OPTICAL MEASUREMENTS OF LUNG MICROVASCULAR FILTRATION COEFFICIENT USING POLYSULFONE FIBERS

Lung fluid balance, which is governed by the product of net transvascu lar pressure difference and lung filtration coefficient, can be altere d in pulmonary diseases. A simple measurement of the lung filtration c oefficient (K-fc) would be clinically useful and has been examined by several researchers. Current methods of determining K-fc include gravi metric measurement in isolated lungs and lymph node cannulation, neith er of which can be extended to human use. Optical measurements of prot ein concentration changes in venous blood can be combined with pressur e measurements to calculate K-fc. Blood, though, contains red corpuscl es, which tend to absorb and scatter light, obscuring these optical me asurements. in this study, an optical system was developed in which a polysulfone filter cartridge was used to remove red blood cells before the filtrate was passed through a spectrophotometer. Absorbance chang es caused by changes in concentration of albumin labeled with Evans Bl ue were monitored at 620 nm after venous pressure was elevated by abou t 13 cm H2O. Optical measurements of K-fc averaged 0.401 +/- 0.074 (ml /min cm H2O 100 g DLW) for an isolated canine lung. Optical measuremen ts of K-fc (0.363 +/- 0.120 ml/min cm H2O 100 g DLW) were made for the first time in an intact, closed chest sheep in which pulmonary pressu re was altered by inflating a Foley balloon in the left atrium. We con clude that absorbance and scattering artifacts introduced by red blood cells can be eliminated by first filtering the blood through polysulf one fibers. K-fc measurements using the optical method are similar to values obtained by others using gravimetric methods. Finally, we have demonstrated that the technique can be used to estimate K-fc in an int act animal.