Influence of impeller type on power input in fermentation vessels

Prior investigations comparing radial flow Rushton impellers with axial flow hydrofoil impellers (Maxflo T and A315) were extended at the pilot scale. Six types of impellers (disk-style Rushton, Prochem Maxflo T hydrofoils of three diameters pumping downwards and A315 hydrofoils pumping upwards and downwards) were compared for qualitative differences in power number behavior with Reynolds' number, single versus double impeller power draw, gassed power reduction with aeration number and gas hold-up. Power measurements were obtained using watt transducers which, although limited in accuracy and prone to interferences, were able to provide useful qualitative monitoring results. Measurements were conducted using three model liquid systems: water, glycerol and Melojel (soluble starch). Apparent viscosities for actual Streptomyces cultivations were estimated using measured gassed power values and the experimental relationships obtained for gassed/ungassed power to aeration number and power number to Reynolds' number for the glycerol model system. Results confirmed the lower power number and lower shear environment for hydrofoil impellers, yet suggested useful trends for various process parameters and process fluids.     

Comparing a range of impellers for “stirring as foam disruption”

The effectiveness of a range of impellers for “stirring as foam disruption” (SAFD) is assessed in a vessel of 0.72 m diameter and an aspect ratio of 2:1. Measurement of power drawn by the impeller achieving SAFD and of the three-dimensional flow field close to the dispersion surface are both used to explain the findings along with the global gas hold-up. A large radial flow Rushton turbine can disrupt foam at a great height but requires high power. Down-pumping hydrofoils are only effective when the ungassed liquid height is below the level of the impeller employed to disrupt foam. Up-pumping hydrofoils are the most effective because their flow pattern gives rise to high velocities across the dispersion surface, which are able to entrain foam in the downflow generated at the walls.     

Mass transfer and mixing rates in fermentation vessels

The effects on mass-transfer and overall mixing rates of varying impeller geometry and operating speed have been studied for flat-bladed turbines in laboratory fermentors, in aerated aqueous solutions, and in unaerated and aerated suspensions (1.6% w/v) of paper pulp. In the absence of suspended solid, oxygen absorption rates could be correlated directly with power input. In the pulp suspension, oxygen absorption at a given power input was influenced by impeller geometry and operating speed. The data for the three-phase system can be correlated by a dimensionless equation relating oxygen-transfer rates and mixing times to the geometrical and operating parameters of the impellers.     

Carbon monoxide mass transfer for syngas fermentation in a stirred tank reactor with dual impeller configurations

This study compares the power demand and gas-liquid volumetric mass transfer coefficient, kLa, in a stirred tank reactor (STR) (T = 0.211 m) using different impeller designs and schemes in a carbon monoxide-water system, which is applicable to synthesis gas (syngas) fermentation. Eleven different impeller schemes were tested over a range of operating conditions typically associated with the "after large cavity" region (ALC) of a Rushton-type turbine (D/T = 0.35). It is found that the dual Rushton-type impeller scheme exhibits the highest volumetric mass transfer rates for all operating conditions; however, it also displays the lowest mass transfer performance (defined as the volumetric mass transfer coefficient per unit power input) for all conditions due to its high power consumption. Dual impeller schemes with an axial flow impeller as the top impeller show improved mass transfer rates without dramatic increases in power draw. At high gas flow rates, dual impeller schemes with a lower concave impeller have kLa values similar to those of the Rushton-type dual impeller schemes but show improved mass transfer performance. It is believed that the mass transfer performance can be further enhanced for the bottom concave impeller schemes by operating at conditions beyond the ALC region defined for Rushton-type impellers because the concave impeller can handle higher gas flow rates prior to flooding.     

