Changes In CO2 Concentration Research Articles

The impact of calcination atmosphere on Cr(Ⅵ) conversion in correction raw materials for high iron red mud

ABSTRACT The aim of this study was to investigate a new approach for reducing the production of harmful Cr(VI) heavy metals in the collaborative disposal of Red mud by cement enterprises. The study examined the effects of different ratios on the conversion rate of Cr(VI) in clinker under various calcination temperatures and atmospheres, and analyzed the raw material composition, clinker composition, and Cr(VI) content using XRD and XPS. The results indicate that the conversion rate of Cr(VI) is positively correlated with the concentration of oxygen, with the highest conversion rate of 93.4% achieved at 15% oxygen concentration. XPS analysis revealed that the peak intensity of Cr(VI) in clinker calcined under 4% O2 atmosphere was significantly higher than that of the sample calcined under 4000 mg/kg CO atmosphere. The study also found that the concentration of CO can reduce the conversion rate of Cr(VI) at high calcination temperatures, while at low calcination temperatures, the change in CO concentration has little effect on the conversion rate of Cr(VI). The specific objectives include examining the effects of different ratios, calcination temperatures, and atmospheres on the conversion rate of Cr(VI) in clinker. Additionally, when the ratio is the same as the calcination atmosphere, increasing the calcination temperature leads to an increase in the conversion rate of Cr(VI). The obtained results suggest a new approach for reducing the production of Cr(VI) in the collaborative disposal of Red mud by cement enterprises, which could have practical applications in engineering environmental protection.

Rubisco activity and activation state dictate photorespiratory plasticity in Betula papyrifera acclimated to future climate conditions

Plant metabolism faces a challenge of investing enough enzymatic capacity to a pathway without overinvestment. As it takes energy and resources to build, operate, and maintain enzymes, there are benefits and drawbacks to accurately matching capacity to the pathway influx. The relationship between functional capacity and physiological load could be explained through symmorphosis, which would quantitatively match enzymatic capacity to pathway influx. Alternatively, plants could maintain excess enzymatic capacity to manage unpredictable pathway influx. In this study, we use photorespiration as a case study to investigate these two hypotheses in Betula papyrifera. This involves altering photorespiratory influx by manipulating the growth environment, via changes in CO2 concentration and temperature, to determine how photorespiratory capacity acclimates to environmental treatments. Surprisingly, the results from these measurements indicate that there is no plasticity in photorespiratory capacity in B. papyrifera, and that a fixed capacity is maintained under each growth condition. The fixed capacity is likely due to the existence of reserve capacity in the pathway that manages unpredictable photorespiratory influx in dynamic environments. Additionally, we found that B. papyrifera had a constant net carbon assimilation under each growth condition due to an adjustment of functional rubisco activity driven by changes in activation state. These results provide insight into the acclimation ability and limitations of B. papyrifera to future climate scenarios currently predicted in the next century.

Hemodynamics and vascular oxygenation measured at the forehead during changes in respiration: A SPA-fNIRS study

Cerebral blood flow is influenced by respiration, primarily through changes in the CO2 concentration of arterial blood. The objective of this study was to investigate the effect of changes in arterial CO2 concentration induced by respiratory changes on oxygenation and hemodynamics in the cerebral and extracerebral tissue layers of the forehead. We used systemic physiology augmented functional near-infrared spectroscopy (SPA-fNIRS) to assess changes in forehead hemodynamics and oxygenation as well as systemic physiology in 20 healthy subjects. All participants performed two respiratory tasks (breath-holding and hyperventilation). In our SPA-fNIRS study we found that changes in breathing affected hemodynamics and oxygenation in both the extracerebral and cerebral tissue layers of the forehead in characteristic ways, depending on the two respiratory tasks. The results show that extracerebrovascular reactivity (ECVR) exists in parallel with the well-known cerebrovascular reactivity (CVR). CVR and ECVR must be considered when performing fNIRS neuroimaging studies involving changes in respiration.

