CO2 Tension Research Articles

The wetting of H2O by CO2.

Biphasic interfaces are complex but fascinating regimes that display a number of properties distinct from those of the bulk. The CO2-H2O interface, in particular, has been the subject of a number of studies on account of its importance for the carbon life cycle as well as carbon capture and sequestration schemes. Despite this attention, there remain a number of open questions on the nature of the CO2-H2O interface, particularly concerning the interfacial tension and phase behavior of CO2 at the interface. In this paper, we seek to address these ambiguities using abinitio-quality simulations. Harnessing the benefits of machine-learned potentials and enhanced statistical sampling methods, we present an abinitio-level description of the CO2-H2O interface. Interfacial tensions are predicted from 1 to 500 bars and found to be in close agreement with experiment at pressures for which experimental data are available. Structural analyses indicate the buildup of an adsorbed, saturated CO2 film forming at a low pressure (20 bars) with properties similar to those of the bulk liquid, but preferential perpendicular alignment with respect to the interface. The CO2 monolayer buildup coincides with a reduced structuring of water molecules close to the interface. This study highlights the predictive nature of machine-learned potentials for complex macroscopic properties of biphasic interfaces, and the mechanistic insight obtained into carbon dioxide aggregation at the water interface is of high relevance for geoscience, climate research, and materials science.

The independent effects of hydrostatic pressure and hypercapnic breathing during water immersion on ventilatory sensitivity and cerebrovascular reactivity.

Head-out water immersion (HOWI) induces ventilatory and hemodynamic changes, which may be a result of hydrostatic pressure, augmented arterial CO2 tension, or a combination of both. We hypothesized that the hydrostatic pressure and elevated CO2 tension that occur during HOWI will contribute to an augmented ventilatory sensitivity to CO2 and an attenuated cerebrovascular reactivity to CO2 during water immersion. Twelve subjects [age: 24 ± 3 yr, body mass index (BMI): 25 ± 3 kg/m2] completed HOWI, waist water immersion with CO2 (WWI + CO2), and WWI, where a rebreathing test was conducted at baseline, 10, 30, and 60 min, and postimmersion. End-tidal pressure of carbon dioxide ([Formula: see text]), minute ventilation, expired gases, blood pressure, heart rate, and middle cerebral artery blood velocity were recorded continuously. [Formula: see text] increased throughout all visits (P ≤ 0.011), was similar during HOWI and WWI + CO2 (P ≥ 0.264), and was greater during WWI + CO2 versus WWI at 10, 30, and 60 min (P < 0.001). When HOWI vs. WWI + CO2 were compared, the change in ventilatory sensitivity to CO2 was different at 10 (0.59 ± 0.34 vs. 0.06 ± 0.23 L/min/mmHg; P < 0.001), 30 (0.58 ± 0.46 vs. 0.15 ± 0.25 L/min/mmHg; P < 0.001), and 60 min (0.63 ± 0.45 vs. 0.16 ± 0.34 L/min/mmHg; P < 0.001), whereas there were no differences between conditions for cerebrovascular reactivity to CO2 (P ≥ 0.163). When WWI + CO2 versus WWI were compared, ventilatory sensitivity to CO2 was not different between conditions (P ≥ 0.642), whereas the change in cerebrovascular reactivity to CO2 was different at 30 min (-0.56 ± 0.38 vs. -0.30 ± 0.25 cm/s/mmHg; P = 0.010). These data indicate that during HOWI, ventilatory sensitivity to CO2 increases due to the hydrostatic pressure, whereas cerebrovascular reactivity to CO2 decreases due to the combined effects of immersion.NEW & NOTEWORTHY Although not fully elucidated, the ventilatory and hemodynamic alterations during water immersion appear to be a result of the combined effects of immersion (i.e., elevated [Formula: see text], central hypervolemia, increased cerebral perfusion, increased work of breathing, etc.). Our findings demonstrate that an augmented ventilatory sensitivity to CO2 during immersion may be due to the hydrostatic pressure across the chest wall, whereas an attenuated cerebrovascular reactivity to CO2 may be due to the combined effects of immersion.

The Respiratory Compensation Point: Mechanisms and Relation to the Maximal Metabolic Steady State.

