2] greater than 75 microM (the production of X-FeIII proceeded with intermediate formation of X-FeIV-OH). The reduction of the X-FeIV-OH to X-FeIII could be explained by either of two alternative mechanisms: a O2(-)-mediated X-FeIV-OH---X-FeIII transition or a comproportionation of X-FeIV-OH and X-FeIIO2 to yield X-FeIII (a process mediated by a tyrosine moiety in the hemoprotein). The low rate of X-FeIIO2 autoxidation plus the negligible decrease in the rate of X-FeIII formation in the presence of either native or heat-denatured superoxide dismutase or apoenzyme (1 microM) suggested that O2- does not contribute to the reduction of X-FeIV-OH. Moreover, the dependence of X-FeIII formation on X-FeIIO2 concentration, together with the results of O2 uptake and H2O2 consumption measurements, provide experimental evidence to support the comproportionation reaction. Comproportionation is apparently catalyzed by intermolecular electron transfer between tyrosine residues, since the reaction did not occur when tyrosine residues were blocked by acetylation. Intact red blood cells exposed to the same flow rate of H2O2 presented a spectral profile which could be explained as a transition from X-FeIIO2 to X-FeIII. The intermediate production of X-FeIV-OH was detected by adding Na2S (2 mM), which revealed a spectral profile identical with that obtained with purified X-FeIV-OH. Measurements of concentrations and relative rate constants for the reaction of various intracellular reductants (glutathione, NAD(P)H, uric acid, ascorbic acid) with X-FeIV-OH revealed that comproportionation of X-FeIV-OH with X-FeIIO2 is the favored reaction. Our results provide (to our knowledge) the first definitive evidence for X-FeIV-OH in intact red blood cells. The rapid comproportionation reaction between X-FeIV-OH and X-FeIIO2 (to produce X-FeIII) explains why X-FeIV-OH has been elusive to date.(ABSTRACT TRUNCATED AT 400 WORDS)

Automated systems for measurement of oxygen uptake during exercise testing.

We evaluated three automated systems for measurement of O2 uptake and compared them with the conventional Douglas bag method. One system (9000 IV Ergometric system) was only tested with respect to its oxygen kinetics, the other two (MMC-Horizon and EOS-Sprint) were tested during three exercise programs: (1) steady-state exercise at 50-W steps from 0 to 200 W, (2) progressive increasing exercise to maximal load, and (3) single-step exercise from 0 to 250 W. The regression lines of mean O2 uptake and load for six subjects were different for intercept (MMC-Horizon) or slope (EOS-Sprint) compared with the conventional method. The maximal O2 uptake values of six subjects were not significantly different for the two systems when compared with the Douglas bag method. The time constants of the exponential function describing oxygen kinetics during repeated (6 times) step changes in load in two subjects were different for the three systems. MMC-Horizon and 9000 IV Ergometric system had lower (51.8 s and 55.1 s, respectively, vs 62.5 s) and EOS-Sprint higher time constant (94.6 vs 47.7 s) than the conventional method. The automated systems were convenient and efficient for measurement of O2 uptake during steady-state and maximal exercise. When O2 uptake kinetics are essential, one has to take into account the response time of the system.

Effect of hindlimb suspension on VO2 max and regional blood flow responses to exercise.

Male rodents were studied before and after undergoing one of three treatment conditions for 9 days: 1) cage control (n = 15, CON), 2) horizontal suspension (n = 15, HOZ), and 3) head-down suspension (n = 18, HDT). Testing included measurements of maximal O2 uptake (VO2 max) and select cardiovascular responses to graded treadmill exercise. VO2 max expressed on an absolute basis (ml/min) was significantly decreased after HOZ (-14.1 +/- 2.5%) and HDT (-14.3 +/- 2.0%), while being essentially unchanged in CON (-1.0 +/- 3.3%). Significant reductions in body weight were observed after both HOZ (-10.1 +/- 4.2 g) and HDT (-22.5 +/- 3.3 g), whereas CON animals exhibited a significant increase in weight (10.4 +/- 3.8 g). As a result, when VO2 max was normalized for body weight, all groups exhibited similar significant reductions of 6-7%. Although no differences in heart rate and blood pressure response to graded exercise were observed, the HDT group exhibited greater increases in mesenteric resistance at the same absolute exercise intensity. Furthermore, both suspended groups had higher iliac resistance values during exercise at similar relative exercise conditions, suggesting that muscle blood flow during treadmill running may have been reduced after suspension. In general, the decrements associated with the HOZ and HDT conditions were similar. It was concluded that reduction in exercise capacity and altered cardiovascular responses to exercise observed after 6-9 days of suspension were attributable to a combination of hypokinesia, lack of hindlimb weight bearing, or restraint, rather than to hydrostatic influences associated with HDT.

