Noninvasive optical characterization of muscle blood flow,oxygenation, and metabolism in women with fibromyalgia

Introduction

Women with fibromyalgia (FM) have symptoms of increased muscular fatigue and reduced exercise tolerance, which may be associated with alterations in muscle microcirculation and oxygen metabolism. This study used near-infrared diffuse optical spectroscopies to noninvasively evaluate muscle blood flow, blood oxygenation and oxygen metabolism during leg fatiguing exercise and during arm arterial cuff occlusion in post-menopausal women with and without FM.

Methods

Fourteen women with FM and twenty-three well-matched healthy controls participated in this study. For the fatiguing exercise protocol, the subject was instructed to perform 6 sets of 12 isometric contractions of knee extensor muscles with intensity steadily increasing from 20 to 70% maximal voluntary isometric contraction (MVIC). For the cuff occlusion protocol, forearm arterial blood flow was occluded via a tourniquet on the upper arm for 3 minutes. Leg or arm muscle hemodynamics, including relative blood flow (rBF), oxy- and deoxy-hemoglobin concentration ([HbO₂] and [Hb]), total hemoglobin concentration (THC) and blood oxygen saturation (StO₂), were continuously monitored throughout protocols using a custom-built hybrid diffuse optical instrument that combined a commercial near-infrared oximeter for tissue oxygenation measurements and a custom-designed diffuse correlation spectroscopy (DCS) flowmeter for tissue blood flow measurements. Relative oxygen extraction fraction (rOEF) and oxygen consumption rate (rVO₂) were calculated from the measured blood flow and oxygenation data. Post-manipulation (fatiguing exercise or cuff occlusion) recovery in muscle hemodynamics was characterized by the recovery half-time, a time interval from the end of manipulation to the time that tissue hemodynamics reached a half-maximal value.

Results

Subjects with FM had similar hemodynamic and metabolic response/recovery patterns as healthy controls during exercise and during arterial occlusion. However, tissue rOEF during exercise in subjects with FM was significantly lower than in healthy controls, and the half-times of oxygenation recovery (Δ[HbO₂] and Δ[Hb]) were significantly longer following fatiguing exercise and cuff occlusion.

Conclusions

Our results suggest an alteration of muscle oxygen utilization in the FM population. This study demonstrates the potential of using combined diffuse optical spectroscopies (i.e., NIRS/DCS) to comprehensively evaluate tissue oxygen and flow kinetics in skeletal muscle.     

Oxygenation of Native or UV-Modified Human Hemoglobin in the Presence of Nitric Oxide

The effect of 0.1–10% nitrosohemoglobin (HbNO) on the functional properties of human oxyhemoglobin (HbO₂) was studied before and after UV irradiation at 151–453 J/m². Oxygen binding analysis showed that HbNO intensified the first stage of oxygenation and weakened the cooperative interactions in the tetramer, decreasing the affinity of hemoglobin for oxygen at physiologically important oxygen partial pressures (40–100 mm Hg). Mixtures of HbO₂ and HbNO were highly resistant to therapeutic doses of UV irradiation. Since the functional activity of hemoglobin depended nonlinearly on the concentration of HbNO in the mixture, it was assumed that sophisticated interactions of HbO₂ and HbNO yielded a new product differing in properties from the initial components.     

Comparison of the optimal culture conditions for cell growth and tissue plasminogen activator production by human embryo lung cells on microcarriers

Optimization of culture conditions such as the dissolved O₂ (DO) concentration, temperature and pH was attempted regarding both cell growth and the production of tissue plasminogen activator (TPA) in a microcarrier cell culture of human embryo lung cells. The growth rate was suppressed at a DO concentration below 30% saturation. From the pH range 7.2–7.6, both the specific growth rate and maximal cell concentration decreased. At a lower temperature than 37°C, although both the specific growth rate and the maximal cell concentration decreased, the cell concentration was maintained for a longer time during the production period, high TPA productivity being maintained. As the optimal conditions for culture growth, a DO concentration of 30% saturation or over, temperature of 37°C and pH of 7.4 are recommended. However, for TPA production after cell culture growth, the DO concentration should be in the range 20–30% O₂ saturation, and the temperature and pH should be lowered to 33°C and 6.8, respectively.     

