Conducting airway gas exchange: diffusion-related differences in inert gas elimination

1992 ◽  
Vol 72 (4) ◽  
pp. 1581-1588 ◽  
Author(s):  
E. R. Swenson ◽  
H. T. Robertson ◽  
N. L. Polissar ◽  
M. E. Middaugh ◽  
M. P. Hlastala
Keyword(s):  
Gas Exchange ◽  
Exchange Capacity ◽  
Inert Gases ◽  
Inert Gas ◽  
Diffusion Resistance ◽  
Molecular Weights ◽  
Conducting Airway ◽  
Group 2 ◽  
Airway Gas Exchange ◽  
Group 1

We studied CO2 and inert gas elimination in the isolated in situ trachea as a model of conducting airway gas exchange. Six inert gases with various solubilities and molecular weights (MW) were infused into the left atria of six pentobarbital-anesthetized dogs (group 1). The unidirectionally ventilated trachea behaved as a high ventilation-perfusion unit (ratio = 60) with no appreciable dead space. Excretion of higher-MW gases appeared to be depressed, suggesting a MW dependence to inert gas exchange. This was further explored in another six dogs (group 2) with three gases of nearly equal solubility but widely divergent MWs (acetylene, 26; Freon-22, 86.5; isoflurane, 184.5). Isoflurane and Freon-22 excretions were depressed 47 and 30%, respectively, relative to acetylene. In a theoretical model of airway gas exchange, neither a tissue nor a gas phase diffusion resistance predicted our results better than the standard equation for steady-state alveolar inert gas elimination. However, addition of a simple ln (MW) term reduced the remaining residual sum of squares by 40% in group 1 and by 83% in group 2. Despite this significant MW influence on tracheal gas exchange, we calculate that the quantitative gas exchange capacity of the conducting airways in total can account for less than or equal to 16% of any MW-dependent differences observed in pulmonary inert gas elimination.

Tracheal gas exchange: perfusion-related differences in inert gas elimination

1995 ◽  
Vol 79 (3) ◽  
pp. 918-928 ◽  
Author(s):  
J. E. Souders ◽  
S. C. George ◽  
N. L. Polissar ◽  
E. R. Swenson ◽  
M. P. Hlastala
Keyword(s):  
Gas Exchange ◽  
Partial Pressure ◽  
Positive Function ◽  
Inert Gases ◽  
Inert Gas ◽  
Blood Gas ◽  
Fluorescent Microspheres ◽  
Conducting Airways ◽  
Airway Gas Exchange

Exchange of inert gases across the conducting airways has been demonstrated by using an isolated dog tracheal preparation and has been characterized by using a mathematical model (E. R. Swenson, H. T. Robertson, N. L. Polissar, M. E. Middaugh, and M. P. Hlastala, J. Appl. Physiol. 72: 1581–1588, 1992). Theory predicts that gas exchange is both diffusion and perfusion dependent, with gases with a higher blood-gas partition coefficient exchanging more efficiently. The present study evaluated the perfusion dependence of airway gas exchange in an in situ canine tracheal preparation. Eight dogs were studied under general anesthesia with the same isolated tracheal preparation. Tracheal perfusion (Q) was altered from control blood flow (Qo) by epinephrine or papaverine instilled into the trachea and was measured with fluorescent microspheres. Six inert gases of differing blood-gas partition coefficients were used to measure inert gas elimination. Gas exchange was quantified as excretion (E), equal to exhaled partial pressure divided by arterial partial pressure. Data were plotted as ln [E/(l-E)] vs. In (Q/Qo), and the slopes were determined by least squares. Excretion was a positive function of Q, and the magnitude of the response of each gas to changes in Q was similar and highly significant (P < or = 0.0002). These results confirm a substantial perfusion dependence of airway gas exchange.

Respiratory and inert gas exchange during high-frequency ventilation

1982 ◽  
Vol 52 (3) ◽  
pp. 683-689 ◽  
Author(s):  
H. T. Robertson ◽  
R. L. Coffey ◽  
T. A. Standaert ◽  
W. E. Truog
Keyword(s):  
Gas Exchange ◽  
High Frequency ◽  
Gas Flow ◽  
Inert Gases ◽  
Inert Gas ◽  
High Frequency Ventilation ◽  
Physiological Dead Space ◽  
Volume Ventilation ◽  
Frequency Ventilation ◽  
Carrier Gases

