The relationship between subcutaneous tissue pressures and intramuscular pressures in normal and edematous legs

The interstitial hydrostatic pressure is affecting fluid movements at microvascular level. A disturbance in the Starling equilibrium results in edema formation. The effect of venous outflow and lymphatic obstructions in human, on the interstitial fluid pressures subcutaneously and intramuscularly and the possible interaction between veins and lymphatics was studied. Utilizing a slit-catheter technique, subcutaneous tissue and intramuscular pressures were measured bilaterally in 10 patients with venous outflow obstruction and in 10 patients with lymphatic obstruction. In lymphatic obstruction the subcutaneous tissue pressure was significantly elevated as well as the intramuscular pressure, while in venous obstruction the subcutaneous tissue pressure was normal. The intramuscular pressure was significantly elevated during exercise reaching 60 mm Hg or more, combined with severe pain. Pain did not occur in patients with lymphatic obstruction. This study suggests that in lymphatic obstruction there is also an involvement of either deep lymphatics, venous dysfunction or a combination of both. Intramuscular pressures do not reach the critical level for pain during exercise. In venous obstruction mainly the intramuscular compartment is involved and interstitial pressure reaches values well above 60 mm Hg during exercise, at which level pain occurs, possibly due to tension of painreceptors in the muscle fascias.