Gas-liquid dispersion with dual Rushton turbine impellers

Aerated and unaerated power consumption and flow patterns in a 0.56 m diameter agitated vessel containing water with dual Rushton turbines have been studied. Under unaerated conditions with a liquid height-to-diameter ratio of 2, an impeller spacing of 2 to 3 times the impeller is required for each to draw an amount of power equal to a single impeller. For aerated conditions, if a similar spacing is used, equations for the flooding-loading transition and for power consumption for a single Rushton impeller can be extended relatively easily to dual systems. All results for this spacing are explained by reference to bulk flow patterns and gassed-filled cavity structures and the proportion of sparged gas flowing through the upper impeller is also estimated. Such a spacing is generally recommended since it maximizes the power draw and hence the potential for oxygen mass transfer. Data are presented for other spacings but the results do not fit in easily with single agitator studies because strong impeller-impeller flow pattern interactions occur.     

Are powerful females powerful enough? Acceleration in gravid green iguanas (Iguana iguana)

One demand placed exclusively on the musculoskeletal systemof females is maintaining locomotor performance with an increasingload over the reproductive cycle. Here, we examine whether gravid(i.e., "pregnant") iguanas can increase their force and powerproduction to support, stabilize, and accelerate the additionalmass of a clutch of eggs. At any acceleration, gravid iguanasproduced very high mechanical power (average total power = 673w/kg; total peak power = 1175 w/kg). While the increase in totalpower was partly a result of greater propulsive power (averagepropulsive power = 25% higher, peak propulsive power = 38% higher),increased vertical power (roughly 200% increase) was the maincontributor. Gravid iguanas were also able to increase peakforces (propulsive = 23%, mediolateral = 44%, vertical = 42%),and step duration (44%) resulting in greater impulses (i.e.,the sum of force produced during a step) to accelerate, balance,and support their increased mass. The increase in step durationand smaller increase in peak propulsive force suggests thatgravid iguanas may be force-limited in the direction of motion.We discuss how biomechanical constraints due to females’reproductive role may influence the evolution of the femalemusculoskeletal systems and contribute to the evolution andmaintenance of ecological dimorphism in lizards.     

Power consumption of three impeller combinations in mixing Xanthan fermentation broths

Xanthan gum fermentation represents a good model for the study of the mixing of rheologically complex culture broths. Most of the previous work on power consumption dealt with ‘standard’, single impellers and used model fluids to simulate xanthan broths. This work describes the characterization of three dual-impeller combinations (D/T = 0·53) for the mixing of dehydrated—reconstituted fermentation broths of Xanthomonas campestris that had matched rheology to the actual broths. The bottom impeller was a Rushton turbine (RT) and the top impeller was another RT, a 45° pitched blade turbine (PT) or an A-310 Lightnin mixer (A310). The experiments were carried out in a tank of 0·0094 m³ working volume equipped with an air bearing dynamometer. The power was measured in a wide range of xanthan concentrations (5–40 kg m⁻³) in aerated (0·25, 0·5 and 1·0 vvm) and unaerated conditions. Unaerated power number (Po) vs. Reynolds number (Re) curves showed similar trends for the three combinations. Exponents close to −1 were obtained in the laminar region. A minimum in Po (Po_min) occurred at Re = 30–40, then increasing to a plateau value which was evident at Re> 200. In the transition region Po_min values were 4·3 (RT and RT), 3·6 (RT and PT) and 2·4 (RT and A310). The aerated power data for (RT and PT) and (RT and A-310) showed higher torque instabilities than the dual RT combinations at higher xanthan concentrations. The higher the xanthan concentrations, the higher the drop in power and the less important the effect of the aeration rate. Among the combinations tested, when using Rushton turbines, the well-mixed ‘cavern’ reached the tank wall (i.e., fluid motion was observed) at the lowest volumetric power input. High     

Role of Rho kinases in PKG-mediated relaxation of pulmonary arteries of fetal lambs exposed to chronic high altitude hypoxia

