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Open Access Publications from the University of California

Scholarly Works (63 results)

  • Article
UC San Diego Previously Published Works (1998)

The study of anosmic subjects has allowed to separate the trigeminal from the olfactory input in the detection of airborne chemicals by the nose. Systematic testing of homologous series of chemicals has allowed to probe into the role that physicochemical properties play to make a substance a potent (i.e., low threshold) or weak (i.e., high threshold) odorant or irritant. This combined approach has served to define the gap between olfactory and chemesthetic detection of volatile organic compounds (VOCs), with smell leading in sensitivity by as little as one and as much as five orders of magnitude. It has also paved the way to the description and prediction of the chemesthetic potency of VOCs27-29 (see M. Abraham article, this volume) and to the recognition of the important role of lipophilicity in chemesthesis18.

 Additional indices of trigeminal sensitivity such as eye irritation and nasal localization (or lateralization), that can be measured in normosmics devoid of olfactory influence, have rendered a similar picture of absolute and relative chemesthetic potency of VOCs to that rendered by testing nasal pungency in anosmics, validating this approach.

 The study of olfactory and trigeminal detection of mixtures of VOCs constitutes an important topic for future studies. Initial work looking broadly at the chemosensory detection of mixtures of up to 9 components, and very recent detailed studies of one particular binary mixture have indicated the existence of sensory agonism among individual components. Such agonism seems more robust or, perhaps, more complete for chemesthesis than for olfaction but only further studies could confirm the generality of these findings.

