Tidal breathing model describing end-tidal, alveolar, arterial and mixed venous CO2 and O2

Thermodilution is the current standard for determination of cardiac output. The method is invasive and constitutes a risk for the patient. As an alternative CO₂ rebreathing allows non-invasive cardiac output estimation using Ficks principle. The method relies on estimation of arterial CO₂ partial pressure from end-tidal CO₂ pressure and estimation of mixed venous CO₂ partial pressure from end-tidal CO₂ during rebreathing. Presumably the oxygenation of blood in the lung capillaries increases lung capillary CO₂ pressure due to the Haldane effect, which during rebreathing may result in overestimation of the mixed venous CO₂ pressure. However, the Haldane effect is not discussed in the current literature describing cardiac output estimation using CO₂ rebreathing. The purpose of this study is to construct and verify a compartmental tidal breathing lung model to investigate the physiological mechanisms that influence the CO₂ rebreathing technique. The model simulations show agreement with previous studies describing end-tidal to arterial differences in CO₂ pressure and rebreathing with high and low O₂ fractions in the rebreathing bag. In conclusion the simulations show that caution has to be taken when using end-tidal measurements to estimate CO₂ pressures, especially during rebreathing where the Haldane effect causes mixed venous CO₂ partial pressure to be substantially overestimated.     

Wearing body armour and backpack loads increase the likelihood of expiratory flow limitation and respiratory muscle fatigue during marching

Abstract

The effect of load carriage on pulmonary function was investigated during a treadmill march of increasing intensity. 24 male infantry soldiers marched on six occasions wearing either: no load, 15?kg, 30?kg, 40?kg or 50?kg. Each loaded configuration included body armour which was worn as battle-fit or loose-fit (40?kg only). FVC and FEV₁ were reduced by 6 to 15% with load. Maximal mouth pressures were reduced post load carriage by up to 11% (inspiratory) and 17% (expiratory). Increased ventilatory demands associated with carrying increased mass were met by increases in breathing frequency (from 3 to 26 breaths·min^?1) with minimal changes to tidal volume. 72% of participants experienced expiratory flow limitation whilst wearing the heaviest load. Loosening the armour had minimal effects on pulmonary function. It was concluded that as mass and exercise intensity are increased, the degree of expiratory flow limitation also increases.

Practitioner Summary: This study investigated the effect of soldier load carriage on pulmonary function, to inform the trade-off between protection and burden. Load carriage caused an inefficient breathing pattern, respiratory muscle fatigue and expiratory flow limitation during marching. These effects were exacerbated by increases in mass carried and march intensity.     

Optimization techniques in respiratory control system models

One of the most complex physiological systems whose modeling is still an open study is the respiratory control system where different models have been proposed based on the criterion of minimizing the work of breathing (WOB). The aim of this study is twofold: to compare two known models of the respiratory control system which set the breathing pattern based on quantifying the respiratory work; and to assess the influence of using direct-search or evolutionary optimization algorithms on adjustment of model parameters. This study was carried out using experimental data from a group of healthy volunteers under CO₂ incremental inhalation, which were used to adjust the model parameters and to evaluate how much the equations of WOB follow a real breathing pattern. This breathing pattern was characterized by the following variables: tidal volume, inspiratory and expiratory time duration and total minute ventilation. Different optimization algorithms were considered to determine the most appropriate model from physiological viewpoint. Algorithms were used for a double optimization: firstly, to minimize the WOB and secondly to adjust model parameters. The performance of optimization algorithms was also evaluated in terms of convergence rate, solution accuracy and precision. Results showed strong differences in the performance of optimization algorithms according to constraints and topological features of the function to be optimized. In breathing pattern optimization, the sequential quadratic programming technique (SQP) showed the best performance and convergence speed when respiratory work was low. In addition, SQP allowed to implement multiple non-linear constraints through mathematical expressions in the easiest way. Regarding parameter adjustment of the model to experimental data, the evolutionary strategy with covariance matrix and adaptation (CMA-ES) provided the best quality solutions with fast convergence and the best accuracy and precision in both models. CMAES reached the best adjustment because of its good performance on noise and multi-peaked fitness functions. Although one of the studied models has been much more commonly used to simulate respiratory response to CO₂ inhalation, results showed that an alternative model has a more appropriate cost function to minimize WOB from a physiological viewpoint according to experimental data.     

