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Biomedical subjects

C A Dawson

Publications and source records attributed to C A Dawson.

At least 37 records · Page 2Linked to original sources

Aspergillus fumigatus antigen exposure results in pulmonary airway resistance in wild-type but not in IL-4 knockout mice.

Inhalation of Aspergillus fumigatus, a ubiquitous fungus, results in the development of allergic bronchopulmonary aspergillosis, a disabling allergic lung disease. For better patient management early diagnosis is essential, and understanding of the immune mechanism is important in achieving this goal. Although animal model studies have contributed to the understanding of the disease mechanism, details on the immunopathogenesis are still lacking. In the present study, we have developed an allergic aspergillosis model in wild-type and IL-4 knockout mice and studied the immune and airway responses. The results indicate that the immune response, pulmonary pathology, and airway reactivity comparable to allergic bronchopulmonary aspergillosis are reproducible in wild mice. IL-4 knockout mice showed similar pulmonary pathology, but no increase in airway resistance, suggesting that IgE and hence IL-4 may be important in eliciting the airway response, while other factors may be involved in the inflammatory process.

Airway Resistance↗

A murine model of latex allergy-induced airway hyperreactivity.

Sensitization to latex proteins can cause immediate IgE mast cell-mediated reactions. Health care workers have been found to be particularly at risk because of high exposure. Latex allergy can be produced in mice as demonstrated by IgE and eosinophil responses. Thus the mouse is a potential animal model for studying this disease, but the airway response to latex sensitization in mice has not been evaluated previously. In the present study, we immunized BALB/c mice intranasally with nonammoniated latex proteins. Animals were anesthetized, and lung mechanics were evaluated plethysmographically. Changes in pulmonary conductance (GL) and compliance (Cdyn) were measured in response to a nonspecific challenge with methacholine or to a direct challenge with intravenous latex antigen. Latex sensitization resulted in elevated levels of IgE and latex-specific IgG1 as well as interstitial infiltrates consistent with an allergic response. The methacholine dose-response ED50 for GL was 116.4 microg for the control mice and fell significantly to 20.9 microg for latex-sensitized mice. The ED50 calculated for Cdyn was also significantly lower after latex sensitization. The GL in latex-sensitized mice challenged with latex antigen fell significantly from a prechallenge value of 1.87 +/- 0.41 (S.E.) to 0. 198 +/- 0.03 ml x s-1 x cmH2O after latex antigen challenge. The results indicate that latex-sensitized mice did exhibit increased airway reactivity in the methacholine challenge test. The latex allergic response in mice is unique in that direct challenge with latex antigen itself also resulted in a significant airway response.

Airway Resistance↗

Proline in vasoactive peptides: consequences for peptide hydrolysis in the lung.

To examine the hypothesis that trans isomers of bradykinin and [Gly6]bradykinin are preferentially hydrolyzed by lung peptidases, we studied the fractional inactivation of these peptides in the perfused rat lung using a bioassay after a single-pass bolus injection and high-performance liquid chromatography after lung recirculation. In the bioassay studies, when the peptides passed through the lung, 25.6-fold more bradykinin or 7-fold more [Gly6]bradykinin was required to elicit a contraction equivalent to that produced when the peptides did not pass through the lung. In the recirculation studies, hydrolysis progress curves with rapid and slow phases were observed, with a higher fraction of bradykinin than [Gly6]bradykinin hydrolyzed in the rapid phase. Cyclophilin increased the hydrolysis rate during the slow phase for both peptides. Kinetic analysis indicated that the slowly hydrolyzed peptide fraction, presumably the cis fraction, was 0.13 for bradykinin and 0.43 for [Gly6]bradykinin with cis-trans isomerization rate constants of 0.074 and 0.049 s-1, respectively, consistent with published nuclear magnetic resonance studies.

Animals↗

Structure-function relationships in the pulmonary arterial tree.

