Gas density and the work of breathing

What is the central question of this study? Can a modern proportional assist ventilator (PAV) function sufficiently well to unload the respiratory muscles during exercise? What is the main finding and its importance? A PAV can be constructed with contemporary hardware and software and be used at all exercise intensities to unload the respiratory muscles by up to 70%. Previously, PAVs have allowed researchers to address many fundamental physiological problems in clinical and healthy populations, but those versions are no longer functional or available. We describe the creation of a PAV that permits researchers to use it as an experimental tool. Manipulation of the normally occurring work of breathing (WOB) during exercise can provide insights into whole-body regulatory mechanisms in clinical patients and healthy subjects. One method to reduce the WOB uses a proportional assist ventilator (PAV). Suitable commercially available units are not capable of being used during heavy exercise. This investigation was undertaken in order to create a PAV and assess the degree to which the WOB could be reduced during exercise. A PAV works by creating a positive mouth pressure (Pm ) during inspiration, which consequently reduces the WOB. Spontaneous breathing patterns can be maintained, and the amplitude of Pm is calculated using the equation of motion and predetermined proportionality constants. We generated positive Pm using a breathing apparatus consisting of rigid tubing, solenoid valves to control the airflow direction and a proportional valve connected to compressed gas. Healthy male and female subjects were able to use the PAV successfully while performing cycling exercise over a range of intensities (50-100% of maximal workload) for different durations (from 30s to 20min) and different protocols (constant versus progressive workload). Inspiratory WOB was reduced up to 90%, while total WOB was reduced by 70%. The greatest reduction in WOB (50-75%) occurred during submaximal exercise, but at maximal ventilations (>180lmin(-1) ) a 50% reduction was still possible. The calculated change in WOB and subsequent reduction in respiratory muscle oxygen consumption resulted in equivalent reductions in whole-body oxygen consumption. With adequate familiarization and practice, our PAV can consistently reduce the WOB across a range of exercise intensities.

Electrical waterbath stunning is the most common method used to stun poultry under commercial conditions. The voltage supplied to a multiple bird waterbath stunner must be adequate to deliver the required minimum current to each bird. High frequency (> 300 Hz) electrical waterbath stunning needs further investigation to determine its efficiency. It should always be followed by a prompt neck cutting procedure where all the major blood vessels in the neck are severed. Irrespective of the waveform or frequency of the currents employed, constant current stunners should be installed under commercial conditions to ensure that the minimum currents are delivered to individual birds in waterbath stunners. Head only electrical stunning of poultry is being investigated in detail and there is scope for commercial development. Important features include (a) a constant current capable of delivering a preset current, (b) a bird restraining conveyor and head presentation devices enabling the stunning tongs to be accurately placed, (c) more effective electrical stunning tongs in terms of delivering necessary currents while using low voltages, and (d) induction of cardiac arrest immediately after stunning to eliminate wing flapping. Stunning/killing of poultry still in their transport containers using gas mixtures would appear to be the best future option as far as bird welfare is concerned. However, birds can also be stunned/killed on a conveyor using gas mixtures, thereby eliminating the stress associated with the shackling of live birds before electrical stunning. Under the conveyor system birds should be presented to the gas mixtures in a single layer. Within gas mixtures a minimum of 90% argon in air would appear to be the first choice. A mixture of 30% carbon dioxide and 60% argon in air is better than using a high concentration of carbon dioxide in air, and is therefore considered to be the second choice. A two stage system that involves firstly stunning broilers with a low concentration of carbon dioxide and then killing them with a high concentration of carbon dioxide can be used by those who wish to use this gas for economic reasons. The two stages should be distinctly separated so that the birds are stunned well before exposure to a high concentration of carbon dioxide in air. In comparison with carbon dioxide alone, a mixture of 30% oxygen and 40% carbon dioxide in air prolongs the induction of anaesthesia and the exposure time required to kill the birds. The addition of oxygen to carbon dioxide may therefore not have any benefit to bird welfare or the processors. Mechanical stunning of poultry using penetrating captive bolts or non-penetrating mushroom headed bolts has been developed. However, stunning with these devices results in very severe wing flapping and further research is necessary to find ways of alleviating this problem.

