Changes In PCO2 Research Articles

Preliminary evaluation of the use of high-flow nasal cannula oxygen therapy during recovery from general anesthesia in dogs with obstructive upper airway breathing.

Brachycephalic airway syndrome can pose a risk of complicated recovery from anesthesia as a result of irritation to the excess pharyngeal andlaryngeal tissue present in affected dogs. High-flow nasal cannula (HFNC) oxygen therapy is a respiratory support modality that offers provision of continuous positive airway pressure via high gas flow rates. The HFNC system actively warms and humidifies inspired gases, which improves comfort and facilitates tolerance of the high flow rates in people and dogs. HFNC oxygen therapy was applied to brachycephalic dogs that developed increased work of breathing or hypoxemia in the recovery phase of anesthesia to determine if this device would be tolerable and effective for relief of upper respiratory difficulty. The HFNC nasal prong interface is well suited to the brachycephalic facial structure. The application of HFNC was found to reduce dyspnea scores in patients with signs of upper airway obstruction after general anesthesia. Aerophagia and changes in PCO2 were noted. Application of HFNC in the recovery period may result in improved airflow during times of somnolent obstructive breathing, not unlike the use of continuous positive airway pressure therapy in sleep-disordered breathing in people.

Revisiting the Middle Eocene Climatic Optimum “Carbon Cycle Conundrum” With New Estimates of Atmospheric pCO2 From Boron Isotopes

AbstractThe Middle Eocene Climatic Optimum (MECO) was a gradual warming event and carbon cycle perturbation that occurred between 40.5 and 40.1 Ma. A number of characteristics, including greater‐than‐expected deep‐sea carbonate dissolution, a lack of globally coherent negative δ13C excursion in marine carbonates, a duration longer than the characteristic timescale of carbon cycle recovery, and the absence of a clear trigger mechanism, challenge our current understanding of the Earth system and its regulatory feedbacks. This makes the MECO one of the most enigmatic events in the Cenozoic, dubbed a middle Eocene “carbon cycle conundrum.” Here we use boron isotopes in planktic foraminifera to better constrain pCO2 changes over the event. Over the MECO itself, we find that pCO2 rose by only 0.55–0.75 doublings, thus requiring a much more modest carbon injection than previously indicated by the alkenone δ13C‐pCO2 proxy. In addition, this rise in pCO2 was focused around the peak of the 400 kyr warming trend. Before this, considerable global carbonate δ18O change was asynchronous with any coherent ocean pH (and hence pCO2) excursion. This finding suggests that middle Eocene climate (and perhaps a nascent cryosphere) was highly sensitive to small changes in radiative forcing.

Effects of irradiance, temperature, nutrients, and pCO2 on the growth and biochemical composition of cultivated Ulva fenestrata

Ulva fenestrata is an economically and ecologically important green algal species with a large potential in seaweed aquaculture due to its high productivity, wide environmental tolerance, as well as interesting functional and nutritional properties. Here, we performed a series of manipulative cultivation experiments in order to investigate the effects of irradiance (50, 100, and 160 μmol photons m−2 s−1), temperature (13 and 18 °C), nitrate (< 5, 150, and 500 μM), phosphate (< 1 and 50 μM), and pCO2 (200, 400, and 2500 ppm) on the relative growth rate and biochemical composition (fatty acid, protein, phenolic, ash, and biochar content) in indoor tank cultivation of Swedish U. fenestrata. High irradiance and low temperature were optimal for the growth of this northern hemisphere U. fenestrata strain, but addition of nutrients or changes in pCO2 levels were not necessary to increase growth. Low irradiance resulted in the highest fatty acid, protein, and phenolic content, while low temperature had a negative effect on the fatty acid content but a positive effect on the protein content. Addition of nutrients (especially nitrate) increased the fatty acid, protein, and phenolic content. High nitrate levels decreased the total ash content of the seaweeds. The char content of the seaweeds did not change in response to any of the manipulated factors, and the only significant effect of changes in pCO2 was a negative relationship with phenolic content. We conclude that the optimal cultivation conditions for Swedish U. fenestrata are dependent on the desired biomass traits (biomass yield or biochemical composition).

