Assessment of global function of respiratory muscles

The breathing cycle is controlled by the respiratory muscles that periodically alter the chest volume. A standardized procedure for evaluation of respiratory muscle performance does not exist and many clinics have developed simple techniques to measure mouth pressure at either total lung capacity, functional residual capacity or residual volume as an indices of respiratory muscle function. The objective of this work is to develop a simple noninvasive diagnostic technique for measurement of global respiratory function. For this purpose we built a fully-computerized system that allows for simultaneous measurement of inspired-expired airflow, lung volume and mouth pressure. Mouth pressure is acquired while inspired or expired airflow is obstruct at any desired lung volume, and during the initial period following obstruction. This should provide data that reflects the strength and endurance of respiratory muscle at various lung volumes. The results for normal subjects show that relatively high mouth pressures can be sustained for as long as 10 seconds after flow interruption at any lung volume However, a defined maximal pressure can not be observed, and rather an averaged plateau or parabolic can be obtained from the digitized data. In addition, mouth pressure varies with lung volume.