Reproducibility of Data on Steady-State Gas Exchange and Indices of Maldistribution of Ventilation and Blood Flow

CHEST Journal ◽  
1977 ◽  
Vol 71 (6) ◽  
pp. 758-761
Author(s):  
Enid R. Kafer ◽  
Peter Donnelly
Keyword(s):  
Blood Flow ◽  
Steady State ◽  
Gas Exchange

Ventilation-perfusion inhomogeneity increases gas uptake: theoretical modeling of gas exchange

2001 ◽  
Vol 91 (1) ◽  
pp. 3-9 ◽  
Author(s):  
Philip J. Peyton ◽  
Gavin J. B. Robinson ◽  
Bruce Thompson
Keyword(s):  
Blood Flow ◽  
Nitrous Oxide ◽  
Steady State ◽  
Gas Exchange ◽  
Computer Model ◽  
Theoretical Modeling ◽  
Theoretical Studies ◽  
Gas Uptake

Ventilation-perfusion (V˙a/Q˙) inhomogeneity was modeled to measure its effect on gas exchange in the presence of inspired mixtures of two soluble gases using a two-compartment computer model. Theoretical studies involving a mixture of hypothetical gases with equal solubility in blood showed that the effect of increasing inhomogeneity of distributions of either ventilation or blood flow is to paradoxically increase uptake of the gas with the lowest overall uptake in relation to its inspired concentration. This phenomenon is explained by the concentrating effects that uptake of soluble gases exert on each other in low V˙a/Q˙ compartments. Repeating this analysis for inspired mixtures of 30% O2and 70% nitrous oxide (N2O) confirmed that, during “steady-state” N2O anesthesia, uptake of N2O is predicted to paradoxically increase in the presence of worsening V˙a/Q˙ inhomogeneity.

Mechanisms of improvement in pulmonary gas exchange during isovolemic hemodilution

1999 ◽  
Vol 87 (1) ◽  
pp. 132-141 ◽  
Author(s):  
Steven Deem ◽  
Richard G. Hedges ◽  
Steven McKinney ◽  
Nayak L. Polissar ◽  
Michael K. Alberts ◽  
...  
Keyword(s):  
Blood Flow ◽  
Fractal Dimension ◽  
Gas Exchange ◽  
Spatial Correlation ◽  
Pulmonary Blood Flow ◽  
Minute Ventilation ◽  
Flow Distribution ◽  
Pulmonary Gas Exchange ◽  
Normal Lung ◽  
Blood Flow Distribution

Severe anemia is associated with remarkable stability of pulmonary gas exchange (S. Deem, M. K. Alberts, M. J. Bishop, A. Bidani, and E. R. Swenson. J. Appl. Physiol. 83: 240–246, 1997), although the factors that contribute to this stability have not been studied in detail. In the present study, 10 Flemish Giant rabbits were anesthetized, paralyzed, and mechanically ventilated at a fixed minute ventilation. Serial hemodilution was performed in five rabbits by simultaneous withdrawal of blood and infusion of an equal volume of 6% hetastarch; five rabbits were followed over a comparable time. Ventilation-perfusion (V˙a/Q˙) relationships were studied by using the multiple inert-gas-elimination technique, and pulmonary blood flow distribution was assessed by using fluorescent microspheres. Expired nitric oxide (NO) was measured by chemiluminescence. Hemodilution resulted in a linear fall in hematocrit over time, from 30 ± 1.6 to 11 ± 1%. Anemia was associated with an increase in arterial [Formula: see text] in comparison with controls ( P < 0.01 between groups). The improvement in O2 exchange was associated with reducedV˙a/Q˙heterogeneity, a reduction in the fractal dimension of pulmonary blood flow ( P = 0.04), and a relative increase in the spatial correlation of pulmonary blood flow ( P = 0.04). Expired NO increased with anemia, whereas it remained stable in control animals ( P < 0.0001 between groups). Anemia results in improved gas exchange in the normal lung as a result of an improvement in overallV˙a/Q˙matching. In turn, this may be a result of favorable changes in pulmonary blood flow distribution, as assessed by the fractal dimension and spatial correlation of blood flow and as a result of increased NO availability.

