[Non-invasive functional evaluation of the reserve in fatigue and the diaphragm structure using transthoracic echography in B and M modes]

Abstract

The diaphragm is the principal respiratory muscle. Its special characteristics have made it difficult to design instruments capable of performing a non-invasive evaluation of its structure and function in humans. The present study was designed to evaluate the potential use of echography as a non-invasive method to fulfil these objectives.

Methods: The study consisted of three phases: (1) echographic study in autopsy samples (n=10) of a segment of the thoracic-abdominal wall, from the bottom to the parietal peritoneum (i.e., thoracic wall, diaphragm, pleura and peritoneum structures), (2) static echographic study of the previous structures and the diaphragm in healthy subjects (n=10) to standardised lung volumes; and (3) dynamic echographic study of the contraction-relaxation of the diaphragm in the same subjects, calculating its maximum velocity of relaxation (MVrdi, mm/sec) during a specific inspiratory resistance test.

Results: The echography enabled the pleural and peritoneal limits of the diaphragm to be identified, and quantitate its thickness (Tdi), both ex-vivo and in-vivo, in all cases. The dynamic study of the Tdi showed a linear increase directly associated with the lung volume measurement, as well as a cyclical increase during inspiratory movements at rest. In the resistance test, the MVrdi was maximal with low loads and gradually decrease until reaching a minimum nadir (Δ≈-70% of the initial value) in claudication (fatigue). The MVrdi has a high precision in diagnosing claudication.

Conclusions: Transthoracic echography of the diaphragm is a non-invasive method that gives promising results in the structural and functional evaluation (i.e. fatigue risk) of that muscle. These findings are of pathophysiological interest and could be of use in the clinical care context.