Airway Closure: Occluding Liquid Bridges in Strongly Buckled Elastic Tubes

1999 ◽  
Vol 121 (5) ◽  
pp. 487-493 ◽  
Author(s):  
M. Heil
Keyword(s):  
Surface Tension ◽  
High Surface ◽  
Elastic Shell ◽  
External Pressure ◽  
Physiological Parameter ◽  
Liquid Bridges ◽  
Deformation Characteristics ◽  
Airway Closure ◽  
Elastic Tubes ◽  
Parameter Values

This paper is concerned with the airway closure problem and investigates the quasi-steady deformation characteristics of strongly collapsed (buckled) airways occluded by liquid bridges of high surface tension. The airway wall is modeled as a thin-walled elastic shell, which deforms in response to an external pressure and to the compression due to the surface tension of the liquid bridge. The governing equations are solved numerically using physiological parameter values. It is shown that axisymmetric configurations are statically unstable, as are buckled tubes whose opposite walls are not in contact. The quasi-steady deformation characteristics of strongly collapsed airways whose walls are in opposite wall contact show a pronounced hysteresis during the collapse/reopening cycle. Buckling is shown to occur over a short axial length with moderate circumferential wavenumbers. Finally, further implications of the results for the airway collapse/reopening problem are discussed.

Minimal liquid bridges in non-axisymmetrically buckled elastic tubes

1999 ◽  
Vol 380 ◽  
pp. 309-337 ◽  
Author(s):  
MATTHIAS HEIL
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Liquid Bridge ◽  
Tube Wall ◽  
External Pressure ◽  
Elastic Tube ◽  
Liquid Bridges ◽  
Elastic Tubes ◽  
Highly Nonlinear ◽  
Existence And Stability

This study investigates the existence and stability of static liquid bridges in non-axisymmetrically buckled elastic tubes. The liquid bridge which occludes the tube is formed by two menisci which meet the tube wall at a given contact angle along a contact line whose position is initially unknown. Geometrically nonlinear shell theory is used to describe the deformation of the linearly elastic tube wall in response to an external pressure and to the loads due to the surface tension of the liquid bridge. This highly nonlinear problem is solved numerically by finite element methods.It is found that for a large range of parameters (surface tension, contact angle and external pressure), the compressive forces generated by the liquid bridge are strong enough to hold the tube in a buckled configuration. Typical meniscus shapes in strongly collapsed tubes are shown and the stability of these configurations to quasi-steady perturbations is examined. The minimum volume of fluid required to form an occluding liquid bridge in an elastic tube is found to be substantially smaller than predicted by estimates based on previous axisymmetric models. Finally, the implications of the results for the physiological problem of airway closure are discussed.

Surface-tension-induced buckling of liquid-lined elastic tubes: a model for pulmonary airway closure

2005 ◽  
Vol 461 (2058) ◽  
pp. 1847-1868 ◽  
Author(s):  
Andrew L Hazel ◽  
Matthias Heil
Keyword(s):  
Surface Tension ◽  
Liquid Layer ◽  
Solid Mechanics ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Compressive Load ◽  
Elastic Tube ◽  
Airway Closure ◽  
Elastic Tubes ◽  
Pulmonary Airway

We use a fully coupled, three-dimensional, finite-element method to study the evolution of the surface-tension-driven instabilities of a liquid layer that lines an elastic tube, a simple model for pulmonary airway closure. The equations of large-displacement shell theory are used to describe the deformations of the tube and are coupled to the Navier–Stokes equations, describing the motion of the liquid. The liquid layer is susceptible to a capillary instability, whereby an initially uniform layer can develop a series of axisymmetric peaks and troughs, analogous to the classical instability that causes liquid jets to break up into droplets. For sufficiently high values of the liquid's surface tension, relative to the bending stiffness of the tube, the additional compressive load induced by the development of the axisymmetric instability can induce non-axisymmetric buckling of the tube wall. Once the tube has buckled, a strong destabilizing feedback between the fluid and solid mechanics leads to an extremely rapid further collapse and occlusion of the gas-conveying core of the tube by the liquid. We find that such occlusion is possible even when the volume of the liquid is too small to form an occluding liquid bridge in the axisymmetric tube.

