Real-time monitoring of nasal mucosal pH during carbon dioxide stimulation: Implications for stimulus dynamics

Dennis Shusterman*, P. C. Avila

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

41 Scopus citations


Carbon dioxide is a commonly employed irritant test compound in nasal chemesthetic studies because it is essentially free of olfactory stimulus properties. CO2 is thought to act via hydration to H2CO3 and dissociation to H+ in nasal mucus, with resulting activation of acid sensors. However, transient changes in nasal mucosal pH have not been documented during CO2 stimulation in humans. We placed a small pH probe on the floor of the right anterior nasal cavity during CO2 stimulation in eight human subjects with historically high (>30%) and low (≤20%) CO2 detection thresholds. Three second pulses of CO2 (15-45% v/v) paired with air in random order (12-15 s inter-stimulus interval; 60 s inter-trial interval) were administered by nasal cannula at 5 l/min. in an ascending series. For each subject, both a CO2 detection threshold and suprathreshold psychophysical ratings [Ψ; labeled magnitude scale] were generated. All subjects showed phasic drops in pH associated with CO2 stimulation (ΔpH). For all subjects combined, a positive correlation was apparent between applied [CO2] and both ΔpH and Ψ, as well as between ΔpH and Ψ themselves (P < 0.0001 for each comparison). Subjects with historically low CO2 thresholds showed steeper dose-response curves for Ψ as a function of both applied [CO2] and ΔpH, but not for ΔpH as a function of applied [CO2]. For the six of eight subjects with measurable pH changes at threshold, ΔpH was positively related to log [CO2 threshold] (P < 0.01). These data imply that variability in CO2 detection thresholds and suprathreshold rating may derive from intrinsic differences in neural sensitivity, rather than differences in stimulus activation to hydrogen ion.

Original languageEnglish (US)
Pages (from-to)595-601
Number of pages7
JournalChemical Senses
Issue number7
StatePublished - Sep 2003


  • Carbon dioxide
  • Nasal mucosal pH
  • Psychophysical testing
  • Sensory irritation

ASJC Scopus subject areas

  • Physiology
  • Sensory Systems
  • Physiology (medical)
  • Behavioral Neuroscience

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