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H K Chang

Publications and source records attributed to H K Chang.

At least 145 records · Page 8Linked to original sources
PubMed1981

Hydrodynamic features of pulmonary air embolism: a model study.

To elucidate the hydrodynamic events during pulmonary air embolism, experiments were conducted in a branching-tube apparatus and in small vessels. It was found that, as long as there existed an elevation differential between the two branches of a bifurcation, the vast majority of air bubbles always entered the higher branch. This finding is explained in terms of buoyancy, shear forces, and liquid flow velocity and is consistent with the in vivo finding of increased blood perfusion in the dependent lung regions during air embolization (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 51: 211-217, 1981). The pressures required to drive air bubbles through various small vessels were determined using three aqueous solutions of different surface tensions. Based on these measurements and a theoretical analysis, the diameter of air bubbles that could not pass through the pulmonary vessels was calculated to be 20-30 micrometers, agreeing well with a recent in vivo measurement (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 47: 537-543, 1979).

Capillaries↗
PubMed1981

Steady and unsteady pressure-flow relationships in central airways.

We measured pressure-flow relationships in a noncompliant five-generation cast of human central airways using air, HeO2, and SF6O2 at 0, 0.25, 0.50, 1.0, and 2.0 Hz with tidal volumes of 0.25, 0.5, and 1.0 liter. When dimensionless pressure drops for steady inspiratory and expiratory flows of the various gas mixture were plotted against Reynolds' number on a log-log scale (Moody diagram), they formed two curves as fluid mechanical theory predicts. At frequencies higher than 0.25 Hz, data obtained from 1) the same gas and same stroke volume, 2) the same frequency and same stroke volume but different gases, and 3) the same gas at the same frequency but with different stroke volumes, all deviated from the steady flow curves in the Moody diagram, always tending to increase the dimensionless pressure drop. The increase was largest when instantaneous flow was near zero and was minimal at the peak flow in a given inspiration or expiration. These data led to the identification of a dimensionless parameter (epsilon) that reflects the relative importance of local acceleration (unsteadiness) to convective acceleration at any given instant during a flow cycle. A dimensional analysis then reveals that the pressure-flow relationship in a given airway system is uniquely and completely determined by a combination of three dimensionless parameters: Reynolds number (Re), Womersley number (alpha), and the new parameter (epsilon). With this set of parameters we can explain all reported apparent paradoxes as well as the present findings.

Airway Resistance↗
PubMed1980

Non-equimolar counter-diffusion in ternary gas systems.

Previous studies of multicomponent gas diffusion, using mathematical and physical models, have dealt with equimolar diffusion in closed systems. To simulate respiratory gas transport more faithfully, we have investigated ternary gas diffusion in open systems, which allow non-equimolar diffusion to occur. Theoretical results showed the effects of gas composition on the induced fluxes. A unique state in which the diffusion system satisfies both the equimolar and non-equimolar conditions was found for gas systems in which the net flux changes as the composition varies. To verify the non-equimolar film theory, we conducted experiments with a diffusion cell apparatus. Diffusional fluxes across a porous membrane were obtained for N2-O2-SF6, N2-O2-Ne, and N2-O2-He combinations. The experimental results agreed with the predicted values, validating the theoretical film approach.

Animals↗
PubMed1980

Ternary diffusion and effective diffusion coefficients in alveolar spaces.

An experimentally verified mathematical model of non-equimolar ternary gas diffusion is applied to simulate the conditions existing in the alveolar spaces. When a fictitious gas film is erected a certain distance away from the alveolar membrane, and when the compositions at the two boundaries of the film are, respectively, the alveolar gas composition and a proportional mixture of inspired gas with the alveolar gas, the resulting fluxes of O2 and CO2 are essentially linearly related to their respective partial pressure gradients. From the slopes of these flux lines, effective diffusion coefficients are obtained. Ramifications of the effective diffusion coefficients approach are discussed.

Animals↗
PubMed1980

Multicomponent diffusion in the lung.

Since breathing involves more than two gases, the physics of multicomponent diffusion is relevant to respiratory physiology. Fundamental principles and important studies in this area are reviewed, some pertain to equimolar diffusion, others to nonequimolar diffusion. As the lung is an open-system nonequimolar exchanger, emphasis is placed on the latter. A mathematical model that has been verified by both physical and biological experiments is presented. This model is used to study ternary diffusion in the alveolar spaces and to obtain effective diffusion coefficients. Based on the cumulative studies up to now, it may be concluded that Fick's law still holds when normal air is breathed under normal pressure and when tracer amounts of inert gases are added to normal air. Fick's law no longer holds when helium is used as a carrier gas or when breathing is under extreme hyperbaric conditions.

