Pamela Dalton

The nature and duration of adaptation following long-term odor exposure

Any individual living or working in an odorous environment can experience changes in odor perception, some of which are long lasting. Often, these individuals report a significant reduction in the perception of an odor following long-term exposure to that odor (adaptation). Yet, most experimental analyses of olfactory adaptation use brief odorant exposures which may not typify real-world experiences. Using a procedure combining long-term odor exposure in a naturalistic setting with psychophysical tests in the laboratory, we present evidence to show that reduced odor intensity following long-term exposure is accompanied by odorant-specific shifts in threshold. Subjects were exposed continuously to one of two odorants while in their home for a period of 2 weeks. Exposure produced an odorant-specific reduction in sensitivity and perceived intensity compared with preexposure baselines: Detection thresholds for the adapting odorant were elevated following exposure and perceived intensity ratings for weak concentrations were reduced. For most individuals, reduced sensitivity to the test odorant was still evident up to 2 weeks following the last exposure. The persistence of the change, as evidenced by the duration of recovery from adaptation, distinguishes this phenomenon from the adaptation seen following shorter exposures and highlights the need for the study of exposure durations that are more similar to real-world exposures.

Cognitive influences on health symptoms from acute chemical exposure.

Symptom reports, perceived adverse health effects, and public health concerns are increasingly precipitated by the perception of chemical odors. This study examined the interaction between health cognitions, odor perception, and symptom reports. A group of 180 healthy men and women were exposed to 1 of 3 ambient odors, normatively rated as healthful (methyl salicylate, or wintergreen), harmful (butanol or alcohol), and ambiguous (isobomyl acetate, or balsam), after receiving 1 of 3 odorant characterizations (harmful, healthful, and neutral). Individuals given a harmful bias reported significantly more health symptoms following exposure and more intense odor and irritation during exposure than did those given a neutral or healthful bias. The overall pattern of results suggests that many of the health-related effects of exposure to odorants are mediated not by a direct agency of odors but by cognitive variables, such as mental models of the relationship between environmental odors and health.

Upper airway irritation, odor perception and health risk due to airborne chemicals

Chemosensory irritation associated with the manufacture and use of volatile materials has been a public and employee health concern for many years. Because odor properties can often be detected at much lower concentrations than those capable of eliciting upper respiratory tract irritation, confusion between odor and irritation coupled with variability in odor sensitivity and response can produce significant obstacles for evaluating the potential for adverse effects or annoyance from worker and community exposures. Although rigorous research methods have been developed to accurately quantify chemosensory irritation in human evaluations, several important considerations should be included in the design and interpretation of such studies. Specifically, research studies evaluating chemosensory irritation from volatile materials should be capable of (1) distinguishing between the annoyance or concern elicited by odor sensation and that elicited by true sensory irritation, (2) evaluating exposure-related factors that affect odor or irritancy responses, and (3) separating true adverse health effects from those mediated via psychosocial factors. Objective measures of upper respiratory tract irritation onset obtained in conjunction with subjective reports can lend valuable input to the decision process for determining occupational exposure limits. Subjective reports of irritation at low levels that cannot be reconciled with objective measures should prompt a careful investigation into the other factors (e.g. cognitive or emotional) that may be modulating the sensory response. Distinguishing between the exposure that elicits local effects of sensory irritation in the upper respiratory tract and the exposure that elicits self-reports of irritation is a key component in establishing occupational exposure limits that are protective of exposed workers.

