Attenuated Hering-Breuer inflation reflex 4 years after pulmonary vagal denervation in ponies.

This study researched the recovery of the Hering-Breuer inflation reflex in ponies’ lungs following hilar nerve denervation surgery over a period of three to four years. The findings revealed no significant reinnervation or ventilatory control system changes to compensate for the loss of the hilar nerve, indicating that the denervation was permanent and didn’t significantly impact the ponies’ breathing frequency or inspiratory time.

Background and Objective of the Study

• This research was aimed at determining whether any recovery of the Hering-Breuer inflation reflex in ponies takes place between 2 weeks to 3-4 years after a surgical process called hilar nerve denervation (HND).
• The Hering-Breuer reflex helps regulate breathing by sending signals to the brain when the lungs are inflated, thus preventing over-inflation. The hilar nerves play a significant role in this reflex.

Methodology

• The researchers used two main tests to conduct the experiments on the ponies under anesthesia.
• Before HND, airway occlusion – covering or blocking the airway – after a three-liter lung inflation increased the subsequent occluded breath duration by nearly ten times compared to the control breath duration.
• Another maneuver was applied, occluding the airway at the end of expiration. This increased the subsequent inspiratory effort duration by 71% in ponies with an intact hilar nerve, but only by 20-25% 2-4 weeks and 3-4 years after HND.

Findings

• For both tests, the differences before and after HND were statistically significant (P less than 0.05), suggesting that the surgical denervation had a significant impact.
• However, there were no significant differences (P greater than 0.10) between the readings 2-4 weeks and 3-4 years after HND, indicating that no meaningful recovery or reinnervation occurred in this period.
• In awake ponies, both at rest and during mild and moderate treadmill exercise, the breathing frequency was generally lower and inspiratory time was greater after HND than before, suggesting altered respiratory patterns due to the denervation.

Conclusion

• Based on the study results, the researchers concluded that the surgical procedure for HND does not allow for any significant reinnervation, and there are no notable changes within the ventilatory control system to compensate for the loss of hilar nerve afferents.
• These findings suggest that once the hilar nerves are denervated, the Hering-Breuer reflex does not significantly recover, leading to lasting changes in respiratory patterns.