The ventilatory effect of high velocity nasal insufflation compared to non-invasive positive-pressure ventilation in the treatment of hypercapneic respiratory failure: A subgroup analysis

PurposeOxygen delivery by high flow nasal cannula (HFNC) is effective in providing respiratory support. HFNC has utility in clearing the extra-thoracic dead space, making it potentially beneficial in the treatment of hypercapnic respiratory failure. This study compares high velocity nasal insufflation (HVNI), a form of HFNC, to non-invasive positive pressure ventilation (NIPPV) in their abilities to provide ventilatory support for patients with hypercapnic respiratory failure. MethodsThis is a pre-defined subgroup analysis from a larger randomized clinical trial of Emergency Department (ED) patients with respiratory failure requiring NIPPV support. Patients were randomized to HVNI or NIPPV. Subgroup selection was done for patients with discharge diagnoses of acute hypercapnic respiratory failure or acute exacerbation of chronic obstructive pulmonary disease. The primary outcomes were change in pCO2 and pH over time. Secondary outcomes were treatment failure and intubation rate. Results65 patients with hypercapnic respiratory failure were compared. 34 were randomized to HVNI and 31 to NIPPV. The therapeutic impact on PCO2 and pH over time was similar in each group. The intubation rate was 5.9% in the HVNI group and 16.1% in the NIPPV group (p = 0.244). The rate of treatment failure was 23.5% in the HVNI group and 25.8% in the NIPPV group (p = 1.0). ConclusionHVNI may provide ventilatory support similar to NIPPV in patients presenting with acute hypercapnic respiratory failure, but further study is needed to corroborate these findings.

Seasonal patterns of surface inorganic carbon system variables in the Gulf of Mexico inferred from a regional high-resolution ocean biogeochemical model

Abstract. Uncertainties in carbon chemistry variability still remain large in the Gulf of Mexico (GoM), as data gaps limit our ability to infer basin-wide patterns. Here we configure and validate a regional high-resolution ocean biogeochemical model for the GoM to describe seasonal patterns in surface pressure of CO2 (pCO2), aragonite saturation state (ΩAr), and sea–air CO2 flux. Model results indicate that seasonal changes in surface pCO2 are strongly controlled by temperature across most of the GoM basin, except in the vicinity of the Mississippi–Atchafalaya river system delta, where runoff largely controls dissolved inorganic carbon (DIC) and total alkalinity (TA) changes. Our model results also show that seasonal patterns of surface ΩAr are driven by seasonal changes in DIC and TA, and reinforced by the seasonal changes in temperature. Simulated sea–air CO2 fluxes are consistent with previous observation-based estimates that show CO2 uptake during winter–spring, and CO2 outgassing during summer–fall. Annually, our model indicates a basin-wide mean CO2 uptake of 0.35 molm-2yr-1, and a northern GoM shelf (&lt; 200 m) uptake of 0.93 molm-2yr-1. The observation and model-derived patterns of surface pCO2 and CO2 fluxes show good correspondence; thus this study contributes to improved constraints of the carbon budget in the region.

Changes in the high-latitude Southern Hemisphere through the Eocene–Oligocene transition: a model–data comparison

