The collected data were analyzed to examine psychological and somatic effects of the use of EM, HEM, and AHEM.
Physiological indicators
Studies have reported that the LF/HF in the very calm state is <2.0; ordinary state, 2–3; and excited state, >4.0 [12]. In this study, the LF/HF values in all three groups were decreased at the end of the intervention and showed no changes after the intervention was completed. However, the LF/HF values 10 min after the intervention remained to be lower than those before the intervention. These results indicate that the use of EM, HEM, and AHEM can be expected to decrease the sympathetic nervous activity at the end of the intervention, and the effect remains for 10 min after the intervention is completed. The EM use brought about the largest LF/HF decrease at the end of the intervention, followed by the HEM use and the AHEM use. Since inhalation of essential oils communicates signals to the olfactory system and stimulates the brain to exert neurotransmitters (e.g., serotonin and dopamine) [13], the observed weaker effect of the AHEM may be attributable to the “scent”.
The earlobe is a standard measurement site for the research laser blood flowmeter because of an abundance of capillaries. No differences in the blood flow among the three groups were found in this study. The blood flow at the end of the intervention was increased in all three groups. AHEM use brought about an additional increase in the blood flow after the intervention was completed. A previous study has reported that a hot pack was able to increase the eyelid tissue blood flow in eyes significantly and that these effects can be sustained until 20 min [14]. The present study demonstrated the effect of using EM, HEM, or AHEM to increase the blood flow in earlobe tissue at the end of the intervention and the continuance of the effect for 10 min after the intervention was completed. Additionally, the HEM and AHEM data showed that the blood flow in earlobe tissue increased further after the intervention was completed, suggesting that the “heat” and “scent” stimuli may remain effective even after removal of the stimuli.
The LF/HF values and blood flow measurements in earlobe tissue suggest the dominance of the parasympathetic nerves at the end of and 10 min after the intervention in all three groups. The activated parasympathetic nerves induce dilation of peripheral blood vessels, which likely results in increases in blood flow and axillary temperature. This explains the observed elevation of axillary temperature at the end of and 10 min after the intervention compared with that before the intervention in all three groups. Previous studies using the warming EM have reported that the warming EM significantly increased the distal skin temperatures (hands and feet) without affecting the proximal skin temperature (infraclavicular region) or core body temperatures and provoked physiological heat loss [6, 7]. The elevation of axillary temperature in the present study may not be attributable to the heat stimuli only and is consistent with a previous study showing that neither the truncal skin temperature nor the core body temperature was influenced by the periocular warming [6].
In the EM group, the pulse rate at the end of the intervention was lower than that before the intervention, and the pulse rate 10 min after the intervention was even lower than that at the end of the intervention. The “scent” stimulus may have prevented the pulse rate from decreasing. In the HEM and AHEM groups, no changes were observed after the intervention was completed. The removal of the heat source may have prevented further decreases in the pulse rate. The effects of the three interventions on the pulse rate were similar to the effect of the warming EM observed in a previous study [7], with no appreciable differences among the three groups.
Blood pressure values have never used as indicators to see the effects of warm compresses around the eyes in previous studies. Our results are consistent with a previous study [15] on warm foot bath as an intervention applying a heat stimulus showing that, compared to the base values, systolic and diastolic blood pressures did not change.
As described above, physiological indicators were used to discuss the effects of the EM, HEM, or AHEM use. The changes in the LF/HF, blood flow in the earlobe tissue, axillary temperature, and pulse rate suggest that parasympathetic nerves were dominant at the end of and 10 min after the EM or HEM intervention and 10 min after the AHEM intervention. The data on some measurement items suggest that parasympathetic nerves became further dominant after the EM intervention. With the AHEM use, no changes at the end of the intervention were observed for some items, and the data on some other items suggested that parasympathetic nerves became further dominant after the intervention was completed. Removal of the source of thermal stimulus or stimulation by the “scent” may interfere with the rapid decrease of sympathetic nerve activities. These data suggest that “scent” can exert its effects even after the intervention is completed.
Biochemical indicator
While a previous study has reported that SAA is sensitive to psychosocial stress [16], no SAA changes were observed after the EM, HEM, and AHEM intervention in this study. The authors of previous studies using SAA to assess the effects of back massage [17] and warm foot bath [15] have concluded that changes in the salivary biomarkers tested here may not indicate changes in psychological status following intervention. Similar results were obtained in the present study.
Psychological indicator
The TMD score 10 min after the intervention improved compared with that before the intervention in the EM, HEM, and AHEM groups. The EM, HEM, and AHEM interventions also showed improvements in scores for (AH), (CB), (DD), (FI), (TA), and (F) subscales. In particular, the AHEM use resulted in more decreases in (DD) and (FI) scores than the HEM use.
In previous studies, POMS tests revealed that inhalation of the aromatic lavender oil significantly decreased two POMS subscales, (DD) and (CB) [18], and the findings using the brain activities provided evidence the relaxing effect of inhaling lavender oil [19]. The results of the present study suggest that the lavender “scent” stimulus tends to alleviate negative moods, in particular, depression, dejection, fatigue, and inertia.
Limitations of the study
In this study, the short-term effects of the EM, HEM, and AHEM interventions immediately and 10 min after the intervention were evaluated. Therefore, the findings obtained refer to the short-term effects of these interventions. Moreover, participants in this study were female healthcare professionals; studies including diverse participants are necessary to generalize the findings of this study.