Human alveolar gas-mixing efficiency for gases of differing diffusivity in health and airflow limitation

1987 ◽  
Vol 73 (4) ◽  
pp. 351-359 ◽  
Author(s):  
E. A. Harris ◽  
P. R. Buchanan ◽  
R. M. L. Whitlock
Keyword(s):  
Dead Space ◽  
Open Circuit ◽  
Airflow Limitation ◽  
Mixing Efficiency ◽  
Ventilation Distribution ◽  
Asthmatic Patients ◽  
Before And After ◽  
Heavy Gas ◽  
Conducting Airways ◽  
Diffusive Mixing

1. Incomplete mixing of alveolar gas may be expressed as an equivalent alveolar dead space serving a remaining alveolar space in which mixing is regarded as complete. Calculation of this dead space during multiple-breath, inert gas wash-in or wash-out leads to an estimate of ‘multiple-breath alveolar mixing efficiency’ (MBME). 2. We measured MBME in 25 healthy subjects and six patients with chronic airflow limitation (CAL), and in three asthmatic patients before and after bronchial provocation with histamine aerosol, from successive breaths during open-circuit, multiple-breath wash-in of a mixture containing helium (He) and sulphur hexafluoride (SF6). The simultaneous use of a light and a heavy gas helps to identify diffusive mechanisms. 3. MBME fell almost linearly with log Z, the proportion of total wash-in remaining uncompleted. For a given Z, MBME was always lower for SF6 than for He in the same subject. In health the lowest MBME (52.2%) was seen for SF6 in a man aged 21 years. The same wash-in yielded a ventilation distribution with an extreme range of specific ventilation of less than 1 decade. MBME of this order is thus consistent with estimates of ventilation distribution in health. 4. Patients with CAL showed a big increase in the volume of the conducting airways or ‘series dead space’ (VDS) for both gases, and VDS was always bigger for SF6 than for He. This very large VDS appears to be the main reason for wash-in delay in these patients, followed by impaired diffusive mixing in the peripheral air spaces. Ventilation maldistribution may play little part in the mixing defect. 5. In asthma, bronchoconstriction by histamine reduced VDS and MBME, but MBME did not differ between He and SF6. This suggests a shortening of diffusion distances beyond the narrowed bronchioles which may help to mitigate the (here predominant) effects of maldistribution on mixing efficiency.

Distal effects of tracheal gas insufflation: changes with catheter position and oleic acid lung injury

1996 ◽  
Vol 81 (3) ◽  
pp. 1121-1127 ◽  
Author(s):  
A. Nahum ◽  
S. A. Ravenscraft ◽  
A. B. Adams ◽  
J. J. Marini
Keyword(s):  
Oleic Acid ◽  
Lung Injury ◽  
Dead Space ◽  
Minute Ventilation ◽  
Catheter Position ◽  
Tracheal Gas Insufflation ◽  
Before And After ◽  
Dead Space Volume ◽  
Catheter Tip ◽  
Conducting Airways

We separated distal (turbulence-related) and proximal (dead space washout-related) effects of tracheal gas insufflation (TGI) by comparing the effects of straight and inverted catheters. We reasoned that the inverted catheter was unlikely to remove CO2 from conducting airways distal to its orifice. In six normal dogs during TGI at 10 l/min, advancing the catheters from 10 to 1 cm above the main carina decreased dead space volume by 29 +/- 12 and 12 +/- 6 ml (P < 0.04) with the straight and inverted catheters, respectively. By comparison, the tracheal volume between 10 and 1 cm above the carina was 15 +/- 2 ml. In another set of dogs (n = 5), we examined the distal effects of TGI before and after oleic acid-induced lung injury. During TGI at 10 l/min before and after oleic acid injury, the differences in arterial PCO2 between the straight and inverted catheters were 5 +/- and 9 +/- 6 Torr (P < 0.18), respectively. Our data suggest that distal effects of TGI become more pronounced as the catheter tip is positioned closer to the main carina. The distal effects of TGI were not diminished after oleic acid injury when minute ventilation was maintained constant.

