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F R Haselton

Publications and source records attributed to F R Haselton.

32 records · Page 2Linked to original sources
PubMed1990

Angiotensin-converting enzyme kinetics in an endothelial cell column.

The kinetics of saturable endothelial metabolic functions have been assessed in vivo by transient (indicator-dilution) measurements and in culture by steady-state measurements, but comparisons between the two are difficult. Therefore, we used indicator-dilution methods to assess the kinetics of angiotensin-converting enzyme (ACE) activity in cultured endothelium. Bovine fetal aortic endothelial cells were grown to confluence on microcarrier beads. Cell-covered beads were poured into polypropylene columns and perfused with serum-free culture medium. Six injections, containing [3H]benzol-Phe-Ala-Pro [( 3H]BPAP, an ACE substrate) and varying amounts of unlabeled BPAP, were applied to each column and effluent was collected in serial samples. The apparent kinetics of BPAP metabolism were determined by four models used previously to determine pulmonary endothelial ACE kinetics in vivo, the most useful model incorporating transit time heterogeneity. The Km averaged 5 microM, which is close to values determined previously in vivo and in vitro. The Amax (Vmax.reaction volume) and Amax/Km averaged 6 nmol/min and 1.5 ml/min, respectively, which are lower than estimates in vivo. In conclusion, we have developed a new method for investigating saturable metabolic activity in cultured endothelium, which after further exploration should also enable better comparisons of endothelial metabolic functions in vivo and in culture.

Animals↗
PubMed1989

Convective mixing mechanisms in high frequency intermittent jet ventilation.

A liquid flow visualization technique was used to identify the location of neutrally buoyant bead clouds injected into airway models during flows simulating high frequency intermittent jet ventilation (HFIJV) in neonatal lungs. The motions of these bead clouds show that the convective or bulk mixing that occurs during HFIJV is made up of two parts; a turbulent convective exchange with the atmosphere caused by the jet in the trachea and a streaming motion along the airways driven by an interaction between the jet and the expansion and contraction of the airways due to their compliance. These convective streaming motions combine with molecular diffusion to produce augmented diffusion which transports O2 and CO2 between the trachea and the peripheral alveoli. Optimizing HFIJV (as well as other forms of HFV) depends on maximizing these airway convective streaming flows which depend on many more lung and fluid mechanical parameters than are necessary to describe conventional mechanical ventilation.

High-Frequency Jet Ventilation↗
PubMed1989

Chromatographic demonstration of reversible changes in endothelial permeability.

This report describes a new in vitro method for measuring the diffusional permeability of an endothelial monolayer and its use in investigating the modulation of permeability by various agents, e.g., isoproterenol, propranolol, dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP), and cytochalasin D. To determine permeability, tracers of different molecular weights were applied simultaneously on a chromatography column containing confluent endothelial cells cultured on porous microcarrier beads. The Sangren-Sheppard model was used to determine the permeability of the endothelial monolayer from the tracer elution profiles. For six radiolabeled tracers the mean (+/- SD) permeabilities (cm/s x 10(-5)) in order of increasing tracer molecular weight were [3H]water, 82.0 +/- 28.8; [14C]urea, 49.5 +/- 9.5; [14C]mannitol, 13.3 +/- 4.7; [14C]-sucrose, 14.1 +/- 2.5; [3H]polyethylene glycol (900 mol wt), 4.80 +/- 1.61; and [3H]polyethylene glycol (4,000 mol wt), 1.97 +/- 1.01. These permeabilities deviate less from in vivo values than those obtained in other in vitro systems and are 10 times higher than in vivo estimates. The values were reproducible for up to the 4 h tested. Modulation of endothelial monolayer permeability was studied in a separate series of experiments. The beta-adrenergic agonist isoproterenol (10(-6) M) decreased the permeability to mannitol by 36% and to polyethylene glycol (900 mol wt) by 49%; in both instances the decrease in permeability was reversed by propranolol. Propranolol alone had no effect. Dibutyryl cAMP (10(-3) M) decreased the permeability to mannitol by 40% and to polyethylene glycol by 47%; permeability returned to base line when dibutyryl cAMP was removed. Cytochalasin D (1 microgram/ml) increased permeability by 350% for mannitol and 380% for polyethylene glycol; the permeability change was reversed after removal of cytochalasin D. The results indicate that cell-column chromatography is a powerful method that can be used to characterize the permeability of endothelial monolayers and to investigate permeability changes produced by various agents.

Animals↗
PubMed1989

Pulmonary extraction of propranolol in normal and oxygen-toxic sheep.