Passive heat exposure induced by hot water leg immersion increased oxyhemoglobin in pre-frontal cortex to preserve oxygenation and did not contribute to impaired cognitive functioning

This study investigated the effects of passive heat exposure on pre-frontal cortex oxygenation and cognitive functioning, specifically to examine whether the change in pre-frontal cortex oxygenation coincided with cognitive functioning during heat exposure. Eleven male students who participated in this study immersed their lower legs to the knees in three different water temperatures, 38 °C, 40 °C, and 42 °C water in an air temperature of 28?º C and 50 % relative humidity for 60 min. After 45 min of leg immersion they performed cognitive functioning tasks assessing their short-term memory while immersing their lower legs. There were higher rectal temperature (P?<?0.05) and higher increase of oxyhemoglobin in both left (P?<?0.05) and right (P?<?0.05) pre-frontal cortex at the final stage of 45-min leg immersion in the 42 °C condition with unaltered tissue oxygenation index among the three conditions (P?>?0.05). No statistical difference in cognitive functioning among the three conditions was observed with a higher increase of oxyhemoglobin during the cognitive functioning in the 42 °C condition for the left (P?=?0.05) and right (P?<?0.05) pre-frontal cortex. The findings of this study suggest, first, passive heat exposure increases oxygen delivery in the pre-frontal cortex to maintain pre-frontal cortex oxygenation; second, there is no evidence of passive heat exposure in cognitive functioning in this study; and third, the greater increases of oxyhemoglobin in the pre-frontal cortex during cognitive functioning at the hottest condition suggests a recruitment of available neural resources or greater effort to maintain the same performance at the same level as when they felt thermally comfortable.     

Thermoacclimatory changes in blood oxygen binding properties and gill secondary lamellar structure ofSalmo gairdneri

Summary The blood oxygen binding properties and gill secondary lamellar structure of rainbow trout acclimated to several temperatures were studied. The blood oxygen carrying capacity decreased as acclimation temperature increased from 2 to 15 °C; the decrease was probably caused by an increase in plasma volume. Also the blood oxygen affinity decreased as the acclimation temperature increased from 2 to 15 °C. This change had no effect on the oxygen loading in gills, since the efferent arterial oxygen tension was adequate for approximately 100% erythrocytic O₂ saturation at all acclimation temperatures, but facilitated the oxygen unloading in tissues. At the highest acclimation temperature (18 °C) the oxygen loading in gills was facilitated by the changes in the secondary lamellar structure; the proportion of erythrocytes in the secondary lamellar capillaries was higher than at the other acclimation temperatures (2 and 10 °C).     

Optimization of extracorporeal membrane oxygenation therapy using near‐infrared spectroscopy to assess changes in peripheral circulation: A pilot study

Near‐infrared spectroscopy (NIRS) has been proposed as a noninvasive modality for detecting complications in patients undergoing extracorporeal membrane oxygenation (ECMO), and it can simultaneously reveal the global circulatory status of these patients. We optimized ECMO therapy on the basis of real‐time peripheral NIRS probing. Three patients underwent venoarterial (VA) ECMO and one patient underwent venovenous (VV) ECMO. All patients received peripheral ECMO cannulation with routine distal perfusion catheter placement. We designed an experimental protocol to adjust ECMO blood flow over 1 hour. Hemodynamic responses were measured using NIRS devices attached to the calf at approximately 60% of the distance from the ankle to the knee. HbO₂ levels change substantially with adjustments in ECMO flow, and they are more sensitive than HHb levels and the tissue saturation index (TSI) are. NIRS for optimizing ECMO therapy may be reliable for monitoring global circulatory status.     

Oxyhemoglobin dissociation curve as expo-exponential paradigm of asymmetric sigmoid function.

From the assumption that the fractional increase of HbO₂ as a function of pO₂ is proportional to HbO₂, and that the proportionality coefficient of that relation decreases exponentially with pO₂, an equation can be derived that gives an excellent fit to the full range of the oxyhemoglobin dissociation curve. To generate this asymmetric sigmoid curve, only one rate constant is required. In addition, the initial and final conditions specify an intermediate constant B, the “shift factor” that determines the horizontal displacement of the curve. The rate constant K specifies the rate of change of the specific rate of increase of HbO₂ with respect to O₂. Governing the slope of the curve, K decreases as temperature and acidity increase, while the B factor remains constant. For Hb in solution, B decreases with decrease of concentration, but K appears to be unchanged. The expo-exponential constants provide convenient specification of the full course and position of the oxyhemoglobin dissociation curve.     