Pulmonary gas exchange during high-frequency low-tidal volume ventilation (HFV) (10 Hz, 4.8 ml/kg) was compared with conventional ventilation (CV) and an identical inspired fresh gas flow in pentobarbital-anesthetized dogs. Comparing respiratory and infused inert gas exchange (Wagner et al., J. Appl. Physiol. 36: 585--599, 1974) during HFV and CV, the efficiency of oxygenation was not different, but the Bohr physiological dead space ratio was greater on HFV (61.5 +/- 2.2% vs. 50.6 +/- 1.4%). However, the elimination of the most soluble inert gas (acetone) was markedly enhanced by HFV. The increased elimination of the soluble infused inert gases during HFV compared with CV may be related to the extensive intraregional gas mixing that allows the conducting airways to serve as a capacitance for the soluble inert gases. Comparing as exchange during HFV with three different density carrier gases (He, N2, and Ar), the efficiency of elimination of Co2 or the intravenously infused inert gases was greatest with He-O2. However, the alveolar-arterial partial pressure difference for O2 on He-O2 exceeded that on N2-O2 by 5.4 Torr during HFV. The finding agrees with similar observations during CV, suggesting that this aspect of gas exchange is not substantially altered by HFV.

Pulmonary gas exchange during exercise in athletes. I. Ventilation-perfusion mismatch and diffusion limitation

1994 ◽  
Vol 77 (2) ◽  
pp. 912-917 ◽  
Author(s):  
S. R. Hopkins ◽  
D. C. McKenzie ◽  
R. B. Schoene ◽  
R. W. Glenny ◽  
H. T. Robertson
Keyword(s):  
Gas Exchange ◽  
Aerobic Capacity ◽  
Maximal Exercise ◽  
Cycle Ergometer ◽  
Pulmonary Gas Exchange ◽  
Inert Gases ◽  
Inert Gas ◽  
Diffusion Limitation ◽  
Maximal Aerobic Capacity ◽  
Arterial Blood

To investigate pulmonary gas exchange during exercise in athletes, 10 high aerobic capacity athletes (maximal aerobic capacity = 5.15 +/- 0.52 l/min) underwent testing on a cycle ergometer at rest, 150 W, 300 W, and maximal exercise (372 +/- 22 W) while trace amounts of six inert gases were infused intravenously. Arterial blood samples, mixed expired gas samples, and metabolic data were obtained. Indexes of ventilation-perfusion (VA/Q) mismatch were calculated by the multiple inert gas elimination technique. The alveolar-arterial difference for O2 (AaDO2) was predicted from the inert gas model on the basis of the calculated VA/Q mismatch. VA/Q heterogeneity increased significantly with exercise and was predicted to increase the AaDO2 by > 17 Torr during heavy and maximal exercise. The observed AaDO2 increased significantly more than that predicted by the inert gas technique during maximal exercise (10 +/- 10 Torr). These data suggest that this population develops diffusion limitation during maximal exercise, but VA/Q mismatch is the most important contributor (> 60%) to the wide AaDO2 observed.

Elevated alveolar PCO2 relative to predicted values during normal gas exchange

1977 ◽  
Vol 43 (2) ◽  
pp. 357-364 ◽  
Author(s):  
H. T. Robertson ◽  
M. P. Hlastala
Keyword(s):  
Gas Exchange ◽  
Dead Space ◽  
Anomalous Behavior ◽  
Inert Gases ◽  
Solubility Data ◽  
Inert Gas ◽  
Solubility Curve ◽  
Predicted Values ◽  
Respiratory Dead Space ◽  
Haldane Effect

A negative aADCO2 has been demonstrated during ventilation with hypercarbic gas mixtures and during rebreathing, but has never been demonstrated during normal gas exchange. This anomalous behavior of CO2 was studied by comparing it to the behavior of five infused inert gases during normal gas exchange in 10 anesthetized mongrel dogs. The distribution of VA/Q heterogeneity and the respiratory dead space in the animals was quantitated using excretion-solubility data from the five infused inert gases. The predicted excretion fraction (PACO2/PVCO2) for CO2 was obtained from the inert gas excretion-solubility curve, using a measured solubility for CO2. The measured excretion fraction for CO2 (PACO2/PVCO2), even after correction for Haldane effect, was significantly greater than the predicted fraction (P less than 0.001). This corresponded to an alveolar PCO2 that exceeded the predicted value by a mean of 5.0 Torr.

Graphical analysis of multiple inert gas elimination data

1983 ◽  
Vol 55 (1) ◽  
pp. 32-36 ◽  
Author(s):  
W. E. Stewart ◽  
S. M. Mastenbrook
Keyword(s):  
Gas Exchange ◽  
Companion Paper ◽  
Graphical Analysis ◽  
Inert Gases ◽  
Inert Gas ◽  
Additional Test ◽  
Multicompartmental Model ◽  
Simple Rules ◽  
Gas Measurements ◽  
Mixed Venous

