Robert Roselli | Vanderbilt University (original) (raw)
Papers by Robert Roselli
Innovations in Engineering Education: Mechanical Engineering Education, Mechanical Engineering/Mechanical Engineering Technology Department Heads, 2004
This paper presents the organizational structure for teaching the bioheat transfer component of a... more This paper presents the organizational structure for teaching the bioheat transfer component of a biotransport course based on the How People Learn (HPL) pedagogical model. The presentation to students consists of a series of design challenges in a sequence that directs learning through the major components of bioheat transfer knowledge taxonomy. Students encounter various taxonomic subjects in either a primary learning context or in a secondary application in which adaptive expertise is developed. The primary and secondary intersections between the challenge and taxonomy vectors are displayed in a matrix format.
This paper presents the VaNTH Biomechanics learning modules and discusses their implementation in... more This paper presents the VaNTH Biomechanics learning modules and discusses their implementation in a Fall 2004 engineering course. These Biomechanics learning modules were developed as part of the VaNTH NSF educational coalition formed by multiple institutions in the USA. The pedagogical framework for these modules is based on the widely publicized book "How People Learn" (HPL). The HPL teaching framework presents the learning material as a series of challenges that are posed through a "Legacy Cycle." The educational significance of this effort is that these challenge-based Biomechanics modules were the main mode of instructional delivery in the course. The VaNTH biomechanics modules were presented in an undergraduate Mechanical Engineering course titled "Biomechanics of Human Movement" in Fall 2004. The class (N=18) was divided into three-member teams. All challenges were performed by the teams using computer-based homework assignments that were supplied by the instructor on a CD. Pre-tests, post-tests, and affect rankings were administered for each modular topic to assess the course. The students were also surveyed on the learning effectiveness of the various components of each module. At the end of the semester, the students completed a Biomechanics topics matrix that mapped the challenges to the various class topics. Results of this classroom experience and data gathering are presented in the paper. Conclusions are drawn on the pedagogical efficacy of this approach to instruction.
Ann Biomed Eng, 1979
In previously proposed models of capillary tracer exchange, red cell membranes have usually been ... more In previously proposed models of capillary tracer exchange, red cell membranes have usually been assumed to be either infinitely permeable or completely impermeable to tracer molecules. Permeability of the extravascular cellular compartment has been treated previously, but never in conjunction with finite capillary and red cell permeability effects. Our objective was to examine the situation encountered with multiple indicator experiments in which tracer exchange may be limited by red cell, tissue and capillary membranes. A four phase model is presented which accounts for plasma, red cell, interstitial, and extravascular cellular regions. Results from this model indicate that transcapillary tracer exchange is affected by a minimum of seven dimensionless parameters. The influence of relatively low red cell permeability is most pronounced when the dimensionless capillary permeability is high (i.e., ~cap ~> 1). Deviations in transcapillary extraction values from those corresponding to infinitely permeable erythrocytes can be kept below 5% when capillary permeability is low (i.e., 0tca p ~< .15) by pre-equilibrating the injectate with tracer prior to injection. The additional barrier in the extravascular region necessarily decreases overall transvascular tracer exchange but does not affect extraction values in the vicinity of the appearance time. w~ " ERYTHROCYTES " ~ I O X L FIGURE 1. Four phase capillary model.
The steady-state lymph to plasma concentration ratios (L/Ps) of neutral dextrans, cationic DEAE d... more The steady-state lymph to plasma concentration ratios (L/Ps) of neutral dextrans, cationic DEAE dextrans, and endogenous proteins were determined under normal and increased permeability conditions in six unanesthetized yearling sheep prepared with chronic lung lymph fistulas. Fluorescent dextrans with radii ranging from 1-30 nm were intravenously infused, and after 24 hours, Perilla ketone (PK) was given to alter permeability while maintaining the dextran infusion. Plasma and lymph samples were collected before and after PK administration and analyzed for dextran and protein concentrations following HPLC size separation. Under both baseline and increased permeability conditions, DEAE dextrans had higher L/Ps than neutral dextrans of similar size, but lower L/Ps than proteins of similar size. Comparison of L/Ps before and after PK revealed that the percentage change in permeability for neutral and DEAE dextrans was significantly larger than for proteins. These results suggest that 1) the pulmonary microvascular barrier behaves as a net negative barrier, 2) some transport mechanisms for proteins and dextrans are different, and 3) neutral and cationic dextrans are more sensitive markers than proteins of the same size for assessing changes in pulmonary capillary permeability.
Lymphology
In chronically instrumented unanesthetized sheep, we measured steady-state hemodynamic and lung l... more In chronically instrumented unanesthetized sheep, we measured steady-state hemodynamic and lung lymph responses to mechanically increased pressure and to intravenous infusions of histamine, Pseudomonas bacteria and E. coli endotoxin. Histamine, Pseudomonas bacteria and E. coli endotoxin caused exchanging vessel permeability to increase, as evidenced by high flows of protein rich lung lymph. This contrasts to the effects of increased pressure where lymph protein concentration falls as lymph flow increases. Microvascular sieving of proteins less than 100 Angstrom radius persisted in all increased permeability states, but with endotoxin, lymph clearance of larger proteins increased much more than with histamine or Pseudomonas. We compared several approaches to quantitative interpretations of lymph data and found that direct methods for calculating permeability-surface area products and reflection coefficients for proteins produced values which were difficult to interpret, probably because fundamental assumptions of the methods were violated in our experiments. A mathematical model based on multiple pore theory produced more plausible coefficients.
