Background: In assessments of inspiratory muscle endurance using threshold loading devices, previous papers made use of homemade devices that are not commercially available. Objective: To verify the applicability and reproducibility of an inspiratory muscle endurance test using an adaptation of an old model of the Threshold® IMT (not available commercially), with a wide range of pressures, and to analyze its intrinsic inspiratory airflow resistance, threshold pressure characteristics and relative airflow independence in pressure generation during the tests. Methods: An old model of the Threshold® IMT was opened up. Its internal spring was removed and its internal piston was adapted. It was mounted vertically and a system of external weights was installed for load generation. Valves were installed to avoid carbon dioxide re-inhalation. This adaptation was tested by applying different airflows without the presence of the internal piston and loads, to evaluate intrinsic resistance. Different airflows were applied with external loads from 10 to 130 cmH2O, to evaluate the real valve opening pressure and the pressure behavior at large airflows. Results: The mean resistance was 4.8 ± 0.7 cmH2O/L/s, and this increased proportionally with airflow. The real opening pressure was less than the expected value (p = 0.002), as also found in other studies. The pressure behavior after valve opening was similar at all loads: a mean rise of 3.8 ± 2.0 cmH2O for every 1.0 L/s of airflow generated. Conclusion: The proposed adaptation of the Threshold® IMT produced an inexpensive and reliable device for use in inspiratory muscle endurance tests.
respiratory muscles; respiratory function tests; respiratory work
