Diaphragm electrical activity during negative lower torso pressure in quadriplegic men

Abstract

We recorded the diaphragm electromyogram (EMG) of quadriplegic men before and during exposure of the lower torso to continuous negative pressure, which caused shortening of the inspiratory muscles by expanding the respiratory system by one tidal volume. The moving-time-averaged diaphragm EMG was larger during expansion of the respiratory system. When we repeated the experiment with subjects who breathed through a mouthpiece, we found qualitatively similar EMG changes and little or no change in tidal volume or end-tidal CO2 partial pressure. When the pressure was applied or removed rapidly, changes in EMG occurred within one or two breaths. Because end-tidal CO2 partial pressure did not increase, and because the response was rapid, we suggest that the response results from proprioceptive, rather than chemoreceptive, reflexes. As most of these men had complete spinal lesions at C6 or C7 the afferent pathways are likely to be vagal or phrenic.

Diaphragmatic function in patients on continuous ambulatory peritoneal dialysis

“…Only when the diaphragm is stretched beyond the optimal length, and is therefore placed on the descending limb of its force-length curve, is its electrical activity increased [29]. The same happens when the diaphragm gets shorter and is therefore placed in a more disadvantageous position from a mechanical point of view [1,13]. These studies imply that the drive to the inspiratory muscles is adjusted for shifts in position along the muscle lengthtension curve to provide stability in pulmonary ventilation.…”

“…If the increased EMGdi activity in the filled state simply represents a reflex mechanism caused by the instillation of dialysate, the EMGdi/Pdi ratio will then spuriously underestimate the diaphragmatic efficiency. Several animal and human studies have shown, however, that the efferent drive to the diaphragm is very well adjusted to account for changes in diaphragmatic mechanical efficiency [1,6,13,27]. Conditions that lead to an increased diaphragmatic operating length (the diaphragm is placed in a more advantageous position from a mechanical point of view) are associated with a reduced neural activation of the diaphragm [6,27].…”

The effect of lung transplantation on the neural drive to the diaphragm in patients with severe COPD

“…Several animal and human studies have shown that the efferent drive to the diaphragm is very well adjusted to account for changes in diaphragmatic mechanical efficiency [23][24][25][26]. The conditions that lead to an increased diaphragmatic operating length (the diaphragm is placed in a mechanically more advantageous position) are associated with a reduced neural activation of the diaphragm [24,26].…”

Respiratory muscle activity during rapid eye movement (REM) sleep in patients with chronic obstructive pulmonary disease.

“…Moreover, previous work has shown EMG activity from transmandibular electrodes to be qualitatively similar to signals from genioglossus intramuscular electrodes,21 and surface diaphragmatic EMG recordings are qualitatively similar to signals obtained from oesophageal electrodes even during changes in lung volume. 22 In patients with COPD it has been shown that the surface diaphragmatic EMG correlates well with transdiaphragmatic pressure. 7 We found no evidence of abdominal muscle activity during sleep, but cutaneous electrodes are probably less sensitive for detection of expiratory activity as recent work has shown that the most frequently active expiratory muscle in awake subjects with COPD is transversus abdominis, which is the least accessible to surface recording.…”

“…Others 22 In patients with COPD it has been shown that the surface diaphragmatic EMG correlates well with transdiaphragmatic pressure. 7 We found no evidence of abdominal muscle activity during sleep, but cutaneous electrodes are probably less sensitive for detection of expiratory activity as recent work has shown that the most frequently active expiratory muscle in awake subjects with COPD is transversus abdominis, which is the least accessible to surface recording.…”