The concentration and isotopic abundances of carbon dioxide in rural and marine air

BACKGROUND: Elevated levels of carbon dioxide in gym air can diminish the benefits of physical activity and pose health risks for children.. AIM: to access carbon dioxide concentration in the air of school gyms during physical education classes. MATERIAL AND METHODS: A total of 612 measurements were taken to estimate the concentration of carbon dioxide in the air. These measurements were conducted in two separate gymnasiums: in Gym 1, designated for primary classes with an area of 77 m2, and Gym 2, used by middle and high school students with an area of 293 m2. Measurements were taken at 12 different points, both around the perimeter and in the central part of each gym. The height when measuremenmts were taken ranged from 0 to 230 cm. To assess the carbon dioxide concentration in the gym air, the background level was calculated based on GOST 30494-2011 standards (761.5 ppm). Student’s t-tests for independent samples were used to compare the data. Additionally, a regression analysis was utilized to estimate the spatial distribution of carbon dioxide within the gymnasiums. RESULTS: In Gym 1, the initial concentrations ranged from 845 to 1267 ppm, slightly exceeding the expected throughput. Throughout the training session, the carbon dioxide content increased by 1.6 to 2.3 times. By the end of the session, the carbon dioxide content reached 1934 to 1948 ppm at an estimated respiration level of 1.0 to 1.9 m. In Gym 2, the carbon dioxide content increased by 1.1 to 1.2 times by the end of the class. At a height of 0.0 to 1.7 m, the concentration of carbon dioxide was measured at 1016 to 1023 ppm. CONCLUSION: After 20 minutes of training at the expected intensity, carbon dioxide levels in the air exceed not only the background level of 761.5 ppm, but also the permissible level of 1000 ppm. This study highlights the importance of daily monitoring of carbon dioxide levels in school gymnasiums during training sessions and sporting events. Such monitoring is crucial for ensuring the health and safety of students and athletes.

Combined effect of carbon monoxide mixed with carbon dioxide in air on the mortality of stored-grain insects

Mixtures of carbon dioxide and oxygen are commonly used in the treatment of central retinal artery obstruction to improve retinal oxygenation. While oxygen alone causes retinal vasoconstriction, it is thought that the carbon dioxide balances this effect, even causing a net vasodilatation. To test this hypothesis, normal, healthy volunteers were given 100% oxygen, a mixture of 95% oxygen and 5% carbon dioxide, and a mixture of 5% carbon dioxide in air to breathe. The caliber of large, fluorescein-filled retinal arteries and veins was then measured using computer processing of digitized television images. The marked decrease in arterial and venous caliber caused by 100% oxygen was not reversed by the subsequent addition of 5% carbon dioxide. Moreover, 5% carbon dioxide in air did not cause substantial vasodilatation of the retinal vasculature. The efficacy of adding 5% carbon dioxide to oxygen to treat retinal vascular obstructive diseases is questioned.

The use of anaerobic incubation for the culture of Streptococcus pneumoniae from sputum was compared with incubation in carbon dioxide in air. A coagglutination test for pneumococcal antigen was used as an index of the number of specimens containing pneumococci. A total of 334 specimens were examined. There was evidence of pneumococcal colonisation by culture or coagglutination, or both, in 48 (14.37%), of which 41 (12.27%) yielded S pneumoniae on culture. Anaerobic incubation was better than incubation in carbon dioxide in air for the primary culture of S pneumoniae from sputum. Primary isolation of S pneumoniae was achieved in 11 of the 41 strains (26.82%) by anaerobic incubation alone, by incubation only in carbon dioxide in air in one strain (2.43%), and by both anaerobic incubation and incubation in carbon dioxide in air in 29 strains (70.73%). Anaerobic incubation gave large moist or mucoid colonies that were easy to recognise, but it suppressed the typical draughtsman colony of S pneumoniae. The factor V supplement routinely used in our medium also inhibited the formation of draughtsman colonies. It is suggested that draughtsman colonies occur because of a relative lack of the coenzyme nicotinamide adenine dinucleotide (factor V), which is required as a reducing agent in aspartate and glutamate metabolism. This nutritional deficiency may lead to bacterial cell wall defect and hence to the autolysis which gives the typical draughtsman colony.

