scholarly journals Ideal alveolar gas defined by modal gas exchange in ventilation-perfusion distributions

2021 ◽  
Author(s):  
Philip J. Peyton
Keyword(s):  
Gas Exchange ◽  
Partial Pressure ◽  
Intraclass Correlation ◽  
Elimination Rate ◽  
Compartment Model ◽  
Partial Pressures ◽  
Wide Range ◽  
Significant Difference ◽  
Log Normal ◽  
Alveolar Capillary

Under the three-compartment model of ventilation-perfusion (VA/Q) scatter, Bohr-Enghoff calculation of alveolar deadspace fraction (VDA/VA) uses arterial CO2 partial pressure measurement as an approximation of "ideal" alveolar CO2(ideal PACO2). However, this simplistic model suffers from several inconsistencies. Modelling of realistic physiological distributions of VA and Q instead suggests an alternative concept of "ideal" alveolar gas at the VA/Q ratio where uptake or elimination rate of a gas is maximal. The alveolar-capillary partial pressure at this "modal" point equals the mean of expired alveolar and arterial partial pressures, regardless of VA/Q scatter severity or overall VA/Q. For example, modal ideal PACO2 can be estimated from Estimated modal ideal PACO2 = (PACO2+PaCO2)/2 Using a multicompartment computer model of log normal distributions of VA and Q, agreement of this estimate with the modal ideal PACO2 located at the VA/Q ratio of maximal compartmental VCO2 was assessed across a wide range of severity of VA/Q scatter and overall VA/Q ratio. Agreement of VDA/VA for CO2 from the Bohr equation using modal idealPCO2 with that using the estimated value was also assessed. Estimated modal ideal PACO2 agreed closely with modal ideal PACO2, intraclass correlation (ICC) > 99.9%. There was no significant difference between VDA/VACO2 using either value for ideal PACO2. Modal ideal PACO2 reflects a physiologically realistic concept of ideal alveolar gas where there is maximal gas exchange effectiveness in a physiological distribution of VA/Q, which is generalizable to any inert gas, and is practical to estimate from arterial and end-expired CO2 partial pressures.

scholarly journals End-tidal to Arterial Gradients and Alveolar Deadspace for Anesthetic Agents

2020 ◽  
Vol 133 (3) ◽  
pp. 534-547
Author(s):  
Philip J. Peyton ◽  
Jan Hendrickx ◽  
Rene J. E. Grouls ◽  
Andre Van Zundert ◽  
Andre De Wolf
Keyword(s):  
Carbon Dioxide ◽  
Partial Pressure ◽  
Compartment Model ◽  
Lung Model ◽  
Anesthetic Agents ◽  
Partial Pressures ◽  
Three Compartment Model ◽  
Log Normal ◽  
End Tidal ◽  
Blood Solubility

Background According to the “three-compartment” model of ventilation-perfusion () inequality, increased scatter in the lung under general anesthesia is reflected in increased alveolar deadspace fraction (Vda/Va) customarily measured using end-tidal to arterial (a-a) partial pressure gradients for carbon dioxide. a-a gradients for anesthetic agents such as isoflurane are also significant but have been shown to be inconsistent with those for carbon dioxide under the three-compartment theory. The authors hypothesized that three-compartment Vda/Va calculated using partial pressures of four inhalational agents (Vda/Vag) is different from that calculated using carbon dioxide (Vda/Vaco2) measurements, but similar to predictions from multicompartment models of physiologically realistic “log-normal” distributions. Methods In an observational study, inspired, end-tidal, arterial, and mixed venous partial pressures of halothane, isoflurane, sevoflurane, or desflurane were measured simultaneously with carbon dioxide in 52 cardiac surgery patients at two centers. Vda/Va was calculated from three-compartment model theory and compared for all gases. Ideal alveolar (Pag) and end-capillary partial pressure (Pc’g) of each agent, theoretically identical, were also calculated from end-tidal and arterial partial pressures adjusted for deadspace and venous admixture. Results Calculated Vda/Vag was larger (mean ± SD) for halothane (0.47 ± 0.08), isoflurane (0.55 ± 0.09), sevoflurane (0.61 ± 0.10), and desflurane (0.65 ± 0.07) than Vda/Vaco2 (0.23 ± 0.07 overall), increasing with lower blood solubility (slope [Cis], –0.096 [–0.133 to –0.059], P < 0.001). There was a significant difference between calculated ideal Pag and Pc’g median [interquartile range], Pag 5.1 [3.7, 8.9] versus Pc’g 4.0[2.5, 6.2], P = 0.011, for all agents combined. The slope of the relationship to solubility was predicted by the log-normal lung model, but with a lower magnitude relative to calculated Vda/Vag. Conclusions Alveolar deadspace for anesthetic agents is much larger than for carbon dioxide and related to blood solubility. Unlike the three-compartment model, multicompartment scatter models explain this from physiologically realistic gas uptake distributions, but suggest a residual factor other than solubility, potentially diffusion limitation, contributes to deadspace. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New