マイクロコンピュータ利用による青果物のO<sub>2</sub>吸収量, CO<sub>2</sub>排出量及びC<sub>2</sub>H<sub>4</sub>発生量の自動計測

マイクロコンピュータ利用による青果物のO<sub>2</sub>吸収量, CO<sub>2</sub>排出量及びC<sub>2</sub>H<sub>4</sub>発生量の自動計測

Propelling efficiency of front-crawl swimming

In this study the propelling efficiency (ep) of front-crawl swimming, by use of the arms only, was calculated in four subjects. This is the ratio of the power used to overcome drag (Pd) to the total mechanical power (Po) produced including power wasted in changing the kinetic energy of masses of water (Pk). By the use of an extended version of the system to measure active drag (MAD system), Pd was measured directly. Simultaneous measurement of O2 uptake (VO2) enabled the establishment of the relationship between the rate of the energy expenditure (PVO2) and Po (since when swimming on the MAD system Po = Pd). These individual relationships describing the mechanical efficiency (8-12%) were then used to estimate Po in free swimming from measurements of VO2. Because Pd was directly measured at each velocity studied by use of the MAD system, ep could be calculated according to the equation ep = Pd/(Pd + Pk) = Pd/Po. For the four top class swimmers studied, ep was found to range from 46 to 77%. Total efficiency, defined as the product of mechanical and propelling efficiency, ranged from 5 to 8%.

Capacitation- and fertilization-related alterations in mouse sperm oxygen consumption.

On the basis of experiments performed some years ago, it has been generally accepted that mammalian sperm metabolic activity, as determined by manometric measurement of O2 uptake, increases during capacitation. However, when mouse sperm suspensions were incubated for a total of 120 min in glucose-containing medium which promotes both capacitation and fertilization, O2 consumption, measured with an O2 electrode at 30 and 120 min, consistently declined with time. This same pattern was also observed when pyruvate was the sole exogenous energy substrate, despite the fact that these cells, although capacitated, cannot fertilize eggs until supplied with glucose. Since mouse spermatozoa require a suitable glycolysable substrate to express full functional ability, these results suggest that a shift in metabolic activity from oxidative phosphorylation to glycolysis normally accompanies the onset of fertilizing ability in this species. It was further demonstrated that this pattern, in the presence of glucose, can be markedly modified by alterations in the medium composition which have been shown to modulate fertilizing ability. All conditions chosen inhibit fertilization while retarding (Ca2+-free), accelerating (hyperosmotic high Na+) or nor affecting (iso-osmotic high K+) the rate of capacitation. When suspensions were assessed in these media, O2 consumption increased rather than decreased over the 120 min, despite the continuous presence of glucose. When these same suspensions were assessed at 30 and 120 min in media altered to permit expression of fertilizing ability, the pattern observed was one of declining O2 consumption.(ABSTRACT TRUNCATED AT 250 WORDS)

Pressure increases oxygen affinity of whole blood and erythrocyte suspensions.

Effect of hydrostatic pressure (HP) on whole blood (WB) or erythrocyte suspension hemoglobin (Hb) O2 affinity has been studied using newly developed techniques. O2 partial pressure at which hemoglobin is half-saturated with O2 (P50) measurements were made at 5 HP (1, 26, 51, 76, and 126 ATA) on thin films of human WB or erythrocytes at 37 degrees C. CO2 partial pressure of WB was either 28 or 57 Torr (film pH 7.51 or 7.31). HP increased affinity of erythrocytes and WB. For erythrocytes in tris(hydroxymethyl)aminomethane buffer, the ratio (r) of P50 (1 ATA)/P50 (51 ATA) was 1.089 (P less than 0.01) at pH 7.0. WB P50 decreased with HP at a rate of -3.3 X 10(-2) Torr X atm-1; change in P50 at higher HP vs. 1 ATA was highly significant (P less than 0.01). No effect of HP was seen on the CO2 Bohr coefficient. Inert gas choice, N2 vs. helium (He), had no effect. Measurement of decrease of P50 with HP at 76 ATA in hemolyzed WB gave an r of 1.15, as great or greater than that found in WB, indicates that Donnan equilibrium alteration is not involved. No effect of HP was found in WB on the ratio of P50 of erythrocytes with normal (5 mmol/l erythrocytes) 2,3-diphosphoglycerate (DPG) to P50 of erythrocytes with less than 5% of normal DPG; i.e., no effect of pressure was seen on the independent influence of DPG on P50. WB measurements of Hb O2 uptake under simulated physiological conditions are characterized by a net decrease in partial molal volume on oxygenation of 30-35 ml/mol Hb4.

