The influence of a mouthpiece and noseclip on breathing pattern at rest is reduced at high altitude.

The effects of the instrumentation by a mouthpiece (MP) and a noseclip (NC) on the ventilatory response to short time hypobaric hypoxia were studied in 10 healthy volunteers at rest. The subjects were exposed to simulated altitude of 500 m, 3000 m, 4000 m and again 500 m, each altitude being applied for 30 min in a hypobaric chamber. Resting minute ventilation (VE), tidal volume (VT) and respiratory frequency (fR) using inductive plethysmography were continuously measured in all subjects in a standardized half lying position. The recordings were carried out at each altitude during the first 10 min without MP and NC, then 10 min with them, and the last 10 min again without them. At 500 m during MP+NC breathing VE and VT were increased, whereas fR was not significantly changed. At 3000 m, the VE increase with MP+NC was no more significant and fR was decreased. These effects of MP+NC on respiration disappeared at 4000 m and reappeared after the descent to 500 m. Furthermore, with and without MP and NC the variability of VE at 4000 m was significantly higher than at 500 m before ascent, and in all altitudes the variability of VT was significantly reduced by the MP+NC. It is concluded that the influence of MP+NC on VE, VT and fR is reduced or even abolished at high altitude, whereas the hypoxia induced increase of VE variability is not affected by the instrumentation.