Short-Term Prediction Method for Gas Concentration in Poultry Houses Under Different Feeding Patterns

Ammonia (NH3) and carbon dioxide (CO2) are the main gases that affect indoor air quality and the health of the chicken flock. Currently, the environmental control strategy for poultry houses mainly relies on real-time temperature, resulting in lag and singleness. Indoor air quality can be improved by predicting the change in CO2 concentration and proposing an optimal control strategy. Combining the advantages of seasonal-trend decomposition using loess (STL), Granger causality (GC), long short-term memory (LSTM), and extreme gradient boosting (XGBoost), an ensemble method called the STL-GC-LSTM-XGBoost model is proposed. This model can set fast response prediction results at a lower cost and has strong generalization ability. The comparative analysis shows that the proposed STL-GC-LSTM-XGBoost model achieved high prediction accuracy, performance, and confidence in predicting CO2 levels under different environmental regulation modes and data volumes. However, its prediction accuracy for NH3 was slightly lower than that of the STL-GC-LSTM model. This may be due to the limited variability and regularity of the NH3 dataset, which likely increased model complexity and decreased predictive ability with the introduction of XGBoost. Nevertheless, in general, the proposed integrated model still provides a feasible approach for gas concentration prediction and health-related risk control in poultry houses.

Significant Links Between Photosynthetic Capacity, Atmospheric CO2 and the Diversification of C3 Plants During the Last 80 Million Years.

Changing CO2 concentrations will continue to affect plant growth with consequences for ecosystem functioning. The adaptive capacity of C3 photosynthesis to changing CO2 concentrations is, however, insufficiently investigated so far. Here, we focused on the phylogenetic dynamics of maximum carboxylation rate (Vcmax) and maximum electron transport rate (Jmax)-two key determinants of photosynthetic capacity in C3 plants-and their relation to deep-time dynamics in species diversification, speciation and atmospheric CO2 concentrations during the last 80 million years. We observed positive relationships between photosynthetic capacity and species diversification as well as speciation rates. We furthermore observed a shift in the relationships between photosynthetic capacity, evolutionary dynamics and prehistoric CO2 fluctuations about 30 million years ago. From this, we deduce strong links between photosynthetic capacity and evolutionary dynamics in C3 plants. We furthermore conclude that low CO2 environments in prehistory might have changed adaptive processes within the C3 photosynthetic pathway.

A regression-based approach to the CO2 airborne fraction

The global fraction of anthropogenically emitted carbon dioxide (CO2) that stays in the atmosphere, the CO2 airborne fraction, has been fluctuating around a constant value over the period 1959 to 2022. The consensus estimate of the airborne fraction is around 44%. In this study, we show that the conventional estimator of the airborne fraction, based on a ratio of changes in atmospheric CO2 concentrations and CO2 emissions, suffers from a number of statistical deficiencies. We propose an alternative regression-based estimator of the airborne fraction that does not suffer from these deficiencies. Our empirical analysis leads to an estimate of the airborne fraction over 1959–2022 of 47.0% (± 1.1%; 1σ), implying a higher, and better constrained, estimate than the current consensus. Using climate model output, we show that a regression-based approach provides sensible estimates of the airborne fraction, also in future scenarios where emissions are at or near zero.

Confirmation of the feasibility of using agrobyproduct biochar in thermal power plants through oxygen pyrolysis and conventional pyrolysis

This study investigates the feasibility of utilizing agrobyproduct biochar as a substitute for fossil fuels in thermal power plants by comparing oxygen-rich and oxygen-lean pyrolysis processes. The biomass types examined include soybean pods (BE), bamboo (BB), and wood pellets (WP). Results demonstrate that oxygen-lean pyrolysis at high temperatures enhances biochar's carbon content and energy density. Mass yields varied, with WP showing the highest yield at 500℃ under oxygen-lean conditions. Elemental analysis indicated increased carbon content and improved fuel properties with higher pyrolysis temperatures. Proximate composition analysis revealed decreased volatile matter and increased fixed carbon and ash content, leading to higher fuel ratios. Calorific values increased significantly across all biomasses, particularly under oxygen-lean conditions. Gas analysis showed significant changes in O2, CO2, and CO concentrations with temperature variations. Combustion indices and physical properties like aromaticity and Hardgrove grindability index improved with higher temperatures. Optimal pyrolysis conditions were identified as 325℃ for WP, 350℃ for BB, and 300℃ for BE, with BE also performing well at 500℃. The study concludes that optimized agrobyproduct biochar can effectively replace conventional fossil fuels, offering high energy yield and enhanced combustion properties.