Aflatoxin inhibition of rat liver mitochondrial cytochrome oxidase activity.

Aflatoxins B1, B2, G1, G2, and M1 have been evaluated for activity toward cytochrome oxidase in isolated rat liver mitochondria employing ferrocytochrome c and p-phenylene diamine as reductants. The aflatoxins inhibited the cytochrome oxidase activity to a greater extent when monitored by O2 uptake measurements than by substrate oxidation. AFG2 and AFM1 were the most potent (50-70%). Using oligomycin and 2,4-DNP as respiratory inhibitor and uncoupler, respectively, the aflatoxins appear to inhibit e- rather than energy transfer reactions. These toxins did not uncouple cytochrome oxidase activity.

Evidence from O2 uptake measurements for Na+ -K+ -2 Cl- co-transport in the rabbit submandibular gland.

There is evidence that the production of primary saliva by acinar cells is a consequence of Na+ -Cl- co-transport but more recently it has been proposed that in fact Na+ -K+ -2 Cl- co-transport is responsible. The latter would be energetically more efficient and the present experiments were designed to measure the stoichiometry of acinar secretion in order to distinguish between these two mechanisms. Submandibular salivary glands from anaesthetised rabbits were isolated vascularly and oxygen consumption measured from the oxygen content of arterial inflow and venous effluent blood and the total flow through the gland. Measurements were made in the steady-state at rest and during different secretion rates induced by parasympathetic nerve stimulation. The rate of sodium transport across the acinar and ductal epithelium was determined from plasma and salivary sodium concentration and salivary flow rate. Multiple regression analysis of this data showed that 22.1 mol Na+ was secreted per mol O2 consumed while 11.9 mol Na+ was reabsorbed per mol O2 consumed. Since acinar secretion is energetically about twice as efficient as ductal absorption, a mechanism for Na+ transport other than that for tight epithelia must be involved. Na+ -K+ -2 Cl- co-transport is thus more likely than Na+ -Cl- and it is suggested that Na+ -K+ -2 Cl- co-transport is the main mechanism involved in salivary acinar secretion.

Copper(I) Schiff-base complexes: reversible carbon monoxide binding, reactions with dioxygen, and the structure of a dinuclear complex containing co-ordinated and unco-ordinated alkene groups

Copper(I) complexes of a series of acyclic Schiff-base ligands (L1–L5) derived from the condensation of 2,6-diacetylpyridine with 2 mol of 4-aminobut-1-ene (L1), allylamine (L2), 1-aminobutane (L3), 1 -aminopropane (L4), and 2-(ethylthio)ethylamine (L5), have been prepared. Crystals of the dinuclear complex[Cu2L12][BPh4]2 are orthorhombic with a= 17.74(1), b= 17.78(1), c= 21.90(1)Å, Z= 4, and space group Pb21a(no. 29). In the dimeric cation each CuI atom is bonded to the pyridine nitrogen and one imino nitrogen of one ligand molecule and to one imino nitrogen and one alkene group of the second ligand molecule in a distorted tetrahedral geometry. The second alkene group of each ligand remains unco-ordinated. In order to accommodate to this unusual co-ordination mode one imino group is severely twisted (by 83, 86° in the two ligand molecules) out of the plane of the pyridine ring, leading to two distinct ν(CN) vibrations in the i.r. spectrum. On the basis of i.r. and other properties, it is proposed that the complexes of L2–L5, as well as [Cu2L12][BPh4]2 in MeCN solution, have mononuclear structures in which the trimethine pyridyldi-imine group retains its customary planarity and acts as a tridentate ligand. For [CuL3][ClO4] and [CuL4][ClO4] having no side-arm donor groups, and for [CuL2][ClO4]·H2O having propene side chains, a T-shaped three-co-ordinated structure is suggested. For [CuL5][ClO4], as well as for [Cu2L12][BPh4]2 and [CuL2][ClO4]·H2O in solution, spectroscopic evidence indicates at least partial side-arm donor group co-ordination leading to four-co-ordinate species. All the complexes bind CO reversibly in MeCN solution to an extent dependent on the competition exercised by the pendant side-arm donor groups, where present. The complexes also bind O2 in solution in a 0.25:1 O2: Cu stoicheiometry at rates which parallel the CO affinities. The O2 binding is partially reversible in some cases as evidenced by electronic spectral and O2-uptake measurements on successive oxygenation/deoxygenation treatments. Among the ultimate products of the accompanying irreversible oxidation are the bis(ligand) CuII complexes [CuL2]2+.

