Dependence of central airway resistance on frequency and tidal volume: a model study

1986 ◽  
Vol 61 (1) ◽  
pp. 113-126 ◽  
Author(s):  
D. Isabey ◽  
H. K. Chang ◽  
C. Delpuech ◽  
A. Harf ◽  
C. Hatzfeld
Keyword(s):  
Steady State ◽  
Pressure Drop ◽  
Tidal Volume ◽  
Strouhal Number ◽  
Airway Resistance ◽  
Peak Flow ◽  
Flow Reversal ◽  
Peak Flows ◽  
Wide Range ◽  
40 Hz

The resistance of a hollow cast of human central airways was measured during true sinusoidal airflow oscillations over a wide range of frequencies (0.5–40 Hz) and for various flow amplitudes up to 8 l/s. Pressure and flow were measured in the trachea with high-performance transducers, digitized and averaged over 100 cycles. Data were studied at two points in the flow cycle: at peak inspiratory and expiratory flows and in the two neighborhoods around zero flow where airway resistance (Rv approximately equal to o) was taken as the average slope of the pressure-flow (P-V) curve in each zone. When data obtained near peak flow were plotted in terms of dimensionless pressure drop vs. peak Reynolds number (Rem) and compared with steady-state data, we found no difference up to 2 Hz as previously reported (Isabey and Chang, J. Appl. Physiol. 51: 1338–1348, 1981), a slight decay in pressure drop between 4 and 8 Hz, a frequency-dependent increase in peak flow resistance at high frequencies (10–40 Hz) governed by the Strouhal number alpha 2/Rem beyond alpha 2/Rem = 0.5. On the other hand RV approximately equal to o was found to increase relative to steady state as local acceleration increases, e.g., as peak flow increases at a fixed frequency; this differs from the classical linear theory of oscillatory flow in a long straight tube. To explain these results, we had to use, as in our previous study, an alternative expression for the Strouhal number, i.e., epsilon = L X A X (dV/dt)/V2 (where L and A are the length and cross-sectional area of the trachea and V is a constant flow range over which resistance around flow reversal was computed), which accurately reflects the ratio of local acceleration [d(V/A)/dt)] to convective acceleration [(V/A)2/L] in developing branching flow. Finally, to delineate the regions of dominance of each of the dimensionless parameters, we compiled frequency-tidal volume diagrams for peak flows as well as for reversal. Epsilon, which is negligible near peak flows, appeared to govern the oscillatory P-V relationship near flow reversal in a transitional region of the diagram located between regions of steadiness, or moderate unsteadiness, and a region of dominant unsteadiness governed by alpha.

scholarly journals Revealing Hidden Debottlenecking Potential in Flare Systems on Offshore Facilities Using Dynamic Simulations -- a Preliminary Investigation

2020 ◽  
Author(s):  
Ana Xiao Outomuro Somozas ◽  
Rudi P. Nielsen ◽  
Marco Maschietti ◽  
Anders Andreasen
Keyword(s):  
Steady State ◽  
Peak Flow ◽  
Preliminary Investigation ◽  
System Size ◽  
Dynamic Simulations ◽  
Wide Range ◽  
Total Plant ◽  
Steady State Simulation ◽  
State Case

Three flare systems are modeled and total plant depressurization is investigated using dynamic simulations in order to access the debottlenecking potential. Usually steady-state simulation of the flare network is used for sizing and rating of the flare system. By using dynamic simulations effects from line packing in the flare system can be studied. The results show that peak flow during a dynamic simulations is significantly lower than the peak flow used in a steady-state case. <br>The three systems investigated span a wide range in flare system size, both in terms of number of process segments disposing into the flare network, in terms of peak design rate and the flare network pipe dimensions and total hold-up volume. Generally, it is observed that the larger the flare system, the larger debottlenecking potential.

Lung-Air-Sac Anatomy and Respiratory Pressures in the Bird

1972 ◽  
Vol 57 (2) ◽  
pp. 543-550
Author(s):  
JOHN H. BRACKENBURY
Keyword(s):  
Steady State ◽  
Tidal Volume ◽  
Pressure Wave ◽  
Airway Resistance ◽  
Equilibrium Distribution ◽  
Wave Form ◽  
Pressure Waves ◽  
Air Sacs ◽  
Maximum Value ◽  
Respiratory Phase

