Authors: Jihyoung Lee, Kenta Matsumura, Takehiro Yamakoshi, Peter Rolfe,
Naoto Tanaka, Kyungho Kim, & Ken-ichi Yamakoshi

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

Journal(書誌情報): Physiological Measurement, 34(3), 359-375, 2013

doi: 10.1088/0967-3334/34/3/359


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.

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