End-tidal carbon dioxide tension reflects arterial carbon dioxide tension in the heat-stressed human with and without simulated hemorrhage

End-tidal carbon dioxide tension (Pet(CO(2))) is reduced during an orthostatic challenge, during heat stress, and during a combination of these two conditions. The importance of these changes is dependent on Pet(CO(2)) being an accurate surrogate for arterial carbon dioxide tension (Pa(CO(2))), the latter being the physiologically relevant variable. This study tested the hypothesis that Pet(CO(2)) provides an accurate assessment of Pa(CO(2)) during the aforementioned conditions. Comparisons between these measures were made: 1) after two levels of heat stress (N = 11); 2) during combined heat stress and simulated hemorrhage [via lower-body negative pressure (LBNP), N = 8]; and 3) during an end-tidal clamping protocol to attenuate heat stress-induced reductions in Pet(CO(2)) (N = 7). Pet(CO(2)) and Pa(CO(2)) decreased during heat stress (P < 0.001); however, there was no group difference between Pa(CO(2)) and Pet(CO(2)) (P = 0.36) nor was there a significant interaction between thermal condition and measurement technique (P = 0.06). To verify that this nonsignificant trend for the interaction was not due to a type II error, Pet(CO(2)) and Pa(CO(2)) at three distinct thermal conditions were also compared using paired t-tests, revealing no difference between Pa(CO(2)) and Pet(CO(2)) while normothermic (P = 0.14) and following a 1.0 ± 0.2°C (P = 0.21) and 1.4 ± 0.2°C (P = 0.28) increase in internal temperature. During LBNP while heat stressed, measures of Pet(CO(2)) and Pa(CO(2)) were similar (P = 0.61). Likewise, during the end-tidal carbon dioxide clamping protocol, the increases in Pet(CO(2)) (7.5 ± 2.8 mmHg) and Pa(CO(2)) (6.6 ± 3.4 mmHg) were similar (P = 0.31). These data indicate that mean Pet(CO(2)) reflects mean Pa(CO(2)) during the evaluated conditions.     

百菌清对土壤氧化亚氮和二氧化碳排放的影响

在25 ℃、60%WHC（最大持水量）的好氧条件下进行14 d的培养试验,研究杀菌剂百菌清在添加水平为0 mg·kg^-1（CK）、5.5 mg·kg^-1（田间施用量,FR）及110 mg·kg^-1(20FR)和220 mg·kg^-1（40FR）时对酸性、中性和碱性土壤中N₂O和CO₂排放的影响.结果表明：百菌清对N₂O和CO₂排放的影响取决于土壤类型和施用浓度.与对照相比,百菌清在20FR和40FR时显著抑制了酸性土壤N₂O的产生与排放;3种施用量均显著促进了中性土壤N₂O的排放,其中FR水平的促进效果最显著;高浓度（20FR和40FR）的百菌清在培养初期抑制了碱性土壤N₂O的排放,而在培养后期显著促进了N₂O的排放.田间用量的百菌清对土壤CO₂排放量没有明显影响;高浓度（20FR和40FR）时显著促进了酸性土壤CO₂的排放,显著抑制了中性和碱性土壤CO₂的排放.     

Biofeedback of alveolar carbon dioxide tension and levels of arousal

This is a preliminary study designed to investigate the potential usefulness of alveolar (lung) CO₂ feedback training in promoting sleep onset in primary insomniacs. The present study was undertaken to determine if normal subjects could, without obvious manipulation of breathing, bring alveolar (lung) CO₂ tension under voluntary control using biofeedback techniques and, if so, whether this control would be accompanied by shifts in level of wakefulness. Subjects participated in five baseline and five training sessions in which EEG, alveolar CO₂ tension, and thoracic/abdominal respiratory movement were monitored. The feedback consisted of a pitch-modulated tone plus visual scores. We found that CO₂ tension in awake portions of up trials was significantly higher than for awake portions of down trials (p<.01), indicating that learning had occurred. In the initial trials, when subjects raised CO₂ tension they became drowsy and often fell asleep, and when they lowered CO₂ tension they aroused themselves. However, when subjects were awakened immediately upon falling asleep, there developed a decoupling of EEG and CO₂ changes. The presence of such a decoupling phenomenon makes it unclear whether CO₂ feedback will be useful in promoting sleep onset in primary insomniacs.This study was supported by National Institute of Mental Health Research Fellowship MH05151, Research Grant MH29369, Research Scientist Development Award MH38897, and by a Biomedical Research Support Grant to Langley Porter Institute, 507RR05755.     