Animals↗
PubMed1979

On the boundary conditions used in calculations of gas mixing in alveolar lungs.

The lung boundaries exhibit a tight barrier for any insoluble gas; hence boundary conditions for lung gas mixing have to account for the absence of both diffusive and convective fluxes across the lung walls. Scrimshire et al. (1978) have, in contrast, used the less rigid boundary condition that only the net flux be zero. As we believe this boundary condition to be inappropriate for the study of insoluble gases, the results derived appear to have no physiological significance.

Humans↗
PubMed1978

Effect of ventilation with different gas mixtures on experimental lung air embolism.

In six anesthetized, curarized and mechanically ventilated dogs, air was infused via a jugular vein at 0.1 cm3/kg/min for 25 min. This induced a progressive increase in pulmonary artery pressure (Pap) while arterial PO2 (PaO2) and end tidal PCO2 (PETCO2) decreased. Systemic arterial pressure, dynamic lung compliance and total pulmonary resistances were not affected. Changes tended to plateau by 20 min with a peak increase in Pap of 80 +/- 13% and decrease in PaO2 and PETCO2 of 22.2 +/- 2.8% and 14.5 +/- 2.1% respectively. When embolization was stopped these values returned to control levels within 30 min. During air infusion (at 20 min) some dogs were switched from ventilation with air to ventilation with the following gas mixtures: SF680%-O220%, He80%-O220%, N2O80%-O220%. During the final 5 min of air infusion. He and, to a greater extent, N2O breathing results in an immediate and marked further increase in Pap and decrease in PaO2 and PETCO2. In contrast SF6 produced rapid improvement in these parameters with return to near control levels. The recovery time after stopping infusion was greatly shortened with SF6 but was unaffected by He or N2O. These results are explained by different rates of gas transfer between the intravascular bubbles and the various alveolar gases. These findings show that ventilation with SF6 results in marked improvement in the gas exchange abnormalities produced by air embolism.

Animals↗
PubMed1973

Trauma of the erythrocyte membrane associated with low shear stress.

Studies have been performed on erythrocytes that have been subjected to a low shear stress of less than 100 dyn/cm(2) in a cone-and-plate viscometer. Alterations that were observed included decreased red cell survival, increased osmotic fragility, changes in the cation permeability of the red cell membrane, and a reduction in membrane-associated acetylcholinesterase activity. Some of these alterations are similar to those accompanying aging. The observed data suggest that one segment of the erythrocyte population is more susceptible to shear-induced damage than the rest of the cells.

Acetylcholinesterase↗
PubMedDate not supplied

SLC11A1 gene polymorphisms in Korean patients with Behçet's disease.

OBJECTIVE: To investigate the potential susceptibility to the solute carrier family 11 member 1 (SLC11A1) gene polymorphisms of Korean patients with Behçet's disease (BD). METHODS: Ninety-nine patients with BD and 98 controls were recruited. Analyses of three polymorphisms of the SLC11A1 gene [the 5'-promoter (GT)n, D543N and A318V] were performed, either by denaturing high-performance liquid chromatography for D543N and A318V or by using automatic DNA sequencing for the (GT)n. The genotypes and alleles between patients with BD and the controls were compared using the chi2 test and Yate's correction test. RESULTS: No significant differences were found in the distribution of genotypes and alleles of the (GT)n polymorphism between BD patients and the controls. However, subjects with the allele 3 or the genotype allele 3/allele 3 of this polymorphism had a significantly lower risk of developing BD than those without this allele or genotype [allele: p = 0.029, pc = 0.039, odds ratio (OR) = 0.60, 95% confidence interval (CI) 0.37-0.95; genotype: p = 0.036, pc = 0.048, OR = 0.54, 95% CI 0.31-0.96]. In addition, the distributions of genotypes and alleles of D543N were similar between BD patients and controls (p>0.05). In the case of A318V, all of the BD patients and controls had a wild-type genotype. CONCLUSION: The allele 3 and the genotype allele 3/allele 3 of the 5'-promoter (GT)n in the SLC11A1 gene may have a protective effect for the development of BD in the Korean population. Further studies in other populations are required to confirm our results.

Adult↗