Abstract. The global and regional climate changed dramatically with the expansion of the Antarctic Ice Sheet at the Eocene–Oligocene transition (EOT). These large-scale changes are generally linked to declining atmospheric pCO2 levels and/or changes in Southern Ocean gateways such as the Drake Passage around this time. To better understand the Southern Hemisphere regional climatic changes and the impact of glaciation on the Earth's oceans and atmosphere at the EOT, we compiled a database of 10 ocean and 4 land-surface temperature reconstructions from a range of proxy records and compared this with a series of fully coupled, low-resolution climate model simulations from two models (HadCM3BL and FOAM). Regional patterns in the proxy records of temperature show that cooling across the EOT was less at high latitudes and greater at mid-latitudes. While certain climate model simulations show moderate–good performance at recreating the temperature patterns shown in the data before and after the EOT, in general the model simulations do not capture the absolute latitudinal temperature gradient shown by the data, being too cold, particularly at high latitudes. When taking into account the absolute temperature before and after the EOT, as well as the change in temperature across it, simulations with a closed Drake Passage before and after the EOT or with an opening of the Drake Passage across the EOT perform poorly, whereas simulations with a drop in atmospheric pCO2 in combination with ice growth generally perform better. This provides further support for previous research that changes in atmospheric pCO2 are more likely to have been the driver of the EOT climatic changes, as opposed to the opening of the Drake Passage.

Stability of bicarbonate in normal saline: a technical report

The benefit of intravenous sodium bicarbonate administration in patients with severe metabolic acidosis remains controversial, partly due to lack of double-blind trials. From a practical viewpoint, such blinding requires testing of the stability of sodium bicarbonate in polyolefin bags. We examined seven samples of 100 mL 8.4% sodium bicarbonate diluted in 150 mL normal saline within a 250 mL polyolefin bag at time 0, 24 and 48 hours after preparation. We measured pH, Pco2, and bicarbonate concentration. Over a period of 48 hours, both pH and Pco2 decreased significantly (hourly rate of change, -0.001 [P = 0.043) and -0.098 [P < 0.001] respectively). However, the concentration of bicarbonate did not decrease, with an hourly rate of change of only -0.009 (P = 0.42). When 100 mL of 8.4% sodium bicarbonate are diluted in 150 mL of normal saline within a 250 mL polyolefin bag, changes in pH and Pco2 over a 48-hour period are small and bicarbonate concentration remains stable.

Effect of acetazolamide on susceptibility to central sleep apnea in chronic spinal cord injury.

Spinal cord injury (SCI) is an established risk factor for central sleep apnea. Acetazolamide (ACZ), a carbonic anhydrase inhibitor, has been shown to decrease the frequency of central apnea by inducing mild metabolic acidosis. We hypothesized that ACZ would decrease the propensity to develop hypocapnic central apnea and decrease the apneic threshold. We randomized 16 participants with sleep-disordered breathing (8 SCI and 8 able-bodied controls) to receive ACZ (500 mg twice a day for 3 days) or placebo with a 1-wk washout before crossing over to the other drug arm. Study nights included polysomnography and determination of the hypocapnic apneic threshold and CO2 reserve using noninvasive ventilation. For participants with spontaneous central apnea, CO2 was administered until central apnea was abolished, and CO2 reserve was measured as the difference in end-tidal Pco2 () before and after. Steady-state plant gain, the response of end-tidal Pco2 to changes in ventilation, was calculated from and V̇e ratio during stable sleep. Controller gain, the response of ventilatory drive to changes in end-tidal Pco2, was defined as the ratio of change in V̇e between control and hypopnea to the ΔCO2 during stable non-rapid eye movement sleep. Treatment with ACZ for three days resulted in widening of the CO2 reserve (-4.0 ± 1.2 vs. -3.0 ± 0.7 mmHg for able-bodied, -3.4 ± 1.9 vs. -2.2 ± 2.2 mmHg for SCI, P < 0.0001), and a corresponding decrease in the hypocapnic apnea threshold (28.3 ± 5.2 vs. 37.1 ± 5.6 mmHg for able-bodied, 29.9 ± 5.4 vs. 34.8 ± 6.9 mmHg for SCI, P < 0.0001), respectively. ACZ significantly reduced plant gain when compared with placebo (4.1 ± 1.7 vs. 5.4 ± 1.8 mmHg/L min for able-bodied, 4.1 ± 2.0 vs. 5.1 ± 1.7 mmHg·L-1·min for SCI, P < 0.01). Acetazolamide decreased apnea-hypopnea index (28.8 ± 22.9 vs. 39.3 ± 24.1 events/h; P = 0.05), central apnea index (0.6 ± 1.5 vs. 6.3 ± 13.1 events/h; P = 0.05), and oxyhemoglobin desaturation index (7.5 ± 8.3 vs. 19.2 ± 15.2 events/h; P = 0.01) compared with placebo. Our results suggest that treatment with ACZ decreases susceptibility to hypocapnic central apnea due to decreased plant gain. Acetazolamide may attenuate central sleep apnea and improve nocturnal oxygen saturation, but its clinical utility requires further investigation in a larger sample of patients.NEW & NOTEWORTHY Tetraplegia is a risk factor for central sleep-disordered breathing (SDB) and is associated with narrow CO2 reserve (a marker of susceptibility to central apnea). Treatment with high-dose acetazolamide for 3 days decreased susceptibility to hypocapnic central apnea and reduced the frequency of central respiratory events during sleep. Acetazolamide may play a therapeutic role in alleviating central SDB in patients with cervical spinal cord injury, but larger clinical trials are needed.

