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Viola HL, Vasani V, Washington K, Lee JH, Selva C, Li A, Llorente CJ, Murayama Y, Grotberg JB, Romanò F, Takayama S. Liquid plug propagation in computer-controlled microfluidic airway-on-a-chip with semi-circular microchannels. LAB ON A CHIP 2024; 24:197-209. [PMID: 38093669 PMCID: PMC10842925 DOI: 10.1039/d3lc00957b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2024]
Abstract
This paper introduces a two-inlet, one-outlet lung-on-a-chip device with semi-circular cross-section microchannels and computer-controlled fluidic switching that enables a broader systematic investigation of liquid plug dynamics in a manner relevant to the distal airways. A leak-proof bonding protocol for micro-milled devices facilitates channel bonding and culture of confluent primary small airway epithelial cells. Production of liquid plugs with computer-controlled inlet channel valving and just one outlet allows more stable long-term plug generation and propagation compared to previous designs. The system also captures both plug speed and length as well as pressure drop concurrently. In one demonstration, the system reproducibly generates surfactant-containing liquid plugs, a challenging process due to lower surface tension that makes the plug formation less stable. The addition of surfactant decreases the pressure required to initiate plug propagation, a potentially significant effect in diseases where surfactant in the airways is absent or dysfunctional. Next, the device recapitulates the effect of increasing fluid viscosity, a challenging analysis due to higher resistance of viscous fluids that makes plug formation and propagation more difficult particularly in airway-relevant length scales. Experimental results show that increased fluid viscosity decreases plug propagation speed for a given air flow rate. These findings are supplemented by computational modeling of viscous plug propagation that demonstrates increased plug propagation time, increased maximum wall shear stress, and greater pressure differentials in more viscous conditions of plug propagation. These results match physiology as mucus viscosity is increased in various obstructive lung diseases where it is known that respiratory mechanics can be compromised due to mucus plugging of the distal airways. Finally, experiments evaluate the effect of channel geometry on primary human small airway epithelial cell injury in this lung-on-a-chip. There is more injury in the middle of the channel relative to the edges highlighting the role of channel shape, a physiologically relevant parameter as airway cross-sectional geometry can also be non-circular. In sum, this paper describes a system that pushes the device limits with regards to the types of liquid plugs that can be stably generated for studies of distal airway fluid mechanical injury.
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Affiliation(s)
- Hannah L Viola
- School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA
- The Parker H. Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA, 30332, USA.
| | - Vishwa Vasani
- The Parker H. Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA, 30332, USA.
- The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA
| | - Kendra Washington
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory School of Medicine, Atlanta, GA, 30332, USA
| | - Ji-Hoon Lee
- The Parker H. Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA, 30332, USA.
- School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA
| | - Cauviya Selva
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory School of Medicine, Atlanta, GA, 30332, USA
| | - Andrea Li
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory School of Medicine, Atlanta, GA, 30332, USA
| | - Carlos J Llorente
- Department of Physics & Astronomy, Michigan State University, Lansing, MI, 48824, USA
| | - Yoshinobu Murayama
- Department of Electrical and Electronics Engineering, College of Engineering, Nihon University, Fukushima, Japan
| | - James B Grotberg
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Francesco Romanò
- Univ. Lille, CNRS, ONERA, Arts et Métiers Institute of Technology, Centrale Lille, FRE 2017-LMFL-Laboratoire de Mécanique des Fluides de Lille - Kampé de Fériet, F-59000, Lille, France
| | - Shuichi Takayama
- The Parker H. Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA, 30332, USA.
