CO2 Reserve Research Articles

Enhanced expiratory rebreathing space for high loop gain sleep apnea treatment

The pathophysiology of sleep apnea goes beyond anatomic predisposition to airway collapse and includes additional factors such as arousal threshold and loop gain. High loop gain is a prominent feature in central and complex sleep apnea (with a mixture of obstructive and central features) where relative hypocapnia can lead to respiratory instability and periodic breathing. Existing therapies, including continuous positive airway pressure (CPAP) and adaptive servo-ventilators, often inadequately treat sleep apnea with high loop gain features. Enhanced expiratory rebreathing space (EERS) targets prevention of the hypocapnia that triggers central events in sleep by increasing dead space in amounts less than typical tidal volumes. This is accomplished by covering traditional exhalation ports on positive airway pressure masks and adding small additional tubing with distal exhalation and safety valves. This technique reduces carbon dioxide (CO2) blow-off during arousals and the associated large recovery breaths, typically producing a maximal increase in resting CO2 by 1–2 mmHg, thus increasing the CO2 reserve and making it less likely to encounter the hypocapnic apneic threshold. Typically, the amount of EERS is titrated in response to central events and periodic breathing rather than aiming for a goal CO2 level. Ideally CO2 monitoring is used during titration of EERS and the technique is avoided in the setting of baseline hypercapnia. This method has been used in clinical practice at our sleep center for over 15 years, and retrospective data suggests an excellent safety profile and high rates of successful therapy including in patients who have previously failed CPAP therapy. Limitations include decreased effectiveness in the setting of leak and decreased tolerance of the bulkier circuit. EERS represents a simple, affordable modification of existing positive airway pressure modalities for treatment of central and complex sleep apnea. Areas of future study include randomized controlled trials of the technique and study of use of EERS in combination with adaptive ventilation, and pharmacologic adjuncts targeting high loop gain physiology.

Selecting Technologies for Sour and Ultra‐Sour Gas Treating

AbstractAs the cleanest fossil fuel, natural gas plays a key role in the path towards renewables. Considering the increasing gas demand, rich CO2 and H2S gas reserves, in the past considered economically unviable, are becoming fruitful. However, the non‐conventional nature of this kind of gases, in addition to the potentially higher production cost, raises the need of new strategies for their monetization, bypassing the conventional approaches. Starting from the huge number of novel large‐scale projects for the exploitation of rich‐H2S gas fields, this paper overviews the current tendencies in sour and ultra‐sour natural gas production, focusing on the removal of sulfur‐based compounds, together with H2S and CO2. At first, available technologies for ultra‐sour gas treatment are discussed. Then, simulations of the absorption processes based on a real case‐study are carried out, in order to verify the effectiveness of the proposed alternatives for the removal of mercaptans, as well as CO2 and H2S. Results are critically analyzed, in view of providing a practical guide of industrial interest for the selection of the most suitable method.

Numerical Simulation of CO2-ECBM Based on Multi-Physical Field Coupling Model

In this paper, heat injection and CO2 injection are combined, and the influence of coal seam parameters on CO2-ECBM is analyzed to improve the production of CH4 and CO2 reserves and the effective control of both greenhouse gases. A multi-physical field coupling model of CO2-ECBM was established based on Darcy’s law, Fick’s law of diffusion, the extended Langmuir model for adsorption, and the equation of state. Numerical simulation of CO2-ECBM under different coal seam parameters was carried out by COMSOL Multiphysics. The results show that increasing the injection pressure of the CO2 injection well and the initial pressure of the coal seam can effectively increase the gas pressure and concentration gradient, which has a positive effect on improving the extraction concentration of CH4 and the sequestration concentration of CO2 in the coal seam. The increase of the initial temperature of the coal seam will promote the desorption and diffusion of the binary elemental gas, resulting in a decrease in the concentration of coalbed methane and a decrease in the displacement effect. In the process of displacement, the greater the initial permeability, the greater the fracture opening of the coal seam, which is more conducive to the seepage transport of the gas. The closer to the position of the injection well, the better the displacement effect and the lower the permeability rate ratio.