Airway closure: surface-tension-driven non-axisymmetric instabilities of liquid-lined elastic rings

2002 ◽  
Vol 462 ◽  
pp. 79-109 ◽  
Author(s):  
MATTHIAS HEIL ◽  
JOSEPH P. WHITE
Keyword(s):  
Surface Tension ◽  
Stokes Equations ◽  
Fluid Structure Interaction ◽  
Compressive Load ◽  
External Pressure ◽  
Theory Model ◽  
Large Displacement ◽  
Airway Closure ◽  
Fluid Structure ◽  
Structure Interaction

This paper investigates the stability and large-displacement post-buckling behaviour of liquid-lined elastic rings. The fluid flow and the wall deformation are described by the free-surface Navier–Stokes equations and by geometrically nonlinear shell theory, respectively. The fluid–structure interaction problem is solved numerically by a finite element method. The compressive load on the ring is a combination of the external pressure and the effect of surface tension. Once this combined load exceeds a critical value, the subsequent non-axisymmetric collapse of the ring is controlled by the dynamics of the surface-tension-driven redistribution of fluid in the liquid lining. It is shown that, for sufficiently large surface tension, the ring can undergo a catastrophic collapse which leads to a complete occlusion of its lumen. A novel lubrication theory model, which ensures exact volume conservation for flows on strongly curved substrates, is developed and found to be capable of accurately describing the motion of the air–liquid interface and the fluid–structure interaction in the large-displacement regime, even in cases where the film thickness is large.The findings have important implications for the occurrence of airway closure in lung diseases (such as oedema) which cause an increase in the thickness of the airways' liquid lining. It is shown that under such conditions, airways can become occluded even if the volume of fluid in their liquid lining is much smaller than that required to occlude them in their axisymmetric state.

scholarly journals Filling of Chrysotile Nanotubes with Metals

2002 ◽  
Vol 17 (5) ◽  
pp. 1129-1135 ◽  
Author(s):  
C. Métraux ◽  
B. Grobéty ◽  
P. Ulmer
Keyword(s):  
Surface Tension ◽  
High Surface ◽  
External Pressure ◽  
Limiting Factors ◽  
Infrared Spectrometry ◽  
Molten Metals ◽  
Stability Range ◽  
Transmission Electron ◽  
The Stability ◽  
Almost All

Nanowires were produced by injection of molten Hg and Pb into chrysotile nanotubes. The breakdown of chrysotile and the surface tension of the molten metals are the limiting factors for the filling procedure. The thermal stability of chrysotile nanotubes was investigated by infrared spectrometry, thermogravimetry, differential thermal analysis, and x-ray diffraction analyses. For short-term thermal annealing (30 min) the tube morphology remains stable up to 700 °C. The high surface tension of both molten Pb and Hg (γLV > 200 mN/m) requires external pressure for the melts to penetrate into the tubes. Filling of the tubes was achieved under high pressure and high temperature conditions compatible with the stability range for chrysotile determined in the annealing experiments. Transmission electron microscopy observations confirmed high filling yields for both metals. Almost all nanotubes were partially filled with lead. The length of continuous wires ranged from tens to hundreds of nanometers. Additional experiments with tin were not successful.

Tracing surfactant transformation from cellular release to insertion into an air-liquid interface

2004 ◽  
Vol 286 (5) ◽  
pp. L1009-L1015 ◽  
Author(s):  
T. Haller ◽  
P. Dietl ◽  
H. Stockner ◽  
M. Frick ◽  
N. Mair ◽  
...  
Keyword(s):  
Surface Tension ◽  
Cultured Cells ◽  
High Surface ◽  
Lamellar Body ◽  
Liquid Interface ◽  
Alveolar Type ◽  
Tensile Forces ◽  
Modify Surface ◽  
Fluorescence Imaging Microscopy ◽  
Air Liquid Interface

