The effect of extrinsic and intrinsic factors on oxygen consumption by the southern rock lobster, Jasus edwardsii

The oxygen consumption rate of the southern rock lobster, Jasus edwardsii, was evaluated in response to body weight, temperature, activity, handling, diurnal rhythm, feeding and oxygen saturation level. There was a positive relationship between standard oxygen consumption (M(O(2))) and both body weight and water temperature. The relationship between total oxygen consumption and wet whole body weight was described by the equation: LogM(O(2))=0.595log W-0.396 (r(2)=0.83). The relationship between weight-specific oxygen consumption and temperature was described by the equation: LogM(O(2))=0.047T-2.25 (r(2)=0.94). Activity had a significant influence on the oxygen consumption rate, causing a three-fold increase above the standard rate at the temperature of acclimation (13 degrees C). However, at temperatures approaching the upper and lower extremes, lobsters had a decreased ability to increase their oxygen consumption rates during activity. Lobsters took 4.5-5 h to return to standard oxygen consumption rates after a period of emersion and handling. A strong diurnal rhythm to oxygen consumption was recorded. J. edwardsii displayed a classic postprandial increase in oxygen consumption. A peak (1.72 times standard M(O(2))) occurred 10-13 h after feeding with an increase above standard M(O(2)) being maintained for 42 h. In its rested state J. edwardsii was an oxygen regulator down to a critical oxygen tension of 58 Torr, whilst activity resulted in the critical oxygen tension increasing to 93 Torr.     

Oxygen uptake during early life in the fresh water fish, Esomus danricus (Ham) (Pisces, Cypriniformes)

O2 uptake in Esomus danricus has been determined in relation to body weight, length and thickness of the water-blood diffusion barrier at 27-28 degrees C temperature. Total O2 consumption in larvae was 1311 ml/kg/h but decreased significantly in juvenile fishes (720 ml/kg/h). The increase in the thickness of water-blood diffusion barrier at the secondary gill lamellae of the fish was found to be an important factor for the decrease in VO2. Logarithmic analyses of data for O2 uptake in relation to body weight gave a slope of 0.8865 for larvae and 0.5053 for juveniles. The exponent values of O2 uptake against diffusion barrier for larvae and juveniles were 1.7383 and 2.0956, respectively. The results obtained indicated that fish have an extra device which helps in extracting about 24% of the total VO2 required for the fulfilment of the metabolic oxygen demand of the body.     

Decreased O2 consumption and cardiac output during normobaric hyperoxia in conscious dogs

Recent reports indicate that under certain restricted conditions hyperoxia may decrease tissue O2 consumption. However, this effect has not been established for whole body O2 consumption in the intact healthy conscious state. The goal of the present study was to document the effect of hyperoxia on resting whole body O2 consumption and hemodynamics under these latter more general physiological conditions. The inspired gas was delivered by mask to six fasted resting conscious dogs and alternated hourly between air and O2-enriched air (hyperoxia) for 5 h, while hemodynamics and blood gas data were obtained every 20 min. Compared with air breathing, hyperoxia increased the mean arterial O2 tension from 95 to 475 Torr and decreased heart rate, cardiac output, pulmonary vascular resistance, and right and left ventricular work rates and thus, presumably, myocardial O2 consumption. Hyperoxia also increased systemic vascular resistance and right atrial pressure but did not change stroke volume or systemic arterial pressure. The increase in arterial O2 content during hyperoxia was counterbalanced by the decrease in cardiac output, so that O2 delivery was unchanged by hyperoxia. Surprisingly, hyperoxia decreased the arterial-to-mixed venous difference in O2 content; this decrease together with the decrease in cardiac output produced a decrease in resting whole body O2 consumption from 5.88 +/- 0.68 to 4.80 +/- 0.62 ml O2.min-1.kg-1 (P = 0.0002). It is concluded that under physiological conditions normobaric hyperoxia may decrease metabolic rate in addition to cardiac output, which may have important implications for the metabolic regulation of O2 utilization as well as for the medical and nonmedical uses of O2.     

