Respiratory muscle electromyogram responses to acute hypoxia in awake ponies.

The research investigates the impact of sudden, short-term oxygen shortage (acute hypoxia) on the breathing and electromyogram responses in awake, freely breathing ponies’ respiratory muscles, focusing on the inspiratory (diaphragm) and expiratory (transversus abdominis) muscles. It compares outcomes between ponies with functioning carotid bodies (CBI) and ponies where these bodies are severed (CBD).

Study Design

• The study was conducted on a combined group of 17 ponies, 11 of whom had intact carotid bodies (CBI) and the remaining six had their carotid bodies surgically denervated (chronically removed, CBD).
• Four CBI and five CBD ponies were also hilar nerve (otherwise known as pulmonary vagal) denervated. This denotes cutting or blocking a nerve to decrease its functioning.
• These ponies were observed under normal oxygen concentration (normoxia, fractional inspired O2 concentration [FIO2] = 0.21) and two levels of reduced oxygen concentration (hypoxia, FIO2 approximately 0.15 and 0.12; for 6 to 10 minutes per period).

Observations and Findings

• CBI ponies demonstrated higher mean VE responses (ventilatory response or breathing rates) to hypoxia than their CBD counterparts.
• Both CBI and CBD ponies showed an increase in the rate of rise and mean activity of diaphragm electromyogram (EMG) during hypoxia compared to normoxia.
• The duration of diaphragm activity decreased in CBI ponies during hypoxia, while it remained unchanged for CBD ponies.
• During hypoxia, total and per breath activities of the expiratory muscle (transversus abdominis) diminished in both groups without a drop in the activity’s rate of rise. Time to peak and total duration of this muscle’s activity significantly declined under hypoxic conditions.
• Hilar nerve denervation did not alter the electromyogram responses to hypoxia.

Interpretation

• According to the research, the presence or absence of functional carotid bodies, which are vital for detecting changes in the oxygen content of blood, impacts the breathing responses in ponies subjected to sudden, short-term oxygen shortage—the reactions were more pronounced in ponies with intact carotid bodies.
• The activity patterns of both the inspiratory and expiratory muscles differed markedly between the two groups, indicating that the carotid bodies relay an essential influence on respiratory muscle activity during hypoxia.
• Moreover, the study suggests that the pulmonary vagal nerve (hilar nerve) does not contribute to modifying electromyogram responses in hypoxic conditions.