CO2 Output Research Articles

Minute ventilation and heart rate relationship for estimation of the ventilatory compensation point at high altitude: a pilot study.

BackgroundThe ventilatory compensation point (VCP) is an exercise threshold which has been used in the design of training programs in sports medicine and rehabilitation. We recently demonstrated that changes in the slope of the minute ventilation to heart rate relationship () can be utilized for estimation of the VCP during incremental exercise at sea level (SL). We hypothesized that in hypoxic conditions, such as high altitude (HA), VCP can be also reliably estimated by .MethodsAt SL and on immediate ascent to HA (5,050 m), six healthy subjects (42 ± 14 SD years) performed a maximal incremental exercise test on a cycle ergometer; O2 uptake (), CO2 output (), , and HR were measured breath-by-breath. The method for VCP estimation was compared to the standard method using the ventilatory equivalent for CO2 () and end-tidal PCO2 (PETCO2). The slope values below (S1) and above (S2) VCP were computed by linear regression analysis.ResultsA significant difference between S1 and S2 was observed, at SL and HA, for both the and methods for VCP estimation. A good agreement between the two methods ( vs. ) was found for both environmental conditions; the mean difference ± 2 SD of at VCP (VCP-) was −22 ± 112 ml/min at SL and 39 ± 81 ml/min at HA. The VCP- was significantly lower at HA compared to SL; in addition, S1 and S2 mean values were significantly higher at HA compared to SL.ConclusionAt HA, VCP may be reliably estimated by the method.

Comparison of the behavior of biofuel based on castor and sunflower oils

This article presents the results of the comparison of two experimental studies to obtain biodiesel from castor and sunfl ower oils. During the development of the projects a standard methodology was adopted that defi ned the physical and chemical parameters of the biodiesel as a sunfl ower and Castor oil originated biofuel. To obtain a comparative model and maximize the performance of castor and sunfl ower oils, the NTC 100/04 standard was chosen, using the mix ratio 5, 10, and 20%, respectively, of biodiesel. Complying with the NTC 100/04 standard, the recommended parameters were followed in the tests performed to compare the results obtained. The methodology chosen allowed assessing the behavior of the combustion gases to achieve the final combustion composition, as well as the development of a comparison between the two biofuels with the fossil fuel (pure diesel) used in diesel engines in Colombia. This study was carried out in Bogota (2600 m above sea level), and as a result there was a slight decrease in CO2 and CO output of combustion gases comparing the pure ACPM (oil fuel for engines) and the Biodiesel, for the various mixtures proposed under the ICONTEC norm.

Next Scale Chemical Looping Combustion: process Integration and Part Load Investigations for a 10MW Demonstration Unit

Chemical looping combustion (CLC) is a second generation carbon capture process and is discussed as a potential breakthrough technology with respect to CO2 avoidance costs. The potential of CLC has already been successfully demonstrated at scales up to 140kW power input, using gaseous fuels. The next stage of process evolution is the development of a CLC demonstration plant at industrial scale, to gain sufficient confidence in the technology for further up-scaling. In this work, the integration of a next scale CLC demonstration plant at 10MW fuel power input into a steam generating system of a commercial natural gas combined cycle (NGCC) plant with supplementary firing is investigated. The attached CLC demonstration plant is designed to substitute the energy input of the supplementary firing which in turn can easily compensate fluctuation from demonstration plant operation with very little response time or even increase the overall power output in parallel operation with the CLC plant. Such a system exhibits the advantage that power output from the CLC unit would not contribute to the CO2 footprint of the site, thus improving the CO2 output balance. Demonstration plant operation including part load and control behavior is investigated by detailed mass and energy balance investigations. This work can be used as a basis for detailed engineering of a next scale 10MW chemical looping combustion demonstration unit.

Feasibility of CO2 Geological Storage in the Xingou Oil Field, Jianghan Basin, China

Geological storage of CO2 as an effective way of reducing CO2 output to the atmosphere receives growing attention worldwide. To evaluate the feasibility of this technique in the Xingou oil field of Jianghan Basin in China, 2D and 3D models of CO2 geological storage were established using TOUGH2 software. Results showed that CO2 gas can be stored in the deepest reservoir through continuous injection over 50 years, and will remain effectively confined within the space under the second caprock during its diffusion over 500 years. Compared with 2D models, 3D models showed that the diffusion process of CO2 gas in the reservoir will create a mushroom-shaped zone of influence.

