Healthy Buildings 2017 Europe July 2-5, 2017, Lublin, Poland. Influence of Intermittent Exposure of Odor on Odor Intensity and Olfactory Adaptation

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1 Healthy Buildings 07 Europe July -5, 07, Lublin, Poland Paper ID 098 ISBN: Influence of Intermittent Exposure of Odor on Odor Intensity and Olfactory Adaptation Hiromi Yamada,*, Shin-ichi Tanabe, Motoya Hayashi Nagasaki Institute of Applied Science, Japan Waseda University, Japan National Institute of Public Health, Japan * YAMADA_Hiromi@NiAS.ac.jp SUMMARY The issue of odor control has become increasingly important for residents living in airtight homes. Olfactory adaptation has been studied in recent years, but it is necessary to consider the ability to recover the sense of smell after breathing clean air. The purpose of this study was to investigate the effects of intermittent odor exposure on odor intensity and olfactory adaptation. Participants were exposed to three odor conditions: clean air, constant exposure to Hinoki Cypress, and intermittent exposure to Hinoki Cypress. In the case of constant odor exposure, olfactory adaptation was indicated immediately, and in the case of intermittent exposure, the participants sense of smell recovered after breathing clean air for only min. For the calculated results of the model estimate, the estimate was obtained when the odor intensity was modeled in the primary stage (for 5 min). However, the calculated values under odorless conditions were lower than the experimentally obtained values. KEYWORDS Hinoki Cypress; olfactory adaptation; odor intensity; intermittent exposure INTRODUCTION The issue of odor control has become increasingly important for residents living in airtight homes. Olfactory adaptation has been studied in recent years, but it is necessary to consider the ability to recover the sense of smell after breathing clean air (Fig.). The purpose of this study was to investigate the effects of intermittent odor exposure on odor intensity and olfactory adaptation. Gap Notice Time Fig. Outline of recovery of olfactory function

2 MATERIALS/METHODS Materials and methods Research participants were exposed to three odor conditions: clean air, constant exposure to Hinoki Cypress, and intermittent exposure to Hinoki Cypress. Observations of the participants were then subjectively evaluated. Participants Six paid volunteers, five male and one female, participated in the experiment. The participants were randomly divided into two groups (group A and group B). They were told not to use perfume or any scented hair products the day before and the day of the experiment and to also abstain from coffee beverages. Odor presentation system We used an odor test room and odor presentation system in the study. The odor presentation system is shown in Fig.. Flow meter Charcoal filter Valve B Fan Valve A Cypress chips Duct made of stainless steel Small chamber Fig. Odor presentation system Although a liquid-dilution olfactometer is generally used to study odor adaptation, we employed the odor presentation system shown in Fig. to examine the influence of cognitive effects on the perceived intensity in the adaptation processes under the intermittent condition. The odor presentation system consisted of a fan, charcoal filter, flow meter, valve, small chamber, duct, and nasal mask. Controlling the factors related to olfactory perception was possible with a flow meter and control valve that controlled the odorant concentration and emission interval. The air in the experimental room was pumped through charcoal filters to create clean air. After cleaning the air, the odorized air was created by wood chips cut 5-mm thick in a small chamber (φ 50 mm H = 50 mm) and was delivered to the participants through a nasal mask. The odorized air was controlled by two valves, one connected with the nasal mask directly and the other connected first to a small chamber and then to the sampling mask. Participants sampled the odorants by positioning their nose inside a vented nasal mask made of polyethylene terephthalate. Perceived intensity evaluation The experimenter guided the participants to ensure they were able to perform the perceived intensity evaluation. Before the evaluation, all participants received experimental instructions that defined odor intensity and comfort level used in the questionnaire. During the evaluation process, participants were asked to evaluate in real time the odor intensity and preference level of the odor by marking it on a horizontal line on an LCD display of a laptop computer. The subjects evaluated odor intensity on a six-point scale, from 0 = No odor to 5 = Very

