Influence of hypercapnia on certain aspects of heat exchanges at room temperature in the rabbit

Heat production as well as heat loss from the surface of the ear and airways during and after hypercapnia induced by one hour inhalation of 10% mixture was studied in conscious rabbits. The arterial CO2 tension increased by about 45 mm Hg and pH fell by about 0.3. These changes were associated with decreasing of heat production while heat loss from the ears and airways increased significantly. Consequently the rectal temperature fell meanly by about 0.9 degrees C. The data show that fall of body temperature in the rabbits exposed on 10% CO2 at room temperature is due both to heat production changes and heat loss changes.     

Effect of upper airway CO2 on breathing in awake ponies

We determined whether the [CO2] in the upper airways (UA) can influence breathing in ponies and whether UA [CO2] contributes to the attenuation of a thermal tachypnea during periods of elevated inspired CO2. Six ponies were studied 1 mo after chronic tracheostomies were created. For one protocol the ponies were breathing room air through a cuffed endotracheal tube. Another smaller tube was placed in the tracheostomy and directed up the airway. By use of this tube, a pump, and prepared gas mixtures, UA [CO2] was altered without affecting alveolar or arterial PCO2. When the ponies were at a neutral environmental temperature (TA) and breathing frequency (f) was 8 breaths X min-1, increasing UA [CO2] up to 18-20% had no effect on f. However, when TA was increased 20 degrees C to increase f to 50 breaths X min-1, then increasing UA [CO2] to 6% or to 18-20% reduced f by 5 +/- 1.7 (SE) and 12 +/- 1.6 breaths X min-1, respectively (t = 3.3, P less than 0.01). These data suggest that in the pony there exists a UA CO2-H+ sensory mechanism. For a second protocol the ponies were breathing a 6% CO2 gas mixture for 15 min in the normal fashion over the entire airway (nares breathing, NBr) or they were breathing this gas mixture for 15 min through the cuffed endotracheal tube (TBr). At a neutral TA, increasing inspired [CO2] to 6% resulted in a 6-breaths X min-1 increase in f during both NBr and TBr.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cold-induced changes in breathing pattern as a strategy to reduce respiratory heat loss

Thermoregulatory benefits of cold-induced changes in breathing pattern and mechanism(s) by which cold induces hypoventilation were investigated using male Holstein calves (1-3 mo old). Effects of ambient temperatures (Ta) between 4 and 18 degrees C on ventilatory parameters and respiratory heat loss (RHL) were determined in four calves. As Ta decreased, respiratory frequency decreased 29%, tidal volume increased 35%, total ventilation and RHL did not change, and the percentage of metabolic rate attributed to RHL decreased 26%. Total ventilation was stimulated by increasing inspired CO2 in six calves (Ta 4-6 degrees C), and a positive relationship existed between respiratory frequency and expired air temperature. Therefore, cold-exposed calves conserve respiratory heat by decreasing expired air temperature and dead space ventilation. Compared with thermoneutral exposure (16-18 degrees C), hypoventilation was induced by airway cold exposure (4-6 degrees C) alone and by exposing the body but not the airways to cold. Blocking nasal thermoreceptors with topical lidocaine during airway cold exposure prevented the ventilatory response but did not lower hypothalamic temperature. Hypothalamic cooling (Ta 16-18 degrees C) did not produce a ventilatory response. Thus, airway temperature but not hypothalamic temperature appears to control ventilation in cold-exposed calves.     

"Paradoxical" effect of carbon dioxide on common carotid artery blood flow in rabbits during hypothermia and hyperthermia

The relative effects of temperature and CO2 on the blood flow in the common carotid artery (CCBF) were investigated in vagotomized, paralyzed rabbits under urethane-chloralose general anaesthesia with artificial ventilation. During hypothermia a 52% fall of CCBF was observed in rabbits ventilated by the classic method. Administration of a hyperkapnic mixture for breathing caused a further 16% CCBF fall, with a simultaneous rise in PaCO2 by 23%. During ventilation with a respirator triggered by phrenic nerve activity hypothermia caused a 30% CCBF fall without changes in PaCO2 value. Administration of the hyperkapnic mixture for breathing caused, in these circumstances, a 9% CCBF fall with a 7% PaCO2 increase. Hyperthermia caused during ventilation by the classic method a 42% rise in CCBF and a 22% PaCO2 rise. The hyperkapnic mixture given for breathing decreased the CCBF by 9% and increased the PaCO2 by 15%. On the other hand, during ventilation with the respirator triggered by phrenic nerve activity no changes were observed in these parameters. This suggests that the thermic stimulus exerts a direct effect on the regulation of the blood flow to the brain, and during hypothermia it prevails over the stimulus produced by CO2.     