Knowledge of the relationship between structure and function of the normal pulmonary arterial tree is necessary for understanding normal pulmonary hemodynamics and the functional consequences of the vascular remodeling that accompanies pulmonary vascular diseases. In an effort to provide a means for relating the measurable vascular geometry and vessel mechanics data to the mean pressure-flow relationship and longitudinal pressure profile, we present a mathematical model of the pulmonary arterial tree. The model is based on the observation that the normal pulmonary arterial tree is a bifurcating tree in which the parent-to-daughter diameter ratios at a bifurcation and vessel distensibility are independent of vessel diameter, and although the actual arterial tree is quite heterogeneous, the diameter of each route, through which the blood flows, tapers from the arterial inlet to essentially the same terminal arteriolar diameter. In the model the average route is represented as a tapered tube through which the blood flow decreases with distance from the inlet because of the diversion of flow at the many bifurcations along the route. The taper and flow diversion are expressed in terms of morphometric parameters obtained using various methods for summarizing morphometric data. To help put the model parameter values in perspective, we applied one such method to morphometric data obtained from perfused dog lungs. Model simulations demonstrate the sensitivity of model pressure-flow relationships to variations in the morphometric parameters. Comparisons of simulations with experimental data also raise questions as to the "hemodynamically" appropriate ways to summarize morphometric data.

Algorithms↗

Detection of changes in lung tissue properties with multiple-indicator dilution.

We evaluated the potential utility of a group of indicators, each of which targets a particular tissue property, as indicators in the multiple-indicator dilution method to detect and to identify abnormalities in lung tissue properties resulting from lung injury models. We measured the pulmonary venous outflow concentration vs. time curves of [14C]diazepam, 3HOH, [14C]phenylethylamine, and a vascular reference indicator following their bolus injection into the pulmonary artery of isolated perfused rabbit lungs under different experimental conditions, resulting in changes in the lung tissue composition. The conditions included granulomatous inflammation, induced by the intravenous injection of complete Freund's adjuvant (CFA), and intratracheal fluid instillation, each of which resulted in similar increases in lung wet weight. Each of these conditions resulted in a unique pattern among the concentration vs. time outflow curves of the indicators studied. The patterns were quantified by using mathematical models describing the pulmonary disposition of each of the indicators studied. A unique model parameter vector was obtained for each condition, demonstrating the ability to detect and to identify changes in lung tissue properties by using the appropriate group of indicators in the multiple-indicator dilution method. One change that was particularly interesting was a CFA-induced change in the disposition of diazepam, suggestive of a substantial increase in peripheral-type benzodiazepine receptors in the inflamed lungs.

Animals↗

Pulmonary inflammation alters the lung disposition of lipophilic amine indicators.

Many lipophilic amine compounds are rapidly extracted from the blood on passage through the pulmonary circulation. The extent of their extraction in normal lungs depends on their physical-chemical properties, which affect their degree of ionization, lipophilicity, and propensity for interacting with blood and tissue constituents. The hypothesis of the present study was that changes in the tissue composition that occur during pulmonary inflammation would have a differential effect on the pulmonary extraction of lipophilic amines having different properties. If so, measurement of the extraction patterns for a group of lipophilic amines, having different physical-chemical properties, might provide a means for detecting and identifying lung tissue abnormalities. To evaluate this hypothesis, we measured the pulmonary extraction patterns for four lipophilic amines, [(14)C]diazepam, [(3)H]alfentanil, [(14)C]lidocaine, and [(14)C]codeine, along with two hydrophilic compounds, (3)HOH and [(14)C]phenylethylamine, after the bolus injection of these indicators into the pulmonary artery of isolated lungs from normal rabbits and from rabbits with pulmonary inflammation induced by an intravenous injection of complete Freund's adjuvant. The pulmonary extraction patterns, parameterized using a previously developed mathematical model, were, in fact, differentially altered by the inflammatory response. For example, the tissue sequestration rate, k(seq) (ml/s), per unit (3)HOH accessible extravascular lung water volume significantly increased for diazepam and lidocaine, but not for codeine and alfentanil. The results are consistent with the above hypothesis and suggest the potential for using lipophilic amines as indicators for detection and quantification of changes in lung tissue composition associated with lung injury and disease.

Algorithms↗

Immune response and airway reactivity in wild and IL-4 knockout mice exposed to latex allergens.

