Applications of mechanistic modelling to clinical and experimental immunology: an emerging technology to accelerate immunotherapeutic discovery and development.

The application of in-silico modelling is beginning to emerge as a key methodology to advance our understanding of mechanisms of disease pathophysiology and related drug action, and in the design of experimental medicine and clinical studies. From this perspective, we will present a non-technical discussion of a small number of recent and historical applications of mathematical, statistical and computational modelling to clinical and experimental immunology. We focus specifically upon mechanistic questions relating to human viral infection, tumour growth and metastasis and T cell activation. These exemplar applications highlight the potential of this approach to impact upon human immunology informed by ever-expanding experimental, clinical and 'omics' data. Despite the capacity of mechanistic modelling to accelerate therapeutic discovery and development and to de-risk clinical trial design, it is not utilized widely across the field. We outline ongoing challenges facing the integration of mechanistic modelling with experimental and clinical immunology, and suggest how these may be overcome. Advances in key technologies, including multi-scale modelling, machine learning and the wealth of 'omics' data sets, coupled with advancements in computational capacity, are providing the basis for mechanistic modelling to impact on immunotherapeutic discovery and development during the next decade.

Evaluation of the impact of weaning food messages on infant feeding practices and child growth in rural Bangladesh.

In rural Bangladesh, a community-based weaning intervention used volunteers to teach complementary feeding to families of 62 breast-fed infants aged 6-12 mo. Over 5 mo, treatment children gained on average 0.46 SD (approximately 460 g) more in weight-for-age (WAZ) than the 55 control subjects, and were approximately 0.5 kg heavier at the final measure. The differences were statistically significant (P < 0.001). The percent median weight-for-age (WAPM) of treatment children held steady at 76% of the National Center for Health Statistics' reference, whereas the WAPM of control subjects dropped from 78% to 72%. The increase in percentage points of severe malnutrition (below -3 WAZ) was only 5% in the treatment group compared with 26% in the control subjects. Treatment children consumed a significantly greater percent of their energy and protein requirements from complementary foods than did control subjects. The affordable complementary foods consisted mainly of cereal porridge with oil and brown sugar. These findings suggest that educational interventions teaching families to feed hygienic, simple, cheap, energy-enriched complementary foods to breast-fed infants after 5-6 mo can improve child growth, even under impoverished conditions.

Effects of electric charge on hydraulic conductivity of pulmonary interstitium.

The hydraulic conductivity of pulmonary interstitium was measured in a short isolated segment of interstitium surrounding a large pulmonary artery (1-3 mm diam) of the rabbit. The flow rate of the following solutions was measured sequentially: normal saline, polycation protamine sulfate (0.08 mg/ml), cationic dextran (0.1 or 1.5%) or anionic dextran (0.1 or 1.5%), and hyaluronidase (testes, 0.02%) solution. The pH of all solutions was adjusted to 7.35-7.40. The ratios of the flow of protamine sulfate and cationic dextran to that of saline averaged 2.3 +/- 0.92 (SD, n = 7) and 3.0 +/- 1.2 (n = 6), respectively. The anionic dextran-to-saline flow ratio averaged 0.72 +/- 0.28 (n = 13). Flow increased in the presence of positively charged molecules and decreased in the presence of negatively charged molecules. At a lower pH of 5.0-6.0, only 0.1% cationic dextran had an effect on interstitial conductivity. Thus pulmonary interstitium at physiological pH has the properties of a negatively charged membrane. The increased interstitial conductivity caused by the positively charged molecules was not observed after treatment with hyaluronidase. These effects of electric charge on interstitial conductivity were partly attributed to the presence in the interstitium of negatively charged hyaluronan.

Effects of albumin, dextran, and hyaluronidase on pulmonary interstitial conductivity.