Analysis Distribution of Biomass Carbon of Grasslands, Shrubs, and Rainfed Rice Fields on Dry Land in the Aceh Besar District Indonesia

Abstract This research was conducted to determine plant biomass, carbon potential, and CO2 reserve potential in understory vegetation in general, namely grasslands, shrubs, and rainfed rice fields. The sampling of the research was carried out randomly and intentionally, and was limited to the vegetation of reeds, shrubs and rainfed land bushes in the Aceh Besar District of Indonesia. The sample was taken based on a digitized map obtained from overlaying the land use map, slope map, soil type map, and Aceh Besar government map. Measurement of biomass in the vegetation of Imperata, shrubs, and rainfed rice fields is in accordance with procedures from the Indonesian National Standard (2011) and the World Agroforestry Center. The area of bush vegetation is larger than that of rainfed rice fields and grasslands. In general, the plants found in bush vegetation are Acacia leucoeplhoea, Mimosa pudica, Cyperus rotundus, and Eleusine indica. Grassland vegetation has one plant only, namely, Pennisetum purpureum. The vegetation of rainfed rice fields consists of the Oryza sativa type of plant. Plant biomass, carbon [C] content, and carbon potential in bush vegetation are greater than that of grassland and rainfed rice fields, as well as plant biomass reserves, plant biomass carbon and total CO2 reserves. Shrubs and woody plants render the potential for biomass, carbon, and CO2 absorption greater than that of grassland and rainfed rice fields. This is in accordance with the research that the increase in biomass is followed by an increase in potential carbon storage. Parameters that affect biomass indirectly will also affect carbon storage in a biomass and in an ecosystem, namely, individual density, stem diameter, tree species diversity, and soil. The density of trees in an area will affect the increase in carbon stocks through an increase in biomass. This is because the vegetation of shrubs does not only consist of undergrowth, but also of woody stems such as Acacia leucoeploea, making carbon stock potential in bush vegetation greater than that of grassland and rainfed rice fields, as shrubs cover an area of 96,962.2 ha, hence larger than that of grasslands and rainfed rice fields.

Assesment of the Quality of Reporting Information on CO2 Emission Rights on the Example of Energy Sector Groups Listed on the Warsaw Stock Exchange

Abstract Poland is a participant to the European Union Emissions Trading System, which aims at reducing greenhouse gas emissions. Trading CO2 emission rights has become a strategic area from the point of view of managing entities that emit CO2. The aim of the paper is to investigate and identify discrepancies in the presentation and valuation of CO2 emission allowances, CO2 emission provision liabilities in reporting, and to assess the impact of these discrepancies on compliance with the true and fair view principle on top of the informative value of the financial statements. An in-depth qualitative analysis was used to examine disclosures of CO2 emission rights in the 2020 consolidated financial statements coming from the largest energy sector groups listed in the WIG Energy Index of the Warsaw Stock Exchange in light of the relevant legal acts and literature. As a result of the research conducted, it was confirmed that groups of companies carry out a range of CO2 emission rights balance classification and valuation. There were also significant discrepancies in the disclosure of information about the creation and valuation of provisions for liabilities due to CO2 emissions. The discrepancies observed in the audited entities’ balance-sheet presentations and valuation of the acquired CO2 emission allowances and reserves resulting from IAS/IFRS in practice distorts the comparability of data presented in the financial statements. The research also revealed differences in scope of disclosed information, as well as its fragmentary nature. As a result, the comparison of data between groups in the energy sector in terms of their assets is impossible. Our study fills a research gap on the effects of using IFRS for the presentation and valuation of CO2 emission rights in the Polish energy sector and the impact of a differentiated approach to disclosures on the true and fair view conception in financial reporting.

Effect of Zolpidem on nocturnal arousals and susceptibility to central sleep apnea.

