Changes in Subcutaneous Interstitial Fluid Pressure,Tissue Oxygenation,and Skin Red Cell Flux during Venous Congestion Plethysmography in Men

Objective : Venous congestion plethysmography enables noninvasive assessment of microvascular filtration capacity (K_f) in limbs. However, increases in fluid filtration might alter the balance of Starling forces; for example, progressive increases in interstitial fluid pressure (P_i) would reduce net fluid flux, thus underestimating K_f. Furthermore, elevation of cuff pressure to values close to diastolic blood pressure, as used in the protocol, may by itself impair tissue perfusion with unknown effects on the microvascular parameters investigated. Methods : P_i was measured in healthy volunteers (n = 14) with a modified “Wick in needle” technique during small (8 mm Hg) cumulative increases in venous pressure (0–95 mm Hg). Changes in the hemoglobin (Hb) concentration, oxygenated hemoglobin (HbO₂) concentration, and oxidized cytochrome aa3 concentration were assessed in the calf using noninvasive near-infrared spectroscopy. Skin red blood cell flux close to the strain gauge was evaluated by laser Doppler fluxmetry. Results : P_i at control was ?0.89 ± 0.8 mm Hg and during elevation of venous pressure 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 flux was significantly reduced when cuff pressure exceeded 30 mm Hg and, following cuff deflation, evidence of reactive hyperemia was obtained. Hb concentration increased significandy as a result of venous pressure elevation. No change in either HbO₂ or cytochrome aa3 concentration was observed as long as cuff pressure remained under diastolic blood pressure. Conclusions : The small increase in P_i together with an absence of impaired tissue oxygenation during the venous congestion plethysmography protocol described by Gamble et al. supports the contention mat this protocol enables accurate assessment of filtration capacity.