Hindlimb vascular responses to sympathetic augmentation during acute anemia.

The effect of increased sympathetic activity on skeletal muscle blood flow during acute anemic hypoxia was studied in 16 anesthetized dogs. Sympathetic activity was altered by clamping the carotid arteries bilaterally below the carotid sinus. One group (n = 8) was beta blocked by administration of propranolol (1 mg/kg); a second group (n = 8) was untreated. Venous outflow from the left hindlimb was isolated for measurement of blood flow and O2 uptake (VO2). After a 20-min control period, both carotid arteries were clamped (CC) for 20 min followed by a 20-min recovery period. The sequence was repeated after hematocrit was lowered to about 15% by dextran exchange for blood. Prior to anemia, CC did not alter cardiac output or limb blood flow in either group. After induction of anemia, hindlimb resistance was higher with CC in the beta block than in the no block group. Both limb blood flow and VO2 fell in the beta-block group with CC during anemia. Beta block also prevented the additive increases in whole body VO2 seen with CC and induction of anemia. The data showed that the increased vasoconstrictor tone that was obtained with beta block during anemia was successful in redistributing the lower viscosity blood away from resting skeletal muscle, even to the point that muscle VO2 was decreased.

Carbon flow through oxygen and sulfate reduction pathways in salt marsh sediments1

We measured surface O2 uptake, 35SO42− reduction, and total sediment metabolism (CO2 production) in sediments (0–30 cm) supporting stands of short Spartina alterniflora in a New England salt marsh. Sediment CO2 production was highest at the surface where O2 was present and declined rapidly with depth. In deeper sediments (below 5 cm) CO2 production was equal to 35SO42− reduction as determined by the Cr2+ reduction technique. Time‐course experiments using CO2 production and 35SO42− reduction (by Cr2+ reduction and aqua regia digest) indicate that the aqua regia technique is not reliable for measuring SO42− reduction and that the rate of SO42− reduction is much less than previously reported for this marsh.Our estimates of annual O2 uptake conform with those for CO2 production and belowground production. We estimate carbon mineralization to average about 180 mmol C·m−2·d 1, among the highest measured for marine sediments. Our simultaneous measurements of O2 uptake, CO2 production, and SO42− reduction suggest that at least half of this decomposition occurs via SO42− reduction. We conclude that the mechanisms underlying carbon and sulfur cycling in salt marsh sediments are much more similar to subtidal sediments than previously recognized.

Calibration methods in respiratory calorimetry.

Methods for calibration of respiratory gas exchange measurement systems are evaluated. A new method is described in which O2 is removed from the subject chamber or gas stream and measured gravimetrically in a small combustion chamber containing steel wool. The "Fe-burner" method was tested by comparison with the N2-injection method and found to be of similar accuracy. The new method is easy to perform, quick, and readily applicable to both open- and closed-circuit respiratory systems. It has a rate of O2 uptake that can be adjusted to be similar to the rate by an experimental subject (10-600 kg). Complete calibration of open- and closed-circuit indirect calorimetric systems can be achieved when the Fe-burner method, involving measurement of O2 uptake, is combined with the gravimetric injection of specific gases (CO2, methane) produced by the subject.

Development of cardiorespiratory function in circumpubertal boys: a longitudinal study.

To investigate cardiorespiratory function during circumpubertal growth, 62 boys (aged 9-10 yr) were studied annually for 6 yr. Measurements of O2 uptake (VO2), cardiac output, and arteriovenous O2 difference were made during a submaximal bicycle test. Values were interpolated to a heart rate of 155 beats X min-1 (VO2 at a heart rate of 155) for comparisons across ages 10.8-14.8 yr. To account for growth differences among the boys, data were also aligned at yearly intervals relative to their individual age of peak height velocity (PHV; maturative age). The group was further divided into early, mid, and late maturers based on their year of PHV. VO2 and stroke volume (SV) of late maturers were larger at each maturative age. SV mirrored the increase in VO2 at all stages of development except during the period of most rapid growth. Arteriovenous O2 difference showed an increase in the year of peak growth with little change during any of the other maturative age intervals. Multiple regression analysis indicated that VO2 was determined primarily by the size of SV throughout this age range.

