Abstract:The mechanics of the regional airways and tissues was studied in isolated dog lobes by means of a modified wave-tube technique. Small-amplitude pseudorandom forced oscillations between 0.1 and 48 Hz were applied through catheters wedged in 2-mm-diameter bronchi in three regions of each lobe at translobar pressures (PL) of 10, 7, 5, 3, 2, and 1 cmH2O. The measured regional input impedances were fitted by a model containing the resistance (R1) and inertance (I) of the regular (segmental) airways, the resistance … Show more
“…These data are then fit to a constant-phase model to separate a central Newtonian airway resistance (R aw ) from tissue resistance (R ti ) due to tissue viscous energy dissipation (damping; G) and stored tissue energy (elastance; H) that contribute to total respiratory system (R rs ) ventilation (14,15), endotoxin injury (23), or elastase injury (226). However, collapse of alveoli and small airways results in an increase in the elastance parameter, H, which can be reversed by a deep inspiratory sigh (15,189,284,285). Since heterogeneous tissue injury produced an overestimation of the tissue component of lung resistance using the single compartment model, Suki et al (459) proposed a distributed model with multiple resistance and elastance compartments that more accurately characterized the tissue response to heterogeneous regional injury.…”
Section: Indirect Estimates Of Lung Edemamentioning
Acute lung injury is a general term that describes injurious conditions that can range from mild interstitial edema to massive inflammatory tissue destruction. This review will cover theoretical considerations and quantitative and semi-quantitative methods for assessing edema formation and increased vascular permeability during lung injury. Pulmonary edema can be quantitated directly using gravimetric methods, or indirectly by descriptive microscopy, quantitative morphometric microscopy, altered lung mechanics, high-resolution computed tomography, magnetic resonance imaging, positron emission tomography, or x-ray films. Lung vascular permeability to fluid can be evaluated by measuring the filtration coefficient (Kf) and permeability to solutes evaluated from their blood to lung clearances. Albumin clearances can then be used to calculate specific permeability-surface area products (PS) and reflection coefficients (σ). These methods as applied to a wide variety of transgenic mice subjected to acute lung injury by hyperoxic exposure, sepsis, ischemia-reperfusion, acid aspiration, oleic acid infusion, repeated lung lavage, and bleomycin are reviewed. These commonly used animal models simulate features of the acute respiratory distress syndrome, and the preparation of genetically modified mice and their use for defining specific pathways in these disease models are outlined. Although the initiating events differ widely, many of the subsequent inflammatory processes causing lung injury and increased vascular permeability are surprisingly similar for many etiologies.
“…These data are then fit to a constant-phase model to separate a central Newtonian airway resistance (R aw ) from tissue resistance (R ti ) due to tissue viscous energy dissipation (damping; G) and stored tissue energy (elastance; H) that contribute to total respiratory system (R rs ) ventilation (14,15), endotoxin injury (23), or elastase injury (226). However, collapse of alveoli and small airways results in an increase in the elastance parameter, H, which can be reversed by a deep inspiratory sigh (15,189,284,285). Since heterogeneous tissue injury produced an overestimation of the tissue component of lung resistance using the single compartment model, Suki et al (459) proposed a distributed model with multiple resistance and elastance compartments that more accurately characterized the tissue response to heterogeneous regional injury.…”
Section: Indirect Estimates Of Lung Edemamentioning
Acute lung injury is a general term that describes injurious conditions that can range from mild interstitial edema to massive inflammatory tissue destruction. This review will cover theoretical considerations and quantitative and semi-quantitative methods for assessing edema formation and increased vascular permeability during lung injury. Pulmonary edema can be quantitated directly using gravimetric methods, or indirectly by descriptive microscopy, quantitative morphometric microscopy, altered lung mechanics, high-resolution computed tomography, magnetic resonance imaging, positron emission tomography, or x-ray films. Lung vascular permeability to fluid can be evaluated by measuring the filtration coefficient (Kf) and permeability to solutes evaluated from their blood to lung clearances. Albumin clearances can then be used to calculate specific permeability-surface area products (PS) and reflection coefficients (σ). These methods as applied to a wide variety of transgenic mice subjected to acute lung injury by hyperoxic exposure, sepsis, ischemia-reperfusion, acid aspiration, oleic acid infusion, repeated lung lavage, and bleomycin are reviewed. These commonly used animal models simulate features of the acute respiratory distress syndrome, and the preparation of genetically modified mice and their use for defining specific pathways in these disease models are outlined. Although the initiating events differ widely, many of the subsequent inflammatory processes causing lung injury and increased vascular permeability are surprisingly similar for many etiologies.