Impact of Paleogeography on the Stratospheric Polar Vortex in the Geological Past

AbstractThe stratospheric polar vortex (SPV) significantly influences current weather and climate patterns. However, its state in the geological past remains largely unexplored. This study investigates SPV variations in the past 250 million years, using a fully coupled Earth System Model. It is found that midlatitude paleogeography primarily drove substantial SPV variations in the deep time, while changes in CO2 concentrations and solar insolation play a minor role. Both the Arctic and Antarctic SPV were strengthened when the supercontinent Pangea broke up. The increased asymmetry of midlatitude land‐sea contrast tended to weaken the upward propagation of wavenumber‐1 planetary waves, thereby strengthening the SPV. This SPV strengthening correlated with the decelerated stratospheric Brewer‐Dobson circulation and uplift of the polar tropopause. Our results highlight the crucial role of paleogeography in regulating SPV variations and stratosphere–troposphere coupling in deep‐time climate.

Complex imprint of air pollution in the basal area increments of three European tree species

The impact of atmospheric pollution on the growth of European forest tree species, particularly European beech, Silver fir and Norway spruce, is examined in five mesic forests in the Czech Republic. Analyzing of basal area increment (BAI) patterns using linear mixed effect models reveals a complex interplay between atmospheric nitrogen (N) and sulphur (S) deposition, climatic variables and changing CO2 concentrations. Beech BAI responds positively to N deposition (in tandem with air CO2 concentration), with soil phosphorus (P) availability emerging as a significant factor influencing overall growth rates. Fir BAI, on the other hand, was particularly negatively influenced by S deposition, although recent growth acceleration suggests growth resilience in post-pollution period. This fir growth surge likely coincides with stimulation of P acquisition following the decline of acidic pollution. The consequence is the current highest productivity among the studied tree species. The growth dynamics of both conifers were closely linked to the stoichiometric imbalance of phosphorus in needles, indicating the possible sensitivity of exogenous controls on nutrient uptake. Furthermore, spruce BAI was positively linked to calcium availability across sites. Despite enhanced water-use efficiency under elevated CO2, spruce growth is constrained by precipitation deficit and demonstrates weakening resilience to increasing growing season air temperatures. Overall, these findings underscore the intricate relationships between atmospheric pollution, nutrient availability, and climatic factors in shaping the growth dynamics of European forest ecosystems. Thus, incorporating biogeochemical context of nutrient availability is essential for realistic modelling of tree growth in a changing climate.

Soil priming effect in the organic and mineral layers regulated by nitrogen mining mechanism in a temperate forest

AbstractSoil organic carbon (SOC) in temperate forests is a crucial part of the global C cycle. The C and nitrogen (N) inputs may greatly increase in forest ecosystems affected by atmospheric CO2 concentration, N deposition, and other climate change, which may further affect SOC dynamics in temperate forests. Nevertheless, how C and N inputs interact to influence the soil priming effect (PE) in the organic and mineral layers of temperate forests remains unclear. Here, we used easily available C and N sources, such as 13C‐glucose with 2% SOC contents and ammonium nitrate (input C:N ratio = 10), to examine the effects and mechanisms of exogenous C and N inputs on soil CO2 production and PE in both soil layers of a temperate forest. Our research revealed that exogenous C input caused a positive PE in both soil layers, with the mineral layer showing a larger PE per unit of SOC than the organic layer (OL). Although C input increased C loss from native SOC, soil net C accumulation still increased. The C and N inputs decreased the soil PE in both soil layers, suggesting that N input alleviates substrate N limitation and weakens microbial N mining in both soil layers. Meanwhile, the C and N inputs increased the exogenous C remaining in the organic layer, which was beneficial for soil C sequestration. Compared to the organic layer, the response of the mineral layer to C and N inputs was weaker. This study suggests that C and N interact to affect PE on SOC decomposition and this interaction should be considered in modeling and prediction of soil C cycling.

Analysis of wheat fungal community succession in traditional storage structures using Illumina MiSeq sequencing technology

The diversity of fungi in wheat with different deoxynivalenol (DON) content at various periods post-harvest and in the environment of storage were investigated. The changes in DON content were measured with ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC-MS/MS), and an amplicon sequence analysis of fungi was performed in traditional storage structures using high-throughput sequencing. The changes in temperature, humidity, and CO2 concentration were collected by sensors. In addition, we analyzed principal component analysis, species composition, species differences, and community differences of fungi. There was an obvious separation of the fungal communities under different storage conditions and times. Many fungal genera were gradually decreasing during storage and were eventually undetectable, and many fungal genera that were undetectable at first gradually increased during storage and even became dominant fungal genera. The competition between fungi was fierce. The competition between fungi were affected by the presence of DON. As the initial DON content increased, the contribution of inter-group differences became more obvious. The temperature, humidity, and CO2 concentration of wheat in the silo's environment changed with extended storage time. The content of DON decreased with extended storage time. We had investigated the changes in DON content and their correlation with the changes in fungal communities and environmental factors, which showed a high degree of correlation. This study offers theoretical justification for optimizing safe wheat grain in traditional storage conditions.