scholarly journals Advanced Constitutive Modeling of the Thixotropic Elasto-Visco-Plastic Behavior of Blood: Steady-State Blood Flow in Microtubes

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 367
Author(s):  
Konstantinos Giannokostas ◽  
Yannis Dimakopoulos ◽  
Andreas Anayiotos ◽  
John Tsamopoulos
Keyword(s):  
Blood Flow ◽  
Steady State ◽  
Constitutive Model ◽  
Blood Plasma ◽  
Constitutive Modeling ◽  
Flow Direction ◽  
Momentum Balance ◽  
Plastic Behavior ◽  
Flow Investigation ◽  
The Impact

The present work focuses on the in-silico investigation of the steady-state blood flow in straight microtubes, incorporating advanced constitutive modeling for human blood and blood plasma. The blood constitutive model accounts for the interplay between thixotropy and elasto-visco-plasticity via a scalar variable that describes the level of the local blood structure at any instance. The constitutive model is enhanced by the non-Newtonian modeling of the plasma phase, which features bulk viscoelasticity. Incorporating microcirculation phenomena such as the cell-free layer (CFL) formation or the Fåhraeus and the Fåhraeus-Lindqvist effects is an indispensable part of the blood flow investigation. The coupling between them and the momentum balance is achieved through correlations based on experimental observations. Notably, we propose a new simplified form for the dependence of the apparent viscosity on the hematocrit that predicts the CFL thickness correctly. Our investigation focuses on the impact of the microtube diameter and the pressure-gradient on velocity profiles, normal and shear viscoelastic stresses, and thixotropic properties. We demonstrate the microstructural configuration of blood in steady-state conditions, revealing that blood is highly aggregated in narrow tubes, promoting a flat velocity profile. Additionally, the proper accounting of the CFL thickness shows that for narrow microtubes, the reduction of discharged hematocrit is significant, which in some cases is up to 70%. At high pressure-gradients, the plasmatic proteins in both regions are extended in the flow direction, developing large axial normal stresses, which are more significant in the core region. We also provide normal stress predictions at both the blood/plasma interface (INS) and the tube wall (WNS), which are difficult to measure experimentally. Both decrease with the tube radius; however, they exhibit significant differences in magnitude and type of variation. INS varies linearly from 4.5 to 2 Pa, while WNS exhibits an exponential decrease taking values from 50 mPa to zero.

scholarly journals Is there a role for selective vasodilation in the management of sickle cell disease?

Blood ◽  
1988 ◽  
Vol 71 (3) ◽  
pp. 597-602 ◽  
Author(s):  
GP Rodgers ◽  
MS Roy ◽  
CT Noguchi ◽  
AN Schechter
Keyword(s):  
Blood Flow ◽  
Steady State ◽  
Sickle Cell Disease ◽  
Sickle Cell ◽  
Sickle Cell Anemia ◽  
Microvascular Obstruction ◽  
Controlled Study ◽  
Control Group ◽  
Cell Disease ◽  
Retinal Arteriolar

Abstract To test the hypothesis that microvascular obstruction to blood flow at the level of the arteriole may be significant in individuals with sickle cell anemia, the ophthalmologic effects of orally administered nifedipine were monitored in 11 steady-state patients. Three patients with evidence of acute peripheral retinal arteriolar occlusion displayed a prompt reperfusion of the involved segment. Two other patients showed fading of retroequatorial red retinal lesions. Color vision performance was improved in six of the nine patients tested. The majority of patients also demonstrated a significant decrease in the amount of blanching of the conjunctiva which reflects improved blood flow to this frequently involved area. Such improvements were not observable in a control group of untreated stable sickle cell subjects. These findings support the hypothesis that inappropriate vasoconstriction or frank vasospasm may be a significant factor in the pathogenesis of the microvascular lesions of sickle cell disease and, further, that selective microvascular entrapment inhibition may offer an additional strategy to the management of this disorder. We believe a larger, placebo-controlled study with nifedipine and similar agents is warranted.

