Temperature and CO2 effect on phrenic activity and tracheal occlusion pressure.

The present investigation was undertaken to study the interaction of CO2 and body temperature on phrenic activity (moving average) and tracheal occlusion pressure. Studies were performed on spontaneously ventilated cats anesthetized with pentobarbital sodium at different body temperatures (32-41 degrees C) while breathing room air, 2 and 4% CO2 in 50% O2. At any given chemical drive, increased body temperature caused a similar increase in rate of phrenic activity and tracheal occlusion pressure, while their peak values remained virtually unchanged. At any given body temperature, increased chemical drive caused an increase in both rate of rise and peak values of phrenic activity and tracheal occlusion pressure. These results confirm previous findings that body temperature affects the rate of rise of the central inspiratory activity (CIA), but not the inspiratory "off-switch" threshold, while CO2 increases both the rate of rise of CIA and off-switch threshold. In addition the results indicate that tracheal occlusion pressure provides a similar index of CIA as "integrated" phrenic activity.