Ventilatory and metabolic responses of a bat,Phyllostomus discolor,to hypoxia and CO2: implications for the allometry of respiratory control

The ventilatory and metabolic responses of lesser spear-nosed bats to hypoxia and hypercapnia were measured to determine whether these corresponded to preliminary allometries and a positive relationship between hypoxic ventilatory threshold andP ₅₀. Ventilatory responses of lesser spear-nosed bats to 3, 5 and 7% CO₂ differed significantly from ventilation on air and each other. The magnitude of their ventilatory response to CO₂ is consistent with the prediction of a smaller ventilatory response to hypercapnia in small compared to large mammals [ ; Williams et al. (1994)]. Among 12, 10 and 8% O₂ treatments only the ventilatory response to 8% O₂ differed significantly from ventilation on air or the other treatments. Metabolic rate was significantly reduced at both 10 and 8% O₂. The hypoxic ventilatory response of these bats does not support the prediction of a greater response in small compared to large mammals [ ; Boggs and Tenney (1984)]. Their metabolic response is consistent with the hypoxic hypometabolism typical of small mammals, though not of comparable magnitude. The response, expressed as percent change in convection requirement ( ), is also less than that observed in other small mammals. This relative insensitivity to hypoxia may be associated with this bat's unusually high affinity hemoglobin (P₅₀=27.5 torr).     

Muscle mass as a factor limiting physical work

Maximal exercise has been performed by eight men and eight women, using four types of ergometer (2-leg, 1-leg, arm + shoulder, and arm) while breathing room air and while breathing 12% O2. Results have been related to anthropometric estimates of muscle mass in the active limbs. Although significant sex differences of O2 transfer and power output are shown, the sex-specific aerobic performance was roughly proportional to active muscle volume (both when comparing individuals on a given type of ergometer and when comparing average scores of the several types of ergometer). However, the relationship was closer for steady power output than for peak O2 intake (where the scores for arm work were boosted by the use of accessory muscles and by hyperventilation). When breathing 12% O2, the 2-leg performance was substantially reduced (an average of 28.7% for O2 transport and 19.2% for power output). This effect dropped to 9.1% for O2 transport and 12% for power output in one-leg ergometry and was negligible for arm or arm plus shoulder work. It is argued that because of difficulty in perfusing small muscles, arm work is limited largely by the intrinsic power of the active muscles, that single-leg ergometry is limited rather equally by central circulatory and muscular factors, and that two-leg ergometry is almost entirely dependent on the central circulatory transport of O2.     

Effect of hypoxia on the content and stoichiometry of cytochromes in muscle of the gray mullet Liza aurata

The maintenance of the gray mullet Liza aurata under conditions of hypoxia ( $ P_{O_2 } The maintenance of the gray mullet Liza aurata under conditions of hypoxia ( 55–82 GPa) for 1–2 days led to a decrease of oxygen tension in arterial blood by 47%, while in venous blood—by 28%. The mean muscle oxygen tension decreased by 19.2%. The number of hypoxic and anoxic zones in muscle tissue decreased significantly, in particular in red muscle. The maintenance of the fish in hypoxic waters for 15 days led to a rise of the content of cytochromes in muscle and a qualitative readjustment of the mitochondrial respiratory chain manifested in an increase of the content of cytochromes a and a3 and a decrease of cytochrome b. In discussion, literature data are presented which support the described regularity. Original Russian Text ? A. A. Soldatov, M. V. Savina, 2008, published in Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, 2008, Vol. 44, No. 5, pp. 508–512.     

Dynamics of cardiorespiratory function in Standardbred horses during different intensities of constant-load exercise

