Absorption force of the capillaries of the visceral pleura in determination of the intrapleural pressure.

AGOSTONI, E., A. TAGLIETTI AND I. SETNIKAR. Absorption jome oj the capillaries of the visceral pleura in determination of the intrapleural pressure. Am. J. Physiol. 191(2): 277-282. qg.--A method is described for the measurement of the net absorption pressure of the capillaries at the level of the visceral pleura. This pressure was found to be about 15 mm Hg and due to the difference between the plasma colloid osmotic pressure and the hydrostatic pressure in the pulmonary capillaries; such a difference does not exist in the parietal pleura. The hydrostatic pressure of the pulmonary capillaries estimated by this method has the same value as that observed by cardiac catheterization. From the results and theoretical considerations it appears that the negative intrapleural pressure is the result of the net absorption pressure of the visceral pleura. This force is higher than the elastic retraction force of the lung and therefore it holds the visceral and the parietal pleura together. T HE PRINCIPAL factors regulating the transfer of fluid through the capillary membranes were hypothesized by Hamburger (I) and outlined by Starling (2). The latter, with experiments performed on perfused hindlegs of dogs, suggested that the fluid exchange between the capillaries and the interstitial tissue is determined by the difference between hydrostatic pressures on each side of the capillary membranes, by the difference between the colloid osmotic pressure of the plasma proteins and that of the interstitial &id and by the physical properties of the capillary membrane, which has the characteristic of an ultrafilter. Quantitative data in support of Starling’s hypothesis were provided by Landis (3), who measured hydrostatic pressure and liquid flow directly in a capillary of the frog mesentery. membrane and demonstrated the relations between these quantities. As is known from the experiments of Starling (2) protein-free fluids are absorbed by the serous membranes especially through blood capillaries, whereas lymphatic vessels are mainly devoted to the absorption of colloids and particles. It seemed of interest to know the pressure-of absorption of fluid in the pleural cavity because in the capillaries of the visceral pleura, that are mainly supplied by the pulmonary artery (5), the hydrostatic pressure has a particular low value (ca. 8 mm Hg) and the colloid osmotic pressure of plasma proteins is ca. 25 mm Hg. A net absorption pressure of ca. 17 mm Hg should therefore be present at the level of the visceral pleura and tha t pressure could account for the negative intrapleural pressure (6). More recently Pappenheimer and Soto-Rivera In order to determine whether or not the (4) measured with accuracy in isolated pernegative intrapleural pressure could result by fused hindlegs of cats and dogs the mean capilthe absorption of fluid through the capillaries lary pressure, the colloid osmotic pressure, the of the visceral pleura the following series of net rate of fluid transfer across the capillary experiments was undertaken with a method Received for publication February 27, 1957. that enabled us to test the Starling hypothesis 1 A preliminary report of this research appeared in on the exchanges of fluid through the capilAtti accad. naz. Lincei, Rend. 20: 106, 1956. laries. 277 by 10.2.32.247 on A ril 9, 2017 http://ajple.physiology.org/ D ow nladed fom 278 E. AGOSTONI, A. TAGLIETTI AND I. SETNIKAR