Dynamic diaphragmatic MRI during apnea struggle phase in breath-hold divers

• The second phase of apnea, the so-called struggle phase, is characterized by onset of involuntary breathing movements (IBM).
• It is not clear if different segments of the diaphragm contribute to the same extent to IBMs, and whether the intensity of IBMs correlates with lung volumes.
• The range of diaphragmatic excursions increases toward the end of apneas.
• The diaphragm actively participates in IBM occurrence.
• Various segments of the diaphragm behave asynchronously both in tidal breathing and IBMs.

The purpose of the study was to provide insight in diaphragmatic involuntary breathing movements (IBM) during struggle phase of apnea at total lung capacity (TLC) and functional residual capacity (FRC) using magnetic resonance imaging along with measurements of hemodynamics and arterial oxygenation. The study was performed in eight elite breath-hold divers. There was a similar increase in diaphragmatic cranio-caudal excursions towards the end of TLC and FRC apnea. The greatest diaphragmatic excursion in both apneas and during tidal breathing was in the middle and posterior part of the diaphragm. Diaphragm thickness in elite BHD was within the reference range of normal values suggesting no diaphragmatic hypertrophy in this population. We found that the range of diaphragmatic excursions increases toward the end of apneas. Additionally, our data suggest that the diaphragm participates in IBM occurrence and that various segments of the diaphragm behave nonhomogenously both in tidal breathing and IBMs.