Mechanism of the alcohol cyclic pattern: role of the hypothalamic-pituitary-thyroid axis

The cause of the cycle of urinary alcohol levels (UALs) in rats fed ethanol continually at a fixed rate is unknown. Rats were fed ethanol intragastrically at a constant dose for 2 mo, and daily body temperatures and UALs were recorded. Body temperature cycled inversely to UAL, suggesting that the rate of metabolism could be mechanistically involved in the rate of ethanol elimination during the cycle. To document this, whole body O(2) consumption rate was monitored daily during the cycle. The rate of O(2) consumption correlated positively with the change in body temperature and negatively with the change in UAL. Since the metabolic rate responds to changes in body temperature, thyroid hormone levels were measured during the UAL cycle. T(4) levels correlated positively with the O(2) consumption rate and negatively with the UALs. In a second experiment using propylthiouracil treatment, UALs did not cycle and a fall in body temperature failed to stimulate an increase in the rate of ethanol elimination. Consequently, rats died of overdose. Likewise, in a third experiment using rats with severed pituitary stalks, UALs failed to cycle and rats died of overdose. From these observations it was concluded that the UAL cycle depends on an intact hypothalamic-pituitary-thyroid axis response to the ethanol-induced drop in body temperature by increasing the rate of ethanol elimination.     

Effects of meal size,meal type,body temperature,and body size on the specific dynamic action of the marine toad,Bufo marinus

Specific dynamic action (SDA), the accumulated energy expended on all physiological processes associated with meal digestion, is strongly influenced by features of both the meal and the organism. We assessed the effects of meal size, meal type, body temperature, and body size on the postprandial metabolic response and calculated SDA of the marine toad, Bufo marinus. Peak postprandial rates of O(2) consumption (.V(O2)) and CO(2) production (.V(CO2)) and SDA increased with meal size (5%-20% of body mass). Postprandial metabolism was impacted by meal type; the digestion of hard-bodied superworms (Zophobas larva) and crickets was more costly than the digestion of soft-bodied earthworms and juvenile rats. An increase in body temperature (from 20 degrees to 35 degrees C) altered the postprandial metabolic profile, decreasing its duration and increasing its magnitude, but did not effect SDA, with the cost of meal digestion remaining constant across body temperatures. Allometric mass exponents were 0.69 for standard metabolic rate, 0.85 for peak postprandial .V(O2), and 1.02 for SDA; therefore, the factorial scope of peak postprandial .V(O2) increased with body mass. The mass of nutritive organs (stomach, liver, intestines, and kidneys) accounted for 38% and 20% of the variation in peak postprandial .V(O2) and SDA, respectively. Toads forced to exercise experienced 25-fold increases in .V(O2) much greater than the 5.5-fold increase experience during digestion. Controlling for meal size, meal type, and body temperature, the specific dynamic responses of B. marinus are similar to those of the congeneric Bufo alvarius, Bufo boreas, Bufo terrestris, and Bufo woodhouseii.     

Enhancement of finger blood flow response of postprandial human subjects to the increase in body temperature during exercise

The present study was performed to investigate the effect of food intake on thermoregulatory vasodilatation in seven healthy male volunteers. The changes in oesophageal (Toes) and mean skin temperatures, finger and forearm blood flows (BF), oxygen consumption (VO2) and heart rate (fc) with and without food intake were measured before and during a 40-min exercise at an intensity of 35% maximal O2 consumption at an ambient temperature of 25 degrees C. Exercise commenced 60 min after food intake. Ingestion of food equivalent to 50.2 kJ.kg body mass-1 elevated mean body temperature, BF, VO2 and fc in 60 min. Four subjects responded to exercise with a marked increase in finger BF and with no sweating (non-sweating group), while the other three responded with perspiration over almost the whole skin area and with little change in finger BF. Further analyses were made mainly in the non-sweating group. The postprandial increases in Toes, BF, VO2 and fc were persistent during exercise. The rate of increase in finger BF with the increase in Toes and mean body temperature was significantly greater with food intake than without. However, there was no difference in the response of forearm BF to exercise between the two conditions. These results suggested that food intake enhanced finger BF response to the increase in deep body temperature during exercise. It was also concluded that there was a regional difference in cutaneous vasomotor response to thermal load in the postprandial subjects.     