Journal of applied physiology: respiratory, environmental and exercise physiology
This study was performed to measure the effects of a sustained reduction in coronary flow on lung... more This study was performed to measure the effects of a sustained reduction in coronary flow on lung lymph flow and protein content. Ten halothane-anesthetized sheep with cannulated lymphatic vessels were provided with a carotid-to-left anterior descending coronary artery cannula containing an electromagnetic flowmeter. One group of five animals was observed at base line and after coronary flow was reduced to 38% of base line. A second group of five animals acted as controls and was observed at base line, for 111 min of increased left atrial pressure, and a second period of normal pressures. Sustained coronary flow reduction led to significant increases in pulmonary arterial pressure, left atrial pressure, lymph flow, total protein lymph-to-plasma concentration ratio (L/P), and protein lymph clearance (L/P X lymph flow). Analysis of the pressure, lymph, protein, and indicator data with a two-pore model of the microvascular barrier showed that the observations were consistent with the concept that coronary flow reduction decreased functioning lung capillary surface but increased the size of the large pore and the number of small pores relative to the number of larger pores. Control studies showed increases in lymph flow and decreases in L/P with increased pressure but no significant changes in any variable between the first and second period of normal pressures. We conclude that coronary flow reduction increases lung vascular-tissue transport by decreasing the resistance of the microvascular barrier to protein and fluid movement. However, increased pressure secondary to left ventricular dysfunction plays a role in the magnitude of this response.
Journal of Applied Physiology
The purpose of these studies was a comparison of [14C]urea (U) and 1,3-[14C]propanediol (Pr) as m... more The purpose of these studies was a comparison of [14C]urea (U) and 1,3-[14C]propanediol (Pr) as measures of lung vascular permeability-surface area (PS) under base-line conditions and after lung injury caused by alloxan infusion in isolated perfused dog lungs. Indicator mixtures of 125I-albumin, 51Cr-red blood cells, 3HOH, and U or Pr were injected under base-line conditions, after 1.2 g of alloxan, and after an additional 0.8 g of alloxan. Indicator-dilution curves were analyzed from sampled outflow blood to provide PS, the square root of effective extravascular diffusivity multiplied by exchange surface area (D1/2S), and extravascular lung water (EVLW) from the tracer mean transit times (VW). Results show that alloxan increases PS and D1/2S for U, D1/2S for Pr, and VW and EVLW by desiccation. All indicator-dilution parameters correlate significantly with alloxan dose. Interpretation of Pr transport suggests that materials with lipid and hydrophilic pathways might be used in conjunction with U to minimize the effects of surface area changes and increase the sensitivity of these tracers to permeability alteration. In addition Pr may be a useful alternative to U as a marker of vascular damage.
Journal of Applied Physiology
The effects of pulmonary arterial embolization on calculated pulmonary capillary pressure as dete... more The effects of pulmonary arterial embolization on calculated pulmonary capillary pressure as determined by the venous occlusion technique are examined using a simple pressure-flow model for the lung. It is predicted that pulmonary, arterial embolization can induce significant underestimation of pulmonary capillary pressure in flowing vessels. This underestimation is related to the percent of vessels embolized and the caliber of pulmonary arteries that are embolized (i.e., the size of the emboli). Experimental verification of these theoretical findings is necessary before the conclusions can be extended to the interpretation of venous occlusion experiments in the lung.
Journal of Applied Physiology
We analyzed the effects of Escherichia coli endotoxin infusion on pulmonary microvessels in sheep... more We analyzed the effects of Escherichia coli endotoxin infusion on pulmonary microvessels in sheep by using a two-pore mathematical model of the microvascular barrier. Five sheep were prepared with lung lymph fistulas and instrumented to measure pulmonary arterial and left atrial pressures. Multiple indicator-dilution curves (with 125I-labeled albumin, 51Cr-labeled erythrocytes, [14C]urea, and 3H2O) were measured at base line and during phases 1 and 2 of the endotoxin response. Alterations in the membrane integrity in response to endotoxin infusion were quantified by using a two-pore theory of the microvascular barrier that incorporated lymph, protein, pressure, and multiple indicator measurements. The modeling results showed a slight change in the size of the pores during phase 1 but a 56% decrease in the number of small pores and a twofold increase in the number of large pores with respect to base-line values. During phase 2 the large pore size increased by 40%, and the total number of pores returned to base-line values. The analysis showed that endotoxin effects on fluid and protein exchange in the lung cannot be explained by hemodynamic and surface area changes alone. An apparent increase in lung microvascular permeability occurs during phases 1 and 2 of the endotoxin reaction, with a substantial decrease in perfused microvascular surface area during phase 1.