An increase in Rho kinase (ROCK) activity is implicated in chronic hypoxia-induced pulmonary hypertension. In the present study, we determined the role of ROCKs in cGMP-dependent protein kinase (PKG)-mediated pulmonary vasodilation of fetal lambs exposed to chronic hypoxia. Fourth generation pulmonary arteries were isolated from near-term fetuses ( approximately 140 days of gestation) delivered from ewes exposed to chronic high altitude hypoxia for approximately 110 days and from control ewes. In vessels constricted to endothelin-1, 8-bromoguanosine-cGMP (8-Br-cGMP) caused a smaller relaxation in chronically hypoxic (CH) vessels compared with controls. Rp-8-Br-PET-cGMPS, a PKG inhibitor, attenuated relaxation to 8-Br-cGMP in control vessels to a greater extent than in CH vessels. Y-27632, a ROCK inhibitor, significantly potentiated 8-Br-cGMP-induced relaxation of CH vessels and had only a minor effect in control vessels. The expression of PKG was increased but was not accompanied with an increase in the activity of the enzyme in CH vessels. The expression of type II ROCK and activity of ROCKs were increased in CH vessels. The phosphorylation of threonine (Thr)696 and Thr850 of the regulatory subunit MYPT1 of myosin light chain phosphatase was inhibited by 8-Br-cGMP to a lesser extent in CH vessels than in controls. The difference was eliminated by Y-27632. These results suggest that chronic hypoxia in utero attenuates PKG-mediated relaxation in pulmonary arteries, partly due to inhibition of PKG activity and partly due to enhanced ROCK activity. Increased ROCK activity may inhibit PKG action through increased phosphorylation of MYPT1 at Thr696 and Thr850.     

Influence of impeller type on mass transfer in fermentation vessels

Radial flow Rushton impellers were compared qualitatively with axial flow hydrofoil impellers (Maxflo T and A315) at the pilot scale. Six types of impellers were compared for qualitative differences in mass transfer. Measurements were conducted using three model systems: water, glycerol and Melojel (soluble starch). Power measurements were obtained using watt transducers, which although limited in accuracy and prone to interferences, were able to provide useful qualitative monitoring results. While there was little effect of impeller type on mass transfer as measured by the rapid pressure increase technique, significant qualitative differences were observed using the rapid temperature increase technique specifically for the Melojel and glycerol model systems. The Miller correlation, relating gassed-to-ungassed power, was used effectively to qualitatively evaluate the power drop upon gassing for both the model systems and a Streptomyces fermentation for the various impeller types. A high oxygen demand Streptomcyes fermentation then was conducted in fermenters possessing each type of impeller. Performance was not adequate with the A315 impellers pumping upwards and the small diameter Maxflo T impellers. Peak titers and profiles of the estimated apparent broth viscosity varied depending upon the impeller type. Mass transfer rates generally declined with higher viscosities when other fermentation operating conditions where held constant. Overall, values for OUR, k _L a, P _g /V _L and other calculated mass transfer and power input quantities for the A315 pumping upwards and undersized Maxflo T (D _T /D _I ?=?2.3) impellers were at the lower end of the range obtained for the larger Maxflo T (D _T /D _I ?=?1.8–2.0) and A315 impellers pumping downwards. Rushton impellers generally behaved qualitatively similar to hydrofoil impellers based on these calculated quantities.     

Mixing design for enzymatic hydrolysis of sugarcane bagasse: methodology for selection of impeller configuration

One of the major process bottlenecks for viable industrial production of second generation ethanol is related with technical–economic difficulties in the hydrolysis step. The development of a methodology to choose the best configuration of impellers towards improving mass transfer and hydrolysis yield together with a low power consumption is important to make the process cost-effective. In this work, four dual impeller configurations (DICs) were evaluated during hydrolysis of sugarcane bagasse (SCB) experiments in a stirred tank reactor (3 L). The systems tested were dual Rushton turbine impellers (DIC1), Rushton and elephant ear (down-pumping) turbines (DIC2), Rushton and elephant ear (up-pumping) turbines (DIC3), and down-pumping and up-pumping elephant ear turbines (DIC4). The experiments were conducted during 96 h, using 10 % (m/v) SCB, pH 4.8, 50 °C, 10 FPU/g_biomass, 470 rpm. The mixing time was successfully used as the characteristic parameter to select the best impeller configuration. Rheological parameters were determined using a rotational rheometer, and the power consumptions of the four DICs were on-line measured with a dynamometer. The values obtained for the energetic efficiency (the ratio between the cellulose to glucose conversion and the total energy) showed that the proposed methodology was successful in choosing a suitable configuration of impellers, wherein the DIC4 obtained approximately three times higher energetic efficiency than DIC1. Furthermore a scale-up protocol (factor scale-up 1000) for the enzymatic hydrolysis reactor was proposed.     

