THE FORCED expiratory volume (F.E.V.), or volume of air expired during a forced expiration from full inspiration in usually 0.75 or 1 second, is widely accepted as a useful measure of ventilatory capacity. Two types of apparatus are in common use for its measurement. The recording spirometer with the fast-moving kymograph has the advantage of providing a permanent record which can later be analysed in various ways.1, 2 The simple spirometer with electronic timer described originally by Gaensler3 and modified by McKerrow et al.4 shows the volume of air expired in a preset time period by a pointer indicating on a scale on the spirometer wheel. The advantages of this type of machine are its greater portability, ease of use, and the provision of the reading immediately without the necessity of analysing a record—features which make it especially valuable for routine clinical use and in field
McKerrow CB, Edwards P. The McKesson Vitalor. JAMA. 1961;177(12):865–867. doi:10.1001/jama.1961.73040380026011a
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