Moisture content and CO2 exchange of lichens

Summary Net photosynthesis (10 klx light intensity, 150 E m^-2 s^-1 PAR) and dark respiration of the lichen Ramalina maciformis at different temperatures are measured in relation to thallus water content. Both first increase with increasing hydration. Dark respiration then remains constant with increased water content until thallus saturation. In contrast, a further increase in water content leads to a depression of net photosynthesis, as shown in previous studies, after a maximum of CO₂ uptake has been attained. However, the extent of this depression depends strongly on temperature. In saturated thalli (160% water content in relation to lichen dry weight) the depression amounts to about 15% and 63% of the maximum unsaturated rate at 5°C and 25°C thallus temperature, respectively. The moisture compensation-point of net photosynthesis is also decisively determined by temperature (for 0°C at 20% water content; for 25°C at 15%), and the water content that allows maximum rates of CO₂ uptake (for 0°C at 80%; for 25°C at less than 40% water content). An electrical analogue of CO₂ exchange in a lichen thallus is presented, and it is suggested that the experimental results may be interpreted in terms of temperature-dependent CO₂ diffusion resistances in imbibed lichen thalli.     

Nodulation and N2 fixation of guar at high root temperature

Guar (Cyamopsis tetregonoloba (L.) may be grown when soil temperatures are potentially high enough at the time of planting to inhibit nodulation and N₂ fixation. An experiment was conducted using controlled conditions to determine the influence of high root temperature on growth and N₂ fixation of guar. The experiment included two strains of rhizobia, two varieties of guar, two mineral N treatments, and root temperatures of 34, 37, and 40°C. Plants were grown for 44 days. The root temperature of 40°C reduced N fixation by at least 80% and nodule weight by more than 50%. Significant interactions occurred between most factors in influencing nodulation, N₂ fixation and dry matter production. Guar, nodulated by rhizobial strain GAR022-1 and fully dependent on N₂ fixation or provided with starter mineral N (25 mg pot^–1), was not influenced by the root temperature of 37°C as compared to 34°C. Nodulation and N₂ fixation by strain 32H1 was reduced by at least 40% when no starter mineral N was provided and the root temperature was 37°C. Providing starter mineral N to one variety of guar doubled the quantity of N₂ fixed by strain 32H1 at both 34 and 37°C but N₂ fixation was lower at the higher root temperature. It appears that root temperatures between 37° and 40°C bracketed the critical root temperature for N₂ fixation by nodulated guar and that the critical root temperature for guar dependent on mineral N was above 40°C.     

Thermal adaptability and disease association in common carp (Cyprinus carpio communis) acclimated to different (four) temperatures

The present study was designed to investigate the effect of temperature (20 °C, 24 °C, 28 °C and 32 °C) on the heamato-biochemical and histological alterations of Cyprinus carpio communis. Increase in the temperature showed significant decrease in the serum protein, while a reduced level of blood glucose at high temperature of 32 °C was observed leading to hypoglycemic conditions in the experimental fishes. A significant correlation (P<0.01) was observed between cholesterol (Cho) and triglycerides (TG) for different temperature treatments. Elevated blood urea nitrogen (BUN) at high temperatures was a good indicator of gill osmoregulatory failure. A variation of 86.40% and 38.33%, respectively, was noticed in alanine aminotransferase (ALT) and aspartate aminotransferase (AST) at 32 °C over minimum experimental temperature of 20 °C. The increase in red blood cell (RBC) and Heamoglobin (Hb) concentration is associated with the decrease of mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC), could be the reason for observed poikilo-anisocytosis. Histological studies of different organs of experimental fishes showed accumulation of MMC's (melanomacrophagic centers) and atrophy of the interrenal tissue on exposure to various levels of temperature. These changes were related to severity of thermal stress, being most marked when high temperature was prolonged during acclimatization. Some fishes were found infested by protozoan parasite at elevated temperature of 32 °C. Increased levels of certain biochemical and haemotological parameters studied were strongly correlated with disease in the Cyprinus carpio communis species.     