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory School of Medicine, Atlanta, GA, 30332, USA
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Kavishvar D, Ramachandran A. The yielding behaviour of human mucus. Adv Colloid Interface Sci 2023; 322:103049. [PMID: 38039907 DOI: 10.1016/j.cis.2023.103049] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2023] [Revised: 10/03/2023] [Accepted: 11/06/2023] [Indexed: 12/03/2023]
Abstract
Mucus is a viscoelastic material with non-linear rheological properties such as a yield stress of the order of a few hundreds of millipascals to a few tens of pascals, due to a complex network of mucins in water along with non-mucin proteins, DNA and cell debris. In this review, we discuss the origin of the yield stress in human mucus, the changes in the rheology of mucus with the occurrence of diseases, and possible clinical applications in disease detection as well as cure. We delve into the domain of mucus rheology, examining both macro- and microrheology. Macrorheology involves investigations conducted at larger length scales (∼ a few hundreds of μm or higher) using traditional rheometers, which probe properties on a bulk scale. It is significant in elucidating various mucosal functions within the human body. This includes rejecting unwanted irritants out of lungs through mucociliary and cough clearance, protecting the stomach wall from the acidic environment as well as biological entities, safeguarding cervical canal from infections and providing a swimming medium for sperms. Additionally, we explore microrheology, which encompasses studies performed at length scales ranging from a few tens of nm to a μm. These microscale studies find various applications, including the context of drug delivery. Finally, we employ scaling analysis to elucidate a few examples in lung, cervical, and gastric mucus, including settling of irritants in lung mucus, yielding of lung mucus in cough clearance and cilial beating, spreading of exogenous surfactants over yielding mucus, swimming of Helicobacter pylori through gastric mucus, and lining of protective mucus in the stomach. The scaling analyses employed on the applications mentioned above provide us with a deeper understanding of the link between the rheology and the physiology of mucus.
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Affiliation(s)
- Durgesh Kavishvar
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, ON, Canada.
| | - Arun Ramachandran
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, ON, Canada.
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3
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Viola HL, Vasani V, Washington K, Lee JH, Selva C, Li A, Llorente CJ, Murayama Y, Grotberg JB, Romanò F, Takayama S. Liquid plug propagation in computer-controlled microfluidic airway-on-a-chip with semi-circular microchannels. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.24.542177. [PMID: 37292706 PMCID: PMC10245866 DOI: 10.1101/2023.05.24.542177] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
This paper introduces a two-inlet, one-outlet lung-on-a-chip device with semi-circular cross-section microchannels and computer-controlled fluidic switching that enables a broader systematic investigation of liquid plug dynamics in a manner relevant to the distal airways. A leak-proof bonding protocol for micro-milled devices facilitates channel bonding and culture of confluent primary small airway epithelial cells. Production of liquid plugs with computer-controlled inlet channel valving and just one outlet allows more stable long-term plug generation and propagation compared to previous designs. The system also captures both plug speed and length as well as pressure drop concurrently. In one demonstration, the system reproducibly generates surfactant-containing liquid plugs, a challenging process due to lower surface tension that makes the plug formation less stable. The addition of surfactant decreases the pressure required to initiate plug propagation, a potentially significant effect in diseases where surfactant in the airways is absent or dysfunctional. Next, the device recapitulates the effect of increasing fluid viscosity, a challenging analysis due to higher resistance of viscous fluids that makes plug formation and propagation more difficult particularly in airway-relevant length scales. Experimental results show that increased fluid viscosity decreases plug propagation speed for a given air flow rate. These findings are supplemented by computational modeling of viscous plug propagation that demonstrate increased plug propagation time, increased maximum wall shear stress, and greater pressure differentials in more viscous conditions of plug propagation. These results match physiology as mucus viscosity is increased in various obstructive lung diseases where it is known that respiratory mechanics can be compromised due to mucus plugging of the distal airways. Finally, experiments evaluate the effect of channel geometry on primary human small airway epithelial cell injury in this lung-on-a-chip. There is more injury in the middle of the channel relative to the edges highlighting the role of channel shape, a physiologically relevant parameter as airway cross-sectional geometry can also be non-circular. In sum, this paper describes a system that pushes the device limits with regards to the types of liquid plugs that can be stably generated for studies of distal airway fluid mechanical injury.