BACKGROUND: Natural rubber latex has been reported as a major cause of allergy and asthma in a number of individuals. One of the occupational groups most affected by latex allergy are the health care workers who are frequently exposed to natural rubber latex products in their patient care activities. The immunopathogenesis of latex allergy is not well understood. In order to understand the immune mechanism in latex allergy, we have developed a mouse model of latex allergy. METHODS: Both wild-type and IL-4 knockout BALB/c mice were challenged intranasally with latex proteins and their immune responses, lung pathology, and airway reactivity were evaluated. RESULTS: The total serum IgE and latex specific IgE, IgG1, and peripheral blood and lung eosinophil levels in wild type BALB/c mice were enhanced by the latex exposure, while no IgE or eosinophil were detected in IL-4 knockout mice. Latex-specific IgG1 levels in the sera were lower in IL-4 knockout animals compared to wild mice. However, latex-specific IgG2a antibody was higher in all the IL-4 knockout mice compared to wild type mice. Both the wild type and IL-4 knockout animals developed increased airway resistance after antigen challenge when compared to control animals, although the airway resistance response of IL-4 knockout animals was attenuated compared to the wild-type animals. The histology of the lungs of these two groups of animals was similar. CONCLUSION: In spite of the differences in the immune responses in the two groups of mice, there were comparable lung inflammatory responses, suggesting a multifactorial pathogenetic mechanism.

Animals↗

Activation by systemic angiotensin II of neurochemically identified neurons in rat hypothalamic paraventricular nucleus.

Using the immunohistochemical localization of the protein product of the immediate early gene, c-fos, to localize activated neurons in the paraventricular nucleus of the hypothalamus (PVN), we studied the chemical phenotypes of neurons activated by circulating angiotensin II (AII). We determined the proportions of activated PVN neurons that expressed AII type I receptor-like immunoreactivity (AT1-L) or the neurohormones vasopressin (VP) and oxytocin (OXY). In addition, we identified activated PVN neurons that putatively produce nitric oxide (NO) on the basis of histochemical staining for nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d). Conscious rats received intravenous AII infusions at a rate sufficient to elevate mean arterial pressure by 40-60 mmHg for 90 min; control rats received infusions of vehicle. Brains were prepared for double immunohistochemistry [Fos-like immunoreactivity (FLI)/AT1-L, FLI/VP or FLI/OXY] or FLI/ NADPH-d histochemistry. Systemic AII infusions led to activation of 149+/-14 PVN neurons per section. In contrast, control animals showed activation of 21+/-6 PVN neurons per section. AII infusions elicited the activation of the following numbers of chemically identified PVN neurons per section: AT1-L, 24+/-5; VP, 26+/-5; OXY, 11+/-2; NADPH-d, 22+/-4. Control animals had few activated PVN neurons per section. For each of the chemically identified populations of PVN neurons, the following proportions were activated: AT1-L, 12.5%; VP, 15.2%; OXY, 7.2%; NADPH-d, 17.3%. The results suggest that PVN neurons producing the AT1 receptor, VP, OXY, and NO, participate in the mediation of the central responses to circulating AII.

Angiotensin II↗

Feldkamp and circle-and-line cone-beam reconstruction for 3D micro-CT of vascular networks.

Detailed morphometric knowledge of the microvascular network is needed for studies relating structure to haemodynamic function in organs like the lung. Clinical volumetric CT is limited to millimetre-order spatial resolution. Since evidence suggests that small arterioles (50 to 300 micrometres) dominate pulmonary haemodynamics, we built a micro-CT scanner, capable of imaging excised lungs in 3D with 100 microm resolution, for basic physiology research. The scanner incorporates a micro-focal (3 microm) x-ray source, an xyz theta stage and a CCD-coupled image intensifier detector. We imaged phantoms and contrast-enhanced rat lungs, reconstructing the data with either the Feldkamp or the circle-and-line cone-beam reconstruction algorithm. We present reconstructions using 180 views over 360 degrees for the circular trajectory, augmented with views from a linear scan for the circle-and-line algorithm. Especially for platelike features perpendicular to the rotation axis and remote from the midplane, the circle-and-line algorithm produces superior reconstructions compared with Feldkamp's algorithm. We conclude that the use of nonplanar source trajectories to perform micro-CT on contrast-enhanced, excised lungs can provide data useful for morphometric analysis of vascular trees, currently down to the 130 microm level.

Algorithms↗

Ascorbate-mediated transplasma membrane electron transport in pulmonary arterial endothelial cells.