The fluid conductivity of albumin solutions of various concentrations relative to that of saline was measured in the interstitium surrounding a short segment of a large (1.5- to 3-mm-diam) blood vessel of an isolated rabbit lung of which air spaces and vasculature were filled with silicon rubber. At a constant driving pressure, the flow of the following solutions was measured sequentially: normal saline and albumin solution (3, 5.5, 8, or 15 g/100 ml saline), hyaluronidase solution (0.02 g/100 ml), and albumin solution (same concentration used before hyaluronidase solution). The albumin-to-saline flow ratios averaged 1.00 +/- 0.23 (SD), 1.01 +/- 0.21, 1.32 +/- 0.63, and 1.54 +/- 0.36 for albumin concentrations of 3, 5.5, 8, and 15 g/100 ml, respectively. These ratios were higher than the corresponding values of 0.88, 0.78, 0.72, and 0.5 expected if the flow of albumin solution were to depend only on fluid viscosity. The flow of dextran and hyaluronan solutions was more viscosity dependent than the flow of albumin solutions. The increased flow of albumin solution could be the result of a reduced excluded volume of albumin caused by collagen and glycosaminoglycans with an increased albumin concentration. The flow of hyaluronidase solution was 24 +/- 22 (SD)-fold (n = 36) larger than the flow of albumin solution. Thus hyaluronan was responsible for most of the hydraulic resistance of the interstitium to bulk flow. After its degradation, the flow of albumin solution became more viscosity dependent. The interaction between plasma proteins and glycosaminoglycans in the pulmonary interstitium could serve to enhance clearance of microvascular filtrate, particularly under conditions of large protein leaks.

Effect of hydration on lung interstitial permeability response to albumin and hyaluronidase.

Previous studies showed that the flows of albumin and hyaluronidase solutions increased relative to that of saline in isolated segments of rabbit lung interstitium (Lai-Fook et al. J. Appl. Physiol. 67:606-613, 1989). We questioned whether these effects were hydration dependent. In interstitial segments the flows of lactated Ringer, albumin (5 and 10 g/dl), and hyaluronidase (0.02%) solutions were measured at mean interstitial pressures (Pm) between -5 and 15 cmH2O with a constant driving pressure of 5 cmH2O. The albumin-to-Ringer flow ratio increased monotonically from near the viscosity-dependent value (0.75-0.77) at -5 cmH2O Pm to values of 1.6-2.1 at 15 cmH2O Pm. A similar behavior was observed for the flow of the hyaluronidase solution relative to that of Ringer solution. The increased permeability response to albumin was independent of the albumin concentration used. By contrast, the response to hyaluronidase was lower when the interstitium was perfused with the higher concentration albumin solution (10 g/dl) before the flow of hyaluronidase, indicating an inhibitory effect of albumin on the hyaluronidase response. Estimates of interstitial hydration from Pm indicated an increased interstitial permeability (conductivity) to the flows of albumin and hyaluronidase solutions only after interstitial volume had doubled, whereas interstitial permeability was viscosity dependent at normal interstitial hydration.

Effect of increased acceleration on regional pleural pressure in dogs.

The variation of pleural pressure was measured in anesthetized spontaneously breathing dogs subjected to increased acceleration (0-4 G) in a centrifuge. Two groups of animals were studied. In one group, the resultant acceleration was in a direction either ventral-to-dorsal (+Gx) or dorsal-to-ventral (-Gx), with a relatively small residual cranial-to-caudal acceleration. In the other group, the resultant acceleration was either cranial-to-caudal (+Gz) or caudal-to-cranial (-Gz), with a relatively small residual dorsal-to-ventral acceleration. Pleural liquid pressure (Ppl) was measured by two rib capsules that were separated by 7-9 cm and oriented either in the dorsal-to-ventral or cranial-to-caudal direction. At functional residual capacity, Ppl in the nondependent lung region became more negative when the acceleration was in the +Gx or +Gz direction. Thus the lung would be susceptible to damage that results from overexpansion in these acceleration directions. By contrast, acceleration in the -Gx or -Gz direction produced values of Ppl at functional residual capacity that were positive. Thus, in these acceleration directions, the respiratory muscles must provide greater force during inspiration to overcome lung compression before lung ventilation can occur. The Ppl gradients with respect to the acceleration directions increased approximately in proportion to acceleration in the +Gx, -Gx, and -Gz directions but remained relatively constant in the +Gz direction.