Emergence of matched airway and vascular trees from fractal rules

2011 ◽  
Vol 110 (4) ◽  
pp. 1119-1129 ◽  
Author(s):  
Robb W. Glenny
Keyword(s):  
Blood Flow ◽  
Gas Exchange ◽  
Mathematical Models ◽  
Fetal Development ◽  
Fractal Geometry ◽  
Branching Morphogenesis ◽  
Emergent Behavior ◽  
Complex Structures ◽  
Airway Trees ◽  
Vascular Trees

The bronchial, arterial, and venous trees of the lung are complex interwoven structures. Their geometries are created during fetal development through common processes of branching morphogenesis. Insights from fractal geometry suggest that these extensively arborizing trees may be created through simple recursive rules. Mathematical models of Turing have demonstrated how only a few proteins could interact to direct this branching morphogenesis. Development of the airway and vascular trees could, therefore, be considered an example of emergent behavior as complex structures are created from the interaction of only a few processes. However, unlike inanimate emergent structures, the geometries of the airway and vascular trees are highly stereotyped. This review will integrate the concepts of emergence, fractals, and evolution to demonstrate how the complex branching geometries of the airway and vascular trees are ideally suited for gas exchange in the lung. The review will also speculate on how the heterogeneity of blood flow and ventilation created by the vascular and airway trees is overcome through their coordinated construction during fetal development.

Effects of Vaporized Perfluorocarbon on Pulmonary Blood Flow and Ventilation/Perfusion Distribution in a Model of Acute Respiratory Distress Syndrome

2001 ◽  
Vol 95 (6) ◽  
pp. 1414-1421 ◽  
Author(s):  
Matthias Hübler ◽  
Jennifer E. Souders ◽  
Erin D. Shade ◽  
Nayak L. Polissar ◽  
Carmel Schimmel ◽  
...  
Keyword(s):  
Blood Flow ◽  
Oleic Acid ◽  
Gas Exchange ◽  
Lung Injury ◽  
Repeated Measures ◽  
Pulmonary Blood Flow ◽  
Analysis Of Covariance ◽  
Inert Gas ◽  
Low Flow ◽  
Repeated Measures Analysis

Background Perfluorocarbon (PFC) liquids are known to improve gas exchange and pulmonary function in various models of acute respiratory failure. Vaporization has been recently reported as a new method of delivering PFC to the lung. Our aim was to study the effect of PFC vapor on the ventilation/perfusion (VA/Q) matching and relative pulmonary blood flow (Qrel) distribution. Methods In nine sheep, lung injury was induced using oleic acid. Four sheep were treated with vaporized perfluorohexane (PFX) for 30 min, whereas the remaining sheep served as control animals. Vaporization was achieved using a modified isoflurane vaporizer. The animals were studied for 90 min after vaporization. VA/Q distributions were estimated using the multiple inert gas elimination technique. Change in Qrel distribution was assessed using fluorescent-labeled microspheres. Results Treatment with PFX vapor improved oxygenation significantly and led to significantly lower shunt values (P &lt; 0.05, repeated-measures analysis of covariance). Analysis of the multiple inert gas elimination technique data showed that animals treated with PFX vapor demonstrated a higher VA/Q heterogeneity than the control animals (P &lt; 0.05, repeated-measures analysis of covariance). Microsphere data showed a redistribution of Qrel attributable to oleic acid injury. Qrel shifted from areas that were initially high-flow to areas that were initially low-flow, with no difference in redistribution between the groups. After established injury, Qrel was redistributed to the nondependent lung areas in control animals, whereas Qrel distribution did not change in treatment animals. Conclusion In oleic acid lung injury, treatment with PFX vapor improves gas exchange by increasing VA/Q heterogeneity in the whole lung without a significant change in gravitational gradient.