Summary Six Standardbred horses were used to evaluate the time course of pulmonary gas exchange, ventilation, heart rate (HR) and acid base balance during different intensities of constant-load treadmill exercise. Horses were exercised at approximately 50%, 75% and 100% maximum oxygen uptake ( max) for 5 min and measurements taken every 30 s throughout exercise. At all work rates, the minute ventilation, respiratory frequency and tidal volume reached steady state values by 60 s of exercise. At 100% max, the oxygen consumption ( ) increased to mean values of approximately 130 ml/kg·min, which represents a 40-fold increase above resting . At the low and moderate work rates, showed no significant change from 30 s to 300 s of exercise. At the high work rate, the mean at 30 s was 80% of the value at 300 s. The HR showed no significant change over time at the moderate work rate but differing responses at the low and high work rates. At the low work rate, the mean HR decreased from 188 beats/min at 30 s to 172 beats/min at 300 s exercise, whereas at the high work rate the mean HR increased from 204 beats/min at 30 s to 221 beats/min at 300 s exercise. No changes in acid base status occurred during exercise at the low work rate. At the moderate work rate, a mild metabolic acidosis occurred which was nonprogressive with time, whereas the high work rate resulted in a progressive metabolic acidosis with a base deficit of 16 mmol/l by 300 s exercise. It is concluded that the kinetics of gas exchange during exercise are more rapid in the horse than in man, despite the relatively greater change in in the horse when going from rest to high intensity exercise.Symbols and abbreviations E minute ventilation - V _T tidal volume - oxygen uptake - carbon dioxide output - oxygen pulse - ventilatory equivalent for oxygen - ventilatory equivalent for carbon dioxide - R respiratory exchange ratio - HR heart rate - SBC standard bicarbonate - STPD standard temperature and pressure dry - BTPS body temperature and pressure saturated - arterial oxygen content - arteriovenous oxygen content difference - Rf respiratory frequency     

Effects of β-alanine supplementation on the onset of neuromuscular fatigue and ventilatory threshold in women

Summary. This study examined the effects of 28 days of β-alanine supplementation on the physical working capacity at fatigue threshold (PWC_FT), ventilatory threshold (VT), maximal oxygen consumption ( O_2-MAX), and time-to-exhaustion (TTE) in women. Twenty-two women (age ± SD 27.4 ± 6.1 yrs) participated and were randomly assigned to either the β-alanine (CarnoSyn™) or Placebo (PL) group. Before (pre) and after (post) the supplementation period, participants performed a continuous, incremental cycle ergometry test to exhaustion to determine the PWC_FT, VT, O_2-MAX, and TTE. There was a 13.9, 12.6 and 2.5% increase (p < 0.05) in VT, PWC_FT, and TTE, respectively, for the β-alanine group, with no changes in the PL (p > 0.05). There were no changes for O_2-MAX (p > 0.05) in either group. Results of this study indicate that β-alanine supplementation delays the onset of neuromuscular fatigue (PWC_FT) and the ventilatory threshold (VT) at submaximal workloads, and increase in TTE during maximal cycle ergometry performance. However, β-alanine supplementation did not affect maximal aerobic power ( O_2-MAX). In conclusion, β-alanine supplementation appears to improve submaximal cycle ergometry performance and TTE in young women, perhaps as a result of an increased buffering capacity due to elevated muscle carnosine concentrations.     

Comparison of the aerobic performance of leg and arm muscles in cross-country skiers

In the last fifteen years, a trend has appeared in cross-country ski racing to increase the use of double poling and, therefore, to increase the load on the shoulder girdle (arm) muscles. The purpose of this study was to compare the aerobic performance of elite cross-country skiers in incremental running (treadmill) and double poling (with manual ski ergometer) tests to exhaustion. Four junior cross-country skiers and four biathletes ( $ \dot V_{O_{2max} } $ = 70 (66?C72) mL/min per kg body weight) participated in the experiment. In the double poling test, the lactate concentration increased more rapidly than in the running test, and the peak oxygen consumption ( $ \dot V_{O_{2peak} } $ ) in the double poling test was 88 (84?C93)% of the maximal oxygen consumption ( $ \dot V_{O_{2max} } $ ) in the running test. The relative anaerobic threshold, which characterizes the relative level of current aerobic performance, in the double poling test was significantly lower than in the running test (79 (57?C83)% vs 94 (90?C98)%, respectively). On the basis of these data, it can be concluded that the main reserve for a further increase in the aerobic performance of cross-country skiers and biathletes is the increase in the aerobic capacity of arm and trunk muscles.     