Dead space in the breathing apparatus; interaction with ventilation

Dead space in breathing apparatus may cause increased ventilation and/or CO₂ retention. Interactions between ventilation and dead space were tested in the breathing apparatus of three divers: a full face mask with an oro-nasal cup (AGA), a full face mask without an oro-nasal cup (EXO-26) but designed to minimize dead space, and one mouthpiece. Experiments were performed at three depths; 0, 30 and 45 m seawater (msw). The breathing gas was air except at 30 msw where it was 36 O₂ in N₂. Five certified SCUBA divers were exercised at three levels (0, 50 and 100 W), Ventilation and gas exchange were measured. The dead space in the AGA mask was not influenced by either depth or exercise (mean 0·201). The mean dead space of the EXO-26 was 0·341, but it increased with exercise (p<0·001) and decreased with depth (p<0·03). Since the dead space can vary with ventilation levels it is not sufficient to test breathing apparatus only at rest as is required by the US National Institute of Occupational Safety and Health. The mean ventilation with the EXO-26 was higher than with the AGA by 10% at SOW (p<0·05) and by 12% (p < 0·01) at 100 W. The same comparison for end-tidal CO₂ showed mean increase by 0·30 kPa at the 100-W workload (P < 0·05); changes at other workloads were not statistically significant. Comparisons of the mean inspired PCO₂ to the maximum values considered acceptable by various organizations showed that the mouthpiece was always acceptable, the AGA mask was marginally acceptable or better, while sometimes the EXO-26 was not acceptable.     

Asserting the utility of using the Cowichan Problem Set

Parallel programming environments provide a way for programmers to reap the benefits of parallelism, while reducing the effort required to create parallel applications. The CO₂P₃S parallel programming system is one such tool that uses a pattern-based approach to express concurrency. Using the Cowichan Problems, we demonstrate that CO₂P₃S contains a rich set of parallel patterns for implementing a wide variety of applications running on shared-memory or distributed-memory hardware. An example of these parallel patterns, the Search-Tree pattern, is described and it is shown how the pattern was used to solve the Fifteen Puzzle problem. Code metrics and performance results are presented for the Cowichan applications to show the usability of the CO₂P₃S system and its ability to reduce programming effort, while producing programs with reasonable performance.     

Effects of the self-contained breathing apparatus and fire protective clothing on maximal oxygen uptake

To examine the effects of firefighting personal protective ensemble (PPE) and self-contained breathing apparatus (SCBA) on exercise performance, 12 males completed two randomly ordered, graded exercise treadmill tests (GXT_PPE and GXT_PT). Maximal oxygen consumption (VO_2max) during GXT_PPE was 17.3% lower than the GXT_PT in regular exercise clothing (43.0 ± 5.7 vs. 52.4 ± 8.5 ml/kg per min, respectively). The lower VO_2max during the PPE condition was significantly related (r = 0.81, p < 0.05) to attenuated peak ventilation (142.8 ± 18.0 vs. 167.1 ± 15.6 l/min), which was attributed to a significant reduction in tidal volume (2.6 ± 10.4 vs. 3.2 ± 0.4 l). Breathing frequency at peak exercise was unchanged (55 ± 7 vs. 53 ± 7 breaths/min). The results of this investigation demonstrate that PPE and the SCBA have a negative impact on VO_2max. These factors must be considered when evaluating aerobic demands of fire suppression work and the fitness levels of firefighters.     