Evidence for structural heterogeneities and a study of exchange coupling. M?ssbauer studies of cytochrome c1aa3 from Thermus thermophilus

We have studied samples of oxidized (as isolated) cytochrome c1aa3 from Thermus thermophilus in the pH range 5.7 to 9.3 with M?ssbauer spectroscopy. In this pH range, the spectra of cytochromes c1 and a are independent of pH, whereas the spectra of cytochrome a3 are not. Most importantly, spectra taken in applied fields up to 6.0 T reveal the presence of multiple ferric forms of cytochrome a3. At any given pH value, at least two high-spin ferric cytochrome a3 species can be distinguished; in addition, most samples contain a low-spin ferric cytochrome a3 species (less than 20% of cytochrome a3). The M?ssbauer spectra show clearly that all forms of cytochrome a3 are spin coupled (to CuB). We have analyzed the high field (H greater than or equal to 1.5 tesla) spectra of a sample at pH 6.5 in the framework of a model that considers isotropic exchange-coupling, JS1.S2, between a high-spin ferric (S1 = 5/2) cytochrome a3 and cupric CuB (S2 = 1/2). In strong applied fields, the spectra can be fitted with any value for J greater than or equal to 0.5 cm-1. In the strong coupling case (J/D1 approximately greater than 3), a zero field splitting parameter D1 approximately 2.5 cm-1 is required for cytochrome a3; this value is distinctly smaller than those observed for high-spin ferric hemes (4-20 cm-1). A model assuming weak coupling magnitude of J approximately 1 cm-1, yields D1 approximately 8 cm-1 and a parameter set for cytochrome a3 quite similar to that reported for metmyoglobin. A J-value of approximately 1 cm-1 does not demand the presence of a ligand bridging between cytochrome a3 and CuB.     

H2O2 increases production of constrictor prostaglandins in smooth muscle leading to enhanced arteriolar tone in Type 2 diabetic mice

Our previous study showed that arteriolar tone is enhanced in Type 2 diabetes mellitus (T2-DM) due to an increased level of constrictor prostaglandins. We hypothesized that, in mice with T2-DM, hydrogen peroxide (H(2)O(2)) is involved in the increased synthesis of constrictor prostaglandins, hence enhanced basal tone in skeletal muscle arterioles. Isolated, pressurized gracilis muscle arterioles ( approximately 100 microm in diameter) of mice with T2-DM (C57BL/KsJ-db(-)/db(-)) exhibited greater basal tone to increases in intraluminal pressure (20-120 mmHg) than that of control vessels (at 80 mmHg, control: 25 +/- 5%; db/db: 34 +/- 4%, P < 0.05), which was reduced back to control level by catalase (db/db: 24 +/- 4%). Correspondingly, in carotid arteries of db/db mice, the level of dichlorofluorescein-detectable and catalase-sensitive H(2)O(2) was significantly greater. In control arterioles, exogenous H(2)O(2) (0.1-100 micromol/l) elicited dilations (maximum, 58 +/- 10%), whereas in arterioles of db/db mice H(2)O(2) caused constrictions (-28 +/- 8%), which were converted to dilations (maximum, 16 +/- 5%) by the thromboxane A(2)/prostaglandin H(2) (TP) receptor antagonist SQ-29548. In addition, arteriolar constrictions in response to the TP receptor agonist U-46619 were not different between the two groups of vessels. Endothelium denudation did not significantly affect basal tone and H(2)O(2)-induced arteriolar responses in either control or db/db mice. Also, in arterioles of db/db mice, but not in controls, 3-nitrotyrosine staining was detected in the endothelial layer of vessels. Thus we propose that, in mice with T2-DM, arteriolar production of H(2)O(2) is enhanced, which leads to increased synthesis of the constrictor prostaglandins thromboxane A(2)/prostaglandin H(2) in the smooth muscle cells, which enhance basal arteriolar tone. These alterations may contribute to disturbed regulation of skeletal muscle blood flow in Type 2 diabetes mellitus.     

