P0.1 during exercise in normal subjects breathing mixtures of gas with varying densities.
OBJECTIVE
The aim of the study was to re-examine the occlusion pressure measured simultaneously in the mouth (P0.1) and the oesophagus (Poes.1) during exercise in normal subjects submitted to different gas mixtures.


METHODS
7 healthy men breathing random gas mixtures containing 21% oxygen with either by 79% helium (He-O2) or sulphur hexafluoride (SF6-O2) and room-air, were studied during a steady-state 90w exercise performed on a cyclo-ergometer. Ventilatory parameters were derived from the flow signal recorded by a pneumotachograph calibrated with the different gas mixtures. Three pressure transducers (mouth, eosophageal and gastric) were checked to have iso-time identical responses up to 4Hz. P0.1, Poes.1, deltaPoes (difference in oesophageal pressure between end-inspiratory and end-expiratory levels) and deltaPdi (variation of transdiaphragmatic pressure between end-inspiratory and end-expiratory levels) were measured.


RESULTS
Hyperventilation associated with a similar deltaPoes/deltaPdi but a lower P0.1/deltaPdi ratio was observed in He-O2 breathing compared to SF6-O2 and air. Variable time delays between oesophageal and mouth pressures were observed during air and SF6-O2. Whatever the condition involved, no change was detected in the shape of the inspiratory pressure during the occlusion manoeuvres.


CONCLUSIONS
He-O2 breathing probably induced a change in the shape of the pressure wave later on in the inspiratory phase, making P0.1 not representing the total inspiratory drive. On the contrary in air and SF6-O2 conditions, P0.1 seemed to remain a useful tool for looking at the output of the respiratory controller.
Van Meerhaeghe
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Department of Pneumology, CHU A. Vésale, 706 route de gozée, Montigny-le - Tilleul 6110, Belgium. alain.vanmeerhaeghe@chu-charleroi.be
Sergysels
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D000328:Adult; D000704:Analysis of Variance; D001794:Blood Pressure / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology; D011659:Pulmonary Gas Exchange; D012119:Respiration; D012129:Respiratory Function Tests
D010100:Oxygen