Diaphragmatic Electromyogram Power-Spectral Analysis as a Function of Reduced End-Expiratory Lung Volume

Abstract

ABSTRACT. We examined the centroid frequency (Fc) of the electromyogram power-frequency spectra from the costal (EMGco) and crural (EMGcr) diaphragms at functional residual capacity and at reduced end-expiratory lung volume (EELV) (induced by abdominal banding) in six anesthetized newborn piglets. EMGco and EMGcr were recorded from bipolar electrodes embedded in the costal and crural diaphragms respectively. A fast Fourier transformation of ECG free EMGco and EMGcr was used to compute the power-frequency spectra and calculate Diaphragmatic EMG power-frequency spectral analysis has been used to index diaphragmatic fatigue in newborns (1-3) and adults (4). Such analysis involves EMG monitoring in which the power or amplitude of the EMG signal is examined as a function of its various frequency components (5). The assignment of the label diaphragmatic fatigue rests on the observation that fatigue in limb skeletal muscle is associated with characteristic changes in the power of the EMG frequency components. These changes include I ) a rapid decrease in high-frequency power, 2) a progressive increase in low frequency power, and 3) a fall in the centroid or median frequency and high-to-low frequency ratio (6, 7). Supported by a grant from the West Penn Hospital Foundation. 61EMG power-frequency spectral analysis, however, can be affected by various changes in the environmental milieu of the muscle including alterations in ambient temperature (8), pH (9), and muscle blood flow (8) and by changes in muscle length/ configuration (10, 11). Few of these physiologic alterations have been examined with reference to the diaphragm (9, 12). No investigation has examined the effect of changes in lung volume (and, by inference, diaphragm length/configuration) on the EMG power-frequency spectrum of this muscle. Studies on appendicular muscle have demonstrated that EMG power shifts to lower frequencies with increasing muscle length (10, 1 1). In this regard, an increase in diaphragm length occurs when EELV is reduced (1 3-15). We, therefore, examined the effect that reductions in EELV have on the power-frequency spectrum of the costal and crural diaphragm of piglets. We hypothesized that a reduction in EELV would be associated with a significant decline in the EMG Fc of both the costal and crural diaphragm. MATERIALS AND METHODSFarm bred piglets, obtained from a local breeder who provided accurate times of farrowing, served as our study animals. Experiments were performed on six 1-to 3-d-old (weight 1.8 + 0.2 kg) piglets. Anesthesia was induced with halothane (1.0%) delivered in a background of 40% O2 via a securely fitting face mask. After cannulation of the femoral artery and vein, anesthesia was maintained with an i.v. combination of a-chloralose (50 mg/kg) and urethane (200 mg/kg); halothane administration was discontinued. Subsequent infusions of chloralose and urethane were given if the piglet developed jaw clonus. The trachea was surgically exposed and cut horizontally. A 3-mm inner diameter endotracheal tube with adapter was...

Ventilatory failure during resistive loaded breathing in the newborn primate

“…15,16,17 Changes in muscle temperature 16 and length 15 can alter the EMG power frequency spectrum of nonfatigued muscle. As applied to the current study, an expected increase in diaphragmatic muscle length and temperature, as well as a decrease in endexpiratory lung volume 18 during loaded breathing should all serve to decrease Fc and potentially falsely indicate fatigue. The lack of a Fc shift in the present study would suggest these phenomena were not operative and that diaphragm fatigue was not a major component in the failed trials.…”