Measuring the heart rate of captive great apes is essential for both health management and animal studies. However, most existing methods are invasive or inaccurate. Now, researchers in Japan have investigated the potential of using millimeter-wave radar technology to estimate heart rate from subtle body movements in chimpanzees. Their efforts are expected to pave the way toward better practices and techniques for monitoring heart rate in wild and captive primates.
As in humans, heart rate is a critically important and informative vital sign in non-human primates. Heart disease is among the leading causes of death in non-human primates in captivity, and monitoring their heart rates regularly can help veterinarians detect symptoms early. Beyond the obvious health reasons, monitoring heart rate is also really useful in cognitive studies in animals. For example, it is well documented that a chimpanzee’s heart rate changes under psychological stress, when emotionally aroused by images, or when encountering familiar humans.
Therefore, it is not surprising that some techniques have been devised to measure heart rate in great apes. In addition to standard contact measurements, the most widespread involves attaching a wireless device to the animal to monitor and transmit its heart rate remotely. However, installation of the device often requires anesthesia, which carries risks. Additionally, the device itself could cause stress to the animal or other members of its group. A less invasive method is heart rate estimation from video images, which has been tested in some primate species. Still, the accuracy of these methods is quite sensitive to lighting conditions and animal movement.
In all these contexts, a research team including Assistant Professor Takuya Matsumoto of Shinshu University, Japan, set out to find a better alternative. In his latest study, which was published in the American Journal of Primatology On May 22, 2024, researchers investigated whether millimeter-wave radar-based techniques originally developed for humans could be used to measure heart rate in chimpanzees. Co-authors include Dr. Itsuki Iwata, Dr. Takuya Sakamoto, and Dr. Satoshi Hirata, all affiliated with Kyoto University.
In essence, the proposed approach involves emitting high-frequency electromagnetic pulses directed at the animal’s chest and capturing the resulting echoes. From these echoes, subtle body movements can be detected, which are ultimately used to estimate heart rate using specialized algorithms. Dr. Matsumoto highlights the motivation for the study, stating: “Millimeter-wave radar technology has been developed extensively for applications in automated driving and medicine, but after speaking with a radar researcher at an academic conference reception, we felt it could open up a new field of study if applied to primates other than humans; This is how we began our joint investigation“.
To test their approach, the researchers conducted experiments during annual health checks of two adult chimpanzees at the Kumamoto Sanctuary, Wildlife Research Center of Kyoto University. During these checks, the animals were anesthetized and the radar system was hung approximately half a meter above their chest. Traditional electrocardiography (ECG) signals were also recorded and used to evaluate the accuracy of the radar-based technique.
Fortunately, heart rates recorded using ECG closely matched those obtained using millimeter-wave radar for both chimpanzees, validating the proposed strategy. “Although chimpanzees have muscular bodies, which creates uncertainty about measuring their heart rate similar to measurements in humans, the results of this study demonstrated the feasibility of non-contact heart rate measurements by analyzing subtle movements of the body surface.” Dr. Matsumoto highlights and adds “These findings could expand the potential applications of such techniques in studies of animal psychology and wild primatology.“
Using millimeter wave radar-based methods to monitor heart rate offers significant advantages over standard practices. These techniques are completely non-invasive and allow frequent use without causing stress to the animals. Heart rate can also be measured remotely using video analysis with a visible light digital camera, which does not require specialized equipment and can reuse existing videos. Two main techniques are used: imaging photoplethysmography, which detects changes in blood volume, and periodic motion extraction, which measures heart and respiratory rates from body movements; Both have been validated in non-human primates but have certain limitations.
The researchers hope that the findings of this work will pave the way for greater innovation in the methods used to monitor vital signs in captive animals, including heart rate and respiratory rate. “If it were possible to remotely measure the heart rate of angry apes, their health management and well-being in captivity, such as in zoos, could improve.“concludes Dr. Matsumoto. Further feasibility studies will be necessary to validate the use of the proposed method in routine practice, where animals can move freely in their enclosure.
With a little luck, these techniques could help us not only keep our closest family members healthy, but also understand them better. This advance opens avenues for deeper research into primate behavior and physiology, benefiting captive and wild primates and improving our understanding of these creatures and their environment.