    Cover page: Human Trigeminal and Olfactory Chemosensitivity: Detection of Single Chemicals and Binary Mixtures
      UC San Diego Previously Published Works (1996)
      In order to measure "odor unbiased" nasal pungency (e.g., sensory irritation) thresholds, we have resorted in the past to testing subjects with no olfaction (i.e., anosmics). The present study illustrates another way to gain insight into the separate response of the nasal trigeminal and olfactory nerves without resorting to anosmics. Thresholds for nasal localization of airborne n-alcohols to the right or left nostril, measured in normosmics, fell into register with nasal pungency thresholds measured in an anosmic, and with eye irritation thresholds measured in normosmics and the anosmic. As expected, odor thresholds fell well below the other three sensory thresholds.
        Cover page: Sensory Irritation Potency of VOCs Measured Through Nasal Localization Thresholds
        • Peer Reviewed
        UC San Diego Previously Published Works (1993)
          Cover page: Irritation and Odor: Symptoms of Indoor Air Pollution
          • Peer Reviewed
          UC San Diego Previously Published Works (1995)
          Olfactory adaptation exerts its influence in almost all aspects of the functioning of the sense of smell. An adapted olfactory sense is characterized by elevated odor thresholds, reduced responses to suprathreshold sensations, slower reaction times to odors, and, sometimes, a shift in perceived odor qualities. The presence of trigeminal properties (i.e., pungency) in an odorous stimulus slows the adaptation process. Studies of olfactory adaptation, perhaps even more than any other aspect of human smell function, need to control for subject bias and expectations. Presently, standardized clinical tests of olfaction do not include an olfactory adaptation component, largely because of practicality considerations. Recent reports show that aging speeds olfactory adaptation and slows recovery. In view of this, it might prove revealing to explore olfactory adaptation in patients with diseases known to affect the sense of smell and compare the results with those obtained in matched control subjects.
            Cover page: Olfactory Adaptation
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (1993)
            Sensory irritation (pungency) figures prominently among the symptoms associated with polluted indoor environments. In order to separate the pungent from the olfactory response, we measured nasal pungency thresholds in subjects lacking olfaction (anosmics) and odor thresholds in normal controls (normosmics) for a homologous series of ketones, and selected secondary and tertiary alcohols and acetates. As seen before for homologous alcohols and acetates, both types of nasal thresholds decreased with increasing carbon chain length. Pungency thresholds decreased exponentially with chain length. For all nonreactive chemicals studied so far, threshold nasal pungency is achieved at a fairly constant percentage of vapor saturation, irrespective of molecular size or chemical functional group. Such a relationship does not hold for odor thresholds. The outcome for pungency implies an important role for a physical, rather than chemical, interaction with the nasal mucosa.
              Cover page: Efficacy of Volatile Organic Compounds in Evoking Nasal Pungency and Odor
                UC San Diego Previously Published Works (1995)
                Thresholds for detection of odor, nasal pungency (irritation), and eye irritation were measured for single volatile organic compounds (VOCs) (1-propanol, 1-hexanol, ethyl acetate, heptyl acetate, 2-pentanone, 2-heptanone, toluene, ethyl benzene, and propyl benzene) and certain mixtures of them (two three-component mixtures, two six-component mixtures and one nine-component mixture). Nasal pungency was measured in persons lacking a functional sense of smell to avoid interference from olfaction. The results showed the existence of various degrees of stimulus agonism (additive effects) in the three sensory channels. Such agonism increased with the complexity of the mixtures and with the lipophilicity of their components. Eye irritation even showed synergistic stimulus agonism for the most lipophilic (one of the six-component) and the most complex (the nine-component) mixtures. The results indicate that complex chemical environments may enable chemosensory, and particularly irritative, detection when single VOCs lie far below their individual thresholds. Even the present rather rudimentary state of knowledge of how lipophilicity influences detection of single VOCs and how it and complexity (number of components) influence detection of mixtures would presumably allow refinement of a measure such as total mass (or concentration) of volatile organic compounds (TVOC) into a much more meaningful index that we might call the perceptually weighted level of VOCs, or PWVOC. Such an index, like the index dB(A) for sound, could make an otherwise strictly physical measurement at least somewhat predictive of human responses.
                  Cover page: Mixtures of Volatile Organic Compounds: Detection of Odor, Nasal Pungency, and Eye Irritation
                  • Article
                  • Peer Reviewed
                  UC San Diego Previously Published Works (1994)
                  We tested nasal detection thresholds for airborne chemicals in a group of anosmics (i.e., subjects lacking a functional sense of smell) and in a group of age-, gender-, and smoking-status-matched normosmics (i.e., subjects with normal olfaction). Anosmics provided odor unbiased nasal pungency (irritation) thresholds. Normosmics provided odor thresholds. Homologous series of alcohols, acetates, and ketones served as stimuli. Eye irritation thresholds were also measured for selected acetates. Most substances evoked pungency (i.e., were detected by the anosmics). All sensory thresholds decreased systematically with carbon chain length. The gap between pungency and odor grew larger with increasing carbon chain length. Pungency thresholds — but not odor thresholds — showed a uniform linear relationship of slope close to unity with saturated vapor concentration, irrespective of chemical functionality or carbon chain length. This suggests that pungency from nonreactive airborne chemicals rests heavily on a relatively unspecific physical interaction with a susceptible biophase. Of relevance to indoor environments, such an interaction opens the possibility for a high degree of sensory addition of pungency from individual components of complex mixtures resulting in noticeable irritation even when each component is at a level well below threshold.
                    Cover page: Perception of Odor and Nasal Pungency from Homologous Series of Volatile Organic Compounds
                    • Article
                    • Peer Reviewed
                    UC San Diego Previously Published Works (1984)
                    Four experiments explored possible temporal summation in olfaction and the common chemical sense. In one experiment, participants judged the perceived magnitude of various concentrations and durations (1.25 - 3.75 s) of the pungent odorant ammonia and the nonpungent odorant isoamyl butyrate. The perceived magnitude of ammonia increased during an inhalation whereas the magnitude of isoamyl butyrate did not. Time-intensity trading relations for ammonia indicated nearly perfect temporal summation. In another experiment, modulation of the concentration of ammonia during an inhalation led to assessments of perceived magnitude that confirmed the high degree of temporal summation seen in the first experiment. That is, approximately equal time-integrated mass of inhaled ammonia led to approximately equal perceived intensity. A third experiment indicated that temporal summation for ammonia arose from its pungency rather than from its odor, a fourth that trigeminally-mediated reflex apnea in response to ammonia also exhibits temporal summation. The degree of temporal summation measured with the reflex came very close to that assessed psychophysically. When stimulated with ammonia, the common chemical sense behaves more like a total mass detector than a concentration detector. The investigation raises the possibility that the short-term sensory reaction to most pungent stimuli may follow this simple rule.
                      Cover page: Temporal integration of pungency
                      • Article
                      • Peer Reviewed
                      UC San Diego Previously Published Works (1995)
                        Cover page: Irritation and odor as indicators of indoor pollution
                        • Article
                        • Peer Reviewed
                        UC San Diego Previously Published Works (1995)
                        We measured thresholds for eye irritation and odor in homologous series of alcohols (ethanol, 1-butanol, 1-hexanol, and 1-octanol), ketones (2-propanone, 2-pentanone, 2-heptanone, and 2-nonanone), and alkylbenzenes (toluene, ethyl benzene, and propyl benzene). Eye irritation thresholds were well above odor thresholds for all series. Both sensory thresholds declined with carbon chain length, a trend that has implicated lipophilicity in the potency of these and related stimuli. Eye irritation thresholds were remarkably close to nasal pungency thresholds obtained previously in persons lacking olfaction (i.e., anosmics). The agreement between the two thresholds implies that, despite differences in the mucus layer at the two sites and in the epithelial tissue itself, there is remarkable similarity at the site of stimulation. As a practical matter, the eyes could serve as the sites to assess potency for induction of nasal pungency, an assessment previously limited to testing anosmics. Presumably — for our brief stimulus presentations (1-3 sec) — the differences between ocular and nasal mucosae have little relevance to chemical sensitivity. Studies of the ability of homologous chemical series to evoke threshold eye irritation, nasal pungency, and odor not only have practical value but also can help to define the physicochemical properties of the receptor and perireceptor biophases.
                          Cover page: Relative Sensitivity of the Ocular Trigeminal, Nasal Trigeminal and Olfactory Systems to Airborne Chemicals
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