Influence of freezing temperatures on a cactus,Coryphantha vivipara

Summary Coryphantha vivipara (Nutt.) Britton & Rose var. deserti (Engelm.) W.T. Marshall (Cactaceae) survived snow and tissue temperatures of-12°C in southern Nevada. However, the freezing point depression of the cell sap was only about 0.9°C. When the nocturnal air temperature in the laboratory was reduced from 10°C to-10°C for one night, the optimum temperature for CO₂ uptake shifted from 10°C to 6°C and uptake was reduced 70%, but full recovery to the original values occurred in 4 days. Nocturnal temperatures of-15°C killed 2 out of 5 plants and-20°C killed 5 out of 5, as judged by lack of net CO₂ uptake at night over a 2-month observation period. when the stems were cooled at 2° C/h, supercooling to about-6°C occurred followed by an exothermic reaction that presumably represented the freezing of extracellular water. When the subzero temperature was lowered further, no other exothermic reaction was observed and the cells became progressively dehydrated. Freezing-induced tissue death was ascribed to this cellular dehydration, which led to about 94% loss of intracellular water at-15°C. when the tissue temperature was lowered, the ability of chlorenchyma cells to plasmolyze and to take up a stain decreased, both being nearly 70% inhibited at-15°C and completely abolished at-20°C. Some cold-bardening occurred, since lowering the air temperature from 30° to-10°C in 10°C increments at weekly intervals caused the subzero temperature for 50% inhibition of staining to decrease from-10°C to-17°C. Extension of the range of C. vivipara to regions with wintertime freezing apparently reflects the tolerance of considerable freeze dehydration by its protoplasts.     

Temperature insensitive O2 in blood of the tree frogChiromantis petersi

Summary Respiratory gas exchange and blood respiratory properties have been studied in the East-African tree frogChiromantis petersi. This frog is unusually xerophilous, occupies dry habitats and prefers body temperatures near 40°C and direct solar exposure. Total O₂ uptake was low at 81 l O₂·g^–1·h^–1±19.0 (SD) at 25°C increasing to 253.5 l O₂·g^–1·h^–1±94.8 (SD) at 40°C giving aQ ₁₀ value of 2.1. Skin O₂ uptake at 25°C was 38.5% of total. The gas exchange ratio was 0.71 for whole body gas exchange, 0.61 for the lungs and 1.02 for the skin at 25°C.Blood O₂ affinity was low with aP ₅₀ of 47.5 mmHg at 25°C and pH 7.65. Then _H-value at 25°C increased from 2.7 aroundP ₅₀ to 5.0 at O₂ saturations exceeding 70–80%. Surprisingly, blood O₂ affinity was nearly insensitive to temperature expressed by a H value of ±1.0 kcal·mole between 25 and 40°C.The adaptive significance of the low O₂ affinity, the increase ofn _H with O₂ saturation and the temperature insensitive O₂-Hb binding is discussed in relation to the high and fluctuating body temperatures ofChiromantis.     

Circular dichroism spectra of human hemoglobin reveal a reversible structural transition at body temperature

Previously we have shown that human red blood cells (RBCs) undergo a sudden change from blocking to passing through a 1.3±0.2-µm micropipette when applying an aspiration pressure of 2.3 kPa at a critical transition temperature (T_c=36.4±0.3 °C). Low-shear viscosity measurements suggested that changes in the molecular properties of hemoglobin might be responsible for this effect. To evaluate structural changes in hemoglobin at the critical temperature, we have used circular dichroism (CD) spectroscopy. The thermal denaturation curves of human hemoglobin A (HbA) and hemoglobin S (HbS) upon heating between 25 and 60 °C were non-linear and showed accelerated denaturation between 35 and 39 °C with a midpoint at 37.2±0.6 °C. The transition was reversible below 39 °C and independent of solution pH (pH 6.8–7.8). It was also independent of the oxygenation state of hemoglobin, since a sample that was extensively deoxygenated with N₂ showed a similar transition by CD. These findings suggest that a structural change in hemoglobin may enable the cellular passage phenomenon as well as the temperature-dependent decrease in viscosity of RBC solutions.     

Hematological responses to thermal acclimation in a cold water squaliform (Heterodontus francisci girard)

Summary The hematological modifications occurring as a result of acclimation to increased temperature in the cold water horn shark,Heterodontus francisci, were evaluated. Sharks were maintained under constant conditions except for temperature (15°C and 25°C) in a closed marine system. The total red blood cell (RBC) number decreased in the 25°C sharks. In contrast, hemoglobin concentration, hematocrit, mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) significantly increased at 25°C compared to the control animals. RBC size was increased at 25°C, but the surface area/mm³ whole blood was reduced. Folic acid levels were not different between the groups. Vitamin B₁₂ levels decreased and testosterone increased at 25°C. Blood pH, number of erythroblasts, number of white blood cells (WBC) and WBC differential analyses were essentially unchanged at the two temperatures, except that the relative neutrophil number was increased. The major hematological changes occur in the erythrocytes and appear to be sequential in nature with an initial loss of RBC followed by increased hemoglobin synthesis and increased RBC size, but lack of recovery of RBC numbers.Abbreviations Hb hemoglobin - Hct hematocrit - MCH(C) mean corpuscular hemoglobin (concentration) - MCV mean corpuscular volume - RBC red blood cells - WBC white blood cells Contribution Number 359, Department of Biology     

