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.

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.

Breath-by-breath variation of FRC: effect on VO2 and VCO2 measured at the mouth

1979 ◽  
Vol 46 (6) ◽  
pp. 1122-1126 ◽  
Author(s):  
H. U. Wessel ◽  
R. L. Stout ◽  
C. K. Bastanier ◽  
M. H. Paul
Keyword(s):  
Steady State ◽  
Gas Exchange ◽  
Gas Flow ◽  
Co2 Gas ◽  
Mean Values ◽  
Gas Uptake ◽  
Source Data ◽  
Alveolar Level ◽  
Age Range

We examined breath-by-breath (B-B) variations of FRC (delta FRC) and their effect on measured O2 and CO2 gas exchange in 52 2- to 4-min segments of continuous air breathing obtained in 29 patients (age range 6--50 yr). Respiratory frequency ranged from 13 to 43 breaths/min, VE from 6.7 to 22.5 l/min (BTPS), and expired VT from 234 to 1,370 ml (BTPS). Computer analysis was based on the following source data measured at the mouth: inspired (VI) and expired (VE) gas flow, FN2, FO2 and FCO2. The analysis provides B-B evaluation of VI, VE, delta FRC in terms of VN2, and VO2 and VCO2 at the mouth and at the alveolar level, i.e., after correction for delta FRC. Significant B-B variations of FRC were found in all studies. delta FRC ranged from +360 to -360 ml (BTPS). For single respiratory cycles VI - VE is primarily a function of N2 exchange at the mouth (VMN2). VO2 and VCO2, uncorrected for delta FRC, are significantly more dispersed about mean values than the corrected gas uptakes (P less than 0.0005). The data support the view that the assumption of VIN2 = VEN2 is invalid for single respiratory cycles. Determination of breath-by-breath VO2 and VCO2 should therefore, not be based on steady-state gas uptake equations. It requires measurement of both inspired and expired breath volumes and evaluation of N2 gas exchange.

The effect of blood flow and diffusion impairment on pulmonary gas exchange: A computer model

1987 ◽  
Vol 20 (5) ◽  
pp. 497-506 ◽  
Author(s):  
Wesley M. Granger ◽  
David A. Miller ◽  
Ina C. Ehrhart ◽  
Wendell F. Hofman
Keyword(s):  
Blood Flow ◽  
Gas Exchange ◽  
Computer Model ◽  
Pulmonary Gas Exchange ◽  
And Diffusion

scholarly journals Comparison between the uptake of nitrous oxide and nitric oxide in the human nose

1998 ◽  
Vol 85 (4) ◽  
pp. 1203-1209 ◽  
Author(s):  
Patrick M. Kelley ◽  
Arthur B. DuBois
Keyword(s):  
Nitric Oxide ◽  
Blood Flow ◽  
Nitrous Oxide ◽  
Steady State ◽  
Partition Coefficient ◽  
Capillary Blood ◽  
Capillary Blood Flow ◽  
Unidirectional Flow ◽  
Steady State Rate ◽  
State Rate

The absorption of nitrous oxide (N2O) during unidirectional flow was compared with the rate of uptake of nitric oxide (NO). At flow rates of 10, 20, and 60 ml/min from one nostril to the other, with the soft palate closed, the N2O reached a steady-state rate of absorption in 5–15 min. The mean superficial capillary blood flow ( n = 5) calculated from solubility and the steady-state rate of N2O absorption ranged from 13.3 to 15.9 ml/min. The relation between absorption of N2O in the nose and capillary blood flow fits a ventilation-perfusion model used by others to describe uptake of inert, soluble gases in the rat nose. By contrast, the rate of uptake of NO gas, which is chemically reactive, is 25–31 times as great as predicted by just its blood-to-air partition coefficient. Exogenous NO (16.9 parts/million) did not induce nasal vasodilation as measured with laser Doppler and N2O absorption methods. The difference between the measured rate of uptake of NO and the rate of uptake attributable to its partition coefficient in blood at the rate of blood flow calculated from N2O uptake is probably due to chemical reaction of NO in mucous secretions, nasal tissues, and capillary blood.

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.

Assessment of cardiorespiratory function using oscillating inert gas forcing signals

1994 ◽  
Vol 76 (5) ◽  
pp. 2130-2139 ◽  
Author(s):  
E. M. Williams ◽  
J. B. Aspel ◽  
S. M. Burrough ◽  
W. A. Ryder ◽  
M. C. Sainsbury ◽  
...  
Keyword(s):  
Blood Flow ◽  
Nitrous Oxide ◽  
Dead Space ◽  
Confidence Limit ◽  
Pulmonary Blood Flow ◽  
Mean Difference ◽  
Alveolar Volume ◽  
Single Breath ◽  
Cardiorespiratory Function ◽  
Airway Dead Space

A theoretical model (Hahn et al. J. Appl. Physiol. 75: 1863–1876, 1993) predicts that the amplitudes of the argon and nitrous oxide inspired, end-expired, and mixed expired sinusoids at forcing periods in the range of 2–3 min (frequency 0.3–0.5 min-1) can be used directly to measure airway dead space, lung alveolar volume, and pulmonary blood flow. We tested the ability of this procedure to measure these parameters continuously by feeding monosinusoidal argon and nitrous oxide forcing signals (6 +/- 4% vol/vol) into the inspired airstream of nine anesthetized ventilated dogs. Close agreement was found between single-breath and sinusoid airway dead space measurements (mean difference 15 +/- 6%, 95% confidence limit), N2 washout and sinusoid alveolar volume (mean difference 4 +/- 6%, 95% confidence limit), and thermal dilution and sinusoid pulmonary blood flow (mean difference 12 +/- 11%, 95% confidence limit). The application of 1 kPa positive end-expiratory pressure increased airway dead space by 12% and alveolar volume from 0.8 to 1.1 liters but did not alter pulmonary blood flow, as measured by both the sinusoid and comparator techniques. Our findings show that the noninvasive sinusoid technique can be used to measure cardiorespiratory lung function and allows changes in function to be resolved in 2 min.

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