ABSTRACTING SERVICE

1. The methods which are commonly used in work physiology for rapid sampling, laboratory storage and analysis of expired air have been examined

2. The rapid fractional sampling of expired air from both a mixing chamber and a side arm sampling device produces significant differences in [Vdot]o_a values when compared to the standard Douglas method. However, provided the volume of the mixing chamber is above 4 litres, the differences are small for this technique, (293 ±18.1 mls) compared with the side arm technique (263.4± 62.9 mls), and introduce negligible error into the estimation of energy expenditure

3. The selective loss of CO₂ from butyl rubber bladders, Douglas bags and syringes was found to be 0.11 per cent/hr., 0.2 per cent/hr. and 0.007 per cent/hr. respectively during the 8 hr. period. Loss of CO₂ during the first 30 min was high in the case of the bladders and they were found to be very unsatisfactory storage containers. Douglas bags showed a negligible loss of CO₂ during the first 2 hours, but the concentration began to fall shortly thereafter. Syringes, on the other hand, showed no appreciable decline of CO₂ until after the 8th hour of storage Samples collected in glass tonometers by mercury siphoning and displacement of acidulated water still maintained their concentrations of O₂ and CO₂ after 56 days of storage

4. The Pauling (Beckman E₂ analyser was found to be an accurate, simple and fast method of estimating the O₂ concentration in expired air. The discrepancy between the methods was found to be of the order of ±0.15 vol per cent when compared with the conventional Haldane gas analysis method.     

Analysis on the variations of atmospheric CO2 concentrations along the urban–rural gradients of Chinese cities based on the OCO-2 XCO2 data

Anthropogenic CO₂ emissions contribute the most to the growth of atmospheric CO₂ concentrations. These emissions are largely concentrated in urban areas where human activities are intense. Studies have been conducted to explore the urban and rural difference in CO₂ concentrations based on ground-based measurements. The launch of NASA’s Orbiting Carbon Observatory-2 (OCO-2) satellite provides a new opportunity to monitor CO₂ concentrations and their spatial and temporal variations at city scale. The objective of this study is to analyse the spatial and temporal distributions of CO₂ concentrations along the urban–rural gradients of Chinese cities, using the column averaged CO₂ dry air mole fraction (XCO₂) data derived from OCO-2. We used both conceptual and physical urban–rural gradients to analyse variations in CO₂ concentrations over space. The results show that the urban and rural difference in CO₂ concentrations of these cities can be monitored. And, the seasonal variations of CO₂ concentrations in these cities can also be detected using the XCO₂ data. Moreover, the variations in CO₂ concentrations along the urban–rural gradients have four main types with significant enhancements of CO₂ concentrations were observed in urban areas, urban–rural transitional areas, rural areas, and without regular patterns, respectively. The results are generally different from the common assumption that CO₂ concentrations peak in central urban areas and decline in rural areas. In conclusion, the XCO₂ data can be used to analyse the spatial-temporal variations of CO₂ concentrations along the urban–rural gradients of Chinese cities, and the results have important policy implications for mitigating CO₂ emissions.     

Hyperoxia improves maximal exercise with the self-contained breathing apparatus (SCBA)

The effects of hyperoxia on maximal exercise while breathing from a self-contained breathing apparatus (SCBA) were studied in 25 males. Each participant completed three graded exercise tests (GXT) for the assessment of maximal oxygen uptake (Vdot;O _2max): two with 20.95 ± 0.28% O₂ and the third (GXT₄₀) while breathing hyperoxia (40.64 ± 1.29% O₂). No significant differences were found between the two normoxic tests, except for a 16W increase in maximal power output (PO_max) in the second trial (GXT₂₁). Compared to GXT₂₁, hyperoxia significantly increased Vdot;O _2max and PO_max by 10.0 ± 3.8% and 10.2 ± 7.1%, respectively. This was likely due to an increase in O₂ delivery as suggested by the significantly higher oxyhemoglobin saturation. The increase in Vdot;O _2max with hyperoxia was similar to the increase in carbon dioxide production (9.3 ± 6.5%). No other significant differences were found at maximal exercise. However, at the intensity that elicited Vdot;O _2max in GXT₂₁, pulmonary ventilation and SCBA mask pressure were significantly lower during GXT₄₀, suggesting a decrease in the work of breathing. These findings could have significant implications for occupations that involve heavy work with SCBA.     