Gas Exchange

2017 ◽  
Author(s):  
John W. Kreit
Keyword(s):  
Carbon Dioxide ◽  
Gas Exchange ◽  
Partial Pressure ◽  
Capillary Blood ◽  
Pressure Gradients ◽  
Arterial Blood ◽  
Pulmonary Capillary ◽  
Partial Pressures ◽  
Pulmonary Capillary Blood ◽  
And Diffusion

Gas Exchange explains how four processes—delivery of oxygen, excretion of carbon dioxide, matching of ventilation and perfusion, and diffusion—allow the respiratory system to maintain normal partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2) in the arterial blood. Partial pressure is important because O2 and CO2 molecules diffuse between alveolar gas and pulmonary capillary blood and between systemic capillary blood and the tissues along their partial pressure gradients, and diffusion continues until the partial pressures are equal. Ventilation is an essential part of gas exchange because it delivers O2, eliminates CO2, and determines ventilation–perfusion ratios. This chapter also explains how and why abnormalities in each of these processes may reduce PaO2, increase PaCO2, or both.

Single-phase aluminum nitride films by dc-magnetron sputtering

1990 ◽  
Vol 5 (11) ◽  
pp. 2677-2681 ◽  
Author(s):  
J. S. Morgan ◽  
W. A. Bryden ◽  
T. J. Kistenmacher ◽  
S. A. Ecelberger ◽  
T. O. Poehler
Keyword(s):  
Aluminum Nitride ◽  
Magnetron Sputtering ◽  
Partial Pressure ◽  
Single Phase ◽  
Target Surface ◽  
Partial Pressures ◽  
Wide Range ◽  
Single Crystal Sapphire ◽  
Deposited Film ◽  
Deposited Films

Single-phase aluminum nitride films were deposited onto fused quartz and single-crystal sapphire by current-controlled, reactive, de magnetron sputtering from an aluminum metal target. Optical and structural properties were observed to correlate systematically with the composition of the sputter gas over a wide range of nitrogen partial pressures. A transition in the electrical conductivity of the deposited films occurred as a function of N2 partial pressure. This transition is driven by the condition of the target surface. When the N2 partial pressure was high and the target surface was substantially covered with AlNx, the deposited film was insulating, stoichiometric AlN. When the N2 partial pressure was low and the target surface was substantially Al°, the deposited film was conducting, substoichiometric AlNx.

scholarly journals The alveolar gas equation: do lessons from WW2 research into high flying pilots provide insights into the adaptation to high altitude flight in birds?

