Abdominal muscle activation by expiratory threshold loading in awake dogs

Area of Science:

• Physiology
• Respiratory Mechanics
• Comparative Physiology

Background:

• Expiratory threshold loading (ETL) aids in maintaining functional residual capacity (FRC) and tidal volume (VT) by engaging abdominal muscles.
• Anesthesia and body position can influence abdominal muscle activation patterns, necessitating further investigation in awake subjects and different positions.

Purpose of the Study:

• To assess the individual abdominal muscle response to ETL in awake dogs positioned laterally.
• To determine the role of specific abdominal muscles in defending lung volumes under ETL conditions in a non-supine position.

Main Methods:

• Eight tracheotomized dogs were instrumented with sonomicrometer transducers and EMG electrodes in all four abdominal muscles.
• The dogs were studied in the lateral decubitus position while undergoing ETL.

Main Results:

• ETL induced active expiratory shortening in the transversus abdominis (TA), internal oblique (IO), and external oblique (EO) muscles.
• Tonic activity increased in the IO muscle, and while FRC increased, the rise was attenuated by abdominal muscle activation.
• Tidal volume and breathing frequency were preserved, with preferential recruitment of the internal abdominal muscle layer (TA and IO).

Conclusions:

• The internal abdominal muscle layer (TA and IO) plays a crucial role in defending lung volume against increases in FRC during ETL.
• Abdominal muscle activation, particularly tonic activity in the IO, contributes to maintaining respiratory parameters like VT and breathing frequency during ETL.
• Findings support the hypothesis that the internal abdominal muscles are preferentially recruited for lung volume defense, irrespective of body position in awake animals.