Arterial, capillary, and venous transit times and dispersion measured in isolated rabbit lungs.

Transit time and relative dispersion of the arterial, capillary, and venous segments of the pulmonary circulation were measured in isolated perfused rabbit lungs. Fluorescence videomicroscopy was used to record the passage of dye through the main pulmonary artery, subpleural microcirculation, and venous outflow. Dye dilution curves were obtained at the main pulmonary artery, subpleural arterioles and venules, and pulmonary vein. Measurements were made at 5-cmH2O airway pressure, at blood flows of approximately 80, 50, and 25 ml.min-1.kg-1, and at left atrial pressures of approximately 0 cmH2O (zone 2) and approximately 12 cmH2O (zone 3). The dye dilution curves were modeled as lagged normal density curves that were used to calculate transit time and relative dispersion between the pulmonary artery and arteriole (artery), arteriole and venule (capillary), venule and pulmonary vein (vein), and pulmonary artery and pulmonary vein (whole lung). In open-chest anesthetized dogs, the passage of dye was recorded from the subpleural arterioles and venules between the seventh and eighth ribs in the left lateral position. At comparable blood flows, capillary transit time was larger in the dog than in the rabbit lung [3.4 +/- 2.4 (SD) vs. 0.87 +/- 0.47 s]. In the rabbit lung, relative dispersion was greater in pulmonary capillaries (average values 0.83-1.6) and veins (0.91-1.6) than in arteries (0.39-0.50), which was similar to the whole lung dispersion (0.47-0.52). A similarly high dispersion (0.93) was measured in the dog's pulmonary capillaries. Thus high dispersion in pulmonary capillaries and veins cannot be detected by whole lung dispersion measurements.

Effect of concentration on albumin diffusion in lung interstitium.

The transport of macromolecules through the lung interstitium depends on both bulk transport of fluid and diffusion. In the present study, we studied the diffusion of albumin. Isolated rabbit lungs were inflated with silicon rubber via airways and blood vessels, and two chambers were bonded to the sides of a 0.5-cm-thick slab that enclosed a vessel with an intersititial cuff. One chamber was filled with either albumin solution (2 or 5 g/dl) containing tracer 125I-albumin or with tracer 125I-albumin alone; the other was filled with Ringer solution. Unbound 125I was removed from the tracer by dialysis before use. The chamber with Ringer solution was placed in the well of a NaI(Tl) scintillation detector. Diffusion of tracer through the interstitium was measured continuously for 60 h. Tracer mass (M) showed a time (t) delay followed by an increase to a steady-state flow (dM/dt constant). Albumin diffusion coefficient (D) was given by L2/(6T), where T was the time intercept of the steady-state M-t line at zero M, and L was interstitial length. Interstitial cuff thickness-to-vessel radius ratio (Th0/R) was estimated by using Fick's law for steady-state diffusion. Both D and Th0/R were independent of albumin concentration. D averaged 6.6 x 10(-7) cm2/s, similar to the free D for albumin. Values of Th0/R averaged 0.047 +/- 0.024 (SD), near the values measured histologically. Thus pulmonary interstitial constituents offered no restriction to the diffusion of albumin.

Effects of lung inflation and blood flow on capillary transit time in isolated rabbit lungs.