Heterogeneous effect of peroxisome proliferator-activated receptor gamma2 Ala12 variant on type 2 diabetes risk

Conflicting results have been reported regarding whether the PPARgamma2 Pro12Ala polymorphism plays a role in the risk of type 2 diabetes (T2D), suggesting genetic heterogeneity. To investigate this issue, a meta-analysis of 41 published and 2 unpublished studies (a total of 42,910 subjects) was conducted. Ala12 carriers had a 19% T2D risk reduction, but this association was highly heterogeneous (p = 0.005). A great proportion (48%) of heterogeneity was explained by the controls' BMI, with risk reduction being greater when BMI was lower. Risk reduction of Ala12 carriers in Asia (35%) was higher than in Europe (15%, p = 0.02) and tended to be higher than in North America (18%, p = 0.10). Difference between Asians and Europeans was no longer significant (p = 0.15) after adjusting for the controls' BMI. Studies from Europe were still heterogeneous (p = 0.02) with risk reduction in Ala12 carriers being progressively smaller (test for trend in the odds ratios, p = 0.02) from Northern (26% reduction, p < 0.0001) to Central (10%, p = 0.04) and Southern (0%, p = 0.94) Europe. In conclusion, in our meta-analysis, the reduced risk of T2D in Ala12 carriers is not homogeneous. It is greater in Asia than in Europe and, among Europeans, it is higher in Northern Europe, barely significant in Central Europe, and nonexistent in Southern Europe.     

The influence of impeller type in pilot scale xanthan fermentations

The rheological complexity of Xanthan fermentations presents an interesting problem from a mixing viewpoint, because the phenomena of poor bulk blending and low oxygen mass transfer rates inherent in highly viscous fermentations (and their consequences) can be systematically investigated, even at the pilot plant scale. This study in a 150 L fermentor compares the physical and biological performance of four pairs of impellers: a standard Rushton turbine, a large diameter Rushton turbine, a Prochem Maxflo T, and a Scaba 6SRGT. Accurate in-fermentor power measurements, essential for the comparison of impellers in relation to operating costs are also reported. It is demonstrated that the agitator performance in Xanthan fermentations is very specific and the choice of which impeller to use in bioreactors to obtain enhanced performance is dependant on the applied criterion. None of the criterion favored the use of the standard Rushton turbine, therefore suggesting that there are strong grounds for retrofitting these impellers with either large diameter impellers of similar design or with novel agitators. In addition, fluid dynamic modeling of cavern formation has clearly highlighted the importance of a well mixed and oxygenated region for providing the capacity for high microbial oxygen uptake rates which govern Xanthan productivity and quality. Copyright 1998 John Wiley & Sons, Inc.     

CFD simulation of mixing for high-solids anaerobic digestion

A computational fluid dynamics (CFD) model that simulates mechanical mixing for high-solids anaerobic digestion was developed. Numerical simulations of mixing manure slurry which exhibits non-Newtonian pseudo-plastic fluid behavior were performed for six designs: (i) one helical ribbon impeller; (ii) one anchor impeller; (iii) one curtain-type impeller; (iv) three counterflow (CF-2) impellers; (v) two modified high solidity (MHS 3/39°) impellers; and (vi) two pitched blade turbine impellers. The CFD model was validated against measurements for mixing a Herschel-Bulkley fluid by ribbon and anchor impellers. Based on mixing time with respect to mixing energy level, three impeller types (ribbon, CF-2, and MHS 3/39°) stand out when agitating highly viscous fluids, of these mixing with two MHS 3/39° impellers requires the lowest power input to homogenize the manure slurry. A comparison of digestion material demonstrates that the mixing energy varies with manure type and total solids concentration to obtain a given mixing time. Moreover, an in-depth discussion about the CFD strategy, the influences of flow regime and impeller type on mixing characteristics, and the intrinsic relation between mixing and flow field is included.     

Maturational changes in extracellular matrix and lung tissue mechanics.