Journal of applied physiology: respiratory, environmental and exercise physiology
Models of steady-state fluid and solute transport in the microcirculation are used primarily to c... more Models of steady-state fluid and solute transport in the microcirculation are used primarily to characterize filtration and permeability properties of the transport barrier. Important transient relationships, such as the rate of fluid accumulation in the tissue, cannot be predicted with steady-state models. In this paper we present three simple models of unsteady-state fluid and protein exchange between blood plasma and interstitial fluid. The first treats the interstitium as a homogeneous well-mixed compliant compartment, the second includes an interstitial gel, and the third allows for both gel and free fluid in the interstitium. Because we are primarily interested in lung transvascular exchange we used the multiple-pore model and pore sizes described by Harris and Roselli (J. Appl. Physiol.: Respirat . Environ. Exercise Physiol. 50: 1-14, 1981) to characterize the microvascular barrier. However, the unsteady-state transport theory presented here should apply to other organ systems and can be used with different conceptual models of the blood-lymph barrier. For a step increase in microvascular pressure we found good agreement between theoretical and experimental lymph flow and lymph concentrations in the sheep lung when the following parameter ranges were used: base-line interstitial volume, 150-190 ml; interstitial compliance, 7-10 ml/Torr; initial interstitial fluid pressure, -1 Torr; pressure in initial lymphatics, -5 to -6 Torr; and conductivity of the interstitium and lymphatic barrier, 4.25 X 10(-4) ml X s-1 X Torr-1. Based on these values the model predicts 50% of the total change in interstitial water volume occurs in the first 45 min after a step change in microvascular pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
Journal of applied physiology: respiratory, environmental and exercise physiology
In this study, we have compared an effective diffusivity model with several models previously use... more 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.
Journal of Applied Physiology
Seven dog lower left lung lobes were statically inflated and perfused at a constant rate for each... more 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.
Journal of applied physiology: respiratory, environmental and exercise physiology
The purposes of this research were to derive a mathematical model of blood-intestinal transport f... more The purposes of this research were to derive a mathematical model of blood-intestinal transport for the lung and to study the ability of this model to describe the results of previous lymph-collection and multiple-indicator experiments on the lungs of unanesthetized sheep. We used a three-pore model of the microvascular barrier to describe lymph flow, lymph-to-plasma ratios (L/P) of eight endogenous proteins, and the microvascular permeability-surface area (PST) of the lungs to [14C]urea in sheep experiments under base-line conditions and after acute elevation of the left atrial pressure. The results indicate that endothelial pathways consisting of a small pore (28 A), intermediate pore (180 A), and a large pore (1,000 A) can describe experimental L/P values and PST. The description of lymph flow required either than interstitial fluid pressure increase with left atrial pressure or that postcapillary venous resistance decrease relative to precapillary values. We concluded that multiple-pore theory is a useful approach to the description of lung blood-interstitial transport.
Journal of Applied Physiology
Experiments were conducted in seven chronically instrumented unanesthetized sheep to estimate the... more Experiments were conducted in seven chronically instrumented unanesthetized sheep to estimate the osmotic reflection coefficient (sigma d) for total proteins and the solvent-drag reflection coefficients (sigma f) for six endogenous protein fractions. We measured the lymph-to-plasma ratio of total proteins (CL/CP) and six protein fractions during base-line conditions and after left atrial pressure elevations of 24-26 h per elevation. We also monitored pulmonary arterial pressure, left atrial pressure, systemic arterial pressure, and lung lymph flow at the various levels of pulmonary microvascular pressure. Our results indicate the CL/CP may require up to 24 h to reach a true steady state. It was found that sigma d is at least 0.89 for total proteins and sigma f is at least 0.84, 0.87, 0.86, 0.92, 0.95, and 0.96 for protein fractions with effective molecular radii of 36, 39.5, 44, 66, 105, and 123 A, respectively. In addition, the sigma f values for various protein fractions obtained from this investigation are compared with the predicted values of various mathematical models of the lung microcirculation.
Journal of Applied Physiology
Experiments were conducted on five chronically instrumented unanesthetized sheep to determine the... more Experiments were conducted on five chronically instrumented unanesthetized sheep to determine the effects of sustained hypoproteinemia on lung fluid balance. Plasma total protein concentration was decreased from a control value of 6.17 +/- 0.019 to 3.97 +/- 0.17 g/dl (mean +/- SE) by acute plasmapheresis and maintained at this level by chronic thoracic lymph duct drainage. We measured pulmonary arterial pressure, left atrial pressure, aortic pressure, central venous pressure, cardiac output, oncotic pressures of both plasma and lung lymph, lung lymph flow rate, and lung lymph-to-plasma ratio of total proteins and six protein fractions for both control base-line conditions and hypoproteinemia base-line conditions. Moreover, we estimated the average osmotic reflection coefficient for total proteins and the solvent drag reflection coefficients for the six protein fractions during hypoproteinemia. Hypoproteinemia caused significant decreases in lung lymph total protein concentration, lung lymph-to-plasma total protein concentration ratio, and oncotic pressures of plasma and lung lymph. There were no significant alterations in the vascular pressures, lung lymph flow rate, cardiac output, or oncotic pressure gradient. The osmotic reflection coefficient for total proteins was found to be 0.900 +/- 0.004 for hypoproteinemia conditions, which is equal to that found in a previous investigation for sheep with a normal plasma protein concentration. Our results suggest that hypoproteinemia does not alter the lung filtration coefficient nor the reflection coefficients for plasma proteins. Possible explanations for the reported increase in the lung filtration coefficient during hypoproteinemia by other investigators are also made.
