Effect of Olfactory Stimulation by Fresh Rose Flowers on Autonomic Nervous Activity

Abstract

Objective:

To clarify the effect of olfactory stimulation by fresh rose flowers, which exude a strong fragrance, on heart rate variability.

Settings:

A chamber with an artificial climate maintained at 25°C with 50% relative humidity and 230 lux illumination at the Center for Environment, Health, and Field Sciences, Chiba University, Japan.

Participants:

Nineteen female university and graduate students (mean age, 21.6±1.5 years; age range, 19.0–26.0 years).

Interventions:

Fresh rose flowers as an olfactory stimulant, with air as a control.

Outcome measures:

Heart rate variability and subjective evaluations. The power levels of the high-frequency (HF) (0.15–0.40 Hz) and low-frequency (LF) (0.04–0.15 Hz) components of heart rate variability were calculated by the maximum-entropy method. The HF power was considered to reflect parasympathetic nervous activity. The LF/HF power ratio was determined to reflect the sympathetic nervous activity. A modified semantic differential method was used to perform subjective evaluations.

Results:

Fresh rose flowers induced (1) a significant increase in parasympathetic nervous activities and (2) an increase in “comfortable” and “natural” feelings.

Conclusion:

The findings indicated that olfactory stimulation by fresh rose flowers induced physiological and psychological relaxation.

Introduction

In modern societies, individuals are exposed to many stressors in daily life,^1

–4 and consequently, many individuals seek contact with nature to relax. One means of achieving contact with nature is viewing fresh flowers, such as roses. Roses are among the most popular flowers, are a common gift for women, and are used to decorate rooms.

The authors' earlier study showed that visual stimulation by fresh rose flowers (Rosa “Dekora”) induces physiological relaxation in female medical staff.⁵ To date, few studies have evaluated the physiological effects of the odor of roses on humans. Inhalation of the odor of rose essential oil (Rosa damascena MILL.) decreases relative sympathetic activity and adrenaline concentration in healthy adults.⁶ Moreover, Stankewitz et al. explored neuronal processing in response to olfactory stimulation with rose oil in patients with migraine by using event-related functional magnetic resonance imaging and found that the odor of rose oil induces significantly higher blood oxygen level–dependent signal intensities in several brain areas during spontaneous and untreated migraine attacks.⁷ In addition, Fukui et al. reported that rose odor (essential oil of Rosa alba) inhalation decreases cortisol levels in healthy volunteers.⁸ Fukada et al. showed that inhaling odor of rose essential oil (R. alba) inhibits increases in salivary cortisol and skin-barrier disruption in humans exposed to stress.⁹ Regarding subjective evaluations of effects, Ayan et al. used a visual analog scale of pain scores ranging from “no pain” to “very severe pain” to demonstrate that inhalation of odor of rose essential oil (R. damascena) is a useful supplementary and adjunctive therapy for relieving renal colic.¹⁰ Thus, the effects of olfactory stimulation by rose extracts, including rose essential oil, have been investigated using both physiological and subjective evaluations.

The present study is novel in many respects. First, no previous study has been performed using fresh rose flowers. Second, no other study has evaluated the physiological effects of olfactory stimulation by fresh rose flowers on women from the perspective of autonomic nervous activity, particularly by assessing heart rate variability (HRV), which is a measure of sympathetic and parasympathetic nervous activity. Finally, this study included a qualitative analysis of the characteristic odor of R. hybrida “Meikarouz,” also known as Rouge Royale.¹¹

As mentioned earlier, HRV has been used as a measure of autonomic nervous activity. The maximum-entropy method (MemCalc/Win; GMS, Tokyo, Japan) was used to calculate the power levels of high-frequency (HF, 0.15–0.40 Hz) and low-frequency (LF, 0.04–0.15 Hz) components. The HF power was considered to reflect parasympathetic nervous activity, and the LF/HF power ratio was considered to reflect sympathetic nervous activity.^12,13 Physiological relaxation effects were evaluated by using various previously described stimuli.^14

–19

The aim of the present study was to clarify the effect of olfactory stimulation by fresh rose flowers, which exude a strong fragrance, on HRV.

Materials and Methods

Participants

In this experiment, 19 healthy female volunteers were recruited from approximately 500 students at the authors' university and graduate school (mean age±standard deviation, 21.6±1.5 years; age range, 19.0–26.0 years). Women with breathing disorders, such as colds and nasal inflammation, were excluded. Participants were requested to get sufficient sleep the day before the experiment, to avoid drinking alcohol, and to control their conditions. All were informed of the aims and procedures involved in the experiment and provided written informed consent to participate. This study was performed in accordance with the regulations of the Ethics Committee of the Center for Environment, Health, and Field Sciences, Chiba University, Japan.

