Effects of inspiratory strength training on the detection of inspiratory loads.

Pressure-threshold loads (DeltaPT) are inspiratory force-related loads, which contrast with resistive loads (DeltaR), 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 DeltaPT but have less effect on detection of DeltaR. DeltaR and DeltaPT 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 DeltaR detection threshold and DeltaR-breathing pattern. IMST decreased DeltaPT detection percent and DeltaPT-breathing pattern. Comparing DeltaR and DeltaPT at the same mouth pressure-generating level, the detection percent was different. We conclude that IMST affects the detection of DeltaPT, but not DeltaR. 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.