“…Zrs measurements were corrected for the cylindrical mouthpiece by treating the latter as another wavetube segment. 16 Volume change was obtained by integrating flow obtained from a pneumotachometer P3 (Hans Rudolph, MO, USA). Two types of FOT measurements were made with the subjects in the sitting position:…”
Respiratory system input impedance (Zrs) at low to medium frequencies below 100 Hz, and study of its volume dependence, have been used extensively to quantify airway and tissue mechanics. Zrs at high oscillation frequencies including the first antiresonant frequency (far,1) may contain important information about airway mechanics. Changes in high-frequency Zrs with lung volume have not been studied. The volume-dependent behavior of high-frequency Zrs, specifically far,1 and respiratory system resistance at first antiresonance (Rrs(far,1)), was characterized in 16 healthy adults. Zrs was measured with a forced oscillation signal (5-302.5 Hz) through a wavetube setup. To track Zrs, subjects performed slow deep inspiratory and expiratory maneuvers over 30-s measurements, during which average impedance was calculated over 0.4-s intervals, with successive overlapping estimates every 0.156 s. Flow was measured using a pneumotachometer and integrated to obtain volume. Transpulmonary pressure dependence (Ptp) of Zrs was separately determined in five subjects. Both far,1 and Rrs(far,1) decreased with increasing lung volume and Ptp, consistent with an increase in airway caliber and decreased airway wall compliance as volume increased. These characterizations provide insight into airway mechanics, and are furthermore a necessary first step toward determining whether volume dependence of the first antiresonance is altered in disease.
“…O.-C-H R κ and the characteristic impedance Z S (6) For a normal lung, the recursive computation of the impedance is started at terminal link with Κ = 23 using equations (2)(3)(4)(5)(6) where Z U2 3 is the impedance condition at termination. However, for an occlusion at a particular generation N, the terminal impedance Z LT " is where recursion starts, using the same equations, and until K= 0.…”
Section: Modellingmentioning
confidence: 99%
“…This branching network found within the multiple succussive bifurcation of the pulmonary tree has received theoretical attention [1], Several attempts have been made to investigate the characteristics of healthy and unhealthy lungs. Some of them theoretical [1][2][3][4] while others are experimental [5][6], On the other hand, modelling of dynamic respiratory system has occupied a good bulk of those literatures. However, the mechanical and physical properties, which are believed to have a considerable impact on the overall dynamics of the system, have been overlooked with the exception of [4], Airway passages modelling in normal lungs is still another area of considerable attention, however, modelling during asthma or abnormal constriction has been the main driving force behind several investigations.…”
Section: Introductionmentioning
confidence: 99%
“…However, the mechanical and physical properties, which are believed to have a considerable impact on the overall dynamics of the system, have been overlooked with the exception of [4], Airway passages modelling in normal lungs is still another area of considerable attention, however, modelling during asthma or abnormal constriction has been the main driving force behind several investigations. References [6][7][8][9] have investigated the respiratory system characteristics with and without abnormal constrictions, which may be caused by an asthma attack. Further, Kaczka et al [10] examined the partitioning of total lung resistance into airway resistance and tissue resistance in patients with mild to moderate asthma before and after albuterol inhalation.…”
A theoretical model is developed to study the dynamic response of the respiratory system using Weibel symmetric model based on the acoustic wave approach. Both rigid and compliant walls with rigid and compliant termination are investigated separately. For each case the response (normalised input impedance against prorogation frequency) is examined for occlusion at each generation from alveolar sacs up to the distal end of the trachea systematically.
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