An improved noninvasive method for measuring heartbeat of intertidal animals

Abstract

Since its emergence two decades ago, the use of infrared technology for noninvasively measuring the heartbeat rates of invertebrates has provided valuable insight into the physiology and ecology of intertidal organisms. During that time period, the hardware needed for this method has been adapted to currently available electronic components, making the original published description obsolete. This article reviews the history of heartbeat sensing technology, and describes the design and function of a modern and simplified infrared heartbeat rate sensing system compatible with many intertidal and marine invertebrates. This technique overcomes drawbacks and obstacles encountered with previous methods of heartbeat rate measurement, and due to the sensor's small size, versatility, and noninvasive nature, it creates new possibilities for studies across a wide range of organismal types.

Noninvasive crayfish cardiac activity monitoring system

“…Except for a capacitor suppressing high frequency noise on the input to ADC the sensor's output, the signal does not require any specific amplification and/or filtering circuits, unlike the CAPMON system (Depledge and Andersen 1990) or the improved CAPMON system (Burnett et al 2013). Increased efficiency of LEDs in the last decade allows obtaining considerably more optical power from a single device at the same electrical power consumption.…”

“…The benefits of not using external hardware amplification and filtering circuits include preserving the original signal shape for further software processing, minimizing signal distortion caused by improper hardware adjustments, eliminating of clipping problems (Burnett et al 2013), and the greater simplicity and lower cost of hardware.…”

“…The CAP-MON system proposed by Depledge and Andersen (1990) utilizes a transducer consisting of an infrared (IR) light-emitting diode (LED) and a phototransistor fixed on the animal's dorsal carapace and connected to the external amplification and filtering circuit via thin flexible electrical wires. Improved and renovated CAPMON system for intertidal animals was recently developed by Burnett et al (2013). Another photoplethysmograph system proposed by Fedotov et al (2000) is based on the same operating principle as the CAPMON system but utilizes optical fibers as light guides between the crayfish and an externally placed IR semiconductor laser and photo receiver.…”

“…The main drawback of the noninvasive systems described above is that they are focused on measuring and analyzing (Burnett et al 2013) depending on its size, age, physiology, and species, analysis of the shape of the cardiac signal can provide additional information about the crayfish state. Another drawback of the systems is the complexity of their hardware: both the original (Depledge and Andersen 1990;Aagaard et al 1991) and the improved CAPMON (Burnett et al 2013) systems require a conditioning circuit for filtering and amplification of the signal, whereas a photoplethysmograph (Fedotov et al 2000) additionally requires precise optic components.…”

“…Another drawback of the systems is the complexity of their hardware: both the original (Depledge and Andersen 1990;Aagaard et al 1991) and the improved CAPMON (Burnett et al 2013) systems require a conditioning circuit for filtering and amplification of the signal, whereas a photoplethysmograph (Fedotov et al 2000) additionally requires precise optic components. Recent advances in electronics and optoelectronics eliminate the need in hardware amplification circuit, whereas the increased computational power of modern personal computers allows real-time digital filtering of the signal in software.…”