Elevated pCO2 affects behavioural patterns and mechano-sensation in predatory phantom midge larvae Chaoborus obscuripes

Aquatic acidification is a major consequence of fossil fuel combustion. In marine ecosystems it was shown, that increasing pCO2 levels significantly affect behavioural and sensory capacities in a diversity of species. This can result in altered predator and prey interactions and thereby change community structures. Just recently also CO2 dependent acidification of freshwater habitats has been shown. Also here, increased levels of pCO2 change organisms’ behaviour and sensory capacities. For example, the freshwater crustacean Daphnia’s ability to detect predators and accurately develop morphological defences was significantly reduced, rendering Daphnia more susceptible to predation. It was speculated that this may have cascading effects on freshwater food webs. However, for a comprehensive understanding of how increased levels of CO2 affect trophic interactions, it is also important to study how CO2 affects predators. We tested this using the dipeteran phantom midge larva Chaoborus obscuripes, which is a world-wide abundant inhabitant of freshwater impoundments. We monitored activity parameters, predation parameters, and predation rate. Chaoborus larvae are affected by increased levels of pCO2 as we observed an increase in undirected movements and at the same time, reduced sensory abilities to detect prey items. This is likely to affect the larvae’s energy budgets. Chaoborus is a central component of many freshwater food-webs. Therefore, CO2 effects on predator and prey levels will likely have consequences for community structures.

Rapid Loss of CO2 From the South Pacific Ocean During the Last Glacial Termination

AbstractDuring the termination of the last ice age, atmospheric CO2 rose ~80 ppm, but the origin of this carbon has not been fully resolved. Here we present novel constraints on the patterns and processes of deglacial CO2 release using three marine sediment cores from the southwest Pacific. Carbon isotopes (δ13C) and boron to calcium ratios (B/Ca) of benthic foraminiferal calcite provide records of the δ13C of total dissolved inorganic carbon (DIC) and carbonate ion concentrations ([CO32−]) in seawater, respectively. Together these properties indicate enhanced storage of respired CO2 between 1.2‐ and 2.5‐km water depth during the Last Glacial Maximum (19–23 thousand years ago, ka). The first major rise in atmospheric CO2 during the last deglaciation, at the time of Heinrich Stadial 1, was accompanied by increases in δ13C and [CO32−] at all core depths. The initial increases could be attributed to southward shifted westerly winds driving increased upwelling in the Southern Ocean, sending a signal of enhanced ventilation northward into the Pacific. Our results confirm that southern Pacific interior water masses served as an important reservoir for CO2 during the last glacial period, likely extracted from the atmosphere via the biologic pump. Some abrupt changes in Pacific carbon storage coincide with changes in Southern Ocean pH (Rae et al., 2018, https://doi.org/10.1038/s41586‐018‐0614‐0), upwelling indicators (Anderson et al., 2009, https://doi.org/10.1126/science.1167441), and pCO2 (Monnin et al., 2001, https://doi.org/10.1126/science.291.5501.112), indicating that portions of the deep Pacific carbon pool can be ventilated rapidly to the atmosphere via the Southern Ocean.