2020 ◽  
Author(s):  
Michael Seear
Keyword(s):  
Gas Exchange ◽  
Partial Pressure ◽  
High Altitude ◽  
Oxygen Transport ◽  
Predictive Accuracy ◽  
Gas Diffusion ◽  
Respiratory Physiology ◽  
Partial Pressures ◽  
Starting Point ◽  
Sequential Addition

AbstractDalton’s law of partial pressures applies equally to birds and mammals so, as gas moves from the nostrils to the smallest gas-diffusion airways, the sequential addition of water vapour and CO2, steadily reduce the partial pressure of O2 (PO2) within the gas mixture. The PO2, at the point of gas exchange, at sea level, will be about 60 mm Hg less than the original PO2 within atmospheric air. As a result, the inspired PO2 is an inaccurate starting point for any model of oxygen transport. In humans, the interactions of gases at the point of diffusion, is described and quantified by the Alveolar Gas Equation (AGE). Its development during WW2, provided valuable insights into human gas exchange and also into the responses to high altitude flight in pilots but, except for an early study of hypoxia in pigeons, the AGE is not mentioned in the avian literature. Even detailed models of oxygen transport in birds omit the effect of CO2 clearance on pulmonary oxygen transfer. This paper develops two related arguments concerning the application of the AGE to birds. The first is that avian blood gas predictions, based on the theory of multicapillary serial arterialization (MSA), are inaccurate because they do not account for the added partial pressure of diffused CO2. The second is that the primary adaptation to hypobaric hypoxia is the same for both classes and consists of defending PaO2 by reducing PaCO2 through increasing hyperventilation. Support for the first is demonstrated by comparing PaO2 predictions made using the AGE, with published values from avian studies and also against values predicted by the theory of MSA. The second is illustrated by comparing the results of high altitude studies of both birds and humans. The application of the AGE to avian respiratory physiology would improve the predictive accuracy of models of the O2 cascade and would also provide better insights into the primary adaptation to high altitude flight.

Alveolar capillary temperature compared with aortic and bronchial wedge temperatures

1964 ◽  
Vol 19 (4) ◽  
pp. 760-764 ◽  
Author(s):  
A. W. T. Edwards
Keyword(s):  
Body Temperature ◽  
Gas Exchange ◽  
Technical Assistance ◽  
Bronchial Tree ◽  
The Body ◽  
Inert Gases ◽  
Significant Difference ◽  
The Right ◽  
Capillary Temperature ◽  
Alveolar Capillary

Temperature for gas exchange in the alveolar capillaries was determined by the helium-argon method in nine dogs over a range of body temperatures from 37–42 C. The experiments were much more prolonged than those previously carried out in man. Results were compared with simultaneous measurements in the aortic arch, right ventricle, gastrointestinal tract, and bronchial tree. There was no significant difference between alveolar capillary temperatures and those in the right and left heart and bronchial wedge position, even when body temperature was changing. Deep rectal temperatures gave a reasonable estimate of alveolar temperature provided the body temperature was steady, but esophageal and gastric measurements were not reliable, the reading increasing as the stomach was approached. The results support the validity of the helium-argon method and indicate that accurate estimates of alveolar capillary temperature may be obtained by direct measurements in the central circulation or bronchial wedge position. Note: With the Technical Assistance of Judith Laurie alveolar gas exchange; intravascular temperatures; inert gases; solubility of gases; esophageal temperature; gastric temperature Submitted on December 16, 1963

Systematic trends of YBa2Cu3O7−δ thin films post annealed in low oxygen partial pressures

1994 ◽  
Vol 9 (8) ◽  
pp. 1936-1945 ◽  
Author(s):  
S.Y. Hou ◽  
Julia M. Phillips ◽  
D.J. Werder ◽  
T.H. Tiefel ◽  
J.H. Marshall ◽  
...  
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Low Oxygen ◽  
Normal State Resistivity ◽  
Film Properties ◽  
Ion Channeling ◽  
Partial Pressures ◽  
High Annealing ◽  
Wide Range ◽  
Different Characteristics

Systematic studies have been performed on 1000 Å YBa2Cu3O7−δ films produced by the BaF2 process and annealed in an oxygen partial pressure (Po2) range from 740 Torr to 10 mTorr as well as a temperature range from 600 to 1050 °C. The results show that while high quality films can be annealed in a wide range of oxygen partial pressure, they have different characteristics. In general, crystalline quality and Tc are optimized at high Po2 and high annealing temperature, while strong flux pinning and low normal state resistivity are achieved at lower values of both variables. Under optimized low Po2 conditions, an ion channeling Xmin of 6% is obtained on films as thick as 5000 Å. This study will serve as a useful guide to tailoring film properties to the application at hand.