At a point during the latter third of an incremental exercise protocol, ventilation begins to exceed the rate of clearance of carbon dioxide (CO2) at the lungs ( CO2). The onset of this hyperventilation, which is confirmed by a fall from a period of stability in end-tidal and arterial CO2 tensions (PCO2), is referred to as the respiratory compensation point (RCP). The mechanisms that contribute to the RCP remain debated as does its surrogacy for the maximal metabolic steady state of constant-power exercise (i.e., the highest work rate associated with maintenance of physiological steady state). The objective of this current opinion is to summarize the original research contributions that support and refute the hypotheses that: (i) the RCP represents a rapid, peripheral chemoreceptor-mediated reflex response engaged when the metabolic rate at which the buffering systems can no longer constrain the rise in hydrogen ions ([H+]) associated with rising lactate concentration and metabolic CO2 production is surpassed; and (ii) the metabolic rate at which this occurs is equivalent to the maximal metabolic steady state of constant power exercise. In doing so, we will shed light on potential mechanisms contributing to the RCP, attempt to reconcile disparate findings, make a case for its adoption for exercise intensity stratification and propose strategies for the use of RCP in aerobic exercise prescription.

Elimination of Intestinal Hypoxia in Complex Treatment of Intestinal Failure (Case Report)

INTRODUCTION: Currently, various approaches to the treatment of intestinal failure (IF) are considered. In search for pathogenetically justified therapy, it is possible to use oxygenated saline enteral solution (OSES). АIM: To demonstrate, by gas analysis of the introduced oxygenated saline enteral solution and the excreted intestinal fluid, the possibility of gas exchange in the intestine with increased oxygen extraction under hypoxic conditions. An 8-year-old child with burdened premorbid history and severe community–acquired bilateral pleuropneumonia kept on mechanical ventilation, had signs of IF (disorder in passage, absence of independent defecation for more than two days). During treatment and observation of the child, enteral feeding was attempted with pharmacological stimulation with prokinetics, and introduction of laxative sorbent with prebiotic effect (lactulose). Because of non-effectiveness of these measures, it was decided to perform intestinal lavage with OSES introduced through the nasogastral tube. In 30 minites after start of OSES introduction, the gastrointestinal tract motility notably enhanced, in 1.5 hour from the beginning of the procedure, fractional passage of a significant amount of thick fecal masses was noted, after which intestinate — liquid stool stained yellow with bile, was obtained. During the procedure, a comparative analysis of the gas composition of the introduced OSES and excreted intestinate was done. In the excreted solution, 97-fold decrease of рО2 from 659 to 6.8 mm Hg, and 3.6-fold increase in CO2 tension from 23 to 85.7 mm Hg, were noted. CONCLUSION: Oxygenation of the enteral environment by barbotage of a saline enteral solution introduced through a tube is an effective component of intensive therapy for intestinal failure syndrome, taking into account the ability of the gastrointestinal tract tissues to actively participate in gas exchange: extract oxygen and release carbon dioxide.

Recent Advances in Geochemical and Mineralogical Studies on CO2–Brine–Rock Interaction for CO2 Sequestration: Laboratory and Simulation Studies

The urgent need to find mitigating pathways for limiting world CO2 emissions to net zero by 2050 has led to intense research on CO2 sequestration in deep saline reservoirs. This paper reviews key advancements in lab- and simulation-scale research on petrophysical, geochemical, and mineralogical changes during CO2–brine–rock interactions performed in the last 25 years. It delves into CO2 MPD (mineralization, precipitation, and dissolution) and explores alterations in petrophysical properties during core flooding and in static batch reactors. These properties include changes in wettability, CO2 and brine interfacial tension, diffusion, dispersion, CO2 storage capacity, and CO2 leakage in caprock and sedimentary rocks under reservoir conditions. The injection of supercritical CO2 into deep saline aquifers can lead to unforeseen geochemical and mineralogical changes, possibly jeopardizing the CCS (carbon capture and storage) process. There is a general lack of understanding of the reservoir’s interaction with the CO2 phase at the pore/grain scale. This research addresses the gap in predicting the long-term changes of the CO2–brine–rock interaction using various geochemical reactive transport simulators. Péclet and Damköhler numbers can contribute to a better understanding of geochemical interactions and reactive transport processes. Additionally, the dielectric constant requires further investigation, particularly for pre- and post-CO2–brine–rock interactions. For comprehensive modeling of CO2 storage over various timescales, the geochemical modeling software called the Geochemist’s Workbench was found to outperform others. Wettability alteration is another crucial aspect affecting CO2–brine–rock interactions under varying temperature, pressure, and salinity conditions, which is essential for ensuring long-term CO2 storage security and monitoring. Moreover, dual-energy CT scanning can provide deeper insights into geochemical interactions and their complexities.