Journal of Applied Physiology
Because pulmonary edema has been associated clinically with airway obstruction, we sought to dete... more Because pulmonary edema has been associated clinically with airway obstruction, we sought to determine whether decreased intrathoracic pressure, created by selective inspiratory obstruction, would affect lung fluid balance. We reasoned that if decreased intrathoracic pressure caused an increase in the transvascular hydrostatic pressure gradient, then lung lymph flow would increase and the lymph-to-plasma protein concentration ratio (L/P) would decrease. We performed experiments in six awake sheep with chronic lung lymph cannulas. After a base-line period, we added an inspiratory load (20 cmH2O) and allowed normal expiration at atmospheric pressure. Inspiratory loading was associated with a 12-cmH2O decrease in mean central airway pressure. Mean left atrial pressure fell 11 cmH2O, and mean pulmonary arterial pressure was unchanged; calculated microvascular pressure decreased 8 cmH2O. The changes that occurred in lung lymph were characteristic of those seen after other causes of increased transvascular hydrostatic gradient, such as increased intravascular pressure. Lung lymph flow increased twice base line, and L/P decreased. We conclude that inspiratory loading is associated with an increase in the pulmonary transvascular hydrostatic gradient, possibly by causing a greater fall in interstitial perimicrovascular pressure than in microvascular pressure.
Journal of Applied Physiology
The purpose of this study is to determine the roles of cardiac output and microvascular pressure ... more The purpose of this study is to determine the roles of cardiac output and microvascular pressure on changes in lung fluid balance during exercise in awake sheep. We studied seven sheep during progressive treadmill exercise to exhaustion (10% grade), six sheep during prolonged constant-rate exercise for 45-60 min, and five sheep during hypoxia (fraction of inspired O2 = 0.12) and hypoxic exercise. We made continuous measurements of pulmonary arterial, left atrial, and systemic arterial pressures, lung lymph flow, and cardiac output. Exercise more than doubled cardiac output and increased pulmonary arterial pressures from 19.2 +/- 1 to 34.8 +/- 3.5 (SE) cmH2O. Lung lymph flow increased rapidly fivefold during progressive exercise and returned immediately to base-line levels when exercise was stopped. Lymph-to-plasma protein concentration ratios decreased slightly but steadily. Lymph flows correlated closely with changes in cardiac output and with calculated microvascular pressures. The drop in lymph-to-plasma protein ratio during exercise suggests that microvascular pressure rises during exercise, perhaps due to increased pulmonary venous pressure. Lymph flow and protein content were unaffected by hypoxia, and hypoxia did not alter the lymph changes seen during normoxic exercise. Lung lymph flow did not immediately return to base line after prolonged exercise, suggesting hydration of the lung interstitium.
Journal of Applied Physiology
We studied the effects of three different doses (15, 20, and 25 mg/kg) of Perilla ketone (PK) on ... more We studied the effects of three different doses (15, 20, and 25 mg/kg) of Perilla ketone (PK) on the blood-perfused in situ sheep lung while obtaining external measurements of lung transvascular protein flux. Lymph flow and lymphatic protein clearance increased significantly after all doses of PK. Severe pulmonary edema was confirmed by high postmortem wet-to-dry lung weight ratios and increased extravascular lung water from multiple indicator-dilution studies. Urea permeability-surface area product and effective diffusivity from multiple indicator-dilution studies also increased after PK infusion. Because we observed no evidence of increased capillary pressure or increased microvascular surface area after PK, we conclude that PK significantly increased pulmonary microvascular permeability. Certain aspects of the in situ PK response appeared to be dose dependent. The lungs responded rather quickly to high doses of PK, but an apparent latency period was noted with low doses of PK. Postmortem wet-to-dry lung weight ratios were always high but did not suggest dose dependence. However, times of postmortem measurements were not the same for all doses of PK. The external scan technique appeared to be sensitive to changes that occurred in the lung after PK. Externally detected albumin interstitial-to-plasma mass (mass I/P) ratios were substantially higher after PK than during control in situ studies. In some experiments, final mass I/P ratios increased above 4 approximately 2.0 h after PK compared with control values of 0.2 and 0.4. A delay time between injection and change in mass I/P slope was also observed, which decreased with increasing dose of PK. PK causes a permeability injury in the in situ sheep lung and provides a useful model for studying the sensitivity of permeability measurement techniques such as the external gamma-ray detection method.