Metabolic activation of carotid body glomus cells by hypoxia

The effects of low O2 on glucose consumption in the rabbit carotid body were studied using the in vitro 2-deoxyglucose technique. Metabolically active structures within the tissue were localized autoradiographically after freeze-drying and vacuum fixation/embedding of selected incubated tissue samples. In 100% O2-equilibrated media, the mean basal glucose consumption calculated from the rate of 2-[1,2-3H]deoxy-D-glucose phosphorylation and its specific activity in the incubation media was 61 nmol.g tissue-1.min-1 in the carotid body and 42 nmol.g tissue-1.min-1 in parallel experiments with nodose ganglia. Low PO2 (20% O2-equilibrated media in vitro) increased glucose consumption in the carotid body by 44% but did not alter glucose metabolism of nodose ganglia. Autoradiographic data showed that preneural type I parenchymal cells are the principal site of glucose consumption in carotid chemosensory tissue. The mechanisms responsible for the hypoxia-induced increase in glucose consumption by the type I cells are discussed in relation to sensory transduction by the carotid body chemoreceptors.     

Renal O2 consumption during progressive hemorrhage

Most mammalian tissues regulate O2 utilization such that O2 consumption (VO2) is relatively constant at O2 delivery (DO2) higher than a critical value (DO2c). We studied the relationship between VO2 and DO2 of kidney and whole body during graded progressive exsanguination. The relationship between whole body VO2 and DO2 was biphasic, and whole body VO2 decreased by 5.6 +/- 14.4% (P = NS) from the initial value to the value nearest whole body DO2c. Kidney DO2 decreased in direct proportion to whole body DO2 such that the average R2 value describing the linear regression of kidney DO2 vs. whole body DO2 was 0.94 +/- 0.02. The relationship between kidney, like whole body, VO2 and DO2 appeared biphasic; however, kidney VO2 decreased by 63.3 +/- 10.4% (P less than 0.0001) from the initial value to the value nearest kidney DO2c. Renal O2 extraction ratio was relatively constant over a wide range of kidney DO2, whereas whole body O2 extraction ratio increased progressively at all whole body DO2 values as whole body DO2 decreased. However, final values of O2 extraction ratio were indistinguishable for whole body (0.86 +/- 0.1) and kidney (0.86 +/- 0.06) (P = NS). We conclude that the pattern of kidney and whole body VO2 response to decreasing DO2 differs during hemorrhage, particularly in the range of DO2 normally associated with tissue wellness.     

Regulation of breathing and body temperature of a burrowing rodent during hypoxic-hypercapnia

Burrowing mammals usually have low respiratory sensitivity to hypoxia and hypercapnia. However, the interaction between ventilation (V), metabolism and body temperature (Tb) during hypoxic-hypercapnia has never been addressed. We tested the hypothesis that Clyomys bishopi, a burrowing rodent of the Brazilian cerrado, shows a small ventilatory response to hypoxic-hypercapnia, accompanied by a marked drop in Tb and metabolism. V, Tb and O(2) consumption (V?O(2)) of C. bishopi were measured during exposure to air, hypoxia (10% and 7% O(2)), hypercapnia (3% and 5% CO(2)) and hypoxic-hypercapnia (10% O(2)+ 3% CO(2)). Hypoxia of 7% but not 10%, caused a significant increase in V, and a significant drop in Tb. Both hypoxic levels decreased V?O(2) and 7% O(2) significantly increased V/V?O(2). Hypercapnia of 5%, but not 3%, elicited a significant increase in V, although no significant change in Tb, V?O(2) or V/V?O(2) was detected. A combination of 10% O(2) and 3% CO(2) had minor effects on V and Tb, while V?O(2) decreased and V/V?O(2) tended to increase. We conclude that C. bishopi has a low sensitivity not only to hypoxia and hypercapnia, but also to hypoxic-hypercapnia, manifested by a biphasic ventilatory response, a drop in metabolism and a tendency to increase V/V?O(2). The effect of hypoxic-hypercapnia was the summation of the hypoxia and hypercapnia effects, with respiratory responses tending to have hypercapnic patterns while metabolic responses, hypoxic patterns.     