Arousals may contribute to the pathogenesis of sleep-disordered breathing (SDB) and central sleep apnea (CSA). We aimed to determine the effect of the nonbenzodiazepine hypnoticzolpidemon the frequency of respiratory-related arousals and central apneain patients withmoderate-to-severe SDB.We hypothesized thatzolpidemdecreasesthe severity of SDB by decreasingthe frequency ofrespiratory-related arousals. Patients with apnea-hypopnea index ≥ 15 events/hour and central apnea-hypopnea index ≥ 5 events/hour underwent a sleep study on zolpidem 5mg and a sleep study with no medication in a randomized order. The respiratory arousal index was compared between the two studies using a randomized crossover design. Sleep, respiratory, and physiologic parameters, including the CO2 reserve and the respiratory arousal threshold, were also compared. Eleven participants completed the study. Compared to no treatment, zolpidem reduced the respiratory arousal index (39.7 ± 7.7 vs. 23.3 ± 4.4 events/h, P = 0.031). Zolpidem also lowered the total apnea-hypopnea index (55.6 ± 8.5 vs. 41.3 ± 7.5 events/hour, P = 0.033) but did not affect other clinical and physiologic parameters. Compared to control, zolpidem did not widen CO2 reserve (- 0.44 ± 1.47 vs. - 0.63 ± 0.86mmHg, P = 0.81). The respiratory arousal threshold did not show a significant change on zolpidem compared to control (- 8.72 ± 2.1 vs. - 8.25 ± 2.81 cmH2O, P = 0.41). Nocturnal arousals and overall SDB severity were reduced with a single dose of zolpidem in patients with moderate-to-severe sleep-disordered breathing with increased susceptibility for central apnea. Zolpidem did not widen the CO2 reserve or increase the arousal threshold. Clinicaltrials.gov. Sleep and Breathing in the General Population - Chemical Stimuli (NCT04720547).

Mirtazapine reduces susceptibility to hypocapnic central sleep apnea in males with sleep-disordered breathing: a pilot study.

Studies in humans and animal models with spinal cord injury (SCI) have demonstrated that medications targeting serotonin receptors may decrease the susceptibility to central sleep-disordered breathing (SDB). We hypothesized that mirtazapine would decrease the propensity to develop hypocapnic central sleep apnea (CSA) during sleep. We performed a single-blind pilot study on a total of 10 men with SDB (7 with chronic SCI and 3 noninjured) aged 52.0 ± 11.2 yr. Participants were randomly assigned to either mirtazapine (15 mg at bedtime) or a placebo for at least 1 wk, followed by a 7-day washout period before crossing over to the other intervention. Split-night studies included polysomnography and induction of hypocapnic CSA using a noninvasive ventilation (NIV) protocol. The primary outcome was CO2 reserve, defined as the difference between eupneic and end of NIV end-tidal CO2 ([Formula: see text]) preceding induced hypocapneic CSA. Secondary outcomes included controller gain (CG), other ventilatory parameters, and SDB severity. CG was defined as the ratio of change in minute ventilation (V̇e) between control and hypopnea to the change in CO2 during sleep. CO2 reserve was significantly widened on mirtazapine than placebo (-3.8 ± 1.2 vs. -2.0 ± 1.5 mmHg; P = 0.015). CG was significantly decreased on mirtazapine compared with placebo [2.2 ± 0.7 vs. 3.5 ± 1.9 L/(mmHg × min); P = 0.023]. There were no significant differences for other ventilatory parameters assessed or SDB severity between mirtazapine and placebo trials. These findings suggest that the administration of mirtazapine can decrease the susceptibility to central apnea by reducing chemosensitivity and increasing CO2 reserve; however, considering the lack of changes in apnea-hypopnea index (AHI), further research is required to understand the significance of this finding.NEW & NOTEWORTHY To our knowledge, this research study is novel as it is the first study in humans assessing the effect of mirtazapine on CO2 reserve and chemosensitivity in individuals with severe sleep-disordered breathing. This is also the first study to determine the potential therapeutic effects of mirtazapine on sleep parameters in individuals with a spinal cord injury.

Chronic Opioid Use and Central Sleep Apnea, Where Are We Now and Where To Go? A State of the Art Review.