Innovations in Engineering Education: Mechanical Engineering Education, Mechanical Engineering/Mechanical Engineering Technology Department Heads, 2004
This paper presents the organizational structure for teaching the bioheat transfer component of a... more This paper presents the organizational structure for teaching the bioheat transfer component of a biotransport course based on the How People Learn (HPL) pedagogical model. The presentation to students consists of a series of design challenges in a sequence that directs learning through the major components of bioheat transfer knowledge taxonomy. Students encounter various taxonomic subjects in either a primary learning context or in a secondary application in which adaptive expertise is developed. The primary and secondary intersections between the challenge and taxonomy vectors are displayed in a matrix format.
This paper presents the VaNTH Biomechanics learning modules and discusses their implementation in... more This paper presents the VaNTH Biomechanics learning modules and discusses their implementation in a Fall 2004 engineering course. These Biomechanics learning modules were developed as part of the VaNTH NSF educational coalition formed by multiple institutions in the USA. The pedagogical framework for these modules is based on the widely publicized book "How People Learn" (HPL). The HPL teaching framework presents the learning material as a series of challenges that are posed through a "Legacy Cycle." The educational significance of this effort is that these challenge-based Biomechanics modules were the main mode of instructional delivery in the course. The VaNTH biomechanics modules were presented in an undergraduate Mechanical Engineering course titled "Biomechanics of Human Movement" in Fall 2004. The class (N=18) was divided into three-member teams. All challenges were performed by the teams using computer-based homework assignments that were supplied by the instructor on a CD. Pre-tests, post-tests, and affect rankings were administered for each modular topic to assess the course. The students were also surveyed on the learning effectiveness of the various components of each module. At the end of the semester, the students completed a Biomechanics topics matrix that mapped the challenges to the various class topics. Results of this classroom experience and data gathering are presented in the paper. Conclusions are drawn on the pedagogical efficacy of this approach to instruction.
Ann Biomed Eng, 1979
In previously proposed models of capillary tracer exchange, red cell membranes have usually been ... more In previously proposed models of capillary tracer exchange, red cell membranes have usually been assumed to be either infinitely permeable or completely impermeable to tracer molecules. Permeability of the extravascular cellular compartment has been treated previously, but never in conjunction with finite capillary and red cell permeability effects. Our objective was to examine the situation encountered with multiple indicator experiments in which tracer exchange may be limited by red cell, tissue and capillary membranes. A four phase model is presented which accounts for plasma, red cell, interstitial, and extravascular cellular regions. Results from this model indicate that transcapillary tracer exchange is affected by a minimum of seven dimensionless parameters. The influence of relatively low red cell permeability is most pronounced when the dimensionless capillary permeability is high (i.e., ~cap ~> 1). Deviations in transcapillary extraction values from those corresponding to infinitely permeable erythrocytes can be kept below 5% when capillary permeability is low (i.e., 0tca p ~< .15) by pre-equilibrating the injectate with tracer prior to injection. The additional barrier in the extravascular region necessarily decreases overall transvascular tracer exchange but does not affect extraction values in the vicinity of the appearance time. w~ " ERYTHROCYTES " ~ I O X L FIGURE 1. Four phase capillary model.
The steady-state lymph to plasma concentration ratios (L/Ps) of neutral dextrans, cationic DEAE d... more The steady-state lymph to plasma concentration ratios (L/Ps) of neutral dextrans, cationic DEAE dextrans, and endogenous proteins were determined under normal and increased permeability conditions in six unanesthetized yearling sheep prepared with chronic lung lymph fistulas. Fluorescent dextrans with radii ranging from 1-30 nm were intravenously infused, and after 24 hours, Perilla ketone (PK) was given to alter permeability while maintaining the dextran infusion. Plasma and lymph samples were collected before and after PK administration and analyzed for dextran and protein concentrations following HPLC size separation. Under both baseline and increased permeability conditions, DEAE dextrans had higher L/Ps than neutral dextrans of similar size, but lower L/Ps than proteins of similar size. Comparison of L/Ps before and after PK revealed that the percentage change in permeability for neutral and DEAE dextrans was significantly larger than for proteins. These results suggest that 1) the pulmonary microvascular barrier behaves as a net negative barrier, 2) some transport mechanisms for proteins and dextrans are different, and 3) neutral and cationic dextrans are more sensitive markers than proteins of the same size for assessing changes in pulmonary capillary permeability.
Lymphology
In chronically instrumented unanesthetized sheep, we measured steady-state hemodynamic and lung l... more In chronically instrumented unanesthetized sheep, we measured steady-state hemodynamic and lung lymph responses to mechanically increased pressure and to intravenous infusions of histamine, Pseudomonas bacteria and E. coli endotoxin. Histamine, Pseudomonas bacteria and E. coli endotoxin caused exchanging vessel permeability to increase, as evidenced by high flows of protein rich lung lymph. This contrasts to the effects of increased pressure where lymph protein concentration falls as lymph flow increases. Microvascular sieving of proteins less than 100 Angstrom radius persisted in all increased permeability states, but with endotoxin, lymph clearance of larger proteins increased much more than with histamine or Pseudomonas. We compared several approaches to quantitative interpretations of lymph data and found that direct methods for calculating permeability-surface area products and reflection coefficients for proteins produced values which were difficult to interpret, probably because fundamental assumptions of the methods were violated in our experiments. A mathematical model based on multiple pore theory produced more plausible coefficients.