Adjustments in oxygen transport during head-out immersion in water at different temperatures

Respiratory gas exchange was investigated in human subjects immersed up to the shoulders in water at different temperatures (Tw = 25, 34, and 40 degrees C). Cardiac output (Qc) and pulmonary tissue volume (Vti) were measured by a rebreathing technique with the inert gas Freon 22, and O2 consumption (VO2) was determined by the closed-circuit technique. Arterial blood gases (PaO2, PaCO2) were analyzed by a micromethod, and alveolar gas (PAO2) was analyzed during quiet breathing with a mass spectrometer. The findings were as follows. 1) Immersion in a cold bath had no significant effect on Qc compared with the value measured at Tw = 34 degrees C, whereas immersion in a hot bath led to a considerable increase in Qc. Vti was not affected by immersion at any of the temperatures tested. 2) A large rise in metabolic rate VO2 was only observed at Tw = 25 degrees C (P less than 0.001). 3) Arterial blood gases were not significantly affected by immersion, whatever the water temperature. 4) O2 transport during immersion is affected by two main factors: hydrostatic pressure and temperature. Above neutral temperature, O2 transport is improved because of the marked increase in Qc resulting from the combined actions of hydrostatic counter pressure and body heating. Below neutral temperature, O2 transport is altered; an increase in O2 extraction of the tissue is even calculated.     

Role of K(ATP)(+) channels in regulation of systemic, pulmonary, and coronary vasomotor tone in exercising swine

The role of ATP-sensitive K(+) (K(ATP)(+)) channels in vasomotor tone regulation during metabolic stimulation is incompletely understood. Consequently, we studied the contribution of K(ATP)(+) channels to vasomotor tone regulation in the systemic, pulmonary, and coronary vascular bed in nine treadmill-exercising swine. Exercise up to 85% of maximum heart rate increased body O(2) consumption fourfold, accommodated by a doubling of both cardiac output and body O(2) extraction. Mean aortic pressure was unchanged, implying that systemic vascular conductance (SVC) also doubled, whereas pulmonary artery pressure increased almost in parallel with cardiac output, so that pulmonary vascular conductance (PVC) increased only 25 +/- 9% (both P < 0.05). Myocardial O(2) consumption tripled during exercise, which was paralleled by an equivalent increase in O(2) supply so that coronary venous PO(2) was maintained. Selective K(ATP)(+) channel blockade with glibenclamide (3 mg/kg iv), decreased SVC by 29 +/- 4% at rest and by 10 +/- 2% at 5 km/h (both P < 0.05), whereas PVC was unchanged. Glibenclamide decreased coronary vascular conductance and hence myocardial O(2) delivery, necessitating an increase in O(2) extraction from 76 +/- 2% to 86 +/- 2% at rest and from 79 +/- 2% to 83 +/- 1% at 5 km/h. Consequently, coronary venous PO(2) decreased from 25 +/- 1 to 17 +/- 1 mmHg at rest and from 23 +/- 1 to 20 +/- 1 mmHg at 5 km/h (all values are P < 0.05). In conclusion, K(ATP)(+) channels dilate the systemic and coronary, but not the pulmonary, resistance vessels at rest and during exercise in swine. However, opening of K(ATP)(+) channels is not mandatory for the exercise-induced systemic and coronary vasodilation.     

