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.     

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     

Metabolism,temperature relations,maternal behavior,and reproductive energetics in the ball python (Python regius)

Summary Thermogenic incubation has been documented in two large species of pythons, but the phenomenon has not been studied in small species with concomitantly large heat transfer coefficients. We describe behavior, metabolic rates, mass changes, and temperature relations for adult ball pythons (Python regius), the smallest member of the genus, during the reproductive cycle. Egg and hatchling metabolism and hatchling growth rates were also examined.Rates of oxygen consumption ( ) of both gravid and non-gravid snakes showed typical ectothermic responses to changing ambient temperature (T _a). TheQ ₁₀ forT _a's of 20–35°C was 2.2–2.3. The of gravid females was significantly greater than that of non-gravid snakes at allT _a. Maximum oxygen consumption ( max) during forced exercise was about 12 times resting atT _a=30°C.Eggs (5–6 per female) were laid in April. Total clutch mass was approximately 32% of the females' pre-oviposition mass. After oviposition, mother snakes coiled tightly around their clutches and remained in close attendance until the eggs hatched in June. Sudden decreases inT _a elicited abrupt but transient 2- to 4-fold increases in the of incubating females. Similar responses were not observed in non-incubating snakes. The steady-state of incubating females was independent ofT _a. In no case was body temperature (T _b) elevated more than a few tenths of a degree aboveT _a in steady-state conditions.The of developing eggs increased sigmoidally through the 58–70 day incubation period. Total oxygen consumption during incubation atT _a=29.2°C was about 3.61 per egg. Young snakes quadrupled their mass during their first year of growth.Compared to larger python species which are endothermic during incubation, ball pythons have similar aerobic scopes and higher mass-specific max. However, effective endothermy in ball pythons is precluded by high thermal conductance and limited energy stores.     

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 cold acclimation on norepinephrine stimulated oxygen consumption in muscle

Summary The purpose of this study was to determine the effect of norepinephrine (NE) on oxygen consumption ( ) of perfused (constant flow) muscle in cold acclimated (CA) and control rats. Infusion of NE for a five minute period caused an increase in of similar magnitude in both groups. Infusion of NE for 30 min resulted in an elevated steady state in the cold acclimated group, while the control group showed only an initial increase in followed by a continual decline during the remainder of the 30 min infusion period. These results suggest that when rats are challenged by cold exposure, the magnitude of the initial muscle response to NE by control and acclimated rats is the same, but a useful sustained higher muscle oxygen consumption is found only in the cold acclimated animals.Abbreviations CA cold acclimated - NE norepinephrine     

Effects of long scotophase and cold acclimation on heat production in two diurnal rodents

Summary Heat production of two diurnal rodents,Rhabdomys pumilio andLemniscomys griselda was measured in long scotophase-LS (8L: 16D; 25°C) acclimated and long scotophase and cold — LSAC (8L: 16D; 6°C) acclimated animals and compared to a control group (12L: 12D; 25°C).LS increased in both species. Further acclimation of LSAC increased inR. pumilio and decreased inL. griselda. LS increased body temperature (T _b) inL. griselda only. LS increased overall thermal conductance in both species. LSAC caused a further increase in this parameter inR. pumilio.A singificant (P<0.001) increase in the magnitude of maximal nonshivering thermogenesis (NST) was observed in both species due to LS acclimation. LSAC did not change this maximal NST but increased its obligatory part (minimal , P<0.05, inL. griselda, andP<0.001, inR. pumilio).The results of this study show that winter acclimatization of heat production mechanisms, in both species, may be due to extension of scotophase.Abbreviations LS long scotophase - LSAC long scotophase and cold - NA noradrenaline - NST nonshivering thermogenesis - RMR resting metabolic rate     

Energetics of vocalization by an anuran amphibian (Hyla versicolor)

