Using SCENTinel® to predict SARS-CoV-2 infection: insights from a community sample during dominance of Delta and Omicron variants

Introduction

Based on a large body of previous research suggesting that smell loss was a predictor of COVID-19, we investigated the ability of SCENTinel®, a newly validated rapid olfactory test that assesses odor detection, intensity, and identification, to predict SARS-CoV-2 infection in a community sample.

Methods

Between April 5, 2021, and July 5, 2022, 1,979 individuals took one SCENTinel® test, completed at least one physician-ordered SARS-CoV-2 PCR test, and endorsed a list of self-reported symptoms.

Results

Among the of SCENTinel® subtests, the self-rated odor intensity score, especially when dichotomized using a previously established threshold, was the strongest predictor of SARS-CoV-2 infection. SCENTinel® had high specificity and negative predictive value, indicating that those who passed SCENTinel® likely did not have a SARS-CoV-2 infection. Predictability of the SCENTinel® performance was stronger when the SARS-CoV-2 Delta variant was dominant rather than when the SARS-CoV-2 Omicron variant was dominant. Additionally, SCENTinel® predicted SARS-CoV-2 positivity better than using a self-reported symptom checklist alone.

Discussion

These results indicate that SCENTinel® is a rapid assessment tool that can be used for population-level screening to monitor abrupt changes in olfactory function, and to evaluate spread of viral infections like SARS-CoV-2 that often have smell loss as a symptom.

More spice, less salt: How capsaicin affects liking for and perceived saltiness of foods in people with smell loss

People who lose their sense of smell self-report consuming more salt to compensate for a lack of flavor and enhance eating enjoyment. However, this may contribute to excess sodium intake. Capsaicin may help increase salt taste intensity and eating enjoyment in people with smell loss, but this has not been studied in this population. The purpose of this study was to determine 1) whether salt intake in those with smell loss differs from population averages, 2) whether capsaicin increases flavor and salt taste intensity, and 3) if adding spice to foods increases liking in individuals with smell loss. Thirty-three participants 18-65 years old with confirmed smell loss for at least 12 weeks completed two sets of replicate test sessions (four total). In two sessions participants rated overall flavor intensity, taste qualities' intensities, spicy intensity, and liking for model tomato soups with low or regular sodium content and three levels of capsaicin (none, low, or moderate). In the other two sessions, participants rated the same sensory attributes for model food samples with three levels of added spice (none, low, or moderate). 24-hour urine samples were collected to determine sodium intake. Results indicate that although sodium intake is higher than recommended (<2300 mg/day) in those with smell loss (2893 ± 258 mg/day), they do not consume more sodium than population averages (3039 ± 100 mg/day; p = 0.3). Adding low and moderate amounts of capsaicin to a model tomato soup increased the intensity of overall flavor (p < 0.001) and saltiness (p = 0.004) compared to a model tomato soup without capsaicin. However, capsaicin's effect on liking differed by food type. Thus, capsaicin can improve flavor, salt taste intensity, and eating enjoyment in people with smell loss.

Patient Insights into the Diagnosis of Smell and Taste Disorders in the United States

OBJECTIVES

Diagnosis of smell/taste dysfunction is necessary for appropriate medical care. This study examines factors affecting testing and diagnosis of smell/taste disorders .

METHODS

The online USA Smell and Taste Patient Survey was made available to US patients with smell/taste disorders between April 6-20, 2022. 4,728 respondents were included.

RESULTS

1,791 (38%) patients reported a documented diagnosis. Patients most often saw family practitioners (34%), otolaryngologists (20%), and Taste/Smell clinics (6%) for smell/taste dysfunction. 64% of patients who went to Taste/Smell clinics received smell testing, followed by 39% of patients who saw otolaryngologists, and 31% of patients who saw family practitioners. Factors associated with increased odds of diagnosis included age (25-39 years (OR 2.97, 95% CI [2.25, 3.95]), 40-60 (OR 3.3, 95% CI [2.56, 4.52]), and >60 (OR 4.25, 95% CI [3.21, 5.67]) vs. 18-24 years), male gender (OR 1.26, 95% CI [1.07, 1.48]), insurance status (private (OR 1.61, 95% CI [1.15, 2.30]) or public (OR 2.03, 95% CI [1.42, 2.95]) vs. uninsured), perception of their family practitioner to be knowledgeable (OR 2.12, 95% CI [1.16, 3.90]), otolaryngologic evaluation (OR 6.17, 95% CI [5.16, 7.38]), and psychophysical smell testing (OR 1.77, 95% CI [1.42, 2.22]).

