Abstract
<title>Abstract</title> <p> The present study examined whether presenting a pleasant odor during paced breathing at resonance frequency (RF) enhances autonomic nervous activity, as assessed by heart rate variability (HRV) and baroreflex sensitivity (BRS), in 28 healthy college students. Electrocardiogram, respiration, and noninvasive continuous blood pressure were recorded during 5 min of paced breathing at RF, followed by two successive 5-min periods of paced breathing at RF with geranium essential oil in the odor group or purified water in the placebo group. The amplitude of the low-frequency (LF) component of HRV increased significantly during paced breathing at RF in the odor group, whereas it remained unchanged in the placebo group ( <italic>p</italic> = .001). A gradual increase in R-R interval, indicating a decrease in heart rate, was also observed in the odor group during paced breathing at RF ( <italic>p</italic> < .001). BRS did not change significantly across measurement sessions in either group. These results suggest that olfactory stimulation induced by a pleasant odor during paced breathing at RF enhances cardiac parasympathetic nervous activity. The findings provide a rationale for the adjunctive use of pleasant odors in HRV biofeedback treatment. </p>