Diffuse volcanic degassing and thermal energy release from Hengill volcanic system, Iceland

We report the first detailed study of spatial variations on the diffuse emission of carbon dioxide (CO2) and hydrogen sulfide (H2S) from Hengill volcanic system, Iceland. Soil CO2 and H2S efflux measurements were performed at 752 sampling sites and ranged from nondetectable to 17,666 and 722 g m−2 day−1, respectively. The soil temperature was measured at each sampling site and used to evaluate the heat flow. The chemical composition of soil gases sampled at selected sampling sites during this study shows they result from a mixing process between deep volcanic/hydrothermal component and air. Most of the diffuse CO2 degassing is observed close to areas where active thermal manifestations occur, northeast flank of the Hengill central volcano close to the Nesjavellir power plant, suggesting a diffuse degassing structure with a SSW–NNE trend, overlapping main fissure zone and indicating a structural control of the degassing process. On the other hand, H2S efflux values are in general very low or negligible along the study area, except those observed at the northeast flank of the Hengill central volcano, where anomalously high CO2 efflux and soil temperatures were also measured. The total diffuse CO2 emission estimated for this volcanic system was about 1,526 ± 160 t day−1 of which 453 t day−1 (29.7 %) are of volcanic/hydrothermal origin. To calculate the steam discharge associated with the volcanic/hydrothermal CO2 output, we used the average H2O/CO2 mass ratio from 12 fumarole samples equal to 88.6 (range, 9.4–240.2) as a representative value of the H2O/CO2 mass ratios for Hengill fumarole steam. The resulting estimate of the steam flow associated with the gas flux is equal to 40,154 t day−1. The condensation of this steam results in thermal energy release for Helgill volcanic system of 1.07 × 1014 J day−1 or to a total heat flow of 1,237 MWt.

CO2 output discharged from Stromboli Island (Italy)

Total CO2 output from soil gas and plume, discharged from the Stromboli Island, was estimated. The CO2 emission of the plume emitted from the active crater was estimated on the basis of the SO2 crater output and C/S ratio, while CO2 discharged through diffuse soil emission was quantified on the basis of 419 measurements of CO2 fluxes from the soil of the whole island, performed by using the accumulation chamber method. The results indicate an overall output of ≅416tday−1 of CO2 from the island. The main contribution to the total CO2 output comes from the summit area (396tday−1), with 370t/day from the active crater and 26tday−1 from the Pizzo sopra La Fossa soil degassing area. The release of CO2 from peripheral areas is ≅20tday−1 by soil degassing (Scari area mainly). The result of the soil degassing survey confirms the persistence of the highest CO2 degassing areas located on the North-East crater side and Scari area.

Respiratory metabolism of the pea aphid, Acyrthosiphon pisum (Hemiptera: Aphididae)

The respiratory metabolism of different polyphenic forms of the pea aphid, including wingless and winged asexual females (virginoparae), sexual females (oviparae) and winged or wingless adult males, was investigated using a micro-respirographic method. The records revealed sub-nanoliter amounts per min of O2 consumption or CO2 output. Respiratory metabolism of individuals was monitored for 3 to7 h after removal of the aphid from the food plant. Most of the recordings were for relatively large (3.5 mg), wingless asexual females (virginoparae). These aphids exhibited a continuous and very regular respiratory gas exchange (example: specimen of 3.5 mg body mass consumed 180 nl of O2 per min; released simultaneously 300 nl CO2 per min; = standard metabolic rate of 3085 µl O2 / g / h; R.Q. = 1.66). This continuous pattern of respiration occurred only when the aphids were kept at relatively high humidity. By contrast, aphids of various seasonal forms exhibited discontinuous respiratory gas exchange when kept in relatively dry air (atmospheric, room conditions). These patterns can be briefly described as follows: (a) Short and rather small micro-cycles of CO2 emission, manifested usually by the sudden expiration of 60-120 nl of CO2 once every 5 min; (b) Larger bursts of 240-480 nl of CO2 with a periodicity of one hour; (c) Enormously large, discontinuous bursts of 10-14 µl CO2, duration 10-30 min, repeated with a periodicity of several hours. There was no constant pattern of diffusive CO2 emission (DGC). The aphids exhibited a pattern of CO2 release that was appropriate for the external conditions, such as temperature and humidity, and internal physiological conditions such as metabolic activity, availability of reserve substances (carbohydrate, lipid) and water. Certain stages (wingless virginoparae) exhaled volumes of CO2 greatly in excess of their O2 consumption (R.Q. over 1.5). Sudden exhalations of CO2 from the body were a consequence of a bulk production and outflow of CO2 and not due to the diffusion of CO2 previously accumulated within the tracheal system. Due to their generally high metabolic activity (1142 to 6780 µl O2 / g / h), aphid tissue and organs produced relatively large amounts of metabolically formed carbonic acid. The resulting respiratory acidaemia was moderated by outbursts of gaseous CO2, liberated from liquid carbonate buffers by a regulatory mechanism based on enzymatic hydration and neutralization of carbonic acid by discontinuous formation of gaseous CO2.