Analytical expressions for the work of breathing under conditions of laminar and turbulent flow have been derived. Helium-oxygen mixtures of greater viscosity but lower density than air, and sulfur ftexafiuoride-oxygen mixtures of greater density than air were used to test these expressions. The work of breathing was determined by measuring the oxygen consumption during quiet breathing and during hyperventilation produced by 7% carbon dioxide. Increased oxygen consumption per minute on hyperventilation with air was 55 ml, standard temperature and pressure, dry (STPD); on breathing helium-oxygen mixtures it was 57 ml STPD. Increased oxygen consumption per minute on hyperventilation with sulfur hexafluoride-oxygen mixtures was 249 ml STPD. Increasing the viscosity of the inspired gas or decreasing its density did not significantly affect the work of breathing; a substantial increase in the density of the inspired gas lead to an increased work of breathing.

Gas chromatographic measurement of nitrous oxide and carbon dioxide in air using electron capture detection

BackgroundEndotracheal tubes used for neonates are not as resistant to breathing as originally anticipated; therefore, spontaneous breathing trials (SBTs) with continuous positive airway pressure (CPAP), without pressure support (PS), are recommended. However, PS extubation criteria have predetermined pressure values for each endotracheal tube diameter (PS 10 cmH2O with 3.0- and 3.5-mm tubes or PS 8 cmH2O with 4.0-mm tubes). This study aimed to assess the validity of these SBT criteria for neonates, using an artificial lung simulator, ASL 5000™ lung simulator, and a SERVO-i Universal™ ventilator (minute volume, 240–360 mL/kg/min; tidal volume, 30 mL; respiratory rate, 24–36/min; lung compliance, 0.5 mL/cmH2O/kg; resistance, 40 cmH2O/L/s) in an intensive care unit. We simulated a spontaneous breathing test in a 3-kg neonate after cardiac surgery with 3.0–3.5-mm endotracheal tubes. We measured the work of breathing (WOB), trigger work, and parameters of pressure support ventilation (PSV), T-piece breathing, or ASL 5000™ alone.ResultsWOB displayed respiratory rate dependency under intubation. PS compensating tube resistance fluctuated with respiratory rate. At a respiratory rate of 24/min, the endotracheal tube did not greatly influence WOB under PSV and the regression line of WOB converged with the WOB of ASL 5000™ alone under PS 1 cmH2O; however, at 36/min, endotracheal tube was resistant to breathing under PSV because trigger work increased exponentially with PS ≤ 9 cmH2O. The regression line of WOB under PSV converged with the WOB of T-piece breathing under PS 1 cmH2O. Furthermore, PS compensating endotracheal tube resistance was 6 cmH2O. The WOB of ASL 5000™ alone approached that of respiratory distress syndrome (RDS); however, the pressure of patient effort was normal physiological range at PS 10 cmH2O. PS equalizing WOB under PSV with that after extubation depended on the respiratory rate and upper airway resistance. If WOB after extubation equaled that of T-piece breathing, the PS was 0 cmH2O regardless of the respiratory rates. If WOB after extubation approximated to that of ASL 5000™ alone, the PS depended on the respiratory rate.ConclusionSBT strategies should be selected per neonatal respiratory rates and upper airway resistance.

Lung volumes, arterial blood gases, respiratory control system sensitivity, and oxygen cost of breathing were studied in obese but otherwise normal individuals and compared to similar studies in nonobese control subjects. Respiratory control system sensitivity as measured by the response to 5% carbon dioxide in air was normal in most obese subjects but reduced in certain obese individuals indistinguishable from the others on the basis of clinical evaluation or resting air studies. While breathing 5% carbon dioxide, the ventilation required to maintain any given alveolar carbon dioxide tension was directly dependent on weight. Oxygen cost of breathing in the ventilation range of 10–30 l/min. was elevated in 4 of 12 obese subjects, and in 6 of 9 obese subjects in the range of 20–40 l/min. There was no correlation between oxygen cost of breathing and respiratory control system sensitivity. Submitted on April 29, 1960