In a previous study, direct measurements of pulmonary capillary transit time by fluorescence video microscopy in anesthetized rabbits showed that chest inflation increased capillary transit time and decreased cardiac output. In isolated perfused rabbit lungs we measured the effect of lung volume, left atrial pressure (Pla), and blood flow on capillary transit time. At constant blood flow and constant transpulmonary pressure, a bolus of fluorescent dye was injected into the pulmonary artery and the passage of the dye through the subpleural microcirculation was recorded via the video microscope on videotape. During playback of the video signals, the light emitted from an arteriole and adjacent venule was measured using a video photoanalyzer. Capillary transit time was the difference between the mean time values of the arteriolar and venular dye dilution curves. We measured capillary transit time in three groups of lungs. In group 1, with airway pressure (Paw) at 5 cmH2O, transit time was measured at blood flow of approximately 80, approximately 40, and approximately 20 ml.min-1.kg-1. At each blood flow level, Pla was varied from 0 (Pla less than Paw, zone 2) to 11 cmH2O (Pla greater than Paw, zone 3). In group 2, at constant Paw of 15 cmH2O, Pla was varied from 0 (zone 2) to 22 cmH2O (zone 3) at the same three blood flow levels. In group 3, at each of the three blood flow levels, Paw was varied from 5 to 15 cmH2O while Pla was maintained at 0 cmH2O (zone 2).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood-brain barrier breach following cortical contusion in the rat.

Adult Fisher 344 rats were subjected to a unilateral impact to the dorsal cortex above the hippocampus at 3.5 m/second, resulting in a 2-mm cortical depression. This caused severe cortical damage and neuronal loss in hippocampus subfields CA1, CA3, and hilus. Breakdown of the blood-brain barrier (BBB) was assessed by injecting the protein horseradish peroxidase (HRP) 5 minutes prior to or at various times after injury (5 minutes, 1, 3, 6, and 12 hours, 1, 2, 5, and 10 days). Animals were killed 1 hour after HRP injection and brain sections were reacted with diaminobenzidine to visualize extravascular accumulation of the protein. Maximum staining occurred in animals injected with HRP 5 minutes prior to or 5 minutes after cortical contusion. Staining at these time points was observed in the ipsilateral cortex of the impact area and areas adjacent to it, as well as in the ipsilateral hippocampus. Some modest staining occurred in the dorsal contralateral cortex near the superior sagittal sinus. Cortical HRP staining gradually decreased at increasing time intervals postinjury. By 10 days, no HRP staining was observed in any area of the brain. In the ipsilateral hippocampus, HRP staining was absent by 3 hours postinjury and remained so at the 6- and 12-hour time points. Surprisingly, HRP staining was again observed in the ipsilateral hippocampus 1 and 2 days after cortical contusion, indicating a biphasic opening of the BBB following head trauma and a possible second wave of secondary brain damage days after the contusion injury. These data indicate that regions not initially destroyed by cortical impact, but evidencing BBB breach, may be accessible to neurotrophic factors administered intravenously both immediately and days after brain trauma.

Two-component arterial blood pressure conditional response in rat.

The objective of these experiments was to quantify the pattern of change in arterial blood pressure (BP) during a discriminative aversive classical conditioning paradigm in rat using a new "high resolution" computer analysis. Sprague-Dawley rats (n = 5) were restrained in a soft, conical cloth pouch and conditioned using a 6 sec. pulsed tone (CS+) followed by a 0.5 sec. tail shock; a steady tone, never followed by shock, served as a CS-. BP peaked at 16.4 +/- 6.5 mm Hg (mean +/- SD) above control at 1.5 +/- 0.1 sec. after onset of CS+. This "first component" ("C1") also occurred during CS- (12.1 +/- 3.8 mm Hg), although the magnitudes of the two were significantly (p < 0.05) different. Another group of rats (n = 8) was treated identically except the tones were 15 seconds long. The conditional BP response consisted of two components. C1 was reminiscent of that seen using the short tone: for CS+ a peak of 13.6 +/- 5.6 mm Hg at 1.5 sec. or, for CS-, of 10.0 +/- 4.3 at 1.3 sec. (p < 0.05). In CS+ trials BP peaked again ("C2," 7.4 +/- 2.5 mm Hg) at 8.3 +/- 1.2 sec. There was no statistically significant C2 for CS- trials, clearly demonstrating discrimination between tones. The unconditional BP response in both groups consisted of two large, closely spaced peaks in BP. Respiration was recorded in 3 additional rats. After shock delivery these subjects often showed a sudden shift between (1) a regular respiratory pattern with moderate chest excursion and (2) apneic episodes interspersed with single, deep breaths. This latter pattern was associated with large, low frequency fluctuations in BP. Continued development of the rat conditioning paradigm is especially warranted because of the ability to record sympathetic nerve activity in intact, awake subjects and the large number of readily available genetic strains, which model human pathological states.