Analysis of long- and short-term temporal variations of the diffuse CO2 emission from Timanfaya volcano, Lanzarote, Canary Islands

Abstract Reported herein are the results of eight soil CO2 efflux surveys performed from 2006 to 2011 at Timanfaya Volcanic Field (TVF), Lanzarote Island with the aim of evaluating the long- and short-term temporal variations of the diffuse CO2 emission. Soil CO2 efflux values ranged from non-detectable up to 34.2 g m−2 d−1, with the highest values measured in September 2008. Conditional sequential Gaussian simulations (sGs) were applied to construct soil CO2 efflux distribution maps and to estimate the total CO2 output from the studied area at the TVF. Soil CO2 efflux maps showed a high spatial and temporal variability. Total CO2 emission rates ranged between 41 and 518 t d−1, February 2011 (winter) being the season when maximum diffuse CO2 emission rates were observed. To investigate the influence of external variables on the soil CO2 efflux, a geochemical station (LZT01) was installed at TVF to measure continuously the soil CO2 efflux between July 2010 and March 2012 Since external factors such as barometric pressure, rainfall, soil water content, soil and air temperatures, and wind speed influence strongly the observed soil CO2 effluxes, multiple regression analysis was applied to the time series recorded by the automatic geochemical station LZT01 to remove the contribution of these external factors. The influence of meteorological variables on soil CO2 efflux oscillations accounts for 13% of total variance, with barometric pressure, rainfall and/or soil water content having the most influence in the control of the soil CO2 efflux. These observations along with the results from the eight soil gas surveys performed at TVF indicate that the short and long-term trends in the diffuse CO2 degassing are mainly controlled by environmental factors.

The green paradox: a supply-side approach to global warming

The Earth is getting warmer. Yet, as Hans-Werner Sinn points out in this provocative book, the dominant policy approach -- which aims to curb consumption of fossil energy -- has been ineffective. Despite policy makers' efforts to promote alternative energy, impose emission controls on cars, and enforce tough energy-efficiency standards for buildings, the relentlessly rising curve of CO2 output does not show the slightest downward turn. Some proposed solutions are downright harmful: cultivating crops to make biofuels not only contributes to global warming but also uses resources that should be devoted to feeding the world's hungry. In The Paradox, Sinn proposes a new, more pragmatic approach based not on regulating the demand for fossil fuels but on controlling the supply. The owners of carbon resources, Sinn explains, are pre-empting future regulation by accelerating the production of fossil energy while they can. This is the Green Paradox: expected future reduction in carbon consumption has the effect of accelerating climate change. Sinn suggests a supply-side solution: inducing the owners of carbon resources to leave more of their wealth underground. He proposes the swift introduction of a Super-Kyoto system -- gathering all consumer countries into a cartel by means of a worldwide, coordinated cap-and-trade system supported by the levying of source taxes on capital income -- to spoil the resource owners' appetite for financial assets. Only if we can shift our focus from local demand to worldwide supply policies for reducing carbon emissions, Sinn argues, will we have a chance of staving off climate disaster.