Application of satellite remote sensing techniques for estimating air–sea CO2 fluxes in Hudson Bay,Canada during the ice-free season

The role of coastal seas as either a sink or a source of CO₂ is subject to a great deal of uncertainty. This uncertainty largely arises from a lack of observations in the coastal zones. Remote sensing offers an avenue for expanding these observations by allowing for the extrapolation of relatively limited data sets of dissolved CO₂ (pCO_2sw). In this paper, predictive algorithms for pCO_2sw that could be applied to remote sensing products were created from a field data set collected from September–October, 2005 in Hudson Bay, Canada. The field data showed that an effective pCO_2sw interpolation algorithm could be created using sea surface temperature (SST) as a predictor, and that a slight improvement of the algorithm could be achieved if measurements of absorption due to coloured dissolved organic material (a_CDOM) were included. Unfortunately, satellite retrievals of a_CDOM did not match well with in situ observations, and so only SST (obtained from the MODIS Aqua sensor) was used to create monthly maps of pCO_2sw for the period of August–October. To estimate fluxes of CO₂, constructed surfaces of pCO_2sw were combined with estimates of gas transfer velocity derived from QuikSCAT wind retrievals, and pCO_2air based on field observations. The results of these calculations revealed that Hudson Bay acts as a source of CO₂ during August and September, but reverts to a sink of CO₂ in October as the water temperature decreases. Overall, a positive flux of 1.60 TgC was estimated for the region during the ice-free season. This result is in contrast to most Arctic or sub-Arctic continental shelf seas, where usually strong absorptions of CO₂ are observed.     

The energetics of walking on sand and grass at various speeds

This study investigated the energetics of walking on sand and grass. Fourteen adult males, participated in the study. Participants had a mean age of 34.6 years old, 72.6 kg in mass and 172.5 cm in stature, who walked at 3, 4, 5, 6 and 7 km per h on sand and grass surfaces. Physiological measures included heart rate, O₂ uptake, CO₂ exhalation, ventilation and relative O₂ uptake using a MetaMax Ergospirometer. Speed was controlled in a methodology similar to the ‘Multistage 20-m Shuttle Run Test’. Data were collected during physiological steady rate at each determined speed. A minimum of 2 h rest was enforced between randomized conditions. Results indicate that there was a significant increase (p < 0.01) in all measured physiological indices indicative of energy expenditure when walking on sand compared to grass at 3–7 km per h, with the greatest disparity between the surfaces (ratio = 1.63) in relative O₂ consumption at 5 km per h.     

The effects of sand dust storms on greenhouse gases

In Asia, sand dust storms (SDSs) occur nearly every year, especially in northern China. However, there is little research about the relationship between SDSs and greenhouse gases (GHGs). In this article, we selected four SDSs that occurred in Asia in the spring of 2009 and 2010. We monitored the areas covered by these SDSs using Moderate Resolution Imaging Spectroradiometer (MODIS) data, then we used Greenhouse Gases Observing Satellite (GOSAT) data to check how the SDSs affected the concentrations of CO₂ and CH₄. We then compared the concentrations of CO₂ and CH₄ on SDS days with the monthly mean values of the months in which SDSs occurred. We also compared the concentrations of CO₂ and CH₄ on SDS days with the values before and after the SDSs. After analysis, we found that SDSs had increased the concentrations of CO₂ and CH₄ in the atmosphere. When the SDSs occurred, the concentrations of CO₂ and CH₄ increased and reached peak values on the last or penultimate days of the storms and then decreased to their normal values. Atmospheric flow is the main reason for the increase in concentration of CO₂, and the lack of the free radical (OH) during SDSs and the presence of CH₄ sources in southeast China are the main reasons for the increase in concentration of CH₄. We also found that in arid and semi-arid areas, SDSs had little effect on the concentration of these two GHGs.     

Frequency and time domain analysis of airflow breath patterns in patients with chronic obstructive airway disease

