Selective diaphragm muscle weakness after contractile inactivity during thoracic surgery

Area of Science:

• Physiology
• Surgical Science
• Muscle Biology

Background:

• Postoperative pulmonary complications are a major cause of morbidity after major surgeries.
• Inspiratory muscle weakness may contribute to these complications.
• The specific impact of surgery on inspiratory muscles remains unclear.

Purpose of the Study:

• To investigate the immediate effects of thoracic surgery on diaphragm function.
• To determine if surgery induces selective or generalized muscle weakness.

Main Methods:

• Diaphragm and latissimus dorsi muscle biopsies were collected from 6 patients during thoracotomy at two time points (t(0) and t(2)).
• Contractile performance, fiber morphology, and proteolysis markers were analyzed.
• Myosin heavy chain type and MuRF-1 expression were assessed.

Main Results:

• Diaphragm muscle fibers showed a significant ~35% reduction in force-generating capacity after 2 hours of surgery.
• Type 2 diaphragm fibers experienced more pronounced force loss than type 1 fibers.
• Latissimus dorsi muscle function remained preserved, indicating selective diaphragm weakness. Myosin heavy chain type 2 was reduced and MuRF-1 expression increased in the diaphragm.

Conclusions:

• Even short durations (2 hours) of thoracic surgery induce significant and selective weakness in diaphragm muscle fibers.
• This diaphragmatic dysfunction may contribute to postoperative pulmonary complications.