Changes in respiratory muscle activity in ponies when end-expiratory lung volume is increased.

The research examines how the muscle activity in the respiratory system of ponies changes when there is an increase in the end-expiratory lung volume. The study shows that the afferents in the lung and diaphragm are instrumental in these alterations.

Objective of the Research

• The main objective of the study was to identify if the lung and diaphragm afferents (nerve cells which carry impulses towards the central nervous system) contribute to changes or modifications in respiratory muscle activity. Specifically, when there’s a change in pony’s end-expiratory lung volume (EELV), which refers to the volume of air left in the lungs after a standard exhalation.

Research Methodology

• The study involved observing the responses of the diaphragm and the transversus abdominis (TA) muscle in ponies when there’s a passive, without muscle contraction, increase in EELV. The subjects were tested in four states: intact (I), diaphragm deafferented (DD), pulmonary vagal denervated (HND), and both DD and HND.
• Increase in ELLV in the ponies was achieved by applying negative pressure around their torsos, which created a positive transrespiratory (TR) pressure. The TR pressure’s impact on the rate of increase of the diaphragmatic electromyogram (EMG), a measure of electrical activity in the diaphragm muscle, and the duration and activity of TA muscle were carefully noted.

Research Findings

• In general, positive TR pressure caused an increase in EELV in all ponies, with varied responses among the different groups.
• Intact ponies, under positive TR pressure, showed an increase in the rate of rise of diaphragmatic EMG signaling an increased drive or activation to the muscle. This rise was comparatively lower in DD and HND ponies.
• Ponies with both DD and HND didn’t show any significant change in the activation of the diaphragm under positive TR pressure.
• Increased EELV resulted in modified breathing patterns in the ponies depending on their deafferented and denervated status.

Conclusion

• The researchers concluded that during a scenario of positive TR pressure, when the diaphragm is presumably at a mechanical disadvantage, the diaphragm and vagal afferents contribute to an increased drive to the diaphragm to prevent tidal volume reduction.
• In addition, vagal afferents were found to mediate an increase in the duration of TA activity during positive TR pressure, which helps control the increase in EELV.