Frequency‐domain analysis of diaphragm muscle EMG activity across ventilatory and non‐ventilatory motor behaviors

Abstract

Diaphragm motor units are recruited in an orderly fashion across ventilatory and non-ventilatory behaviors such that slow-twitch and fatigue-resistant fast-twitch units are exclusively recruited at low levels of force whereas fatigable and intermediate fast-twitch units are additionally recruited at high force levels. In models describing the relationship between power density spectrum (PDS) of the EMG signal and average conduction velocity of active muscle fibers, as muscle fibers with higher conduction velocities are recruited, PDS of the EMG signal will shift to higher frequencies. However, there are conflicting results in the literature which depend on species, muscles involved and contraction and/or activation patterns. We hypothesized that the PDS of the diaphragm muscle EMG signal will shift to higher frequencies as diaphragm muscle activation increases across ventilatory and non-ventilatory behaviors. We found a significant increase in the ratio of high frequency components to low frequency components during expulsive non-ventilatory behaviors such as airway occlusion and sneezing compared to ventilatory behaviors such as eupnea and hypoxia-hypercapnia. These findings are consistent with additional recruitment of fatigable and intermediate fast-twitch units during motor behaviors of increasing demand.