Comparison of the Orthonasal and Retronasal Detection Thresholds for Carbon Dioxide in Humans

Several studies have investigated the orthonasal detection threshold for carbon dioxide (CO2) in humans. The aim of current study was to investigate whether 24 healthy young subjects exhibited differences of CO2 detection thresholds during orthonasal or retronasal stimulation. As nasal mucosa is believed to desensitise to CO2 concentrations at or below 4% (vol./vol.) during expiration, the second aim of the study was to explore the influence during nasal versus oral breathing on the detection thresholds. CO2 stimuli of varying concentrations and a duration of 1000 ms were applied with an air-dilution olfactometer in either the anterior nasal cavity or the nasopharynx during nasal respiratory oral breathing. In these 4 conditions, the mean CO2 detection thresholds using the staircase forced-choice procedure were between 3.9% and 5.3% (vol./vol.). Statistical analysis revealed a significant difference between orthonasal and retronasal stimulation. The CO2 detection threshold was lower in retronasal stimulation. The nasopharyngeal mucosa is more sensitive to perithreshold CO2 stimuli than the nasal mucosa. The breathing route had no influence on the detection thresholds. The results of this study indicate that the natural contact of the nasal mucosa with approximately 4% (vol./vol.) CO2 during nasal expiration does not influence CO2 detection thresholds.

Authors: Melzner, Johannes; Bitter, Thomas; Guntinas-Lichius, Orlando; Gottschall, Reiner; Walther, Mario; Gudziol, Hilmar ;Full Source: Chemical Senses 2011, 36(5), 435-441 (Eng) ;