Absolute or relative work load in exercise testing significance of individual differences in working capacity

A commun multistage bicycle ergometer test (50 W increases every third minute until exhaustion) was analysed for significance of individual differences in working capacity in six young borderline hypertensive and six young normotensive males. From measurements of O2 uptake (VO2) during each of the prescribed work rates, up to and including maximal effort, relationships with relative work load (% VO2 max) could be established for each of the variables observed in the study. An alternative procedure was tested in which the relative work load was established on the basis of the individual's maximal mechanical power output (Wmax). In heavy exercise the variation coefficients for some variables were nearly halved when observed at a given relative (% VO2 max or % Wmax) rather than absolute (number of watts) exercise level. In light exercise the effect of this normalization was negligible. The two expressions of relative work load were closely correlated. Relative work load in % VO2 max could be predicted from the relative work load in % Wmax with an average standard error of estimate of 2.8%. Exercise heart rate and rate of perceived exertion (Borg scale) were also significantly correlated with relative work load. However, these latter variables were less precise as indicators of relative work load, the standard error of estimates being 3 and 5 times larger than that of % Wmax, respectively. The procedure of establishing relative work load on the basis of Wmax may be of value if a precise setting is desirable when measurements of VO2 are impracticable. The method may also be of use if an individual's HR-work load relationship is abnormal, for example because of medication.(ABSTRACT TRUNCATED AT 250 WORDS)

On the SMSI state in [formula omitted] system: Measurements of gas consumption during the high-temperature treatments

The evolution of the morphology, phase composition, and activity in benzene hydrogenation of Co/SiO2 catalysts, prepared from cobalt nitrate and porous (390 m2/g) or nonporous (35 m2/g) silica, upon reduction with hydrogen at 350–900 °C have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), magnetic measurements, oxygen uptake, BET, and hydrogen chemisorption. A rapid decline of the activity of Co/SiO2 catalysts to zero was observed with reduction temperature increasing from 400 to 600 °C. This effect could not be simply explained by a sintering of cobalt particles or by the reaction of Co with the support and alloys or compound formation. The TEM, H2 chemisorption, O2 uptake, and magnetic measurements revealed that at Tred⩾500 °C coverage (encapsulation) of the metal with a thin, most probably SiO2, overlayer was likely to be the reason. Both Co/SiO2 catalysts reduced at Tred>500 °C exhibited a higher and growing with reduction temperature resistance to oxidation when exposed to oxygen or air as it was evidenced by oxygen uptake, magnetic data, and decreasing H2 chemisorption capacity. At higher temperature (⩾700 °C) the formation of a thicker, easily observable with TEM, SiO2 or SiOx, overlayer covering the Co particles took place. As a consequence, the catalysts reduced at 900 °C were nearly insensitive to the exposure to air. Oxygen uptake and magnetic measurements ruled out the hypothesis on the Co–Si solid solution or cobalt silicide formation at least in quantities higher than the reliability limits of the experimental methods used. The sintering of Co particles and the significant growth of the mean size of Co crystallites was observed at reduction temperatures of 800 and 850 °C for nonporous and porous silica, respectively. An apparent growth of the cobalt content to 107 and 114% of the initial value was noted after reduction at 700 and 900 °C, respectively, for both catalysts studied, probably due to the strong support dehydroxylation and/or partial reduction.

Ventilatory thresholds during short- and long-term exercise.

The ventilatory (anaerobic) threshold for short-term exercise was defined as the work rate or O2 uptake (VO2) immediately below the work rate at which ventilation increased disproportionately relative to work rate or VO2, and the ventilatory threshold for long-term exercise as the work rate or VO2 immediately below the work rate at which ventilation continued to increase with time rather than attain a steady state. The purpose of the present study was to investigate how both thresholds relate to each other and how they relate to other measures of physical performance capacity. The subjects were eight healthy males, 20-53 yr of age. Maximal performance capacity was estimated by measurements of maximal O2 uptake (VO2 max) and by endurance performance during a 12-min distance run. A high interrelationship was found between the two thresholds (r = 0.84), and each threshold expressed in VO2 (ml X min-1 X kg-1) correlated highly with VO2 max (r = 0.87 and r = 0.75, for short-term and long-term exercise, respectively). When the two thresholds were expressed as a percentage of VO2 max, neither threshold showed a significant relationship with VO2 max. Endurance performance was significantly correlated with both the ventilatory threshold for short-term and long-term exercise (r = 0.73 and 0.82, respectively). A stepwise multiple regression analysis indicated that the distance run in 12 min was best predicted by VO2 max (R2 = 0.66) or the ventilatory threshold for long-term exercise (R2 = 0.63). It is concluded that the ventilatory threshold for long-term exercise is a more specific measure to explain running performance than is the threshold during graded exercise.