Influence of training on sweating responses during submaximal exercise in horses.

Sweating responses were examined in five horses during a standardized exercise test (SET) in hot conditions (32-34 degrees C, 45-55% relative humidity) during 8 wk of exercise training (5 days/wk) in moderate conditions (19-21 degrees C, 45-55% relative humidity). SETs consisting of 7 km at 50% maximal O(2) consumption, determined 1 wk before training day (TD) 0, were completed on a treadmill set at a 6 degrees incline on TD0, 14, 28, 42, and 56. Mean maximal O(2) consumption, measured 2 days before each SET, increased 19% [TD0 to 42: 135 +/- 5 (SE) to 161 +/- 4 ml. kg(-1). min(-1)]. Peak sweating rate (SR) during exercise increased on TD14, 28, 42, and 56 compared with TD0, whereas SRs and sweat losses in recovery decreased by TD28. By TD56, end-exercise rectal and pulmonary artery temperature decreased by 0.9 +/- 0.1 and 1.2 +/- 0.1 degrees C, respectively, and mean change in body mass during the SET decreased by 23% (TD0: 10.1 +/- 0.9; TD56: 7.7 +/- 0.3 kg). Sweat Na(+) concentration during exercise decreased, whereas sweat K(+) concentration increased, and values for Cl(-) concentration in sweat were unchanged. Moderate-intensity training in cool conditions resulted in a 1.6-fold increase in sweating sensitivity evident by 4 wk and a 0.7 +/- 0.1 degrees C decrease in sweating threshold after 8 wk during exercise in hot, dry conditions. Altered sweating responses contributed to improved heat dissipation during exercise and a lower end-exercise core temperature. Despite higher SRs for a given core temperature during exercise, decreases in recovery SRs result in an overall reduction in sweat fluid losses but no change in total sweat ion losses after training.     

Effects of meal size,meal type,and body temperature on the specific dynamic action of anurans

Specific dynamic action (SDA), the increase in metabolism stemming from meal digestion and assimilation, varies as a function of meal size, meal type, and body temperature. To test predictions of these three determinants of SDA, we quantified and compared the SDA responses of nine species of anurans, Bombina orientalis, Bufo cognatus, Ceratophrys ornata, Dyscophus antongilli, Hyla cinerea, Kassina maculata, Kassina senegalensis, Pyxicephalus adspersus, and Rana catesbeiana subjected to meal size, meal type, and body temperature treatments. Over a three to seven-fold increase in meal size, anurans experienced predicted increases in postprandial rates of oxygen consumption the duration of elevated and SDA. Meal type had a significant influence on the SDA response, as the digestion and assimilation of hard-bodied, chitinous crickets, mealworms, and superworms required 76% more energy than the digestion and assimilation of soft-bodied earthworms, waxworms, and neonate rodents. Body temperature largely effected the shape of the postprandial metabolic profile; peak increased and the duration of the response decreased with an increase in body temperature. Variation in body temperature did not significantly alter SDA for four species, whereas both H. cinerea and R. catesbeiana experienced significant increases in SDA with body temperature. For 13 or 15 species of anurans ranging in mass from 2.4 to 270 g, SMR, postprandial peak and SDA scaled with body mass (log–log) with mass exponents of 0.79, 0.93, and 1.05, respectively.     

