The measurement of total respiratory resistance in small children.

A new, simplified apparatus to determine total respiratory resistance (Rrs) was presented. This apparatus, which utilizes the principle of forced oscillation, is portable, relatively simple to operate and calibrate, and small children can be tested with no apparent difficulties. To investigate the usefulness of the apparatus, total respiratory resistance was measured in 101 healthy children, ages 3-5. Rrs was found to be the highest in the younger children and was decreased with increasing age. The greatest variability in Rrs was found among the youngest children. Linear regression equations for Rrs versus height, weight, and body surface area were established. The best correlation was found between Rrs and height (r = -.325; P less than 0.01) of the children. Utilizing the described apparatus, Rrs can be determined relatively easily without requiring special effort by the subject and is a useful tool to monitor the airways function of young patients.