1. Regardless of its tidal volume an individual air sac shows a respiratory pressure-wave which is similar to that of every other sac. These is a process of pressure equilibration within the lung-air-sac system involving very short-lived streams of air between air sacs, whose significance becomes larger as pressure accelerations become bigger; and when a steady state has been achieved in any respiratory phase the pressure wave becomes normalized in all parts of the system. 2. Small pressure differentials between sacs are part of the equilibrium distribution of pressure within the lung-air-sac system. They result from differences in the resistance path through the lung to each sac, and differences in their respective tidal volumes. Their wave-form closely resembles that of the parent pressure waves and has a maximum value of one-tenth their value. 3. In general, the bronchial pathways to the posterior sacs have greater resistances to air flow than those to the anterior sacs. 4. During vocalization pressures in the coelom and air sacs exceed normal respiratory pressures by about 40 times. Airway resistance vastly increases as the syringeal membranes begin to vibrate.

scholarly journals Revealing Hidden Debottlenecking Potential in Flare Systems on Offshore Facilities Using Dynamic Simulations -- a Preliminary Investigation

2020 ◽  
Author(s):  
Ana Xiao Outomuro Somozas ◽  
Rudi P. Nielsen ◽  
Marco Maschietti ◽  
Anders Andreasen
Keyword(s):  
Steady State ◽  
Peak Flow ◽  
Preliminary Investigation ◽  
System Size ◽  
Dynamic Simulations ◽  
Wide Range ◽  
Total Plant ◽  
Steady State Simulation ◽  
State Case

Three flare systems are modeled and total plant depressurization is investigated using dynamic simulations in order to access the debottlenecking potential. Usually steady-state simulation of the flare network is used for sizing and rating of the flare system. By using dynamic simulations effects from line packing in the flare system can be studied. The results show that peak flow during a dynamic simulations is significantly lower than the peak flow used in a steady-state case. <br>The three systems investigated span a wide range in flare system size, both in terms of number of process segments disposing into the flare network, in terms of peak design rate and the flare network pipe dimensions and total hold-up volume. Generally, it is observed that the larger the flare system, the larger debottlenecking potential.

scholarly journals Revealing Hidden Debottlenecking Potential in Flare Systems on Offshore Facilities Using Dynamic Simulations -- a Preliminary Investigation

2020 ◽  
Author(s):  
Ana Xiao Outomuro Somozas ◽  
Rudi P. Nielsen ◽  
Marco Maschietti ◽  
Anders Andreasen
Keyword(s):  
Steady State ◽  
Peak Flow ◽  
Preliminary Investigation ◽  
System Size ◽  
Dynamic Simulations ◽  
Wide Range ◽  
Total Plant ◽  
Steady State Simulation ◽  
State Case

Three flare systems are modeled and total plant depressurization is investigated using dynamic simulations in order to access the debottlenecking potential. Usually steady-state simulation of the flare network is used for sizing and rating of the flare system. By using dynamic simulations effects from line packing in the flare system can be studied. The results show that peak flow during a dynamic simulations is significantly lower than the peak flow used in a steady-state case. <br>The three systems investigated span a wide range in flare system size, both in terms of number of process segments disposing into the flare network, in terms of peak design rate and the flare network pipe dimensions and total hold-up volume. Generally, it is observed that the larger the flare system, the larger debottlenecking potential.

Pressure Drop in Mini-Scale Coiled Tubing

2013 ◽  
Author(s):  
M. Ghobadi ◽  
Y. S. Muzychka
Keyword(s):  
Steady State ◽  
Pressure Drop ◽  
Reynolds Numbers ◽  
Tube Length ◽  
Radius Of Curvature ◽  
Steady State Flow ◽  
Dean Number ◽  
Coiled Tubing ◽  
Wide Range ◽  
Simple Empirical Model

In the present study, laminar, steady state flow in mini-scale coiled tubes was studied experimentally. Three different tube diameters: 1.6 mm, 1.27 mm and 1.016 mm with different lengths of 1 m and 0.5 m were coiled with different radius of curvature to provide data over a wide range of Reynolds numbers from 5 to 2300. A simple empirical model is developed based on the experimental results to predict the pressure drop increase based on Dean number. The results and simple model are also compared to a well-known existing model for circular tubing. The coiled tube lengths used in this study were long enough to consider the flow to be fully developed. The effects of varying curvature and tube length are also studied. The pitch of the coils is restricted to the diameter of the tube to minimize the effect of coiling. Dean number is used instead of Coiled number (modified Dean number) which allows the results to be expanded to spiral and curved tubing.