Model simulations of gas mixing and ventilation distribution in the human lung

1990 ◽  
Vol 69 (6) ◽  
pp. 2269-2279 ◽  
Author(s):  
S. Verbanck ◽  
M. Paiva
Keyword(s):  
Dead Space ◽  
Human Lung ◽  
Large Range ◽  
Lung Model ◽  
Mixing Efficiency ◽  
Model Parameters ◽  
Ventilation Distribution ◽  
Model Simulations ◽  
Consistent Picture ◽  
Diffusion And Convection

A new lung model that incorporates intra-acinar diffusion- and convection-dependent inhomogeneities (DCDI) and interregional and intraregional convection-dependent inhomogeneities (CDI) is described. The model is divided into two regions, each containing two subunits. Each of the four subunits in the model consists of a multi-branch-point structure, based on the anatomic data from Haefeli-Bleuer and Weibel (Anat. Record 220: 401-414, 1988). The subunit turnover (TO), i.e., the ratio of subunit tidal to resting volume, and the flow sequences (FS) between the subunits are used as model parameters. The model simulates the normalized alveolar slope (Sn), Fowler and Bohr dead space (VDF and VDB), and alveolar mixing efficiency (AME) as a function of breath number (n) during a multiple-breath N2 washout (MBNW). For the first breath of the MBNW, these indexes are poorly sensitive to the TO distribution or FS between the subunits. However, as the washout proceeds, the n dependence of both Sn and VDB becomes markedly distinct for simulations with different TO and FS. VDF increases only slightly with n during the MBNW for a large range of TO and FS combinations, and AME is independent of FS. Comparison of published experimental observations with model simulations gave a consistent picture of ventilation maldistribution in the human lung. MBNW simulations in conditions of weightlessness, which will be performed shortly in Spacelab, suggest that it will be possible to evaluate quantitatively the intraregional elastic inhomogeneities in the human lung.

Methacholine-induced bronchoconstriction in dogs: effects of lung volume and O3 exposure

1988 ◽  
Vol 65 (6) ◽  
pp. 2679-2686 ◽  
Author(s):  
S. T. Kariya ◽  
S. A. Shore ◽  
W. A. Skornik ◽  
K. Anderson ◽  
R. H. Ingram ◽  
...  
Keyword(s):  
Lung Volume ◽  
Maximal Response ◽  
Maximal Effect ◽  
Response Curves ◽  
Lung Volumes ◽  
Before And After ◽  
Residual Capacity ◽  
Induced Changes ◽  
Conducting Airways ◽  
Concentration Response Curve

The maximal effect induced by methacholine (MCh) aerosols on pulmonary resistance (RL), and the effects of altering lung volume and O3 exposure on these induced changes in RL, was studied in five anesthetized and paralyzed dogs. RL was measured at functional residual capacity (FRC), and lung volumes above and below FRC, after exposure to MCh aerosols generated from solutions of 0.1-300 mg MCh/ml. The relative site of response was examined by magnifying parenchymal [RL with large tidal volume (VT) at fast frequency (RLLS)] or airway effects [RL with small VT at fast frequency (RLSF)]. Measurements were performed on dogs before and after 2 h of exposure to 3 ppm O3. MCh concentration-response curves for both RLLS and RLSF were sigmoid shaped. Alterations in mean lung volume did not alter RLLS; however, RLSF was larger below FRC than at higher lung volumes. Although O3 exposure resulted in small leftward shifts of the concentration-response curve for RLLS, the airway dominated index of RL (RLSF) was not altered by O3 exposure, nor was the maximal response using either index of RL. These data suggest O3 exposure does not affect MCh responses in conducting airways; rather, it affects responses of peripheral contractile elements to MCh, without changing their maximal response.

scholarly journals Fatigue is Highly Prevalent in Patients with Asthma and Contributes to the Burden of Disease

2018 ◽  
Vol 7 (12) ◽  
pp. 471 ◽  
Author(s):  
Maarten Van Herck ◽  
Martijn Spruit ◽  
Chris Burtin ◽  
Remco Djamin ◽  
Jeanine Antons ◽  
...  
Keyword(s):  
Quality Of Life ◽  
Asthma Control ◽  
Global Strategy ◽  
Airflow Limitation ◽  
Stepwise Multiple Regression ◽  
Life Questionnaire ◽  
Exacerbation Rate ◽  
Asthmatic Patients ◽  
Severe Fatigue