Effect of temperature on the microbial flora of herring fillets stored in air or carbon dioxide

The microbial development on fillets of herring from the Baltic Sea was studied at temperatures from 0-15 C in air or 100% carbon dioxide (96-100% CO2). The shelf-life of the fillets , defined as the time for the 'total aerobic count' to reach 1 X 10(7) c.f.u./g increased with decreased temperature from 1 d at 15 degrees C to 7 d at 0 degrees C (air). The corresponding values in CO2 were 3 d and 33 d, respectively. The initial flora of the herring fillets was dominated by Alteromonas putrefaciens and Pseudomonas spp. and so was the spoilage flora after storage in air (together 62-95% of the flora: all temperatures). Alteromonas putrefaciens predominated slightly at 2 degrees C to 15 degrees C, while Pseudomonas spp. dominated at 0 degrees C. The Pseudomonas flora was mainly split between Ps. fragi , Ps. fluorescens and a heterogenous group of unidentified Pseudomonas spp. The proportions were not influenced by temperature. In 100% CO2 at the time of spoilage the flora consisted of a significant number of Lactobacillus spp. Below 4 C the domination was almost complete while at 10 degrees C and 15 degrees C. Enterobacteriaceae, Vibrionaceae and Alt. putrefaciens was also found. It was concluded that the microbiological shelf-life of herring fillets is improved by refrigeration storage in 100% CO2 but for good results the temperature should not exceed 2 degrees C.     

Valorization of cotton stalks by fast pyrolysis and fixed bed air gasification for syngas production as precursor of second generation biofuels and sustainable agriculture

In the present study, the potential of cotton stalks utilization for H(2) and syngas production with respect to CO(2) mitigation, by means of thermochemical conversion (pyrolysis and gasification) was investigated. Pyrolysis was conducted at temperature range of 400-760 degrees C and the main parametric study concerned the effect of temperature on pyrolysis product distribution. Atmospheric pressure, air gasification at 750-950 degrees C for various lambda (0.02-0.07) was also studied. Experimental results showed that high temperature favors gas production in both processes; while low lambda gasification gave high gas yield. Syngas (CO and H(2)) was increased with temperature, while CO(2) followed an opposite trend. By pyrolysis, higher H(2) concentration in the produced gas (approximately 39% v/v) was achieved and at the same time lower amounts of CO(2) produced, compared to air gasification.     

Man's physiologic response to long-term work during thermal and pollutant stress.

Metabolic, temperature, and cardiorespiratory responses of 19 healthy males, age range 18-30 yr for one group and 40-55 yr for another, were studied during 210 minutes submaximal work at 35% Vo2 max. The subjects were exposed to four different pollutant gas mixtures at two different temperatures, 25 degrees C and 35 degrees C (relative humidity 30%). The four gas mixtures were filtered air (FA), 50 ppm carbon monoxide in filtered air (CO), 0.24 ppm peroxyacetyl nitrate in filtered air (PAN), and a combination of all three mixtures (PANCO). In the CO exposure, the heart rate was significantly greater than that observed during FA conditions (P less than 0.05). Metabolic and thermoregulatory responses to long-term work were not different in the various pollutant environments. Significant decreases in stroke volume and increases in heart rate were observed during the course of the 25 degrees C exposures with no alteration in cardiac output. Heart rates were higher during 35 degrees C exposures while cardiac output remained at the same level with a consequent further reduction in stroke output.     

Effect of altered ambient temperature on breathing in ponies

The objective was to determine the effect of moderate changes in ambient temperature (TA) on breathing and body temperature in ponies chronically exposed to a TA of 21 degrees C in the summer and 5 degrees C in the winter. Normal (n = 6) and chronic carotid body-denervated (n = 6, 1-2 yr) ponies were studied during 1) winter months over 3-4 days at 5 (control TA) and 23 degrees C and 2) summer months over 2-4 days at 21 (control TA), 30, and 12 degrees C. Neither rectal nor arterial temperature changed with any alteration of TA (P greater than 0.10). Skin temperature (Tsk) always changed by 2-4 degrees C in the same direction as changes in TA (P less than 0.01), and Tsk was the only variable that differed between summer and winter control TA. While breathing room air 24-48 h after TA was altered, pulmonary ventilation (VE) and breathing frequency (f) were approximately 100 and 300%, respectively, above control with elevated TA and approximately 25-50% below control with reduced TA (P less than 0.01). Changes in f were closely related to changes in Tsk. Tidal volume (VT) changed inversely with changes in TA. Generally, while breathing room air, arterial PCO2 (Paco2) did not change from control during the first 48 h of altered TA. In studies when inspired CO2 was elevated VT increased by the same amount at all TA; f increased at low and control TA but decreased at elevated TA; and VE and Paco2 both increased relatively less at elevated TA, but the VE-Paco2 slope was independent of TA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Temperature regulation in adult quail (Colinus virginianus) during acute thermal stress