Data-based modeling of cerebral hemodynamics quantifies impairment of cerebral blood flow regulation in type-2 diabetes

We studied the regulation dynamics of cerebral blood velocity (CBv) at middle cerebral arteries (MCA) in response to spontaneous changes of arterial blood pressure (ABP), termed dynamic cerebral autoregulation (dCA), and end-tidal CO2 as proxy for blood CO2 tension, termed dynamic vasomotor reactivity (DVR), by analyzing time-series data collected at supine rest from 36 patients with Type-2 Diabetes Mellitus (T2DM) and 22 age/sex-matched non-diabetic controls without arterial hypertension. Our analysis employed a robust dynamic modeling methodology that utilizes Principal Dynamic Modes (PDM) to estimate subject-specific dynamic transformations of spontaneous changes in ABP and end-tidal CO2 (viewed as two “inputs”) into changes of CBv at MCA measured via Transcranial Doppler ultrasound (viewed as the “output”). The quantitative results of PDM analysis indicate significant alterations in T2DM of both DVR and dCA in terms of two specific PDM contributions that rise to significance (p < 0.05). Our results further suggest that the observed DVR and dCA alterations may be due to reduction of cholinergic activity (based on previously published results from cholinergic blockade data) that may disturb the sympatho-vagal balance in T2DM. Combination of these two model-based “physio-markers” differentiated T2DM patients from controls (p = 0.0007), indicating diabetes-related alteration of cerebrovascular regulation, with possible diagnostic implications.

Does central chemoreceptor blood flow increase with CO2 tension?

Does central chemoreceptor blood flow increase with CO2 tension?

Physiologically based modeling reveals different risk of respiratory depression after fentanyl overdose between adults and children.

Despite a rapid increase in pediatric mortality rate from prescription and illicit opioids, there is limited research on the dose-dependent impact of opioids on respiratory depression in children, the leading cause of opioid-associated death. In this article, we extend a previously developed translational model to cover pediatric populations by incorporating age-dependent pharmacokinetic, pharmacodynamic, and physiological changes compared to adults. Our model reproduced previous perioperative clinical findings that adults and children have similar risk of respiratory depression at the same plasma fentanyl concentration when specific endpoints (minute ventilation, CO2 tension in the blood) were used. However, our model points to a potential caveat that, in a perioperative setting, routine use of mechanical ventilation and supplemental oxygen maintained the blood and tissue oxygen partial pressures in patients and prevented the use of oxygen-related endpoints to evaluate the consequences of respiratory depression. In a community setting when such oxygenation procedures are not immediately available, our model suggests that the higher oxygen demand and reduced cerebrovascular reactivity could make children more susceptible to severe hypoxemia and brain hypoxia, even with the same plasma fentanyl concentration as adults. Our work indicates that when developing intervention strategies to protect children from opioid overdose in a community setting, these pediatric-specific factors may need to be considered.

Evaluating the efficacy of a standardized 4 mL/kg fluid bolus technique in critically ill patients with elevated PvaCO2: secondary analysis of two prospective studies.