Engineering Controls for Scaling CO2 Electrolyzers

The electrochemical CO2 reduction (CO2R) to ethylene on copper-based catalysts has garnered significant attention for its potential in sustainable industrial practices. While substantial progress has been achieved in the development of small-scale electrolyzers with geometric areas ranging from 1 to 5 cm2, the imperative to address larger scales for industrial decarbonization necessitates a shift in focus. There are inherent critical risks when scaling a nascent technology like CO2 electrolysis. There can be emergent phenomena observed only at larger scales, that can prevent it from reaching commercialization, such as change in local CO2 concentration, defects in the porous transport layer, and temperature gradients The optimized conditions for operating a 5 cm2 electrolyzer may not work well with a 25 cm2 electrolyzer leading to failures. Therefore, there is a need to develop a systematic way to test for these phenomena to address these challenges to successfully operate a CO2R electrolyzer at an industrially relevant scale. In this work, we highlight the performance of a Cu-based catalyst designed for the selective reduction of CO2 to ethylene across varying scales, ranging from 5 to 100 cm2. This investigation shows the changes in the electrolyzer performance at different scales. Our findings highlight the critical importance of implementing engineering controls to overcome challenges associated with the scaling of electrolyzers. Specifically, we explore the impact of anolyte flow rate, gasket compression, and electrochemical pulsing techniques on maintaining the desired selectivity of the electrocatalyst across different scales. By systematically adjusting these parameters, we demonstrate the ability to mitigate non-linear effects and uphold the efficiency of CO2 reduction to ethylene, even on larger electrode surfaces.This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Converged ensemble simulations of climate: possible trends in total solar irradiance cannot explain global warming alone

We address the hypothetical question of whether an increasing total solar irradiance (TSI) trend, without anthropogenic contributions, could be sufficient to explain the ongoing global warming. To this end, the intermediate-complexity climate model PlaSim is used. To consider the total internal variability, we present a set of ensemble simulations, with different forcing histories in TSI and CO2 concentration, that have converged sufficiently tightly to the relevant probability distributions to provide a satisfactory bound on any spurious trend possibly arising from a sampling bias; similar bounds on any other unforced contributions to ensemble mean trends are also estimated. A key point is the consideration, among the forcing histories, the steepest increasing trend in TSI that is still consistent with observations according to a recent study; thereby, we essentially revisit corresponding TSI reconstructions, more than 20 years after their last modeling-based evaluation, by improving the analysis through taking care of all possible sources of error or uncertainty and incorporating data that have become available since then. Without any change in CO2 concentration, our TSI trend (i.e., and upper bound on actual TSI trends) is found to be insufficient to produce outcomes compatible with the observational record in global mean surface temperature (GMST) with a nonnegligible probability. We formalize our statement for quantifiers of GMST trends through evaluating their distributions over the ensemble, and we speculate that the hypothesis about the exclusive role of an increasing TSI remains implausible even beyond our particular model setup. At the same time, if we consider a constant TSI, and the observational record in CO2 concentration is applied as forcing, the simulation results and the recorded GMST match well. While we currently need to leave the question of a precise attribution open, we conclude by pointing out that an attribution of the ongoing global warming to an increasing TSI alone could be made plausible only if a bias in the set of land-based instrumental temperature measurements were increasing more rapidly than commonly estimated; an assessment of the latter possibility is out of the scope of our study, as well as addressing solar forcing mechanisms beyond the effect of TSI.

Effects of atmospheric CO2 concentration on transpiration and leaf elongation responses to drought in Triticum aestivum, Lolium perenne and Festuca arundinacea.