CONCLUSION

Psychophysical testing, otolaryngologic evaluation, patient assessment of family practitioner knowledge level, insurance, age, and gender are significant factors in obtaining smell/taste dysfunction diagnosis. This study identifies barriers to diagnosis including lack of insurance or access to specialist evaluation and highlights the importance of educating family practitioners in diagnosis and management of patients with smell/taste disorders.

Exploring Olfactory Dysfunction as a Marker of Frailty and Postoperative Outcomes in Head and Neck Cancer

Importance

Olfactory dysfunction (OD) is increasingly recognized as a robust marker of frailty and mortality. Despite broad recognition of frailty as a critical component of head and neck cancer (HNC) care, there is no standardized frailty assessment.

Objective

To assess the prevalence of OD and its association with frailty and postoperative outcomes in HNC.

Design, Setting, and Participants

In this prospective cohort study with enrollment between February 17, 2021, to September 29, 2021, at a tertiary academic medical center, 85 eligible adult patients with primary, treatment-naive HNC of mucosal or cutaneous origin were included. Patients with a history of COVID-19, neurocognitive, or primary smell/taste disorders were excluded.

Exposures

Prospective olfactory assessments (self-reported, visual analog scale [VAS] and psychophysical, University of Pennsylvania Smell Identification Test [UPSIT]) with concurrent frailty assessment (Risk Analysis Index [RAI]) were used. Olfactory-specific quality of life (QOL) was examined with brief Questionnaire of Olfactory Disorders-Negative Statements (QOD-NS).

Main Outcome(s) and Measure(s)

The primary outcome was the prevalence of OD as assessed by VAS (0-10, no to normal smell) and UPSIT (0-40, higher scores reflect better olfaction) and its association with frailty (RAI, 0-81, higher scores indicate greater frailty). For surgical patients, secondary outcomes were associations between OD and postoperative length of stay (LOS), 30-day postoperative outcomes, and QOD-NS (0-21, higher scores indicate worse QOL).

Results

Among 51 patients with HNC (mean [SD] age, 63 [10] years; 39 [77%] male participants; 41 [80%] White participants), 24 (47%) were frail, and 4 (8%) were very frail. Despite median (IQR) self-reported olfaction by VAS of 9 (8-10), 30 (59%) patients demonstrated measured OD with psychophysical testing. No meaningful association was found between self-reported and psychophysical testing (Hodges-Lehmann, <0.001; 95% CI, -2 to 1); a total of 46 (90%) patients did not report decreased olfaction-specific QOL. Median UPSIT scores were lower in frail patients (Hodges-Lehmann, 6; 95% CI, 2-12). Multivariate modeling demonstrated severe microsmia/anosmia was associated with 1.75 (95% CI, 1.09-2.80) times odds of being frail/very frail and approximately 3 days increased LOS (β, 2.96; 95% CI, 0.29-5.62).

Conclusions and Relevance

Although patients with HNC are unaware of olfactory changes, OD is common and may serve as a bellwether of frailty. In this prospective cohort study, a dose-dependent association was demonstrated between increasing degrees of OD and frailty, and the potential utility of olfaction was highlighted as a touchstone in the assessment of HNC frailty.

More spice, less salt: how capsaicin affects liking for and perceived saltiness of foods in people with smell loss

People who lose their sense of smell self-report consuming more salt to compensate for a lack of flavor and enhance eating enjoyment. However, this can contribute to excess sodium intake and a poor diet. Capsaicin may help increase salt taste intensity and eating enjoyment in this population, but this has not been studied. The purpose of this study was to determine 1) whether salt intake in those with smell loss differs from population averages, 2) whether capsaicin increases flavor and salt taste intensity, and 3) if adding spice to foods increases food liking in individuals with smell loss. Participants 18-65 years old with confirmed partial or total smell loss for at least 12 weeks completed two sets of replicate test sessions (four total). In two sessions participants rated overall flavor intensity, taste qualities' intensities, spicy intensity, and liking for model tomato soups with low or regular sodium content and three levels of capsaicin (none, low, or moderate). In the other two sessions, participants rated the same sensory attributes for model food samples with three levels of added spice (none, low, or moderate). 24-hour urine samples were also collected to determine sodium intake. Results indicate that although sodium intake is higher than recommended in those with smell loss (2893 ± 258 mg/day), they do not consume more sodium than population averages. Adding low and moderate amounts of capsaicin to a model tomato soup increased the intensity of overall flavor and saltiness compared to a model tomato soup without capsaicin. However, the effect of capsaicin on liking differed by food type. In conclusion, the addition of capsaicin can improve flavor, salt taste intensity, and eating enjoyment in people with smell loss.

