Capacitive Modulation of Micropipet Impedance

Quantitative theoretical and experimental evidence is presented suggesting that the saline-filled, glass micropipets employed in microvascular pressure measurements behave electrically as simple, parallel resistor-capacitor combinations in which the capacitance is dependent upon the length of the pipet in contact with the conductive fluid surrounding the tip. Changes in the apparent pipet impedance arising from modest alterations in the immersion length are sufficient to cause zero-level shifts in the measured pressure.