Balance of CO2/CH4 exchange sorption in a coal briquette

The article presents findings of a study on CO2/CH4 exchange sorption taking place in a coal briquette, initiated by the injection of a CO2 into a briquette that was previously saturated with CH4. The briquette was subjected to multiple cycles consisting of vacuum outgassing, CH4 saturation under 10bar pressure, and an exchange sorption process. In each experiment input CO2 pressure and output gas mixture pressure were stabilized. The chosen pressure levels were 12, 13 and 11bar at the input and 10bar at the output of the briquette. Flow rate of gas streams flowing to and flowing out of the briquette, as well as gas concentration at the output of the briquette, was measured. During the process of exchange sorption, the flow rate of gas streams at the input and output of the briquette varied, even though the input and output pressures were constant. In all the experiments, the entire CH4 was displaced from the briquette after injecting about twice the rate of the CO2 mass in relation to the previously sorptive bonded CH4. The results thus obtained were confronted with results obtained by other researchers, available in relevant sources, for the purpose of their comparison.

Simulation of industrial-scale CO2 storage: Multi-scale heterogeneity and its impacts on storage capacity, injectivity and leakage

Heterogeneities in porosity and permeability of geological CO2 storage reservoirs and surrounding strata have a significant influence on storage capacity, design of injection wells, CO2 injection rate, potential leakage, CO2 plume migration, and risk assessment. This study develops a methodology that applies a transition probability based Markov chain model to generate facies-based heterogeneous fields of reservoir and cap-rock porosity and permeability at the Rock Springs Uplift, Wyoming. This site was chosen for its proximity to the Jim Bridger power plant that generates 18Mt of CO2 per year. The heterogeneous fields are then used as input to simulations of CO2 injection in a numerical domain with geologic strata based on a 3D seismic model. We next use the multiphase flow simulator FEHM in Monte Carlo mode to generate 42 realizations of injection into the Weber sandstone. The model is constrained by two requirements. First, the effects of storage must be contained in the 16×16km working footprint (i.e. the injection pressure pulse and CO2 plume are not allowed to expand beyond the simulation domain) and second, injection pressures must not exceed 75% of the lithostatic load to limit seismic risks. Analysis of simulation results reveals that: (1) CO2 storage capacity for the Weber formation in the entire Rock Springs Uplift is 6614±256Mt at 95% confidence interval, about 36% of a previous estimate based on homogeneous and isotropic properties; (2) single well CO2 injection rates vary with time and with local permeability distributions. The injectivity at the end of 50 years of injection follows a log normal distribution and reaches a mean of 0.43Mt/year with a range of 0.06–3.22Mt/year within two standard deviations (1σ=0.09Mt/year); and (3) CO2 leakage into the cap-rock (Chugwater formation) is limited to 0.8±3.4Mt over the 50 years of injection. In addition, brine production rates required to maintain pressure in the working footprint are of nearly equal volume to the injected CO2. Within the CO2 plume at this deep site, CO2 has density of greater than 80% of the ambient brine, indicating that the CO2 plume evolution will be controlled more by fluid pressure gradients than by buoyant flow. These results suggest that injection into the Weber sandstone in a single 16×16km working footprint on the Rock Springs Uplift could likely store the total CO2 output of the Jim Bridger power plant for approximately 35 years with less than 1% leakage into the cap-rock. This plan would require 26±3 injection wells with likely an equal number or more of brine production wells around the perimeter of the working footprint. Assuming wells at a cost of $6M each, this would add less than $1/tonne to the cost of the storage, a small fraction of current capture costs. Finally, brine production on the order of 1km3 is required to minimize the risk of geomechanical failure and ensure limited pressure perturbation outside the working footprint.

Ventilatory efficiency in juvenile elite cyclists

ObjectivesVentilation (V′E) as a function of CO2 output, and oxygen uptake (V′O2) as a function of log10 V′E, define cardio-respiratory efficiency, although few data compare efficiency with maximum oxygen uptake (V′O2max), or consider reproducibility. Currently there are no data for trained juveniles. DesignTwenty-five trained juvenile cyclists (mean age 14.7 years), performed maximal exercise testing on two occasions, separated by 16 weeks. MethodsV′E vs. V′CO2 slope, oxygen uptake efficiency slope, and V′O2max were measured during cycle ergometer exercise to volitional exhaustion on two occasions, 16 weeks apart. ResultsMean (SD) V′E vs. V′CO2 slope, oxygen uptake efficiency slope, and V′O2max were 28.14 (3.89), 4.16 (0.73), and 75.4 (8.9) mlkg−1min−1 on visit 1, and 27.92 (4.63), 4.22 (0.76), and 73.6 (9.3) mlkg−1min−1 on visit 2. Good reproducibility (differences ≤2.4%), but poor correlations (r≤0.29) between efficiency and V′O2max were recorded. ConclusionsReproducibility of efficiency measures was comparable to V′O2max, however, poor associations between efficiency and V′O2max suggested independence. Efficient ventilation may be of limited importance in determining the V′O2max in a trained juvenile cyclist.