Study protocol

Physiological measurements were performed in a chamber with an artificial climate maintained at 25°C with 50% relative humidity and 230 lux illumination.²⁰ Fresh rose flowers (R. hybrida “Meikarouz,” also known as Rouge Royale,¹¹ from Enomoto Rose Garden, Japan) were used as an olfactory stimulant and air was used as a control. Four flowers were put into a 24-L odor bag (polyethylene terephthalate film heat seal bag; NS-KOKEN Co., Ltd. Kyoto, Japan), and the odors were presented to each participant by means of a device fixed on the chest and situated approximately 10 cm under the nose (Fig. 1). The flow rate of the odor was set at 3.0 L/min. Preliminary investigations determined the subjective sensitivity to odor as, for example, weak or easily sensed. The odor was administered for 90 seconds while the participants sat with their eyes closed.

FIG. 1.

The scene during olfactory stimulation and the device used to administer the odors.

A within-subject experiment was performed. To eliminate the effect of the order of olfactory stimulation, approximately half the participants were administrated stimuli in the following order: control, then rose. The remaining participants were then presented with the rose first, then control.

HRV

As a physiological measurement, HRV was analyzed for the periods between consecutive R waves in the electrocardiogram (RR intervals) as measured by a portable electrocardiograph (Activtracer AC-301; GMS).^21,22 This device performs measurements using a 3-lead electrocardiogram (lead II). The power levels of the HF (0.15–0.4 Hz) and the LF (0.04–0.15 Hz) components of HRV were calculated by the maximum-entropy method (MemCalc/Win). The HF power was considered to reflect parasympathetic nervous activity. Furthermore, the LF/HF power ratio was determined to reflect the sympathetic nervous activity. The means of data acquired for 90 seconds were analyzed.

Semantic differential method

Regarding psychological measurements, to subjectively evaluate the emotional effect of the odors, participants were tested by the modified semantic differential method.²³ The modified semantic differential method used two pairs of adjectives assessed on 13 scales, including “comfortable–uncomfortable,” and “natural–artificial.”

Measurement of volatile organic compounds

Volatile organic compounds emitted from the flowers were collected in PEJ-02 tubes (Supelco Inc., Bellefonte, PA) by enclosing one weighed flower inside a 5.0-L Tedlar bag (GL Science Inc., Tokyo, Japan).²⁴ The air flow rate through the bag was approximately 80 mL/min, and the temperature of the bag was 25.0±2.0°C. The collected volatile compounds were removed from the PEJ-02 tube by heating the trap with an Automatic Thermal Desorption System (ATD400, Perkin Elmer) at 280°C for 15 minutes. The compounds were cryofocused in a cold trap (air monitoring trap) at 2°C. By heating the cold trap, volatiles were transferred to a HP-5MS capillary column (30 m×0.25 mm i.d.×0.25-μm film thickness, Agilent Technology) and analyzed using gas chromatography-mass spectrometry (GC-MS, Hewlett Packard GC type 6890, MSD 5973).²⁵ The temperature program for GC-MS was 40°C for 15 minutes, from 40°C to 180°C at 4°C/min, 180°C for 15 minutes, from 180°C to 280°C at 5°C/min, and 280°C for 15 minutes. All mass numbers between 15 and 550 m/z were recorded (SCAN technique). Individual compounds were identified by comparing their mass spectra with the data from NIST Library. Literature values and nuclear magnetic resonance spectra were detailed as in a previous report.²⁶

Statistical analysis

SPSS software, version, 20.0 (IBM Corp., Armonk, NY, USA) was used for all statistical analyses. The HRV power level data were presented as means±SEM. A paired t-test was used to compare physiological responses to the fresh rose flowers and controls. Wilcoxon signed-rank test was applied to analyze differences in psychological indices between the responses to the fresh rose flowers and to the control. In both cases, one-sided tests were used because of the hypothesis that humans would be relaxed by fresh rose flowers.

Results

Physiological effects

Figure 2A shows the HF value associated with olfactory stimulation by fresh rose flowers. When the results of the HRV power level data were compared, a significant difference was found in the HF power level between the fresh rose flowers and the control (p=0.0495). The HF power level of fresh rose flowers (527.36±99.02 msec²) was 19.2% higher than that of the control (442.54±97.11 msec²). It was clear that the olfactory stimulation by the fresh rose flowers induced a significant increase in parasympathetic nervous activities, thereby inducing physiological relaxation. Furthermore, the LF/HF power ratio of the fresh rose flowers (1.00±0.25) was 43.8% lower than that of the control (1.78±0.59). The difference was not significant, but the results suggested that fresh rose flowers induced a trend toward decreased sympathetic nervous activities (p=0.0595) (Fig. 2B).