1. Evaporative heat loss, O2 consumption, CO2 production, and internal body temperature were measured in unanesthetized, unrestrained bobwhite (Colinus virginianus) at specific ambient temperatures (Ta). 2. No significant change in body temperature occurred at any Ta tested, but metabolic heat production (H) increased from 42.17 W/m2 at Ta 35 degrees C to 102.89 W/m2 at Ta 10 degrees C. 3. Evaporative heat loss (E) increased approximately two-fold from Ta 10-35 degrees C, with E/H increasing exponentially over the same temperature range. 4. No significant change in thermal insulation occurred from Ta 10-30 degrees C. 5. Combined convective and radiative heat transfer for the bobwhite was 2.96 W/m2 X C from Ta 10-35 degrees C.     

Salinity treatment shows no effects on photosystem II photochemistry,but increases the resistance of photosystem II to heat stress in halophyte Suaeda salsa

Photosynthetic gas exchange, modulated chlorophyll fluorescence, rapid fluorescence induction kinetics, and the polyphasic fluorescence transients were used to evaluate PSII photochemistry in the halophyte Suaeda salsa exposed to a combination of high salinity (100-400 mM NaCl) and heat stress (35-47.5 degrees C, air temperature). CO(2) assimilation rate increased slightly with increasing salt concentration up to 300 mM NaCl and showed no decrease even at 400 mM NaCl. Salinity treatment showed neither effects on the maximal efficiency of PSII photochemistry (F(v)/F(m)), the rapid fluorescence induction kinetics, and the polyphasic fluorescence transients in dark-adapted leaves, nor effects on the efficiency of excitation energy capture by open PSII reaction centres (F(v)'/F(m)') and the actual PSII effciency (Phi(PSII)), photochemical quenching (q(P)), and non-photochemical quenching (q(N)) in light-adapted leaves. The results indicate that high salinity had no effects on PSII photochemistry either in a dark-adapted state or in a light-adapted state. With increasing temperature, CO(2) assimilation rate decreased significantly and no net CO(2) assimilation was observed at 47.5 degrees C. Salinity treatment had no effect on the response of CO(2) assimilation to high temperature when temperature was below 40 degrees C. At 45 degrees C, CO(2) assimilation rate in control plants decreased to zero, but the salt-adapted plants still maintained some CO(2) assimilation capacity. On the other hand, the responses of PSII photochemistry to heat stress was modified by salinity treatment. When temperature was above 35 degrees C, the declines in F(v)/F(m), Phi(PSII), F(v)'/F(m)', and q(P) were smaller in salt-adapted leaves compared to control leaves. This increased thermostability was independent of the degree of salinity, since no significant changes in the above-described fluorescence parameters were observed among the plants treated with different concentrations of NaCl. During heat stress, a very clear K step as a specific indicator of damage to the O(2)-evolving complex in the polyphasic fluorescence transients appeared in control plants, but did not get pronounced in salt-adapted plants. In addition, a greater increase in the ratio (F(i)-F(o))/(F(p)-F(o)) which is an expression of the proportion of the Q(B)-non-reducing PSII centres was observed in control plants rather than in salt-adapted plants. The results suggest that the increased thermostability of PSII seems to be associated with the increased resistance of the O(2)-evolving complex and the reaction centres of PSII to high temperature.     

