Valores normativos e equações de referência nacionais para as medidas de performance muscular inspiratória do Test of Incremental Respiratory Endurance (TIRE)

Abstract

Introduction: Maximal inspiratory pressure (MIP) measurements are traditionally obtained to reflect the strength of an individual's inspiratory muscles. Although this classic measure of inspiratory muscle performance is widely accepted, MIP data only provide information on muscle strength, without encompassing other key elements of inspiratory muscle performance. The Test of Incremental Respiratory Endurance (TIRE) overcomes this limitation by allowing a more comprehensive assessment of the inspiratory muscles, offering not only MIP measurements but also sustained maximum inspiratory pressure (SMIP), inspiratory duration (ID), and fatigue susceptibility (Fatigue Index Test or FIT). Despite the widespread popularity and clinical use of these variables globally, normative values and reference equations for TIRE measurements in the Brazilian population did not previously exist. Objective: To determine normative values and establish national reference equations for TIRE measures of inspiratory muscle performance (i.e., MIP, SMIP, ID, and FIT) in the Brazilian population. Methods: This was a prospective cross-sectional study. The study included a convenience sample of 120 healthy individuals (60 men and 60 women) aged between 20 and 80 years. Once participant eligibility was confirmed, data collection began with spirometry, following international guidelines. After confirming the absence of ventilatory disorders, the evaluation continued using a standardized assessment form containing identification, sociodemographic, anthropometric, and clinical data. The MIP, SMIP, ID, and FIT variables were then obtained using the TIRE method via the PrO2, an electronic pressure manometer. Correlation and multivariate regression analyses were performed to identify significant predictors and produce reference equations for MIP, SMIP, ID, and FIT. Results: The multivariate regression models explained 26% to 41% of the variance in inspiratory muscle performance measures (MIP, SMIP, ID, and FIT). Age, sex, and weight were significant predictors in the equations, with age having the greatest impact. Including physical activity level (IPAQ) improved the models' explanatory power. Men exhibited higher mean values across all variables. Conclusion: This study presented the first normative values and predictive equations for MIP, SMIP, ID, and FIT obtained via TIRE in healthy Brazilians. The results are applicable in clinical practice and research, contributing to the clinical and prognostic assessment of inspiratory muscle performance in individuals aged 20 to 80 years.