Use of the force-velocity test to determine the optimal braking force for a sprint exercise on a friction-loaded cycle ergometer

A group of 15 untrained male subjects pedalled on a friction-loaded cycle ergometer as fast as possible for 5–7 s to reach the maximal velocity (V{immax}) against different braking forces (F _B). Power was averaged during a complete crank rotation by adding the power dissipated againstF _B to the power necessary to accelerate the flywheel. For each sprint, determinations were made of peak power output ( ) power output attained atV _max ( ) calculated as the product ofV _max andF _B and the work performed to reachV _max expressed in mean power output ( ). The relationships between these parameters andF _B were examined. A biopsy taken from the vastus lateralis muscle and tomodensitometric radiographs of both thighs were taken at rest to identify muscle metabolic and morphometric properties. The value was similar for allF _B. Therefore, the average of values was defined as corrected maximal power ( ). This value was 11 higher than the maximal power output uncorrected for the acceleration. Whereas the determination did not require high loads, the highest value ( ) was produced when loading was heavy, as evidenced by the -F _B parabolic relationship. For each subject, the braking force ( ) giving was defined as optimal. The , equal to 0.844 (SD 0.108) N · kg⁻¹ bodymass, was related to thigh muscle area (r = 0.78,P < 0.05). The maximal velocity ( ) reached against this force seemed to be related more to intrinsic fibre properties (% fast twitch b fibre area and adenylate kinase activity). Thus, from the determination, it is suggested that it should be possible to predict the conditions for optimal exercise on a cycle ergometer.     

Energy metabolism and ATP free-energy change of the intertidal wormSipunculus nudus below a critical temperature

The intertidal wormSipunculus nudus was exposed to various temperatures for an analysis of the integrated changes in energy and acid-base status. Animals were incubated in sea water or maintained for up to 8 days at 4 and 0°C while dwelling in the sediment. Cannulation of the animals prior to experimentation allowed the analysis of blood gas parameters ( , and pH). fell to 0 torr within 8 days at 0°C. A simultaneous reduction of ventilatory activity was derived from measurements of the pattern of coelomic fluid pressure changes associated with ventilatory movements. The increase in and an onset of anaerobic metabolism, indicated by the accumulation of end products like acetate and propionate both in the coelomic fluid and the body wall musculature, led to the development of a progressive acidosis and a deviation from the alphastat regulation of intracellular pH seen in unburied animals. The drop in intracellular pH together with the depletion of the adenylates and the phosphagen, phospho-l-arginine, reflect a significant decrease in the Gibb's free-energy change of ATP hydrolysis. These changes are interpreted to indicate lethal cold injuries, because recovery was not possible when the animals were returned to 12°C after more than 2 days of exposure to 0°C. A low critical temperature indicating the onset of cold-induced anaerobiosis is concluded to exist below 4°C owing to the insufficient response of the ventilatory system to the developing hypoxia.     

A model of oxygen uptake kinetics in response to exercise: Including a means of calculating oxygen demand/deficit/debt

We present a new model of the underlying dynamics of the oxygen uptake kinetics for various exercise intensities. This model is in the form of a set of nonlinear coupled vector fields for the and , the derivative of the exercise intensity with respect to time. We also present a new and novel means for calculating the oxygen demand, D(v, t), and hence also the oxygen deficit and debt, given the time series of the . This enables us to give better predictions for these values especially for when exercising at or close to maximal exercise intensities. Our model also allows us to predict the oxygen uptake time series given the time series for the exercise intensity as well as to investigate the oxygen uptake response to nonlinear exercise intensities. Neither of these features is possible using the currently used three-phase model. We also present a review of both the underlying physiology and the three-phase model. This includes for the first time a complete set of the analytical solutions of the three-phase model for the oxygen deficit and debt.     

Respiratory responses of elite oarsmen, former oarsmen, and highly trained non-rowers during rowing, cycling and running

The position of the body and use of the respiratory muscles in the act of rowing may limit ventilation and thereby reduce maximal aerobic power relative to that achieved in cycling or running, in spite of the greater muscle mass involved in rowing. This hypothesis was investigated for three groups of male subjects: nine elite senior oarsmen, eight former senior oarsmen and eight highly trained athletes unskilled in rowing. The subjects performed graded exercise to maximal effort on a rowing ergometer, cycle ergometer and treadmill while respiratory minute volume and oxygen consumption were monitored continuously. The VE at a given during intense submaximal exercise (greater than 75% of maximal ) was not significantly lower in rowing compared with that in cycling and treadmill running for any group, which would suggest that submaximal rowing does not restrict ventilation. At maximal effort, and for rowing were less than those for the other types of exercise in all the groups, although the differences were not statistically significant in the elite oarsmen. These data are consistent with a ventilatory limitation to maximal performance in rowing that may have been partly overcome by training in the elite oarsmen. Alternatively, a lower maximal VE in rowing might have been an effect rather than a cause of a lower maximal if maximal was limited by the lower rate of muscle activation in rowing.     

