Research on the Spatiotemporal Evolution,and Optimized Paths of Carbon Pressure in Northwestern Sichuan under the Carbon Peaking and Carbon Neutrality Goals

Consolidating carbon sink capacity and reducing carbon pressure are important channels to achieve the carbon peaking and carbon neutrality goals actively yet prudently.In order to study the current situation of carbon pressure in the Northwestern Sichuan,we took the carbon pressure of the Aba Tibetan-Qiang autonomous prefecture(Aba prefecture)as an example and used the Intergovernmental Panel on Climate Change(IPCC)approach to measure the carbon emissions,carbon uptake,and the carbon balance index(CBI)of each county-level city in Aba prefecture from 2012 to 2020.The study found that:(a)There was a continuous trend of declining carbon emissions,increased carbon uptake,and decreased CBI in Aba prefecture during the sample period,but there is a large variability among county-level cities;(b)Aba prefecture differs in the spatiotemporal distribution of carbon emissions,carbon uptake,and CBI.Based on the research results,we propose several optimized paths for alleviating the current carbon pressure situation in the Northwestern Sichuan.

Carbon dioxide partial pressure and carbon fluxes of air-water interface in Taihu Lake, China

To obtain carbon dioxide （CO2） flux between water-air interface of Taihu lake, monthly water samplers at 14 sites and the local meteorological data of the lake were collected and analyzed in 1998. Carbon dioxide partial pressures （pCO2） at air-water interface in the lake were calculated using alkalinity, pH, ionic strength, active coefficient, and water temperature. The carbon fluxes at different sublakes and areas were estimated by concentration gradient between water and air in consideration of Schmidt numbers of 600 and daily mean windspeed at 10 m above water surface. The results indicated that the mean values of pCO2 in Wuli Lake,Meiliang Bay, hydrophyte area, west littoral zone, riverine mouths, and the open lake areas were 1 807.8±1 071.4（mean±standard deviation）μatm （latm=1.013 25×10^5pa）, 416.3±217.0μatm, 576.5±758.8μatm, 304.2±9.43.5μatm, 1 933.6±1 144.7 μatm, and 448.5±202.6μatm, respectively. Maximum and minimum pCO2 values were found in the hypertrophic （4 053.7μatm） and the eutrophic （3.2 μatm） areas. The riverine mouth areas have the maximum fluxes （82.0±62.8 mmol/m^2a）. But there was no significant difference between eutrophic and mesotrophic areas in pCO2 and the flux of CO2. The hydrophyte area, however, has the minimum （--0.58±12.9mmol/m^2a）. In respect to CO2 equilibrium, input of the rivers will obviously influence inorganic carbon distribution in the riverine estuary. For example, the annual mean CO2 flux in Zhihugang River estuary was 19 times of that in Meiliang Bay, although the former is only a part of the latter. The sites in the body of the lake show a clear seasonal cycle with pCO2 higher than atmospheric equilibrium in winter, and much lower than atmospheric in summer due to CO2 consumption by photosynthesis. The CO2 amount of the net annual evasion that enters the atmosphere is 28.42×10^4 t/a, of which those from the west littoral zone and the open lake account for 53.8% and 36.7%, respectively.

Drivers for decoupling carbon footprint pressure from economic growth in China’s provinces

A growing imbalance between energy carbon emissions and vegetation carbon sequestration is a major imped-iment to achieving Sustainable Development Goals. Decoupling the growing imbalance from economic growthneeds a stringent and coordinated package of sustainable policies. Previously, enhancing efficiency and vegeta-tion carbon sequestration were dominant drivers to decouple. However, the role and magnitude of restructuringsin the energy sector and economy in decoupling were underestimated. In this context, China’s 30 provinces wereselected as study areas. By employing a carbon footprint pressure (CFP) indicator to represent the imbalance, awidely decoupling method was adopted to describe the decoupling state and trend of CFP and economic growth.An extended IPAT equation and the Logarithmic Mean Divisia Index method were further used to reveal the roleand magnitude of drivers on decoupling. The findings revealed that the CFP climbed significantly in 26 provincesbetween 2006 and 2015. We discovered that 22 provinces were working toward absolute decoupling, with 15provinces achieving it during the 12-th Five-Year Plan. Our analysis revealed that improving energy efficiencywas the primary driver of absolute decoupling, while substituting natural gas and oil for coal, reducing industryshare, and enhancing carbon sequestration accelerated absolute decoupling. Considering the limited future roleof improving energy efficiency and vegetation carbon sequestration, there is an urgent need to optimize andupgrade the structures of the energy sector and economy to mitigate the future climate risk.