Opioids are commonly used for pain management, perioperative procedures, and addiction treatment. There is a current opioid epidemic in North America that is paralleled by a marked increase in related deaths. Since 2000, chronic opioid users have been recognized to have significant central sleep apnea (CSA). After heart failure-related Cheyne-Stokes breathing (CSB), opioid-induced CSA is now the second most commonly seen CSA. It occurs in around 24% of chronic opioid users, typically after opioids have been used for more than 2 months, and usually corresponds in magnitude to opioid dose/plasma concentration. Opioid-induced CSA events often mix with episodes of ataxic breathing. The pathophysiology of opioid-induced CSA is based on dysfunction in respiratory rhythm generation and ventilatory chemoreflexes. Opioids have a paradoxical effect on different brain regions, which result in irregular respiratory rhythm. Regarding ventilatory chemoreflexes, chronic opioid use induces hypoxia that appears to stimulate an augmented hypoxic ventilatory response (high loop gain) and cause a narrow CO2 reserve, a combination that promotes respiratory instability. To date, no direct evidence has shown any major clinical consequence from CSA in chronic opioid users. A line of evidence suggested increased morbidity and mortality in overall chronic opioid users. CSA in chronic opioid users is likely to be a compensatory mechanism to avoid opioid injury and is potentially beneficial. The current treatments of CSA in chronic opioid users mainly focus on continuous positive airway pressure (CPAP) and adaptive servo-ventilation (ASV) or adding oxygen. ASV is more effective in reducing CSA events than CPAP. However, a recent ASV trial suggested an increased all-cause and cardiovascular mortality with the removal of CSA/CSB in cardiac failure patients. A major reason could be counteracting of a compensatory mechanism. No similar trial has been conducted for chronic opioid-related CSA. Future studies should focus on (1) investigating the phenotypes and genotypes of opioid-induced CSA that may have different clinical outcomes; (2) determining if CSA in chronic opioid users is beneficial or detrimental; and (3) assessing clinical consequences on different treatment options on opioid-induced CSA.

Buspirone decreases susceptibility to hypocapnic central sleep apnea in chronic SCI patients.

Spinal cord injury (SCI) is a risk factor for central sleep apnea (CSA). Previous studies in animal models with SCI have demonstrated a promising recovery in respiratory and phrenic nerve activity post-injury induced by the systemic and local administration of serotonin receptor agonists such as Buspirone and Trazodone. Human trials must be performed to determine whether individuals with SCI respond similarly. We hypothesized that Buspirone and Trazodone would decrease the propensity to hypocapnic CSA during sleep. We studied eight males with chronic SCI and sleep-disordered breathing (SDB) [age: 48.8 ± 14.2 yr; apnea-hypopnea index (AHI): 44.9 ± 23.1] in a single-blind crossover design. For 13 days, participants were randomly assigned either Buspirone (7.5-15 mg twice daily), Trazodone (100 mg), or a placebo followed by a 14-day washout period before crossing over to the other interventions. Study nights included polysomnography and induction of CSA using a noninvasive ventilation protocol. We assessed indexes of SDB, CO2 reserve, apneic threshold (AT), controller gain (CG), plant gain (PG), and ventilatory parameters. CO2 reserve was significantly widened on Buspirone (-3.6 ± 0.9 mmHg) compared with both Trazodone (-2.5 ± 1.0 mmHg, P = 0.009) and placebo (-1.8 ± 1.5 mmHg, P < 0.001) but not on Trazodone vs. placebo (P = 0.061). CG was significantly decreased on Buspirone compared with placebo (1.8 ± 0.4 vs. 4.0 ± 2.0 L/(mmHg·min), P = 0.025) but not on Trazodone compared with placebo (2.5 ± 1.1 vs. 4.0 ± 2.0 L/(mmHg·min); P = 0.065). There were no significant differences for PG, AT, or any SDB indexes (AHI, obstructive apnea index, central apnea index, oxygen desaturation index). The administration of Buspirone decreased the susceptibility to induced hypocapnic central apnea by reducing chemosensitivity and increasing CO2 reserve in chronic SCI patients.NEW & NOTEWORTHY This research study is novel as it is the first study in a humans that we are aware of that demonstrates the ability of Buspirone to increase CO2 reserve and hence decrease susceptibility to hypocapnic central apnea in patients with spinal cord injury.

Determination of optimum CO2 water alternating gas (CO2-WAG) ratio in Sumatera Light Oilfield

The CO2 Water Alternating Gas (CO2-WAG) injection method, allows the oil to first expand and become better able to flow because of the CO2, and then the water increases the pressure in the reservoir to flush this newly freed oil to production wells. This study is in Sarolangun District, Jambi Province which is prospect of CO2 injection tertiary recovery project due to its abundant CO2 reserve. The success of CO2-WAG injection can be determined by investigating ratios between CO2 and water. The goal of this study is to determine optimum CO2-WAG injection ratio in Sumatera Light Oilfield. This study is done through a numerical simulation of immiscible CO2-WAG which is conducted under three scenarios of ratio using both CMG WINPROP and GEM simulator. The CO2/water ratios are varied from 1:1, 2:1 and 1:2. The study results show that the CO2/water 1:2 is the best CO2-WAG injection ratio that gives highest additional oil recovery factor of 35.24%. Additional recovery factor given by CO2/water ratio 2:1 and 1:1 is 1.49% and 19.52% respectively. Based on this study, the effect of CO2-WAG ratio to oil productivity is depending of amount of water injected. Lower initial oil viscosity lead to an insignificant effect of CO2. Proper CO2-WAG injection ratio will give an optimum oil recovery. This works will have a great use in the CO2-Enhanced Oil Recovery (EOR) application.