Reversed bohr and root shifts in hemocyanin of the marine prosobranch,Buccinum undatum: Adaptations to a periodically hypoxic habitat

Summary Oxygen binding properties of the hemocyanin-containing blood ofBuccinum undatum were examined in vitro and in vivo under normoxic ( 150 mmHg) and hypoxic ( 50 mmHg) conditions at 10°C. Blood pH and showed a decrease in vivo under hypoxic conditions. Oxygen uptake at high water , was about 18 ml O₂/kg·h (wet weight) and the critical oxygen tension between 25 and 50 mm Hg. In vitro the O₂ binding to hemocyanin showedn-values independent of pH, while both O₂ affinity and oxygen carrying capacity were strongly pH dependent. Oxygen affinity increased below pH=8.1 and thus showed a pronounced reversed Bohr shift in the physiological pH range (7.5<pH<8.1). The oxygen carrying capacity similarly increased markedly with falling pH in the physiological pH range (reversed Root shift). Astrup titration curves showed a metabolic and respiratory acidosis under hypoxic conditions ( 50 mm Hg). The role of hemocyanin in the transport of oxygen in relation to ambient O₂ availability is discussed.     

Oxidative power and intracellular distribution of mitochondria control cell oxygen regime when arterial hypoxemia occurs

The regulatory impact of the mitochondria spatial distribution and enlargement in their oxidative power $q_{O_2 } $ on tissue oxygenation of skeletal muscle during hypoxia were studied. Investigations were performed by mathematical modeling of 3D O₂ diffusion-reaction in muscle fiber. The oxygen consumption rate $V_{O_2 } $ and tissue $p_{O_2 } $ were analyzed in response to a decrease in arterial blood oxygen concentration from 19.5 to 10 vol % at moderate load. Cells with evenly (case 1) and unevenly (case 2) distributed mitochondria were considered. According to calculations, owing to a rise in mitochondria oxidative power from 3.5 to 6.5 mL/min per 100 g of tissue it is possible to maintain muscle oxygen $V_{O_2 } $ at a constant level of 3.5 mL/min per 100 g despite a decrease in O₂ delivery. The minimum value of tissue $p_{O_2 } $ was about 0 and an area of hypoxia appeared inside the cell in case 1. Whereas hypoxia disappeared and minimum value of $p_{O_2 } $ increased from 0 to 4 mmHg if mitochondria were distributed unevenly (case 2). The possibilities of such regulation depended on the relationship “the degree of hypoxemia — the level of oxygen delivery.” It was assumed that an increase in mitochondrial enzyme activity and their migration to places of the greatest oxygen consumption rate can improve the oxygen regime in the cell as it adapts to hypoxia.     

Control approach for high sensitivity cardiopulmonary exercise testing during stimulated cycle ergometry in spinal cord injured subjects

AimPeople with complete lower-limb paralysis resulting from spinal cord injury (SCI) can perform cycle ergometry by means of functional electrical stimulation. Here, we propose and evaluate new exercise testing methods for estimation of cardiopulmonary performance parameters during this form of exercise.MethodsWe utilised a customised ergometer incorporating feedback control of stimulated exercise workrate and cycling cadence. This allowed the imposition of arbitrary workrate profiles with high precision with the potential for improved sensitivity in exercise testing. New incremental exercise test (IET) and step exercise test (SET) protocols for determination of peak and steady-state performance parameters were assessed.ResultsThe IET protocol allowed reliable determination of the ventilatory threshold, peak workrate and oxygen uptake-workrate relationship, but gave unrepresentative peak oxygen uptake values and highly variable measures of oxygen uptake kinetics. The SET protocol gave reliable estimation of steady-state oxygen uptake and metabolic efficiency of constant load exercise, but high variability in the estimation of oxygen uptake kinetics.ConclusionThe feedback-controlled testbed and the new IET and SET protocols have the potential for estimation of cardiopulmonary performance parameters with improved sensitivity during stimulated cycle ergometry in subjects with SCI.     