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Affiliation(s)
- Hannah L Viola
- School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, USA, 30332
- The Parker H. Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA, USA, 30332
| | - Vishwa Vasani
- The Parker H. Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA, USA, 30332
- The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA, 30332
| | - Kendra Washington
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory School of Medicine, Atlanta, GA, USA, 30332
| | - Ji-Hoon Lee
- The Parker H. Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA, USA, 30332
- School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA, USA, 30332
| | - Cauviya Selva
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory School of Medicine, Atlanta, GA, USA, 30332
| | - Andrea Li
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory School of Medicine, Atlanta, GA, USA, 30332
| | - Carlos J Llorente
- Department of Physics & Astronomy, Michigan State University, Lansing, MI, USA, 48824
| | - Yoshinobu Murayama
- Department of Electrical and Electronics Engineering, College of Engineering, Nihon University, Fukushima, Japan
| | - James B Grotberg
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA, 48109
| | - Francesco Romanò
- Univ. Lille, CNRS, ONERA, Arts et Métiers Institute of Technology, Centrale Lille, FRE 2017 -LMFL-Laboratoire de Mécanique des Fluides de Lille - Kampé de Fériet, F-59000, Lille, France
| | - Shuichi Takayama
- The Parker H. Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA, USA, 30332
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory School of Medicine, Atlanta, GA, USA, 30332
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Munir B, Xu Y. The steady motion of microbubbles in bifurcating airways: Role of shear-thinning and surface tension. Respir Physiol Neurobiol 2021; 290:103675. [PMID: 33915302 DOI: 10.1016/j.resp.2021.103675] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2021] [Accepted: 04/21/2021] [Indexed: 12/11/2022]
Abstract
Mucous fluid is non-Newtonian secretions in the lower lung airways that accumulates when the alveolar-capillary membrane ruptures during acute respiratory distress syndrome. The mucus fluid has, therefore, different types of non-Newtonian properties like shear-thinning, viscoelasticity, and non-zero yield stress. In this paper, we numerically solved the steady Stokes equations along with arbitrary Eulerian-Lagrangian moving mesh techniques to study the microbubble propagation in a two-dimensional asymmetric bifurcating airway filled with non-Newtonian fluid where the fluid has shear-thinning behavior described by the power-law model. Numerical results show that both shear-thinning and surface tension characterized by the behavior index (n) and Capillary number (Ca), respectively, had a significant impact on microbubble flow patterns and the magnitude of the pressure gradient. At low values of both n and Ca, the microbubble leaves a thin film-thickness with the airway wall while a large and sharp peak of the pressure gradient near the thin bubble tip. Interestingly, increasing both n and Ca, leads to an increase in film thickness and a decrease in the pressure gradient magnitude in both the daughter airway walls. It is observed the magnitude of the pressure gradient is more sensitive to Ca compared to n. We concluded that shear-thinning and surface tension not only significantly impact the patterns of microbubble propagation but also the hydrodynamic stress magnitudes at the airway wall.
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Affiliation(s)
- Bacha Munir
- School of Natural and Applied Sciences, Department of Applied Mathematics, Northwestern Polytechnical University, Xi'an, Shaanxi, 710029, People's Republic of China.
| | - Yong Xu
- School of Natural and Applied Sciences, Department of Applied Mathematics, Northwestern Polytechnical University, Xi'an, Shaanxi, 710029, People's Republic of China
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Shi J, Wu B, Li S, Song J, Song B, Lu WF. Shear stress analysis and its effects on cell viability and cell proliferation in drop-on-demand bioprinting. Biomed Phys Eng Express 2018. [DOI: 10.1088/2057-1976/aac946] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Abstract
The ability to deliver drugs to specific sites in the lung could radically improve therapeutic outcomes of a variety of lung diseases, including cystic fibrosis, severe bronchopneumonia, chronic obstructive pulmonary disease, and lung cancer. Using conventional methods for pulmonary drug administration, precise, localized delivery of exact doses of drugs to target regions remains challenging. Here we describe a more controlled delivery of soluble reagents (e.g., drugs, enzymes, and radionuclides) in microvolume liquid plugs to targeted branches of the pulmonary airway tree: upper airways, small airways (bronchioles), or the most distal alveoli. In this approach, a soluble liquid plug of very small volume (<1 mL) is instilled into the upper airways, and with programmed air ventilation of the lungs, the plug is pushed into a specific desired (more distal) airway to achieve deposition of liquid film onto the lung epithelium. The plug volume and ventilation conditions were determined by mathematical modeling of plug transport in a tubular geometry, and targeted liquid film deposition was demonstrated in rat lungs by three different in vivo imaging modalities. The experimental and modeling data suggest that instillation of microvolumes of liquid into a ventilated pulmonary airway could be an effective strategy to deliver exact doses of drugs to targeted pathologic regions of the lung, especially those inaccessible by bronchoscopy, to increase in situ efficacy of the drug and minimize systemic side effects.