Evolution of the Global Carbon Cycle and Climate Regulation on Earth

AbstractThe existence of stabilizing feedbacks within Earth's climate system is generally thought to be necessary for the persistence of liquid water and life. Over the course of Earth's history, Earth's atmospheric composition appears to have adjusted to the gradual increase in solar luminosity, resulting in persistently habitable surface temperatures. With limited exceptions, the Earth system has been observed to recover rapidly from pulsed climatic perturbations. Carbon dioxide (CO2) regulation via negative feedbacks within the coupled global carbon‐silica cycles are classically viewed as the main processes giving rise to climate stability on Earth. Here we review the long‐term global carbon cycle budget, and how the processes modulating Earth's climate system have evolved over time. Specifically, we focus on the relative roles that shifts in carbon sources and sinks have played in driving long‐term changes in atmospheric pCO2. We make the case that marine processes are an important component of the canonical silicate weathering feedback, and have played a much more important role in pCO2 regulation than traditionally imagined. Notably, geochemical evidence indicate that the weathering of marine sediments and off‐axis basalt alteration act as major carbon sinks. However, this sink was potentially dampened during Earth's early history when oceans had higher levels of dissolved silicon (Si), iron (Fe), and magnesium (Mg), and instead likely fostered more extensive carbon recycling within the ocean‐atmosphere system via reverse weathering—that in turn acted to elevate ocean‐atmosphere CO2 levels.

Physiological Changes in CO &lt;sub&gt;2&lt;/sub&gt; Modulate the Firing of Neurons in the VTA and Substantia Nigra

The substantia nigra (SN) and ventral tegmental area (VTA) are vital for control of movement, goal-directed behaviour and encoding reward respectively. Surprisingly we find that firing of neurons in these nuclei can be modulated by physiological changes in PCO2. CO2 is a waste product of cellular metabolism, and its levels in blood are a key regulator of breathing. In humans, PCO2 in blood is normally ~40 mmHg but can be increased in conditions such as COPD and sleep apnoea and decreased by hyperventilation. Blood PCO2 can be detected by hemichannels of Connexin 26 (Cx26), which are expressed by glial cells on the medullary surface and play a key role in the control of breathing. Hemichannel-mediated CO2 -sensing has not been described in other brain regions. However dopaminergic neurons (DNs) in the SN of young rodents (P7-10) express mRNA for Cx26 and Cx30 which are CO2-sensitive. By P17-21 the DNs express only CO2-insensitive connexins. Here we show that the DNs (at P7-10) possess functional Cx26 hemichannels that allow physiological variations of CO2 to modulate their excitability. As predicted from their connexin mRNA profile, these neurons lose their CO2 sensitivity at later ages. Unexpectedly, we also found a nearby population of GABAergic neurons in the VTA which possess CO2 sensitive hemichannels of Cx26. These neurons retain their CO2 sensitivity throughout postnatal development. Our findings reveal an unexpected role for CO2 in regulating the activity of these key brain regions and demonstrates a mechanism by which autonomic state can alter complex movement-related and goal-directed behaviours.

At‐sea intercomparison of three underway pCO2 systems

AbstractOcean surface partial pressure of carbon dioxide (pCO2) is a key factor controlling air–sea CO2 fluxes. Most surface pCO2 data are collected with relatively large and complex air–water equilibrators coupled to stand‐alone infrared analyzers installed on Ships of OPportunity (SOOP‐CO2). This approach has proven itself through years of successful deployments, but expansion and sustainability of the future measurement network faces challenges in terms of certification, autonomy, and maintenance, which motivates development of new systems. Here, we compare performance of three underway pCO2 measurement systems (General Oceanics, SubCtech, and Pro‐Oceanus), including a recently developed compact flow‐through, sensor‐based system. The systems were intercompared over a period of 34 days during two crossings of the subpolar North Atlantic Ocean. With a mean difference from the General Oceanics system of −5.7 ± 4.0 μatm (Pro‐Oceanus) and −4.7 ± 2.9 μatm (SubCtech) during the 1st crossing, our results indicate potential for good agreement between the systems. The study highlighted the challenge of assuring accuracy over long periods of time, particularly seen in a worse agreement during the 2nd crossing, and revealed a number of sources of systematic errors. These can influence accuracy of the measurements, agreement between systems and include slow response of membrane‐based systems to pCO2 changes, “within‐ship” respiration due to biofouling, and bias in measurement of the temperature of equilibration. These error sources can be controlled or corrected for, however, if unidentified, their magnitude can be significant relative to accuracy criteria assigned to the highest‐quality data in global databases. The advantages of the compact flow‐through system are presented along with a discussion of future solutions for improving data quality.

