TrueForce: a new digital manometer to measure maximal respiratory pressures at functional residual capacity

Purpose: This study aimed to develop a digital manometer capable of measuring the maximal respiratory pressures at functional residual capacity level—pulmonary volume where the pressures related to the elastic recoil of the respiratory system are minimized—and to validate its functionally in healthy individuals. Methods: The proposed device was built based on three main components: the hardware, electronic part; the firmware, computational part; and the mechanics, composed of the device housing, connections, and filters used. Also, the software was updated to allow measurements at functional residual capacity. Functional validation was performed with 30 healthy individuals (15 men), aged between 20 and 40 years. The intraclass correlation coefficient (ICC) verified concurrent validity and test-retest reliability reproducibility, and pressures at functional residual capacity were compared to pressures at residual volume and total lung pulmonary capacity, by paired t test. Results: The developed device met the desired functional and non-functional requirements. The volume calculated from the acquired flow values showed variability of less than 2%. There was total agreement between the expected and obtained pressures. Regarding functional validation, an ICC ≥ 0.84; p < 0.001 was observed for both concurrent validity and test-retest reliability. Measurements at functional residual capacity were significantly lower than measurements performed at residual volume and total lung capacity (p < 0.05). Conclusion: The TrueForce can be considered a valid and reliable instrument for measures of maximum respiratory pressures performed in the functional residual capacity, and it can be used in clinical trial research. © 2021, Sociedade Brasileira de Engenharia Biomedica.