Sustained preinspiratory cortical potentials during prolonged inspiratory threshold loading in humans.

Humans can program and control movements, including breathing-related movements. On the electroencephalogram (EEG), this preparation is accompanied by a low-amplitude negativity starting approximately 2.5 s before inspiration that is best known as a Bereitschaftspotential (BP). The presence of BPs has been described during the compensation of mechanical inspiratory loading, thus identifying a cortical involvement in the corresponding ventilatory behavior. The pathophysiological interpretation of this cortical involvement depends on its transient or enduring nature. This study addressed this issue by looking for BPs during sustained inspiratory loading (1 h). Nine healthy male volunteers were studied during unloaded quiet breathing and inspiratory threshold loading (with unloaded expiration). Analyses of EEG signal and ventilatory variables were used to compare beginning and end of sessions. Inspiratory threshold loading caused ventilatory modifications that persisted, unchanged, for an hour. The presence of a BP at the beginning and end of a session was the most frequent occurrence (6 of 9 cases with a 17-cmH2O threshold load; 8 of 9 cases with a 23-cmH2O load). These observations support the hypothesis that the cerebral cortex is involved in the compensation of sustained experimental inspiratory loading. How this translates to respiratory disease involving acute changes in respiratory mechanics remains to be determined.

'Oxygen uptake efficiency slope' in trained and untrained subjects exposed to hypoxia.

We assessed the ability of the oxygen uptake efficiency slope, whether calculated on 100 and 80% of maximal exercise test duration (OUES(100) and OUES(80)), to identify the change in cardiorespiratory capacities in response to hypoxia in subjects with a broad range of V(O2 peak). Four maximal exercise tests were performed in trained (T) and untrained subjects (UT) in normoxia and at 1000, 2500 and 4500 m. The mean reductions in maximal exercise capacities at 4500 m were the same in T subjects for V(O2 peak) (-30%), OUES(80) (-26%) and OUES(100) (-26%) whereas in UT subjects only OUES(100) (-14%), but not OUES(80) (-20%), was lower compared with V(O2 peak) (-21%, p<0.05). OUES(100) and OUES(80) were correlated with V(O2 peak) and the ventilatory anaerobic threshold in both groups. Multiple regression analyses showed that V(O2 peak), OUES(100) and OUES(80) were significantly linked to O(2) arterial-venous difference. The OUES(80) could be considered as an interesting sub-maximal index of cardiorespiratory fitness in normal or hypoxemic subjects unable to reach V(O2 peak).