Determination of total respiratory resistance in health and disease by added external resistance.

Previous studies have indicated that total respiratory resistance (Rrs) can be measured by addition of an external resistor. In an earlier study, the apparatus used to accomplish this included a multiperforated steel plate. In this study, we sought to improve the device. Details of this are given in this article. With this device, resistance was found to be reproducible over five consecutive days, and was sensitive to the increase in airway resistance induced by head and neck flexion. We also report on a comparison between this method and a commercially available device that works on the "interruptor" principle. There was no significant difference in either mean or variance of resistance between the two methods. The instrumentation required for the newly designed method is minimal, and its operation is simple. Furthermore, the measurement can be performed without invasive procedures during tidal breathing.