Control of acid-base status in active and dormant land snails,Otala lactea (Pulmonata,Helicidae)

Summary Control of extracellular acid-base status was examined during activity and dormancy inOtala lactea (Pulmonata, Helicidae). Active snails showed little variation in hemolymph pH and at constant temperature. With increase of temperature, hemolymph increased from about 6 Torr at 5°C to 13 Torr at 24°C and pH decreased by about 0.017 pH units/°C, a pattern consistent with alphastat regulation of pH via ventilatory control of .During dormancy, mean hemolymph increased to about 50 Torr. Venous pH declined by about 0.4 units due to hypercapnia and fluctuated more widely than in active snails due to variability of . Hemolymph pH declined further in prolonged dormancy due to progressive metabolic acidosis; after one year of dormancy the mean hemolymph pH was about 0.8 units lower than that of active snails at similar temperature.Active snails exposed experimentally to high showed a large increase in hemolymph [HCO ₃ ^– ]. However, [HCO ₃ ^– ] declined by up to 50% during dormancy, despite the naturally occurring hypercapnia. Hemolymph osmolality and the concentrations of solutes other than [HCO ₃ ^– ] increased with increasing duration of dormancy. Concentrations of magnesium and calcium increased about 2.5 times more rapidly than those of sodium and chloride, indicating that acidosis is partially offset by the dissolution of carbonates from the shell or tissues.     

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 study of the effects of water carbonate alkalinity on some parameters of blood acid-base status in rainbow trout (Salmo gairdneri R.)

Summary The effects of two levels of water carbonate alkalinity (CA=0.3–0.5 meq·l⁻¹ and CA=12–13.5 meq·l⁻¹) on arterial blood acid-base status ( , pHa, [HCO ₃ ⁻ ]+[CO ₃ ⁻⁻ ]), oxygen consumption ( ) and plasma ionic composition (Na⁺, K⁺, Cl⁻) were investigated in trout living in normoxic-normocapnic water at 15°C. The results show that a high level of carbonate alkalinity induced a decrease in and a situation of mixed respiratory and metabolic acidosis compared to that in low CA water. These changes are accompanied by significant changes in ionic composition but the levels of oxygen consumption are unchanged. The role of the different capacitance coefficients of water for CO₂ and the effects of the different ionic composition of water on ionic and gascous exchanges are discussed. Equipe de Recherche associée au CNRS N° 070622     

Carbonic anhydrase activity in the blood and the gills of rainbow trout during long-term hypercapnia in hard,bicarbonate-rich freshwater

Summary Carbonic anhydrase (CA) activities in gills and venous blood, acid-base balance, and haematological variables were studied during environmental hypercapnia in rainbow trout (Salmo gairdneri). Batches of 8–10 fish were exposed to about 3 or 13 mmHg in flow-through tests of various duration from 4 h to 80 days.After initial acidosis, blood pH rose above pre-experimental values. At 3 mmHg it became normal again within 21 days, while at 13 mmHg the overshoot lasted for 80 days. In fish acclimated for 3 weeks or more to 13 mmHg , blood HCO ₃ ^– increased four to five times while plasma Cl^– levels were lower and K⁺ higher. Na⁺ levels did not show any consistent trend associated with exposure to hypercapnia. After an initial acidaemia, Hct, Hb, and RBC remained relatively constant.Patterns of change in CA activity differed between gills and erythrocytes. Initially, blood CA decreased at both levels. It then began rising after about 3 weeks and tended to reach pre-experimental values by 80 day's hypercapnia. At 13 mmHg , gill CA increased to twice the pre-experimental level. Compared with blood CA, gill CA appeared to be more specifically involved in fish acclimation to hypercapnia, which demands an increase in blood bicarbonate to provide a sufficient buffering capacity. Increased CA indicates that the gill enzyme may play a more important role than blood CA in acid-base regulation in fish during hypercapnia.Abbreviations CA carbonic anhydrase - Hb haemoglobin - Hct haematocrit value - RBC red blood cells     

Respiratory responses to long-term temperature exposure in the box turtle,Terrapene ornata

