Infrared photoplethysmogram (IR-PPG) and magnetic resonance image (MRI) of the Mytilus galloprovincialis heart were obtained simultaneously. Heart rate was varied by changing temperature, aerial exposure and hypoxia. Higher heart rates (35-20 beat min−1) were usually observed at 20°C under the aerobic condition, typical IR-PPG represented a single peak (peak v). The upward and downward slopes of the peak v corresponded to the filling and contraction of the ventricle, respectively. A double-peak IR-PPG was observed in a wide range of heart rates (35 to 5 beats min−1) under various conditions. The initial peak v corresponded to the filling of the ventricle, and the origin of the second peak (v') varied with the heart rate. A flat IR-PPG with a noise-level represented cardiac arrest. Although large movement of the shells and the foot caused slow waves or a baseline drift of the IR-PPG, the heart rate can be calculated from the v-v interval. Based on these results, we assembled a portable IR-PPG recording system, and measured the heartbeats of Bathymodiolus septemdierum (Mytilidae) for 24 h on a research vessel just after sampling from the deep-sea, showing that IR-PPG is a noninvasive, economical, robust method that can be used in field experiments.
- Received July 25, 2016.
- Accepted October 17, 2016.
- © 2016. Published by The Company of Biologists Ltd
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