The viscoelastic properties of the pulmonary parenchyma change rapidly postparturition. We compared changes in mechanical properties with changes in tissue composition of rat lung parenchymal strips in three groups of Sprague-Dawley rats: baby (B; 10-14 days), young (Y; approximately 3 wk), and adult (A; approximately 8 wk). Strips were suspended in an organ bath, and resistance (R), elastance (E), and hysteresivity (eta) were calculated during sinusoidal oscillations before and after the addition of acetylcholine (ACh) (10(-3) M). Strips were then fixed in formalin, and sections were stained with hematoxylin and eosin, Verhoff's elastic stain, or Van Gieson's picric acid-fuchsin stain for collagen. The volume proportion of collagen (%Col), the length density of elastic fibers (L(V)/Pr(alv)), and the arithmetic mean thickness of alveolar septae (T(a)) were calculated by morphometry. Tissue was also stained for alpha-smooth muscle actin (ASMA), and the volume proportion of ASMA (%ASMA) was calculated. Hyaluronic acid (HA) was quantitated by radioimmunoassay in separate strips. R and E in B strips were significantly higher, whereas eta was significantly smaller than in Y or A strips. Changes in these parameters with ACh were greater in B strips. T(a), %ASMA, and HA were greatest in B strips, whereas %Col and L(V)/Pr(alv) were least. There were significant positive correlations between R and E vs. T(a) and between percent change in R and eta post-ACh vs. T(a) and vs. %ASMA, and significant negative correlations between R and E vs. %Col and vs. L(V)/Pr(alv) and percent increase in all three mechanical parameters post-ACh vs. %Col. These data suggest that the relatively high stiffness, R, and contractile responsiveness of parenchymal tissues observed in newborns are not directly attributable to the amount of collagen and elastic fibers in the tissue, but rather they are related to the thickened alveolar wall and the relatively greater percent of contractile cells.     

An Intensified Vibratory Milling Process for Enhancing the Breakage Kinetics during the Preparation of Drug Nanosuspensions

As a drug-sparing approach in early development, vibratory milling has been used for the preparation of nanosuspensions of poorly water-soluble drugs. The aim of this study was to intensify this process through a systematic increase in vibration intensity and bead loading with the optimal bead size for faster production. Griseofulvin, a poorly water-soluble drug, was wet-milled using yttrium-stabilized zirconia beads with sizes ranging from 50 to 1500 μm at low power density (0.87 W/g). Then, this process was intensified with the optimal bead size by sequentially increasing vibration intensity and bead loading. Additional experiments with several bead sizes were performed at high power density (16 W/g), and the results were compared to those from wet stirred media milling. Laser diffraction, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, and dissolution tests were used for characterization. Results for the low power density indicated 800 μm as the optimal bead size which led to a median size of 545 nm with more than 10% of the drug particles greater than 1.8 μm albeit the fastest breakage. An increase in either vibration intensity or bead loading resulted in faster breakage. The most intensified process led to 90% of the particles being smaller than 300 nm. At the high power intensity, 400 μm beads were optimal, which enhanced griseofulvin dissolution significantly and signified the importance of bead size in view of the power density. Only the optimally intensified vibratory milling led to a comparable nanosuspension to that prepared by the stirred media milling.     

Diameter-dependent axial prestretch of porcine coronary arteries and veins

The pressure-diameter relation (PDR) and the wall strain of coronary blood vessels have important implications for coronary blood flow and arthrosclerosis, respectively. Previous studies have shown that these mechanical quantities are significantly affected by the axial stretch of the vessels. The objective of this study was to measure the physiological axial stretch in the coronary vasculature; i.e., from left anterior descending (LAD) artery tree to coronary sinus vein and to determine its effect on the PDR and hence wall stiffness. Silicone elastomer was perfused through the LAD artery and coronary sinus trees to cast the vessels at the physiologic pressure. The results show that the physiological axial stretch exists for orders 4 to 11 (> 24 μm in diameter) arteries and orders -4 to -12 (>38 μm in diameter) veins but vanishes for the smaller vessels. Statistically, the axial stretch is higher for larger vessels and is higher for arteries than veins. The axial stretch λ(z) shows a linear variation with the order number (n) as: λ(z) = 0.062n + 0.75 (R(2) = 0.99) for artery and λ(z) = -0.029n + 0.89 (R(2) = 0.99) for vein. The mechanical analysis shows that the axial stretch significantly affects the PDR of the larger vessels. The circumferential stretch/strain was found to be significantly higher for the epicardial arteries (orders 9-11), which are free of myocardium constraint, than the intramyocardial arteries (orders 4-8). These findings have fundamental implications for coronary blood vessel mechanics.     