INFLUENCE OF HEAT TREATMENT ON OXIDATION PROPERTIES OF C/C COMPOSITES FABRICATED BY HIGH PRESSURE IMPREGNATION CARBONIZATION

Felt base carbon/carbon composites fabricated by super-high pressure impregnation carbonization process (SPIC) were heat treated at high temperature 2773K. The oxidation properties of felt base carbon/carbon composites were investigated at different temperatures (773-1173K), and the microstructures of carbon/carbon composites were studied by SEM and X-ray diffraction. The experimental results showed that the inter-laminar distance of (002) plane (d002) deceased while the microcrystalline stack height (Lc) increased. The oxidation rate of felt base carbon/carbon composites was invari-able at certain temperatures. The oxidation mechanism of carbon/carbon composites changed remarkably at the oxidation temperature 973K. At the initial oxidation stage of carbon/carbon composites, carbon matrix was oxidized much more rapidly than carbon felt.

Influence of Compaction Pressure on the Accelerated Carbonation of Calcium Hydroxide

Mineral carbonation using waste cement is a promising method to solve the problems caused by CO_2 emission and waste cement. Compaction pressure is an important parameter for mineral carbonation of calcium hydroxide, one of the most dominant composite of waste cement that can be carbonated. The carbonation degree, morphology of products and compressive strength of carbonated compacts are influenced by compaction pressure significantly. Results show that the carbonation degree of calcium hydroxide increases at first（0-8 MPa） and then decreases in the higher compaction pressure range（10-14 MPa）. At the meantime, results also indicate that lower compaction pressure accelerates the early carbonation but hinder carbonation in the later stages. For the morphologies of carbonation products, calcium carbonate tends to form typical crystal morphology of calcite（rhombohedral） under lower compaction pressure, while it will become ellipsoidlike when compaction pressure reaches 8 MPa. TGA and water content results show that there is an optimal water content for the carbonation. In addition, lower water content is adverse to the carbonation at later stage and the CO_2 is difficult to penetrate into the inside of compacts when water content is high, which will hinder the carbonation. XRD and TGA results show that the carbonation products are calcite and small amount of amorphous calcium carbonate.

Optimized Synthesis of Carbon Aerogels via Ambient Pressure Drying Process as Electrode for Supercapacitors

Carbon aerogels were synthesized via ambient pressure drying process using resorcinolformaldehyde as precursor and P123 to strengthen their skeletons. CO2 activation technology was implemented to improve surface areas and adjust pore size distribution. The synthesis process was optimized, and the morphology, structure, adsorption properties and electrochemical behavior of different samples were characterized. The CO2-activated samples achieved a high specific capacitance of 129.2 F/g in 6 M KOH electrolytes at the current density of 1 m A/cm^2 within the voltage range of 0-0.8 V. The optimized activation temperature and duration were determined to be 950 ℃ and 4 h, respectively.

High-efficiency Carbonation Modification Methods of Recycled Coarse Aggregates

To solve the problem of only surface carbonation and realize high-efficiency carbonation of recycled coarse aggregate,the method of carbonated recycled coarse aggregate with nano materials pre-soaking was first put forward.The carbonation effect of modified recycled coarse aggregate with three different carbonation methods was evaluated,and water absorption,apparent density and crush index of modified recycled coarse aggregate were measured.Combined with XRD,SEM,and MIP microscopic analysis,the high-efficiency carbonation strengthening mechanism of modified recycled coarse aggregate was revealed.The experimental results show that,compared with the non-carbonated recycled coarse aggregate,the physical and microscopic properties of carbonated recycled coarse aggregate are improved.The method of carbonation with nano-SiO_(2) pre-soaking can realize the high-efficiency carbonation of recycled coarse aggregate,for modified recycled coarse aggregate with the method,water absorption is reduced by 23.03%,porosity is reduced by 44.06%,and the average pore diameter is 21.82 nm.The high-efficiency carbonation strengthening mechanism show that the pre-socked nano-SiO_(2) is bound to the hydration product Ca(OH)_(2) of the old mortar with nano-scale C-S-H,which can improve the CO_(2) absorption rate,accelerate the carbonation reaction,generate more stable CaCO_(3) and nano-scale silica gel,and bond to the dense three-dimensional network structure to realize the bidirectional enhancement of nano-materials and pressurized carbonation.It is concluded that the method of carbonation with nano-SiO_(2) pre-soaking is a novel high-efficiency carbonation modification of recycled coarse aggregate.