Pore pressure changes accompanying exchange sorption of CO2/CH4 in a coal briquette

The paper presents the study of CO2/CH4 exchange sorption in a coal briquette. The briquette was formed inside a heavy-walled steel pipe that served the purpose of a measuring chamber. The briquette with a porosity of 8.3%, a diameter of 0.096m and a length of 0.280m was used. Three laboratory experiments were conducted. The experiments consisted in CO2 injecting onto the input of the briquette previously saturated with CH4. In each experiment, during the exchange sorption process, the input CO2 pressure and output gas mixture pressure were stabilized at the level of 11, 12 and 13bar at the input and 10bar at the output of the briquette. Pressure changes along the briquette and concentration of the gas mixture flowing out of the briquette were analyzed. It was observed that a pore pressure depression moving along the briquette accompanies the exchange sorption. The presence of the pore pressure depression indicated existence of a separated zone where exchange sorption takes place. It was also observed that from the moment that CO2 appeared at the output of the briquette, sudden changes of its concentration were recorded. This phenomenon confirms the thesis of the exchange zone occurrence accompanying the CO2/CH4 exchange sorption in the briquette. A description method of the observed phenomenon was proposed.

Gastric CO2 output via the esophagus increases during systemic hypercapnia in anesthetized cat

The stomach extracts arterial CO2 during respiratory acidosis to produce HCl & HCO3−, which react in the lumen to re‐form CO2. This study tested the hypothesis that hypercapnia stimulates gastric CO2 removal via the esophagus. Tracheal and esophageal CO2 (PEsCO2) and flows were measured in 13 anesthetized, pyloric occluded cats. Tracheal and gastric CO2 output (V̇ GCO2) and gastric minute ventilation (V̇ G) were calculated during tracheal air breathing for 30min (Control) and CO2 breathing: 10%CO2 in air (1hr), recovery in air (30min), followed by 6×10min alternating paired bouts of 10%CO2 and air (10CO2, 10air). CO2 breathing increased PEsCO2 above control 77% after 1hrCO2 and 123% during 10CO2. Coughing revealed more CO2 was present in the stomach: PEsCO2 increased 134% (in air) and 115% (after 1hrCO2) compared to pre‐cough PEsCO2. V̇ GCO2 ranged from 0–15% (X̄=2.5%) of total CO2 output during 1hrCO2. V̇ G was 27% higher during 10CO2 versus 10air. Relative to control, V̇ G increased 95% after 1 hrCO2 and 148% after the first bout of 10minCO2. The results show a dynamic, supplemental CO2‐eliminating response by the gastroesophageal system during systemic hypercapnia (NIH HL89104, HL103415 & ONR).

A useful, innovative, and visual method to quantify fitness and heart failure

We have reported that the highest ratios of O2 uptake and CO2 output to ventilation (VO2/VE and VCO2/VE) occur during moderate rather than maximal exercise and that lower ratios better predict early cardiac death than lower peak VO2 or anaerobic threshold values. Therefore we postulated that plotting simultaneous VO2/VE‐vs‐VCO2/VE values of incremental exercise studies against each other on X‐Y axes would give an easy‐to‐understand single display that might quantify cardiovascular performance exceptionally well. Plots of 90‐s rolling averages of VO2/VE‐vs‐VCO2/VE were optimal. The diagonal oval racetrack patterns of VO2/VE‐vs‐VCO2/VE in normal subjects were distinctive. In over 300 normal subjects, reference formulas in mL (STPD)/L (BTPS) for highest VO2/VE = 42.2 – 0.189yrs +0.036cm less 3.0 for women and for highest VCO2/VE = 38.9 – 0.155yrs + 0.038cm less 1.9 for women. The patterns and highest values for patients with left or right heart failure were also examined. Patients with more severe heart failure had lower VO2/VE‐vs‐VCO2/VE values at rest with exercise values moving in an abnormal direction. We conclude that highest VO2/VE and VCO2/VE values, elicited without maximal exercise, are important parameters. Further, plots of VO2/VE‐vs‐VCO2/VE yield distinctive patterns that alone well assess cardiac performance and disease. No government, industry, or institutional support.

