Development of an automated pressure‐threshold loading device for evaluation of inspiratory muscle performance

In 1996 Johnson et al. (Medicine and Science in Sports and Exercise, 28, 1129–1137) concluded that respiratory muscle fatigue may limit human performance whereby the work done by the respiratory muscles to drive the ventilatory pump might significantly affect exercise tolerance. As a result of these and similar findings there is a growing interest in respiratory muscle performance. However, methods for appraising inspiratory muscle function which are relevant to exercise performance are limited. The purpose of the present paper is to describe the development and validation of an automated pressure‐threshold loading device for use in evaluating the maximum incremental performance of the inspiratory muscles and other endurance‐based measures of inspiratory muscle performance. The device utilizes a stepper motor to vary the resistance of a spring‐loaded poppet valve arrangement, thereby permitting automatic selection of various inspiratory muscle loading profiles. The device is accurate to within 1.5% (0.1–1.5 cmH2O) of selected load across its range and permits continuous incremental loading with a resolution of 0.1 cmH2O·min–1. This apparatus allows an endurance‐based measure of inspiratory muscle endurance to be obtained which is distinctly different from measures of inspiratory muscle strength such as peak inspiratory mouth pressure. Furthermore, reproducible measures can be attained without the need to regulate breathing pattern or to maintain isocapnia. In summary, the current device is useful when a simple yet reproducible endurance‐based measure of inspiratory muscle performance is required.