Relationship of transdiaphragmatic pressure and latencies for detecting added inspiratory loads

The purpose of this investigation was to measure changes in transdiaphragmatic pressure (Pdi) developed during graded elastic (E) and resistive (R) loaded breaths and to correlate the emergence of such changes with the load-dependent alterations in latency for detection (Tdet). Five healthy adults were studied using three protocols, i.e., graded E, graded R, and graded R in the presence of elevated background R. In each protocol, loads were added for single inspirations, 10 times in random order and separated by three to five unloaded breaths. Subjects pressed a signal marker as soon as loads were detected. Inspiratory flow (VI), inspired volume (VI), mouth pressure, and Pdi of loaded breaths and the preceding unloaded breaths were recorded and computer averaged. Patterns of VI and VI were not altered prior to detection of the smallest added E and R loads but decreased with the higher loads. Group mean patterns of Pdi showed graded increases during loaded breaths. Augmentation of Pdi preceded Tdet and occurred earlier as Tdet decreased with graded E and R loads. Elevating the background R delayed both Tdet of added R and the augmentation of Pdi. Results are consistent with the hypothesis that load-induced changes in diaphragmatic tension may play a sensory role in detection of inspiratory loads.