Measures of Respiratory Pattern Variability

The possible causes of breath to breath variability in the pattern of breathing have been discussed in a recent review[1]. This variability may be due to stochastic factors (e.g., random disturbances), to the dynamical behaviors of chemoreflex and mechanoreflex feedback loops, or to interactions between these stochastic and dynamical non-stochastic mechanisms. The recognition that the type and structure of breath to breath variability in respiratory pattern may reflect the actions of various underlying respiratory control mechanisms has motivated the desire to quantity this variability. Although some prior work has attempted to separate respiratory variability into its stochastic and various non-stochastic components[2], such a separation is difficult in general and is not considered here. A more fundamental question is whether a change in state or condition of a subject alters overall respiratory pattern variability. This report will discuss this more fundamental question and compare several methods for quantifying overall breath to breath variability in breathing pattern using a specific example.