Pulmonary endothelial cells are capable of reducing certain electron acceptors at the luminal plasma membrane surface. Motivation for studying this phenomenon comes in part from the expectation that it may be important both as an endothelial antioxidant defense mechanism and in redox cycling of toxic free radicals. Pulmonary arterial endothelial cells in culture reduce the oxidized forms of thiazine compounds that have been used as electron acceptor probes for studying the mechanisms of transplasma membrane electron transport. However, they reduce another commonly studied electron acceptor, ferricyanide, only very slowly by comparison. In the present study, we examined the influence of ascorbate [ascorbic acid (AA)] and dehydroascorbate [dehydroascorbic acid (DHAA)] on the ferricyanide and thiazine reductase activities of the bovine pulmonary arterial endothelial cell surface. The endothelial cells were grown on microcarrier beads so that the reduction of ferricyanide and methylene blue could be studied colorimetrically in spectrophotometer cuvettes and in flow-through cell columns. The ferricyanide reductase activity could be increased 80-fold by adding DHAA to the medium, with virtually no effect on methylene blue reduction. The DHAA effect persisted after the DHAA was removed from the medium. AA also stimulated the ferricyanide reductase activity but was less potent, and the relative potencies of AA and DHAA correlated with their relative rates of uptake by the cells. The results are consistent with the hypothesis that AA is an intracellular electron donor for an endothelial plasma membrane ferricyanide reductase and that the stimulatory effect of DHAA is the result of increasing intracellular AA. Adding sufficient DHAA to markedly increase extracellular ferricyanide reduction had little effect on the plasma membrane methylene blue reductase activity, suggesting that pulmonary arterial endothelial cells have at least two separate transplasma membrane electron transport systems.

Animals↗

Anatomic distribution of pulmonary vascular compliance.

Previously, the pressure changes after arterial and venous occlusion have been used to characterize the longitudinal distribution of pulmonary vascular resistance with respect to vascular compliance using compartmental models. However, the compartments have not been defined anatomically. Using video microscopy of the subpleural microcirculation, we have measured the flow changes in approximately 40-micron arterioles and venules after venous, arterial, and double occlusion maneuvers. The quasi-steady flows through these vessels after venous occlusion permitted an estimation of the compliance in three anatomic segments: arteries > 40 microns, veins > 40 microns, and vessels < 40 microns in diameter. We found that approximately 65% of the total pulmonary vascular compliance was in vessels < 40 microns, presumably mostly capillaries. The transient portions of the pressure and flow data after venous, arterial, and double occlusion were consistent with most of the arterial compliance being upstream from most of the arterial resistance and most of the venous compliance being downstream from most of the venous resistance.

Animals↗

Pulmonary disposition of lipophilic amine compounds in the isolated perfused rabbit lung.

We measured the pulmonary venous concentration vs. time curves for [3H]alfentanil, [14C]lidocaine, and [3H]codeine after the bolus injection of each of these lipophilic amine compounds (LAC) and a vascular-reference indicator (fluorescein isothiocyanate-dextran) into the pulmonary artery of isolated perfused rabbit lungs. A range of flows and perfusate albumin concentrations was studied. To evaluate the information content of the data, we developed a kinetic model describing the pulmonary disposition of these LAC that was based on indicator dilution theory, and we sought a robust approach for interpreting the estimated model parameters. We found that the distribution of the kinetic model rate constants of the lipophilic amine-tissue interactions can be described by alpha, H, and psi, where alpha is a measure of the capacity of the rapidly equilibrating interactions between the lipophilic amine and the tissue; H is a measure of the equilibrium capacity of the slowly equilibrating interactions between the lipophilic amine and the tissue; and psi is the mean sojourn time. The values of alpha, H, and psi were 0.8 +/- 0.1 (SE), 0.6 +/- 0.1, and 1.6 +/- 0.5 s; 1.9 +/- 0.1, 5.3 +/- 0.4, and 5.6 +/- 0.5 s; and 1.1 +/- 0.1, 9.8 +/- 0.4, and 4.7 +/- 0.2 s for alfentanil, lidocaine, and codeine, respectively. These values for alpha, H, and psi reveal the relative dominance of the slowly equilibrating interactions for lidocaine and codeine in comparison with alfentanil. This approach to data analysis may have utility for the potential use of LAC to reveal and to quantify changes in lung tissue composition associated with lung disease.

Alfentanil↗

Transit time dispersion in the pulmonary arterial tree.