A plot of measured retention-excretion ratios [(Ri/Ei)obs] vs. reciprocal solubility (1/lambda i) for selected inert gases allows quick detection of shunt and ventilation-perfusion (V/Q) inhomogeneity in the lung. We derive simple rules for constructing a smooth R/E function from the data, using a multicompartmental model of the lung. If mixed venous inert gas measurements are available, the values [lambda i(1-Ri)/Ei]obs for the infused gases can be used to estimate the overall VT/QT ratio and provide an additional test of the consistency of the data. For any set of equilibrium compartments ventilated and perfused in parallel, we show that d(R/E)/d(1/lambda) cannot be negative, nor can d2(R/E)/d(1/lambda)2 be greater than zero. A rectilinear R/E function implies a narrow distribution of V/Q among the gas exchange compartments, whereas a downward-concave curve implies a broader distribution. The shunt perfusion and dead-space ventilation can be estimated from the asymptotes of the R/E function. The range of V/Q for the gas exchange compartments can also be bracketed if a well-defined region of curvature is present in the graph. Finally, from the R/E vs. 1/lambda graph and (if mixed venous data are available) from the lambda(1-R)/E values, we can determine quickly whether the data deserve the detailed numerical analysis outlined in our companion paper.

Soluble gas exchange in the pulmonary airways of sheep

2004 ◽  
Vol 97 (5) ◽  
pp. 1702-1708 ◽  
Author(s):  
Carmel Schimmel ◽  
Susan L. Bernard ◽  
Joseph C. Anderson ◽  
Nayak L. Polissar ◽  
S. Lakshminarayan ◽  
...  
Keyword(s):  
Gas Exchange ◽  
Partial Pressure ◽  
Bronchial Artery ◽  
Left Pulmonary Artery ◽  
Inert Gases ◽  
Bronchial Circulation ◽  
Arterial Blood ◽  
Pulmonary Airways ◽  
Airway Gas Exchange

We studied the airway gas exchange properties of five inert gases with different blood solubilities in the lungs of anesthetized sheep. Animals were ventilated through a bifurcated endobronchial tube to allow independent ventilation and collection of exhaled gases from each lung. An aortic pouch at the origin of the bronchial artery was created to control perfusion and enable infusion of a solution of inert gases into the bronchial circulation. Occlusion of the left pulmonary artery prevented pulmonary perfusion of that lung so that gas exchange occurred predominantly via the bronchial circulation. Excretion from the bronchial circulation (defined as the partial pressure of gas in exhaled gas divided by the partial pressure of gas in bronchial arterial blood) increased with increasing gas solubility (ranging from a mean of 4.2 × 10−5 for SF6 to 4.8 × 10−2 for ether) and increasing bronchial blood flow. Excretion was inversely affected by molecular weight (MW), demonstrating a dependence on diffusion. Excretions of the higher MW gases, halothane (MW = 194) and SF6 (MW = 146), were depressed relative to excretion of the lower MW gases ethane, cyclopropane, and ether (MW = 30, 42, 74, respectively). All results were consistent with previous studies of gas exchange in the isolated in situ trachea.

Influence of Gas Composition on Recurrence of Atelectasis after a Reexpansion Maneuver during General Anesthesia

1995 ◽  
Vol 82 (4) ◽  
pp. 832-842. ◽  
Author(s):  
Hans Ulrich Rothen ◽  
Bengt Sporre ◽  
Greta Engberg ◽  
Goran Wegenius ◽  
Marieann Hogman ◽  
...  
Keyword(s):  
Gas Exchange ◽  
General Anesthesia ◽  
Respiratory System ◽  
Vital Capacity ◽  
Recruitment Maneuver ◽  
Arterial Oxygen ◽  
Gas Composition ◽  
Group 2 ◽  
The Impact ◽  
Group 1

Background Atelectasis, an important cause of impaired gas exchange during general anesthesia, may be eliminated by a vital capacity maneuver. However, it is not clear whether such a maneuver will have a sustained effect. The aim of this study was to determine the impact of gas composition on reappearance of atelectasis and impairment of gas exchange after a vital capacity maneuver. Methods A consecutive sample of 12 adults with healthy lungs who were scheduled for elective surgery were studied. Thirty minutes after induction of anesthesia with fentanyl and propofol, the lungs were hyperinflated manually up to an airway pressure of 40 cmH2O. FIO2 was either kept at 0.4 (group 1, n = 6) or changed to 1.0 (group 2, n = 6) during the recruitment maneuver. Atelectasis was assessed by computed tomography. The amount of dense areas was measured at end-expiration in a transverse plane at the base of the lungs. The ventilation-perfusion distributions (VA/Q) were estimated with the multiple inert gas elimination technique. The static compliance of the total respiratory system (Crs) was measured with the flow interruption technique. Results In group 1 (FIO2 = 0.4), the recruitment maneuver virtually eliminated atelectasis for at least 40 min, reduced shunt (VA/Q &lt; 0.005), and increased at the same time the relative perfusion to poorly ventilated lung units (0.005 &lt; VA/Q &lt; 0.1; mean values are given). The arterial oxygen tension (PaO2) increased from 137 mmHg (18.3 kPa) to 163 mmHg (21.7 kPa; before and 40 min after recruitment, respectively; P = 0.028). In contrast to these findings, atelectasis recurred within 5 min after recruitment in group 2 (FIO2 = 1.0). Comparing the values before and 40 min after recruitment, all parameters of VA/Q were unchanged. In both groups, Crs increased from 57.1/55.0 ml.cmH2O-1 (group 1/group 2) before to 70.1/67.4 ml.cmH2O-1 after the recruitment maneuver. Crs showed a slow decrease thereafter (40 min after recruitment: 61.4/60.0 ml.cmH2O-1), with no difference between the two groups. Conclusions The composition of inspiratory gas plays an important role in the recurrence of collapse of previously reexpanded atelectatic lung tissue during general anesthesia in patients with healthy lungs. The reason for the instability of these lung units remains to be established. The change in the amount of atelectasis and shunt appears to be independent of the change in the compliance of the respiratory system.

