Electromyography of some respiratory muscles in the horse.

This research investigates the activity of various respiratory muscles in horses, both when the animals are conscious and under anesthesia, using electromyographic recordings obtained with insulated wire electrodes. The main findings suggest that different muscles play a crucial role in respiration under different conditions, and the normal functions observed in conscious horses change significantly under anesthesia.

Experiment Setup and Methodology

• The scientists used insulated wire electrodes to record electromyographic (EMG) activity in several respiratory muscles. The muscles studied were the costal diaphragm, intercostal muscles, serratus ventralis, internal abdominal oblique, transversalis, and rectus abdominis.
• The research was carried out on conscious horses as well as the same animals under anesthesia to understand the difference in muscle functioning during these two states.
• The recorded EMG activity was then related to the respiratory phases which were concurrently recorded with a stethograph strapped around the chest wall of the horses.

Key Findings

• The costal diaphragm showed constant (tonic) and inhalation (inspiratory) activity in both conscious and anesthetized horses.
• The transversalis muscle was found to be the principal muscle actively involved in exhalation (expiration).
• Any increased activity in the second stage of either inhalation or exhalation that was observed in conscious horses was absent under anesthesia. This applies specifically to the intercostal muscle activity.
• There was a marked and constant tonic activity found in the serratus ventralis muscle in standing horses. However, this activity disappeared during anesthesia.

Conclusion

• The study concludes that the chest wall stabilization provided by the serratus ventralis and intercostal muscles in conscious, standing horses decreases considerably during anesthesia.
• This suggests that the normal respiratory function and muscle engagement of horses change significantly under anesthesia, potentially affecting their breathing rhythm and effectiveness.