Acetone Odor and Irritation Thresholds Obtained From Acetone-Exposed Factory Workers and From Control (Occupationally Unexposed) Subjects

Sensitivity of olfaction (smell) and chemesthesis (irritation) was evaluated for 2-propanone (acetone) and 1-butanol in acetone-exposed workers (AEW; N = 32) during a workday and unexposed subjects (microES; N = 32). Irritation sensitivity was assessed using a method that relies on the ability of individuals to localize irritants on the body. When a volatile compound is inhaled into one nostril and air into the other, the stimulated side can be determined (lateralized) only after the concentration reaches a level that stimulates the trigeminal nerve (irritation); compounds stimulating olfaction alone cannot be lateralized. Intranasal lateralization thresholds offer an objective measure of sensory irritation elicited by volatile compounds. Test results indicated that neither olfactory nor lateralization thresholds for butanol differed between AEW and microES. Olfactory thresholds to acetone in AEW (855 ppm) were elevated relative to those of microES (41 ppm), as were lateralization thresholds (36,669 ppm and 15,758 ppm, respectively). Within AEW, level of occupational exposure was not correlated with thresholds. Other measures revealed that microES used more irritation descriptors than did AEW on trials where the acetone concentration was below the lateralization threshold. This is noteworthy because microES received lower concentrations of acetone to evaluate than did AEW. These results suggest that exposures to acetone induce changes in acetone sensitivity that are specific to acetone. The acetone concentrations eliciting sensory irritation using the lateralization technique were all well above current occupational exposure standards. The current study indicates that acetone is a weak sensory irritant and that sensory adaptation is an important factor affecting its overall irritancy.

Numerical modeling of nasal obstruction and endoscopic surgical intervention: Outcome to airflow and olfaction

Background Mechanical obstruction of odorant flow to the olfactory neuroepithelium may be a primary cause of olfactory loss in nasal-sinus disease patients. Surgical removal of nasal obstruction may facilitate the recovery of olfactory ability. Unfortunately, quantifying the functional impact of nasal obstruction and subsequent surgical outcomes using acoustic rhinometry, rhinomanometry, or CT scans is inadequate. Methods Using computational fluid dynamics (CFD) techniques, we can convert patient CT scans into anatomically accurate 3D numerical nasal models that can be used to predict nasal airflow and odorant delivery rates. These models also can be rapidly modified to reflect anatomic changes, e.g., surgical removal of polyps. Results CFD modeling of one patients nose pre- and postsurgery showed significant improvement in postsurgical ortho- and retronasal airflow and odorant delivery rate to olfactory neuroepithelium (<1000 times), which correlated well with olfactory recovery. Conclusion This study has introduced a novel technique (CFD) to calculate nasal airflow dynamics and its effects on olfaction, nasal obstruction, and sinus disease. In the future, such techniques may provide a quantitative evaluation of surgical outcome and an important preoperative guide to optimize nasal airflow and odorant delivery.

Perceived odor, irritation, and health symptoms following short-term exposure to acetone

The subjectivity of irritancy judgments can bias attempts to establish exposure guidelines that protect individuals from the sensory irritation produced by volatile chemicals. At low to moderate chemical concentrations, naive and occupationally exposed individuals often show considerable variation in the reported levels of perceived irritation. Such variation could result from differences in exposure history, differences in the perceived odor of a chemical, or differences in generalized response tendencies to report irritation, or response bias. Thus, experimental evaluation of sensory irritancy must dissociate sensory irritation from response bias. To this end, judgments of perceived irritation from 800 ppm acetone were obtained from acetone-exposed workers and age- and gender-matched naive controls. To assess the role of response bias during exposure to odorants, subjects were also exposed to phenylethyl alcohol (PEA), an odorant that does not produce sensory irritation. Following exposure, subjects completed a subjective symptom survey that included symptoms that have been associated with long-term solvent exposures and symptoms that have not. Acetone-exposed workers and naive controls reported large differences in the perceived intensity of odor and irritation from acetone, yet no differences in the perception of PEA. However, for both groups, the most significant factors mediating reported irritancy and health symptoms from acetone were the perceived intensity of its odor and an individuals bias to report irritation from PEA. The perception of odor intensity and degree of response bias will differ between and within groups of exposed and naive individuals; hence, an assessment of the influence of these factors in experimental and workplace studies of chemical irritancy is warranted.