A Method of Using a Carbon Fiber Spiral-Contact Electrode to Achieve Atmospheric Pressure Glow Discharge in Air

During discharge, appropriately changing the development paths of electron avalanches and increasing the number of initial electrons can effectively inhibit the formation of filamentary discharge. Based on the aforementioned phenomenon, we propose a method of using microdischarge electrodes to produce a macroscopic discharge phenomenon. In the form of an asymmetric structure composed of a carbon fiber electrode, an electrode structure of carbon fiber spiral-contact type is designed to achieve an atmospheric pressure glow discharge in air, which is characterized by low discharge voltage, low energy consumption, good diffusion and less ozone generation.

pCO_2 and carbon fluxes across sea-air interface in the Changjiang Estuary and Hangzhou Bay

Partial pressure of CO2(pCO2) was investigated in the Changjiang(Yangtze River) Estuary,Hangzhou Bay and their adjacent areas during a cruise in August 2004,China.The data show that pCO2 in surface waters of the studied area was higher than that in the atmosphere with only exception of a patch east of Zhoushan Archipelago.The pCO2 varied from 168 to 2 264 μatm,which fell in the low range compared with those of other estuaries in the world.The calculated sea-air CO2 fluxes decreased offshore and varied from -10.0 to 88.1 mmol m-2 d-1 in average of 24.4 ± 16.5 mmol m-2 d-1.Although the area studied was estimated only 2 × 104 km2,it emitted(5.9 ± 4.0) × 103 tons of carbon to the atmosphere every day.The estuaries and their plumes must be further studied for better understanding the role of coastal seas playing in the global oceanic carbon cycle.

Changes of end-tidal carbon dioxide during cardiopulmonary resuscitation from ventricular f ibrillation versus asphyxial cardiac arrest

BACKGROUND: Partial pressure of end-tidal carbon dioxide(PETCO2) has been used to monitor the effectiveness of precordial compression(PC) and regarded as a prognostic value of outcomes in cardiopulmonary resuscitation(CPR). This study was to investigate changes of PETCO2 during CPR in rats with ventricular fi brillation(VF) versus asphyxial cardiac arrest.METHODS: Sixty-two male Sprague-Dawley(SD) rats were randomly divided into an asphyxial group(n=32) and a VF group(n=30). PETCO2 was measured during CPR from a 6-minute period of VF or asphyxial cardiac arrest.RESULTS: The initial values of PETCO2 immediately after PC in the VF group were signifi cantly lower than those in the asphyxial group(12.8±4.87 mmHg vs. 49.2±8.13 mmHg, P=0.000). In the VF group, the values of PETCO2 after 6 minutes of PC were significantly higher in rats with return of spontaneous circulation(ROSC), compared with those in rats without ROSC(16.5±3.07 mmHg vs. 13.2±2.62 mmHg, P=0.004). In the asphyxial group, the values of PETCO2 after 2 minutes of PC in rats with ROSC were signifi cantly higher than those in rats without ROSC(20.8±3.24 mmHg vs. 13.9±1.50 mmHg, P=0.000). Receiver operator characteristic(ROC) curves of PETCO2 showed signifi cant sensitivity and specifi city for predicting ROSC in VF versus asphyxial cardiac arrest.CONCLUSIONS: The initial values of PETCO2 immediately after CPR may be helpful in differentiating the causes of cardiac arrest. Changes of PETCO2 during CPR can predict outcomes of CPR.

Temporal and spatial variability of the carbon cycle in the east of China's seas:a three-dimensional physical-biogeochemical modeling study