Limiting the fluid bolus (FB) volume may attenuate side effects, including hemodilution and increased filling pressures, but it may also reduce hemodynamic responsiveness. The minimum volume to create hemodynamic effects is considered to be 4 mL/kg. In critically ill patients, the hemodynamic effects of FB with this volume have not been adequately investigated and compared to higher quantities. We hypothesized that a standardized FB approach using 4 mL/kg has comparable hemodynamic and metabolic effects to the common practice of physician-determined FB in critically ill patients. We conducted post hoc analysis of two trials in non-selected critically ill patients with central venous-to-arterial CO2 tension (PvaCO2) >6 mmHg and no acute bleeding. All patients received crystalloids either at a physician-determined volume and rate or at 4 mL/kg pump-administered at 1.2 L/h. Cardiac index (CI) was calculated with transthoracic echocardiogram, and arterial and venous blood gas samples were assessed before and after FB. Endpoints were changes in CI and oxygen delivery (DO2) >15%. A total of 47 patients were eligible for the study, 15 of whom received physician-determined FB and 32 of whom received standardized FB. Patients in the physician-determined FB group received 16 (12-19) mL/kg at a fluid rate of 1.5 (1.5-1.9) L/h, compared to 4.1 (3.7-4.4) mL/kg at a fluid rate of 1.2 (1.2-1.2) L/h (p < 0.01) in the standardized FB group. The difference in CI elevations between the two groups was not statistically significant (8.8% [-0.1-19.9%] vs. 8.4% [0.3-23.2%], p = 0.76). Compared to physician-determined FB, the standardized FB technique had similar probabilities of increasing CI or DO2 by >15% (odds ratios: 1.3 [95% CI: 0.37-5.18], p = 0.66 and 1.83 [95% CI: 0.49-7.85], p = 0.38). A standardized FB protocol (4 mL/kg at 1.2 L/h) effectively reduced the volume of fluid administered to critically ill patients without compromising hemodynamic or metabolic effects.

Agreement between arterial and end-tidal carbon dioxide in adult patients admitted with serious traumatic brain injury.

Low-normal levels of arterial carbon dioxide (PaCO2) are recommended in the acute phase of traumatic brain injury (TBI) to optimize oxygen and CO2 tension, and to maintain cerebral perfusion. End-tidal CO2 (ETCO2) may be used as a surrogate for PaCO2 when arterial sampling is less readily available. ETCO2 may not be an adequate proxy to guide ventilation and the effects on concomitant injury, time, and the impact of ventilatory strategies on the PaCO2-ETCO2 gradient are not well understood. The primary objective of this study was to describe the correlation and agreement between PaCO2 and ETCO2 in intubated adult trauma patients with TBI. This study was a retrospective analysis of prospectively-collected data of intubated adult major trauma patients with serious TBI, admitted to the East of England regional major trauma centre; 2015-2019. Linear regression and Welch's test were performed on each cohort to assess correlation between paired PaCO2 and ETCO2 at 24-hour epochs for 120 hours after admission. Bland-Altman plots were constructed at 24-hour epochs to assess the PaCO2-ETCO2 agreement. 695 patients were included, with 3812 paired PaCO2 and ETCO2 data points. The median PaCO2-ETCO2 gradient on admission was 0.8 [0.4-1.4] kPa, Bland Altman Bias of 0.96, upper (+2.93) and lower (-1.00), and correlation R2 0.149. The gradient was significantly greater in patients with TBI plus concomitant injury, compared to those with isolated TBI (0.9 [0.4-1.5] kPa vs. 0.7 [0.3-1.1] kPa, p<0.05). Across all groups the gradient reduced over time. Patients who died within 30 days had a larger gradient on admission compared to those who survived; 1.2 [0.7-1.9] kPa and 0.7 [0.3-1.2] kPa, p<0.005. Amongst adult patients with TBI, the PaCO2-ETCO2 gradient was greater than previously reported values, particularly early in the patient journey, and when associated with concomitant chest injury. An increased PaCO2-ETCO2 gradient on admission was associated with increased mortality.

Cerebral uptake of microvesicles occurs in normocapnic but not hypocapnic passive hyperthermia in young healthy male adults.

