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R T Yen

Publications and source records attributed to R T Yen.

At least 19 recordsLinked to original sources
PubMed2006

Mechanical properties of human lung parenchyma.

In order to have a detailed analysis of the distribution of stresses in the lung, one needs to understand the mechanical behavior of the lung material. For the stress-strain relationship of human lung, the present state of the art is that the form of the constitutive equations is known, but associated material constants are unknown. In this study, biaxial loading experiments were done on specimens of excised cadaver lung parenchyma without the effects of large blood vessels, bronchi, and pleura. Curves of strain vs. stress were recorded. A non-linear form of strain energy function was used to examine the stress-strain relationship. This relationship fits the experimental data well. The analysis based on data from 11 specimens of excised human lung parenchyma yielded that the physical constants are C/delta = 3.06 +/- 0.84 K x dyn/cm2, alpha = 4.47 +/- 1.94, and beta = -4.20 +/- 2.55.

Adult↗
PubMed2000

Microcirculation impedance analysis in cat lung.

An analysis of pulsatile microcirculation in cat lung, with special attention to the pulmonary microvascular impedance, is presented. A theoretical calculation is made on the basis of a complete set of experimental data on the morphology and elasticity of cat's pulmonary capillary sheets. The transfer matrix of the pulmonary microvascular impedance is obtained. The input impedance at the capillary entrance and exit are determined. The input impedance at the pulmonary arterial trunk is compared under various physiological conditions. It is shown that although the impact of pulmonary microcirculation on the relationship between the steady mean flow and pressure in the pulmonary arteries and veins is decisively large, the influence of the alveolar microcirculation on the input impedance at the pulmonary arterial trunk is small.

Animals↗
PubMed1998

Zero-stress states of human pulmonary arteries and veins.

The zero-stress states of the pulmonary arteries and veins from order 3 to order 9 were determined in six normal human lungs within 15 h postmortem. The zero-stress state of each vessel was obtained by cutting the vessel transversely into a series of short rings, then cutting each ring radially, which caused the ring to spring open into a sector. Each sector was characterized by its opening angle. The mean opening angle varied between 92 and 163 degrees in the arterial tree and between 89 and 128 degrees in the venous tree. There was a tendency for opening angles to increase as the sizes of the arteries and veins increased. We computed the residual strains based on the experimental measurements and estimated the residual stresses according to Hooke's law. We found that the inner wall of a vessel at the state in which the internal pressure, external pressure, and longitudinal stress are all zero was under compression and the outer wall was in tension, and that the magnitude of compressive stress was greater than the magnitude of tensile stress.

Adult↗
PubMed1996

Morphometry of the human pulmonary vasculature.

The morphometric data on the branching pattern and vascular geometry of the human pulmonary arterial and venous trees are presented. Arterial and venous casts were prepared by the silicone elastomer casting method. Three recent innovations are used to describe the vascular geometry: the diameter-defined Strahler ordering model is used to assign branching orders, the connectivity matrix is used to describe the connection of blood vessels from one order to another, and a distinction between vessel segments and vessel elements is used to express the series-parallel feature of the pulmonary vessels. A total of 15 orders of arteries were found between the main pulmonary artery and the capillaries in the left lung and a total of 15 orders of veins between the capillaries and the left atrium in the right lung. The elemental and segmental data are presented. The morphometric data are then used to compute the total cross-sectional areas, blood volumes, and fractal dimensions in the pulmonary arterial and venous trees.

Adult↗
PubMed1994

Effect of chronic thromboembolism on the pulmonary artery pressure-flow relationship in dogs.

To understand the hemodynamic alterations associated with chronic thromboembolic pulmonary hypertension, the large pulmonary arteries of mongrel dogs were chronically obstructed with lysis-resistant thrombi. Pulmonary hemodynamics were experimentally measured and described by multipoint pulmonary arterial pressure (PAP) vs. flow plots. In nine anesthetized chronically embolized dogs, but not in six control dogs, the PAP-flow line shifted significantly upward in a parallel fashion by 4.2 +/- 0.7 mmHg. The postembolic pulmonary circulation was further characterized by predictions from a morphometric-based elastic tube and sheet flow model of the canine pulmonary circulation. After model validation with the preembolic PAP-flow data, the derived postembolic PAP matched the in vivo results to within 1 mmHg. A detailed analysis of the model-derived PAP drop revealed that the PAP-flow line shift can be accounted for by a novel fixed resistor in the largest obstructed pulmonary artery.