Effects of decreased O2 and elevated CO2 on survival, development, and gene expression in cowpea bruchids

Use of modified atmospheres with depleted O2 and/or elevated CO2 is an environmentally friendly alternative to currently used fumigants for control of stored grain insect pests. In the present study, we examined the impact of hypoxia and hypercapnia on cowpea bruchids (Callosobruchus maculatus), a storage pest of cowpea and other legumes. Two O2/CO2 combinations were used; (i) 10% O2+10% CO2, (ii) 2% O2+18% CO2. In both cases, N2 was maintained at 80%, equivalent to normal atmospheric concentration. In ambient atmosphere, the rate of O2 consumption and CO2 output at different stages (from low to high) was: eggs≈1st instar<2nd instar≈pupae≈adults<3rd instar<4th instar. When exposed to 10% O2+10% CO2, eggs, larvae and pupae were able to complete development and successfully enter the next developmental stage, although developmental time and mortality varied at different stages. In contrast, more severe hypoxic/hypercapnic treatment, i.e. 2% O2+18% CO2, led to cessation of development of all stages. Effects on eggs and adults were most dramatic as they could only withstand 2–3days exposure. Further, eggs at early (4–6h old) and later stages (102–104h old, black-headed) were more susceptible compared to those at intermediate stage (52–54h old). The 3rd and 4th instar larvae were least sensitive and could survive up to 20days treatment. To gain some insight into molecular mechanisms underpinning the hypoxic/hypercarpnic response, we performed qPCR reactions on selected metabolic genes involved in TCA cycle and in protein digestion, as well as genes encoding stress-responsive heat shock proteins. Patterns of gene expression and proteolysis suggest that cowpea bruchids suppress their metabolic activity and increase stress tolerance when challenged by O2 deprivation. Transcript abundance as well as proteolytic activity recovered once normoxic conditions resumed. Taken together, cowpea bruchids were found able to cope with hypoxic and hypercapnic stress. This ability was particularly strong in the late larval stage.

Total CO2 output from Vulcano island (Aeolian Islands, Italy)

Total CO2 output from fumaroles, soil gas, bubbling gas discharges and water dissolved gases discharged from the island, was estimated for Vulcano island, Italy. The CO2 emission from fumaroles from the La Fossa summit crater was estimated from the SO2 crater output, while CO2 discharged through diffuse soil emission was quantified on the basis of 730 measurements of CO2 fluxes from the soil of the island, performed by using the accumulation chamber method. The results indicate an overall output of ≅500 t day−1 of CO2 from the island. The main contribution to the total CO2 output comes from the summit area of the La Fossa cone (453 t day−1), with 362 t day−1 from crater fumaroles and 91 t day−1 from crater soil degassing. The release of CO2 from peripheral areas is ≅20 t day−1 by soil degassing (Palizzi and Istmo areas mainly), an amount comparable to both the contribution of water dissolved CO2 (6 t day−1), as well as to seawater bubbling CO2 (4 t day−1 measured in the Istmo area). Presented data (September 2007) refer to a period of moderate solphataric activity, when the fumaroles temperature were 450°C and gas/water molar ratio of fumaroles was up to 0.16. The calculated total CO2emission allows the estimation of the mass release and related thermal energy from the volcanic‐hydrothermal system.