Leaf elongation is vital for Poaceae species' productivity, influenced by atmospheric CO2 concentration ([CO2]) and climate-induced water availability changes. Although [CO2] mitigates the effects of drought on reducing transpiration per unit leaf area, it also increases total leaf area and water use. These complex interactions associated with leaf growth pose challenges in anticipating climate change effects. This study aims to assess [CO2] effects on leaf growth response to drought in perennial ryegrass (Lolium perenne), tall fescue (Festuca arundinacea) and wheat (Triticum aestivum). Plants were cultivated in growth chambers with [CO2] at 200 or 800ppm. At leaf six to seven unfolding, half of the plants were subjected to severe drought treatment. Leaf elongation rate (LER) was measured daily, whereas plant transpiration was continuously recorded gravimetrically. Additionally, water-soluble carbohydrate (WSC) content along with water and osmotic potentials in the leaf growing zone were measured at drought onset, mid-drought and leaf growth cessation. Elevated [CO2] mitigated drought impacts on LER and delayed growth cessation across species. A positive correlation between LER and soil relative water content (SRWC) was observed. At the same SRWC, perennial grasses exhibited a higher LER with elevated [CO2], likely due to enhanced stomatal regulation. Despite stomatal closure and WSC accumulation, CO2 did not influence nighttime water potential or osmotic potential. The marked increase in leaf area across species resulted in similar (wheat and tall fescue) or higher (ryegrass) total water use by the experiment's end, under both watered and unwatered conditions. In conclusion, elevated [CO2] mitigates the adverse effects of drought on leaf elongation in three Poaceae species, due to its impact on plant transpiration. Overall, these findings provide valuable insights into CO2 and drought interactions that may help anticipate plant responses to climate change.

Relation of Changes in CO2 Concentration over Large Water Areas of the Boreal and Subarctic Zones of the Northern Hemisphere with Their Phenological Phases Determined from SMOS Satellite Data

Relation of Changes in CO2 Concentration over Large Water Areas of the Boreal and Subarctic Zones of the Northern Hemisphere with Their Phenological Phases Determined from SMOS Satellite Data

Tree-Ring δ13C and Intrinsic Water-Use Efficiency Reveal Physiological Responses to Climate Change in Semi-Arid Areas of North China

Climate change has had a widespread and profound impact on global temperature and precipitation patterns, especially in semi-arid areas. Plant δ13C and iWUE indicate the trade-off between carbon uptake and water loss, which is pivotal for understanding plant responses to climate change. Information about the long-term responses of the physiological and ecological processes of different tree species to climate change is also required. To investigate the impact of different forest stand structures and site conditions on long-term growth and physiological processes of coniferous and broad-leaved trees in the mountainous area of Beijing, we analyzed the tree-ring δ13C variation of four tree species (Platycladus orientalis, Pinus tabuliformis, Quercus variabilis, Robinia pseudoacacia) sampled from 64 plots with varying site and stand conditions. We found that the tree-ring δ13C of the four tree species varied from each other and was mainly affected by density and slope aspect, followed by slope and age. Both tree-ring δ13C and iWUE of the four tree species showed increasing trends over time, mechanistically linked to long-term changes in global CO2 concentration. This indicates the four native tree species have adapted well to climate change, and the risk of decline is relatively low. The increased iWUE translated into different growth patterns which varied with tree species, site, and stand condition. Different tree species have varying sensitivities to environmental factors. The iWUE of coniferous tree species is more sensitive to climate change than that of broad-leaved tree species, especially to temperature (T), the Standardized Precipitation Evapotranspiration Index (SPEI), and vapor pressure deficit (VPD).

Increased ecological land and atmospheric CO2 dominate the growth of ecosystem carbon sinks under the regulation of environmental conditions in national key ecological function zones in China

Increased ecological land (IEL) such as forests and grasslands can greatly enhance ecosystem carbon sinks. Understanding the mechanisms for the magnitude of IEL-induced ecosystem carbon sinks is crucial for achieving carbon neutrality. We estimated the impact of IEL, specifically the increase in forests and grasslands, as well as global changes including atmospheric CO2 concentration, nitrogen deposition, and climate change on net ecosystem productivity (NEP) in National Key Ecological Function Zones (NKEFZs) in China using a calibrated ecological process model. The NEP in NKEFZs in China was calculated to be 119.4 Tg C yr−1, showing an increase of 42.6 Tg C yr−1 from 2001 to 2021. Compared to the slight contributions of climate change (−8.0%), nitrogen deposition (11.5%), and reduction in ecological land (−3.5%), the increase in NEP was primarily attributed to CO2 (66.5%) and IEL (33.5%). Moreover, the effect of IEL (14.8 Tg C yr−1) surpassed that of global change (13.1 Tg C yr−1) in the land use change zone. The IEL-induced NEP is significantly associated with CO2 fertilization, regulated by precipitation and nitrogen deposition. The high values of IEL-induced NEP occurred in areas with precipitation exceeding 800 mm and nitrogen deposition exceeding 25 kg N ha−1 yr−1. We recommend prioritizing the expansion of ecological land in areas with sufficient water and nutrients to enhance CO2 fertilization, while avoiding increasing ecological land in regions facing unfavorable climate change conditions. This study serves as a foundation for comprehending the NEP response to ecological restoration and global change.