Temperature and pH/CO(2) modulate respiratory activity in the isolated brainstem of the bullfrog (Rana catesbeiana)

The effects of temperature and pH/CO(2) were examined in isolated brainstem preparations from adult North American bullfrogs (Rana catesbeiana). These experiments were undertaken to determine the effects of temperature on fictive breathing, central pH/CO(2) chemoreception, and to examine potential alphastat regulation of respiration in vitro. Adult bullfrog brainstem preparations were isolated, superfused with an artificial cerebrospinal fluid (aCSF) and respiratory-related neural activity was recorded from cranial nerves V, X and XII. In Series I experiments (N=8), brainstem preparations were superfused with aCSF equilibrated with 2% CO(2) at temperatures ranging from 10 to 30 degrees C. Neural activity was present in all preparations in the temperature range of 15-25 degrees C, but was absent in most preparations when aCSF was at 10 or 30 degrees C. The absence of fictive breathing at high (30 degrees C) temperatures was transient since fictive breathing could be restored upon returning the preparation to 20 degrees C. In Series II experiments (N=10), preparations were superfused with aCSF equilibrated with 0%, 2% and 5% CO(2) at temperatures of 15, 20 and 25 degrees C. Fictive breathing frequency (f(R)) was significantly dependent upon aCSF pH at all three temperatures, with slopes ranging from -0.82 min(-1) pH unit(-1) (15 degrees C) to -3.3 min(-1) pH unit(-1) (20 degrees C). There was a significant difference in these slopes (P<0.02), indicating that central chemoreceptor sensitivity increased over this temperature range. Fictive breathing frequency was significantly dependent upon the calculated alpha-imidazole (alpha(Im)) ionization (P<0.05), consistent with the alphastat hypothesis for the effects of temperature on the regulation of ventilation. However, most of the variation in f(R) was not explained by alpha(Im) (R(2)=0.05), suggesting that other factors account for the regulation of fictive breathing in this preparation. The results indicate that the in vitro brainstem preparation of adult bullfrogs has a limited temperature range (15-25 degrees C) over which fictive breathing is consistently active. Although there is a close correspondence of ventilation in vitro and in vivo at low temperatures, these data suggest that, as temperature increases, changes in ventilation in the intact animal are likely to be more dependent upon peripheral feedback which assumes a greater integrative role with respect to chemoreceptor drive, respiratory frequency and tidal volume.     

Pulmonary gas exchange in panting dogs

Pulmonary gas exchange during panting was studied in seven conscious dogs (32 kg mean body wt) provided with a chronic tracheostomy and an exteriorized carotid artery loop. The animals were acutely exposed to moderately elevated ambient temperature (27.5 degrees C, 65% relative humidity) for 2 h. O2 and CO2 in the tracheostomy tube were continuously monitored by mass spectrometry using a special sample-hold phase-locked sampling technique. PO2 and PCO2 were determined in blood samples obtained from the carotid artery. During the exposure to heat, central body temperature remained unchanged (38.6 +/- 0.6 degrees C) while all animals rapidly switched to steady shallow panting at frequencies close to the resonant frequency of the respiratory system. During panting, the following values were measured (means +/- SD): breathing frequency, 313 +/- 19 breaths/min; tidal volume, 167 +/- 21 ml; total ventilation, 52 +/- 9 l/min; effective alveolar ventilation, 5.5 +/- 1.3 l/min; PaO2, 106.2 +/- 5.9 Torr; PaCO2, 27.2 +/- 3.9 Torr; end-tidal-arterial PO2 difference [(PE' - Pa)O2], 26.0 +/- 5.3 Torr; and arterial-end-tidal PCO2 difference, [(Pa - PE')CO2], 14.9 +/- 2.5 Torr. On the basis of the classical ideal alveolar air approach, parallel dead-space ventilation accounted for 54% of alveolar ventilation and 66% of the (PE' - Pa)O2 difference. But the steepness of the CO2 and O2 expirogram plotted against expired volume suggested a contribution of series in homogeneity due to incomplete gas mixing.     

Microbiological analysis of rock cod (Sebastes spp.) stored under elevated carbon dioxide atmospheres

The numbers and types of microorganisms on fresh rock cod fillets and fillets stored in air or in a modified atmosphere (MA; 80% CO(2), 20% air) at 4 degrees C were compared. Samples were analyzed after 0, 7, 14, and 21 days of storage. The isolation plates were incubated aerobically, anaerobically, or under MA at 4, 20, or 35 degrees C. After 7 days of storage in air, the fillets were obviously spoiled and had a 3- to 4-log cycle increase in microbial counts. Plate counts increased more slowly on MA-stored fillets. After 21 days, the counts on the latter had increased only 2 log cycles, and the fillets did not seem spoiled. The microbial flora changed greatly during MA storage. Only Lactobacillus spp. (70%) and an Aeromonas sp.-like isolate (30%) were found on plates incubated aerobically at 4 and 20 degrees C, and only Lactobacillus spp. was found on plates incubated aerobically and anaerobically at 35 and at 20 degrees C under MA. Isolation plates incubated at 20 degrees C in air gave the highest counts in the shortest incubation time and the greatest diversity of bacterial types recovered. No Vibrio parahaemolyticus, Staphylococcus aureus, or Clostridium botulinum type E were isolated from the fresh or MA-stored fillets.     

