Methods for averaging irregular respiratory flow profiles in awake humans

Respiratory flow profiles have been of interest as an output of the respiratory controller. In determining average flow profiles, however, previous methods that align individual breaths in the time domain are susceptible to distortions caused by the great variability, both between breaths and within breaths. We aimed to develop a method for determining typical flow profiles that circumvents such distortions. Our method aligns different breaths by phase of respiratory cycle, which is defined as the angle associated with the point on the normalized flow-volume diagram (a phase-plane plot). Over a number of breaths, median values for flow, volume, and elapsed time from the start of the breath at each phase angle are determined. Because these estimates are mutually semi-independent and in general violate the laws of mass balance, an adjustment was performed such that the volume was precisely the time integral of the flow. The method produced typical flow profiles with characteristics that were significantly closer to the mean values obtained from the individual cycles than those obtained by the technique of Benchetrit and co-workers (Benchetrit G, Shea SA, Dinh TP, Bodocco S, Baconnier P, and Gut A, Respir Physiol 75: 199-210, 1989), which reconstructs the typical flow profile from Fourier coefficients.