To help define the mechanisms involved in the handling of propranolol by normal and injured lungs, we studied the pulmonary extraction of [3H]propranolol in 23 unanesthetized sheep. Extraction of propranolol by normal lungs during a single circulation was characterized by 1) subsequent back-diffusion and pulmonary retention of the drug, 2) no evidence of saturable uptake or binding, 3) no effect of isoproterenol or imipramine, and 4) no effect of increasing cardiac output by treadmill exercise. In lungs damaged by oxygen toxicity, [3H]propranolol extraction decreased progressively to 63% of base line, paralleling progressive arterial hypoxemia and hypercapnia. In contrast, [14C]serotonin extraction remained unchanged from base line. Our results suggest that in normal unanesthetized sheep, pulmonary extraction of propranolol occurs primarily by passive diffusion that is flow-limited. Also, lung injury induced by oxygen toxicity in sheep reduces the pulmonary extraction of propranolol. Indeed, in oxygen toxicity, the depressed extraction of propranolol is a more sensitive marker of lung injury than is serotonin extraction.

Animals↗
PubMed1988

Permeability characteristics of cultured endothelial cell monolayers.

The purpose of this study was to characterize the permeability characteristics of an in vitro endothelial cell monolayer system and relate this information to available in vivo data. We cultured bovine fetal aortic endothelial cells on fibronectin-coated polycarbonate filters and confirmed that our system was similar to others in the literature with regard to morphological appearance, transendothelial electrical resistance, and the permeability coefficient for albumin. We then compared our system with in vivo endothelium by studying the movement of neutral and negatively charged radiolabeled dextran tracers across the monolayer and by using electron microscopy to follow the pathways taken by native ferritin. There were a number of differences. The permeability of our monolayer was 10-100 times greater than seen in intact endothelium, there was no evidence of "restricted" diffusion or charge selectivity, and ferritin was able to move freely into the subendothelial space. The reason for these differences appeared to be small (0.5-2.0 micron) gaps between 5 and 10% of the endothelial cells. Although the current use of cultured endothelial cells on porous supports may provide useful information about the interaction of macromolecules with the endothelium, there appear to be differences in the transendothelial permeability characteristics of these models and in vivo blood vessels.

Animals↗
PubMed1988

Convective exchange between the nose and the atmosphere.

It is generally accepted that there is little rebreathing of gas exhaled through the nose. A detailed physical model system has been used to quantify and identify the mechanisms responsible for this phenomenon. By the use of a cast of the upper respiratory tract and oscillating flows with a Reynolds number of 500 and nondimensional frequency of 1.6, corresponding to quiet tidal breathing through the nose, dye dilution measurements indicated an efficiency of tidal exchange of 0.95. Flow visualization studies performed to trace the expiratory flow, as well as the streamlines during steady inspiratory flow, support the hypothesis that the high efficiency of exchange is due to radical differences in the velocity fields between inspiratory and expiratory phases of this oscillatory flow. These findings confirm that convective gas exchange between the nose and the atmosphere is highly efficient; however, the underlying mechanism responsible for this exchange also maximizes the exposure of the respiratory system to aerosols contained in the ambient atmosphere.

Atmosphere↗
PubMed1986

Effect of perfusate hematocrit on urea permeability-surface area in isolated dog lung.

Seven dog lower left lung lobes were statically inflated and perfused at a constant rate for each lobe with a perfusate in which the hematocrit was altered over a wide range. The permeability-surface area of urea was calculated from multiple indicator dilution curves using two separate injectates for each hematocrit level. One injectate contained only 125I-albumin as the vascular reference tracer and the other contained both 51Cr-erythrocytes and 125I-albumin as the vascular reference tracers; both contained [14C]urea as the permeating tracer. The results strongly indicate that the phenomenon of "erythrocyte trapping" of urea does not affect the calculation of urea permeability-surface area product provided the appropriate albumin-erythrocyte composite reference tracer is utilized in its calculation.

Animals↗
PubMed1985

Passage of uncharged dextrans from blood to lung lymph in awake sheep.

To examine how molecular size alone influences the passage of macromolecules from the pulmonary microcirculation into lymph collected from the caudal mediastinal lymph node of the sheep, we infused polydisperse uncharged [3H]dextrans intravenously at a constant rate over a period of 7.5 h in nine awake sheep with lung lymph fistulas. Lymph and plasma were collected during hours 5.5-7.5 of the infusions, and the [3H]dextrans were separated by molecular sieve chromatography into fractions that ranged from 1.6 to 8.4 nm in effective molecular (Stokes-Einstein) radius. Lymph-to-plasma (L/P) ratios for [3H]dextrans were near 1.0 at 1.6-nm radius, decreased with increasing molecular size, and approached zero at radii above 5.0 nm. We confirmed that these L/P ratios represented steady-state values by extending the duration of the infusion to approximately 30 h in two of the nine sheep and finding that the L/P ratios remained unchanged. These results were consistent with molecular sieving through a homoporous membrane with cylindrical pores of 5.0-nm radius. We also found that the L/P ratio for albumin [0.76 +/- 0.13 (SE)] in five of the same sheep was much higher than that for the [3H]dextran fraction of the same effective molecular radius [0.11 +/- 0.02 (SE)]. These results suggest that the movement of macromolecules from the pulmonary microcirculation into pulmonary lymph collected from the caudal mediastinal node of the sheep is influenced by both molecular size and molecular charge and that, compared with uncharged dextrans, the steady-state passage of anionic endogenous proteins from plasma to lymph is enhanced.