Determination of the overall volumetric mass transfer coefficient kLa,by a temperature dependent change of gas solubility

Summary The solubility of oxygen in the liquid phase of a bioreactor was changed by a ramp change of temperature, and k_La was determined from the resulting return to equilibrium of dissolved oxygen activity. The maximum k_La that can be measured by this method in a standard laboratory scale bioreactor is 145 h^–1 corresponding to a temperature change rate of 320°C h^–1.Nomenclature p Difference between p_G and p_L (% saturation) - T Ramp change of temperature (°C) - E Temperature-compensated output from the oxygen electrode (A) - E_u Uncompensated output from the oxygen electrode (A) - k_La Overall volumetric mass transfer coefficient (h^–1) - k_La_Tm Overall volumetric mass transfer coefficient at temperature T_m (h^–1) - P_G Dissolved oxygen activity in equilibrium with the gas phase (% saturation) - p_L Dissolved oxygen activity (% saturation) - p_Lm Dissolved oxygen activity at time t_m (% saturation) - t Time (h) - t_m Time of maximum p (h) - T Temperature (°C) - T_cal Calibration temperature of the oxygen electrode (°C) - T_m Final temperature after a temperature shift (°C) - T_n Temperature at time t_n     

The use of a temperature-profiled position transducer for the study of low-temperature growth in Gramineae

A device is described for measuring linear extension of grass leaves during controlled cooling and heating of the growing region. The instrument was employed to investigate the sensitivity to temperature of the expanding third and fourth leaves of Lolium temulentum L. seedlings. Using a stepped temperature profile it was established that there was no lag in the response of growth rate to rapid changes in temperature below 16°C. If cooling was continued to the point where growth ceased (1°C) but no further, then rates of growth on rewarming were enhanced over the chilling range and reverted to the original rate at 20°C. Cooling to successively lower subzero temperatures before rewarming abolished the hysteretic enhancement, progressively raised the temperature at which growth resumed and decreased the rate of extension until, at-5.3°C, no recovery occurred. The temperature sensitivity of growth, measured as Q₁₀, was essentially constant when cooling from 20°C to 5°C, with 5°C-grown leaf tissue exhibiting a higher mean Q₁₀ than tissue developed at 20°C. The possible physiological significance of these data is discussed.Abbreviations LVDT linear variable displacement transformer - Pe, Fx temperatures at which growth ceases during cooling and resumes during rewarming     

Stability of diether C(25,25) liposomes from the hyperthermophilic archaeon Aeropyrum pernix K1

Temperature and pH effects were studied for stability, structural organization, fluidity and permeability of vesicles from a polar lipid methanol fraction isolated from the Aeropyrum pernix. We determined the permeability of C_25,25 liposomes using fluorescence intensity of released calcein. At pH 7.0 and 9.0, and from 85 °C to 98 °C, only 10% of entrapped calcein was released. After 10 h at 90 °C, calcein release reached 27%, independent of pH. Fluorescence anisotropy measurements of hydrophobic probe 1,6-diphenyl-1,3,5-hexatriene revealed gradual changes up to 60 °C. At higher temperatures, the anisotropy did not change significantly. Fluorescence alone did not provide detailed and direct structural information about these C_25,25 liposomes, so we used electron paramagnetic resonance spectroscopy (EPR) and differential scanning calorimetry (DSC). From EPR spectra, mean membrane fluidity determined according to maximal hyperfine splitting and empirical correlation times showed continuous increases with temperature. Computer simulation of EPR spectra showed heterogeneous membranes of these C_25,25 liposomes: at low temperatures, they showed three types of membrane regions characterized by different motional modes. Above 65 °C, the membrane becomes homogeneous with only one fluid-like region. DSC thermograms of C_25,25 liposomes reveal a very broad and endothermic transition in the temperature range from 0 °C to 40 °C.     