Changes in Metabolism and Function of Platelets Stored at Different Temperature

Samples were collected from platelets stored at 4 ℃ in 2, 4, 6, 11, 15 and 21 days, and from ones stored at 22 ℃ with agitation during the same days, the metabolism indicators and thromboelastogram (TEM) were analysed. In metabolism, there were no significant changes of pH, GLU，PCO2, PCO2 and MPV levels of platelets stored at 4 ℃ for <6 days (P＞0.05), However, the Plt count decreased, the PDW and LDH level incrseased (P＜0.05). At the same time, only MPV had no changes of platelets stored at 22 ℃ during above-mentioned same days (P＞0.05), while the pH, PCO2, GLU, Plt all decreased, and PO2, LDH, PDW incrseased (P＜0.05). There were significant changes about the pH value, PO2, Plt, MPV, LDH, GLU levels between the two kinds of stored platelets during the same storing period (P＜0.05). The pH value and MPV of platelets stored at 4 ℃ were obviously lower than ones stored at 22 ℃, while GLU, PO2, LDH and Plt levels showed reverse changes (P＜0.05). Meanwhile, the PCO2 of platelets stored at 4 ℃ not could be detected and the Plt count reduced rapidly from d15. In function, the MA level of platelets stored at 4 ℃ was slower than that of platelets stored at 22 ℃, that is, the MA level of platelets stored at 4 ℃ were higher than that of platelets stored at 22 ℃ during the same storeing period (P＜0.05). Platelets stored at 4 ℃ have much slower metabolism than ones stored at 22 ℃, and the aggregation is stronger of platelets stored at 4 ℃ than that of ones at 22 ℃ during the same conservation period.

Impact of physical and biological processes on temporal variations of the ocean carbon sink in the mid-latitude North Atlantic (2002–2016)

The ocean is currently a significant net sink for anthropogenically remobilised CO2, taking up around 24% of global emissions. Numerical models predict a diversity of responses of the ocean carbon sink to increased atmospheric concentrations in a warmer world. Here, we tested the hypothesis that increased atmospheric forcing is causing a change in the ocean carbon sink using a high frequency observational dataset derived from underway pCO2 (carbon dioxide partial pressure) instruments on ships of opportunity (SOO) and a fixed-point mooring between 2002 and 2016. We calculated an average carbon flux of 0.013 Pg yr−1 into the ocean at the Porcupine Abyssal Plain (PAP) site, consistent with past estimates. In spite of the increase in atmospheric pCO2, monthly average seawater pCO2 did not show a statistically significant increasing trend, but a higher annual variability, likely due to the decreasing buffer capacity of the system. The increasing ΔpCO2 led to an increasing trend in the estimated CO2 flux into the ocean of 0.19 ± 0.03 mmol m−2 day−1 per year across the entire 15 year time series, making the study area a stronger carbon sink. Seawater pCO2 variability is mostly influenced by temperature, alkalinity and dissolved inorganic carbon (DIC) changes, with 77% of the annual seawater pCO2 changes explained by these terms. DIC is in turn influenced by gas exchange and biological production. In an average year, the DIC drawdown by biological production, as determined from nitrate uptake, was higher than the DIC increase due to atmospheric CO2 dissolution into the surface ocean. This effect was enhanced in years with high nutrient input or shallow mixed layers. Using the rate of change of DIC and nitrate, we observed Redfieldian carbon consumption during the spring bloom at a C:N ratio of 6.2 ± 1.6. A comparison between SOO and PAP sustained observatory data revealed a strong agreement for pCO2 and DIC. This work demonstrates that the study area has continued to absorb atmospheric CO2 in recent years with this sink enhancing over time. Furthermore, the change in pCO2 per unit nitrate became larger as surface buffer capacity changed.