BACKGROUNDIn addition to the reduction in lung elastance and diaphragm function, aging is associated with a greater ventilatory response for a given metabolic rate. Together these age‐related pulmonary alterations may result in a higher energetic cost (i.e. work) of breathing for the elderly during exercise.PURPOSETo examine the impact of aging on the inspiratory and expiratory components of exercise‐induced respiratory work in physically active participants.METHODSPhysical activity (PA) was monitored in seven healthy young (25 ± 4 yr) and older (72 ± 6 yr) participants for one week. The Tiffeneau‐Pinelli Index (TFPI) of pulmonary function (forced expiratory volume in one second (FEV1)/forced vital capacity (FVC)) was quantified prior to exercise. Following a 6 min warmup at 30 W, all participants performed an incremental cycling exercise test (30 W + 30 W/2 min) to exhaustion. The work of breathing (WOB) was acquired during the final minute of each stage by integrating the averaged esophageal pressure‐volume loop (~10 breaths). Furthermore, the WOB was partitioned into inspiratory (elastic + resistive) and expiratory work by 1) drawing a line connecting end‐expiratory lung volume (EELV) and end‐inspiratory lung volume (EILV) and 2) forming a right angle by adding an isovolume line from EILV and an iso‐pressure line from EELV. As there were no differences were found between inspiratory elastic or resistive work, combined inspiratory work is presented. In order to examine age‐related differences in WOB, the following two analyses were performed. First, for each individual, a 3rd order polynomial fit was calculated for the WOB across all minute ventilations (VE) obtained during the incremental test. T‐tests were then performed for each coefficient of the regression equation to determine if the slope for VE and WOB were different between groups. Second, to compare the impact of aging on total, inspiratory, and expiratory WOB, a mixed model ANOVA was performed including 3 matched flow rates (40, 70, and 100 L·min−1).RESULTSPA (~8700 steps/day) and TFPI (~80%) were similar between groups (P > 0.28). During exercise, the young attained a greater peak workrate compared to the older participants (291 ± 66 W vs 184 ± 37 W, respectively, P < 0.05). Furthermore, at any given workrate, VE was 18 to 29% greater in the old and this was reflected in a higher VE/VCO2 compared to the young (P < 0.05). At each matched VE, the older individuals demonstrated a 17 to 28% greater EELV (P < 0.05). While the total WOB increased with VE in both groups, the slope coefficient was greater in the old (P < 0.05). Specifically, both expiratory and total WOB were greater in the old at 100 L·min−1 (representing 58% and 90% of maximal VE in young and old, respectively). Additionally, 5 of the 7 old and 1 of the 7 young participants demonstrated expiratory flow limitation (> 15%) at 100 L·min−1.CONCLUSIONThe WOB increases with advancing age due to both a greater ventilatory response to a given workrate and a greater WOB at a given ventilatory rate. The greater WOB at a given VE is primarily accounted for by the elevated expiratory work which is likely attributable to the age‐related reduction in elastic recoil of the lung.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

This study is to explore the components and related mechanism responsible for the increase of work of breathing (WB) in chronic obstructive pulmonary disease (COPD) patients. Eight COPD patients and eight healthy volunteers were recruited in the study. The rebreathing method was used to increase end-tidal CO2 partial pressure (PetCO2) and stimulate the increase in ventilation (VE). The increase in VE, WB, and changes in the compositions of WB were observed and analyzed. The WB and its components were calculated using the Campbell diagram. The inspiratory work (Wi) of breathing, a major component of total work of breathing (Wtot), in the COPD group was significantly higher than the control group during quiet breathing (P<0.05). As the minute VE increased, Wtot and Wi increased in a linear manner, and the slope of increase was significantly higher in the COPD group as compared to the normal group (P<0.05). The analyses of changes in overcoming airway resistance (Wrs) and lung/chest-wall elastance (Wel) indicated that the slope of increase (response to VE increase) of Wrs was not significantly different between the two groups (P>0.05) although the Wrs in the COPD group was always higher than the normal group (P<0.05). However, as the VE increased, the slope of the increase in Wel was significantly higher in the COPD group than the normal group. Work done to overcome the intrinsic PEEP (WPEEPi), a component of the Wel, was not observed in the control group. However, WPEEPi increased gradually as VE increased and accounted for 56% of Wel at the end of rebreathing trial in COPD group. Airway resistance was the main cause for increased WB during quiet breathing. As the VE increased, an increase of WPEEPi became an important part of increased WB in COPD patients, so it is important to reduce dynamic hyperinflation in COPD patients.

Construction details are described for a minichamber device that maintains a localized atmosphere of carbon dioxide in air over the stage of an inverted microscope. This device is easily constructed from Plexiglas and its specifications can be adjusted to fit virtually any inverted microscope. A flow of warm, humidified carbon dioxide in air gas mixture can be directed over a petri dish or unsealed culture flask to maintain the pH of bicarbonate-CO2 buffered media. By this means, prolonged culture of cells directly on the microscope stage is made possible without occurrence of detrimental pH changes. If the microscope is fitted with an environmental control chamber to maintain temperature, cells can be maintained on the microscope stage for days, permitting frequent observation of cell growth and activity. Alternatively, continuous cine or video recordings can be made. For example, using this device, hamster and rhesus monkey embryos have been cultured for 2 to 5 d on an inverted microscope while continuous time-lapse recordings were made of cell division and differentiation and activity of cellular organelles.