Passive hyperthermia causes cerebral hypoperfusion primarily from heat-induced respiratory alkalosis. However, despite the cerebral hypoperfusion, it is possible that the mild alkalosis might help to attenuate cerebral inflammation. In this study, the cerebral exchange of extracellular vesicles (microvesicles), which are known to elicit pro-inflammatory responses when released in conditions of stress, were examined in hyperthermia with and without respiratory alkalosis. Ten healthy male adults were heated passively, using a warm water-perfused suit, up to core temperature+2°C. Blood samples were taken from the radial artery and internal jugular bulb. Microvesicle concentrations were determined in platelet-poor plasma via cells expressing CD62E (activated endothelial cells), CD31+ /CD42b- (apoptotic endothelial cells), CD14 (monocytes) and CD45 (pan-leucocytes). Cerebral blood flow was measured via duplex ultrasound of the internal carotid and vertebral arteries to determine cerebral exchange kinetics. From baseline to poikilocapnic (alkalotic) hyperthermia, there was no change in microvesicle concentration from any cell origin measured (P-values all >0.05). However, when blood CO2 tension was normalized to baseline levels in hyperthermia, there was a marked increase in cerebral uptake of microvesicles expressing CD62E (P=0.028), CD31+ /CD42b- (P=0.003) and CD14 (P=0.031) compared with baseline, corresponding to large increases in arterial but not jugular venous concentrations. In a subset of seven participants who underwent hypercapnia and hypocapnia in the absence of heating, there was no change in microvesicle concentrations or cerebral exchange, suggesting that hyperthermia potentiated the CO2 /pH-mediated cerebral uptake of microvesicles. These data provide insight into a potential beneficial role of respiratory alkalosis in heat stress. KEY POINTS: The hyperthermia-induced hyperventilatory response is observed in most humans, despite causing potentially harmful reductions in cerebral blood flow. We tested the hypothesis that the respiratory-induced alkalosis is associated with lower circulating microvesicle concentrations, specifically in the brain, despite the reductions in blood flow. At core temperature+2°C with respiratory alkalosis, microvesicles derived from endothelial cells, monocytes and leucocytes were at concentrations similar to baseline in the arterial and cerebral venous circulation, with no changes in cross-brain microvesicle kinetics. However, when core temperature was increased by 2°C with CO2 /pH normalized to resting levels, there was a marked cerebral uptake of microvesicles derived from endothelial cells and monocytes. The CO2 /pH-mediated alteration in cerebral microvesicle uptake occurred only in hyperthermia. These new findings suggest that the heat-induced hyperventilatory response might serve a beneficial role by preventing potentially inflammatory microvesicle uptake in the brain.

Effect of the Temperature on Interfacial Properties of CO2/H2 Mixtures Contacting with Brine and Hydrophilic Silica by Molecular Dynamics Simulations.

Underground H2 storage (UHS) is a promising technology to achieve large-scale, long-term H2 storage. Using CO2 as a cushion gas to maintain the pressure of the reservoir and withdraw stored H2 in the saline aquifer simultaneously enables the implementation of UHS and underground CO2 storage (UCS). The difference in the molecular properties of CO2 and H2 leads to distinct interfacial behavior when in contact with the brine and rock, thereby affecting the flow patterns and trapping mechanisms of gases in geological formations. Accurate prediction of the interfacial properties of CO2, H2, and the mixtures when interacting with brine and rock is crucial to minimizing the uncertainties in UHS and UCS projects. In this study, molecular dynamics (MD) simulations are performed to predict the interfacial tension, surface excess, bubble evolution, and contact angle of CO2, H2, and the mixtures at 10 MPa and 300-400 K. The MD results show that the interaction of CO2 with H2O and hydrophilic silica is considerably stronger than that of H2. The interfacial tension reduces linearly with the temperature in H2-dominated mixture systems, and the surface adsorption of H2 can diminish in a CO2-dominated system or at high-temperature conditions. The hydrophilic silica is more CO2-wet than H2-wet, and the attached CO2 bubble is more easily disconnected. Ions and the temperature play different roles in the contact angle.

Use of Near-InfraRed Spectroscopy (NIRS) during Vascular Occlusion Test (VOT) for predicting an increase in oxygen consumption after fluid challenge in circulatory shock patients