Metabolic response of juvenile gray snapper (Lutjanus griseus) to temperature and salinity: Physiological cost of different environments

Juvenile gray snapper (Lutjanus griseus) occupy a wide range of estuarine and nearshore habitats that differ in physico-chemical properties. To quantify the energetic cost of inhabiting these different habitats, routine metabolism of individual gray snapper was measured in the laboratory at 20 combinations of temperature (18, 23, 28, and 33 °C) and salinity (5, 15, 25, 35, and 45 psu). An open, flow-through respirometer was used, enabling trials to be run for long periods (∼16 h), while maintaining water quality (dissolved O₂>70% saturation), and providing fish sufficient time to habituate to the chambers undisturbed. Video recordings of fish in the respirometer chambers were analyzed to quantify the spontaneous activity rate of individuals. Analysis of covariance, using fish weight and mean activity rate as covariates, indicated significant temperature and salinity effects on oxygen consumption. Oxygen consumption was significantly higher at high salinities, and the salinity effect was temperature dependent. A polynomial equation describing oxygen consumption as a function of temperature and salinity indicated the increase due to salinity from 5 to 45 psu at high temperatures (30-33 °C) was equivalent to a 3 °C increase in temperature. At intermediate temperatures (24-26 °C), the increase due to salinity from 5 to 45 psu was less dramatic, equivalent to a 2 °C increase in temperature. At the lowest temperatures (18 °C), salinity did not have a significant effect on oxygen consumption. The increased metabolic costs in high salinities (∼7% at the high temperature) represent a significant energy cost for juveniles, that would need to be balanced by lower predation risk or greater food availability to result in similar juvenile production compared to lower salinity environments.     

Effect of temperature on hemolymph lactate and glucose concentrations in spiny lobster Panulirus interruptus during progressive hypoxia

Some metabolic fuels in hemolymph samples from the sinuses at the base of the third walking leg (pre-branchial blood) and from the cardiac sinus (post-branchial blood) in the red lobster, Panulirus interruptus, were evaluated during normoxia, hypoxia, and at the critical oxygen point (P_cr) at two temperatures of acclimatization. Three-way ANOVA indicated a significant effect of oxygen saturation R(6140)=19.84 in metabolic fuel concentrations. Lactate varied from 0.01 to 0.29 mg/ml at 20 °C, from 0.02 to 0.29 mg/ml at 27 °C, and increased significantly during hypoxia (P<0.05). Glucose varied from 0.10 to 0.27 mg/ml at 20 °C, from 0.13 to 0.33 mg/ml at 27 °C, and increased with temperature. Proteins varied from 80.78 to 119.99 mg/ml at 20 °C and from 82.99 to 130.30 mg/ml at 27 °C.     

Influence of temperature and ambient oxygen on the swimming energetics of cyprinid larvae and juveniles

Synopsis The relationship between respiration and swimming speed of larvae and juveniles (2–100 mg fresh mass) of Danube bleak, Chalcalburnus chalcoides (Cyprinidae), was measured at 15° and 20° C under hypoxic (50% air saturation), normoxic, and hyperoxic (140% air saturation) conditions. In a flow-tunnel equipped with a flow-through respirometer the animals swam at speeds of up to 8 lengths · s^-1; speeds were sustained for at least two minutes. The mass specific standard, routine, and active respiration rates declined with increasing body mass at both temperatures. Metabolic intensity increased with temperature, but also the critical swimming speed (at which oxygen uptake reached its maximum) was higher at 20° than at 15° C by about 30%. Nevertheless, the oxygen debt incurred by the fish at the highest speeds was about 40%, and the net cost of swimming about 32%, lower at 20° than at 15°C. The standard metabolic rate was more strongly dependent on temperature (Q₁₀ around 2.5) than the maximum active rate (Q₁₀ below 2). Whereas standard and routine respiration rates were well regulated over the pO₂-range investigated (8.5–25.8 kPa), the active rates showed a conformer-like pattern, resulting in factorial scopes for activity between 2 and 4. Under hypoxia, the critical swimming speed was lower than under normoxia by about 1.51 · s^-1, but the net cost of swimming was also lower by about 30%. On the other hand, hyperoxia neither increased the swimming performance nor did it lead to a further increase of the metabolic cost of swimming. The hypoxia experiments suggest that in response to lowered tensions of ambient oxygen maintenance functions of metabolism not directly related to swimming may be temporarily reduced, leading to increased apparent swimming efficiency under these conditions. The responses of the larvae of Danube bleak to low temperature and low ambient oxygen are discussed in terms of the metabolic strategies by which energy-limited animals meet the challenge of environmental deterioration.