Agreement and Reliability of a Digital Incentive Spirometer Compared with a Volume-Oriented Incentive Spirometry Device Across Different Age Groups

Incentive spirometry is widely used in respiratory rehabilitation to enhance lung expansion and prevent postoperative pulmonary complications. However, conventional devices, including volume-oriented and flow-oriented incentive spirometers, rely on subjective visual interpretation, which may limit measurement accuracy and clinical utility. A digital incentive spirometer (DIS) has been developed to provide objective, real-time measurements of inspiratory volume. This study aimed to evaluate the agreement and reliability between the DIS and a volume-oriented incentive spirometer (VIS) across different age groups. A cross-sectional study was conducted in 150 participants aged 7–80 years, stratified into five age groups with equal sex distribution. Inspiratory volume was measured simultaneously using both devices. Agreement was assessed using Bland–Altman analysis, and reliability was evaluated using intraclass correlation coefficients (ICC). The DIS demonstrated good overall reliability (ICC = 0.868, 95% CI: 0.821–0.903). The mean difference was 48.69 mL, indicating slight overestimation by the DIS. However, the limits of agreement were wide (−469.24 to 566.63 mL), suggesting limited interchangeability. Reliability varied across age groups, with the highest ICC in older adults and the lowest in adolescents. The DIS showed good reliability but limited agreement with the VIS.