Background: The goal of fluid challenge (FC) is to increase cardiac output (CO) and oxygen delivery (DO2) (known as fluid responders) to correct tissue hypoxia. To optimize fluid administration, fluid challenge (FC) during dependence of oxygen consumption on oxygen delivery (VO2/DO2 dependency) would correct tissue hypoxia confirmed by an increase of oxygen consumption (VO2) and oxygen delivery (DO2) after FC (known as VO2 responders) and get more benefit from a reduction in tissue hypoxia. Markers of anaerobic metabolisms, such as blood lactate concentration or the ratio of venous-arterial CO2 tension difference (P(cv-a)CO2) over arterial-to-venous oxygen content difference (C(a-cv)O2), can predict VO2 responders but still have several limitations. Therefore, near-infrared spectroscopy (NIRS) has been developed to evaluate tissue perfusion, presented as tissue oxygen saturation (StO2), at the bedside. Combining StO2 with the vascular occlusive test (VOT) and introducing a short period of forearm ischemia is a non-invasive technique to examine microvascular alterations at the bedside. However, a study validating the ability of these variables to predict VO2 response has not been conducted. Methods: We plan to conduct a single-center prospective study on circulatory failure patients. The cardiac index (CI), oxygen delivery (DO2), oxygen consumption (VO2), arterial lactate, central venous oxygen saturation (ScvO2), ratio of venous-arterial carbon dioxide tension to arterial-to-central venous oxygen content difference (P(cv-a)CO2/ C(a-cv)O2), and tissue oxygen saturation measured by near-infrared spectroscopy (NIRS) probe during vascular occlusion test variables (NIRS-VOT variables) will be collected before and after the fluid challenge. Hypothesis: We hypothesize that markers of reactive hyperemia by NIRs will predict an increase in VO2 after FC in patients with circulatory shock. Ethics: The study protocol has been approved by the ethics committee of the faculty of medicine, Ramathibodi Hospital, Mahidol University (COA. MURA2022/80).

The influence and mechanism of alkyl block polyethers on the interfacial tension and minimum miscibility pressure of CO2 and shale oil

The successful application of CO2 in developing shale oil can increase oil production and reduce CO2 emission. Reducing IFT and facilitating miscibility between CO2 and oil is the critical mechanism for enhancing shale oil recovery by CO2 flooding. Here, the effects of alkyl block polyethers on the interfacial tension and minimum miscibility pressure of CO2 and shale oil has been investigated by experiments and the influence mechanism of polyether on IFT and MMP has been explored by molecular dynamic simulations. The experimental results show that among the three polyethers, C4(PO)6 has the best effect to decrease the IFT and MMP of CO2 and shale oil. The IFT and MMP decrease with the increasing concentration of C4(PO)6 in CO2. The IFT and MMP can be decreased to a lower value when the polyether is dissolved in CO2 than in oil phase. The molecular dynamic simulations show that polyether molecules can diffuse from CO2 phase to the interface of CO2 and oil to decrease the IFT and further diffuse to oil phase to accelerate the miscibility process of CO2 and oil. The presence of polyether molecules can decrease the interaction energy, especially the vdW interactions between CO2 and oil molecules to decrease the IFT and MMP. The reduction of interaction energy is due to the dispersion force and LA-LB interactions between polyether and CO2, as well as the dispersion force interactions between polyether and oil molecules. The finding is significant to the chemical design for decreasing the IFT and MMP of CO2 and oil and further to successfully and efficiently develop shale oil by the CO2-surfactant mixed fluid.

A test of the interaction between central and peripheral respiratory chemoreflexes in humans.