In the east of China＇s seas, there is a wide range of the continental shelf. The nutrient cycle and the carbon cycle in the east of China＇s seas exhibit a strong variability on seasonal to decadal time scales. On the basis of a regional ocean modeling system（ROMS）, a three dimensional physical-biogeochemical model including the carbon cycle with the resolution（1/12）°×（1/12）° is established to investigate the physical variations, ecosystem responses and carbon cycle consequences in the east of China＇s seas. The ROMS-Nutrient Phytoplankton Zooplankton Detritus（NPZD） model is driven by daily air-sea fluxes（wind stress, long wave radiation, short wave radiation, sensible heat and latent heat, freshwater fluxes） that derived from the National Centers for Environmental Prediction（NCEP） reanalysis2 from 1982 to 2005. The coupled model is capable of reproducing the observed seasonal variation characteristics over the same period in the East China Sea. The integrated air-sea CO_2 flux over the entire east of China＇s seas reveals a strong seasonal cycle, functioning as a source of CO_2 to the atmosphere from June to October, while serving as a sink of CO_2 to the atmosphere in the other months. The 24 a mean value of airsea CO_2 flux over the entire east of China＇s seas is about 1.06 mol/（m^2·a）, which is equivalent to a regional total of3.22 Mt/a, indicating that in the east of China＇s seas there is a sink of CO_2 to the atmosphere. The partial pressure of carbon dioxide in sea water in the east of China＇s seas has an increasing rate of 1.15 μatm/a（1μtm/a=0.101 325Pa）, but p H in sea water has an opposite tendency, which decreases with a rate of 0.001 3 a^（–1） from 1982 to 2005.Biological activity is a dominant factor that controls the pCO_2 air in the east of China＇s seas, and followed by a temperature. The inverse relationship between the interannual variability of air-sea CO_2 flux averaged from the domain area and Ni？o3 SST Index indicates that the carbon cycle in the east of China＇s seas has a high correlation with El Ni？o-Southern Oscillation（ENSO）.

Carbon dioxide:Global warning for nephrologists

The large prevalence of respiratory acid-base disordersoverlapping metabolic acidosis in hemodialysis popu-lation should prompt nephrologists to deal with the partial pressure of carbon dioxide （pCO2） complying with the reduced bicarbonate concentration. What the most suitable formula to compute pCO2 is reviewed. Then, the neglected issue of CO2 content in the dialysis fluid is under the spotlight. In fact, a considerable amount of CO2 comes to patients’ bloodstream every hemodialysis treatment and “acidosis by dialysate” may occur if lungs do not properly clear away this burden of CO2. Moreover, vascular access recirculation may be easy diagnosed by detecting CO2 in the arterial line of extracorporeal circuit if CO2-enriched blood from the flter reenters arterial needle.

Calcareous Sodic Soil Reclamation as Affected by Corn Stalk Application and Incubation: A Laboratory Study

A laboratory lysimeter experiment was conducted to investigate the effects of forage corn （Zea rncbys L.） stalk application on the CO2 concentration in soil air and calcareous sodic soil reclamation. The experimental treatments tested were soil exchangeable sodium percentage （ESP） levels of 1, 11, and 19, added corn stalk contents of 0 to 36 g kg^-1, and incubation durations of 30 and 60 days. The experimental results indicated that corn stalk application and incubation significantly increased CO2 partial pressure in soil profile and lowered pH value in soil solution, subsequently increased native CaCO3 mineral dissolution and electrolyte concentration of soil solution, and finally significantly contributed to reduction on soil sodicity level. The reclamation efficiency of calcareous sodic soils increased with the added corn stalk. When corn stalks were added at the rates of 22 and 34 g kg^-1 into the soil with initial ESP of 19, its ESP value was decreased by 56% and 78%, respectively, after incubation of 60 days and the leaching of 6.5 pore volumes （about 48 L of percolation water） with distilled water. Therefore, crop stalk application and incubation could be used as a choice to reclaim moderate calcareous sodic soils or as a supplement of phytoremediation to improve reclamation efficiency.

Urban carbon footprint and carbon cycle pressure： The case study of Nanjing

Urban carbon footprint reflects the impact and pressure of human activities on ur- ban environment. Based on city level, this paper estimated carbon emissions and carbon footprint of Nanjing city, analyzed urban carbon footprint intensity and carbon cycle pressure and discussed the influencing factors of carbon footprint through LMDI decomposition model. The main conclusions are as follows： （1） The total carbon emissions of Nanjing increased rapidly since 2000, in which the carbon emission from the use of fossil energy was the largest Meanwhile, carbon sinks of Nanjing presented a declining trend since 2000, which caused the decrease of carbon compensation rate and the increase of urban carbon cycle pressure. （2） The total carbon footprint of Nanjing increased rapidly since 2000, and the carbon deficit was more than ten times of total land areas of Nanjing in 2009, which means Nanjing confronted high carbon cycle pressure. （3） Generally, carbon footprint intensity of Nanjing was on de- crease and the carbon footprint productivity was on increase. This indicated that energy utilization rate and carbon efficiency of Nanjing was improved since 2000, and the policy for energy conservation and emission reduction taken by Nanjing＇s government received better effects. （4） Economic development, population and industrial structure are promoting factors for the increase of carbon footprint of Nanjing, while the industrial carbon footprint intensity was inhibitory factor. （5） Several countermeasures should be taken to decrease urban carbon footprint and alleviate carbon cycle pressure, such as： improvement of the energy efficiency, industrial structure reconstruction, afforestation and environmental protection and land use control. Generally, transition to low-carbon economy is essential for Chinese cities to realize sustainable development in the future.