Low to moderate genetic influences on the rapid smell test SCENTinel™

SCENTinel™ - a rapid, inexpensive smell test that measures odor detection, intensity, identification, and pleasantness - was developed for population-wide screening of smell function. SCENTinel™ was previously found to screen for multiple types of smell disorders. However, the effect of genetic variability on SCENTinel™ test performance is unknown, which could affect the test's validity. This study assessed performance of SCENTinel™ in a large group of individuals with a normal sense of smell to determine the test-retest reliability and the heritability of SCENTinel™ test performance. One thousand participants (36 [IQR 26-52] years old, 72% female, 80% white) completed a SCENTinel™ test at the 2021 and 2022 Twins Days Festivals in Twinsburg, OH, and 118 of those completed a SCENTinel™ test on each of the festival's two days. Participants comprised 55% percent monozygotic twins, 13% dizygotic twins, 0.4% triplets, and 36% singletons. We found that 97% of participants passed the SCENTinel™ test. Test-retest reliability ranged from 0.57 to 0.71 for SCENTinel™ subtests. Broad-sense heritability, based on 246 monozygotic and 62 dizygotic twin dyads, was low for odor intensity (r=0.03) and moderate for odor pleasantness (r=0.4). Together, this study suggests that SCENTinel™ is a reliable smell test with only moderate heritability effects, which further supports its utility for population-wide screening for smell function.

Characterization of Ethyl Butyrate-Induced Cough Before and After Breath Control Techniques in Healthy Adults

PURPOSE

Methods for cough elicitation frequently involve aerosolized tussive agents. Here, we sought to determine whether healthy individuals demonstrate a quantifiable cough response after inhaling a volatile ester and if breath control techniques modify this chemically induced cough response.

METHOD

Sixty adult male and female participants inhaled prepared liquid dilutions of ethyl butyrate dissolved in paraffin oil at 20%, 40%, and 60% v/v concentrations in triplicate, with presentation order randomized. We delivered stimuli through a face mask connected to an olfactometer and respiratory pneumotachograph. Participants rated sensations of their urge to cough and pleasantness of the odor while cough airflow was measured. Following baseline testing, participants were randomized to implement pursed-lip breathing or slow-paced breathing after inhaling ethyl butyrate to determine the effects of breath control on cough measures.

RESULTS

Inhaled ethyl butyrate elicited cough in 70% of participants. Higher concentrations of ethyl butyrate resulted in significantly greater sensation of the urge to cough, F(2, 80) = 10.72, p < .001, and significantly more generated coughs, F(2, 63) = 13.14, p < .001. Compared to baseline, participants rated significantly decreased urge to cough during breath control techniques, F(1, 40) = 11.01, p = .0019. No significant changes were observed in the number of generated coughs between baseline and breath control techniques, F(1, 31) = 7.23, p = .01.

CONCLUSIONS

Airborne ethyl butyrate is a tussigenic agent in humans. Our findings provide opportunities for future research directions in normal and disordered cough responses to volatile compounds.

Examining the Influence of Chemosensation on Laryngeal Health and Disorders

Inhaled airborne stimuli are associated with laryngeal disorders affecting respiration. Clinically, several themes emerged from the literature that point to specific gaps in the understanding and management of these disorders. There is wide variation in the types of airborne stimuli that trigger symptoms, lack of standardization in provocation challenge testing using airborne stimuli, and vague reporting of laryngeal symptoms. Scientifically, evidence exists outside the field of voice science that could prove useful to implement among patients with impaired laryngeal-respiration. To expand this area of expertise, here we provide a thematic overview of relevant evidence and methodological tools from the discipline of chemosensory sciences. This review provides distinctions across the three chemosensory systems of olfaction, trigeminal chemesthesis, and gustation, guidance on selecting and delivering common chemosensory stimuli for clinical testing, and methods of quantifying sensory experiences using principles of human psychophysics. Investigating the science of chemosensation reveals that laryngeal responses to inhaled airborne stimuli have explanations involving physiological mechanisms as well as higher cognitive processing. Fortunately, these findings are consistent with current pharmacological and nonpharmacological interventions for impaired laryngeal-respiration. Based on the close relationships among inhaled airborne stimuli, respiration, and laryngeal function, we propose that new perspectives from chemosensory sciences offer opportunities to improve patient care and target areas of future research.

