title: Validation of normalized pulse volume in the outer ear as a simple measure of sympathetic activity using warm and cold pressor tests: towards applications in ambulatory monitoring.
abstract: Normalized pulse volume (NPV) derived from the ear has the potential to be a practical index for monitoring daily life stress. However, ear NPV has not yet been validated. Therefore, we compared NPV derived from an index finger using transmission photoplethysmography as a reference, with NPV derived from a middle finger and four sites of the ear using reflection photoplethysmography during baseline and while performing cold and warm water immersion in ten young and six middle-aged subjects. The results showed that logarithmically-transformed NPV (lnNPV) during cold water immersion as compared with baseline values was significantly lower, only at the index finger, the middle finger and the bottom of the ear-canal. Furthermore, lnNPV reactivities (ΔlnNPV; the difference between baseline and test values) from an index finger were significantly related to ΔlnNPV from the middle finger and the bottom of the ear-canal (young: r = 0.90 and 0.62, middle-aged: r = 0.80 and 0.58, respectively). In conclusion, these findings show that reflection and transmission photoplethysmography are comparable methods to derive NPV in accordance with our theoretical prediction. NPV derived from the bottom of the ear-canal is a valid approach, which could be useful for evaluating daily life stress.
authors: Graduate School of Nature Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa-shi, Ishikawa 920-1192, Japan.
authors: Jihyoung
authors: J
authors: Lee
authors: Kenta
authors: K
authors: Matsumura
authors: Takehiro
authors: T
authors: Yamakoshi
authors: Peter
authors: P
authors: Rolfe
authors: Naoto
authors: N
authors: Tanaka
authors: Kyungho
authors: K
authors: Kim
authors: Ken-ichi
authors: K
authors: Yamakoshi
mesh_terms: D001810:Blood Volume / Q000502:physiology*; D004431:Ear, External / Q000098:blood supply* / Q000502:physiology*; D004566:Electrodes; D005260:Female; D005385:Fingers / Q000502:physiology; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D018670:Monitoring, Ambulatory / Q000379:methods*; D017156:Photoplethysmography; D012015:Reference Standards; D015203:Reproducibility of Results; D013564:Sympathetic Nervous System / Q000502:physiology*; D055815:Young Adult