Hemodynamics and O2 uptake during maximal knee extensor exercise in untrained and trained human quadriceps muscle: effects of hyperoxia.

To elucidate the potential limitations on maximal human quadriceps O2 capacity, six subjects trained (T) one quadriceps on the single-legged knee extensor ergometer (1 h/day at 70% maximum workload for 5 days/wk), while their contralateral quadriceps remained untrained (UT). Following 5 wk of training, subjects underwent incremental knee extensor tests under normoxic (inspired O2 fraction = 21%) and hyperoxic (inspired O2 fraction = 60%) conditions with the T and UT quadriceps. Training increased quadriceps muscle mass (2.9 +/- 0.2 to 3.1 +/- 0.2 kg), but did not change fiber-type composition or capillary density. The T quadriceps performed at a greater peak power output than UT, under both normoxia (101 +/- 10 vs. 80 +/- 7 W; P < 0.05) and hyperoxia (97 +/- 11 vs. 81 +/- 7 W; P < 0.05) without further increases with hyperoxia. Similarly, thigh peak O2 consumption, blood flow, vascular conductance, and O2 delivery were greater in the T vs. the UT thigh (1.4 +/- 0.2 vs. 1.1 +/- 0.1 l/min, 8.4 +/- 0.8 vs. 7.2 +/- 0.8 l/min, 42 +/- 6 vs. 35 +/- 4 ml x min(-1) x mmHg(-1), 1.71 +/- 0.18 vs. 1.51 +/- 0.15 l/min, respectively) but were not enhanced with hyperoxia. Oxygen extraction was elevated in the T vs. the UT thigh, whereas arteriovenous O2 difference tended to be higher (78 +/- 2 vs. 72 +/- 4%, P < 0.05; 160 +/- 8 vs. 154 +/- 11 ml/l, respectively; P = 0.098) but again were unaltered with hyperoxia. In conclusion, the present results demonstrate that the increase in quadriceps muscle O2 uptake with training is largely associated with increases in blood flow and O2 delivery, with smaller contribution from increases in O2 extraction. Furthermore, the elevation in peak muscle blood flow and vascular conductance with endurance training seems to be related to an enhanced vasodilatory capacity of the vasculature perfusing the quadriceps muscle that is unaltered by moderate hyperoxia.     

Light-dark differences in the effects of ambient temperature on gaseous metabolism in newborn rats.

Body temperature (T(b)) of rat pups (7-9 days old) raised under a 12:12-h light-dark (L-D) regimen (L: 0700-1900, D: 1900-0700) was consistently higher in D than in L by approximately 1.1 degrees C. We tested the hypothesis that the L-D differences in T(b) were accompanied by differences in the set point of thermoregulation. Measurements were performed on rat pups at 7-9 days after birth. O(2) consumption (VO(2)) and CO(2) production (VCO(2)) were measured with an open-flow method during air breathing, as ambient temperature (T(a)) was decreased from 40 to 15 degrees C at the constant rate of 0.5 degrees C/min. At T(a) >/=33 degrees C, VO(2) was not significantly different between L and D, whereas VCO(2) was higher in L, suggesting a greater ventilation. Over the 33 to 15 degrees C range the VO(2) values in D exceeded those in L by approximately 30%. Specifically, the difference was contributed by differences in thermogenesis at T(a) = 30 to 20 degrees C. As T(a) was decreased, the critical temperature at which VO(2) began to rise was lower in L. We conclude that the higher T(b) of rat pups in D is accompanied by a higher set point for thermoregulation and a greater thermogenesis. These results are consistent with the idea that, in newborns, endogenous changes in the set point of thermoregulation contribute to the circadian oscillations of T(b).