The 2018 update of the Global Strategy for Asthma Management and Prevention does not mention fatigue-related symptoms. Nevertheless, patients with asthma frequently report tiredness, lack of energy, and daytime sleepiness. Quantitative research regarding the prevalence of fatigue in asthmatic patients is lacking. This retrospective cross-sectional study of outpatients with asthma upon referral to a chest physician assessed fatigue (Checklist Individual Strength-Fatigue (CIS-Fatigue)), lung function (spirometry), asthma control (Asthma Control Questionnaire (ACQ)), dyspnea (Medical Research Council (MRC) scale), exercise capacity (six-minute walk test (6MWT)), and asthma-related Quality-of-Life (QoL), Asthma Quality of Life Questionnaire (AQLQ) during a comprehensive health-status assessment. In total, 733 asthmatic patients were eligible and analyzed (47.4 ± 16.3 years, 41.1% male). Severe fatigue (CIS-Fatigue ≥ 36 points) was detected in 62.6% of patients. Fatigue was not related to airflow limitation (FEV1, ρ = −0.083); was related moderately to ACQ (ρ = 0.455), AQLQ (ρ = −0.554), and MRC (ρ = 0.435; all p-values < 0.001); and was related weakly to 6MWT (ρ = −0.243, p < 0.001). In stepwise multiple regression analysis, 28.9% of variance in fatigue was explained by ACQ (21.0%), MRC (6.5%), and age (1.4%). As for AQLQ, 42.2% of variance was explained by fatigue (29.8%), MRC (8.6%), exacerbation rate (2.6%), and age (1.2%). Severe fatigue is highly prevalent in asthmatic patients; it is an important determinant of disease-specific QoL and a crucial yet ignored patient-related outcome in patients with asthma.

Convective and diffusive gas transport in canine intrapulmonary airways

1992 ◽  
Vol 72 (4) ◽  
pp. 1557-1562 ◽  
Author(s):  
H. Schulz ◽  
P. Heilmann ◽  
A. Hillebrecht ◽  
J. Gebhart ◽  
M. Meyer ◽  
...  
Keyword(s):  
Dead Space ◽  
Gas Transport ◽  
Inert Gases ◽  
Differential Analysis ◽  
Mechanically Ventilated ◽  
Convective Mixing ◽  
Conducting Airways ◽  
And Diffusion ◽  
Residual Air ◽  
Space Dispersion

The significance of convective and diffusive gas transport in the respiratory system was assessed from the response of combined inert gas and particle boluses inhaled into the conducting airways. Particles, considered as “nondiffusing gas,” served as tracers for convection and two inert gases with widely different diffusive characteristics (He and SF6) as tracers for convection and diffusion. Six-milliliter boluses labeled with monodisperse di-2-ethylhexyl sebacate droplets of 0.86-microns aerodynamic diameter, 2% He, and 2% SF6 were inspired by three anesthetized mechanically ventilated beagle dogs to volumetric lung depths up to 170 ml. Mixing between inspired and residual air caused dispersion of the inspired bolus, which was quantified in terms of the bolus half-width. Dispersion of particles increased with increasing lung depth to which the boluses were inhaled. The increase followed a power law with exponents less than 0.5 (mean 0.39), indicating that the effect of convective mixing per unit volume was reduced with depth. Within the pulmonary dead space, the behavior of the inert gases He and SF6 was similar to that of the particles, suggesting that gas transport was almost solely due to convection. Beyond the dead space, dispersion of He and SF6 increased more rapidly than dispersion of particles, indicating that diffusion became significant. The gas and particle bolus technique offers a suitable approach to differential analysis of gas transport in intrapulmonary airways of lungs.

Effect of inspired CO2 on ventilation and perfusion heterogeneity in hyperventilated dogs

1993 ◽  
Vol 75 (3) ◽  
pp. 1306-1314 ◽  
Author(s):  
K. B. Domino ◽  
E. R. Swenson ◽  
N. L. Polissar ◽  
Y. Lu ◽  
B. L. Eisenstein ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Partial Pressure ◽  
Respiratory Rate ◽  
Dead Space ◽  
Pressure Difference ◽  
Inert Gas ◽  
Ventilation Distribution ◽  
Pentobarbital Sodium ◽  
Ventilation And Perfusion ◽  
Paco2 Level

We studied the effect of inspired CO2 on ventilation-perfusion (VA/Q) heterogeneity in dogs hyperventilated under two different tidal volume (VT) and respiratory rate conditions with the use of the multiple inert gas elimination technique. Dogs anesthetized with pentobarbital sodium were hyperventilated with an inspired fraction of O2 of 0.21 by using an increased VT (VT = 30 ml/kg at 18 breaths/min) or an increased respiratory rate (VT = 18 ml/kg at 35 breaths/min). The arterial CO2 tension (PaCO2) was varied to three levels (20, 35, and 52 Torr) by altering the inspired PCO2. The orders of type of ventilation and PaCO2 level were randomized. Compared with normocapnia, VA/Q heterogeneity was increased during hypocapnia induced by increased respiratory rate ventilation, which was indicated by an increase in dispersion indexes and arterial-alveolar inert gas partial pressure difference areas (P < 0.01). In contrast, VA/Q heterogeneity was not affected by hypocapnia when a large VT ventilation was used. Under the conditions of our study, hypercapnia did not result in statistically significant changes in VA/Q heterogeneity with either type of ventilation. Increased VT ventilation reduced dead space at all PaCO2 levels (P < 0.01) and reduced the log standard deviation of the ventilation distribution during normocapnia (P < 0.05) and hypocapnia (P < 0.01). We conclude that hypocapnia increased VA/Q heterogeneity when hyperventilation was achieved with a rapid respiratory rate. Therefore, a lack of improvement in VA/Q matching with inhaled CO2 may be associated with the use of a large VT. These data suggest that hypocapnic bronchoconstriction may be important in mediating hypocapnia-induced VA/Q inequality in dogs.

