A THRESHOLD LOADING DEVICE FOR TESTING OF INSPIRATORY MUSCLE PERFORMANCE

Threshold loading is a method of incrementally loading the inspiratory muscles, which requires development of an adjustable threshold pressu re (Pth) before air will flow, In the ideal device, flow is independen t of pressure once Pth is exceeded, A ''weighted plunger'' apparatus i s commonly used, but devices described previously perform unreliably a t high inspiratory load, We have modified this apparatus using the dia phragm and valve seating from a threshold valve used to deliver positi ve airway pressure (AMBU 10, AMBU International, Denmark) to yield imp roved pressure-flow characteristics. With this device, there was a lin ear relationship between Pth and weight on the plunger (r=0,998), and flow was largely independent of pressure once Pth was exceeded: pressu re developed at an inspiratory flow of 1.3+/-0.1 l . s(-1) was 13.6+/- 7.0% below Pth. Our modified weighted plunger apparatus allows consist ent and reliable threshold loading of inspiratory muscles, even at hig h inspiratory loads.