Analysis of metabolic alterations in Arabidopsis following changes in the carbon dioxide and oxygen partial pressures

As sessile organisms,plants are subject to a multitude of environmental variations including several which directly affect their interaction with the atmosphere.Given the indiscriminant nature of Rubisco,the relative rates of photosynthesis and photorespiration are known to be responsive to changes in gas composition.However,comprehensive profiling methods have not yet been applied in order to characterize the wider consequences of these changes on primary metabolism in general.Moreover,although transcriptional profiling has revealed that a subset of photorespiratory enzymes are co-expressed,whether transcriptional responses play a role in short-term responses to atmospheric compositional changes remains unknown.To address these questions,plants Arabidopsis thaliana（Arabidopsis） ecotype Columbia（Col-O） grown under normal air conditions were transferred to different CO_2 and O_2 concentrations and characterized at the physiological,molecular,and metabolic levels following this transition.The results reveal alterations in the components,which are directly involved in,or supporting,photorespiration,including transcripts and metabolite levels.The results further highlight that the majority of the regulation of these pathways is not mediated at the level of transcription and that the photorespiratory pathway is essential also in conditions in which flux through the pathway is minimized,yet suggest that flux through this pathway is not mediated at the level of transcription.

Effect of early goal directed therapy on tissue perfusion in patients with septic shock

BACKGROUND:This study aimed to observe the effect of early goal directed therapy(EGDT)on tissue perfusion,microcirculation and tissue oxygenation in patients with septic shock.METHODS:Patients with early septic shock(<24 hours) who had been admitted to the ICU of Zhongda Hospital Affiliated to Southeast University from September 2009 through May 2011 were enrolled(research time:12 months),and they didn't meet the criteria of EGDT.Patients who had one of the following were excluded:stroke,brain injury,other types of shock,severe heart failure,acute myocardial infarction,age below 18 years,pregnancy,end-stage disease,cardiac arrest,extensive burns,oral bleeding,difficulty in opening the mouth,and the onset of septic shock beyond 24 hours.Patients treated with the standard protocol of EGDT were included.Transcutaneous pressure of oxygen and carbon dioxide(PtcO_2,PtcCO_2) were monitored and hemodynamic measurements were obtained.Side-stream dark field(SDF) imaging device was applied to obtain sublingual microcirculation.Hemodynamics,tissue oxygen,and sublingual microcirculation were compared before and after EGDT.If the variable meets the normal distribution,Student's t test was applied.Otherwise,Wilcoxon's rank-sum test was used.Correlation between variables was analyzed with Pearson's product-moment correlation coefficient method.RESULTS:Twenty patients were involved,but one patient wasn't analyzed because he didn't meet the EGDT criteria.PtcO_2 and PtcCO_2 were monitored in 19 patients,of whom sublingual microcirculation was obtained.After EGDT,PtcO_2 increased from 62.7+24.0 mmHg to 78.0±30.9mmHg(P<0.05) and tissue oxygenation index(PtcO_2/FiO_2) was 110.7+60.4 mmHg before EGDT and 141.6±78.2 mmHg after EGDT(P<0.05).The difference between PtcCO_2 and PCO_2 decreased significantly after EGDT(P<0.05).The density of perfused small vessels(PPV) and microcirculatory flow index of small vessels(MFI) tended to increase,but there were no significant differences between them(P>0.05).PtcO_2,PtcO_2/FiO_2,and PtcCO_2 were not linearly related to central venous saturation,lactate,oxygen delivery,and oxygen consumption(P>0.05).CONCLUSION:Peripheral perfusion was improved after EGDT in patients with septic shock,and it was not exactly reflected by the index of systemic perfusion.