Summary In late February, seven box turtles were collected with body temperatures between 7 and 9°C. Ventilation, gas exchange and end-tidal and were recorded at 5, 10, 15 and 25°C, the animals being at each temperature for 2 to 3 weeks. There was a pronounced diurnal rhythm of breathing frequency at all temperatures. At 5°C the mean 24-h frequency was only 3.7 breaths h^–1. At 15°C the frequency was 16 times higher with a 17-fold increase of ventilation. Oxygen uptake only changed from 3.4 to 12.7 ml·kg^–1·h^–1. Consequently, the ratio (ventilation, ml BTPS/O₂ uptake, ml STPD) increased from 12.5 at 5°C to 48 at 15°C, but decreased to 24 at 25°C. The decrease of this ratio during cold exposure contrasts with an increase of the ratio during cooling earlier reported for fresh water turtles,Pseudemys. Cutaneous CO₂ elimination was important at low temperature. This caused a decrease of the pulmonary gas exchange ratio so that end-tidal remained low at 5°C in spite of an end-tidal of only 54 Torr.     

Ventilation and gas exchange in the diamondback water snake,Natrix rhombifera

Summary Simultaneous measurements of pulmonary and cutaneous oxygen and carbon dioxide exchange, pulmonary ventilation and heart rate were made on the diamondback water snake,Natrix rhombifera at 28°C using body plethysmography. Resting lung volume, maximum lung volume and tracheal volume were also measured.The following mean values were measured in undisturbed snakes breathing room air: total (pulmonary and cutaneous) O₂ uptake 46 mol · (kg min)^–1; total CO₂ output, 49 mol · (kg min)^–1; tidal volume, 12 ml (BTPS) · kg^–1; ventilatory rate, 6.9 min^–1; heart rate, 42 min^–1. From the measurements of tracheal volume, the effective (alveolar) ventilation was estimated as approximately 70% of total ventilation resulting in effective pulmonary and of 130 Torr and 20 Torr respectively. Cutaneous exchange accounted for 8.1% of the total and 12.4% of the total .Resting lung volume of anaesthetized snakes was 75 ml (BTPS) · kg^–1, maximum lung volume was 341 ml (BTPS) · kg^–1 and tracheal volume was 3.9 ml (BTPS) · kg^–1.     

Carbon dioxide desorption from fermentation broth by use of oxygen vectors

The ability of oxygen vector to extract produced carbon dioxide has been tested in an anaerobic fermentation. During the continuous culture of Clostridium acetobutylicum at pH 4.6 and at a dilution rate of 0.124 h^–1, a feed composed of an emulsion of 18.5% by volume of Forane F66E was able to extract about 9% of the total CO₂ produced under CO₂ partial pressure equal to 0.42 atm. A theoretical evaluation of the extracted amount, based on the hypothesis of total saturation of the vector by carbon dioxide, has lead to very good agreement.List of Symbols [AA] g/l acetic acid concentration - [BA] g/l butyric acid concentration - D 1/h Q _w /V dilution rate - [ETH] g/l ethanol concentration - H _w Henry constant of CO₂ for water at 37°C (=23.91 mmol/(l atm)) - H _F Henry constant of CO₂ for Forane at 37°C (=83.4 mmol/(l atm)) - H _i g/mol molar mass of componenti - P _i atm partial pressure of gasi - W _w l/h aqueous flow - Q_f 1/h Forane flow - mmol/(lh) dissolved CO₂ flow in aqueous effluent - mmol/(lh) CO₂ gas flow - mmol/(lh) CO₂ gas flow without Forane - mmol/(lh) CO₂ gas flow with Forane - mmol/(lh) total CO₂ production - r _X g/(lh) biomass production rate - r _G mmol/(lh) total gas flow - mmol/(lh) hydrogen production - mmol/(lh) nitrogen flow - r _S mmol/(lh) glucose input - V 1 fermentor volume     

Effects of rapid transfer from sea water to fresh water on respiratory variables,blood acid-base status and O2 affinity of haemoglobin in Atlantic salmon (Salmo salar L.)

