A comparison of manual and automated methods of measuring airway resistance and thoracic gas volume.

An automated method of measuring airways resistance (Raw) and thoracic gas volume (Vtg) by whole body plethysmography using a digital computer is described. The results obtained by this method are compared with those obtained by an experienced observer and the results of consistency tests on the two methods are given. There was wide variability in the values of Raw obtained using each method, and no significant differences were found between the two methods. The values of Vtg obtained by them were highly correlated, but the results obtained manually were higher than those obtained automatically by an amount proportional to the volume. The consistency of the computer measurements was shown to be greater than that of the manual method. A significant decrease between successive measurements of Raw in some subjects was noted in the manual observations but not in those derived from the automated method. The new method is suitable for the rapid determination of Raw and Vtg.