Alveolar liquid pressure measured by micropipettes in isolated dog lung

Abstract

Micropipettes (2-5 microns), in conjunction with a servo-nulling system, were used to measure liquid pressure (Pliq) in subpleural alveoli of lobes of dog lungs made edematous by perfusing with plasma to a constant extravascular weight gain (W). Pliq was measured at fixed transpulmonary pressure (Ptp) in lungs whose W was more than 0.5 that of the initial weight (Wi). In six lobes at W/Wi = 0.6, Pliq, relative to alveolar pressure (Palv), was -2.6 +/- 0.4 cmH2O (mean +/- SE), -11.8 +/- 0.6, and -17.5 +/- 1.7 at deflation Ptp values of 5, 15, and 25 cmH2O, respectively. The Pliq increased to -2, -7, and -13.7, respectively, at W/Wi = 2.8. Based on a mean alveolar radius of 50 micron at Ptp at 25 cmH2O and values of Palv - Pliq, values for alveolar surface tension (tau) at W/Wi = 0.6 were 6, 30, and 44 dyn/cm at Ptp of 5, 15, and 25 cmH2O, respectively. In five other lobes at W/Wi = 0.5 and at 65 and 84% total lung capacity, tau was much higher on lung inflation than on deflation. If pericapillary interstitial fluid pressure (Pi) and Pliq were identical under edematous conditions, tau would be the main determinant of Pi.

Alveolar liquid pressure measured by micropuncture in isolated lungs of mature and immature fetal rabbits.

“…The number and size of alveoli increases only after birth in most species including the rabbit (30,31), however, to be certain that the differences in Pliqud measurements were not due to differences in the radius ofcurvature ofthe air liquid interface, we determined the mean linear intercept (Lm) of the airspaces at a transpulmonary pressure of 25 cmH2O, in mature and immature lungs. (16). Though others have reported a higher lung water content in liquid-filled lungs ofpreterm as compared with term rabbits (33), in our experiments the water content of the air inflated mature and immature lungs were comparable ( Table I).…”

Surface tension in situ in flooded alveolus unaltered by albumin

“…We record PLIQ through a 2-M saline solution-filled glass micropipette that is connected to a servo-nulling pressure-measurement system (Vista Electronics, Ramona, CA) (23). We insert the pipette tip (ID 2-4 m) into the liquid phase of a flooded alveolus or the liquid lining layer at the corner of an aerated alveolus (see Figs.…”

“…These P LIQ values are consistent with previous reports. Between P ALV of 5 and 15 cmH 2 O, flooded alveolar P LIQ has been found to average 1 to 3.3 cmH 2 O in the presence of mild edema, whether due to intratracheal saline instillation, oleic acid administration, or elevated hydrostatic pressure (9,23,24 Table 1). The discrepancy in T determination by Laplace application as opposed to the microdroplet method requires further investigation.…”

“…Alternatively, we determine T by applying the Laplace relation to the meniscus that forms at the mouth of the flooded alveolus (2,31). Combining alveolar air pressure measurement at the trachea of the constantly inflated lung; alveolar liquid phase pressure measurement through a micropipette connected to a servo-nulling pressure-measurement system (23); and threedimensional meniscus radius determination by confocal microscopy (31), we introduce a method ( Fig. 1) for determining T in situ in the flooded alveolus.…”

Pulmonary Circulation and Regulation of Fluid Balance

“…176 Alveolar wall fluid is propelled by the prevailing pressure gradient away from the alveolus and toward the extra-alveolar space. [194][195][196] Increases in interstitial fluid volume are handled by increases in pulmonary lymph flow. 197,198 However, the relationship between interstitial fluid volume and lymph flow is not linear because, beyond a critical fluid volume, pulmonary lymph flow no longer increases in proportion to the increase in fluid volume.…”