Changes in skeletal muscle oxygenation during incremental exercise measured with near infrared spectroscopy

To determine the change in muscle oxygenation in response to progressively increasing work rate exercise, muscle oxyhemoglobin + oxymyoglobin saturation was measured transcutaneously with near infrared spectroscopy in the vastus lateralis muscle during cycle ergometry. Studies were done in 11 subjects while gas exchange was measured breath-by-breath. As work rate was increased, tissue oxygenation initially either remained constant near resting levels or, more usually, decreased. Near the work rate and metabolic rate where significant lactic acidosis was detected by excess CO₂ production (lactic acidosis threshold, LAT), muscle oxygenation decreased more steeply. As maximum oxygen uptake ( ) was approached, the rate of desaturation slowed. In 8 of the 11 subjects, tissue O₂ saturation reached a minimum which was sustained for 1–3 min before was reached. The LAT correlated with both the (r = 0.95,P < 0.0001) and the work rate (r = 0.94,P < 0.0001) at which the rate of tissue O₂ desaturation accelerated. These results describe a consistent pattern in the rate of decrease in muscle oxygenation, slowly decreasing over the lower work rate range, decreasing more rapidly in the work rate range of the LAT and then slowing at about 80% of , approaching or reaching a minimum saturation at .     

Respiration of the emersed shore crab at variable ambient oxygenation

Summary In the intertidal shore crab,Carcinus maenas, pH and values of the prebranchial venous hemolymph, and , the PO₂ values of the arterialized cardiac hemolymph, , were measured, and the ventilatory activity was assessed by measuring the hydrostatic pressures at the exits of the epibranchial cavities, under four environmental conditions: normoxic water, normoxic air, hypoxic gas, hyperoxic gas.In the crab breathing normoxic air, was lower and higher than in animals breathing normoxic water. With the switch to hypoxic gas, ventilation increased and and decreased. With the switch to hyperoxic gas, ventilation decreased, and increased and decreased.Thus these crabs breathing air were not as well oxygenated as when breathing air-equilibrated water, and because of their low , they were relatively hypervetilating and hypocapnic compared to air-breathing vertebrates. Hyperoxic breathing, increasing and reducing ventilatory drive, led to increased . Conversely, was reduced by hypoxic breathing. These observations suggest that the gas exchanger of intertidal crabs is not as successfully designed for air breathing as that of land-colonizing insects and air-breathing vertebrates.     

A three component model of human bioenergetics

The model described in this article is a generalised three component hydraulic model, proposed to represent net whole body bioenergetic processes during human exercise and recovery. During exercise, fluid flows from the three interconnected vessels in the system represent the breakdown of high energy phosphates (phosphagens), oxygen consumption and lactic acid production. During recovery, replenishment of the fluids represents the repayment of oxygen debt. The model is quantified and solved mathematically, and the solution compared with observed experimental data. Since currently known physiological facts are consistent with four configurations of this model, further experimentation is necessary.     

Whole-Catchment Manipulations of Internal and External Loading Reveal the Sensitivity of a Century-Old Reservoir to Hypoxia

Climate change is predicted to have widespread impacts on freshwater lake and reservoir nutrient budgets by altering both hypolimnetic hypoxia and runoff, which will in turn alter the magnitude of internal and external nutrient loads. To examine the effects of these potential climate scenarios on nitrogen (N) and phosphorus (P) budgets, we conducted a whole-catchment manipulation of hypolimnetic oxygen conditions and external loads to Falling Creek Reservoir (FCR), an old, eutrophic reservoir in a reforested catchment with a history of agricultural land use. Throughout 2 years of monitoring, internal N and P loading during hypoxic conditions dominated the hypolimnetic mass of nutrients in FCR, regardless of changes in external loading. FCR commonly functioned as a net sink of N and P, except during hypoxic conditions, when the reservoir was a net source of ammonium (\( {\text{NH}}_{4}^{ + } \)) to downstream. We observed extremely high nitrate–nitrite (\( {\text{NO}}_{3}^{ - } {-}{\text{NO}}_{2}^{ - } \)), soluble reactive P (SRP), total nitrogen (TN), and total phosphorus (TP) retention rates, indicating that the reservoir served as a sink for greater than 70% of \( {\text{NO}}_{3}^{ - } {-}{\text{NO}}_{2}^{ - } \) inputs and greater than 30% of SRP, TN, and TP inputs, on average. Our study is notable in the length of time since reforestation (>80 years) that a reservoir is still exhibiting high N and P internal loading during hypoxia, potentially as a result of the considerable store of accumulated nutrients in its sediment from historical agricultural runoff. Our whole-catchment manipulations highlight the importance of understanding how multiple aspects of global change, waterbody and catchment characteristics, and land use history will interact to alter nutrient budgets in the future.     

