Thermal problems in plethysmography and pressure/volume recording.

Where volume changes are recorded as the concomitant changes in pressure, modern, fast-responding pressure transducers might record not only the pressure changes due to volume changes in the measured object but also the heat of compression, showing itself as an overshoot or hysteresis phenomenon in the calibration curves. Introduction of an effective heat sink (e.g. copper mesh) within the air space in the plethysmograph might absorb this heat and thereby diminish the overshoot phenomena. The effect is not of practical importance in classical venous occlusion plethysmography where rapid changes only contribute to a smaller part of the total volume change during venous occlusion. When rapid changes, as in volume pulse recordings, are to be evaluated, the effect must be taken into consideration and should be reduced.