Effects of equipment and technique on peak flow measurements

Abstract

Background: Different lung function equipment and different respiratory manoeuvres may produce different Peak Expiratory Flow (PEF) results. Although the PEF is the most common lung function test, there have been few studies of these effects and no previous study has evaluated both factors in a single group of patients.

Methods: We studied 36 subjects (PEF range 80-570 l/min). All patients recorded PEF measurements using a short rapid expiration following maximal inspiration (PEF technique) or a forced maximal expiration to residual volume (FVC technique). Measurements were made using a Wright's peak flow meter, a turbine spirometer and a Fleisch pneumotachograph spirometer.

Results: The mean PEF was 8.7% higher when the PEF technique was used (compared with FVC technique, p < 0.0001). The mean PEF recorded with the turbine spirometer was 5.5% lower than the Wright meter reading. The Fleisch spirometer result was 19.5% lower than the Wright reading. However, adjustment of the Wrights measurements from the traditional Wright's scale to the new EU Peak Flow scale produced results that were only 7.2% higher than the Fleisch pneumotachograph measurements.

Conclusion: Peak flow measurements are affected by the instruction given and by the device and Peak Flow scale used. Patient management decisions should not be based on PEF measurement made on different instruments.

Figure 1

Wright meter – both techniques. Comparison of PEF measurements on Wright Peak Flow meter using "Peak Flow technique" (square symbols) or "FVC technique" (triangles). The values shown are the best of two measurements with each technique. Patients are arranged on the basis of increasing PEF measured using the "PEF technique".

Figure 2

Three devices using "peak flow technique". Comparison of PEF measurements using "Peak Flow technique" on three devices; Wright Peak Flow meter (square symbols), Micro-Medical turbine spirometer (triangles) and Vitalograph Fleisch pneumotachograph spirometer (circles). The values shown are the best of two measurements with each device. Patients are arranged on the basis of increasing PEF measured using the Wright's meter with "PEF technique".

Figure 3

"Peak Flow technique" with Wright meter and Fleisch pneumotachograph spirometer and conversion to new EU scale. Comparison of PEF measurements using "Peak Flow technique" on Wright meter (closed square symbols) or Fleisch pneumotachograph spirometer (circles). The open squares are Wright values converted to the new EU scale. The values shown are the best of two measurements with each technique. Patients are arranged on the basis of increasing PEF measured using the Wright meter.