scholarly journals Potentiometric Response of Ag/AgCl Chloride Sensors in Model Alkaline Medium

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Farhad Pargar ◽  
Hristo Kolev ◽  
Dessi A. Koleva ◽  
Klaas van Breugel
Keyword(s):  
Alkaline Medium ◽  
Open Circuit Potential ◽  
Dynamic Equilibrium ◽  
Chloride Concentration ◽  
Chloride Content ◽  
Cementitious Materials ◽  
Open Circuit ◽  
Potentiometric Response ◽  
Before And After ◽  
The Stability

The stability and reproducibility of an Ag/AgCl sensors’ response in an alkaline medium are important for the application of these sensors in cementitious materials. The sensors’ response, or their open circuit potential (OCP), reflects a dynamic equilibrium at the sensor/environment interface. The OCP response in an alkaline medium is affected by the presence of hydroxide ions. The interference of hydroxide ions leads to inaccuracies or a delay in the sensors’ response to a certain chloride content. In this article, the potentiometric response (or OCP evolution) of the chloride sensors is measured in model solutions, resembling the concrete pore water. The scatter of the sensors’ OCP is discussed with respect to the interference of hydroxide ions at varying chloride concentration in the medium. The deviation of the sensor’s response from its ideal performance (determined by the Nernst law) is attributed to dechlorination of the AgCl layer and the formation of Ag2O on the sensor’s surface. Results from the surface XPS analysis of the AgCl layer before and after treatment in alkaline medium confirm these observations in view of chemical transformation of AgCl to Ag2O.

Longitudinal distribution of O3 absorption in the lung: gender differences and intersubject variability

1996 ◽  
Vol 81 (4) ◽  
pp. 1651-1657 ◽  
Author(s):  
Michele L. Bush ◽  
Patrick T. Asplund ◽  
Kristen A. Miles ◽  
Abdellaziz Ben-Jebria ◽  
James S. Ultman
Keyword(s):  
Gender Differences ◽  
Dead Space ◽  
Ambient Air ◽  
Exposure Dose ◽  
Longitudinal Distribution ◽  
Exposure Condition ◽  
Intersubject Variability ◽  
Quiet Breathing ◽  
Mass Transfer Parameter ◽  
Conducting Airways

Bush, Michele L., Patrick T. Asplund, Kristen A. Miles, Abdellaziz Ben-Jebria, and James S. Ultman. Longitudinal distribution of O3 absorption in the lung: gender differences and intersubject variability. J. Appl. Physiol. 81(4): 1651–1657, 1996.—Because the National Ambient Air Quality Standard for ozone (O3) is intended to protect the most sensitive individuals in the general population, it is necessary to identify sources of intersubject variation in the exposure-dose-response cascade. We hypothesize that differences in lung anatomy can modulate exposure-dose relationships between individuals, and this results in differences between their responsiveness to O3 at a fixed exposure condition. During quiet breathing, the conducting airways remove the majority of inhaled O3, so the volume of this region should have an important impact on O3 dose distribution. Employing the bolus inhalation method, we measured the distribution of O3 absorption with respect to penetration volume (VP), and using the Fowler single-breath N2washout method, we determined the dead space volume (Vd) in the lungs of 10 men and 10 women at a fixed respiratory flow of 250 ml/s. On average, the women absorbed O3 at smaller VP than the men, and the women had smaller Vd than the men. When expressed in terms of VP/ Vd, the absorption distribution of the men and women was indistinguishable. Moreover, an interpretation of the O3 distribution in terms of an intrinsic mass transfer parameter ( Ka) indicated that differences between the O3 dosimetry in all subjects, whether men or women, could be explained by a unique correlation with anatomic dead space: Ka (in s−1) = 610 Vd −1.05(in ml). Application of this result to measurements of O3 exposure response indicated that previously reported gender differences may be due to a failure in properly accounting for tissue surface within the conducting airways.

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