Method for continuous recording of hydrostatic exchange vessel pressure in cat skeletal muscle

A venous microcannulation technique applied to the cat gastrocnemius muscle was developed which, based on morphological and functional demonstrations of anastomotic connections between two supplying segmental vascular circuits at the level of capillaries and/or post-capillary venules, seems to permit continuous recordings of hydrostatic pressure (denoted Pcvenule) transmitted from such anastomoses, that is, from a site close to the main fluid exchange vessels. For validity tests, such Pcvenule recordings were compared with simultaneous estimates of capillary pressure (Pc) with the isogravimetric technique (Pciso) and, further, with data for experimentally evoked changes of Pc derived from volumetric recordings of net transvascular fluid flux divided by the capillary filtration coefficient (delta Pcvol). Simultaneously obtained data for Pcvenule and Pciso showed close agreement, and the Pcvenule and Pcvol data showed a highly significant linear correlation over a wide range of Pc changes. These results indicate that reliable estimates of Pc can be obtained with the Pcvenule method. It allows for continuous Pc recordings without interfering with normal vascular reactivity and can be applied to non-isogravimetric conditions and combined with simultaneous observations of whole-organ transvascular fluid exchange. At normal arterial and venous pressures and vascular tone, Pcvenule averaged 16.2 +/- 0.2 mm Hg, at which a Starling fluid equilibrium prevailed, and increased with decreasing vascular tone, resulting in net transvascular fluid filtration.