Animals↗
PubMed1994

Vascular impedance analysis in dog lung with detailed morphometric and elasticity data.

On the basis of experimentally measured morphometric and elasticity data and model-derived mean pressure-flow conditions, we attempt a theoretical modeling of pulsatile flow in the whole lung. In the model we use the "elastic tube" for arteries and veins, and the vascular impedance in arteries and veins follows Womersley's theory and electric analogue. We employ the "sheet-flow" theory to describe the flow in the capillaries and to obtain the microvascular impedance matrix. The characteristic impedance of each order along the vascular tree, the input impedance at the capillary entrance and exit, and the pulmonary arterial input impedance at the main pulmonary artery are computed under certain physiological conditions. Using the pulsatile flow model, we investigate the effects of arterial vascular obstruction on pulmonary vascular impedance. The model-derived data are compared with the available experimental results in the literature.

Animals↗
PubMed1993

Morphometry of the dog pulmonary venous tree.

The biophysical approach to the study of blood flow in the pulmonary vasculature requires a detailed description of vascular geometry and branching pattern. The description of the pulmonary venous morphometry in the dog is the focus of this paper. Silicone elastomer casts of a dog lung were made and were used to measure the diameters, lengths, and branching pattern of the pulmonary venous vasculature. The anatomic data are presented statistically with a diameter-defined Strahler ordering scheme, a rule for assigning the order numbers of the vessels on the basis of a diameter criterion. The asymmetric branching pattern of the pulmonary venous vasculature is described with a connectivity matrix. Results show that for the dog's right pulmonary venous tree 1) a total of 11 orders of vessels lay between the left atrium and the capillary bed; 2) the average ratios of the diameter, length, and number of branches of successive orders of veins were 1.701, 1.556, and 3.762, respectively; and 3) a fractal description of the tree geometry resulted in diameter and length fractal dimensions of 2.49 and 2.99, respectively. The morphometric data were used to compute the cross-sectional area, vascular volume, and Poiseuillean resistance in the venous vessels.

Animals↗
PubMed1988

Trauma of lung due to impact load.

A quantitative evaluation of lung injury due to impact loading is of general interest. Hemorrhage and edema are the usual sequelae to traumatic pulmonary impact. To gain some quantitative understanding of the phenomena, we perfused excised rabbit lung with Macrodex at isogravimetric condition and monitored lung weight continuously after impact. It is shown that a factor of importance is the rigidity of the surface on which the lung rests. The rate of lung weight increase is smaller if the lung was 'freely' supported on a soft cloth, more if it was supported on a rigid plate. This suggests the influence of stress wave reflection. The critical condition correlates with the initial velocity of impact at the surface of the lung, or with the maximum deflection. For a freely supported lung, the rate of lung weight increase was 22% of the initial total lung weight per h after impact when the impact velocity was 11.5 ms-1, 30% when the velocity was 13.2 ms-1, several 100% at 13.5 ms-1, signaling massive lung injury. Since the velocity of sound in rabbit lung is 33.3 ms-1 when the inflation (transpulmonary) pressure is 10 cm H2O, the critical velocity of 13.5 ms-1 corresponds to a Mach number of 0.4. The maximum surface displacement of the lung is almost linearly proportional to the initial velocity of impact. The exact cause of edema and hemorrhage is unknown; we hypothesize that it is due to tensile stress in the alveolar wall caused by the impact.

Animals↗
PubMed1988

A hypothesis on the mechanism of trauma of lung tissue subjected to impact load.

