Range Of Capillary Pressures Research Articles

A ONE-PARAMETER RELATIONSHIP BETWEEN UNSATURATED HYDRAULIC CONDUCTIVITY AND WATER RETENTION

Estimating unsaturated conductivity often relies on using water characteristics. Because the water curves do not provide information about the pore connectivity, an empirical correction is used in capillary bundle models that are fitted to unsaturated conductivity data. The majority of authors have applied the macroscopic correction expressed as a function of water content. A microscopic correction term expressed as a power function of a pore radius was proposed in the literature but was not tested with a large representative soil data set. The purpose of this work was to apply the hydraulic conductivity-water retention model with the microscopic connectivity correction to a large data set to see what accuracy can be achieved and whether it is possible to relate the connectivity parameters to some readily available soil properties. Data for 147 soil horizons were extracted from the unsaturated soil database UNSODA. Water and conductivity data were in the range of capillary pressures >5 kPa and from 5 to 200 kPa, respectively. The model provided an accurate approximation, and root mean square error (RMSE) in estimated log10k was 0.21. Two parameters of the model appeared to be correlated closely so that using only one connectivity parameter was sufficient. Reducing the number of parameters from two to one and refitting the one-parametric model to data decreased the accuracy of the estimates. The RMSE increased from 0.21 to 0.31. That only one empirical parameter was needed to describe the unsaturated conductivity helps to reduce the number of measurements of this property because a single parameter can be estimated from a limited number of observations.

Effect of capillary pressure and lung distension on capillary recruitment.

To investigate the effect of capillary pressure and alveolar distension on capillary recruitment, we used video-microscopy to quantify capillary recruitment in individual subpleural alveolar walls. Canine lobes were perfused with autologous blood either while inflated by positive airway pressure or while inflated by negative intrapleural pressure in the intact thorax with airway pressure remaining atmospheric. Low flow rates minimized the arteriovenous pressure gradient (< 5 mmHg), permitting capillary pressure estimation by averaging these pressures. Capillary pressure was varied stepwise from airway pressure to 30 mmHg above airway pressure. Capillary recruitment always began as capillary pressure exceeded airway pressure. At low positive airway pressures, the capillaries of the excised lobes opened suddenly over a narrow pressure range. AT higher airway pressures and in the intact thorax, recruitment occurred over a wide range of capillary pressures. We conclude that capillary perfusion begins when intracapillary pressure just exceeds alveolar pressure but that further increases in capillary pressure recruit capillaries depending on tension in the alveolar wall, whether imposed by positive airway pressure or by gravity when the lung is suspended in an intact thorax.

Albumin transport across pulmonary capillary-interstitial barrier in anesthetized dogs

To evaluate albumin transport across the pulmonary capillary endothelial and interstitial barriers, we simultaneously measured blood-to-tissue (QA,t) and blood-to-lymph (QA,l) clearances of 125I-radiolabeled albumin as well as endogenous albumin clearance (Qa,l) in the canine lung in vivo (n = 10). Steady-state prenodal lung lymph flows (Qw,l) and protein clearances were measured over a 2-h period at a constant capillary pressure (Pc, 13-33 cmH2O). Comparison between QA,t and QA,l as a function of Pc suggests that little of the albumin that crossed the capillary wall remained in the lung tissue, with most leaving in the lymph. Qw,l increased significantly as Pc increased, but lung tissue water was minimally affected. From the ratio of the clearance-Pc slopes for albumin and water, the albumin reflection coefficient was estimated to be 0.81 using QA,l and Qw,l and 0.56 using Qa,l and Qw,l. The permeability surface area product for the sum of blood-to-tissue and blood-to-lymph fluxes of labeled albumin (QA,t + QA,l) was 31 +/- 9 microliters/min, whereas that calculated from the blood-to-lymph flux of endogenous albumin (Qa,l) was 97 +/- 22 microliters/min. These data suggest that 1) both tissue and lymph accumulations of albumin must be considered when microvascular permeability is evaluated using protein tracers; 2) lymph clearance, but not tissue accumulation of albumin, was filtration dependent; and 3) lymph flow was an important contributor to the safety factor against edema formation over a moderate range of capillary pressures.

Pulmonary capillary pressure in intact dog lungs.

We used a gravimetric method to determine the ratio (gamma) of pulmonary venous to total pulmonary vascular resistance in intact dog lungs. From this ratio, pulmonary capillary pressure (Pc) can be calculated. The average value of gamma was 0.50 +/- 0.06 (mean +/- SD) in 10 dogs. We found no correlation between gamma and PO2, PCO2, pH, or hematocrit in the narrow ranges of these experiments. Over the capillary pressure range of 22.4--35.2 mmHg we found no correlation between gamma and Pc. The value of gamma found in this study is not significantly different from the value found in isolated perfused lungs.

An Inexpensive Tensiometer for Snow-Melt Research

AbstractThe construction and use of a rugged and easily installed tensiometer for use in snow hydrology is discussed. The tensiometer incorporates a short (380 mm) water manometer, adequate for the small range of capillary pressure in melting snow. The response of a row of tensiometers to the application of a dyed water pulse to the snow surface is compared to the resulting dye stain pattern. The lateral variation of flow in a snow-pack requires the use of many tensiometers to define the capillary pressure regime.

An Inexpensive Tensiometer for Snow-Melt Research

AbstractThe construction and use of a rugged and easily installed tensiometer for use in snow hydrology is discussed. The tensiometer incorporates a short (380 mm) water manometer, adequate for the small range of capillary pressure in melting snow. The response of a row of tensiometers to the application of a dyed water pulse to the snow surface is compared to the resulting dye stain pattern. The lateral variation of flow in a snow-pack requires the use of many tensiometers to define the capillary pressure regime.

Circumference measurement as a criterion for capillary pressure determination

A modification of the original Pappenheimer and Soto-Rivera's isogravimetric method to determine effective capillary pressure ( P c ) is described. As a balancing criterion, the circumference rather than the weight change was utilized. In 120 experimental runs on 17 cats, a very good correlation was found with the conventional isogravimetric technique over a wide range of capillary pressures. The potential areas of application of this technique are also compared with the isoconductometric technique.