Summary Oxygen consumption, gill ventilation, blood acid-base/ionic status and haemoglobin oxygen affinity were studied in seawater-adapted adult salmon (Salmo salar) during five weeks after transfer into fresh water. Freshwater exposure induced the following changes: Standard oxygen consumption ( ) and ventilatory flow ( ) decreased markedly during the first days after transfer, then decreased more gradually until a new steady-state was achieved at which and were about 80% and 56% of the control values, respectively. The marked increase in oxygen extraction coefficient (Ew _{O 2}) and the marked decrease in the oxygen convection requirement ( ) were associated with a reduction in the partial pressure of carbon dioxide in arterial blood (Pa _{CO 2}), in spite of a decrease of both ventilatory flow and water CO₂ capacitance. These results suggested that transfer into fresh water induced an increase in branchial diffusive conductance. A biphasic pattern was observed in the time-course of the changes in both plasma ion concentration and acid-base status. During the first 10 days, plasma Na⁺, K⁺, and Cl^– concentrations fell abruptly, then more gradually. [Cl^–] decreased more than [Na⁺] resulting in a progressive increase in the [Na⁺]/[Cl^–] ratio. During the second phase of acclimation to fresh water plasma Na⁺, K⁺, and Cl^– concentrations progressively increased. [Cl^–] increased more than [Na⁺], so that [Na⁺]/[Cl^–] ratio decreased. Transfer into fresh water did not significantly change plasma lactate concentration. Upon exposure to fresh water, blood pH increased from 7.94±0.04 to 8.43±0.06 at day 10 and then decreased to 8.08±0.03 at day 34. The increase in blood pH induced by transfer to fresh water initially represented a mixed metabolic/respiratory alkalosis. However, after 15 days Pa _{CO 2} had returned to pretransfer values and the alkalosis was purely metabolic. The metabolic component of the alkalosis was associated with appropriate changes in the plasma strong ion difference (S.I.D.). Blood alkalosis moved the oxygen dissociation curve to the left, so that P₅₀ was decreased by 30% below the value in seawater for the maximal increase in blood pH. This rise in haemoglobin affinity for O₂, associated with a marked increase in blood buffer capacity, are regarded as adaptative processes allowing the salmon to cope with the markedly increased energy expenditure required for upstream migration.     

Activity and oxygen consumption during hypoxic exposure in high altitude and lowland sceloporine lizards

Summary Resting rates of O₂ consumption against , exercise endurance times and during recovery from vigorous exercise were measured inSceloporus occidentalis captured near sea level and inS. graciosus captured above 2850 m. Oxygen consumption against was also measured inS. occidentalis captured above 2850 m. When was recorded continuously, as ambient was slowly reduced from 155 Torr, it became directly dependent upon ambient between 110 and 120 Torr. The critical for the high altitude lizards was lower than that for the lowland lizards, which enabled the former to maintain relatively higher 's when ambient was reduced below 120 Torr. The high altitude lizards also had significantly greater endurance when stimulated to exercise at 1600 m ( 130 Torr). Both the higher under hypoxia and the greater endurance roughly parallel a significantly greater maximum in the high altitude lizards. At a simulated altitude of 3600 m ( 100 Torr), maximum and rate of recovery of the O₂ debt calculated from post active were significantly reduced in the lowland but not the high altitude lizards. The effects of simulated altitude conditions on the lowland but not the mountaine animals indicate adaptations to altitude in these sceloporine lizards. We did not find any consistent relationship between organ/body weight ratios or hematocrit and our measures of endurance or the altitude at which the lizards were captured.     

Effect of venous (gut) CO2 loading on intrapulmonary gas fractions and ventilation in the tegu lizard

Summary Studies were conducted to determine regional pulmonary gas concentrations in the tegu lizard lung. Additionally, changes in pulmonary gas concentrations and ventilatory patterns caused by elevating venous levels of CO₂ by gut infusion were measured.It was found that significant stratification of lung gases was present in the tegu and that dynamic fluctuations of CO₂ concentration varied throughout the length of the lung. Mean was greater and less in the posterior regions of the lung. In the posterior regions gas concentrations remained nearly constant, whereas in the anterior regions large swings were observed with each breath. In the most anterior sections of the lung near the bronchi, CO₂ and O₂ concentrations approached atmospheric levels during inspiration and posterior lung levels during expiration.During gut loading of CO₂, the rate of rise of CO₂ during the breathing pause increased. The mean level of CO₂ also increased. Breathing rate and tidal volume increased to produce a doubling ofV _E.These results indicate that the method of introduction of CO₂ into the tegu respiratory system determines the ventilatory response. If the CO₂ is introduced into the venous blood a dramatic increase in ventilation is observed. If the CO₂ is introduced into the inspired air a significant decrease in ventilation is produced. The changes in pulmonary CO₂ environment caused by inspiratory CO₂ loading are different from those caused by venous CO₂ loading. We hypothesize that the differences in pulmonary CO₂ environment caused by either inspiratory CO₂ loading or fluctuations in venous CO₂ concentration act differently on the IPC. The differing response of the IPC to the two methods of CO₂ loading is the cause of the opposite ventilatory response seen during either venous or inspiratory loading.Abbreviations IPC intrapulmonary chemoreceptors - UAC upper airway chemoreceptors - V _T inspiratory tidal volume - CO₂ gas fraction - O₂ gas fraction - V _E minute ventilation     