Knowledge of the contributions of arterial and venous transit time dispersion to the pulmonary vascular transit time distribution is important for understanding lung function and for interpreting various kinds of data containing information about pulmonary function. Thus, to determine the dispersion of blood transit times occurring within the pulmonary arterial and venous trees, images of a bolus of contrast medium passing through the vasculature of pump-perfused dog lung lobes were acquired by using an X-ray microfocal angiography system. Time-absorbance curves from the lobar artery and vein and from selected locations within the intrapulmonary arterial tree were measured from the images. Overall dispersion within the lung lobe was determined from the difference in the first and second moments (mean transit time and variance, respectively) of the inlet arterial and outlet venous time-absorbance curves. Moments at selected locations within the arterial tree were also calculated and compared with those of the lobar artery curve. Transit times for the arterial pathways upstream from the smallest measured arteries (200-micron diameter) were less than approximately 20% of the total lung lobe mean transit time. Transit time variance among these arterial pathways (interpathway dispersion) was less than approximately 5% of the total variance imparted on the bolus as it passed through the lung lobe. On average, the dispersion that occurred along a given pathway (intrapathway dispersion) was negligible. Similar results were obtained for the venous tree. Taken together, the results suggest that most of the variation in transit time in the intrapulmonary vasculature occurs within the pulmonary capillary bed rather than in conducting arteries or veins.

Algorithms↗

Nitric oxide increases the survival of rats with a high oxygen exposure.

The purpose of this study was to begin to examine the influence of inhaled NO on O2 toxicity. The survival of Sprague-Dawley rats exposed to >95% O2, >95% O2 + 10 ppm NO, >95% O2 + 100 ppm NO, and >95% O2 + 3 ppm NO2 was determined. Survival at 120 h was 2/24 in >95% O2, 2/12 in >95% O2 + 10 ppm NO, and 1/12 in >95% O2 + 3 ppm NO2. Survival at 120 h was 21/30 in >95% O2 + 100 ppm NO (p < 0.01 compared with >95% O2). Three additional groups of rats were exposed for 60 h to: 21% O2, >95% O2, or >95% O2 + 100 ppm NO. The lungs were then assayed for total protein, reduced (GSH) and oxidized glutathione (GSSG), and 4-hydroxy-2(E)-nonenal. Both of the high O2 groups had significantly (p < 0.05) lower GSH/mg protein and GSH/GSSG ratios compared with the 21% O2 group. The >95% O2 group had a higher 4-hydroxy-2(E)-nonenal/mg of protein than either the 21% O2 group (p < 0.05), or the >95% O2 + 100 ppm NO group (p < 0.05 compared with >95% O2, not different from the 21% O2 group). Additional groups of rats were exposed to either 21% O2, >95% O2, or >95% O2 + 100 ppm NO for 0, 24, 48, and 60 h. The lungs were examined for neutrophil accumulation, which was increased at 60 h in the two groups exposed to >95% O2, but adding NO had no effect. Thus, the overall result was that 100 ppm inhaled NO improved the survival of rats in high O2.

Aldehydes↗

Regional perfusion parameters from pulmonary microfocal angiograms.

An indicator-dilution model was developed to describe transport of vascular contrast medium through an organ during acquisition of vascular dynamic contrast images. The model provides the theoretical basis for methods of determining regional blood flow, blood volume, and mean transit time from time-absorbance curves acquired from the images of tissue regions of interest (ROI) distal from the inlet site. The robustness of these methods was evaluated using a computer-simulated vessel network, which simulated the passage of a bolus of contrast medium through arterioles, networks of capillaries, and venules. The network was used to evaluate the reliability of ROI parameter estimation methods when the underlying model assumptions are violated. The shape of the ROI inlet concentration curve and moderate amounts of random noise did not affect the ability of the method to recover accurate parameter estimates. The estimates of ROI flow and transit time were degraded in the presence of significant dispersion of the inlet concentration curve as it traveled through arteries upstream from the microvascular ROI or when the flow was redistributed within the ROI. The estimates of ROI volume were relatively robust. The method was applied to image data of the dog pulmonary vasculature obtained using microfocal X-ray angiography to show that the results obtained from the simulations are consistent with actual data.

Angiography↗

Biotinylation of membrane proteins accessible via the pulmonary circulation in normal and hyperoxic rats.