Gas exchange in dogs in the prone and supine positions

1992 ◽  
Vol 72 (6) ◽  
pp. 2292-2297 ◽  
Author(s):  
K. C. Beck ◽  
J. Vettermann ◽  
K. Rehder
Keyword(s):  
Blood Flow ◽  
Gas Exchange ◽  
Prone Position ◽  
Pulmonary Blood Flow ◽  
Random Order ◽  
Arterial Pco2 ◽  
Supine Posture ◽  
Pulmonary Shunting ◽  
The Difference ◽  
Arterial Po2

To determine the cause of the difference in gas exchange between the prone and supine postures in dogs, gas exchange was assessed by the multiple inert gas elimination technique (MIGET) and distribution of pulmonary blood flow was determined using radioactively labeled microspheres in seven anesthetized paralyzed dogs. Each animal was studied in the prone and supine positions in random order while tidal volume and respiratory frequency were kept constant with mechanical ventilation. Mean arterial PO2 was significantly lower (P less than 0.01) in the supine [96 +/- 10 (SD) Torr] than in the prone (107 +/- 6 Torr) position, whereas arterial PCO2 was constant (38 Torr). The distribution of blood flow (Q) vs. ventilation-to-perfusion ratio obtained from MIGET was significantly wider (P less than 0.01) in the supine [ln SD(Q) = 0.75 +/- 0.26] than in the prone position [ln SD (Q) = 0.34 +/- 0.05]. Right-to-left pulmonary shunting was not significantly altered. The distribution of microspheres was more heterogeneous in the supine than in the prone position. The larger heterogeneity was due in part to dorsal-to-ventral gradients in Q in the supine position that were not present in the prone position (P less than 0.01). The decreased efficiency of oxygenation in the supine posture is caused by an increased ventilation-to-perfusion mismatch that accompanies an increase in the heterogeneity of Q distribution.

scholarly journals Contribution of adenosine to compensatory dilation in hypoperfused contracting human muscles is independent of nitric oxide

2011 ◽  
Vol 110 (5) ◽  
pp. 1181-1189 ◽  
Author(s):  
Darren P. Casey ◽  
Michael J. Joyner
Keyword(s):  
Nitric Oxide ◽  
Blood Flow ◽  
Steady State ◽  
Arterial Pressure ◽  
Brachial Artery ◽  
Adenosine Receptor ◽  
Receptor Blockade ◽  
Independent Manner ◽  
Control Value ◽  
Percent Recovery

We previously demonstrated that nitric oxide (NO) contributes to compensatory vasodilation in the contracting human forearm subjected to acute hypoperfusion. We examined the potential role of an adenosine-NO interaction to this response in 17 male subjects (25 ± 2 yr). In separate protocols subjects performed rhythmic forearm exercise (20% of maximum) while hypoperfusion was evoked by balloon inflation in the brachial artery above the elbow. Each trial included exercise before inflation, exercise with inflation, and exercise after deflation (3 min each). Forearm blood flow (FBF; ultrasound) and local [brachial artery catheter pressure (BAP)] and systemic [mean arterial pressure (MAP); Finometer] arterial pressure were measured. In protocol 1 ( n = 10), exercise was repeated during nitric oxide synthase inhibition [ NG-monomethyl-l-arginine (l-NMMA)] alone and during l-NMMA-aminophylline (adenosine receptor blockade) administration. In protocol 2, exercise was repeated during aminophylline alone and during aminophylline-l-NMMA. Forearm vascular conductance (FVC; ml·min−1·100 mmHg−1) was calculated from blood flow (ml/min) and BAP (mmHg). Percent recovery in FVC during inflation was calculated as (steady-state inflation + exercise value − nadir)/[steady-state exercise (control) value − nadir]. In protocol 1, percent recovery in FVC was 108 ± 8% during the control (no drug) trial. Percent recovery in FVC was attenuated with inhibition of NO formation alone (78 ± 9%; P < 0.01 vs. control) and was attenuated further with combined inhibition of NO and adenosine (58 ± 9%; P < 0.01 vs. l-NMMA). In protocol 2, percent recovery was reduced with adenosine receptor blockade (74 ± 11% vs. 113 ± 6%, P < 0.01) compared with control drug trials. Percent recovery in FVC was attenuated further with combined inhibition of adenosine and NO (48 ± 11%; P < 0.05 vs. aminophylline). Our data indicate that adenosine contributes to compensatory vasodilation in an NO-independent manner during exercise with acute hypoperfusion.

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