How central and peripheral chemoreceptor drives to breathe interact in humans remains contentious. We measured the peripheral chemoreflex sensitivity to hypoxia (PChS) at various isocapnic CO2 tensions ( ) to determine the form of the relationship between PChS and central . Twenty participants (10F) completed three repetitions of modified rebreathing tests with end-tidal ( ) clamped at 150, 70, 60 and 45mmHg. End-tidal ( ), , ventilation ( E ) and calculated oxygen saturation (SC O2 ) were measured breath-by-breath by gas-analyser and pneumotach. The E - relationship of repeat-trials were linear-interpolated, combined, averaged into 1mmHg bins, and fitted with a double-linear function ( E S, L min-1 mmHg-1 ). PChS was computed at intervals of 1mmHg of as follows: the difference in E between the three hypoxic profiles and the hyperoxic profile (∆ E ) was calculated; three ∆ E values were plotted against corresponding SC O2 ; and linear regression determined PChS (Lmin-1 mmHg-1 %SC O2 -1 ). These processing steps were repeated at each to produce the PChS vs. isocapnic relationship. These were fitted with linear and polynomial functions, and Akaike information criterion identified the best-fit model. One-way repeated measures analysis of variance assessed between-condition differences. E S increased (P<0.0001) with isoxic from 3.7±1.5 L min-1 mmHg-1 at 150mmHg to 4.4±1.8, 5.0±1.6 and 6.0±2.2 Lmin-1 mmHg-1 at 70, 60 and 45mmHg, respectively. Mean SC O2 fell progressively (99.3±0%, 93.7±0.1%, 90.4±0.1% and 80.5±0.1%; P<0.0001). In all individuals, PChS increased with , and this relationship was best described by a linear model in 75%. Despite increasing central chemoreflex activation, PChS increased linearly with indicative of an additive central-peripheral chemoreflex response. KEY POINTS: How central and peripheral chemoreceptor drives to breathe interact in humans remains contentious. We measured peripheral chemoreflex sensitivity to hypoxia (PChS) at various isocapnic carbon dioxide tensions ( ) to determine the form of the relationship between PChS and central . Participants performed three repetitions of modified rebreathing with end-tidal fixed at 150, 70, 60 and 45mmHg. PChS was computed at intervals of 1mmHg of end-tidal ( ) as follows: the difference in E between the three hypoxic profiles and the hyperoxic profile (∆ E ) was calculated; three ∆ E values were plotted against corresponding calculated oxygen saturation (SC O2 ); and linear regression determined PChS (Lmin-1 mmHg-1 %SC O2 -1 ). In all individuals, PChS increased with , and this relationship was best described by a linear (rather than polynomial) model in 15 of 20. Most participants did not exhibit a hypo- or hyper-additive effect of central chemoreceptors on the peripheral chemoreflex indicating that the interaction was additive.

Dynamic viscosity and interfacial tension of CO2 and n-tetracosane system by dynamic light scattering method and molecular simulation

In this work, the viscosity and interfacial tension of the CO2 + n-tetracosane system were obtained experimentally by dynamic light scattering method at the temperature range of 423.15 ∼ 473.15 K and the pressure range of 1 ∼ 5 MPa. A new coarse-grained force field for n-C24H50 was established with intramolecular parameters fitted according to the LOPLS all-atom force field and intermolecular parameters fitted according to the viscosity and interfacial tension of the pure n-C24H50. The viscosity and interfacial tension of CO2 + n-C24H50 were calculated by molecular simulation, and the average relative deviations between the calculated and experimental data are 5.2% and 9.9%, respectively. The minimum mixed-phase pressures of the CO2 + n-C24H50 were calculated to be 26.93 MPa, 27.14 MPa and 27.47 MPa at 423.15 K, 448.15 K and 473.15 K, respectively.

Effects of greater erythroid Cl-/HCO3- transporter (band 3) expression on ventilation and gas exchange during exhaustive exercise.

Band 3 protein is a Cl-/[Formula: see text] transporter on the red blood cell (RBC) surface with an important role in CO2 excretion. Greater band 3 expression by roughly 20% is found in people with the GP.Mur blood type. Intriguingly, a disproportional percentage of those with GP.Mur excel in field-and-track sports. Could higher band 3 activity benefit an individual's physical performance? This study explored the impact of GP.Mur/higher band 3 expression on ventilation and gas exchange during exhaustive exercise. We recruited 36 nonsmoking, elite male athletes (36.1% GP.Mur) from top sports universities to perform incremental exhaustive treadmill cardiopulmonary exercise testing (CPET). We analyzed CPET data with respect to absolute running time and to individual's %running time and %maximal O2 uptake. We found persistently higher respiratory frequencies and slightly lower tidal volume in GP.Mur athletes, resulting in a slightly larger increase of ventilation as the workload intensified. The expiratory duty cycle (Te/Ttot) was persistently longer and inspiratory duty cycle (Ti/Ttot) was persistently shorter for GP.Mur subjects throughout the run. Consequently, end-tidal pressure of carbon dioxide ([Formula: see text], a surrogate marker for alveolar and arterial CO2 tension-[Formula: see text] and [Formula: see text]) was lower in the GP.Mur athletes during the early stages of exercise. In conclusion, athletes with GP.Mur and higher band 3 expression hyperventilate more during exercise in a pattern that uses a greater fraction of time for expiration than inspiration to increase the rate of CO2 excretion than increased tidal volume. This greater ventilation response reduced Pco2 and may help to extend exercise capacity in high-level sports.NEW & NOTEWORTHY Higher expression of the Cl-/[Formula: see text] transporter band 3 anion exchanger-1 (AE1) on the red blood cell membrane, as in people with the GP.Mur blood type, increases the rate of CO2 excretion during exercise.

