A programmable, microprocessor-controlled temperature stage for burn and freezing studies in the microcirculation

Abstract

A programmable, microprocessor-based thermal control system is interfaced with a specially fabricated variable-temperature light microscope stage to deliver precise burns and freezes to mesentary microcirculatory preparations. The stage is designed around a hollow, transparent pedestal through which both heating and cooling fluxes can be transmitted directly to a tissue which is to be observed. Cooling is produced by a flow of cryogenically refrigerated gas through the stage, whereas heating is effected by the dissipation of electrical energy in a resistive semiconductor film spray deposited onto the surface of a glass plate on which the tissue is placed. Various desired thermal protocols are achieved by continual adjustment between the magnitudes of refrigeration and heating loads imposed simultaneously upon the system. The specimen temperature is monitored at a sampling rate of 512/sec by a microthermocouple mounted in close thermal communication with the tissue, and is used as the input signal to the microprocessor control system. A unique temperature/time profile is selected and assigned to the programmable controller at the time of each individual experiment. In the present configuration the performance limits of this apparatus provide for a tissue temperature range of −48 to 80° with linear thermal transients between 1 and 6000°/min.