Resting metabolic rates in boid snakes: allometric relationships and temperature effects

Summary Resting metabolic rates (RMR) of 34 species from 18 genera of boas and pythons (Serpentes: Boidae), with body masses ranging from 2 to 67,800 g, were determined as oxygen consumption ( ) and carbon dioxide production ( ) at three ambient temperatures (T _a).The temperature coefficient of metabolism (Q₁₀) averaged 2.61 betweenT _a of 20–30°C and 2.65 between 30 and 34°C. The respiratory exchange ratio RE (= / ) increased slightly with increasingT _a (0.795 at 20°C, 0.819 at 30°C, and 0.834 at 34°C). Interspecific differences in Q₁₀ and RE were slight or insignificant.A multiple regression relating metabolism ( ) to mass andT _a explained 97% of the variance in the pooled interspecific data. The mass exponent was 0.806, which is approximately the same as reported for squamates and for all reptilian taxa combined. The mean within-species slope (0.732) was significantly less than the slope for pooled data, but did not differ significantly from 0.75. In 40 of 42 cases (14 species at 3T _a), within-species slopes did not differ from each other. Values of the adjusted mean Y, from covariance analysis, were significantly and positively correlated with mass, indicating that the mass coefficient increases with increasing mass.Considerable variation in metabolic rate is apparent both within and between ecological and taxonomic categories.Original metabolic data are available from the National Auxiliary Publications Services, c/o Microfiche Publication, P.O. Box 3153 Grand Central Station, New York, New York 10017, USA     

Aerobic metabolism of the lizardVaranus exanthematicus: Effects of activity, temperature, and size

Summary Oxygen consumption was measured at rest and during spontaneous activity at body temperatures of 25 and 35°C in 14 fasting Savanna monitor lizards,Varanus exanthematicus ranging in weight from 172 to 7500 g. The allometric relationship between metabolic rate at 25°C and body weight (W) is given by: (ml O₂ STPD·g^–1·hr^–1)=0.88W ^–0.43 (Fig. 2). Although statistical comparisons are equivocal, this intraspecific size dependence exceeds that reported for interspecific comparisons among reptiles and other vertebrate groups (Fig 3). A reproducible diurnal pattern of activity was observed in undisturbed animals with minimum values of between 2400 and 0800 h (Fig. 1). Spontaneous activity and generally reached peak values between 1200 and 2000 hrs. The average ratio of active aerobic metabolic rate (AMR) to minimum (standard) aerobic metabolic rate (SMR) was 8.2. This voluntary AMR/SMR inVaranus exceeds the AMR/SMR for most reptiles stimulated to exhaustion. The high aerobic capacity is consistent with other evidence for efficient exchange and transport of respiratory gases inV. exanthematicus; e.g., low or absent intracardiac shunt flow resulting in high arterial saturation and low ventilation and perfusion requirements.     