Influence of temperature and gas atmosphere on in-vitro fertilization and embryo development in domestic cats

The influence of culture temperature and gas atmosphere on in-vitro fertilization and embryo development was examined in the domestic cat. In Exp. 1, eggs were fertilized and cultured in 5% CO2 in air at 37, 38 or 39 degrees C. Experiment 2 evaluated the effects of 5% CO2 in air; 5% CO2, 5% O2 and 90% N2; and 10% CO2 in air. Fertilization (cleavage) and development to the morula/blastocyst stage were not influenced (P greater than 0.05) by variations in temperature and gas composition. Despite changing these culture conditions, egg cleavage averaged approximately 75% and greater than 80% of the 2-cell embryos proceeded to morulae in vitro. However, the partial in-vitro morula-to-blastocyst developmental block normally observed in this species was not removed.     

Inactivation of Geobacillus stearothermophilus spores by high-pressure carbon dioxide treatment

High-pressure CO2 treatment has been studied as a promising method for inactivating bacterial spores. In the present study, we compared this method with other sterilization techniques, including heat and pressure treatment. Spores of Bacillus coagulans, Bacillus subtilis, Bacillus cereus, Bacillus licheniformis, and Geobacillus stearothermophilus were subjected to CO2 treatment at 30 MPa and 35 degrees C, to high-hydrostatic-pressure treatment at 200 MPa and 65 degrees C, or to heat treatment at 0.1 MPa and 85 degrees C. All of the bacterial spores except the G. stearothermophilus spores were easily inactivated by the heat treatment. The highly heat- and pressure-resistant spores of G. stearothermophilus were not the most resistant to CO2 treatment. We also investigated the influence of temperature on CO2 inactivation of G. stearothermophilus. Treatment with CO2 and 30 MPa of pressure at 95 degrees C for 120 min resulted in 5-log-order spore inactivation, whereas heat treatment at 95 degrees C for 120 min and high-hydrostatic-pressure treatment at 30 MPa and 95 degrees C for 120 min had little effect. The activation energy required for CO2 treatment of G. stearothermophilus spores was lower than the activation energy for heat or pressure treatment. Although heat was not necessary for inactivationby CO2 treatment of G. stearothermophilus spores, CO2 treatment at 95 degrees C was more effective than treatment at 95 degrees C alone.     

Response of superoxide dismutase isoenzymes in tomato plants (Lycopersicon esculentum) during thermo-acclimation of the photosynthetic apparatus

Seedlings of Lycopersicon esculentum Mill. var. Amalia were grown in a growth chamber under a photoperiod of 16 h light at 25 degrees C and 8 h dark at 20 degrees C. Five different treatments were applied to 30-day-old plants: Control treatment (plants maintained in the normal growth conditions throughout the experimental time), heat acclimation (plants exposed to 35 degrees C for 4 h in dark for 3 days), dark treatment (plants exposed to 25 degrees C for 4 h in dark for 3 days), heat acclimation plus heat shock (plants that previously received the heat acclimation treatment were exposed to 45 degrees C air temperature for 3 h in the light) and dark treatment plus heat shock (plants that previously received the dark treatment were exposed to 45 degrees C air temperature for 3 h in the light). Only the heat acclimation treatment increased the thermotolerance of the photosynthesis apparatus when the heat shock (45 degrees C) was imposed. In these plants, the CO(2) assimilation rate was not affected by heat shock and there was a slight and non-significant reduction in maximum carboxylation velocity of Rubisco (V(cmax)) and maximum electron transport rate contributing to Rubisco regeneration (J(max)). However, the plants exposed to dark treatment plus heat shock showed a significant reduction in the CO(2) assimilation rate and also in the values of V(cmax) and J(max). Chlorophyll fluorescence measurements showed increased thermotolerance in heat-acclimated plants. The values of maximum chlorophyll fluorescence (F(m)) were not modified by heat shock in these plants, while in the dark-treated plants that received the heat shock, the F(m) values were reduced, which provoked a significant reduction in the efficiency of photosystem II. A slight rise in the total superoxide dismutase (SOD) activity was found in the plants that had been subjected to both heat acclimation and heat shock, and this SOD activity was significantly higher than that found in the plants subjected to dark treatment plus heat shock. The activity of Fe-SOD isoenzymes was most enhanced in heat-acclimated plants but was unaltered in the plants that received the dark treatment. Total CuZn-SOD activity was reduced in all treatments. Darkness had an inhibitory effect on the Mn-SOD isoenzyme activity, which was compensated by the effect of a rise in air temperature to 35 degrees C. These results show that the heat tolerance of tomatoplants may be increased by the previous imposition of a moderately high temperature and could be related with the thermal stability in the photochemical reactions and a readjustment of V(cmax) and J(max). Some isoenzymes, such as the Fe-SODs, may also play a role in the development of heat-shock tolerance through heat acclimation. In fact, the pattern found for these isoenzymes in heat-acclimated Amalia plants was similar to that previously described in other heat-tolerant tomato genotypes.     