Interactions between Photosynthesis and Respiration in the Green Alga Chlamydomonas reinhardtii (Characterization of Light-Enhanced Dark Respiration)

The rate of respiratory O2 consumption by Chlamydomonas reinhardtii cell suspensions was greater after a period of photosynthesis than in the preceding dark period. This "light-enhanced dark respiration" (LEDR) was a function of both the duration of illumination and the photon fluence rate. Mass spectrometric measurements of gas exchange indicated that the rate of gross respiratory O2 consumption increased during photosynthesis, whereas gross respiratory CO2 production decreased in a photon fluence rate-dependent manner. The rate of postillumination O2 consumption provided a good measure of the O2 consumption rate in the light. LEDR was substantially decreased by the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea or glycolaldehyde, suggesting that LEDR was photosynthesis-dependent. The onset of photosynthesis resulted in an increase in the cellular levels of phosphoglycerate, malate, and phosphoenolpyruvate, and a decrease in whole-cell ATP and citrate levels; all of these changes were rapidly reversed upon darkening. These results are consistent with a decrease in the rate of respiratory carbon flow during photosynthesis, whereas the increase in respiratory O2 consumption during photosynthesis may be mediated by the export of photogenerated reductant from the chloroplast. We suggest that photosynthesis interacts with respiration at more than one level, simultaneously decreasing the rate of respiratory carbon flow while increasing the rate of respiratory O2 consumption.     

Heat production in the ground squirrel Citellus pygmaeus during arousal from hibernation]

Heat production has been both measured experimentally (Qcal) and calculated from oxygen consumption (QO2) in arousing ground squirrels during the rise of their body temperature. Studies were made on total heat production during all the period of their warming as well as on the heat production at various stages of arousal. Qcal was evaluated by changes in body temperature and those in heat losses via convection and irradiation (calorimetrically). During arousal of animals, their body temperature, heat losses, Qcal and QO2 Gradually increase. However, the increase in heat losses is 3-4 times lower as compared to the intrinsic heat production measured both calorimetrically and by oxygen consumption. Limitation of heat losses (due to the constriction of subcutaneous blood vessels) together with activation of the metabolism in muscles and other tissues provide for significant heat accumulation and the increase in body temperature of arousing ground squirrels.     

Critical O2 transport values at lowered body temperatures in rats

Whole-body O2 uptake (VO2) in rats was reported not to increase when total O2 transport (TOT = cardiac output X arterial O2 concentration) was increased above normal ranges when body temperature was kept at 38 degrees C (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 53: 660-664, 1982). Similar experiments were performed to see if hypothermic rats at 34 degrees C would increase VO2 with an increased TOT in an effort to generate heat. Anesthetized rats were ventilated with 9 or 12% O2 (hypoxia), room air (normoxia), and O2 (hyperoxia) to vary TOT from 52.6 to 6.6 ml X kg-1 X min-1. VO2 was measured in a closed-circuit, double servospirometer system. Although VO2 was significantly lower at 34 degrees C than the values previously found at 38 degrees C with normoxia and hyperoxia, there was no increase with increasing values of TOT. In spite of a lower plateau value of VO2 at 34 degrees C, the critical value of TOT below which VO2 could not be maintained was nearly the same as at 38 degrees C (22 ml X kg-1 X min-1). The reason for this was that O2 was less completely extracted as TOT was lowered below the critical value in the hypothermic animal. Some of the difficulty in extracting O2 at the tissues was probably due to the decrease in P50 (PO2 at 50% saturation) that occurs with decreased body temperature.     

Effects of temperature and ration level on the growth and food conversion efficiency of Salmo gairdneri, Richardson

The effects of temperature and ration size on the growth rate and gross efficiency of food conversion of juvenile rainbow trout Salmo gairdneri were evaluated during 25-day seasonal experiments. Rations ranged from near-starvation to repletion levels. Test temperatures were 3 and 6°C higher than the controls which fluctuated dielly and seasonally. At rations near maintenance, elevated temperatures decreased trout growth. As the feeding rate increased the detrimental effect of temperature on growth was ameliorated. At repletion feeding levels, elevated temperature up to 17°C improved trout growth by increasing the maximum food consumption rate. With a temperature increase from 6.9 to 22.5°C maintenance rations increased from 2.2 to 7.5 % body weight per day. Gross efficiency was dependent upon ration level and temperature. As the food consumption rate increased, efficiency increased to a maximum, then generally declined at repletion levels. Elevated temperatures resulted in reduced efficiencies at low consumption rates but temperatures had little effect at high ration levels. A field study provided estimates of the food consumption relationships established in the laboratory, suggested any substantial increase of stream temperature without a concomitant increase of food abundance would result in decreased trout production.     