Testing of novel spectral device sensor in swine model of airway obstruction.

Loss of a patent airway is a significant cause of prehospital death. Endotracheal intubation is the gold standard of care but has a high rate of failure and complications, making development of new devices vital. We previously showed that tracheal tissue has a unique spectral profile which could be utilized to confirm correct airway device placement. Therefore, the goals of this study were twofold: 1‐ to develop an airway obstruction model and 2‐ use that model to assess how airway compromise affects tissue reflectance. Female swine were anesthetized, intubated, and instrumented. Pigs were allowed to breathe spontaneously and underwent either slow‐ or rapid‐onset obstruction until a real‐time pulse oximeter reading of ≤50%. At baseline, 25%, 50%, 75%, and 100% obstruction, a fiber‐optic reflection probe was inserted into the trachea and esophagus to capture reflectance spectra. Both slow‐ and rapid‐onset obstruction significantly decreased arterial oxygen concentration (sO2) and increased partial pressure of CO2 (pCO2). The presence of the tracheal‐defining spectral profile was confirmed and remained consistent despite changes in sO2 and pCO2. This study validated a model of slow‐ and rapid‐airway obstruction that results in significant hypoxia and hypercapnia. This is valuable for future testing of airway device components that may improve airway management. Additionally, our data support the ability of spectral reflectance to differentiate between tracheal and esophageal tissues in the presence of a clinical condition that decreases oxygen saturation.

Low CO2 levels of the entire Pleistocene epoch

Quantifying ancient atmospheric pCO2 provides valuable insights into the interplay between greenhouse gases and global climate. Beyond the 800-ky history uncovered by ice cores, discrepancies in both the trend and magnitude of pCO2 changes remain among different proxy-derived results. The traditional paleosol pCO2 paleobarometer suffers from largely unconstrained soil-respired CO2 concentration (S(z)). Using finely disseminated carbonates precipitated in paleosols from the Chinese Loess Plateau, here we identified that their S(z) can be quantitatively constrained by soil magnetic susceptibility. Based on this approach, we reconstructed pCO2 during 2.6–0.9 Ma, which documents overall low pCO2 levels (<300 ppm) comparable with ice core records, indicating that the Earth system has operated under late Pleistocene pCO2 levels for an extended period. The pCO2 levels do not show statistically significant differences across the mid-Pleistocene Transition (ca. 1.2–0.8 Ma), suggesting that CO2 is probably not the driver of this important climate change event.

The carboxytherapy opportunities in surgery

The carbon dioxide of the body is the most important natural regulator of respiration, blood circulation, metabolism, electrolyte balance, nervous system excitability, smooth muscle tonus. Carboxytherapy is based on the use of carbon dioxide. It is an effective and safe method of many diseases’ treatment due to its rich pharmacodynamics. Inhalation of CO2 is used in resuscitation and anesthesiology practice. Another area of CO2 application in surgery is intra‑abdominal insufflation for all endoscopic laparoscopic procedures. Carbon dioxide is quickly absorbed by the mucous membrane of the gastrointestinal tract, which causes an increased interest in its use as an insufflation agent for all endoscopic procedures. In addition, CO2 has antispasmodic, analgesic, anti‑inflammatory and antiseptic effects, which is important for these diagnostic measures. CO2 insufflation during a colonoscopy causes less post‑procedure pain and distension of the intestine without significant changes in pCO2 compared to air one. An additional mechanism for pain reducing after the CO2 procedure may be the vasodilating effect of CO2 and its spasmolytic action on the wall in the enlarged part of the colon. For the past 50 years, CO2 has been used in cardiothoracic surgery to remove air from the surgical area, which reduces the air embolism probabily during heart surgery. Recently, heated and hydrated CO2 insufflation is used as a method to reduce the infections rate at the surgery site in an open wound. A carbon dioxide laser has physical, biological and surgical properties valuable for the surgeon. Carbon dioxide is also used as an alternative diagnostic contrast agent. Therefore, CO2 due to its antibacterial, antihypoxic, antispasmodic, analgesic, anti‑inflammatory, antioxidant properties and the side effects absence is an important component of therapeutic and diagnostic procedures in surgery, anesthesiology, gynecology, dermatology and other fields of medicine.