Animals↗
PubMed1984

Gas transport in branched airways during high-frequency ventilation.

A theoretical model of high-frequency ventilation (HFV) is presented based on the physical convective exchange process that occurs due to the irreversibility of gas velocity profiles in oscillatory flow through the bronchial airways. Mass transport during the convective exchange process can be characterized by a convective exchange length, LE, which depends only on the irreversibility of bronchial velocity profiles and can be measured by the experimental technique of photographic flow visualization in bronchial tree models. Using the exchange length and the molecular diffusivity, a simple model of overall bronchial mass transfer is developed. The model allows a prediction of the mean gas concentration profiles along the airways, the site of maximum mass transfer resistance, and overall flow rate of the gas of interest in or out of the lung as functions of the parameters of HFV. The results predicted by the model agree with the limited experimental data available for animals and humans. For normal unassisted ventilation, total bronchial cross-sectional area around the 15th Weibel bronchial generation is predicted to be the single most important parameter in controlling the total gas transport rate along the airways. For the breathing of room air, values of the respiratory quotient around 0.78 are predicted, which are insensitive to VT and f. The model represents a fruitful combination of fluid mechanical theory and experiment with physiologic data to yield new and deeper insight into the operation of the human respiratory system during HFV and normal breathing.

Humans↗
PubMed1984

Analysis of lung multiple indicator data with an effective diffusivity model of capillary exchange.

In this study, we have compared an effective diffusivity model with several models previously used to describe lung microvascular exchange of small molecules (multiple indicator curves): the Crone integral extraction model, the Sangren-Sheppard model, and the Rowlett-Harris model. The parameters of each model were adjusted to achieve a best fit of multiple-tracer data from six isolated dog lung preparations perfused under zone III conditions at three flows and from five awake sheep before and after histamine infusion. The effective diffusivity model was the best at matching the data and the unique falling extraction pattern observed in the lung. When the isolated lung data was analyzed, the permeability-surface area products (PS) of three models were all significantly lower at lower flows. However, the effective diffusivity model parameter (D 1/2 S, an effective diffusivity-surface area product) was not significantly affected by flow reduction. Lung lymph flow and lymph-to-plasma protein ratios from the awake sheep indicated that PS and D 1/2 S should have increased, and except for the Sangren-Sheppard model, all models predicted significantly increased values. By use of sensitivity analysis, the parameters of the effective diffusivity model were found to be more independently determined than those of the Sangren-Sheppard model, but data collected at longer times were necessary to reliably identify the extravascular volume parameter (LS, diffusing distance-surface area product) of the effective diffusivity model. We conclude that the effective diffusivity model is a better descriptor of multiple tracer data from the lung, that its parameters are more reliably and independently determined, and that it more reliably describes the effects of flow and histamine infusion on capillary-tissue exchange.

Albumins↗
PubMed1982

Convective exchange in oscillatory flow through bronchial-tree models.

An important and previously unappreciated longitudinal convective-transport mechanism has been shown to operate in tube-bifurcation models geometrically and dynamically similar to upper and lower regions of the bronchial tree. The mechanism depends on the differences in shape that exist between inspiratory and expiratory velocity profiles in laminar and turbulent flow within the bronchial tubes and provides new and deeper physical insight into the flow of gases, aerosol particles, and heat in the airways. By use of dimensional analysis to relate the flows in the physical models to those in the real bronchial tree, the mechanism is shown to be important in normal breathing of gases and aerosols and is likely to be important also in high-frequency ventilation.

Aerosols↗
PubMed1980

Bronchial bifurcations and respiratory mass transport.

A new transport mechanism explains the importance of the shape of bronchial bifurcations in the transfer of gases and particles between the atmosphere and the alveoli. Photographs of flow visualization experiments illustrate the effect in models of bronchial branching. The mechanism provides a means of nondiffusional transport that helps to explain normal respiratory exchange of gases as well as successful ventilation with very low tidal volumes, as in some lung diseases and in the high-frequency panting of dogs.

Animals↗
PubMed1979

Growth of hygroscopic aerosols in a model of bronchial airways.

Experiments have been performed on the "breathing" of micron-size hygroscopic aerosols in and out of a four-generation model of the bronchial tree. Comparison of the experimental results on aerosol growth in the model with the classical theory for dilute aqueous solutions of nonpolar salts shows a) that the theory is applicable to conditions in the airways, b) that to a high degree of approximation the process represents deposition followed by growth, and c) that there is a significant amount of trapping of particles near their equilibrium size in the deeper model tubes. These experiments are the first to verify that the classical particle growth theory is applicable to the particle sizes and environmental conditions present in the human airways during hygroscopic aerosol therapy. This theory will be useful in designing an optimal hygroscopic aerosol delivery system, but several questions including the method of generation and the effect of drug solutions on particle equilibriums remain to be answered.

Aerosols↗