End-tidal carbon dioxide tension is a reliable surrogate of arterial carbon dioxide tension across different oxygen, carbon dioxide and barometric pressures.

End-tidal CO2 tension provides an accurate estimation of P aCO2 in healthy awake individuals over an extensive range of CO2 pressures induced by 17 environmental conditions combining different O2, CO2 and barometric pressures https://bit.ly/3YuKPAY.

Strong ions and charge-balance

It has been shown that the ability to predict the pH in any chemically characterized fluid, together with its buffer-capacity and acid content can be based on the requirement of electroneutrality, conservation of mass, and rules of dissociation as provided by physical chemistry. More is not required, and less is not enough. The charge in most biological fluids is dominated by the constant charge on the completely dissociated strong ions but, nonetheless, a persistent narrative in physiology has problematized the notion that these have any role at all in acid-base homeostasis. While skepticism is always to be welcomed, some common arguments against the importance of strong ions are examined and refuted here. We find that the rejection of the importance of strong ions comes with the prize that even very simple systems such as fluids containing nothing else, or solutions of sodium bicarbonate in equilibrium with known tensions of CO2 become incomprehensible. Importantly, there is nothing fundamentally wrong with the Henderson–Hasselbalch equation but the idea that it is sufficient to understand even simple systems is unfounded. What it lacks for a complete description is a statement of charge-balance including strong ions, total buffer concentrations, and water dissociation.

Acute beetroot juice consumption does not alter cerebral autoregulation or cardiovagal baroreflex sensitivity during lower-body negative pressure in healthy adults.

Beetroot juice (BRJ) improves peripheral endothelial function and vascular compliance, likely due to increased nitric oxide bioavailability. It is unknown if BRJ alters cerebrovascular function and cardiovagal baroreflex control in healthy individuals. We tested the hypotheses that BRJ consumption improves cerebral autoregulation (CA) and cardiovagal baroreflex sensitivity (cBRS) during lower-body negative pressure (LBNP). Thirteen healthy adults (age: 26 ± 4 years; 5 women) performed oscillatory (O-LBNP) and static LBNP (S-LBNP) before (PRE) and 3 h after consuming 500 mL of BRJ (POST). Participants inhaled 3% CO2 (21% O2, 76% N2) during a 5 min baseline and throughout LBNP to attenuate reductions in end-tidal CO2 tension (PETCO2). O-LBNP was conducted at ∼0.02 Hz for six cycles (-70 mmHg), followed by a 3-min recovery before S-LBNP (-40 mmHg) for 7 min. Beat-to-beat middle cerebral artery blood velocity (MCAv) (transcranial Doppler) and blood pressure were continuously recorded. CA was assessed using transfer function analysis to calculate coherence, gain, and phase in the very-low-frequency (VLF; 0.020-0.070 Hz) and low-frequency bands (LF; 0.07-0.20 Hz). cBRS was calculated using the sequence method. Comparisons between POST vs. PRE are reported as mean ± SD. During O-LBNP, coherence VLF was greater at POST (0.55 ± 0.06 vs. 0.46 ± 0.08; P < 0.01), but phase VLF (P = 0.17) and gain VLF (P = 0.69) were not different. Coherence LF and phase LF were not different, but gain LF was lower at POST (1.03 ± 0.20 vs. 1.12 ± 0.30 cm/s/mmHg; P = 0.05). During S-LBNP, CA was not different in the VLF or LF bands (all P > 0.10). Up-cBRS and Down-cBRS were not different during both LBNP protocols. These preliminary data indicate that CA and cBRS during LBNP in healthy, young adults is largely unaffected by an acute bolus of BRJ.