Environmental chamber studies of eye and respiratory irritation from use of a peracetic acid-based hospital surface disinfectant

Objective

To characterize personal exposures and measures of eye and respiratory tract irritation in controlled environmental chamber studies of 44 healthy adult volunteers simulating upper-bound use of peracetic acid (PAA)-based surface disinfectant for terminal cleaning of hospital patient rooms.

Design

Experimental, within-subject, double-blinded cross-over design.

Methods

Objective and subjective exposure effects were assessed for PAA and its components: acetic acid (AA) and hydrogen peroxide (HP). Deionized water was included as a control. Breathing-zone concentrations of PAA, AA, and HP were assessed for 8 female multiday volunteers (5 consecutive days) and 36 single-day volunteers (32 females and 4 males). Wetted cloths were used to wipe high-touch surfaces for 20 minutes per trial. Also, 15 objective measures of tissue injury or inflammation and 4 subjective odor or irritation scores were assessed.

Results

Disinfectant trials showed 95th percentile breathing zone concentrations of 101 ppb PAA, 500 ppb AA, and 667 ppb HP. None of the volunteers observed over 75 test days exhibited significant increases in IgE or objective measures of eye and respiratory tract inflammation. Subjective ratings for disinfectant and AA-only trials showed similar increases for odor intensity and nose irritation, with lower ratings for eye and throat irritation. Females were 2.5-fold more likely than males to assign moderate + irritation ratings.

Conclusions

Simulated upper-bound hospital use of PAA-based disinfectant led to no significant increases in objective markers of tissue injury, inflammation, or allergic sensitization, and no frank signs of eye or respiratory tract irritation.

Proof-of-concept: SCENTinel 1.1 rapidly discriminates COVID-19-related olfactory disorders

It is estimated that 20%-67% of those with COVID-19 develop olfactory disorders, depending on the SARS-CoV-2 variant. However, there is an absence of quick, population-wide olfactory tests to screen for olfactory disorders. The purpose of this study was to provide a proof-of-concept that SCENTinel 1.1, a rapid, inexpensive, population-wide olfactory test, can discriminate between anosmia (total smell loss), hyposmia (reduced sense of smell), parosmia (distorted odor perception), and phantosmia (odor sensation without a source). Participants were mailed a SCENTinel 1.1 test, which measures odor detection, intensity, identification, and pleasantness, using one of 4 possible odors. Those who completed the test (N = 287) were divided into groups based on their self-reported olfactory function: quantitative olfactory disorder only (anosmia or hyposmia, N = 135), qualitative olfactory disorder only (parosmia and/or phantosmia; N = 86), and normosmia (normal sense of smell; N = 66). SCENTinel 1.1 accurately discriminates quantitative olfactory disorders, qualitative olfactory disorders, and normosmia groups. When olfactory disorders were assessed individually, SCENTinel 1.1 discriminates between hyposmia, parosmia, and anosmia. Participants with parosmia rated common odors less pleasant than those without parosmia. We provide proof-of-concept that SCENTinel 1.1, a rapid smell test, can discriminate quantitative and qualitative olfactory disorders, and is the only direct test to rapidly discriminate parosmia.

