[How do pleasant and unpleasant odours change the breathing pattern?].

BACKGROUND

Pleasant odours are thought to stimulate whereas unpleasant odours are thought to shorten it. This common breathing behaviour should be tested with short pure odour stimuli. The question was: Is there an influence on exhalation as well?

METHOD

53 normosmic subjects (33 female, 20 male, mean 22,3 years) had to breathe through one nostril. The other nostril was closed using a foam nose tip with a tube connected to a manometer to record the respiratory pressure. The signal was digitally converted and visualised with LabView-software. Odours were presented in front of the nose with a flow-olfactometer OM 2S by Kobal. Hydrogen sulphide (H2S) as an unpleasant pure odour and phenylethylalcohol (PEA) as a pleasant pure odour were used in weak, moderate and strong concentration. The stimulus duration was 200 ms. The onset of stimulus was triggered manually in late exhalation during regular breathing pattern. The interstimulus interval was at least 3 min. A trial consisted of 16 stimuli (4 weak, 2 moderate, 2 strong of both odours). From the recording the duration and the areas below the respiration curves of inhalation and exhalation were calculated. The changes of these four respiratory parameters were estimated using the ratio of the first breathing cycle after stimulus to the average from the five regular breathing cycles prior to stimulation. Only changes of more than +/- 20 % were defined as an olfactory evoked respiratory response (OERR).

RESULTS

Short PEA stimuli evoked about three times more frequently an increase than a decrease of duration of inhalation. The area below the inhalatory curve was enlarged. The subjects inhaled the pleasant odour more deeply and for longer. Short H2S-stimuli evoked three times more frequently a decrease of duration of exhalation than an increase. Due to the forced exhalation an increase of the area below the exhalatory curve was observed in these cases. Changes of inhalation did not show any trend. The subjects exhaled quickly to breathe fresh air in the following cycle. Every subject showed some OERR. 52 subjects responded to both odours. One subject responded to PEA only. The individual frequency of OERRs in a trial ranged from 16 % to 84 %.

CONCLUSIONS

In all normosmic subjects some OERRs are evoked by repeated H2S- and PEA-stimuli. Strong stimuli do not increase the rate of OERRs. Therefore, the use of perithreshold stimuli is recommended for respiration-olfactometry.