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Diaphragmatic fatigue investigated by phonomyography
M Petitjean1, J Ripart, J Couture
1Département d'Anesthésie-réanimation, Hôtel-Dieu de Montréal, Université de Montréal, Québec, Canada.
Summary
Diaphragmatic phonomyogram (PMG) reliably indicates diaphragm contractility changes after fatigue. This method, using submaximal unilateral phrenic nerve stimulation, reveals fatigue affects all diaphragmatic motor units.
Area of Science:
- Respiratory Physiology
- Neuromuscular Function
Background:
- Diaphragmatic phonomyogram (PMG) via maximal bilateral phrenic nerve stimulation is a known index of diaphragm contractility.
- Evaluating diaphragm contractility changes, especially post-fatigue, can be simplified.
Purpose of the Study:
- To investigate if diaphragmatic contractility changes can be more simply evaluated by analyzing the relationship between PMG and compound motor action potential (CMAP) amplitudes.
- To assess diaphragmatic contractility using graded submaximal unilateral phrenic nerve stimulation.
Main Methods:
- Recorded relationships between CMAPs and PMGs from both hemidiaphragms using surface electrodes and microphones.
- Measurements were taken in five healthy subjects before and after a diaphragmatic fatigue protocol.
- Analyzed the linearity and slope of the CMAP-PMG relationships.
Main Results:
- The relationships between CMAP and PMG amplitudes were linear in all subjects.
- The slope of these relationships significantly decreased post-fatigue (61.1% right, 70.4% left).
- Transdiaphragmatic twitch pressure (PdiT) declined by 49.4% post-fatigue, less than the PMG-based index.
Conclusions:
- Diaphragmatic phonomyogram (PMG) during submaximal unilateral phrenic nerve stimulation is a reliable and sensitive index of diaphragm contractility changes due to fatigue.
- This method demonstrates that diaphragmatic fatigue can impact all diaphragmatic motor units.