On the role of chemical weathering of continental arcs in long-term climate regulation: A case study of the Peninsular Ranges batholith, California (USA)

The long-term stability of atmospheric pCO2 is dominantly determined by the balance between the rate of CO2 input from magmatic/metamorphic degassing and the efficiency of CO2 uptake by silicate weathering via eventual precipitation as marine carbonate and by organic carbon burial. Silicate weathering is thought to represent a negative feedback to changes in atmospheric pCO2. The Late Cretaceous-Early Cenozoic was characterized by elevated atmospheric pCO2 and greenhouse climate, widely thought to be due to increased magmatic flux from mid-ocean ridges, flood basalts and continental arcs. Of interest here is the role of continental arcs in modulating long term atmospheric CO2 contents and climate. Continental arc magmatism is accompanied by rapid uplift and erosion due to magmatic/tectonic thickening of the crust, thus, the development of continental arcs might also enhance the global efficiency of silicate weathering, in turn increasing the efficiency of carbon sequestration. To assess the contribution of continental arcs to global carbon sinks, we conducted a case study in the Cretaceous Peninsular Ranges batholith (PRB) and associated forearc basin in southern California, USA, representing one segment of a Mesozoic circum-Pacific continental arc system. Arc magmatism occurred between 170-85 Ma, peaking at 100 Ma. Erosion occurred during magmatism and continued well into the early Eocene, with forearc sediments representing the products of this protracted unroofing of the arc. By calculating the depletion of Ca in forearc sediments relative to their arc protoliths, we estimate chemical weathering fluxes (in equivalent CO2) to be ∼106 mol km−2yr−1 near the end of magmatism, decreasing to ∼105 mol km−2yr−1 by the Early Eocene. Integrated over the entire magmatic and post-magmatic history of the batholith, the total amount of CO2 consumed through chemical weathering is comparable to that degassed. However, during magmatism, the regional degassing flux exceeds the regional weathering flux even though the efficiency of weathering is increased due to magmatic and tectonic uplift. After magmatism ends, continued erosion from remnant topography causes the arc to transition into a net regional sink, increasing the global efficiency of chemical weathering and amplifying cooling after magmatism ends. Understanding how atmospheric CO2 and climate vary over long timescales requires an understanding of how magmatic orogenies enhance degassing but also increase the strength of the global silicate weathering feedback.

Vegetation and environmental changes in tropical South America from the last glacial to the Holocene documented by multiple cave sediment proxies

δ18O values in speleothems have been utilized to document past changes in South American monsoon intensity. However, changes in regional vegetation and ecosystems have not been part of this discussion, and other cave proxies such as speleothem δ13C values, a useful proxy for vegetation reconstruction, have been neglected due to interpretive complexities. Here we report δ13C values and 87Sr/86Sr ratios in stalagmites, together with XRF-derived elemental chemistry, δ13Corg values and carbon content from a sedimentary profile from the same cave where the stalagmites were collected. In combination with a previously published δ18O record, this enables us to clarify climate and environmental shifts that occurred between the Last Glacial Maximum and the Holocene in central South America. We show that vegetation was sparse during the last glacial period in spite of a previously inferred strong monsoon, and that changes in atmospheric pCO2 combined with local hydrological and temperature feedbacks may have determined vegetation development during this time.