Biofeedback of alveolar carbon dioxide tension and levels of arousal

This is a preliminary study designed to investigate the potential usefulness of alveolar (lung) CO2 feedback training in promoting sleep onset in primary insomniacs. The present study was undertaken to determine if normal subjects could, without obvious manipulation of breathing, bring alveolar (lung) CO2 tension under voluntary control using biofeedback techniques and, if so, whether this control would be accompanied by shifts in level of wakefulness. Subjects participated in five baseline and five training sessions in which EEG, alveolar CO2 tension, and thoracic/abdominal respiratory movement were monitored. The feedback consisted of a pitch-modulated tone plus visual scores. We found that CO2 tension in awake portions of "up" trials was significantly higher than for awake portions of "down" trials (p less than .01), indicating that learning had occurred. In the initial trials, when subjects raised CO2 tension they became drowsy and often fell asleep, and when they lowered CO2 tension they aroused themselves. However, when subjects were awakened immediately upon falling asleep, there developed a decoupling of EEG and CO2 changes. The presence of such a decoupling phenomenon makes it unclear whether CO2 feedback will be useful in promoting sleep onset in primary insomniacs.     

Effects of an experimental drought on soil emissions of carbon dioxide, methane, nitrous oxide, and nitric oxide in a moist tropical forest

Changes in precipitation in the Amazon Basin resulting from regional deforestation, global warming, and El Niño events may affect emissions of carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and nitric oxide (NO) from soils. Changes in soil emissions of radiatively important gases could have feedback implications for regional and global climates. Here we report results of a large‐scale (1 ha) throughfall exclusion experiment conducted in a mature evergreen forest near Santarém, Brazil. The exclusion manipulation lowered annual N₂O emissions by >40% and increased rates of consumption of atmospheric CH₄ by a factor of >4. No treatment effect has yet been detected for NO and CO₂ fluxes. The responses of these microbial processes after three rainy seasons of the exclusion treatment are characteristic of a direct effect of soil aeration on denitrification, methanogenesis, and methanotrophy. An anticipated second phase response, in which drought‐induced plant mortality is followed by increased mineralization of C and N substrates from dead fine roots and by increased foraging of termites on dead coarse roots, has not yet been detected. Analyses of depth profiles of N₂O and CO₂ concentrations with a diffusivity model revealed that the top 25 cm soil is the site of most of the wet season production of N₂O, whereas significant CO₂ production occurs down to 100 cm in both seasons, and small production of CO₂ occurs to at least 1100 cm depth. The diffusivity‐based estimates of CO₂ production as a function of depth were strongly correlated with fine root biomass, indicating that trends in belowground C allocation may be inferred from monitoring and modeling profiles of H₂O and CO₂.     

新疆天山高寒草原不同放牧管理下的CO_2,CH_4和N_2O通量特征

以中国科学院新疆巴音布鲁克草原生态站为依托,于2010年5月—2011年10月利用静态箱-气相色谱法对短期禁牧(2005年围封)、长期禁牧(1984年围封)和自由放牧(冬季放牧)3种草地的CO2、CH4、N2O气体通量进行了野外连续试验研究。结果表明:新疆天山高寒草原对CO2,CH4和N2O通量表现出明显的季节排放特点。在植物的生长季(5—10月),新疆天山高寒短期禁牧、长期禁牧和自由放牧草原的CO2通量平均值分别为:(89.8±49.3)、(52.8±28.7)、(57.0±30.7)mg·m-2·h-1,CH4通量平均值分别为:(-66.3±21.3)、(-104.5±32.8)、(-103.0±39.0)μg·m-2·h-1,N2O通量平均值分别为:(21.2±11.8)、(13.6±6.9)、(13.2±6.2)μg·m-2·h-1;短期禁牧草原与长期禁牧和自由放牧草原CH4平均通量具有显著性差异(P0.05),但CO2和N2O差异不显著(P0.05)。在植物的非生长季(11月—翌年4月),新疆天山高寒短期禁牧、长期禁牧以及自由放牧草原的3种温室气体的通量较低且差异均不显著。     