When a compressive impact load is applied on the chest, as in automobile crash or bomb explosion, the lung may be injured and show evidences of edema and hemorrhage. Since soft tissues have good strength in compression, why does a compression wave cause edema? Our hypothesis is that tensile and shear stresses are induced in the alveolar wall on rebound from compression, and that the maximum principal stress (tensile) may exceed critical values for increased permeability of the epithelium to small solutes, or even fracture. Furthermore, small airways may collapse and trap gas in alveoli at a critical strain, causing traumatic atelectasis. The collapsed airways reopen at a higher strain after the wave passes, during which the expansion of the trapped gas will induce additional tension in the alveolar wall. To test this hypothesis, we made three new experiments: (1), measuring the effect of transient overstretch of the alveolar membrane on the rate of lung weight increase; (2) determining the critical pressure for reopening collapsed airways of rabbit lung subjected to cyclic compression and expansion; (3) cyclic compression of lung with trachea closed. We found that in isolated rabbit lung overstretching increases the rate of edema fluid formation, that the critical strain for airway reopening is higher than that for closing, and that these critical strains are strain-rate dependent, but independent of the state of the trachea, whether it is open or closed. Furthermore, a theoretical analysis is presented to show that the maximum principal (tensile) stress is of the same order of magnitude as the maximum initial compressive stress at certain localities of the lung.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Elasticity of arterioles and venules in postmortem human lungs.

The elasticity and branching order of noncapillary microscopic blood vessels less than 100 microns diam were studied in human lungs obtained 7-30 h postmortem, using a silicone elastomer method that selectively filled pulmonary arterioles or venules. The lungs were inflated to 10 cmH2O pressure and a gradient of transmural vascular pressure of 0-17 cm H2O, from lobe base to apex, was established in the silicone-filled vascular system. Histological materials were obtained after airway fixation by formaldehyde solution and analyzed for vessel diameter in the branching order of 1, 2, and 3, with the smallest noncapillary vessel designated as order 1, in accord with the Strahler system. The change in vessel diameter within a branching order at different levels of transmural pressure is a derived measure of vascular elasticity expressed as compliance coefficient alpha, alpha Values are 0.128, 0.164, and 0.210 micron/cmH2O or 0.682, 0.472, and 0.354%/cmH2O, respectively, of orders 1-3 for arterioles and 0.187, 0.215, and 0.250 micron/cmH2O or 0.992, 0.612, and 0.424%/cmH2O, respectively, of orders 1-3 for venules. The percent is normalized with D0, which is the value of diameter (D) when the transmural pressure is zero. These data are compared with those for the cat where alpha = 0.274 for similar juxta-alveolar vessels.

Adult↗
PubMed1986

A new theory of pulmonary blood flow in zone 2 condition.

In pulmonary blood flow, if arterial pressure (Pa) and pleural pressure (Ppl) were fixed, the flow increases with decreasing venous pressure (Pv) only when venule pressure (Pven) greater than airway pressure (PA) (i.e., in zone 3). When Pven less than or equal to PA (i.e., in zone 2), with Pa fixed, the flow decreases with decreasing Pv. The pressure-flow relationship has a hysteresis loop. This phenomenon can be explained by conservation of mass and momentum and the morphology and material properties of the lung, including the observation that reseparation of adhered cells requires an extra force. The key mathematical observation is that the solution h = 0 (h being the blood sheet thickness in the interalveolar septa) can coexist with the solution h not equal to 0 in zone 2 condition, resulting in "patchy" filling of the alveolar walls. When h = 0, the sheet is collapsed and endothelial cells adhere. Experimental results show that the adhered endothelial cells do not reseparate by raising Pv in zone 2 but can be accomplished under zone 3 condition.

Animals↗
PubMed1986

Speed of stress wave propagation in lung.

The speed of stress waves in the lung parenchyma was investigated to understand why, among all internal organs, the lung is the most easily injured when an animal is subjected to an impact loading. The speed of the sound is much less in the lung than that in other organs. To analyze the dynamic response of the lung to impact loading, it is necessary to know the speed of internal wave propagation. Excised lungs of the rabbit and the goat were impacted with water jet at dynamic pressure in the range of 7-35 kPa (1-5 psi) and surface velocity of 1-15 m/s. The stress wave was measured by pressure transducer. The distance between the point of impact and the sensor at another point on the far side of the lung and the transit time of the stress wave were measured. The wave speed in the goat lung was found to vary from 31.4 to 64.7 m/s when the transpulmonary pressure Pa-Ppl was varied from 0 to 20 cmH2O where Pa represents airway pressure and Ppl represents pleural pressure. In rabbit lung the wave speed varied from 16.5 to 36.9 m/s when Pa-Ppl was varied from 0 to 16 cmH2O. Using measured values of the bulk modulus, shear modulus, and density of the parenchyma, reasonable agreement between theoretical and experimental wave speeds were obtained.