Pulmonary surfactant is secreted by alveolar type II cells as lipid-rich, densely packed lamellar body-like particles (LBPs). The particulate nature of released LBPs might be the result of structural and/or thermodynamic forces. Thus mechanisms must exist that promote their transformation into functional units. To further define these mechanisms, we developed methods to follow LBPs from their release by cultured cells to insertion in an air-liquid interface. When released, LBPs underwent structural transformation, but did not disperse, and typically preserved a spherical appearance for days. Nevertheless, they were able to modify surface tension and exhibited high surface activity when measured with a capillary surfactometer. When LBPs inserted in an air-liquid interface were analyzed by fluorescence imaging microscopy, they showed remarkable structural transformations. These events were instantaneous but came to a halt when the interface was already occupied by previously transformed material or when surface tension was already low. These results suggest that the driving force for LBP transformation is determined by cohesive and tensile forces acting on these particles. They further suggest that transformation of LBPs is a self-regulated interfacial process that most likely does not require structural intermediates or enzymatic activation.

Condensation of Low-Surface-Tension Fluids on Microstructured Surfaces at Low Temperature

2017 ◽  
Author(s):  
Abulimiti Aili ◽  
Qiaoyu Ge ◽  
TieJun Zhang
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Low Temperature ◽  
High Surface ◽  
Condensation Heat Transfer ◽  
Lubricant Oil ◽  
Microstructured Surfaces ◽  
Performance Deterioration ◽  
Coated Surface ◽  
Coated Surfaces

Filmwise condensation of a low surface tension fluid (i.e. refrigerant) on microstructured aluminum surfaces is studied to investigate the effect of the structures on condensation heat transfer at low temperature. The hypothesis is that the structures may cause thinning of the condensate film at micro-scales, thus resulting in an enhancement of condensation heat transfer. However, the structures may also decrease the mobility of the condensate near the surface due to increased friction, thus potentially leading to performance deterioration. The aim of this work is to investigate which of the two counteracting mechanisms dominate during filmwise condensation. Condensation experiments are carried out in a low-temperature vacuum chamber. Compared with the Nusselt model of condensation, the microstructured surfaces, either coated or uncoated, show similar performance, with potentially slight enhancement at low subcooling degree and slight deterioration at high subcooling degree. When the microstructured and silane-coated surface is infused with a non-volatile and very low-surface-tension lubricant oil, the lubricant is displaced by the condensate and there is almost no change in the condensation performance. Our results show that, unlike the case of dropwise condensation of high-surface tension fluids, microstructured and coated surfaces with/without infusing oil is not exciting to enhanced filmwise condensation of low-surface-tension fluids.

The Effect of Intermittent Fasting and Exercise on Some Physiological Parameters

2021 ◽  
Vol 15 (9) ◽  
pp. 2793-2798
Author(s):  
Yunus Berk ◽  
Şaban Ünver ◽  
Hasan Avlayan
Keyword(s):  
Physiological Parameters ◽  
Favorable Effect ◽  
Physiological Parameter ◽  
Control Group ◽  
Intermittent Fasting ◽  
Significant Difference ◽  
Post Test ◽  
Mean Differences ◽  
Parameter Values ◽  
Experimental Group

Background: In this study, the effect of recently popular intermittent fasting on weight loss and the role of exercise combined with intermittent fasting on some physiological parameters were investigated. Aim: This study was conducted to investigate the effect of intermittent fasting combined with exercise and intermittent fasting alone on some physiological parameters. Methods: A total of 36 healthy individuals between 20 and 24 years of age, including 18 in the experimental group (exercising) and 18 in the control group (non-exercising), who were assigned by the random selection method, participated in the study. The individuals in the experimental group exercised 36 minutes a day, 5 days a week, along with intermittent fasting for 30 days. On the other hand, the control group did not exercise during this period. Results: When the within-group pre-test and post-test physiological parameter values were compared, a significant difference was found in all values of the experimental group (p<0.05). Similarly, a significant difference was found in the physiological parameter values of the control group (p<0.05) too, with the exception of body mass index and body fluid ratio. A statistically significant difference was found between the two groups in terms of the mean differences between the pre-test and post-test physiological parameter values (p < 0.05). Conclusion: Based on the findings, it could be concluded that intermittent fasting is an effective method for losing weight and reducing body fat and that adding low-intensity exercise to this routine ensures more effective weight reduction. Hence, starving for a certain period of time has a favorable effect on the physiological parameters, and the practice of exercising in addition to dieting further improves these values. Keywords: Intermittent fasting, Exercise, Health