Airflow patterns from patients with chronic obstructive airway diseases (COAD) and normal subjects were analyzed using time and frequency domain analysis. Data were recorded during tidal breathing with a pause between the breaths, digitized at 320 samples per second (10-bit resolution), and processed with a CDC 6600 computer. The appearance of high-frequency components (10-20 Hz) in the time domain waveform and the spectral curve in the power spectrum were studied. One complete waveform was taken as a reference signal and all subsequent waves were analyzed using the cross-correlation function which was employed via the cross spectrum and the fast Fourier transform algorithm. The energy content from the averaged spectrum and the root mean square (RMS) value from the filtered waveforms were calculated. Our study indicated that the RMS and the power content estimated from a part of the filtered wave (10-20 Hz) which included the time interval from the peak of the expiratory flow (tE) to the end of the flow curve (tN) were significantly greater in normal subjects (n = 13; 0.86 +/- 0.30 X 10(-2) I/s; P less than 0.00005 for RMS value, and 0.76 +/- 0.32 I/s; P less than 0.00005 for the power content) than in patients with chronic airways obstruction (n = 19; 0.40 +/- 0.13 X 10(-2) I/s; for RMS value and 0.35 +/- 0.16 I/s; for the power content). It is concluded that the RMS and the power values of the filtered flow curve during tidal breathing over the time interval tE-tN can detect chronic airway obstruction.     

Optical CO2 sensor with the combination of colorimetric change of α-naphtholphthalein and internal reference fluorescent porphyrin dye

A new optical CO₂ sensor based on the overlay of the CO₂ induced absorbance change of pH indicator dye α-naphtholphthalein with the fluorescence of tetraphenylporphyrin (TPP) was developed. The observed luminescence intensity from TPP at 655 nm increased with increasing the CO₂ concentration. The ratio I₁₀₀/I₀ values of the sensing films consisting of α-naphtholphthalein in ethyl cellulose layer and TPP in polystyrene layer, where I₀ and I₁₀₀ represent the detected luminescence intensities from a layer exposed to 100% nitrogen and 100% CO₂, respectively, that the sensitivity of the sensor, are more than 53.9. The response and recovery times of the sensing films consisting of α-naphtholphthalein in ethyl cellulose layer and TPP in polystyrene layer were less than 5 s for switching from nitrogen to CO₂, and for switching from CO₂ to nitrogen. The signal changes were fully reversible and no hysterisis was observed during the measurements. The highly sensitive optical CO₂ sensor based on fluorescence intensity changes of TPP due to the absorption change of α-naphtholphthalein with CO₂ was achieved.     

Physiological strain during kitchen work in relation to maximal and task-specific peak values

Six female and three male subjects from a hospital kitchen volunteered for the study. The subjects were working on a conveyor belt collecting and sorting dirty plates, glasses and cutlery for cleaning. In the study, a medical examination, a maximal clinical exercise test with a 12-lead electrocardiogram (ECG) and a maximal arm cranking test were performed in the laboratory. Further, each subject was studied for 30 min during a normal work shift in the kitchen. Oxygen uptake (VO₂) and heart rate (HR) were continuously registered. During the work period, a rating of perceived exertion (RPE) was asked at the 5th, 15th and 30th minute. Physiological responses were measured by a portable system (K4) both in the laboratory and in the field. VO₂ and HR measured in the field were proportioned to corresponding maximal values during cycling and to peak values during arm-cranking. The mean VO₂ for the male and the female subjects during kitchen work was 0.65±0.16 l min^-1. This corresponded to 24% of VO_2max and to 41% of VO_2peak during arm-cranking. The difference was significant (p<0.001). Owing to a magnetic field at the conveyor belt, reliable HR values were obtained only from the female subjects. The mean HR during work among the female subjects was 101 beats min^-1. It corresponded to 55% of HRmax and 67% of HR during arm-cranking (p<0.05). The present study shows that the peak relative work intensity is markedly higher when it is expressed relative to the corresponding muscle group's VO_2peak instead of the VO_2max. Similar difference was also seen in the HR response. More task-specific testing of physical capacity may provide improved evaluation of physical strain in a job.     

