Diaphragm

Q: What are the three significant objectives diaphragmatic muscle serves?

Answer: Diaphragm is one of the most important muscles in the human body which maintains life. It serves three main purposes:

• It is the chief inspiratory muscle.
• It keeps a  mechanical barrier between the abdominal and thoracic cavities.
• It maintains the pressure gradient between the abdominal and thoracic cavities.

One of the objectives of the above question is to emphasize that the human body has different muscles for inspiration and expiration.

Inspiratory muscles: Diaphragm,  scalenes, external intercostals, and sternomastoids. 

Expiratory muscles:  Internal intercostals, rectus abdominus, internal and external obliques, and transversus abdominus.

Clinical significance: If on clinical exam, abdominal muscles show paradoxical movement on expiration, respiratory failure is imminent - and if a patient is on spontaneous breathing trial (SBT) while on a ventilator, it is most likely to fail liberation from ventilator.

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References:

1. Roussos C, Macklem PT. The respiratory muscles. N Engl J Med 1982; 307:786.

2. Davis J, Goldman M, Loh L, Casson M. Diaphragm function and alveolar hypoventilation. Q J Med 1976; 45:87.

3. Laroche CM, Carroll N, Moxham J, Green M. Clinical significance of severe isolated diaphragm weakness. Am Rev Respir Dis 1988; 138:862.