Effect of hypoxia on arterial and venous blood levels of oxygen, carbon dioxide, hydrogen ions and lactate during incremental forearm exercise

The purpose of the present study was to investigate whether, in humans, hypoxia results in an elevated lactate production from exercising skeletal muscle. Under conditions of both hypoxia [inspired oxygen fraction (F1O2): 11.10%] and normoxia (F1O2: 20.94%), incremental exercise of a forearm was performed. The exercise intensity was increased every minute by 1.6 kg.m.min-1 until exhaustion. During the incremental exercise the partial pressure of oxygen (PO2) and carbon dioxide (PCO2), oxygen saturation (SO2), pH and lactate concentration [HLa] of five subjects, were measured repeatedly in blood from the brachial artery and deep veins from muscles in the forearm of both the active and inactive sides. The hypoxia (arterial SO2 approximately 70%) resulted in (1) the difference in [HLa] in venous blood from active muscle (values during exercise-resting value) often being more than twice that for normoxia, (2) a significantly greater difference in venous-arterial (v-a) [HLa] for the exercising muscle compared to normoxia, and (3) a difference in v-a [HLa] for non-exercising muscle that was slightly negative during normoxia and more so with hypoxia. These studies suggest that lower O2 availability to the exercising muscle results in increased lactate production.     

Snow depth, soil freezing, and fluxes of carbon dioxide, nitrous oxide and methane in a northern hardwood forest

Soil–atmosphere fluxes of trace gases (especially nitrous oxide (N₂O)) can be significant during winter and at snowmelt. We investigated the effects of decreases in snow cover on soil freezing and trace gas fluxes at the Hubbard Brook Experimental Forest, a northern hardwood forest in New Hampshire, USA. We manipulated snow depth by shoveling to induce soil freezing, and measured fluxes of N₂O, methane (CH₄) and carbon dioxide (CO₂) in field chambers monthly (bi-weekly at snowmelt) in stands dominated by sugar maple or yellow birch. The snow manipulation and measurements were carried out in two winters (1997/1998 and 1998/1999) and measurements continued through 2000. Fluxes of CO₂ and CH₄ showed a strong seasonal pattern, with low rates in winter, but N₂O fluxes did not show strong seasonal variation. The snow manipulation induced soil freezing, increased N₂O flux and decreased CH₄ uptake in both treatment years, especially during winter. Annual N₂O fluxes in sugar maple treatment plots were 207 and 99 mg N m⁻² yr⁻¹ in 1998 and 1999 vs. 105 and 42 in reference plots. Tree species had no effect on N₂O or CO₂ fluxes, but CH₄ uptake was higher in plots dominated by yellow birch than in plots dominated by sugar maple. Our results suggest that winter fluxes of N₂O are important and that winter climate change that decreases snow cover will increase soil:atmosphere N₂O fluxes from northern hardwood forests.     

Effects of an experimental drought and recovery on soil emissions of carbon dioxide,methane, nitrous oxide,and nitric oxide in a moist tropical forest

Changes in precipitation in the Amazon Basin resulting from regional deforestation, global warming, and El Niño events may affect emissions of carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and nitric oxide (NO) from soils. Changes in soil emissions of radiatively important gases could have feedback implications for regional and global climate. Here, we report the final results of a 5‐year, large‐scale (1 ha) throughfall exclusion experiment, followed by 1 year of recovery with natural throughfall, conducted in a mature evergreen forest near Santarém, Brazil. The exclusion manipulation lowered annual N₂O emissions in four out of five treatment years (a natural drought year being the exception), and then recovered during the first year after the drought treatment stopped. Similarly, consumption of atmospheric CH₄ increased under drought treatment, except during a natural drought year, and it also recovered to pretreatment values during the first year that natural throughfall was permitted back on the plot. No treatment effect was detected for NO emissions during the first 3 treatment years, but NO emissions increased in the fourth year under the extremely dry conditions of the exclusion plot during a natural drought. Surprisingly, there was no treatment effect on soil CO₂ efflux in any year. The drought treatment provoked significant tree mortality and reduced the allocation of C to stems, but allocation of C to foliage and roots were less affected. Taken together, these results suggest that the dominant effect of throughfall exclusion on soil processes during this 6‐year period was on soil aeration conditions that transiently affected CH₄, N₂O, and NO production and consumption.     