Proof-of-concept: SCENTinel 1.1 rapidly discriminates COVID-19 related olfactory disorders

It is estimated that 20-67% of those with COVID-19 develop olfactory disorders, depending on the SARS-CoV-2 variant. However, there is an absence of quick, population-wide olfactory tests to screen for olfactory disorders. The purpose of this study was to provide a proof-of-concept that SCENTinel 1.1, a rapid, inexpensive, population-wide olfactory test, can discriminate between anosmia (total smell loss), hyposmia (reduced sense of smell), parosmia (distorted odor perception), and phantosmia (odor sensation without a source). Participants were mailed a SCENTinel 1.1 test, which measures odor detection, intensity, identification, and pleasantness, using one of four possible odors. Those who completed the test (N = 381) were divided into groups based on their self-reported olfactory function: quantitative olfactory disorder (anosmia or hyposmia, N = 135), qualitative olfactory disorder (parosmia and/or phantosmia; N = 86), and normosmia (normal sense of smell; N = 66). SCENTinel 1.1 accurately discriminates quantitative olfactory disorders, qualitative olfactory disorders, and normosmia groups. When olfactory disorders were assessed individually, SCENTinel 1.1 discriminates between hyposmia, parosmia and anosmia. Participants with parosmia rated common odors less pleasant than those without parosmia. We provide proof-of-concept that SCENTinel 1.1, a rapid smell test, can discriminate quantitative and qualitative olfactory disorders, and is the only direct test to rapidly discriminate parosmia.

SCENTinel 1.0: Development of a Rapid Test to Screen for Smell Loss

Commercially available smell tests are primarily used in research or in-depth clinical evaluations and are too costly and time-consuming for population surveillance in health emergencies like COVID-19. To address this need, we developed the SCENTinel 1.0 test, which rapidly evaluates 3 olfactory functions: detection, intensity, and identification. We tested whether self-administering the SCENTinel 1.0 test discriminates between individuals with self-reported smell loss and those with average smell ability (normosmic individuals) and provides performance comparable to the validated and standardized NIH Toolbox Odor Identification Test in normosmic individuals. Using Bayesian linear models and prognostic classification algorithms, we compared the SCENTinel 1.0 performance of a group of self-reported anosmic individuals (N = 111, 47 ± 13 years old, F = 71%) and normosmic individuals (N = 154, 47 ± 14 years old, F = 74%) as well as individuals reporting other smell disorders (such as hyposmia or parosmia; N = 42, 55 ± 10 years old, F = 67%). Ninety-four percent of normosmic individuals met our SCENTinel 1.0 accuracy criteria compared with only 10% of anosmic individuals and 64% of individuals with other smell disorders. Overall performance on SCENTinel 1.0 predicted belonging to the normosmic group better than identification or detection alone (vs. anosmic: AUC = 0.95, specificity = 0.94). Odor intensity provided the best single-feature predictor to classify normosmic individuals. Among normosmic individuals, 92% met the accuracy criteria at both SCENTinel 1.0 and the NIH Toolbox Odor Identification Test. SCENTinel 1.0 is a practical test able to discriminate individuals with smell loss and will likely be useful in many clinical situations, including COVID-19 symptom screening.

Chemosensory loss: functional consequences of the world trade center disaster

BACKGROUND

Individuals involved in rescue, recovery, demolition, and cleanup at the World Trade Center (WTC) site were exposed to a complex mixture of airborne smoke, dust, combustion gases, acid mists, and metal fumes. Such exposures have the potential to impair nasal chemosensory (olfactory and trigeminal) function.

OBJECTIVE

The goal of this study was to evaluate the prevalence of chemosensory dysfunction and nasal inflammation among these individuals.

METHODS

We studied 102 individuals who worked or volunteered at the WTC site in the days and weeks during and after 11 September 2001 (9/11) and a comparison group with no WTC exposure matched to each participant on age, sex, and job title. Participants were comprehensively evaluated for chemosensory function and nasal inflammation in a single session. Individual exposure history was obtained from self-reported questionnaires.

RESULTS

The prevalence of olfactory and trigeminal nerve sensitivity loss was significantly greater in the WTC-exposed group relative to the comparison group [prevalence ratios (95% confidence intervals) = 1.96 (1.2-3.3) and 3.28 (2.7-3.9) for odor and irritation thresholds, respectively]. Among the WTC responders, however, individuals caught in the dust cloud from the collapse on 9/11 exhibited the most profound trigeminal loss. Analysis of the nasal lavage samples supported the clinical findings of chronic nasal inflammation among the WTC-exposed cohort.

CONCLUSIONS

The prevalence of significant chemosensory impairment in the WTC-exposed group more than 2 years after their exposure raises concerns for these individuals when the ability to detect airborne odors or irritants is a critical safety factor.