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.

Numerical Simulation of the Effect of Injected CO2 Temperature and Pressure on CO2-Enhanced Coalbed Methane

The injection of CO2 to displace CH4 in coal seams is an effective method to exploit coalbed methane (CBM), for which the CO2 injection temperature and pressure are important influential factors. We performed simulations, using COMSOL Multiphysics to determine the effect of CO2 injection temperature and pressure on CO2-enhanced coalbed methane (CO2-ECBM) recovery, according to adsorption/desorption, seepage, and diffusion of binary gas (CO2 and CH4) in the coal seam, and deriver a thermal–hydraulic–mechanical coupling equation of CO2-ECBM. The simulation results show that, as CO2 injection pressure in CO2-ECBM increases, the molar concentration and displacement time of CH4 in the coal seam significantly decrease. With increasing injection temperature, the binary gas adsorption capacity in the coal seam decreases, and CO2 reserves and CH4 production decrease. High temperatures are therefore not conducive for CH4 production.

Restriction of gas losses in an overpressurised CO&lt;SUB align="right"&gt;2 reservoir using gel technology

The overpressurised CO2 field Bečej (Serbia) was explored in 1951. At the end of 1968, an uncontrolled gas blowout of Bč-5 well lasted 209 days resulting in 35 bars pressure drop in the reservoir until 2007. Hence, the substantial loss of reserve (> 17 billion m3) became a critical issue of the operator. Environmental friendly chemicals should be used only for well rehabilitation. Therefore, silicate-based method was recommended for the job. A triangle well pattern, inverted injection protocol and huge volume of treating solution were used to cure the problem. Placing the inorganic gel-forming chemicals into the target area, the annual decline of formation pressure was merely 0.03 bar/y compared to 0.9 bar/y prior to treatment. Thus, the uncontrolled gas flow was practically terminated, the loss of CO2 reserve minimised, CO2 emission to atmosphere was limited and the well against repeated gas blowout was also stabilised.

Alternative approaches to treatment of Central Sleep Apnea.

Divergent approaches to treatment of hypocapnic central sleep apnea syndromes reflect the difficulties in taming a hyperactive respiratory chemoreflex. As both sleep fragmentation and a narrow CO2 reserve or increased loop gain drive the disease, sedatives (to induce longer periods of stable non-rapid eye movement (NREM) sleep and reduce the destabilizing effects of arousals in NREM sleep) and CO2-based stabilization approaches are logical. Adaptive ventilation reduces mean hyperventilation yet can induce ventilator-patient dyssynchrony, while enhanced expiratory rebreathing space (EERS, dead space during positive pressure therapy) and CO2 manipulation directly stabilize respiratory control by moving CO2 above the apnea threshold. Carbonic anhydrase inhibition can provide further adjunctive benefits. Provent and Winx may be less likely to trigger central apneas or periodic breathing in those with a narrow CO2 reserve. An oral appliance can meaningfully reduce positive pressure requirements and thus enable treatment of complex apnea. Novel pharmacological approaches may target mediators of carotid body glomus cell excitation, such as the balance between gas neurotransmitters. In complex apnea patients, single mode therapy is not always successful, and multi-modality therapy might need to be considered. Phenotyping of sleep apnea beyond conventional scoring approaches is the key to optimal management.