3 strong odor (Fig. ). The perceived intensity data were sampled and recorded automatically every 0 s. 0 5 No odor Threshold Identifiable Distinct Strong Very strong Fig. Conditions The four experimental conditions in which patients breathed the air are as follows (Fig. ): Condition : odorless air was presented for 0 min ("odorless"), Condition : continuous odor stimulus was presented for 0 min ("continuous"), Condition : after odor stimulus was presented for 5 min, odorless air was presented for 5 min ("intermittent 55"), and Condition : after odor stimulus was presented for 5 min, odorless air was presented for min ("intermittent 5"). 0min 0min a) Odorless b) Continuous min c) Intermittent min d) Intermittent 5 Fig. Experimental conditions Procedure The overall experimental schedule is listed in Table. The presentation order for the experimental conditions for each group was random. Each participant participated in one experimental condition per day and avoided participating continuously because of olfactory fatigue. After the experimenter confirmed that the participants had not consumed a coffee beverage or were wearing perfume or any scented hair products, they were exposed to each condition. Table Schedule Group A: Patients No. Group B: Patients No. 6 (Nov.) guidance, odorless - (Nov.) - guidance, intermittent 5 (Nov.) continuous - (Nov.5) - intermittent 55 5 (Nov.8) intermittent 55-6 (Nov.9) - continuous 7 (Nov.) intermittent 5-8 (Nov.) - odorless Estimating model Several estimation models have been used by different authors in attempts to model the stimulus response relationship of olfactory adaptation (Osako et al., 99; Nagatsugu et al., 00). The perceived odor intensity of a given substance can be expressed as a function of

4 physicochemical variables, its concentration in the air being delivered on the mucosa through the Osako model. The odor intensity model (dx/dt) expressed by Dr. Osako is given by dx = k ( N x) C k x, () dt where k is the adsorption rate constant of odorized substances on sensory receptors, k- is the desorption rate constant of odorized substances on a sensory receptor, C is the concentration of odor at the mucous layer in the nasal cavity, x is the number of odorant substances adsorbed on sensory receptors in the intranasal area, and N is the number of sensory receptors in the intranasal area. The number of odorant substances adsorbed on the sensory receptors is expressed by x k NC k C + k ( { } k e C + k ) t =. () It was necessary to use Osako s Equation (()) to calculate the odor intensity when breathing in and when breathing out separately. Given that the odor intensity depends only on the adsorption rate of odorized substances by sensory receptors, the equation of odor intensity is given as da = k( N x) C, () dt where a is the constant ratio of bond of odorized substances to sensory receptors. Hence, substitution of equation () in equation () leads to ( C+ k t { e } k da knc = k C N ). () dt kc + k RESULTS Experimental results Fig. 5 shows the responses of odor intensity under each condition. In the "continuous" condition, the initial odor intensity was approximately, and then it exhibited a steep dip until the 5-min mark where it became zero, even though the odor intensity values remained at approximately 0.5. The reason for this seems to be the influence of odor adaptation. In both "intermittent 55" and "intermittent 5," the odor intensity also decreased exponentially with time during the 5 min, similar to that of the "continuous" condition. However, after stopping the emission of an odor, the existence of the odor intensity for breathing odorless air was confirmed experimentally. Conversely, after the termination of the odorless period, the participants olfactory ability began to rapidly recover, indicating approximately.5 (between ": Identifiable" and ": Distinct"). The odor intensity after breathing clean air for only min was equal or less than that of the first term, and the olfactory ability recovered rapidly. The results revealed that the recovery of the olfactory nerves required breathing clean air for only min.