Effect of lung volume on plateau response of airways and tissue to methacholine in dogs

1992 ◽  
Vol 73 (5) ◽  
pp. 1908-1913 ◽  
Author(s):  
F. M. Robatto ◽  
S. Simard ◽  
H. Orana ◽  
P. T. Macklem ◽  
M. S. Ludwig
Keyword(s):  
Pressure Drop ◽  
Tidal Volume ◽  
Lung Volume ◽  
Airway Resistance ◽  
Positive End Expiratory Pressure ◽  
Alveolar Pressure ◽  
Lung Elastance ◽  
Tissue Resistance ◽  
Airway Caliber ◽  
Lung Resistance

We have recently shown in dogs that much of the increase in lung resistance (RL) after induced constriction can be attributed to increases in tissue resistance, the pressure drop in phase with flow across the lung tissues (Rti). Rti is dependent on lung volume (VL) even after induced constriction. As maximal responses in RL to constrictor agonists can also be affected by changes in VL, we questioned whether changes in the plateau response with VL could be attributed in part to changes in the resistive properties of lung tissues. We studied the effect of changes in VL on RL, Rti, airway resistance (Raw), and lung elastance (EL) during maximal methacholine (MCh)-induced constriction in 8 anesthetized, paralyzed, open-chest mongrel dogs. We measured tracheal flow and pressure (Ptr) and alveolar pressure (PA), the latter using alveolar capsules, during tidal ventilation [positive end-expiratory pressure (PEEP) = 5.0 cmH2O, tidal volume = 15 ml/kg, frequency = 0.3 Hz]. Measurements were recorded at baseline and after the aerosolization of increasing concentrations of MCh until a clear plateau response had been achieved. VL was then altered by changing PEEP to 2.5, 7.5, and 10 cmH2O. RL changed only when PEEP was altered from 5 to 10 cmH2O (P < 0.01). EL changed when PEEP was changed from 5 to 7.5 and 5 to 10 cmH2O (P < 0.05). Rti and Raw varied significantly with all three maneuvers (P < 0.05). Our data demonstrate that the effects of VL on the plateau response reflect a complex combination of changes in tissue resistance, airway caliber, and lung recoil.

Computational Analysis of Two Phase Flow Distribution in a Horizonatal Pipe

2014 ◽  
Vol 592-594 ◽  
pp. 1466-1471
Author(s):  
V. Jagan ◽  
K. Mohan Babu ◽  
A. Satheesh ◽  
D. Santhosh Kumar
Keyword(s):  
Steady State ◽  
Pressure Drop ◽  
Flow Rate ◽  
Two Phase Flow ◽  
Flow Distribution ◽  
Steady State Solution ◽  
Phase Flow ◽  
Two Phase ◽  
Horizontal Pipe ◽  
Wide Range

In this paper, a two phase flow distribution in a horizontal pipe is numerically analyzed by solving one dimensional steady state momentum equation for predicting the pressure drop (∆P), quality of steam at outlet of the pipe (X), void fraction (α). The heat absorbed by the pipe (Q) and the mass flow rate (W) of water are varied over a wide range to investigate the above parameters. The locations of the two phase mixture are discussed. Pressure drop along the pipe is inconsistent for different flow rate so, the stable and unstable steady state solution is also carried out using Linear Stability analysis. The present numerical results are compared with the reported data from the literature and found that they are in good agreement. This study is used to calculate the pressure, temperature, hold up and quality within the horizontal pipe.

scholarly journals Steady State Flow in the Cigarette and its Influence on Pressure Drop - Die stationäreStrömung in der Cigarette und derenEinfluß auf den Zugwiderstand

1992 ◽  
Vol 15 (3) ◽  
pp. 93-122
Author(s):  
H Gaißer
Keyword(s):  
Fluid Flow ◽  
Steady State ◽  
Pressure Drop ◽  
Flow Rate ◽  
Unit Length ◽  
Parameter Study ◽  
Model Parameters ◽  
Theoretical Treatment ◽  
Flow Process ◽  
Wide Range

AbstractA theoretical treatment of steady state fluid mechanics of filtered cigarettes has been developed. By assuming laminar fluid flow, the well knownKozeny-Carman equation has been used to evaluate the flow resistance of the tobacco rod and the linear relationship of cigarette pressure drop to flow rate. Based on this relationship, models with distributed parameters (using impedances per unit length and differential equations) and lumped parameters (using a four terminal network of flow impedances and difference equations) have been established. These were used to calculate spatial flow variables such as pressure drop, volumetric flow rate and degree of ventilation. The effects of changes in coal resistance and reduction in rod length during smoking are demonstrated in a parameter study. A great advantage of mathematical modeling based on physical principles is the wide range of validity which allows a deeper insight into the behaviour of the fluid flow process. This is illustrated using a canonical example. Invariant model parameters such as the characteristic wave impedance and the propagation coefficient have been calculated and are presented as measurable. In order to calculate the dynamic fluid flow pattern of filtered cigarettes smoked on a conventional smoking machine, the model must be extend to include kinetic terms according to the Bernouilli equation. This will be presented in a later paper.

