Am. J. Respir. Crit. Care Med.,
Volume 161, Number 6, June 2000, 1887-1896
Peak Expiratory Flow Profiles Delivered by
Pump Systems
Limitations due to Wave Action
MARTIN R.
MILLER,
BARRIE
JONES,
YONG
XU,
OLE FIND
PEDERSEN,
and
PHILIP H.
QUANJER
Department of Medicine and School of Manufacturing and Mechanical Engineering, University of Birmingham, Birmingham,
United Kingdom; Institute of Environmental and Occupational Medicine, University of Århus, Århus, Denmark;
and Department of Physiology, University of Leiden, Leiden, The Netherlands
Pump systems are currently used to test the performance of both
spirometers and peak expiratory flow (PEF) meters, but for certain
flow profiles the input signal (i.e., requested profile) and the output profile can differ. We developed a mathematical model of
wave action within a pump and compared the recorded flow profiles with both the input profiles and the output predicted by the
model. Three American Thoracic Society (ATS) flow profiles and
four artificial flow-versus-time profiles were delivered by a pump,
first to a pneumotachograph (PT) on its own, then to the PT with
a 32-cm upstream extension tube (which would favor wave action), and lastly with the PT in series with and immediately downstream to a mini-Wright peak flow meter. With the PT on its own,
recorded flow for the seven profiles was 2.4 ± 1.9% (mean ± SD)
higher than the pump's input flow, and similarly was 2.3 ± 2.3%
higher than the pump's output flow as predicted by the model.
With the extension tube in place, the recorded flow was 6.6 ± 6.4% higher than the input flow (range: 0.1 to 18.4%), but was
only 1.2 ± 2.5% higher than the output flow predicted by the model (range: 
0.8 to 5.2%). With the mini-Wright meter in series, the flow recorded by the PT was on average 6.1 ± 9.1% below the input flow (range: 23.8 to 2.5%), but was only 0.6 ± 3.3% above the pump's output flow predicted by the model
(range: 5.5 to 3.9%). The mini-Wright meter's reading (corrected for its nonlinearity) was on average 1.3 ± 3.6% below the
model's predicted output flow (range: 9.0 to 1.5%). The mini-Wright meter would be deemed outside ATS limits for accuracy for
three of the seven profiles when compared with the pump's input
PEF, but this would be true for only one profile when compared
with the pump's output PEF as predicted by the model. Our study
shows that the output flow from pump systems can differ from the
input waveform depending on the operating configuration. This
effect can be predicted with reasonable accuracy using a model
based on nonsteady flow analysis that takes account of pressure
wave reflections within pump systems.