Effect of chronic acidosis on discharge frequency of intrapulmonary chemoreceptors in the chicken

Summary In order to determine the pH effect on the discharge of intrapulmonary chemoreceptors (IPC) not mediated through , we determined discharge frequency-ln relationships of 28 IPC from ten adult cockerels made acidotic by ingestion of feed containing 6% NH₄Cl for 2 to 5 days. Blood buffer curves — the relationships between pH and — from these cockerels were shifted in parallel towards acidosis by 0.24 pH units (SE=±0.05) compared to control curves. The average slope of the IPC discharge frequenc-ln relationships was less negative than that reported for similar cockerels with normal acid-base balance and the average intercept was decreased. We conclude that pH has an effect on IPC discharge, independent of changes in ; this effect decreases IPC sensitivity to CO₂. We calculate that a shift towards acidosis in the blood buffer curve of one pH unit causes the slope of the IPC discharge frequency-ln relationship to be less negative by 14.7±3.3 imp (s·ln )^–1 and that for any acidotic shift in the blood buffer curve (pH), the average IPC discharge frequency=[–10.7+(14.7·pH)][ln( /25.5)]+3.37. Since IPC discharge is altered by changes in acid-base balance, IPC may contribute to the implementation of respiration responses during metabolic disturbances.Abbreviation IPC intrapulmonary chemoreceptor     

Effects of ambient temperature and altitude on ventilation and gas exchange in deer mice (Peromyscus maniculatus)

Summary The effects of different ambient temperatures (T _a) on gas exchange and ventilation in deer mice (Peromyscus maniculatus) were determined after acclimation to low and high altitude (340 and 3,800 m).At both low and high altitude, oxygen consumption ( ) decreased with increasingT _a atT _a from –10 to 30 °C. The was 15–20% smaller at high altitude than at low altitude atT _a below 30 °C.Increased atT _a below thermoneutrality was supported by increased minute volume ( ) at both low and high altitude. At mostT _a, the change in was primarily a function of changing respiration frequency (f); relatively little change occurred in tidal volume (V _T) or oxygen extraction efficiency (O₂EE). AtT _a=0 °C and below at high altitude, was constant due to decliningV _T and O₂EE increased in order to maintain high .At high altitude, (BTP) was 30–40% higher at a givenT _a than at low altitude, except atT _a below 10 °C. The increased at high altitude was due primarily to a proportional increase inf, which attained mean values of 450–500 breaths/min atT _a below 0 °C. The (STP) was equivalent at high and low altitude atT _a of 10 °C and above. At lowerT _a, (STPD) was larger at low altitude.At both altitudes, respiratory heat loss was a small fraction (<10%) of metabolic heat production, except at highT _a (20–30 °C).Abbreviations EHL evaporative heat loss - f respiration frequency - HL _a heat loss from warming tidal air - HL _e evaporative heat loss in tidal air - HL total respiratory heat loss - MHP metabolic heat production - O ₂ EE oxygen extraction efficiency - RQ respiratory quotient - T _a ambient temperature - T _b body temperatureT _lc lower critical temperature - carbon dioxide production - evaporative water loss - oxygen consumption - minute volume - V _T tidal volume     

Breathing pattern and growth: comparative aspects

Summary The resting oxygen consumption and breathing pattern of nine newborn and adult species (ranging in body size from mouse to human) have been compared on the basis of data collected from the literature. Minute ventilation is similarly linked to at both ages, the percent of extracted as O₂ about 2.2. Tidal volume/kg is an interspecies constant in newborns and adults, approximately 8 ml/kg. Breathing frequency decreases with the increase in size in a different way at the two ages: large species have newborns breathing at rates 2–3 times above the corresponding adults' values, while in the small species newborns and adults breathe at almost the same rate. Therefore the newborns of the smallest species have both and below the expected values, implying a greater inability to cope with the external demands than newborns of larger species. Several considerations indicate that in the smallest newborns the mechanical properties of the respiratory system could be a constraint to resting ventilations larger than observed. It is therefore possible that their low is the cause, and not the effect, of the relatively small .     

Altitudinal and seasonal effects on aerobic metabolism of deer mice

Summary I compared the maximal aerobic metabolic rates ( ), field metabolic rates (FMR), aerobic reserves ( -FMR), and basal metabolic rates (BMR) of wild and recently captured deer mice from low (440 m) and high (3800 m) altitudes. To separate the effects of the thermal environment from other altitudinal effects, I examined mice from different altitudes, but similar thermal environments (i.e., summer mice from high altitude and winter mice from low altitude). When the thermal environment was similar, , FMR, and aerobic reserve of low and high altitude mice did not differ, but BMR was significantly higher at high altitude. Thus, in the absence of thermal differences, altitude had only minor effects on the aerobic metabolism of wild or recently captured deer mice.At low altitude, there was significant seasonal variation in , FMR, and aerobic reserve, but not BMR. BMR was correlated with , but not with FMR. The significant positive correlation of BMR with indicates a cost of high , because higher BMR increases food requirements and energy use during periods of thermoneutral conditions.Abbreviations BMR basal metabolic rate - FMR field metabolic rate - partial pressure of oxygen - T _a ambient temperature - T _b body temperature - T _e operative temperature - maximal aerobic metabolic rate     