High surface tension pulmonary edema induced by detergent aerosol

1985 ◽  
Vol 58 (1) ◽  
pp. 129-136 ◽  
Author(s):  
G. F. Nieman ◽  
C. E. Bredenberg
Keyword(s):  
Surface Tension ◽  
Pulmonary Edema ◽  
High Surface ◽  
Water Volume ◽  
Oncotic Pressure ◽  
Static Compliance ◽  
Surfactant Activity ◽  
Dioctyl Sodium Sulfosuccinate ◽  
Alveolar Surface

The effect of the detergent dioctyl sodium sulfosuccinate on pulmonary extravascular water volume (PEWV) was studied in adult anesthetized mongrel dogs. The detergent was dissolved as a 1% solution in a vehicle of equal volumes of 95% ethanol and normal saline and administered by ultrasonic nebulizer attached to the inspiratory tubing of a piston ventilator. Two hours following detergent aerosol PEWV measured gravimetrically was increased compared with either animals receiving no aerosol or those receiving an aerosol of vehicle alone. Loss of surfactant activity and increased alveolar surface tension were demonstrated by Wilhelmy balance studies of minced lung extracts, by a fall in static compliance, and by evidence of atelectasis and instability noted by gross observation and by in vivo microscopy. No significant changes in colloid oncotic pressure or pulmonary microvascular hydrostatic pressure were observed. These data suggest that pulmonary edema can be induced by increased alveolar surface tension and support the concept that one of the major roles of pulmonary surfactant is to prevent pulmonary edema.

scholarly journals Surfactant Protein B Deficiency Induced High Surface Tension: Relationship between Alveolar Micromechanics, Alveolar Fluid Properties and Alveolar Epithelial Cell Injury

2019 ◽  
Vol 20 (17) ◽  
pp. 4243 ◽  
Author(s):  
Nina Rühl ◽  
Elena Lopez-Rodriguez ◽  
Karolin Albert ◽  
Bradford J Smith ◽  
Timothy E Weaver ◽  
...  
Keyword(s):  
Surface Tension ◽  
Lung Injury ◽  
High Surface ◽  
Surfactant Protein ◽  
Epithelial Injury ◽  
High Surface Tension ◽  
Alveolar Epithelial ◽  
Surfactant Protein B ◽  
Fluid Properties ◽  
Alveolar Epithelial Injury

High surface tension at the alveolar air-liquid interface is a typical feature of acute and chronic lung injury. However, the manner in which high surface tension contributes to lung injury is not well understood. This study investigated the relationship between abnormal alveolar micromechanics, alveolar epithelial injury, intra-alveolar fluid properties and remodeling in the conditional surfactant protein B (SP-B) knockout mouse model. Measurements of pulmonary mechanics, broncho-alveolar lavage fluid (BAL), and design-based stereology were performed as a function of time of SP-B deficiency. After one day of SP-B deficiency the volume of alveolar fluid V(alvfluid,par) as well as BAL protein and albumin levels were normal while the surface area of injured alveolar epithelium S(AEinjure,sep) was significantly increased. Alveoli and alveolar surface area could be recruited by increasing the air inflation pressure. Quasi-static pressure-volume loops were characterized by an increased hysteresis while the inspiratory capacity was reduced. After 3 days, an increase in V(alvfluid,par) as well as BAL protein and albumin levels were linked with a failure of both alveolar recruitment and airway pressure-dependent redistribution of alveolar fluid. Over time, V(alvfluid,par) increased exponentially with S(AEinjure,sep). In conclusion, high surface tension induces alveolar epithelial injury prior to edema formation. After passing a threshold, epithelial injury results in vascular leakage and exponential accumulation of alveolar fluid critically hampering alveolar recruitability.

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