A prospective randomised study comparing oral 13C-bicarbonate tracer technique versus indirect calorimetry for measurement of energy expenditure in adults

Accurate assessment of energy expenditure (EE) is important in guiding nutritional therapy but current methods are unsatisfactory. This study compared the oral 13C-bicarbonate tracer (BT) technique using the IRIS® system (Wagner, Germany) against indirect calorimetry (IC, ventilated-hood) to measure CO2 output (VCO2) and thus estimate EE. Ten overnight-fasted healthy male volunteers were randomised to studies at rest or mild exercise in a crossover manner. During each study BT-IRIS® and IC were used simultaneously to measure VCO2 and thus EE. Participants ingested a drink labelled with 50mg 13C-bicarbonate and breath samples were collected every 5 min for 180 min and analysed using IRIS®. Bland-Altman plots were used to assess agreement between the two techniques in measurements of VCO2 (L/day) and estimates of EE (kJ/day). Mean ± SE age and BMI of participants were 21.1 ± 1.1 yrs and 23.6 ± 0.6 kg/m2. Both at rest and exercise, there was small bias but overall poor agreement between the two techniques as evident by the wide 95% limits of agreement in measurements of VCO2 and EE: rest VCO2 (bias 1.4, SD 93, 95% limits of agreement -180 to 183), rest EE (-8.3, 1830, -3595 to 3578), exercise VCO2 (49.3, 66.1, -80.4 to 178.9) and exercise EE (1083, 1944, -2727 to 4893). Furthermore, there was also evidence of systematic error in these measurements. Prior to clinical application, further optimisation of the BT-IRIS® system should be undertaken, given the poor agreement with IC in measuring VCO2 and estimating EE.

Overshoot Phenomena of Respiratory Gas Variables During Exercise Recovery in Cardiac Patients

Transient increases (overshoot) in respiratory gas variables have been observed during exercise recovery, but their clinical significance is not clearly understood. Our group evaluated the relationship between the presence of overshoot of respiratory gas variables and the parameters obtained from cardiopulmonary exercise testing (CPX). In total, 227 patients with various cardiac diseases underwent CPX. The overshoot phenomena of O₂ uptake (·VO₂), ·VO₂/heart rate (O₂-pulse), and CO₂ output (·VCO₂) were analyzed by respiratory gas analysis during recovery after maximal exercise. The overshoot of ·VO₂, O₂-pulse, and ·VCO₂ were recognized in 11 (5%), 43 (19%), and 12 (5%) patients, respectively. Compared with the patients without a ·VO₂ overshoot, those with a ·VO₂ overshoot had a significantly lower peak ·VO₂ (12.3±3.7 vs. 17.9±6.2ml·min⁻¹·kg⁻¹, P=0.003), lower anaerobic threshold (9.4±1.7 vs. 12.4±3.3 ml·min⁻¹·kg⁻¹, P=0.001), higher ·VE-·VCO₂ slope (38.0±5.2 vs. 33.2±9.6, P=0.013), and lower left ventricular ejection fraction (LVEF) (39.9±22.8 vs. 55.8±16.8%, P=0.003). Similar findings were obtained for the patients with an O₂-pulse overshoot and those with a ·VCO₂ overshoot. The overshoot phenomena of respiratory gas variables during recovery after maximal exercise are correlated with impaired cardiopulmonary function during exercise in cardiac patients.

Prognostic Value of Cardiopulmonary Exercise Testing in Cardiac Patients With Atrial Fibrillation

Parameters obtained from cardiopulmonary exercise testing (CPX) are recognized for their high prognostic value in predicting future cardiac events in cardiac patients. Our group compared the prognostic value of CPX parameters between patients with sinus rhythm (SR) and patients with atrial fibrillation (AF).Peak O2 uptake (VO2), the ratio of the increase in VO2 to the increase in work rate (ΔVO2/ΔWR), and the slope of the increase in ventilation to the increase in CO2 output (VE-VCO2 slope) were obtained from CPX in 72 AF patients and 478 SR patients. The prognostic values of these indices were compared between the two groups.Six cardiac deaths and 25 cardiac events were observed in the AF group and 9 cardiac deaths and 96 cardiac events were observed in the SR group, over a prospective follow-up period of 1,192 days. The percentages of cardiac deaths and cardiac events were higher in the AF group than in the SR group. In a multivariate Cox proportional hazards analysis, peak VO2 was identified as a sole significant predictor of cardiac death and cardiac events in SR patients and VE-VCO2 slope was identified as a sole significant predictor of cardiac death and cardiac events in AF patients.Our results suggest that the VE-VCO2 slope is strongly predictive of future cardiac events in patients with AF and that peak VO2 is strongly predictive of future cardiac events in SR patients.