Effects of Inspiratory Strength Training on the Detection of Inspiratory Loads

Pressure-threshold loads (Delta PT) are inspiratory force-related loads, which contrast with resistive loads (Delta R), are airflow-dependent loads. If detection of respiratory loads is a function of the background load, then pressure-threshold type inspiratory muscle strength training (IMST) would affect the detection of Delta PT but have less effect on detection of Delta R. Delta R and Delta PT detection and ventilatory responses were measured in healthy volunteers. IMST consisted of 4 sets of 6 breaths per day for 4 weeks, at 75% of maximal inspiratory pressure (MIP). MIP increased and a measure of inspiratory dirve, the mouth pressure generated in the initial 100 msec of an occluded inspiration (P-0.1), decreased after IMST. IMST significantly increased MIP after 4 weeks of training. IMST did not change Delta R detection threshold and Delta R-breathing pattern. IMST decreased Delta PT detection percent and Delta PT-breathing pattern. Comparing Delta R and Delta PT at the same mouth pressure-generating level, the detection percent was different. We conclude that IMST affects the detection of Delta PT, but not Delta R. These results also suggest that mouth pressure is not the primary determinant of the inspiratory load detection. The significance of these results is that inspiratory pressure generating capacity can be increased by our pressure threshold training and this increase in respiratory muscle strength increases the ability of pulmonary patients to compensate for increased respiratory load and modulates the threshold for detection of changes in pulmonary mechanics.