Effect of flow on hydraulic conductivity and reflection coefficient of rabbit mesentery.

OBJECTIVE: To measure the hydraulic conductivity and reflection coefficient for albumin, as defined by the Starling equation, in rabbit mesentery. METHODS: A section of rabbit mesentery was fixed between two chambers filled with lactated Ringer solution. Flow (Q) of Ringer solution was measured across the mesentery at driving pressures (delta P) between 1 and 6 cm H2O. Hydraulic conductivity was proportional to the slope of the Q-delta P curve. At constant delta P (approximately -2, -4, or -6 cm H2O), flow was measured at three different albumin concentration differences (0.5, 1, and 1.5 g/dl). Unstirred layer effects were minimized by magnetic stirrers. Reflection coefficient was the negative of the slope of the Q-delta pi curve divided by the slope of the Q-delta P curve, where delta pi was the albumin osmotic pressure difference. Hydraulic conductivity was measured before and after testicular hyaluronidase was added to the Ringer solution. RESULTS: There was no significant difference in conductivity per unit area (Lp) for the three different driving pressures. Hyaluronidase increased hydraulic conductivity significantly (p < 0.01) by 72 +/- 56%, indicating that hyaluronan and other glycosaminoglycans contributed to tissue fluid resistance. Reflection coefficient (sigma) increased from 0.02 to 0.14 as flow increased eightfold. CONCLUSIONS: The results suggest that the mesentery tissue provides little restriction to the passage of albumin. The increase in conductivity in the presence of hyaluronidase indicates that tissue hyaluronan and other glycosaminoglycans provide fluid resistance to bulk flow.

Effects of hypoxia, blood P(CO2) and flow on O2 transport in excised rabbit lungs.

In previous studies using isolated perfused rabbit lungs, an O2 deficit measured by an alveolar gas-to-end capillary blood P(O2) difference (A-aD(O2)) was absent at blood flows (Q) consistent with severe exercise. Thus factors such as VA/Q heterogeneity, shunt and diffusion limitation that contribute to an O2 deficit in vivo were absent. Here we attempted to increase diffusion limitation to O2 transport by reducing the equilibration coefficient D/(betaQ), the ratio of the diffusing capacity (D) to the product of Q and the capacitance coefficient (beta, the slope of the blood O2 content-P(O2) curve). First, we used hypoxic (10% O2) ventilation in conjunction with a low PV(O2) (approximately 25 mmHg) because beta is largest in this region of the O2 dissociation curve. Second, we increased beta by decreasing blood P(CO2) which shifts the O2 dissociation curve to the left (Bohr effect). Third, we increased Q to three times control to reduce D/Q. CO diffusing capacity was measured as a function of blood flow and blood P(O2). A deficit in O2 transport as measured by a significant A-aD(O2) was measured only under conditions of hypoxia and high blood flow. The measured O2 deficit matched the predictions from the equilibration coefficients D/(betaQ) based on measurements of beta, D and Q.

Sympathetic nervous activity and arterial blood pressure control in conscious rat during rest and behavioral stress.

The object of this experiment is to analyze the neural control of arterial blood pressure (BP) during rest and a sudden behavioral stress. Sprague-Dawley rats were classically conditioned by following a 15-s tone (CS+) with a 0.5-s tail shock. Bipolar renal nerve electrodes and a caudal artery catheter were implanted. Two days later BP and sympathetic nervous activity (SNA) were recorded in the behaviorally trained animals. The CS+ evoked a large initial increase in BP (peak, 14 +/- 5 mmHg, mean +/- SD; n = 12) that lasted 3.9 +/- 0.8 s. An abrupt (latency = 0.16 +/- 0.03 s), short (duration = 0.58 +/- 0.12 s), and intense (4.09 +/- 1.02 times average control) burst in sympathetic activity preceded this first component (C1) of the BP conditional response. The size of C1 was related to the magnitude of the SNA burst. SNA then fell below control; this quiet period preceded a fall in BP after the C1 peak. Pressure rose again (C2; peak = 6 +/- 3 mmHg, average increase = 3 +/- 3 mmHg) for the remainder of the CS+. SNA increased to 1.24 +/- 0.14 of control during this second component of the BP conditional response. Ganglionic blockade eliminated the BP and SNA conditional response (n = 3). The C1 pressure increase appears to result from an "open-loop" process in which a brief barrage of nerve activity governs BP changes lasting several seconds. The quite period probably results from a negative feedback (i.e., baroreflex) relationship between SNA and BP.(ABSTRACT TRUNCATED AT 250 WORDS)

