Interstitial fluid pressure in human skin measured by micropuncture and wick-in-needle

Interstitial fluid pressure (Pi) has been measured in human skin by micropipettes (tip diam. 2-4 micron) and compared to pressures obtained by wick-in-needle technique. The micropipettes were connected to a servocontrolled counterpressure system (Wiederhielm) and were introduced into the skin distally at the dorsum of the fifth finger after immobilization of the upper extremity. The wick-in-needle was introduced at the dorsum of the hand. With the finger at heart level and at a room temperature of 24 +/- 1 degree C, the mean Pi measured by micropuncture was -3.1 mmHg (range -5 to -0.5 mmHg), while the corresponding mean Pi measured with wick-in-needle was 0.0 mmHg (range -1.7 to +3 mmHg). During venous stasis Pi increased as measured by both methods, but the increase recorded by micropuncture was largest. It is concluded that the wick-in-needle probably overestimates Pi in the normally hydrated human skin of the hand due to inflammation at the implantation site, and that the overestimation diminishes as tissue hydration increases.