CHANGES IN SUBCUTANEOUS INTERSTITIAL FLUID PRESSURE, TISSUE OXYGENATION, AND SKIN RED-CELL FLUX DURING VENOUS CONGESTION PLETHYSMOGRAPHY INMEN

Objective: Venous congestion plethysmography enables noninvasive asses sment of microvascular filtration capacity (K-f) in limbs. However, in creases in fluid filtration might alter the balance of Starling forces ; for example, progressive increases in interstitial fluid pressure (P -i) would It duce net fluid flux, thus underestimating K-f. Furthermor e, elevation of cuff pressure to values close to diastolic blood press ure. as used in the protocol, may by itself impair tissue perfusion wi th unknown effects on tile microvascular parameters investigated. Meth ods: P-i was measured in healthy volunteers (n = 14) with a modified ' 'Wick in needle'' technique during small (8 mm Hg) cumulative increase s in venous pressure (0-95 mm Hg). Changes in the hemoglobin (Hb) conc entration, oxygenated hemoglobin (HbO(2)) concentration, and oxidized cytochrome aa3 concentration were assessed in the calf using noninvasi ve near-infrared spectroscopy. Skin red blood cell flux close to the s train gauge was evaluated by laser Doppler fluxmetry. Results: P-i at control was -0.89 +/- 0.8 mm Hg and during elevation of venous pressur e remained constant until a cuff pressure of 30 mm Hg was reached. It rose thereafter to 1.57 +/- 1.3 mm Hg (mean +/- SD). Skin red cell flu x was significantly reduced when cuff pressure exceeded 30 mm Hg and, following cuff deflation, evidence of reactive hyperemia was obtained. Hb concentration increased significantly as a result of venous pressu re elevation. No change in either HbO(2) or cytochrome aa3 concentrati on was observed as long as cuff pressure remained under diastolic bloo d pressure. Conclusions: The small increase in P-i together with an ab sence of impaired tissue oxygenation during the venous congestion plet hysmography protocol described by Gamble et al. supports the contentio n thar this protocol enables accurate assessment of filtration capacit y.