5 Time(min) Time(min) Time(min) continuous intermittent 55 intermittent 5 Fig. 5 results (The periods "a" and "b" in the figure show "odor" and "odorless," respectively.) Estimation of the model With this model (Equation ()), the parameters k, k-, N, and C were estimated using a nonlinear regression between elapsed time and odor intensity (according to Equation ) at "intermittent55" and "intermittent5." Table shows the results for the parameters of the estimation model, which are the averages of the experimental results of three trials. A comparison of "intermittent55" and "intermittent5" shows that these parameters were equal. In each condition, the desorption rate constant k- was larger than that of adsorption rate constant k. Table Parameters of the estimation model k k - N C intermittent55.8*0 -.56* intermittent5.88*0 -.*0-6.6 To verify the estimation model, we tried to calculate the change in the constant ratio of bond of odorized substances to sensory receptor and to compare the experimental results with the results calculated by Equation (). To solve this system of equations, the Runge Kutta Fehlberg method was used as an approximation analysis. The estimation model was used to fit data on four parameters under two conditions, "intermittent55" and "intermittent5" (Table ). Fig. 6 shows the results of odor intensity by comparing the experimental and calculated values. In the first stage under each condition, for 5 min, the estimates were obtained when the odor intensity was modeled using Equation. However, the calculated values were not consistent with the experimental values under the "odorless" condition. Despite the fact that there were few odor intensities under the "odorless" condition, hardly any occurred in the calculated values. Although the cause of the difference between the experimental and calculated values is unknown, the existence of the odor intensity under the odorless condition seemed to result from either residual odorized substances on the sensory receptors or the misinterpretation as to which odorants had been emitted. In the second and third intermittent emissions of "intermittent 5," the initial calculated values, which were under at the 7- and -min mark, were lower than the experimental values. These differences in odor intensity showed that the olfactory ability could not recover sufficiently in this model and the effect of the desorption rate constants of odorized substances on sensory receptors, k-, may have been estimated after the continuous odor presentation stopped. In future studies, desorption rate constants in the calculations need to be discussed in more detail.

6 Time(min) Experiment Model Time(min) a) Intermittent55 b) Intermittent5 Fig. 6 Results of calculated values (The periods "a" and "b" in the figure show "odor" and "odorless," respectively.) Experiment Model CONCLUSIONS This study investigated the effect of intermittent exposure of odor on odor intensity and olfactory adaptation using an odor presentation system and estimation model. In constant odor conditions, initial odor intensity was rated as approximately, and then its intensity exhibited a steep downward curve until the 5-min mark because of odor adaptation. Although odor intensity exponentially decreased in both "intermittent 55" and "intermittent 5" cases, the odor intensity after breathing clean air for only min was equal or less than that of the first term and the olfactory ability recovered rapidly. The results revealed that olfactory sense recovery only requires breathing clean air for min. For the calculated results in the model estimate, the estimate was obtained when the odor intensity was modeled in the primary stage (for 5 min). However, the calculated values under odorless conditions were not consistent with the experimental values and resulted in lower values. The initial calculated values after starting the odor emission in the second and third intermittent emissions also differed from the experimental values. Thus, we demonstrated the influence of intermittent exposure of an odor on odor intensity and olfactory adaptation. 5 ACKNOWLEDGEMENT This work was supported by JSPS KAKENHI grant number 5K06. 6 REFERENCES Osako, M., Nishida, K. & Matsui, S. Proposition of Olfactory Adaptation Model and a Study on Method of Applicating the Model to Design of the Comfortable Fragrant Space. Transactions of the Society of Heating, Air-Conditioning and Sanitary Engineers of Japan. (6), 9, Nagatsugu, H., Yamanaka, T., Sagara, K., Kotani, H., Momoi, Y., & Takemura, A. (00). Adaptation process of human olfactory under continuous exposure to odor of ethyl acetate based on subjective estimation of odor intensity. In AIVC International Conference (Vol. 00). BamBa, I., & Azuma, K. (05). Psychological and Physiological Effects of Japanese Cedar Indoors after Calculation Task Performance. Journal of the Human-Environment System, 8(),. Kobayashi, T., Sakai, N., Kobayakawa, T., Akiyama, S., Toda, H., & Saito, S. (008). Effects of cognitive factors on perceived odor intensity in adaptation/habituation processes: from different odor presentation methods. Chemical senses, (), 6 7. Yoder, W. M., LaRue, A. K., Rosen, J. M., Aggarwal, S., Shukla, R. M., Monir, J., & Smith, D. W. (0). Evidence of rapid recovery from perceptual odor adaptation using a new stimulus paradigm. Attention, Perception, & Psychophysics, 76(),