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Koch K, Dew B, Corcoran TE, Przybycien TM, Tilton RD, Garoff S. Surface tension gradient driven spreading on aqueous mucin solutions: a possible route to enhanced pulmonary drug delivery. Mol Pharm 2011; 8:387-94. [PMID: 21250745 PMCID: PMC3070836 DOI: 10.1021/mp1002448] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Surface tension gradient driven, or "Marangoni", flow can be used to move exogenous fluid, either surfactant dispersions or drug carrying formulations, through the lung. In this paper, we investigate the spreading of aqueous solutions of water-soluble surfactants over entangled, aqueous mucin solutions that mimic the airway surface liquid of the lung. We measure the movement of the formulation by incorporating dyes into the formulation while we measure surface flows of the mucin solution subphase using tracer particles. Surface tension forces and/or Marangoni stresses initiate a convective spreading flow over this rheologically complex subphase. As expected, when the concentration of surfactant is reduced until its surface tension is above that of the mucin solution, the convective spreading does not occur. The convective spreading front moves ahead of the drop containing the formulation. Convective spreading ends with the solution confined to a well-defined static area which must be governed by a surface tension balance. Further motion of the spread solution progresses by much slower diffusive processes. Spreading behaviors are qualitatively similar for formulations based on anionic, cationic, or nonionic surfactants, containing either hydrophilic or hydrophobic dyes, on mucin as well as on other entangled aqueous polymer solution subphases. This independence of qualitative spreading behaviors from the chemistry of the surfactant and subphase indicates that there is little chemical interaction between the formulation and the subphase during the spreading process. The spreading and final solution distributions are controlled by capillary and hydrodynamic phenomena and not by specific chemical interactions among the components of the system. It is suggested that capillary forces and Marangoni flows driven by soluble surfactants may thereby enhance the uniformity of drug delivery to diseased lungs.
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Affiliation(s)
- Kevin Koch
- Physics Department, Carnegie Mellon University, Pittsburgh, PA 15213
- Center for Complex Fluids Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Beautia Dew
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
| | | | - Todd M. Przybycien
- Center for Complex Fluids Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
- Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Robert D. Tilton
- Center for Complex Fluids Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
- Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Stephen Garoff
- Physics Department, Carnegie Mellon University, Pittsburgh, PA 15213
- Center for Complex Fluids Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
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Milic-Emili J, Torchio R, D'Angelo E. Closing volume: a reappraisal (1967-2007). Eur J Appl Physiol 2007; 99:567-83. [PMID: 17237952 DOI: 10.1007/s00421-006-0389-0] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/20/2006] [Indexed: 10/23/2022]
Abstract
Measurement of closing volume (CV) allows detection of presence or absence of tidal airway closure, i.e. cyclic opening and closure of peripheral airways with concurrent (1) inhomogeneity of distribution of ventilation and impaired gas exchange; and (2) risk of peripheral airway injury. Tidal airway closure, which can occur when the CV exceeds the end-expiratory lung volume (EELV), is commonly observed in diseases characterised by increased CV (e.g. chronic obstructive pulmonary disease, asthma) and/or decreased EELV (e.g. obesity, chronic heart failure). Risk of tidal airway closure is enhanced by ageing. In patients with tidal airway closure (CV > EELV) there is not only impairment of pulmonary gas exchange, but also peripheral airway disease due to injury of the peripheral airways. In view of this, the causes and consequences of tidal airway closure are reviewed, and further studies are suggested. In addition, assessment of the "open volume", as opposed to the "closing volume", is proposed because it is easier to perform and it requires less equipment.
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Affiliation(s)
- Joseph Milic-Emili
- Meakins-Christie Laboratories, McGill University, 3626 St. Urbain Street, H2X2P2, Montreal, QC, Canada.
