Errors in the measurement of vital capacity. A comparison of three methods in normal subjects and in patients with pulmonary emphysema.

Abstract

<b>Hutchison, D. C. S., Barter, C. E., and Martelli, N. A. (1973).</b><i>Thorax</i>, <b>28</b>, 584-587. <b>Errors in the measurement of vital capacity: a comparison of three methods in normal subjects and in patients with pulmonary emphysema.</b> Three methods of measuring the vital capacity have been compared in six normal subjects and in six with pulmonary emphysema, according to a randomized design. The methods were (<i>a</i>) the inspiratory vital capacity (IVC), (<i>b</i>) the expiratory vital capacity (EVC), and (<i>c</i>) the forced vital capacity (FVC). In normal subjects, there was a small but significant difference between the methods. The residual standard deviation derived from analysis of variance was 94 ml (coefficient of variation 1.7%). A slight but significant rise in vital capacity with repeated effort was observed. In emphysematous subjects, there was no significant difference between the IVC and EVC methods. The FVC gave values which were, on average, approximately 0.5 litre less than those obtained by the other methods. The standard deviation in all three methods was substantially greater than for the normal subjects. The FVC is not a suitable method for the measurement of vital capacity in patients with pulmonary emphysema. The EVC is satisfactory, provided it is used with caution, but in practice the IVC is the preferred method.