PULSE
Basis of operation
Since this system relies on non-invasive technology, it is harmless and can be used on live animals, providing on-the-fly data on their physiological performance. As it works independently from a PC, it can be either used in the lab or deployed in the field. It can record the cardiac frequency of up to eight animals simultaneously. It uses infra-red (IR) sensors that are glued on the shell of molluscs or crustaceans. Mission parameters are supplied via a plain CSV file in a SD card, which also saves heartbeat data.
Hardware
As mentioned above, in contrast to similar systems, the PULSE is a standalone system which does not need to be connected to an oscilloscope or to a computer. After the inicial set-up, it is possible to autonomously monitor several (up to eight) animals. At the end of the sensor cables lies a small sensor which combines an Infra-Red (IR) emitter and detector. The sensor is attached to the exoskeleton of an animal, above its heart. Some of the IR light travels through the shell of the animal and illuminates the heart and nearby circulatory vessels. Changes in the shape or volume of the circulatory structures during a heart contraction, or heartbeat, cause a change in the amount of IR light reflected from the animal’s internal anatomy back to the IR detector. These changes in reflected IR light, transduced to changes in electrical current, are then processed by the electronic circuit and by the software (amplified, filtered, etc). Each sensor is read in sequence. Reading times can be defined by the user. A typical reading scheme is reading each sensor for one minute and repeat the whole cycle every 15 minutes throughout the experiment. The user-defined parameters are stored in the SD card, as well as the collected data. The system can be powered by any 7-28V DC power supply (e.g., by a wall adapter indoors, or by 9V battery outdoors).
Sensors
The infrared sensors we typically use are the Vishay CNY70, but others can be employed as well. There are many shapes and sizes. Some are cubic, some flat, some have the IR emitter and the receiver together while others have them separated. The sensor is connected to a shielded cable that has two wires + shield, and it is glued to the animal's shell with superglue. If handled with caution, each sensor can be glued to an animal, detached and re-used multiple times. You can buy sensors from us or make them on your own (the user's manual provides further instructions if you want to do that).
Data analysis
Data are saved as csv files which can be readily imported into Excel, Matlab, R, or others. It has virtually no memory limitation. We can provide an R program to semi-automatically process large volumes of data, for free. Contact us for more details.
Examples of studies employing this system
- Gurr et al. (2021) Acclimatization in the bay scallop Argopecten irradians along a eutrophication gradient: insights from heartbeat rate measurements during a simulated hypoxic event. Marine and Freshwater Behaviour and Physiology
- Levington et al. (2020) Temperature-related heart rate in water and air and a comparison to other temperature-related measures of performance in the fiddler crab Leptuca pugilator (Bosc 1802). Journal of Thermal Biology, 88: 102502
- Gurr et al. (2018) Cardiac responses of the bay scallop Argopecten irradians to diel-cycling hypoxia. Journal of Experimental Marine Biology and Ecology 500: 18-29
- Seabra et al. (2016) Equatorial range limits of an intertidal ectotherm are more linked to water than air temperature. Global Change Biology 22: 3320-3331
- Olabarria et al. (2016) Response of Two Mytilids to a Heatwave: The Complex Interplay of Physiology, Behaviour and Ecological Interactions. PLOS ONE 11: e0164330
- Burnett et al. (2013) An improved noninvasive method for measuring heartbeat of intertidal animals. Limnology and Oceanography: Methods 11: 91-100