Abstract
Background:Exercise-induced diaphragmatic fatigue (DF) is conventionally considered to reflect impaired diaphragm function resulting from load imposed on the diaphragm during exercise and is known to be reduced by the application of non-invasive ventilation (NIV) during heavy-intensity exercise testing (HEET). On that physiological condition NIV applied for diaphragm unloading during recovery from exercise should be capable of accelerating recovery from DF and therewith prolonging exercise time to exhaustion and limiting the development of DF during a subsequent HEET compared to recovery during spontaneous breathing.Methods: Seven highly-trained subjects (V’O2max 62.7±7.8 ml/kg/min) performed four HEET at 85% V’O2max with 60 min of recovery during I spontaneous breathing and II NIV between two HEET.Results:Twitch transdiaphragmatic pressure (TwPdi) during supramaximal magnetic phrenic nerve stimulation decreased (p<0.04) following first HEET and subsequently completely recovered (p>0.2) during I and II. Following second HEET TwPdi comparably decreased (I 0.24±0.21 vs II 0.32±0.29 kPa; p=0.17). Exercise time to exhaustion during second HEET was equal during I and II (I 514±49 vs II 511±92 s; p=0.88).Conclusions:In conclusion, NIV applied for diaphragm unloading during recovery following HEET does neither affect recovery from DF nor subsequent exercise performance thereby providing further evidence that DF might reflect post-exercise diaphragm shielding rather than impaired diaphragm function.
Highlights
Heavy-intensity exercise testing (HEET) causes fatigue of the human diaphragm [1,2,3]
twitch pressures (TwP) were successfully assessed in all but one subject in whom TwPga and TwPdi was not available for Study Phase 1 due to technical problems caused by gastric catheter displacement during heavy-intensity exercise testing (HEET) as described recently [26]
TwPmo and TwPes were markedly lower after the first HEET compared to pre-exercise values (p=0.005 and p=0.006, respectively)
Summary
Twitch transdiaphragmatic pressure (TwPdi) during supramaximal magnetic phrenic nerve stimulation decreased (p0.2) during I and II. Following second HEET TwPdi comparably decreased (I 0.24±0.21 vs II 0.32±0.29 kPa; p=0.17). Exercise time to exhaustion during second HEET was equal during I and II (I 514±49 vs II 511±92 s; p=0.88)
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