Forced vibration analysis of nano-composite rotating pressurized microbeam reinforced by CNTs based on MCST with temperature-variable material properties

In this study, free and forced vibration analysis of nano-composite rotating pressurized microbeam reinforced by carbon nanotubes （CNTs） under magnetic field based on modify couple stress theory （MCST） with temperature-variable material propertiesis presented. Also, the boundary conditions at two ends of nano-composite rotating pressurized microbeam reinforced by CNTs are considered as simply supported. The governing equations are obtained based on the Hamilton＇s principle and then computed these equations by using Navier＇s solution. The magnetic field is inserted in the thickness direction of the nano-composite microbeam. The effects of various parameters such as angular velocity, temperature changes, and pressure between of the inside and outside, the magnetic field, material length scale parameter, and volume fraction of nanocomposite microbeam on the natural frequency and response systemare studied. The results show that with increasing volume fraction of nano-composite microbeam, thickness, material length scale parameter, and magnetic fields, the natural frequency increases. The results of this research can be used for optimization of micro-structures and manufacturing sensors, displacement fluid, and drug delivery.

Major ion chemistry and control of weathering of Bhimtal Lake，Humaun Himalaya，India

The water chemistry of Bhimtal Lake revealed the dominance of Ca￣(2+) and HCO_3￣- ions.The lake water chemistry is controlled by the dominance of Ca-Mg silicate weathering(mainly pumpellyite and epidote-bearing rocks) supported by anthropogenic activity involving extensive road cutting and house holding activities, increased industrialization in the catchment area of the lake. On the basis of phosphate values. a transitional mesotrophic-eutrophic conditions exist in this lake.The observed chemical data of the Bhimtal Lake was used to predict the mineral assemblages in the carbonate and alumino-silicate system. It demonstrates that the calcite and dolomite are the possible minerals which are in equilibrium with the lake water system and that the lake water is in the range of stability of kaolinite.

Numerical simulations of high pressure carbon dioxide fluid fluidized beds

Hydrodynamics of carbon dioxide fluid-particle mixtures are predicted using a low density ratio-based kinetic theory of granular flow in high pressure carbon dioxide fluid fluidized beds.A coexistence of particle waves and particle aggregates exists along bed height.The threshold to identify the occurrence of particle aggregates is suggested based on standard deviation of solid volume fractions in aggregative fluidization.The existence time fractions and frequencies of particle aggregates are predicted along axial direction.The effect of carbon dioxide fluid temperature and pressure on volume fraction and velocity distributions are analyzed at different inlet carbon dioxide velocities and particle densities in high pressure carbon dioxide fluidized beds.Simulated results indicate that the carbon dioxide-particles fluidization transits from particulate to aggregative states with the increase of inlet carbon dioxide ve-locities.The computed fluid volume fractions and heterogeneity indexes are close to the measurements in a high pressure carbon dioxide fluidized bed.

Relationship between metabolic syndrome and hypercapnia among obese patients with sleep apnea Relationship between metabolic syndrome and hypercapnia among obese patients with sleep apnea

BACKGROUND In the obese patient population,some patients have severe obstructive sleep apnea(OSA)with daytime hypoventilation.Such patients are generally identified on the basis of the presence or absence of daytime hypercapnia,and the condition is called obesity hypoventilation syndrome.However,mechanisms for such daytime hypoventilation remain unclear.AIM To investigate metabolic syndrome and daytime hypercapnia association based on hypercapnia prevalence in obese OSA patients in a nested case-control study.METHODS Consecutive obese patients(body mass index≥30 kg/m2)who underwent polysomnography due to suspected OSA were included.Among them,patients with severe OSA(apnea hypopnea index≥30/h)were divided into two groups according to the presence or absence of hypercapnia during wakefulness(arterial partial pressure of carbon dioxide≥or<45 Torr,respectively).The characteristics and clinical features of these two groups were compared.RESULTS Among 97 eligible patients,25 patients(25.8%)had daytime hypercapnia.There were no significant differences in age,gender,body mass index,apnea-hypopnea index,and Epworth Sleepiness Scale scores between the two groups.However,patients with hypercapnia had a significantly lower arterial partial pressure of oxygen level(75.8±8.2 torr vs 79.9±8.7 torr,P=0.042)and higher arterial partial pressure of carbon dioxide level(46.6±2.5 torr vs 41.0±2.9 torr,P<0.001).Additionally,patients with hypercapnia were more likely to have metabolic syndrome(72.0%vs 48.6%,P=0.043)and a higher metabolic score(the number of satisfied criteria of metabolic syndrome).In multivariate logistic regression analysis,the presence of metabolic syndrome was associated with the presence of hypercapnia(OR=2.85,95%CI:1.04-7.84,P=0.042).CONCLUSION Among obese patients with severe OSA,26%of patients had hypercapnia during wakefulness.The presence of metabolic syndrome was independently correlated with the presence of daytime hypercapnia.