Evaluating the human response to chemicals: odor, irritation and non-sensory factors

Although airborne chemicals can directly elicit adverse reactions via stimulation of the olfactory and trigeminal nerves, such as sensory irritation of the mucous membranes of the eyes, nose and throat, an individuals subjective experience is often the result of a complex sequence of events involving those sensory, physiological signals and psychological processes involved in perception, memory and judgment. To evaluate the contribution of these processes, an information-processing model of chemosensory perception is introduced. The model incorporates (1) the perception of odor and trigeminal irritation, and accompanying physiological and somatic changes that follow directly from the encounter with volatile organic compounds (VOCs) in the environment (bottom-up processing), and (2) any physiological/ somatic changes and subjective experiences of irritancy that are influenced by cognitive processes that have been primed by the perception of odor (top-down processing). The model is illustrated with data from our laboratory, and its utility in the context of setting occupational exposure limits is discussed.

Assessment of ocular and nasal irritation in asthmatics resulting from fragrance exposure

Background Many asthmatics report worsening of symptoms following exposure to odours and sensory irritants commonly found in household and cosmetic products. Despite this, little evidence exists to confirm the degree to which such subjective reports are correlated with localized, objective changes in the upper or lower airways following a fragranced product exposure.

Evaluation of odor and sensory irritation thresholds for methyl isobutyl ketone in humans.

Odor and irritation sensitivity for methyl isobutyl ketone (MIBK) was evaluated by obtaining olfactory detection thresholds and irritation (lateralization) thresholds, as well as perceived odor intensity and irritation ratings for three predetermined concentrations of MIBK, acetone, and phenylethyl alcohol. Subsequently, perceived annoyance ratings for the three concentrations were measured for 25 of the 40 volunteers. The mean odor detection threshold for MIBK was 10 ppm, and mean lateralization threshold was 8874 ppm. Calculating the fifth percentile for lateralization thresholds revealed that 95% of the sample population did not experience sensory irritation at or below 1802 ppm. Thus, while odor thresholds were well below the current recommended exposure limits (50 ppm, threshold limit value; 75 ppm short-term exposure limit, American Conference of Governmental Industrial Hygienists), irritation thresholds were significantly higher. Odor and irritation intensity ratings for the chemicals increased with increasing concentrations and were higher for MIBK than for acetone. However, when the affective component of the irritation response (annoyance) was rated separately from the sensory component (perceived irritation), no significant differences were found between the irritancy of MIBK and acetone, suggesting that negative hedonic evaluations of MIBK (perhaps based on odor unfamiliarity) contributed to ratings of perceived irritation. These results validate coupling affective and sensory ratings to more effectively examine the human response to volatile stimuli. Results indicate that intranasal sensory irritation from MIBK will not be experienced at or near current exposure levels. Notably, the best predictors of perceived irritation to high concentrations of MIBK were those measures related to its odor, not to the threshold for sensory irritation, suggesting that negative responses to MIBK involve reactions to olfactory properties.

Sweet taste and menthol increase cough reflex thresholds.

Cough is a vital protective reflex that is triggered by both mechanical and chemical stimuli. The current experiments explored how chemosensory stimuli modulate this important reflex. Cough thresholds were measured using a single-inhalation capsaicin challenge. Experiment 1 examined the impact of sweet taste: Cough thresholds were measured after rinsing the mouth with a sucrose solution (sweet) or with water (control). Experiment 2 examined the impact of menthol: Cough thresholds were measured after inhaling headspace above a menthol solution (menthol vapor) or headspace above the mineral oil solvent (control). Experiment 3 examined the impact of rinsing the mouth with a (bitter) sucrose octaacetate solution. Rinsing with sucrose and inhaling menthol vapor significantly increased measured cough thresholds. Rinsing with sucrose octaacete caused a non-significant decrease in cough thresholds, an important demonstration of specificity. Decreases in cough reflex sensitivity from sucrose or menthol could help explain why cough syrups without pharmacologically active ingredients are often almost as effective as formulations with an added drug. Further, the results support the idea that adding menthol to cigarettes might make tobacco smoke more tolerable for beginning smokers, at least in part, by reducing the sensitivity of an important airway defense mechanism.