Development of a new psychophysical method to assess intranasal trigeminal chemosensory function.

BACKGROUND: The aim of this study was to develop a new psychophysical test to assess intranasal trigeminal chemosensory function. METHODOLOGY: The test is similar to the Sniffin’ Sticks test, but using pens impregnated with substances preferentially activating trigeminal afferents. Our test comprises detection threshold, discrimination, identification and lateralization tasks. In a first study, we evaluated healthy controls. In a second study, we evaluated the potential usefulness of this test in patients with rhinological conditions. RESULTS: Study 1: 86 controls were included. Threshold, identification and lateralization performance decreased with age. Test-retest reliability was similar to that of olfactory tests. Study 2: results of the controls group were compared to those of 59 patients (14 allergic rhinitis, 11 chronic rhinosinusitis with nasal polyps (CRSwNP), 9 without nasal polyps (CRSsNP), and 25 with an olfactory disorder (OD)). Controls had 1) lower detection thresholds compared to CRSwNP, CRSsNP and OD, 2) better discrimination and identification scores compared to OD, and 3) better lateralization scores compared to CRSwNP and CRSsNP. CONCLUSIONS: Our test allows to identify age-related changes in trigeminal chemosensory function. Trigeminal function seems to be differently affected in different pathologies. Further studies are necessary to validate our results and evaluate the impact of olfactory co-activation on the observed results.

Correlation between olfactory function, trigeminal sensitivity, and nasal anatomy in healthy subjects.

PURPOSE: Few studies have investigated the correlation between chemosensory function (trigeminal and olfactory) and nasal volume in humans, even though nasal anatomy is crucial for the sense of smell. Aim of this study was to evaluate these correlations in normosmic subjects. METHODS: Two hundred and fifty-six healthy volunteers (age range 19-69 years) participated. Olfactory function was investigated for (the rose-like) phenylethyl alcohol odor threshold and odor identification (OI) using the Sniffin' Sticks test, while nasal structure was evaluated by acoustic rhinometry (AR); trigeminal sensitivity was assessed in terms of detection "thresholds" for the odorless carbon dioxide (CO2). RESULTS: There were negative correlations between olfactory sensitivity at threshold level and minimum cross-sectional area (MCSA) in both nostrils. No significant correlations were found between OI and nasal anatomy. Similar to olfactory sensitivity, with regard to the trigeminal stimulus CO2 for the right nostril subjects were the more sensitive the smaller the MCSA. CONCLUSIONS: The current results emphasize the significance of nasal anatomy for trigeminal/olfactory threshold perception. Interestingly, correlations were not found between suprathreshold odor identification and nasal anatomy. Other than odor identification, odor thresholds appear to depend on subtle differences in nasal anatomy.

Automated assessment of intranasal trigeminal function.

BACKGROUND: The intranasal trigeminal system is a key player in the perception of intranasal airflow. Why it has not been studied very well may be due to the lack of techniques that allow for fast, reliable and inexpensive routine investigation of the system. The basis of the current study is the notion that--within limits--the intranasal trigeminal system detects the overall mass of a stimulus and not just its concentration. Thus, changing the duration of the stimulus at a given concentration has a similar effect as changing its concentration. METHODOLOGY: Ninety-nine normosmic subjects participated [48 women and 51 men; mean (range) age = 45 years (20-88 years)]. In addition, 50 patients with olfactory loss were investigated once (28 women, 22 men; mean age 58 years, SD = 14 years; age range 24-88 years; causes of olfactory loss: viral infections n = 22, head trauma n = 8, chronic sinunasal disease n = 3, idiopathic n = 17). CO2-stimuli with various durations (multiples of 50 ms) were presented through a standard bilateral nasal cannula at an interval of 10 s; stimulus duration was increased by 50 ms from one stimulus presentation to the next, until the subject pushed a button indicating a painful sensation. This was the basis for automated assessment of CO2-pain responsiveness. RESULTS: This current study had four main findings: (1) Using the new, automated device CO2 pain responsiveness can be measured reliably, (2) CO2 pain responsiveness correlates with olfactory function, (3) as with olfaction, women are more sensitive to CO2 , and CO2-pain responsiveness also correlates with aging, (4) CO2-pain responsiveness is lower in patients with olfactory loss compared to normosmic, healthy controls, even when controlling for age. CONCLUSION: We have demonstrated that the current approach is a reliable and valid measure of intranasal trigeminal function.