Effect of duration of exercise on excess postexercise O2 consumption

This study was undertaken to determine the effect of exercise duration on the time course and magnitude of excess postexercise O2 consumption (EPOC). Six healthy male subjects exercised on separate days for 80, 40, and 20 min at 70% of maximal O2 consumption on a cycle ergometer. A control experiment without exercise was performed. O2 uptake, respiratory exchange ratio (R), and rectal temperature were monitored while the subjects rested in bed 24 h postexercise. An increase in O2 uptake lasting 12 h was observed for all exercise durations, but no increase was seen after 24 h. The magnitude of 12-h EPOC was proportional to exercise duration and equaled 14.4 +/- 1.2, 6.8 +/- 1.7, and 5.1 +/- 1.2% after 80, 40, and 20 min of exercise, respectively. On the average, 12-h EPOC equaled 15.2 +/- 2.0% of total exercise O2 consumption (EOC). There was no difference in EPOC:EOC for different exercise durations. A linear decrease with exercise duration was observed in R between 2 and 24 h postexercise. No change was observed in recovery rectal temperature. It is concluded that EPOC increases linearly with exercise duration at a work intensity of 70% of maximal O2 consumption.     

Role of nitric oxide in hypoxic hypometabolism in rats.

Because it has been recently suggested that nitric oxide (NO) may mediate the effects of hypoxia on body temperature and ventilation, the present study was designed to assess more completely the effects of a neuronal NO synthase inhibitor (7-nitroindazole, 25 mg/kg ip), at ambient temperature of 26 and 15 degrees C, on the ventilatory (V), metabolic (O(2) consumption), and thermal changes (colonic and tail temperatures) induced by ambient hypoxia (fractional inspired O(2) of 11%) or CO hypoxia (fractional inspired CO of 0.07%) in intact, unanesthetized adult rats. At both ambient temperatures, 7-nitroindazole decreased oxygen consumption, colonic temperature, and V in normoxia. The drug reduced ambient or CO hypoxia-induced hypometabolism and ventilatory response, but the hypothermia persisted. It is concluded that NO arising from neural NO synthase plays an important role in the control of metabolism and V in normoxia. As well, it mediates, in part, the hypometabolic and the ventilatory response to hypoxia. The results are consistent with the notion that central nervous system hypoxia resets the thermoregulatory set point by decreasing brain NO.     

Changes in transcutaneous tcPO2 during water immersion and its effects on the human body

Changes in transcutaneous PO2(tcPO2) during water immersions with O2 and N2 bubbling are presented. Three healthy male volunteers underwent water immersions for 30 min. Water temperature was controlled to 36.5 degrees C to minimize any thermal stress. Minute ventilation (Ve), oxygen consumption (VO2), heart rate (HR), respiratory rate (RR), and body temperature (Tb) were continuously monitored throughout exposure. In addition, tcPO2 electrode was mounted on the volar side of the right forearm in the middle part of immersion and tcPO2 and tcPCO2 were then monitored in the water. Blood flow of the right forearm was also measured following tcPO2/tcPCO2 measurements The tcPO2 values during water immersions with O2 bubbling were higher than those with N2 bubbling for given blood flow. Although end-tidal PO2 remained unchanged for any occasion, Ve, VO2, HR, RR during water immersions with O2 bubbling were significantly decreased compared to those with N2 bubbling. Results suggest that cutaneous respiration facilitated by hydration may contribute higher tcPO2 values during water immersions with O2 bubbling and may be somewhat related to systemic changes.