An evolutionary analytical model of a complementary circular code simulating the protein coding genes, the 5′ and 3′ regions

The self-complementary subset ∪{AAA,TTT} with = {AAC, AAT, ACC, ATC, ATT, CAG, CTC, CTG, GAA, GAC, GAG, GAT, GCC, GGC, GGT, GTA, GTC, GTT, TAC, TTC} of 22 trinucleotides has a preferential occurrence in the frame 0 (reading frame established by the ATG start trinucleotide) of protein (coding) genes of both prokaryotes and eukaryotes. The subsets ∪{CCC} and ∪{GGG} of 21 trinucleotides have a preferential occurrence in the shifted frames 1 and 2 respectively (frame 0 shifted by one and two nucleotides respectively in the 5′-3′ direction). and are complementary to each other. The subset contains the subset which has the rarity property (6 × 10⁻⁸) to be a complementary maximal circular code with two permutated maximal circular codes and in the frames 1 and 2 respectively. is called a C³ code. A quantitative study of these three subsets in the three frames 0, 1, 2 of protein genes, and the 5′ and 3′ regions of eukaryotes, shows that their occurrence frequencies are constant functions of the trinucleotide positions in the sequences. The frequencies of in the frame 0 of protein genes are 49, 28.5 and 22.5% respectively. In contrast, the frequencies of in the 5′ and 3′ regions of eukaryotes, are independent of the frame. Indeed, the frequency of in the three frames of 5′ (respectively 3′) regions is equal to 35.5% (respectively 38%) and is greater than the frequencies and , both equal to 32.25% (respectively 31%) in the three frames. Several frequency asymmetries unexpectedly observed (e.g. the frequency difference between and in the frame 0), are related to a new property of the subset involving substitutions. An evolutionary analytical model at three parameters (p, q, t) based on an independent mixing of the 22 codons (trinucleotides in frame 0) of with equiprobability (1/22) followed by t ≈ 4 substitutions per codon according to the proportions p ≈ 0.1; q ≈ 0.1 and r = 1 − p − q ≈ 0.8 in the three codon sites respectively, retrieves the frequencies of observed in the three frames of protein genes and explains these asymmetries. Furthermore, the same model (0.1, 0.1, t) after t ≈ 22 substitutions per codon, retrieves the statistical properties observed in the three frames of the 5′ and 3′ regions. The complex behaviour of these analytical curves is totally unexpected and a priori difficult to imagine.     

Body temperature regulation,energy metabolism,and foraging in light-seeking and shade-seeking robber flies

Summary Robber flies (Diptera: Asilidae) were studied in Panama from May through August. Of the 16 species examined, 5 perched and foraged in the sun and 11 perched and foraged in the shade. Thoracic body temperatures of light-seeking flies ranged from 35.2–40.6°C during foraging. Light-seeking flies regulated body temperature behaviorally by microhabitat selection and postural adjustments, and physiologically by transferring warmed haemolymph from the thorax to the cooler abdomen. Thoracic temperatures of shade-seeking flies passively followed ambient temperature in the shade and these flies did not thermoregulate. None of these robber flies warmed endothermically in the absence of flight. Resting oxygen consumption ( ) of both groups scaled with body mass to the 0.77 power. The factorial increment in resulting from hovering flight ranged from 12 to 56. The increased markedly with body temperature in light-seeking flies and probably explains the greater foraging effort observed in these species. Wing loading of all 16 species of robber flies scaled with body mass to the 0.39 power. Large light-seeking flies had heavier wing loading than large shade-seeking flies. The differences in body temperature and wing loading between light-seeking and shade-seeking robber flies may be related to differences in flight speed and maneuverability during foraging.