Measurement of dissolved carbon dioxide

1976 ◽  
Vol 22 (1) ◽  
pp. 52-56 ◽  
Author(s):  
J. S. Alford Jr.
Keyword(s):  
Carbon Dioxide ◽  
Partial Pressure ◽  
Operating Conditions ◽  
Exhaust Gas ◽  
Rubber Tubing ◽  
Dissolved Carbon ◽  
Dissolved Carbon Dioxide ◽  
Wide Range ◽  
Significant Difference

Several probes for measuring dissolved carbon dioxide (CO2) concentration were installed in a 68-litre fermentor and their effectiveness compared. Submerged silastic rubber tubing gave reproducible results over a wide range of operating conditions and was generally superior to all other probes evaluated.The silastic rubber probe was used to compare the partial pressure of CO2 in viscous fermentation media with that in the fermentor exhaust gas. No significant difference was found.Results show that determination of the CO2 partial pressure in the exhaust gas gives an excellent approximation of the partial pressure of dissolved CO2 in the liquid medium, eliminating the need for measurement of CO2 concentration in the broth.

Ventilation-perfusion inhomogeneity increases gas uptake in anesthesia: computer modeling of gas exchange

2001 ◽  
Vol 91 (1) ◽  
pp. 10-16 ◽  
Author(s):  
Philip J. Peyton ◽  
Gavin J. B. Robinson ◽  
Bruce Thompson
Keyword(s):  
Steady State ◽  
Standard Deviation ◽  
Gas Exchange ◽  
Partial Pressure ◽  
Computer Model ◽  
Maintenance Phase ◽  
Gas Uptake ◽  
Normal Distributions ◽  
Log Normal ◽  
Mixed Venous

Ventilation-perfusion (V˙a/Q˙) inhomogeneity was modeled to measure its effect on overall gas exchange during maintenance-phase N2O anesthesia with an inspired O2 concentration of 30%. A multialveolar compartment computer model was used based on physiological log normal distributions of V˙a/Q˙ inhomogeneity. Increasing the log standard deviation of the distribution of perfusion from 0 to 1.75 paradoxically increased O2 uptake (V˙o 2) where a low mixed venous partial pressure of N2O [high N2O uptake (V˙n 2 o)] was specified. With rising mixed venous partial pressure of N2O, a threshold was observed where V˙o 2 began to fall, whereas V˙n 2 o began to rise with increasing V˙a/Q˙ inhomogeneity. This phenomenon is a magnification of the concentrating effects thatV˙o 2 andV˙n 2 o have on each other in low V˙a/Q˙ compartments. During “steady-state” N2O anesthesia,V˙n 2 o is predicted to paradoxically increase in the presence of worseningV˙a/Q˙ inhomogeneity.

Gas exchange in a three-compartment lung model analyzed by forcing sinusoids of N2O

1993 ◽  
Vol 75 (4) ◽  
pp. 1863-1876 ◽  
Author(s):  
C. E. Hahn ◽  
A. M. Black ◽  
S. A. Barton ◽  
I. Scott
Keyword(s):  
Blood Flow ◽  
Gas Exchange ◽  
Dead Space ◽  
Animal Studies ◽  
Lung Model ◽  
Distribution Model ◽  
Mixed Venous Blood ◽  
Blood Gas ◽  
Partial Pressures ◽  
Wide Range