Journal of applied physiology: respiratory, environmental and exercise physiology
This study was performed to measure the effects of a sustained reduction in coronary flow on lung... more This study was performed to measure the effects of a sustained reduction in coronary flow on lung lymph flow and protein content. Ten halothane-anesthetized sheep with cannulated lymphatic vessels were provided with a carotid-to-left anterior descending coronary artery cannula containing an electromagnetic flowmeter. One group of five animals was observed at base line and after coronary flow was reduced to 38% of base line. A second group of five animals acted as controls and was observed at base line, for 111 min of increased left atrial pressure, and a second period of normal pressures. Sustained coronary flow reduction led to significant increases in pulmonary arterial pressure, left atrial pressure, lymph flow, total protein lymph-to-plasma concentration ratio (L/P), and protein lymph clearance (L/P X lymph flow). Analysis of the pressure, lymph, protein, and indicator data with a two-pore model of the microvascular barrier showed that the observations were consistent with the concept that coronary flow reduction decreased functioning lung capillary surface but increased the size of the large pore and the number of small pores relative to the number of larger pores. Control studies showed increases in lymph flow and decreases in L/P with increased pressure but no significant changes in any variable between the first and second period of normal pressures. We conclude that coronary flow reduction increases lung vascular-tissue transport by decreasing the resistance of the microvascular barrier to protein and fluid movement. However, increased pressure secondary to left ventricular dysfunction plays a role in the magnitude of this response.
Journal of Applied Physiology
The purpose of these studies was a comparison of [14C]urea (U) and 1,3-[14C]propanediol (Pr) as m... more The purpose of these studies was a comparison of [14C]urea (U) and 1,3-[14C]propanediol (Pr) as measures of lung vascular permeability-surface area (PS) under base-line conditions and after lung injury caused by alloxan infusion in isolated perfused dog lungs. Indicator mixtures of 125I-albumin, 51Cr-red blood cells, 3HOH, and U or Pr were injected under base-line conditions, after 1.2 g of alloxan, and after an additional 0.8 g of alloxan. Indicator-dilution curves were analyzed from sampled outflow blood to provide PS, the square root of effective extravascular diffusivity multiplied by exchange surface area (D1/2S), and extravascular lung water (EVLW) from the tracer mean transit times (VW). Results show that alloxan increases PS and D1/2S for U, D1/2S for Pr, and VW and EVLW by desiccation. All indicator-dilution parameters correlate significantly with alloxan dose. Interpretation of Pr transport suggests that materials with lipid and hydrophilic pathways might be used in conjunction with U to minimize the effects of surface area changes and increase the sensitivity of these tracers to permeability alteration. In addition Pr may be a useful alternative to U as a marker of vascular damage.
Journal of Applied Physiology
The effects of pulmonary arterial embolization on calculated pulmonary capillary pressure as dete... more The effects of pulmonary arterial embolization on calculated pulmonary capillary pressure as determined by the venous occlusion technique are examined using a simple pressure-flow model for the lung. It is predicted that pulmonary, arterial embolization can induce significant underestimation of pulmonary capillary pressure in flowing vessels. This underestimation is related to the percent of vessels embolized and the caliber of pulmonary arteries that are embolized (i.e., the size of the emboli). Experimental verification of these theoretical findings is necessary before the conclusions can be extended to the interpretation of venous occlusion experiments in the lung.
Journal of Applied Physiology
We analyzed the effects of Escherichia coli endotoxin infusion on pulmonary microvessels in sheep... more We analyzed the effects of Escherichia coli endotoxin infusion on pulmonary microvessels in sheep by using a two-pore mathematical model of the microvascular barrier. Five sheep were prepared with lung lymph fistulas and instrumented to measure pulmonary arterial and left atrial pressures. Multiple indicator-dilution curves (with 125I-labeled albumin, 51Cr-labeled erythrocytes, [14C]urea, and 3H2O) were measured at base line and during phases 1 and 2 of the endotoxin response. Alterations in the membrane integrity in response to endotoxin infusion were quantified by using a two-pore theory of the microvascular barrier that incorporated lymph, protein, pressure, and multiple indicator measurements. The modeling results showed a slight change in the size of the pores during phase 1 but a 56% decrease in the number of small pores and a twofold increase in the number of large pores with respect to base-line values. During phase 2 the large pore size increased by 40%, and the total number of pores returned to base-line values. The analysis showed that endotoxin effects on fluid and protein exchange in the lung cannot be explained by hemodynamic and surface area changes alone. An apparent increase in lung microvascular permeability occurs during phases 1 and 2 of the endotoxin reaction, with a substantial decrease in perfused microvascular surface area during phase 1.