Summary The metabolic demands of vocalization byHyla versicolor were determined by measuring oxygen consumption and whole body lactate content of calling animals. A stepwise multiple regression analysis identified both calling rate (calls/h) and call duration (s/call) as significant determinants of oxygen consumption during calling. These two variables accounted for 84% of the total variation in oxygen consumption observed in calling frogs. Aerobic metabolism increased linearly with calling rate and call duration, reaching a peak value of 1.7 ml O₂/(g·h) at the highest vocalization effort. For comparison, metabolic rates of the same individuals were also measured during short bouts of vigorous locomotor exercise induced by mechanical stimulation. The mean value of was only 62% of the peak , and 5 of 13 frogs had rates of oxygen consumption during calling that exceeded their . Whole body lactate levels were measured in two samples of calling frogs, one collected early in the evening (2100–2115 h) and the other 1.5 h later (2230–2245 h). The frogs in the second sample had significantly lower lactate levels (0.10 mg/g) than the frogs collected early in the evening (0.22 mg/g). Hence, vocalization does not entail the use of anaerobic metabolism, although lactate levels may be slightly elevated at the onset of an evening of calling. Calling rates of unrestrained frogs in a large chorus were measured at regular intervals during an evening. During the first half hour of calling, rates increased gradually from an initial mean value of 600 calls/h at 2030 h to nearly 1400 calls/h at 2100 h. These data indicate that acoustic advertisement byHyla versicolor is among the most energetically expensive activities regularly undertaken by any anuran, and indeed, is the most demanding yet measured in an ectothermic vertebrate.Abbreviations resting rate of oxygen consumption - maximum rate of oxygen consumption - rate of oxygen consumption during forced exercise - rate of oxygen consumption during calling     

Skeletal muscle [(V)\dot]O2 \dot V_{O_2 } in rat and lemming: Effect of blood flow rate

Summary The rate of oxygen consumption ( ) by skeletal muscle was investigated in isolated perfused hindlimbs of laboratory rats and lemmings (Lemmus). In both species, increased in proportion to blood flow rate, even at flow rates 4–5 times above resting level. The slope of the line relating to skeletal muscle blood flow was significantly greater in the lemming than in the rat. This may be related to the inverse relationship between body weight and metabolic rate. These data support the hypothesis that in small animals a dependent relationship exists between blood flow and skeletal muscle .     

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     

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     

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.     

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     

Ventilation and gas exchange during rest and exercise in adult green sea turtles

Summary Ventilation and metabolic rate were measured during exercise in adult female green turtles at Tortuguero, Costa Rica. Six turtles were studied at night on the beach while actively covering their nests. Five turtles, captured after nesting, were studied at rest, during 20 min of spontaneous activity, and during recovery from the activity. Arterial blood samples were obtained from the latter animals and analyzed for pH, , O₂ concentration and lactate concentration. Blood was obtained by heart puncture from 8 turtles immediately after nesting and analyzed for blood lactate. Active metabolism ( ) in both groups was almost 10 times the standard resting value (0.024 l/kg·h). The increase in ventilation during exercise, due exclusively to higher breathing frequency, exceeded the increase in , so that the ratio (the air convection requirement), more than doubled. The respiratory exchange ratio, , that averaged 0.56 in the resting turtles, increased to 1.08 during exercise in the captured turtles and was 0.90 in the nesting animals. Arterial and O₂ saturation remained unchanged during exercise, indicating efficient gas exchange in the lungs. Pre-exercise values of all variables were restored 1 h after the end of exercise. Blood acid-base changes associated with activity in the captive turtles were variable and not statistically significant, but suggested partially compensated metabolic acidosis. Lactate concentrations were significantly elevated in the nesting turtles.     