Animals↗
PubMed1984

Morphometry of cat's pulmonary arterial tree.

Morphometic data of the pulmonary artery in the cat's right lung are presented. Silicone elastomer casts of cat's right lung were made, and measured, counted and analyzed. The Strahler system is used to describe the branching pattern of the arterial vascular tree. These data are needed for any quantitative approach to the study of the pulmonary circulation. For all the pulmonary blood vessels of the cat lying between the main pulmonary artery and the capillary beds, there are a total of 10 orders of vessels in the right upper lobe, 9 orders of vessels in the right middle lobe and 11 orders of vessels in the right lower lobe. The ratio of the number of branches in successive orders of vessels or the branching ratio, is 3.58. The corresponding average diameter ratio is 1.72, whereas the average length ratio is 1.81.

Animals↗
PubMed1983

Morphometry of cat pulmonary venous tree.

Morphometric data of the pulmonary veins in the cat right lung are presented. Silicone elastomer casts of the right lungs of five cats were made, measured, counted, and analyzed. The Strahler system is used to describe the branching pattern of the vascular tree. These data are needed for the physicomathematical approach to pulmonary circulation. For all the pulmonary blood vessels lying between the left atrium and the capillary beds, there are a total of 10 orders of vessels in the right upper lobe, 9 orders of vessels in the right middle lobe, and 11 orders of vessels in the right lower lobe. The ratios of the diameters, lengths, and the number of branches in successive orders of vessels are called the diameter, length, and branching ratios, respectively. For the cat pulmonary venous tree, the average branching ratio is 3.521, the average diameter ratio is 1.727, and the average length ratio is 2.402 for vessels of orders 1-3 and 1.532 for vessels of orders 4-10.

Animals↗
PubMed1983

Analysis of blood flow in cat's lung with detailed anatomical and elasticity data.

Recently, a complete set of data on the branching pattern of the cat's pulmonary arterial and venous trees and the elasticity of these blood vessels was obtained in our laboratory. Hence it becomes possible for the first time to perform a theoretical analysis of the blood flow in the lung of an animal based on a set of actual data on anatomy and elasticity. This paper presents an analysis of steady flow of blood in cat's lung. The effect of the vessel elasticity is embodied in the "fifth-power law" and the "sheet-flow" theory. The theory yields the pressure-flow relationship of the whole lung, the longitudinal pressure distribution, and the transit time of blood in the capillaries. These results are compared with available experimental data in the literature.

Animals↗
PubMed1981

Elasticity of small pulmonary veins in the cat.

The distensibility of pulmonary veins of cats, in the diametric range of 100-1200 micrometer, was studied as a function of the venous pressure p upsilon and pleural pressure p PL, while the alveolar air pressure was maintained at zero (atmospheric). The resulting percentage changes in diameter normalized with respect to the diameter at delta P of 10 cm H20 (D10) are expressed as function of delta = p upsilon - p PL. It was found that in most cases the diameter varies linearly with delta P: D/D10 = 1 + alpha (p upsilon - p PL) where alpha is the compliance coefficient. The results show that smaller veins of the cat are more compliant than larger veins. For example, when pleural pressure is -10 cm H2O, the values of alpha for vessels in the ranges of diameters of 100-200 micrometer, 200-400 micrometer, 400-800 micrometer and 800-1200 micrometer are, respectively, 2.05, 1.44, 1.08 and 0.71 percent per cm H2O or Pa-1. The effects of lung inflation on the distensibility of pulmonary veins are also studied. Our results show that for vessel sizes in the range of 400-800 micrometer and 800-1200 micrometer the compliance constant alpha is not affected by the inflation of the lungs (changes in pleural pressure to more negative values). For smaller veins in the size ranges 100-200 micrometer and 200-400 micrometer our results show an increase in compliance from 2.05 to 2.79 and from 1.44 to 2.01 percent per cm H20 or Pa-1, respectively, when pleural pressure is changed from -10 to -15 cm H20. When the pleural pressure is more negative than -15 cm H20, however, the compliance of the vessels in the foregoing two size ranges is observed to decrease.

Animals↗