Effects of increased end-expiratory lung volume on breathing in awake ponies.

This research investigates the effect of altering end-expiratory lung volume (EELV) on the breathing patterns and respiratory muscle signaling in ponies under various nerve conditions. Significant changes in the frequency of breathing, tidal volume, and breathing muscle activity were observed in the study.

Introduction

• The study focuses on understanding the impact of changes in the EELV in horse species – ponies, specifically, how these changes impact their breathing patterns and associated respiratory muscle electromyograms (EMG).
• The different types of ponies observed in the study are normal ponies (N), ones with denervated hilar nerve (HND), denervated carotid body (CBD), and those with both nerve denervations (HND + CBD).

Method

• The increase in EELV is experimentally achieved by applying continuous negative pressure (-10 and -20 cmH2O) around the body of the standing pony.
• Different parameters such as increased EELV, breathing frequency (f), tidal volume, arterial PCO2, the muscular activity of the diaphragm, and expiratory transversus abdominis (TA) muscle were recorded and analyzed for each group.

Results

• Increasing EELV triggered a linear increase in all groups when a negative pressure was applied around the torso.
• The reaction of the ponies to elevated EELV was contingent on their nerve condition. Breathing frequency decreased in normal and CBD ponies, while it increased in HND and HND + CBD ponies.
• The tidal volume results were also group-dependent with unchanged or above control in normal ponies but below or near control in other groups when EELV was increased.
• Arterial PCO2 initially dropped but then rose relative to the control group after approximately 1.5 minutes across all groups during elevated EELV.
• Increased EELV led to noticeable changes in the muscular actions of the diaphragm and the expiratory transversus abdominis (TA) muscle. These changes in the TA muscle were observed in normal but not in HND and HND + CBD ponies.

Conclusion

• The study concludes that increasing EELV, which likely places the diaphragm in a less advantageous position about its length-tension relationship, leads to compensatory heightened stimulation of the diaphragm. This reaction is not primarily reliant on hilar and carotid chemoreceptor afferents.
• However, hilar afferents do contribute to changes in the active duration of the diaphragm and TA during elevated EELV.