FIG. 2.

Comparison of high-frequency (HF) power levels and low-frequency (LF)/HF power level ratios of heart rate variability during olfactory stimulation by fresh rose flowers or control. Data are expressed as means±SEM; n=16. *p<0.05 by paired t-test (one-sided).

Psychological effects

The modified semantic differential method was used to provide subjective reports of “comfortable” and “natural” feelings (Fig. 3). The subjective reports of feeling “comfortable”/“natural” and “very comfortable”/“slightly natural” for fresh rose flowers but as “slightly comfortable”/“indifferent” for the control. The response to fresh rose flowers was therefore perceived as being significantly more comfortable and natural than to the control (p<0.05).

FIG. 3.

Subjective feeling measured by the modified semantic differential questionnaire after olfactory stimulation by fresh rose flowers or control. Data are expressed as mean±standard deviation; n=19. *p<0.05 by Wilcoxon signed-rank test (one-sided).

Volatile compounds

The volatile compounds from the fresh rose flowers are shown in Table 1. The predominant compounds in the fresh rose flowers were limonene, 2-phenethyl acetate, and citral. The physiological effects of these compounds remain unknown, and further detailed studies are required.

Table 1.

Volatile Compounds Emitted from the Fresh Rose Flower

Identified compounds	Relative area (%)
Ethanol	4.0
Methoxy-benzene	3.6
Acetic acid	2.5
α-Pinene	1.6
Camphene	1.4
β-Pinene	1.3
Methoxymethyl benzene	3.1
β-Terpinene	4.8
β-Myrcene	5.8
Hexyl acetate	4.6
o-Ocimene	7.0
Limonene	13.8
β-Ocimene	4.0
α-Ocimene	7.2
Terpinolene	1.8
δ-2-Carene	1.8
4-α-Dimethylstyrene	4.5
Cyclofenchene	1.6
3,4-Dimethyl-2,4,6-octatriene	1.9
β-Citronellal	2.7
2-Phenethyl acetate	9.1
Citral	9.0
δ-Cadinene	1.2

Discussion

This study measured the effects of olfactory stimulation by fresh rose flowers in humans. These results showed that this induced physiological and psychological effects. Some studies previously assessed the effects of olfactory stimulation by rose essential oils.^6

–10 In addition, many studies focused on the rose variety Rosa damascene,^6,10 but none have evaluated the physiological effect and component analysis of Rouge Royale, a relatively new rose created in the 2000s.¹¹ The current study is therefore novel in this regard.

As in the current study, the authors previously studied the effects of nature on human physiology.^{5,14

–18,27,28} They have also reported a decrease in sympathetic nervous activity,^{13,14,16
–18} an increase in parasympathetic nervous activity,^{5,14

–19} a decrease in prefrontal cortex activity,²⁸ and decreased concentrations of stress hormones in forest therapy studies.^{14

–17,19,27,28} In the future, these indices should be comprehensively assessed to determine the effects of olfactory stimulation by fresh rose flowers on human physiological effects and feelings of relaxation. The current study used Rouge Royal, which has a strong fragrance. In the future, it will be necessary to clarify the different effects of other rose varieties. A previous report showed that the main odor components differ between varieties.²⁹ Therefore, it is expected that physiological effects by every component should be clarified.

The main limitation of the study is that it evaluated sympathetic and parasympathetic nervous activity by HRV only as indices of physiological relaxation. Other experimental indices, such as prefrontal cortex activity and stress hormone concentrations, should also be assessed for a more comprehensive determination of the effect of olfactory stimulation by fresh rose flowers on human physiology.

In conclusion, these results showed that olfactory stimulation by fresh rose flowers induced (1) a significant increase in parasympathetic nervous activities that are enhanced a relaxed state, (2) a trend toward decreased sympathetic nervous activities, and (3) an increase in “comfortable” and “natural” feelings.

Footnotes

Acknowledgments

The authors are grateful to Ms. Misako Komatsu and Ms. Mariko Aga for their valuable contributions during the data collection phase of this study. This study was supported by a grant from the Policy Research Institute, Ministry of Agriculture, Forestry and Fisheries, Extramural Research Program for Agricultural Forestry and Fishery Policy Research.

Author Disclosure Statement

No competing financial relationships exist.

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