Sympathetic activity and blood pressure are tightly coupled at 0.4 Hz in conscious rats.

Interactions of sympathetic nerve activity (SNA) with blood pressure (BP) and heart rate (HR) were assessed in conscious rats while they rested quietly in a cloth sock (n = 7), roamed freely in their home cage (n = 6), and then after anesthesia with pentobarbital (30 mg/kg; n = 7). The power and coherence spectra below 3 Hz were calculated from data collected for 9.56 min. In the conscious rat, SNA spectral power peaked at 0.4 Hz, whereas the majority of spectral power for both BP and HR occurred at frequencies lower than 0.4 Hz. However, there was an inconspicuous peak in the BP power spectra at 0.4 Hz that was not seen in the HR spectra. Coherence between SNA and BP peaked at a frequency of approximately 0.4 Hz, the same frequency at which the SNA spectral peaks occurred. In contrast, at frequencies below 0.4 Hz where maximum BP power occurred, the coherence was considerably lower. Anesthesia with pentobarbital lowered spectral power for BP, SNA, and HR but essentially did not change the coherence between SNA and BP. Interactions between respiration and each of the other variables were weak in the conscious rat. However, prominent respiratory interactions at approximately 1.2 Hz were evident after anesthesia. These data indicate a close coupling between SNA and BP at 0.4 Hz, raising the possibility that the BP spectral power at 0.4 Hz reliably reflects sympathetic activity.

Effect of hydration on lung interstitial conductivity response to electrically charged solutions.

In interstitial segments of rabbit lung, we compared the flow of a solution containing cationic protamine sulfate (0.08 mg/ml) or cationic dextran (0.1%) to that of Ringer or neutral dextran solution. Also compared, were the flow of solutions containing anionic dextran (0.1 or 1.5%) to those containing neutral dextran and the flow of hyaluronidase solution (0.02%) to that of Ringer solution, at mean interstitial pressures (Pm) between -5 and 15 cmH2O. Driving pressure was set at 5 cmH2O. Cationic protamine or cationic dextran-to-Ringer flow ratio increased with Pm (presumably as hydration increased) but in nonedematous interstitium (-5 cmH2O Pm), flow ratio was 1, indicating a viscosity-dependent flow. In contrast, the flow of anionic dextran solution decreased relative to that of neutral dextran; this decrease was constant with hydration, but was greater at the higher concentration of dextran. Interstitial conductivity to the flow of hyaluronidase increased with hydration. However, this behavior was absent after the flow of 1.5% anionic dextran, indicating an inhibitory effect of the higher concentration of anionic dextran on the hyaluronidase response. A negative charge in microvascular filtrate may control fluid clearance in normal interstitium, while a positive charge would enhance clearance only in edema formation.

Effect of concentration and hyaluronidase on albumin diffusion across rabbit mesentery.