Exsheathed infective larvae of Haemonchus contortus developed to the fourth stage in a salt solution under carbon dioxide. The changes in morphology were similar to those seen in worms from sheep, but development was slower. Greatest numbers of fourth-stage larvae were obtained from solutions gassed with 40% carbon dioxide. Small numbers of fourth-stage worms were present after 48 hr, and as many as 90% were in the fourth stage after 72 hr. Once larvae had commenced to develop carbon dioxide could be withdrawn, and development proceeded readily under air. Serum labeled with a fluorochrome was not detected in the intestine of third-stage worms cultivated in vitro, but was present in fourth-stage worms. It is concluded that under these conditions third-stage larvae of H. contortus were unable to ingest the medium. Stoll (1940) and Sommerville (1964) have shown that exsheathed infective larvae, i.e., third-stage larvae, of Haemonchus contortus will develop to the fourth stage after incubation in salt solutions at 38 to 39 C. Stoll's experiments demonstrated that more fourthstage larvae developed when an aqueous extract of liver was added to the salt solution and when the supply of oxygen was restricted. Silverman (British Patent 894603) has shown that development of H. contortus to the fourth stage can take place in Earle's salt solution together with hydrolysates of liver and casein. Sommerville (1964) suggested that either dissolved gaseous carbon dioxide or carbonic acid, or both, provided a stimulus which induced development. He failed to demonstrate any effect from the addition of liver extract. This paper reports the results of further experiments on the development of the thirdstage larva to the fourth stage in vitro. MATERIALS AND METHODS Infective larvae of H. contortus were harvested from cultures of sheep feces 7 to 14 days old, and stored in tap water at 5 C for about 1 week before use. They were prepared for culture by passage through three layers of lens tissue in a sterile Baermann apparatus which contained 0.4% sterile sodium chloride at 38 C. Larvae were subsequently washed twice by suspension in 0.4% sterile sodium chloride and centrifuged at 350 g. They were exsheathed by rinsing for 10 min in 20 ml of 0.4% sterile sodium chloride to which had been added 1 ml of "Milton" (1% sodium hypochlorlite: Received for publication 20 April 1965. * Present address: Department of Zoology, University of Adelaide, Adelaide, South Australia. Milton Pharmaceuticals Ltd., London). They were then washed six times in sterile 0.4% sodium chloride and counted. These procedures were essentially those followed by Weinstein and Jones (1956). In some experiments, exsheathment was achieved by gassing with 100% carbon dioxide. The larvae were suspended for 21/ hr at 40 C in a sterile solution of sodium bicarbonate, the concentration of which was adjusted to give pH 6 when gassed with 100% carbon dioxide (Umbreit, Burris, and Stauffer, 1957). Larvae were incubated in screw-capped roller tubes which contained either 2 or 3 ml of the medium and 1,000 larvae, i.e., either 500 or approximately 330 larvae per ml of medium. The roller drum was kept in an incubator in the dark and rotated 12 times each hour. The temperature was 40 ? 0.5 C unless otherwise indicated. The temperature inside the tubes was checked periodically with thermocouples inserted in the tube and connected to an automatic recorder. The medium contained the following components in grams per liter: NaCl, 8.23; KCI, 0.42; CaC12, 0.33; MgS04-7H20, 0.34. Sodium bicarbonate was added to give the required pH with the particular gas mixture used, usually pH 6. The amount of bicarbonate required was calculated from data supplied by Umbreit, Burris, and Stauffer (1957). All components were sterilized by filtration before use, and the final medium contained 500 mg streptomycin and 500 units penicillin G (sodium salt) per ml. Commercially prepared gas mixtures were used. These contained either 5, 20, 40, 60, or 80% carbon dioxide, 10% oxygen, and the balance nitrogen. In some experiments, 100% carbon dioxide or 50% carbon dioxide in air was used. Each gas mixture was passed through sterile cotton wool, a d cultures were gassed for 2 min in a water bath at the same temperature as for subsequent incubation. Tubes were sealed with a screw top containing a silicone rubber lining. Unless otherwise stated, larvae were incubated under the gas mixtures for 72 hr. At the termination of each experiment, sterility tests were made