Energy requirements of Adélie penguin (Pygoscelis adeliae) chicks

Summary The energy requirements of Adélie penguin (Pygoscelis adeliae) chicks were analysed with respect to body mass (W, 0.145–3.35 kg, n=36) and various forms of activity (lying, standing, minor activity, locomotion, walking on a treadmill). Direct respirometry was used to measure O₂ consumption ( ) and CO₂ production. Heart rate (HR, bpm) was recorded from the ECG obtained by both externally attached electrodes and implantable HR-transmitters. The parameters measured were not affected by hand-rearing of the chicks or by implanting transmitters. HR measured in the laboratory and in the field were comparable. Oxygen uptake ranged from in lying chicks to at maximal activity, RQ=0.76. Metabolic rate in small wild chicks (0.14–0.38 kg) was not affected by time of day, nor was their feeding frequency in the colony (Dec 20–21). Regressions of HR on were highly significant (p< 0.0001) in transmitter implanted chicks (n=4), and two relationships are proposed for the pooled data, one for minor activities ( ), and one for walking ( ). Oxygen consumption, mass of the chick (2–3 kg), and duration of walking (T, s) were related as , whereas mass-specific O₂ consumption was related to walking speed (S, m·s^-1) as .Abbreviations bpm beats per minute - D distance walked (m) - ECG electrocardiogram - HR heart rate (bpm) - ns number of steps - RQ respiratory quotient - S walking speed (m·s^-1) - T time walked (s) - W body mass (kg)     

Ventilation and oxygen consumption in rosy finches and house finches at sea level and high altitude

Summary Rosy finches (Leucosticte arctoa) breed at altitudes above 3500 m in eastern California. House finches (Carpodacus mexicanus) belong to the same subfamily (Carduelinae), but breed at much lower elevations. Oxygen consumption ( ) and ventilatory parameters of these two species were measured over a wide range of ambient temperatures (T _a) at low altitude (LA; 150 m) and at high altitude (HA; 3800 m).Minimal nighttime 's of rosy finches and house finches at LA (T _a=30°C) were close to allometrically predicted values for passerine birds. At both altitudes, increased linearly with decreasingT _a betweenT _a=20 and –10°C. Resting 's were slightly higher at HA than at LA on average.In both species, minute volume ( ) was inversely related toT _a.T _a-correlated increases in resulted from significant increases in both ventilatory frequency (f) and tidal volume (V T) at both altitudes. Oxygen extraction efficiency ( ) was independent ofT _a in rosy finches at LA, but declined significantly with decreasingT _a in rosy finches at HA and in house finches at both altitudes.At a givenT _a, both species had significantly greater (BTPS) at HA than at LA. Altitude-correlated increases in resulted primarly from increases inf with little change inV T. was significantly greater at HA than at LA in both species.In spite of the difference in altitudinal distributions of rosy finches and house finches, there were few conspicuous interspecific differences in metabolic or ventilatory adaptation to altitude or lowT _a over the range of conditions examined.Symbols and abbreviations BMR basal metabolic rate - BTPS at body temperature and pressure, saturated - oxygen extraction efficiency - f ventilation frequency - h mean coefficient of heat transfer - HA high altitude - instantaneous oxygen consumption - LA low altitude - RH relative humidity - SMR standard metabolic rate - STPD standard temperature and pressure, dry - T temperature - a ambient - b body - lc lower critical of thermoneutral zone - minute volume - V T tidal volume     

Respiration of the air breathing fishPiabucina festae

Summary Piabucina festae, a Central American stream fish, breathes air frequently, even in air saturated water, however, is not an obligate air breather. Without access to air, it can maintain routine by aquatic respiration down to aP _wO₂ of about 70 Torr which is its critical O₂ tension (P _cO₂, Fig. 5). Aerial respiration averages 10% of total in air saturated water and 70% in hypoxic water (Fig. 4). At lowP _wO₂ air breathing is more frequent (Fig. 1), and more O₂ is utilized from each air breath (Table 3), and tidal volume may increase (Fig. 7). Vascularized respiratory compartments or cells (Fig. 6), located in the second chamber of the physostomus gas bladder, function for aerial respiration. In ventilation air is gulped and forced through a large pneumatic duct into the gas bladder, excess gas is then released through opercula. Inspiration always precedes expiration and tidal volume is small, keeping gas bladderP _{O 2} low (Table 4). Major differences in the air breathing physiology ofP. festae and other species are its higherP _cO₂, a low aerial in normoxic water, even though air gulps are frequent, and its pattern of inhalation prior to expiration. The interrelationship and optimization of the three gas bladder functions (buoyancy, sound reception, and air breathing) inP. festae is discussed. Aerial respiration may have evolved secondarily to the gas bladder's function in buoyancy control.     