Effect of oxygen on the growth (yield) of Chlorella vulgaris

The growth yield of Chlorella vulgaris, Y _kJ defined as g cells harvested per kJ of light energy absorbed by the cells, was assessed in a turbidostat culture by varying CO₂ and O₂ partial pressures ( and ). The value of Y _kJ ranged from 3.1×10^-3 to 5.0×10^-3 g cells/kJ under light-limited conditions [ = 1.02.4%, = 065%; total pressure of gas (composed of CO₂, O₂ and N₂)=1 atm]. In the light-limited environment, the algal specific growth rate deteriorated appreciably with the increase of . The deterioration accounts for the above range of Y _kJ observed. The growth inhibition due to oxygen that was defined by subtracting from 1.0 the ratio of at given values of to that at = 0% extended from 0.07–0.30 (7–30%). However, glycolate could not be detected in the turbidostat culture. Isotopic experiments on the specific rate of ¹⁴CO₂ uptake also revealed that the inhibition due to oxygen was from 22–38% when was varied from 0 to nearly 100%. These effects of oxygen were discussed, referring to the activity of ribulose-1,5-bisphosphate carboxylase that is inhibited competitively by oxygen.Non-Standard Abbreviations INH isonicotinic acid hydrazide - PPO 2,5-diphenyloxazole - DCMU 3-(-3,4-dichlorophenyl)-1,1-dimetylurea - CA carbonic anhydrase - RuP₂ ribulose-1,5-bisphosphate     

Water economy in bird nests

Summary Nest humidity ( ) under an incubating bantam hen was measured at ambient ranging from 1.3 to 25.0 mmHg. Weight loss of eggs was recorded in clutches of varying size. Nest and ambient were also measured in wild incubating willow ptarmigan nests in dry and wet habitats.Nest increased linearly with ambient in a way predictable on the assumption that the water vapour conductance ( ) of brood patch skin, plumage and eggs were constant and independent of ambient . Nest was also dependent of clutch size. Egg dehydration was quantitatively predicted from measured values and the laws of diffusion.Our findings confirm earlier conclusions that the adult bird does not actively regulate nest at varying ambient . Birds can presumably achieve appropriate egg dehydration by a strategy combining nest site, nest construction, egg shell conductance and incubation behaviour which meets the requirements of their breeding climate.Abbreviations water vapur pressure - water vapur conductance - water flux     

Ventilation and control of acid-base status during temperature acclimation in the crab,Cancer magister

Summary Frequencies of scaphognathite (ventilatory,f _sc) and heart (f _h) pumping, oxygen consumption ( ), and hemolymph oxygen, carbon dioxide and pH levels were measured in adult Dungeness crabs (Cancer magister) during 7–10 day periods of exposure to 7, 12, and 17°C seawater. Ventilation volume ( ) was calculated for individual animals fromf _sc and a previously determined relationship between stroke volume and animal mass. increases (Q₁₀=2.3) with temperature were associated with larger increases inf _sc (Q₁₀=3.3) and (Q₁₀=3.5) and smaller increases inf _h (Q₁₀=1.5). The incidence of unilateral scaphognathite pumping and pausing decreased as temperature rose.Postbranchial oxygen tension was maintained in vivo but hemolymph oxygen content decreased both in vivo and in vitro as temperature rose. Postbranchial carbon dioxide tension did not change significantly but relative alkalinity was maintained as temperature rose by loss of hemolymph bicarbonate. The effects of increased ventilation volume and potential mechanisms of bicarbonate regulation are discussed.The responses of the essentially subtidalCancer magister are compared with those of subtidal, intertidal and terrestrial crabs demonstrating that the concepts of acid-base regulation developed for water and air breathing vertebrates are also applicable to water and air breathing crabs, and that intertidal crabs may exhibit transitional states.This work was supported by Grant No. A.5762 National Research Council of Canada     

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