Testosterone Conversion Blockade Increases Breathing Stability in Healthy Men during NREM Sleep

Gender differences in the prevalence of sleep apnea/hypopnea syndrome may be mediated via male sex hormones. Our objective was to determine the exact pathway for a testosterone-mediated increased propensity for central sleep apnea via blockade of the 5α-reductase pathway of testosterone conversion by finasteride. Randomization to oral finasteride vs. sham, single-center study. Sleep research laboratory. Fourteen healthy young males without sleep apnea. Hypocapnia was induced via brief nasal noninvasive positive pressure ventilation during stable NREM sleep. Cessation of mechanical ventilation resulted in hypocapnic central apnea or hypopnea. The apnea threshold (AT) was defined as the end-tidal CO₂(P(ET)CO₂) that demarcated the central apnea closest to the eupneic P(ET)CO₂. The CO₂ reserve was defined as the difference in P(ET)CO₂ between eupnea and AT. The apneic threshold and CO₂ reserve were measured at baseline and repeated after at a minimum of 1 month. Administration of finasteride resulted in decreased serum dihydrotestosterone. In the finasteride group, the eupneic ventilatory parameters were unchanged; however, the AT was decreased (38.9 ± 0.6 mm Hg vs.37.7 ± 0.9 mm Hg, P = 0.02) and the CO₂ reserve was increased (-2.5 ± 0.3 mm Hg vs. -3.8 ± 0.5 mm Hg, P = 0.003) at follow-up, with a significantly lower hypocapnic ventilatory response, thus indicating increased breathing stability during sleep. No significant changes were noted in the sham group on follow-up study. Inhibition of testosterone action via the 5α-reductase pathway may be effective in alleviating breathing instability during sleep, presenting an opportunity for novel therapy for central sleep apnea in selected populations.

Complex Sleep Apnea

Complex sleep apnea currently refers to the emergence and persistence of central apneas and hypopneas following the application of positive airway pressure therapy in patients with obstructive sleep apnea. However, this narrow definition is an "outcome" and does not capture the spectrum of pathological activation of the respiratory chemoreflex in sleep apnea. The International Classification of Sleep Disorders - 3rd edition recognizes the phenomenon of Treatment-Related Central Sleep Apnea, but the phenotype is usually evident prior to onset of therapy. The key polysomnographic characteristics of chemoreflex modulated and mediated sleep apnea are nonrapid eye movement (NREM) dominance of respiratory events, short (<30seconds) or long (>60seconds) cycle time with a self-similar metronomic timing, and spontaneous improvement during rapid eye movement (REM) sleep. Thus, the majority of chemoreflex effects go unrecognized due to the bias toward obstructive sleep apnea's current scoring criteria. Any treatment of apparently obstructive sleep apnea, including surgery and oral appliances, can expose chemoreflex-driven instabilities. As both sleep fragmentation and a narrow CO2 reserve or increased loop gain drive the disease, sedatives (to induce longer periods of stable NREM sleep and reduce the destabilizing effects of arousals in NREM sleep) and CO2-based stabilization approaches are logical. Adaptive ventilation reduces mean hyperventilation yet can induce ventilator-patient desynchrony, while enhanced expiratory rebreathing space (EERS, dead space during positive pressure therapy) and CO2 manipulation directly stabilize respiratory control by moving CO2 above the apnea threshold. Carbonic anhydrase inhibition can provide further adjunctive benefits. Novel pharmacological approaches may target mediators of carotid body hypoxic sensitization, such as the balance between gas neurotransmitters. In complex apnea patients, single mode therapy is unlikely to be successful, and the power of multi-modality therapy should be harnessed for optimal outcomes.

Tetraplegia is a risk factor for central sleep apnea

Sleep-disordered breathing (SDB) is highly prevalent in patients with spinal cord injury (SCI); the exact mechanism(s) or the predictors of disease are unknown. We hypothesized that patients with cervical SCI (C-SCI) are more susceptible to central apnea than patients with thoracic SCI (T-SCI) or able-bodied controls. Sixteen patients with chronic SCI, level T6 or above (8 C-SCI, 8 T-SCI; age 42.5 ± 15.5 years; body mass index 25.9 ± 4.9 kg/m(2)) and 16 matched controls were studied. The hypocapnic apneic threshold and CO2 reserve were determined 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 CO2 (PetCO2) before and after. Steady-state plant gain (PG) was calculated from PetCO2 and VE ratio during stable sleep. Controller gain (CG) was defined as the ratio of change in VE between control and hypopnea or apnea to the ΔPetCO2. Central SDB was more common in C-SCI than T-SCI (63% vs. 13%, respectively; P < 0.05). Mean CO2 reserve for all participants was narrower in C-SCI than in T-SCI or control group (-0.4 ± 2.9 vs.-2.9 ± 3.3 vs. -3.0 ± 1.2 l·min(-1)·mmHg(-1), respectively; P < 0.05). PG was higher in C-SCI than in T-SCI or control groups (10.5 ± 2.4 vs. 5.9 ± 2.4 vs. 6.3 ± 1.6 mmHg·l(-1)·min(-1), respectively; P < 0.05) and CG was not significantly different. The CO2 reserve was an independent predictor of apnea-hypopnea index. In conclusion, C-SCI had higher rates of central SDB, indicating that tetraplegia is a risk factor for central sleep apnea. Sleep-related hypoventilation may play a significant role in the mechanism of SDB in higher SCI levels.