Multiple inert gas elimination technique

1984 ◽  
Vol 56 (1) ◽  
pp. 1-7 ◽  
Author(s):  
M. P. Hlastala
Keyword(s):  
Gas Exchange ◽  
Mathematical Models ◽  
Dead Space ◽  
Experimental Error ◽  
General Pattern ◽  
Pulmonary Gas Exchange ◽  
Inert Gases ◽  
Inert Gas ◽  
Biological Phenomena ◽  
Mixed Venous

The understanding of pulmonary gas exchange has undergone several major advances since the early 1900‣s. One of the most significant was the development of the multiple inert gas elimination technique for assessing the ventilation-perfusion (VA/Q) distribution in the lung. By measuring the mixed venous, arterial, and mixed expired concentrations of six infused inert gases, it is possible to distinguish shunt, dead space, and the general pattern of VA/Q distribution. As with all mathematical models of complex biological phenomena, there are limitations that can result in errors of interpretation if the technique is applied uncritically. In addition, methodological limitations also can lead to both experimental error and errors of interpretation. Despite these limitations, the multiple inert gas elimination technique remains the most powerful tool developed to date to analyze pulmonary gas exchange.

scholarly journals Impact of Airway Gas Exchange on the Multiple Inert Gas Elimination Technique: Theory

2010 ◽  
Vol 38 (3) ◽  
pp. 1017-1030 ◽  
Author(s):  
Joseph C. Anderson ◽  
Michael P. Hlastala
Keyword(s):  
Gas Exchange ◽  
Inert Gas ◽  
Airway Gas Exchange

Modeling steady-state inert gas exchange in the canine trachea

1995 ◽  
Vol 79 (3) ◽  
pp. 929-940 ◽  
Author(s):  
S. C. George ◽  
J. E. Souders ◽  
A. L. Babb ◽  
M. P. Hlastala
Keyword(s):  
Blood Flow ◽  
Gas Exchange ◽  
Sulfur Hexafluoride ◽  
Functional Dependence ◽  
Inert Gases ◽  
Diffusing Capacity ◽  
Relative Contribution ◽  
Airway Gas Exchange ◽  
And Diffusion

The functional dependence between tracheal gas exchange and tracheal blood flow has been previously reported using six inert gases (sulfur hexafluoride, ethane, cyclopropane, halothane, ether, and acetone) in a unidirectionally ventilated (1 ml/s) canine trachea (J. E. Souders, S. C. George, N. L. Polissar, E. R. Swenson, and M. P. Hlastala. J. Appl. Physiol. 79: 918–928, 1995). To understand the relative contribution of perfusion-, diffusion- and ventilation-related resistances to airway gas exchange, a dynamic model of the bronchial circulation has been developed and added to the existing structure of a previously described model (S. C. George, A. L. Babb, and M. P. Hlastala. J. Appl. Physiol. 75: 2439–2449, 1993). The diffusing capacity of the trachea (in ml gas.s-1.atm-1) was used to optimize the fit of the model to the experimental data. The experimental diffusing capacities as predicted by the model in a 10-cm length of trachea are as follows: sulfur hexafluoride, 0.000055; ethane, 0.00070; cyclopropane, 0.0046; halothane, 0.029; ether, 0.10; and acetone, 1.0. The diffusing capacities are reduced relative to an estimated diffusing capacity. The ratio of experimental to estimated diffusing capacity ranges from 4 to 23%. The model predicts that over the ventilation-to-tracheal blood flow range (10–700) attained experimentally, tracheal gas exchange is limited primarily by perfusion- and diffusion-related resistances. However, the contribution of the ventilation-related resistance increases with increasing gas solubility and cannot be neglected in the case of acetone. The increased role of diffusion in tracheal gas exchange contrasts with perfusion-limited alveolar exchange and is due primarily to the increased thickness of the bronchial mucosa.

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