PORTABLE PEAK FLOW METERS - PHYSICAL CHARACTERISTICS, INFLUENCE OF TEMPERATURE, ALTITUDE, AND HUMIDITY

Little is known about the linearity of portable peak flow meters, or a bout physical gas factors affecting peak expiratory flow (PEF) reading s. We therefore tested five portable peak flow meters of three types i n an altitude chamber (sea level to 5,500 m) and in a climate chamber at sea level (7-37 degrees C) to determine the influence of the physic al conditions of the gas on the reading of the meters. The nonlinear r esponse of the variable orifice meters was confirmed and, when this wa s corrected for, the readings of these meters were found to be signifi cantly reduced by higher altitude and lower temperature. The readings from a turbine type of peak now meter were not affected by altitude bu t were reduced at low temperature. A mathematical model for the variab le orifice meters could correct for both their nonlinear behaviour and the effect of gas density (altitude, temperature and humidity). The m odel showed that correction is not necessary for the differences in ga s conditions between calibration and taking of measurements under norm al laboratory conditions. All the meters tested had impedances higher than recommended (0.05 kPa.l(-1).s) and this may influence PEF at high flows. The mean uncorrected PEF of six healthy subjects when measured with a Mini Wright peak flow meter at sea level and at 3,000 m fell b y 5%, but the mean corrected PEF increased by 12%. This increase in PE F was about 60% of that predicted for fully density-dependent flow and agreed with the findings of other similar studies. We conclude that o rifice meters give satisfactory PEF readings at different altitudes an d temperatures, provided adequate correction is made for their nonline arity and the influence of gas density.