Dead Space Mask Eliminates Central Apnea at Altitude

Travelers to high altitude may have disturbed sleep due to periodic breathing with frequent central apneas. We tested whether a mask with added dead space could reduce the central apneas of altitude. 16 subjects were recruited, age 18-35, residing at 4600 ft (1400 m). They each slept one night with full polysomnographic monitoring, including end tidal CO2, in a normobaric hypoxia tent simulating 12,000 ft. (3658 m) altitude. Those who had a central apnea index (CAI) >20/h returned for a night in the tent for dead space titration, during which they slept with increasing amounts of dead space, aiming for a CAI <5/h or <10% of baseline. Then each subject slept another night with the titrated amount of dead space. Of the 16 subjects, 5 had a central apnea index >20/h mean 49.1, range 21.4-131.5/hr. In each of the 5, the dead space mask reduced the CAI by at least 88% to a mean of 3.1, range 0.9-7.1/h, (p=0.04). Hypopnea index was unchanged. Three subjects required 500 cc of dead space or less. One subject required 860 cc, and one required 2.1 L. Morning symptoms and arousal index were not significantly affected by the dead space mask. Dead space did not appear to increase the CO2 reserve. At 12,000 ft., central apneas can be effectively reduced with a dead space mask, but clinical utility will require further evaluation.

The essential role of peripheral respiratory chemoreceptor inputs in maintaining breathing revealed when CO2 stimulation of central chemoreceptors is diminished

Central sleep apnoea is a condition characterized by oscillations between apnoea and hyperpnoea during sleep. Studies in sleeping dogs suggest that withdrawal of peripheral chemoreceptor (carotid body) activation following transient ventilatory overshoots plays an essential role in causing apnoea, raising the possibility that sustaining carotid body activity during ventilatory overshoots may prevent apnoea. To test whether sustained peripheral chemoreceptor activation is sufficient to drive breathing, even in the absence of central chemoreceptor stimulation and vagal feedback, we used a vagotomized, decerebrate dual-perfused in situ rat preparation in which the central and peripheral chemoreceptors are independently and artificially perfused with gas-equilibrated medium. At varying levels of carotid body stimulation (CB PO2/PCO2: 40/60, 100/40, 200/15, 500/15 Torr), we decreased the brainstem perfusate PCO2 in 5 Torr steps while recording phrenic nerve activity to determine the central apnoeic thresholds. The central apnoeic thresholds decreased with increased carotid body stimulation. When the carotid bodies were strongly stimulated (CB 40/60), the apnoeic threshold was 3.6 ± 1.4 Torr PCO2 (mean ± SEM, n = 7). Stimulating carotid body afferent activity with either hypercapnia (60 Torr PCO2) or the neuropeptide pituitary adenylate cyclase-activating peptide restored phrenic activity during central apnoea. We conclude that peripheral stimulation shifts the central apnoeic threshold to very hypocapnic levels that would likely increase the CO2 reserve and have a protective effect on breathing. These data demonstrate that peripheral respiratory chemoreceptors are sufficient to stave off central apnoeas when the brainstem is perfused with low to no CO2.

The Estimation of Appropriateness for CO&lt;sub&gt;2&lt;/sub&gt; Geological Sequestration Based on Well Logging

CO2 geological sequestration is one of the most promising methods for reducing anthropogenic CO2 emission into the atmosphere. To carry out the technology, it is necessary to evaluate the formation geological condition of storage area for the security and effectiveness. The CO2 reserve capability of formation is mostly connected with reservoir physical property. The CO2 storage security is mostly connected with seal quality of cap rock. This paper takes advantage of logging data material to comprehensively evaluate the seal condition and storage capability from the cap rock condition of the supercritical fluid and the reservoir capacity. It gives an evaluation instance of the slected area.