[Hydrogen sulphide stimuli shorten exhalation during sleep as well as in wakefulness]

In the attentive waking state, pleasant odours often prolong inhalation while unpleasant odours often shorten the exhalation. It should be checked whether this induced breathing pattern is maintained even during sleep.

23 healthy normosmic adults were examined by polysomnography for one night and randomized pulsed either with H₂S, phenylethyl alcohol (PEA) or CO₂ via a flow olfactometer. The determination of the sleep stages was based on the standard polysomnography curves. From the breathing curves (respiratory nasal pressure breathing, thoracic or abdominal belt breathing) a low-artefact curve was selected and seven breaths were measured from their breathing signal around the trigger impulse. The duration of inspiration (DIN) and the duration of the expiration (DEX) were determined from the six prestimulatory breaths and from breath with the stimulus onset and thus defined a reaction index (RI) indicating whether there is a significant change in shortening or prolonging DIN and/or DEX. These different RI were corrected by the spontaneous baseline RI and analysed according to the type of stimulus and the sleep stages.

Reaction indices with reductions of DEX were larger than spontaneous RI and RI for PEA and H₂S stimulation. In the case of CO₂ irritation, RI with reductions of DIN and DEX were larger than with olfactory stimulation. All RI were equal in their amount between sleep stages. In REM, the difference between olfactory RI with shortened DEX between H₂S and PEA stimulation was greatest.

When stimulated with an unpleasant smell in sleep, the respiratory reaction pattern from the awake state is preserved. RI with shortened DEX can be considered as an imperfect arousal.