Volumetric assessment of the capillary filtration coefficient in the cat small intestine.

The capillary filtration coefficient of the cat small intestine was measured in four ways; the conventional measurement was compared with the "zero time extrapolation" technique, and with two methods designed to assess the end of the blood volume shift due to venous pressure elevation. If the capillary filtration coefficient (CFC) was determined using small elevations of venous pressure (10 mm Hg or less), there was good agreement between the techniques. Larger elevations of venous pressure resulted in apparent over-estimates of CFC measured by the conventional technique, probably because of increased "smearing" of the blood volume shift into the component of the response measured as the CFC. In general, larger elevations of venous pressure gave smaller CFC's, and using venous pressure elevations of 10 mm Hg or less, the CFC was greater if the final elevated venous pressure was 10 mm Hg than if it was 20 or 30 mm Hg. Changes in CFC due to noradrenaline and isoprenaline (about 15 ng/ml arterial blood concentration) were in agreement when small venous pressure elevations were used and CFC measured in three different ways.