Gas exchange in the incubation mounds of megapode birds

Summary The brush turkey (Alectura lathami) and mallee fowl (Leipoa ocellata) are megapode birds that incubate their eggs by burying them in mounds. Respiratory gas exchange between the buried eggs and the atmosphere occurs mainly by diffusion through about 60 cm of decomposing forest litter (brush turkey) or sand (mallee fowl).Gas fluxes in the brush turkey mound are greatly influenced by the respiration of thermophilic microorganisms which consume O₂ at rates over eight times that of all of the eggs. The respiratory exchange ratio ( ) of the microorganisms is 0.75 and theQ ₁₀ for metabolism is 2.56. Fermentation and nitrogen fixation do not occur in the mounds.If the mound becomes too wet, gas tensions near the eggs can become critical because water increases rates of microbial respiration and impedes gas diffusion. However, field mounds are relatively dry, possibly because the adult bird modifies the shape of the mound and affects the entry of rain water. At egg level in field mounds, and are about 132 and 21 Torr, respectively, in both species. Embryonic respiration decreases and increases about 5 Torr in the immediate environment of individual eggs in late development. Due to a high eggshell gas conductance, which increases during incubation, the gas tensions within the shell of late embryos ( ca. 108 Torr, ca. 47 Torr) are not far from the mean values found in species that nest above ground.     

Physiological responses to cold (10° C) in men after six months' practice of yoga exercises

A study was conducted on 30 healthy soldiers (age: 40–46 years) to assess the effect of selected yogic exercises (asanas) on some physiological responses to cold exposure. They were randomly divided into two groups of 15 each. One group performed regular physical exercises of physical training (PT), while the other group practised yogic exercises. At the end of 6 months of training, both the groups were exposed together to cold stress at 10°C for 2 h, and the following parameters were periodically monitored during cold exposure: heart rate (fH), blood pressure (BP), cardiac output , oral temperature (T_or), skin temperature (T _sk), respiratory rate (fR), minute ventilation , oxygen consumption , and shivering response by integrated electromyogram (EMG). There were progressive increases inBP, fR, , , and and decreases infH,T _or andT _sk during cold exposure in both the groups. However, the decrease inT _or and the increases in and were relatively lower (P<0.01) in the yoga group as compared to the PT group. The shivering response appeared much earlier and was more intense in the PT group. These findings suggest that practice of yoga exercises may improve cold tolerance.     

Effects of temperature and altitude on ventilation and gas exchange in chukars (Alectoris chukar)

Summary The effects of ambient temperature (T _a) on ventilation and gas exchange in chukar partridges (Alectoris chukar) were determined after acclimation to low and high altitute (LA and HA; 340 and 3,800 m, respectively).At both LA and HA, oxygen consumption ( ) increased with decreasingT _a atT _a from 20 to –20°C. AtT _a of 35 to 40°C, increased above thermoneutral values at HA but remained constant and minimal at LA. Water loss rates increased rapidly atT _a>30°C at both altitudes as birds began to pant. Ventilation rates (f) during panting were 5-to 23-fold greater than the minimalf at thermoneutralT _a.Increased atT _a below thermoneutrality was supported by increased minute volume (V i) at both altitudes. The change inV i was primarily a function of changing tidal volume (V t), althoughf increased slightly asT _a declined. Oxygen extraction ( ) remained fairly constant atT _a below 20°C at both altitudes. BothV t and were considerably lower when birds were panting than at lowerT _a.Chukars showed few obvious ventilatory adaptations to HA. The 35% change in between 340 and 3,800 m was accommodated by a corresponding change inV i (btps), most of which was accomplished by increasedf at HA, along with a slight increase in .Abbreviations and symbols HA high altitude - LA low altitude - rate of evaporative water loss - oxygen extraction efficiency - f respiratory frequency - V t tidal volume - V i minute volume - BMR basal metabolic rate - MHP metabolic heat production