Journal of applied physiology: respiratory, environmental and exercise physiology
Models of steady-state fluid and solute transport in the microcirculation are used primarily to c... more Models of steady-state fluid and solute transport in the microcirculation are used primarily to characterize filtration and permeability properties of the transport barrier. Important transient relationships, such as the rate of fluid accumulation in the tissue, cannot be predicted with steady-state models. In this paper we present three simple models of unsteady-state fluid and protein exchange between blood plasma and interstitial fluid. The first treats the interstitium as a homogeneous well-mixed compliant compartment, the second includes an interstitial gel, and the third allows for both gel and free fluid in the interstitium. Because we are primarily interested in lung transvascular exchange we used the multiple-pore model and pore sizes described by Harris and Roselli (J. Appl. Physiol.: Respirat . Environ. Exercise Physiol. 50: 1-14, 1981) to characterize the microvascular barrier. However, the unsteady-state transport theory presented here should apply to other organ systems and can be used with different conceptual models of the blood-lymph barrier. For a step increase in microvascular pressure we found good agreement between theoretical and experimental lymph flow and lymph concentrations in the sheep lung when the following parameter ranges were used: base-line interstitial volume, 150-190 ml; interstitial compliance, 7-10 ml/Torr; initial interstitial fluid pressure, -1 Torr; pressure in initial lymphatics, -5 to -6 Torr; and conductivity of the interstitium and lymphatic barrier, 4.25 X 10(-4) ml X s-1 X Torr-1. Based on these values the model predicts 50% of the total change in interstitial water volume occurs in the first 45 min after a step change in microvascular pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
Journal of applied physiology: respiratory, environmental and exercise physiology
In this study, we have compared an effective diffusivity model with several models previously use... more 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.
Journal of Applied Physiology
Seven dog lower left lung lobes were statically inflated and perfused at a constant rate for each... more 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.
Journal of applied physiology: respiratory, environmental and exercise physiology
The purposes of this research were to derive a mathematical model of blood-intestinal transport f... more The purposes of this research were to derive a mathematical model of blood-intestinal transport for the lung and to study the ability of this model to describe the results of previous lymph-collection and multiple-indicator experiments on the lungs of unanesthetized sheep. We used a three-pore model of the microvascular barrier to describe lymph flow, lymph-to-plasma ratios (L/P) of eight endogenous proteins, and the microvascular permeability-surface area (PST) of the lungs to [14C]urea in sheep experiments under base-line conditions and after acute elevation of the left atrial pressure. The results indicate that endothelial pathways consisting of a small pore (28 A), intermediate pore (180 A), and a large pore (1,000 A) can describe experimental L/P values and PST. The description of lymph flow required either than interstitial fluid pressure increase with left atrial pressure or that postcapillary venous resistance decrease relative to precapillary values. We concluded that multiple-pore theory is a useful approach to the description of lung blood-interstitial transport.
Journal of Applied Physiology
Experiments were conducted in seven chronically instrumented unanesthetized sheep to estimate the... more Experiments were conducted in seven chronically instrumented unanesthetized sheep to estimate the osmotic reflection coefficient (sigma d) for total proteins and the solvent-drag reflection coefficients (sigma f) for six endogenous protein fractions. We measured the lymph-to-plasma ratio of total proteins (CL/CP) and six protein fractions during base-line conditions and after left atrial pressure elevations of 24-26 h per elevation. We also monitored pulmonary arterial pressure, left atrial pressure, systemic arterial pressure, and lung lymph flow at the various levels of pulmonary microvascular pressure. Our results indicate the CL/CP may require up to 24 h to reach a true steady state. It was found that sigma d is at least 0.89 for total proteins and sigma f is at least 0.84, 0.87, 0.86, 0.92, 0.95, and 0.96 for protein fractions with effective molecular radii of 36, 39.5, 44, 66, 105, and 123 A, respectively. In addition, the sigma f values for various protein fractions obtained from this investigation are compared with the predicted values of various mathematical models of the lung microcirculation.
Journal of Applied Physiology
Experiments were conducted on five chronically instrumented unanesthetized sheep to determine the... more Experiments were conducted on five chronically instrumented unanesthetized sheep to determine the effects of sustained hypoproteinemia on lung fluid balance. Plasma total protein concentration was decreased from a control value of 6.17 +/- 0.019 to 3.97 +/- 0.17 g/dl (mean +/- SE) by acute plasmapheresis and maintained at this level by chronic thoracic lymph duct drainage. We measured pulmonary arterial pressure, left atrial pressure, aortic pressure, central venous pressure, cardiac output, oncotic pressures of both plasma and lung lymph, lung lymph flow rate, and lung lymph-to-plasma ratio of total proteins and six protein fractions for both control base-line conditions and hypoproteinemia base-line conditions. Moreover, we estimated the average osmotic reflection coefficient for total proteins and the solvent drag reflection coefficients for the six protein fractions during hypoproteinemia. Hypoproteinemia caused significant decreases in lung lymph total protein concentration, lung lymph-to-plasma total protein concentration ratio, and oncotic pressures of plasma and lung lymph. There were no significant alterations in the vascular pressures, lung lymph flow rate, cardiac output, or oncotic pressure gradient. The osmotic reflection coefficient for total proteins was found to be 0.900 +/- 0.004 for hypoproteinemia conditions, which is equal to that found in a previous investigation for sheep with a normal plasma protein concentration. Our results suggest that hypoproteinemia does not alter the lung filtration coefficient nor the reflection coefficients for plasma proteins. Possible explanations for the reported increase in the lung filtration coefficient during hypoproteinemia by other investigators are also made.