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D'Angelo E, Pecchiari M, Gentile G. Dependence of lung injury on surface tension during low-volume ventilation in normal open-chest rabbits. J Appl Physiol (1985) 2006; 102:174-82. [PMID: 16959911 DOI: 10.1152/japplphysiol.00405.2006] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
To evaluate the role of pulmonary surfactant in the prevention of lung injury caused by mechanical ventilation (MV) at low end-expiratory volumes, lung mechanics and morphometry were assessed in three groups of eight normal, open-chest rabbits ventilated for 3-4 h at zero end-expiratory pressure (ZEEP) with physiological tidal volumes (Vt = 10 ml/kg). One group was left untreated (group A); the other two received surfactant intratracheally (group B) or aerosolized dioctylsodiumsulfosuccinate (group C) before MV on ZEEP. Relative to initial MV on positive end-expiratory pressure (PEEP; 2.3 cmH(2)O), quasi-static elastance (Est) and airway (Rint) and viscoelastic resistance (Rvisc) increased on ZEEP in all groups. After restoration of PEEP, only Rint (124%) remained elevated in group A, only Est (36%) was significantly increased in group B, whereas in group C, Est, Rint, and Rvisc were all markedly augmented (274, 253, and 343%). In contrast, prolonged MV on PEEP had no effect on lung mechanics of eight open-chest rabbits (group D). Lung edema developed in group C (wet-to-dry ratio = 7.1), but not in the other groups. Relative to group D, both groups A and C, but not B, showed histological indexes of bronchiolar injury, whereas all groups exhibited an increased number of polymorphonuclear leukocytes in alveolar septa, which was significantly greater in group C. In conclusion, administration of exogenous surfactant largely prevents the histological and functional damage of prolonged MV at low lung volumes, whereas surfactant dysfunction worsens the functional alterations, also because of edema formation and, possibly, increased inflammatory response.
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Affiliation(s)
- Edgardo D'Angelo
- Istituto di Fisiologia Umana I, Università di Milano, Milan, Italy.
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11
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Bertram CD, Gaver DP. Biofluid Mechanics of the Pulmonary System. Ann Biomed Eng 2005; 33:1681-8. [PMID: 16389513 DOI: 10.1007/s10439-005-8758-0] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2005] [Accepted: 06/03/2005] [Indexed: 01/06/2023]
Abstract
Presents an overview of leading areas of discovery in bio-fluid mechanics related to the pulmonary system, with particular reference to the airways. Areas briefly reviewed include airway gas dynamics, impedance studies, collapsible-tube studies, and airway liquid studies. Emphasis is placed on promising further directions, such as analysis of interacting fluid-mechanical or fluid-structure phenomena, multi-scale modeling across widely varying length and time scales, and integration of advanced simulations into respiratory investigation and pulmonary medicine.
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Affiliation(s)
- Chris D Bertram
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, Australia.
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Naire S, Jensen OE. Epithelial cell deformation during surfactant-mediated airway reopening: a theoretical model. J Appl Physiol (1985) 2005; 99:458-71. [PMID: 15802368 DOI: 10.1152/japplphysiol.00796.2004] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
A theoretical model is presented describing the reopening by an advancing air bubble of an initially liquid-filled collapsed airway lined with deformable epithelial cells. The model integrates descriptions of flow-structure interaction (accounting for nonlinear deformation of the airway wall and viscous resistance of the airway liquid flow), surfactant transport around the bubble tip (incorporating physicochemical parameters appropriate for Infasurf), and cell deformation (due to stretching of the airway wall and airway liquid flows). It is shown how the pressure required to drive a bubble into a flooded airway, peeling apart the wet airway walls, can be reduced substantially by surfactant, although the effectiveness of Infasurf is limited by slow adsorption at high concentrations. The model demonstrates how the addition of surfactant can lead to the spontaneous reopening of a collapsed airway, depending on the degree of initial airway collapse. The effective elastic modulus of the epithelial layer is shown to be a key determinant of the relative magnitude of strains generated by flow-induced shear stresses and by airway wall stretch. The model also shows how epithelial-layer compressibility can mediate strains arising from flow-induced normal stresses and stress gradients.
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Affiliation(s)
- Shailesh Naire
- School of Mathematical Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, UK
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13
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Abstract
The field of respiratory flow and transport has experienced significant research activity over the past several years. Important contributions to the knowledge base come from pulmonary and critical care medicine, surgery, physiology, environmental health sciences, biophysics, and engineering. Several disciplines within engineering have strong and historical ties to respiration including mechanical, chemical, civil/environmental, aerospace and, of course, biomedical engineering. This review draws from a wide variety of scientific literature that reflects the diverse constituency and audience that respiratory science has developed. The subject areas covered include nasal flow and transport, airway gas flow, alternative modes of ventilation, nonrespiratory gas transport, aerosol transport, airway stability, mucus transport, pulmonary acoustics, surfactant dynamics and delivery, and pleural liquid flow. Within each area are a number of subtopics whose exploration can provide the opportunity of both depth and breadth for the interested reader.
