Journal of Applied Physiology, Vol 62, Issue 2 837-843, Copyright © 1987 by American Physiological Society
Respiratory phase detection and delay determination for breath-by-breath analysis
U. Boutellier, T. Kundig, U. Gomez, P. Pietsch and E. A. Koller
The delay between air flow and gas concentration signals is generally
assumed to be constant within a breath as well as from breath to breath,
but it was not possible to examine the constancy of the delay with the
delay determination techniques so far available. Thus we developed new
methods for respiratory phase detection and delay determination. The
presented algorithm for the detection of the start of inspiration and
expiration (phase detection) replaces the generally used valve assembly
with two pneumotachographs. Now, the pneumotachograph is used in a
bidirectional mode, but with a volume criterion for phase detection
replacing the less reliable threshold criterion. To measure the delay
between flow and gas concentration signals, a test gas is periodically
injected as a marker. This test gas contains less N2 than ambient air.
Therefore, the delay is determined as time between the moment of injection
and the drop of N2. These two methods rendered it possible to examine delay
variations and their consequences. The investigation of various breathing
patterns demonstrated that the usually assumed errors caused by delay
uncertainty are underestimated. We suggest reliance on a breath-by-breath
delay determination to account for delay variations.