Exploring Dynamic Impact of Foreign Direct Investment on China’s CO$$_{}$$ Emissions Using Markov-Switching Vector Error Correction Model

The impact of foreign direct investment (FDI) on China’s CO\(_{2}\) emissions is an important index to evaluate the effect of foreign investment policy. This paper uses the monthly data of CO\(_{2}\) emissions and FDI from January 1997 to December 2013 to analyze the regime states, switching probability and regime correlation between FDI and CO\(_{2}\) emissions with the help of nonlinear Markov-switching vector error correction model (MS-VECM), The results indicate that the influence of FDI on CO\(_{2}\) emissions shows the two-regime dynamic characteristics, FDI has played a stimulating role in promoting China’s CO\(_{2}\) emissions during the period from January 1997 to October 2003, while played an inhibiting role during the period from November 2003 to December 2013. The duration of the inhibiting effect of FDI on CO\(_{2}\) emissions is longer, and the frequency is higher than that of the stimulating effect. Therefore, the overall influence of FDI on CO\(_{2}\) emissions during the period from January 1997 to December 2013 is inhibitive, which means FDI has contributed to CO\(_{2}\) emissions reduction. The innovation points of this study are mainly reflected in the following two aspects: first, nonlinear MS-VECM is introduced to dynamically study the relationship between FDI and CO\(_{2}\) emissions in contrast to prior studies that simply use static analysis method; second, the effect of China’s foreign investment policies on CO\(_{2}\) emissions is evaluated in each period according to the empirical results of MS-VECM.     

Numerical investigation of formation and dissolution of CO<Subscript>2</Subscript> bubbles within silicone oil in a cross-junction microchannel

In this paper, a numerical investigation is conducted to study the formation and dissolution process of CO₂ bubbles within silicone oil in a cross-junction microchannel. A coupled multiphase–multicomponent computational fluid dynamics model based on the volume-of-fluid method is used, which is able to capture the physics of the multiphase bubble formation, dissolution mass transfer, and the tracking of the dissolved CO₂ species. The computational model is firstly validated with experimental results where good agreement is attained. Next, the model is used to investigate the bubble formation process at the cross-junction in the presence of dissolution and also the bubble evolution as it is transported along the downstream channel. It is revealed that during bubble formation, there is a high concentration of CO₂ solute around the cross-junction walls, as silicone oil flow to this region is minimal. As the CO₂ bubble travels downstream, the transport of the CO₂ solute is largely driven by the local flow currents of the silicone oil within the vicinity of the bubble. An extensive parametric study is also conducted, looking at the effects of varying the surface tension, diffusion coefficient and flow rates. The results demonstrate that the initial CO₂ bubble length and period of bubble formation are most affected by the flow rate, while the mass transfer is most strongly governed by the diffusion coefficient.     

Measuring and modelling CO2 effects on sugarcane

In order to fully capture the benefits of rising CO₂ in adapting agriculture to climate change, we first need to understand how CO₂ affects crop growth. Several recent studies reported unexpected increases in sugarcane (C₄) yields under elevated CO₂, but it is difficult to distinguish direct leaf-level effects of rising CO₂ on photosynthesis from indirect water-related responses. A simulation model of CO₂ effects, based purely on changes in stomatal conductance (indirect mechanism), showed transpiration was reduced by 30% (initially) to 10% (closed canopy) and yield increased by 3% even in a well-irrigated crop. The model incorporated the results of a field experiment, and a glasshouse experiment designed to disentangle the mechanisms of CO₂ response: whole-plant transpiration and stomatal conductance were both 28% lower for plants growing with high-frequency demand-based watering at 720 vs 390 ppm CO₂, but there was no increase in biomass, indicating that indirect mechanisms dominate CO₂ responses in sugarcane.     

Modelling CO2 policies for the Japanese iron and steel industry

This paper discusses the STEAP model (STeel Environmental Assessment Program). This model has been developed for analysis of the interaction of CO₂ taxes, technological change, market structure and trade effects for iron and steel. New elements compared to previous techno–economic systems optimisation with linear programming models are global interregional trade and changing market structure. The modelling approach is discussed and the model code is presented. This is followed by a discussion of results for Japan. In the case of global taxation, trade effects are negligible. In the case where only Japan and Europe introduce a tax, Japanese production will be reduced significantly and carbon leakage exceeds 50%. However, a CO₂ tax of 2,500 Yen per ton of CO₂ (125 Yen is equal to 1 US$) in combination with an import tariff of 2,500–5,000 Yen per ton of steel can prevent carbon leakage. Such a strategy results in a 41% CO₂ reduction (50 Mt) in 2020. A strategy aiming for large monopolistic producers is less attractive because industry will aim for lower production and increased prices, while the CO₂ reduction effect is similar.