Some new developments in continuous microperfusion technique.

Nine years ago we designed the prototype of a microperfusion pump for calibrated perfusions of tubular segments in vivo(l). The apparatus consists, in principle, of a metal pin whiclh is driven into the fluid-filled shaft of a micropipet. Since the base of this pipet is sealed, the fluid may escape with a constant flow rate only through the tip of the capillary. In the meantime many improvements were developed both in the apparatus and in the perfusion technique. I should like to start this review with a brief description of new details in the equipment. Formerly the pump was driven by an electric synchronous motor and the pump rate was adjusted by regulating the speed of the motor. This resulted in a reliable reproducibility of the pumping rate. However, the constancy of perfusion rate was dependent on a highly stable electric power supply. Furthermore, calibration of the pump was somewhat troublesome since it had a sigma-shaped calibration curve with only a relatively short region in which the pumping rate could be precisely established (Fig. 1). In the new system, constancy of perfusion rate is stabilized by a self-regulating electronic device. Because the calibration curve has a linear characteristic, the calibration procedure is simplified. The new apparatus was built by V. Roslicek and Wolfgang Hampel, the engineer who previouisly had helped us to develop the first type of microperfusion equipment. The new principle is depicted schematically in Fig. 2. In spite of the great advantages whlich the new apparatus provide, it should be emphasized that the most frequent pitfalls encountered with the microperfusion pump remain the same. The most critical point is the careful mounting of the microcapillary to the pump. When the base of the glass capillary does not exactly fit into the Teflon seal around the forward-moving metal pin, then the fluid displaced by the pin does not quantitatively escape througlh the tip of the