OBJECTIVE: To measure the diffusion coefficient of albumin through rabbit mesentery using the steady-state flux of radioactive tracer 125I-albumin. The effect of albumin concentration and testicular hyaluronidase were also studied. METHODS: Mesenteric tissue was bonded between two plates, exposing a 7 mm diameter surface, with two chambers on either side. One chamber was filled with a test solution of albumin containing the radioactive tracer and the other with lactated Ringer solution. The solutions in both chambers were stirred with small magnetic cylinders. The chamber filled with lactated Ringer solution was placed in a well-type NaI(Tl) detector, and the radiation emitted from the tracer that diffused across the mesentery was monitored continuously for 9 hours. The diffusion coefficient (D) was calculated using Fick's law of diffusion. The diffusion coefficient was measured at albumin concentration differences (delta C) between approximately 0 and 10 g/dL. The diffusion coefficient was also measured with testicular hyaluronidase at three different albumin-concentration differences. RESULTS: The diffusion coefficient increased significantly (P < 0.0001) approximately three-fold from a mean value of 2.2 x 10(-8) +/- 1.2 x 10(-8) (SD) cm2/s at 0-0.5 g/dL delta C to 5.9 x 10(-8) +/- 1.1 x 10(-8) (SD) cm2/s at 10 g/dL delta C. The values are much less than the free diffusion coefficient of albumin (6 x 10(-7) cm2/s). Testicular hyaluronidase added to the albumin solution decreased D by approximately 60%, but did not eliminate the increase in D with delta C. CONCLUSIONS: The increase in D with delta C and the reduced D with hyaluronidase were attributed to a reduced albumin-excluded volume caused by an interaction between albumin and hyaluronan. Further studies are required to define this interaction.

Hydraulic conductivity, albumin reflection and diffusion coefficients of pig mediastinal pleura.

Hydraulic conductivity (L), albumin reflection coefficient (sigma), and albumin diffusion coefficient (D) were measured across pig mediastinal pleura. The tissue (7 mm diameter) was bonded between two chambers. Flow (Q) of lactated Ringer solution between the chambers was measured in turn at driving pressures (DeltaP) of 2, 4, and 6 cm H(2)O. Value of L was proportional to the slope of the Q-DeltaP curve. Then Q was measured in turn at three albumin osmotic pressure differences (Deltapi equivalent to -1, -2, and -3 g/dl albumin concentration difference, DeltaC) with DeltaP constant at either 2, 3, 4, or 6 cm H(2)O. From Starling's equation, magnitude of sigma was the slope of the Q-Deltapi curve divided by the slope of the Q-DeltaP curve. We measured the diffusion of 0, 2, 5, and 10 g/dl albumin with tracer (125)I-albumin. Tracer mass (M) that diffused across the pleura was measured for 10 h using a well-type NaI(T1) detector. D was calculated from the slope of the M-time curve. Values of L averaged 2.0 x 10(-8) cm(3). s(-1). dyne(-1) (n = 23). Values of sigma were small (0.02-0.05) and sigma increased as flow increased 20-fold. D (n = 24) increased 3-fold from 2.7 x 10(-8) cm(2)/s as DeltaC increased from 0 to 10 g/dl. The small values of sigma indicated that mediastinal pleura provided little restriction to the passage of protein.

Comparison of the costs of compliance with nutrition education messages to improve the diets of Bangladeshi breastfeeding mothers and weaning-age children.

Local market prices in rural Bangladesh were used to compute the costs of filling the nutrient gaps between actual intakes and safe nutrient requirements, and the costs of compliance with nutrition messages, for 78 lactating mothers and 61 weaning-age breastfed children. (The gap is the difference between the requirement and the amount of nutrient consumed.) To fill the mother's energy gap of approximately 1050 kcal (4393 kJ) would cost an additional 21% of the daily wage, or almost double the value of food she was presently eating. Given social reality, these costs would probably be much greater, as the mother would also need to increase the allocation of food to other household members. The weaning-age children's energy gap could theoretically be closed for less than one-third of the cost of improving the mothers' diets, or about 8% of the daily wage. The increase in food intake equivalent to 2% of the daily wage actually achieved through nutrition education resulted in a significant improvement in child weight gain, though not ideal. These findings suggest that, in the absence of programs which reduce economic barriers, it is economically feasible for families to close the nutrient gaps for weaning-age breastfed children in Bangladesh, but not for lactating women. Thus, education to improve women's diets should be incorporated into programs that make these improvements affordable, whereas education to improve weaning-age children's diets can be implemented with or without other program supports.