Journal of Applied Physiology
Because pulmonary edema has been associated clinically with airway obstruction, we sought to dete... more Because pulmonary edema has been associated clinically with airway obstruction, we sought to determine whether decreased intrathoracic pressure, created by selective inspiratory obstruction, would affect lung fluid balance. We reasoned that if decreased intrathoracic pressure caused an increase in the transvascular hydrostatic pressure gradient, then lung lymph flow would increase and the lymph-to-plasma protein concentration ratio (L/P) would decrease. We performed experiments in six awake sheep with chronic lung lymph cannulas. After a base-line period, we added an inspiratory load (20 cmH2O) and allowed normal expiration at atmospheric pressure. Inspiratory loading was associated with a 12-cmH2O decrease in mean central airway pressure. Mean left atrial pressure fell 11 cmH2O, and mean pulmonary arterial pressure was unchanged; calculated microvascular pressure decreased 8 cmH2O. The changes that occurred in lung lymph were characteristic of those seen after other causes of increased transvascular hydrostatic gradient, such as increased intravascular pressure. Lung lymph flow increased twice base line, and L/P decreased. We conclude that inspiratory loading is associated with an increase in the pulmonary transvascular hydrostatic gradient, possibly by causing a greater fall in interstitial perimicrovascular pressure than in microvascular pressure.
Journal of Applied Physiology
The purpose of this study is to determine the roles of cardiac output and microvascular pressure ... more The purpose of this study is to determine the roles of cardiac output and microvascular pressure on changes in lung fluid balance during exercise in awake sheep. We studied seven sheep during progressive treadmill exercise to exhaustion (10% grade), six sheep during prolonged constant-rate exercise for 45-60 min, and five sheep during hypoxia (fraction of inspired O2 = 0.12) and hypoxic exercise. We made continuous measurements of pulmonary arterial, left atrial, and systemic arterial pressures, lung lymph flow, and cardiac output. Exercise more than doubled cardiac output and increased pulmonary arterial pressures from 19.2 +/- 1 to 34.8 +/- 3.5 (SE) cmH2O. Lung lymph flow increased rapidly fivefold during progressive exercise and returned immediately to base-line levels when exercise was stopped. Lymph-to-plasma protein concentration ratios decreased slightly but steadily. Lymph flows correlated closely with changes in cardiac output and with calculated microvascular pressures. The drop in lymph-to-plasma protein ratio during exercise suggests that microvascular pressure rises during exercise, perhaps due to increased pulmonary venous pressure. Lymph flow and protein content were unaffected by hypoxia, and hypoxia did not alter the lymph changes seen during normoxic exercise. Lung lymph flow did not immediately return to base line after prolonged exercise, suggesting hydration of the lung interstitium.
Journal of Applied Physiology
We studied the effects of three different doses (15, 20, and 25 mg/kg) of Perilla ketone (PK) on ... more We studied the effects of three different doses (15, 20, and 25 mg/kg) of Perilla ketone (PK) on the blood-perfused in situ sheep lung while obtaining external measurements of lung transvascular protein flux. Lymph flow and lymphatic protein clearance increased significantly after all doses of PK. Severe pulmonary edema was confirmed by high postmortem wet-to-dry lung weight ratios and increased extravascular lung water from multiple indicator-dilution studies. Urea permeability-surface area product and effective diffusivity from multiple indicator-dilution studies also increased after PK infusion. Because we observed no evidence of increased capillary pressure or increased microvascular surface area after PK, we conclude that PK significantly increased pulmonary microvascular permeability. Certain aspects of the in situ PK response appeared to be dose dependent. The lungs responded rather quickly to high doses of PK, but an apparent latency period was noted with low doses of PK. Postmortem wet-to-dry lung weight ratios were always high but did not suggest dose dependence. However, times of postmortem measurements were not the same for all doses of PK. The external scan technique appeared to be sensitive to changes that occurred in the lung after PK. Externally detected albumin interstitial-to-plasma mass (mass I/P) ratios were substantially higher after PK than during control in situ studies. In some experiments, final mass I/P ratios increased above 4 approximately 2.0 h after PK compared with control values of 0.2 and 0.4. A delay time between injection and change in mass I/P slope was also observed, which decreased with increasing dose of PK. PK causes a permeability injury in the in situ sheep lung and provides a useful model for studying the sensitivity of permeability measurement techniques such as the external gamma-ray detection method.