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Affiliation(s)
- J B Grotberg
- Biomedical Engineering Department, University of Michigan, 3304 G.G. Brown Bldg., 2350 Hayward St., Ann Arbor, MI 48109-2125, USA.
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14
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Jokic R, Bhagchandani L, Zintel T, Baetz M, Fitzpatrick MF. Effect of high versus low ambient humidity on the severity of obstructive sleep apnoea. Thorax 1999; 54:711-3. [PMID: 10413725 PMCID: PMC1745547 DOI: 10.1136/thx.54.8.711] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
BACKGROUND Surface tension forces appear to make a significant contribution to upper airway closure in patients with obstructive sleep apnoea (OSA). It is possible that drying of the upper airway mucosa at night might contribute to these surface tension forces and the severity of OSA might therefore change with alteration of the ambient humidity. METHODS A randomised single blind crossover study of high ambient relative humidity (HRH) versus low ambient relative humidity (LRH) was performed in 12 men of mean (SD) age 49 (9) years with mild OSA (apnoea/hypopnoea index (AHI) 14 (5.2)). On one night patients slept in continuous HRH (85 (4)%, range 80-93%) and on the other in LRH (16 (4)%, range 11-22%). RESULTS The AHI was similar on the HRH and LRH nights (mean difference 3; 95% CI -2 to 9, p = 0.20 and no statistically significant differences in AHI were observed on the two nights after standardising for body position and sleep stage. Sleep stage distribution and the proportion of time spent in the supine position were similar on the HRH and LRH nights. The number of non-respiratory arousals was also similar on the two nights. CONCLUSION Altering ambient humidity alone has no significant impact on the severity of OSA.
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Affiliation(s)
- R Jokic
- Division of Respiratory Medicine, Saskatoon, Saskatchewan, Canada
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15
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Abstract
In this model study, we simulated the initial airway reopening event in a rigid tube model. The air-liquid interface during airway reopening was assumed to be a simple axisymmetric meniscus similar to that of a two-phase flow in a rigid tube (radius R), where the applied pressures and the meniscus velocities were measured experimentally for fluids of different viscosities and surface tensions (gamma). Bulk flow contribution was deducted from the applied pressure to obtain the pressure accounting for interfacial movement (P*(int)). A semi-empirical formula for the interface was generated by dimensional analysis. The dimensionless interfacial pressure (P(int) = P*(int),R/gamma) was found to approach 2 for sufficiently small velocities, consistent with Bretherton's theoretical prediction. This formula also resembles that previously obtained in collapsible tubes simulating airways. The result suggests that the critical pressures required to reopen a collapsible airway and a non-collapsible one with the same radius are similar in magnitude (approximately 2 - 3gamma/R). However, in a collapsible airway, no significant bulk flow of lining fluids would develop while the interface proceeds, leading to a much smaller overall pressure for further reopening. Airway wall collapsibility thus could play a crucial role in maintaining proper ventilation through rapid reopening of the airway.
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Affiliation(s)
- S H Hsu
- Department of Chemical Engineerng, National Chung Hsing University, Taichung, Taiwan, PR China.
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16
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Low HT, Chew YT, Zhou CW. Pulmonary airway reopening: effects of non-Newtonian fluid viscosity. J Biomech Eng 1997; 119:298-308. [PMID: 9285343 DOI: 10.1115/1.2796094] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
This paper considers the effects of non-Newtonian lining-fluid viscosity, particularly shear thinning and yield stress, on the reopening of the airways. The airway was simulated by a very thin, circular polyethylene tube, which collapsed into a ribbon-like configuration. The non-Newtonian fluid viscosity was described by the power-law and Herschel-Buckley models. The speed of airway opening was determined under various opening pressures. These results were collapsed into dimensionless pressure-velocity relationships, based on an assumed shear rate gamma = U/(0.5 H), where U and H are the opening velocity and fluid film thickness, respectively. It was found that yield stress, like surface tension, increases the yield pressure and opening time. However, shear thinning reduces the opening time. An increased film thickness of the non-Newtonian lining fluid generally impedes airway reopening; a higher pressure is needed to initiate the airway reopening and a longer time is required to complete the opening process.
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Affiliation(s)
- H T Low
- Department of Mechanical & Production Engineering, National University of Singapore, Singapore
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