Suggested methods of testing and standards of resistance for respiratory protective devices

¹ Department of Medicine, University of Birmingham, Birmingham, England

There is need to establish a method of bench testing and standards of allowable resistance for respiratory protective devices. It is suggested that a technique for recording pressure-volume diagrams using a sine-wave pump is satisfactory. Standards of resistance are proposed which are expressed as total rate of respiratory work done on the apparatus, and the percentage of this which is done in expiration. It is suggested that apparatus should be tested at minute volumes up to 100 l/min. Other information derivable by this technique is discussed. Fundamental principles of aerodynamics are also considered in relation to closed-circuit breathing apparatus. It is shown that under conditions of practical use of such systems, flow is only laminar in rare instances. Useful information can be gained about the frictional resistance of a respiratory circuit from simple bench tests at various constant rates of flow of air, and from the results of such experiments theoretical calculations can be made of the rate of work done. They are shown to correspond well with the measured rates of work done by human volunteers when breathing against the same resistance at all levels of exertion on a treadmill.