Some Observations on Peak Expiratory Flow

Abstract

The peak flow meter (Wright and McKerrow, 1959) was originally conceived as a simple port- able method of estimating forced expiratory volume (F.E.V.). However, the correlation with F.E.V. and with maximum voluntary ventilation (M.V.V.) was not always very close, and the peak flow meter reading was therefore advocated as a measure of "ventilatory capacity" in its own right. The present paper reports some normal peak flow readings obtained with the Wright meter: such values are influenced not only by airway resistance but also by the pressure developed by the thoracic musculature, and the results obtained depend largely on co-operation from the patient. I have used peak flow read- ings, obtained before and after introduction of an external resistance, to calculate a value for airway resistance that is less dependent on subjective co-operation and muscular power. The frequency response characteristics of the Wright peak flow meter do not permit measurements with an external resistance; however, if peak flow readings are obtained by high frequency equip- ment, such as a screen pneumotachograph, and a small external resistance is used, the calculated airway resistance does not differ systematically from interrupter valve values.