Effects of temperature and hypercapnia on ventilation and breathing pattern in the lizard Uromastyx aegyptius microlepis

In most reptiles, the ventilatory response to hypercapnia consists of large increases in tidal volume (V(T)), whereas the effects on breathing frequency (f(R)) are more variable. The increased V(T) seems to arise from direct inhibition of pulmonary stretch receptors. Most reptiles also exhibit a transitory increase in ventilation upon removal of CO(2) and this post-hypercapnic hyperpnea may consist of changes in both V(T) and f(R). While it is well established that increased body temperature augments the ventilatory response to hypercapnia, the effects of temperature on the post-hypercapnic hyperpnea is less described. In the present study, we characterise the ventilatory response of the agamid lizard Uromastyx aegyptius to hypercapnia and upon the return to air at 25 and 35 degrees C. At both temperatures, hypercapnia caused large increases in V(T) and small reductions in f(R), that were most pronounced at the higher temperature. The post-hypercapnic hyperpnea, which mainly consisted of increased f(R), was numerically larger at 35 compared to 25 degrees C. However, when expressed as a proportion of the levels of ventilation reached during steady-state hypercapnia, the post-hypercapnic hyperpnea was largest at 25 degrees C. Some individuals exhibited buccal pumping where each expiratory thoracic breath was followed by numerous small forced inhalations caused by contractions of the buccal cavity. This breathing pattern was most pronounced during severe hypercapnia and particularly evident during the post-hypercapnic hyperpnea.     

Metabolic effects of exposure to hypoxia plus cold at rest and during exercise in humans

To determine effects on metabolic responses, subjects were exposed to four environmental conditions for 90 min at rest followed by 30 min of exercise: breathing room air with an ambient temperature of 25 degrees C (NN); breathing room air with an ambient temperature of 8 degrees C (NC); hypoxia (induced by breathing 12% O2 in N2) with a neutral temperature (HN); and hypoxia in the cold (HC). Hypoxia increased heart rate (HR), systolic blood pressure (SBP), pulmonary ventilation (VE), respiratory exchange ratio (R), blood lactate, and perceived exertion during exercise while depressing rectal temperature (Tre) and O2 uptake (VO2). Cold exposure elevated SBP, diastolic blood pressure (DBP), VE, VO2, blood glucose, and blood glycerol but decreased HR, Tre, and R. Shivering and DBP were higher and Tre was lower in HC compared with NC. HR, SBP, VE, R, and lactate tended to be higher in HC compared with NC, whereas VO2 and blood glycerol tended to be depressed. These results suggest that cold exposure during hypoxia results in an increased reliance on shivering for thermogenesis at rest whereas, during exercise, heat loss is accelerated.     

The apparent buffer value of human blood for CO2 as a function of temperature

The influence of temperature on the acid-base status of normal human deoxygenated whole blood was studied in open systems (variable total CO2 content). (1) When the temperature was raised from 26 degrees C to 42 degrees C, the apparent buffering value of deoxygenated whole blood for CO2 increased by 7% of its value at 26 degrees C; this increase was not statistically significant. (2) Comparing the present data with those obtained previously from oxygenated whole blood in the same temperature range (Castaing & Pocidalo, 1979) indicates that arterial and venous blood have slightly different buffering capacities for CO2 in the 26 to 42 degrees C temperature range. It also suggests that, at physiological SO2 levels (SO2 greater than or equal to 30%), the apparent buffering value of venous blood for CO2 would be increased by at least 10% of its value at 26 degrees C when the temperature is raised to 42 degrees C. (3) It is concluded that pH stability would be reduced upon CO2 uptake within tissues with a high metabolism and therefore a high temperature.