Effect of hydrological conditions on nitrous oxide, methane, and carbon dioxide dynamics in a bottomland hardwood forest and its implication for soil carbon sequestration

This study was conducted at three locations in a bottomland hardwood forest with a distinct elevation and hydrological gradient: ridge (high, dry), transition, and swamp (low, wet). At each location, concentrations of soil greenhouse gases (N₂O, CH₄, and CO₂), their fluxes to the atmosphere, and soil redox potential (Eh) were measured bimonthly, while the water table was monitored every day. Results show that soil Eh was significantly (P < 0.001) correlated with water table: a negative correlation at the ridge and transition locations, but a positive correlation at the permanently flooded swamp location. Both soil gas profile analysis and surface gas flux measurements indicated that the ridge and transition locations could be a sink of atmospheric CH₄, especially in warm seasons, but generally functioned as a minor source of CH₄ in cool seasons. The swamp location was a major source of CH₄, and the emission rate was higher in the warm seasons (mean 28 and median 23 mg m^?2 h^?1) than in the cool seasons (both mean and median 13 mg m^?2 h^?1). Average CO₂ emission rate was 251, 380 and 52 mg m^?2 h^?1 for the ridge, transition and swamp location, respectively. At each location, higher CO₂ emission rates were also found in the warm seasons. The lowest CO₂ emission rate was found at the swamp location, where soil C content was the highest, due to less microbial biomass, less CO₂ production in such an anaerobic environment, and greater difficulty of CO₂ diffusion to the atmosphere. Cumulative global warming potential emission from these three greenhouse gases was in an order of swamp > transition > ridge location. The ratio CO₂/CH₄ production in soil is a critical factor for evaluating the overall benefit of soil C sequestration, which can be greatly offset by CH₄ production and emission.     

Cerebral blood flow responses to changes in oxygen and carbon dioxide in humans

This study characterized cerebral blood flow (CBF) responses in the middle cerebral artery to PCO2 ranging from 30 to 60 mmHg (1 mmHg = 133.322 Pa) during hypoxia (50 mmHg) and hyperoxia (200 mmHg). Eight subjects (25 +/- 3 years) underwent modified Read rebreathing tests in a background of constant hypoxia or hyperoxia. Mean cerebral blood velocity was measured using a transcranial Doppler ultrasound. Ventilation (VE), end-tidal PCO2 (PETCO2), and mean arterial blood pressure (MAP) data were also collected. CBF increased with rising PETCO2 at two rates, 1.63 +/- 0.21 and 2.75 +/- 0.27 cm x s(-1) x mmHg(-1) (p < 0.05) during hypoxic and 1.69 +/- 0.17 and 2.80 +/- 0.14 cm x s(-1) x mmHg(-1) (p < 0.05) during hyperoxic rebreathing. VE also increased at two rates (5.08 +/- 0.67 and 10.89 +/- 2.55 L min(-1) m mHg(-1) and 3.31 +/- 0.50 and 7.86 +/- 1.43 L x min(-1) x mmHg(-1)) during hypoxic and hyperoxic rebreathing. MAP and PETCO2 increased linearly during both hypoxic and hyperoxic rebreathing. The breakpoint separating the two-component rise in CBF (42.92 +/- 1.29 and 49.00 +/- 1.56 mmHg CO2 during hypoxic and hyperoxic rebreathing) was likely not due to PCO2 or perfusion pressure, since PETCO2 and MAP increased linearly, but it may be related to VE, since both CBF and VE exhibited similar responses, suggesting that the two responses may be regulated by a common neural linkage.