Seamless reconstruction and spatiotemporal analysis of satellite-based XCO2 incorporating temporal characteristics: A case study in China during 2015–2020

Carbon dioxide (CO2) is a crucial greenhouse gas, and its concentration and spatiotemporal characteristics are among the principal sources of uncertainty in global warming assessments. Satellite remote sensing is a widely adopted, high-accuracy approach for monitoring atmospheric CO2. However, limited swath width and cloud cover significantly reduce satellite observation coverage. This study addresses the temporal changes in CO2 concentration and utilizes a machine learning-based fusion of multiple data sources to generate daily, full-coverage, 0.05° spatial resolution column-averaged CO2 concentration data for China from 2015 to 2020. Ten-fold cross-validation yielded a determination coefficient R2 of 0.97, root mean square error of 0.92 ppm, and mean absolute error of 0.59 ppm. Compared to other datasets, this study’s dataset exhibits superior accuracy and spatiotemporal detail. Using the produced CO2 concentration data in this study, we conducted a spatiotemporal analysis of CO2 concentrations in China. The results indicate that, in general, the Western region exhibits a higher growth rate in CO2 concentration than the Eastern and Central regions, with areas of lower CO2 concentration experiencing higher growth rates while regions with higher CO2 concentration have lower growth rates. Moreover, the highest increase in CO2 concentration occurred in 2016, with a substantial decrease in CO2 concentration growth observed in 2018. Notably, the reduction in CO2 concentration in the Qinghai-Tibet Plateau region during the summer is considerably smaller than in other regions, possibly due to atmospheric transport from the Indian Peninsula.

Research on Resistance Characteristics of Fire Zone of Mine Tunnel Fire and Construction of Calculation Model

To investigate resistance change in the fire area of a roadway caused by roadway fires, a mathematical calculation model for thermal resistance is developed. Theoretical research is conducted to analyze the factors influencing resistance change through theoretical derivation, revealing that temperature is a key factor contributing to the change in thermal resistance. By leveraging the correlation between changes in CO concentration and temperature on the downwind side of the roadway within the fire zone, researchers developed mathematical models to predict temperature increases at various points downwind of the fire source. These models were then used to determine the mathematical relationship governing the change in thermal resistance. The accuracy of the numerical simulation software was validated using Fluent numerical simulation software and scaled-down model experiments. Full-scale numerical simulation experiments were conducted to investigate the fire characteristics of roadway fires and validate the thermal resistance mathematical model. The results indicate that the thermal resistance in the numerical simulation is 7.55 Pa at 20m from the fire source and 5.54 Pa at the end of the roadway. The decrease in resistance is linear. The minimum error between the thermal resistance calculated by the mathematical model and the gradient of the pressure drop in the numerical simulation is 0.03 Pa, approximately 2.3%. Furthermore, the fitting degree of the pressure drop in each section is as high as 97.7%. The calculation model demonstrates high accuracy and offers a theoretical foundation for investigating fire resistance in tunnel fire.

Using respiratory challenges to modulate CSF movement across different physiological pathways: An fMRI study

Abstract With growing evidence signifying the impact of cerebrospinal fluid (CSF) flow in facilitating waste clearance from the brain and potential pathophysiological links to neurodegenerative disorders, it is of vital importance to develop effective methods to modulate CSF flow in the brain. Here, we attempt this by means of simple commonly used respiratory challenges—paced breathing and breath holding. Functional Magnetic Resonance Imaging scans of the brain and neck respectively were used to record the craniad and caudad CSF movements at the fourth ventricle from eight healthy volunteers during paced breathing and breath holding. Further, we utilized a novel approach for the first time to combine these separately acquired unidirectional CSF movement signals to compare the CSF flow in both directions (in the fourth ventricle) with the respiratory stimuli as a physiological control. Our results demonstrate that these respiratory challenges enhance the magnitude as well as control the direction of CSF movement in the fourth ventricle. They also reveal the capability of blood CO2 concentration changes (induced by respiratory challenges) in the low-frequency range to bring about these CSF movement modulations. Finally, we also successfully report our novel approach where we use these breathing challenges as a unique control condition to detect the small net CSF flows from independently captured unidirectional signals.