A mathematical gas exchange model, using sinusoidal forcing functions of inert inspired gas (A. Zwart, R. C. Seagrave, and A. Van Dieren. J. Appl. Physiol. 41: 419#x2013;424, 1976), has been extended by us to include dead space (VD), a single alveolar compartment (VA) perfused with blood flow (Qp), and a shunt (Qs). In this new work we use N2O as the indicator gas in the mathematical model and in the experimental studies, in low enough concentrations [<6% (vol/vol)] to avoid anesthetic effects. Mathematical relationships between the inspired and expired N2O gas partial pressures, the blood gas N2O partial pressures, and their variation with forcing frequency are derived for a continuous ventilation uptake and a conventional anesthetic gas distribution model. We show that these gas and blood gas N2O relationships give direct derivation of cardiorespiratory parameters such as VA, Qp, the dead space-to-total ventilation ratio (VD/VT), and the shunt-to-total blood flow ratio (Qs/QT) without altering the subject's oxygenation and that they are essentially free from recirculation effects at high forcing frequencies > or = 2 min-1. Theoretical results from the model are presented for a wide range of forcing frequencies between 2 x 10(-2) and 10 min-1 (sinusoid periods 30#x2013;0.1 min), and these show that VA, Qp, and VD/VT can all be measured by N2O forcing frequencies > or = 1 min-1. We also present results from five animal studies, with an experimental inspired gas forcing frequency range of 0.125 to 2 min-1, which show qualitative agreement with the predictions of the continuous ventilation model. During these animal studies both mass spectrometric N2O respiratory gas measurements and intravascular polarographic arterial and mixed venous blood N2O partial pressure measurements were made, and examples of these in vivo measurements are presented, together with examples of the calculations derived from them.

Liver Elastography in Healthy Children Using Three Different Systems – How Many Measurements Are Necessary?

2020 ◽  
Author(s):  
Anders Batman Mjelle ◽  
Anesa Mulabecirovic ◽  
Roald Flesland Havre ◽  
Edda Jonina Olafsdottir ◽  
Odd Helge Gilja ◽  
...  
Keyword(s):  
Shear Wave ◽  
Transient Elastography ◽  
Intraclass Correlation ◽  
Age Groups ◽  
Liver Stiffness ◽  
Shear Wave Elastography ◽  
Healthy Children ◽  
Significant Difference ◽  
Pediatric Liver Disease ◽  
Liver Elastography

Abstract Purpose Liver elastography is increasingly being applied in screening for and follow-up of pediatric liver disease, and has been shown to correlate well with fibrosis staging through liver biopsy. Because time is of the essence when examining children, we wanted to evaluate if a reliable result can be achieved with fewer acquisitions. Materials and Methods 243 healthy children aged 4–17 years were examined after three hours of fasting. Participants were divided into four age groups: 4–7 years; 8–11 years; 12–14 years and 15–17 years. Both two-dimensional shear wave elastography (2D-SWE; GE Logiq E9) and point shear wave elastography (pSWE; Samsung RS80A with Prestige) were performed in all participants, while transient elastography (TE, Fibroscan) was performed in a subset of 87 children aged 8–17 years. Median liver stiffness measurement (LSM) values of 3, 4, 5, 6, 7, and 8 acquisitions were compared with the median value of 10 acquisitions (reference standard). Comparison was performed for all participants together as well as within every specific age group. We investigated both the intraclass correlation coefficient (ICC) with absolute agreement and all outliers more than 10 %, 20 % or ≥ 0.5 or 1.0 kPa from the median of 10 acquisitions. Results For all three systems there was no significant difference between three and ten acquisitions, with ICCs ≥ 0.97. All systems needed 4 acquisitions to achieve no LSM deviating ≥ 1.0 kPa of a median of ten. To achieve no LSM deviating ≥ 20 % of a median of ten acquisitions, pSWE and TE needed 4 acquisitions, while 2D-SWE required 6 acquisitions. Conclusion Our results contradict recommendations of 10 acquisitions for pSWE and TE and only 3 for 2D-SWE.

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