It is well established that the phenotype of the pulmonary vascular surface can be affected by injurious stimuli, but the few proteins for which the expression and/or activity have been studied make up only a small fraction of the entire spectrum of luminal cell membrane proteins. To expand the capability for studying such proteins, we developed a method for biotinylating cell membrane proteins accessible via the vascular lumen in the isolated-perfused rat lung and examined the impact of hyperoxia on the spectrum of the biotinylated proteins. Labeling was carried out either by single-pass bolus injection of the cell impermeant biotinylation reagent sulfosuccinimidyl 6-biotin-amido hexanoate (NHS-LC-biotin) into the pulmonary artery cannula or by the addition of NHS-LC-biotin to a lung homogenate. Lung membrane fractions were prepared, and the proteins were separated by SDS-polyacrylamide gel electrophoresis and transferred to nitrocellulose by electroblotting. The biotinylated proteins were visualized using a chemiluminescent substrate for streptavidin-linked horseradish peroxidase. The spectrum of proteins biotinylated via the vasculature was distinct from that of the biotinylated lung homogenate. Lectin affinity purification of biotinylated proteins from the lung membrane fractions of normal lungs biotinylated via the vasculature revealed characteristic spectra that were reproducibly different from those from rats exposed to hyperoxia for 48-60 h. These results demonstrate that biotinylation of membrane proteins accessible to an extracellular reagent during a single transit through the pulmonary vascular bed is feasible and that the spectrum of these labeled proteins reveals the effects of hyperoxic lung injury. The affinity of biotin for streptavidin makes this procedure potentially useful as a means of separating the labeled membrane proteins from the much larger population of membrane proteins that are not accessible via the vasculature, e.g., intracellular membrane proteins and plasma membrane proteins of cell types in luminally inaccessible regions of the intact lung. The consistent changes in the spectrum of labeled proteins seen with hyperoxia suggest that in itself the spectrum may be a useful encryption of certain aspects of vascular pathophysiology.

Animals↗

Pulmonary endothelial thiazine uptake: separation of cell surface reduction from intracellular reoxidation.

The objective of this study was to further evaluate the hypothesis that the accumulation of thiazine dyes, such as methylene blue, by cultured bovine pulmonary arterial endothelial cells involves reduction on the cell surface, followed by diffusion of the lipophilic reduced form of the dye into the cells and intracellular reoxidation to the relatively membrane-impermeant hydrophilic form. The specific question addressed was whether inhibition of methylene blue uptake by cyanide and azide is via inhibition of extracellular reduction or inhibition of intracellular reoxidation. We used the cell membrane-impermeant ferricyanide ion as a secondary electron acceptor to measure the extracellular reduction of methylene blue independently from its uptake by the cells. In addition, toluidine blue O, incorporated into an acrylamide polymer so that it could not permeate the cells in either its reduced or oxidized forms, was used to examine the effects of cyanide and azide on the extracellular reduction. Microscopic observations of the effect of the inhibitors on the intracellular accumulation of methylene blue were also made. The results indicate that the reduction and intracellular sequestration are separate processes and that, in doses that inhibited intracellular reoxidation, and therefore uptake and sequestration, neither cyanide nor azide had an inhibitory effect on extracellular reduction. The intracellular distribution of the observable oxidized form of the dye was consistent with oxidation of the reduced dye within subcellular organelles. The demonstration that extracellular reduction and intracellular sequestration are separate events is consistent with the hypothesized sequence of events.

Acrylic Resins↗

Flow-induced vasodilation in the ferret lung.

To examine the possibility that shear stress may be a pulmonary vasodilator stimulus, we studied the effect of changing blood flow on the diameters of small pulmonary arteries in isolated perfused ferret lung lobes. The arteries studied were in the approximately 0.3- to 1.3-mm-diameter range, and the diameters were measured by using microfocal X-ray imaging. The diameters were measured at two flow rates, 10 and 40 ml/min, with the intravascular pressure in the measured vessels the same at the two flow rates as the result of venous pressure adjustment. The response to a change in flow was studied under both normoxic and hypoxic conditions. Hypoxia was used to elevate pulmonary arterial tone to increase the likelihood of detecting a vasodilator response. Under normoxic conditions, changing flow had little effect on the arterial diameters, but under hypoxic conditions the arteries were consistently larger at the higher flow than at the lower flow, even though the distending pressure was the same at the two flow rates. The results are consistent with the hypothesis that shear stress is a pulmonary vasodilator stimulus.

Animals↗