Rainfall Events as Paths of a Stochastic Process: Problems of Design Storm Analysis

1984 ◽  
Vol 16 (8-9) ◽  
pp. 131-138 ◽  
Author(s):  
Johannes Brummer
Keyword(s):  
Stochastic Process ◽  
Peak Flow ◽  
Rainfall Events ◽  
Peak Flows ◽  
Design Storm ◽  
Adequate Evaluation ◽  
Rainfall Patterns

Problems in the construction of design storms are expressed in mathematical terms. Introduced here is a concept for approximating natural peak flow values by means of the distribution of typical rainfall patterns. A comparison demonstrates the quality of this concept and the competency of some well-known design storms for the adequate evaluation of peak flows.

Spectroscopic Studies of Asparaginyl-tRNA Synthetase from Entamoeba histolytica

2019 ◽  
Vol 26 (6) ◽  
pp. 435-448
Author(s):  
Priyanka Biswas ◽  
Dillip K. Sahu ◽  
Kalyanasis Sahu ◽  
Rajat Banerjee
Keyword(s):  
Circular Dichroism ◽  
Steady State ◽  
Entamoeba Histolytica ◽  
Protein Concentration ◽  
Trna Synthetase ◽  
Solvent Exposure ◽  
Steady State Fluorescence ◽  
State Process ◽  
Wide Range ◽  
Circular Dichroïsm

Background: Aminoacyl-tRNA synthetases play an important role in catalyzing the first step in protein synthesis by attaching the appropriate amino acid to its cognate tRNA which then transported to the growing polypeptide chain. Asparaginyl-tRNA Synthetase (AsnRS) from Brugia malayi, Leishmania major, Thermus thermophilus, Trypanosoma brucei have been shown to play an important role in survival and pathogenesis. Entamoeba histolytica (Ehis) is an anaerobic eukaryotic pathogen that infects the large intestines of humans. It is a major cause of dysentery and has the potential to cause life-threatening abscesses in the liver and other organs making it the second leading cause of parasitic death after malaria. Ehis-AsnRS has not been studied in detail, except the crystal structure determined at 3 Å resolution showing that it is primarily α-helical and dimeric. It is a homodimer, with each 52 kDa monomer consisting of 451 amino acids. It has a relatively short N-terminal as compared to its human and yeast counterparts. Objective: Our study focusses to understand certain structural characteristics of Ehis-AsnRS using biophysical tools to decipher the thermodynamics of unfolding and its binding properties. Methods: Ehis-AsnRS was cloned and expressed in E. coli BL21DE3 cells. Protein purification was performed using Ni-NTA affinity chromatography, following which the protein was used for biophysical studies. Various techniques such as steady-state fluorescence, quenching, circular dichroism, differential scanning fluorimetry, isothermal calorimetry and fluorescence lifetime studies were employed for the conformational characterization of Ehis-AsnRS. Protein concentration for far-UV and near-UV circular dichroism experiments was 8 µM and 20 µM respectively, while 4 µM protein was used for the rest of the experiments. Results: The present study revealed that Ehis-AsnRS undergoes unfolding when subjected to increasing concentration of GdnHCl and the process is reversible. With increasing temperature, it retains its structural compactness up to 45ºC before it unfolds. Steady-state fluorescence, circular dichroism and hydrophobic dye binding experiments cumulatively suggest that Ehis-AsnRS undergoes a two-state transition during unfolding. Shifting of the transition mid-point with increasing protein concentration further illustrate that dissociation and unfolding processes are coupled indicating the absence of any detectable folded monomer. Conclusion: This article indicates that GdnHCl induced denaturation of Ehis-AsnRS is a two – state process and does not involve any intermediate; unfolding occurs directly from native dimer to unfolded monomer. The solvent exposure of the tryptophan residues is biphasic, indicating selective quenching. Ehis-AsnRS also exhibits a structural as well as functional stability over a wide range of pH.

Sign in / Sign up

Export Citation Format

Share Document