Introduction to a new inspiratory threshold loading device

Inspiratory threshold loading is an important tool in assessing inspiratory muscle function and has been widely used in studies of respiratory mechanics. A simple system was designed to provide a pure and precise inspiratory threshold load. The inspiratory threshold loading system comprises a Row generator attached via a pressure chamber, to the inspiratory port of a Hans-Rudolph valve. By limiting the circulation of air generated by the Bow generator between the room and the pressure chamber, different levels of negative pressure are produced in the pressure chamber and applied to the inspiratory valve, An inspiratory pressure equal to the negative pressure in the chamber has to be generated to open the inspiratory valve for Bow, The system was tested in four subjects by measuring mouth pressure (Pm), threshold pl.ess;re (Pth) and valve resistance (R), The Pm at the beginning of inspiratory Row was defined as the opening pressure (Pop), The Pth was constant throughout inspiration, Pop was linearly related to Pth (p<0,0001, with slopes within 2% of identity and intercepts within +/-0.2 cmH(2)O, R was between 0.7-1.1 cmH(2)O . L-1 . s(-1) under all conditions and was independent of both Pth (p=0.76) and inspiratory Row (p=0.24), The results demonstrate that this system can provide a constant inspiratory threshold load throughout inspiration with little Bow resistance, and is therefore ideal for respiratory studies.