RELEVANCE TO CLINICAL PRACTICE

This outcome highlights the need for chemosensory evaluations among individuals with exposure to acute high or chronic levels of airborne pollutants.

Odor and Irritation Thresholds for Ammonia: A Comparison between Static and Dynamic Olfactometry

Odor and lateralization (irritation) thresholds (LTs) for ammonia vapor were measured using static and dynamic olfactometry. The purpose of the study was to explore the test-retest reliability and comparability of dynamic olfactometry methodology, generally used to determine odor thresholds following European Committee for Standardization guidelines in the context of odor regulations to outside emissions, with static olfactometry. Within a 2-week period, odor and LTs for ammonia were obtained twice for each method for 24 females. No significant differences between methods were found: mean odor detection thresholds (ODTs) were 2.6 parts per million (ppm) for either method (P = 0.96), and mean LTs were 31.7 and 60.9 ppm for the static and dynamic method, respectively (P = 0.07). Test-retest reliability was higher for the dynamic than for the static method (r = 0.61 vs. 0.14 for ODTs and r = 0.86 vs. 0.45 for LTs). The choice of optimal method for any application, however, depends not only on psychometric factors but also on practical factors such as physicochemical properties of the compound, availability of equipment and expertise, task efficiency, and costs.

Setting occupational exposure limits in humans: contributions from the field of experimental psychology

Psychophysical methods from the field of experimental psychology are evaluated for their utility in the derivation of occupational exposure limits (OELs) for volatile chemicals based on acute sensory irritation in humans. The lateralization threshold method, which involves the localization of trigeminal vapor to the stimulated nostril, is evaluated for its underlying assumptions, reliability and validity. Whole body exposures, on the other hand, which involve the controlled, ambient exposure of human subjects to the irritant at one or a series of concentrations for an extended period are also discussed. It is concluded that the single-organ psychophysical method is largely resistant to response bias is practical and economical. However, its reliability and validity need further assessment. Whole body exposures, while having enhanced ecological validity, are more prone to demand characteristics, response bias, and subject beliefs than the traditional psychophysical procedures. An approach that involves the exposure of only the most sensitive organs such as the eyes and nose, via a mask or facebox, could facilitate the administration and alternation of odorant/irritant stimuli over a wide range of concentrations while enhancing ecological validity.

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 individual's 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.

Acute sensory irritation from exposure to isopropanol (2-propanol) at TLV in workers and controls: objective versus subjective effects

OBJECTIVES

Phlebotomists occupationally exposed to isopropanol (IPA) (2-propanol) and naïve controls (n = 12 per group) were exposed to the time-weighted average threshold limit value of 400 p.p.m. IPA for 4 h in an environmental chamber to investigate: (i) acute effects of sensory irritation using subjective health symptom reports and objective, physiological end-points; and (ii) differences in measured effects in relation to exposure history.

METHODS

Before, during and after exposure subjects gave self-reports of health complaints. During exposure subjects rated the intensity of the odor, sensory irritation and annoyance. Objective end-points of ocular hyperemia, nasal congestion, nasal secretion and respiration were obtained at various times before, during and after exposure. Results were compared with exposure to phenylethyl alcohol (PEA), a negative control for irritation, and to clean air (CA), a negative control for odor and irritation, using a within-subjects design.

RESULTS

Significantly higher intensity ratings of odor, irritation and annoyance were reported during the exposure to IPA, when compared with exposure to CA or PEA. Nevertheless, the overall level of reported sensory irritation to IPA was low and perceived as 'weak' on average. Health symptom ratings were not significantly elevated for IPA as compared with PEA or CA exposure. The only physiological end-point that showed a change exclusively in the IPA condition was respiration frequency: relative to baseline, respiration frequency increased in response to IPA in both groups. No differences were encountered between the occupationally exposed and the control groups.

CONCLUSIONS

The increase in respiration frequency in response to IPA may reflect either a reflexive change due to sensory irritation (an autonomic event) or a voluntary change in breathing in response to perception of an unpleasant, solvent-like odor (a physiological event caused by cognitive mediation). Our findings on objective end-points, including nasal and ocular sensory irritation, did not confirm subjective irritation reports. Irritation reports and odor intensity decreased, rather than increased, over time, lending credence to the cognitive argument and suggesting that the elevated subjective responses to IPA may be mediated by responses to its odor.

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.