Estimating the cardiac signals of chimpanzees using a digital camera: validation and application of a novel non-invasive method for primate research

Outdoor noncontact respiratory measurements of unrestricted rhesus macaques (Macaca mulatta) using millimeter-wave radar

Respiration is an invaluable signal that facilitates the real-time observation of physiological dynamics. In recent years, the advancement of noncontact measurement technology has gained momentum in capturing physiological activities in natural settings. This technology is anticipated to be found not only in humans but also in nonhuman primates. Currently, the predominant noncontact approach for nonhuman animals involves measuring vital signs through subtle variations in skin color. However, this approach is limited when addressing areas of the body covered with hair or when working in outdoor settings under fluctuating sunlight. To overcome this issue, we focused on noncontact respiratory measurements using millimeter-wave radar. Millimeter-wave radar systems, which employ millimeter waves that can penetrate animal fur and estimate respiration-derived periodic body motion, exhibit minimal susceptibility to sunlight interference. Thus, this method shows potential for conducting noncontact vital measurements in natural and outdoor settings. In this study, we validated a millimeter-wave radar methodology for capturing respiration in outdoor-housed rhesus macaques (Macaca mulatta). The radar was positioned beyond the captive enclosure and maintained at a distance >5 m from the target. Millimeter waves were transmitted to the target, and the reflected waves were used to estimate skin surface displacement associated with respiration. The results revealed periodic skin surface displacement, and the estimated respiratory rates weres within the reported range of respiratory rates for rhesus macaques. These results suggest the potential applicability of millimeter-wave radar for noncontact respiration monitoring in outdoor-living macaques without anesthesia or immobilization. The continued advancement of noncontact vital measurement technology will contribute to understanding primate mental and physical dynamics during their daily life.

First noncontact millimeter-wave radar measurement of heart rate in great apes: Validation in chimpanzees (Pan troglodytes)

Heart rate is a crucial vital sign and a valuable indicator for assessing the physical and psychological condition of a target animal. Heart rate contributes to (1) fundamental information for cognitive research, (2) an indicator of psychological and physical stress, and (3) improving the animal welfare of captive animals, especially in nonhuman primate studies. Heart rate has been measured using a contact-type device; however, the device burdens the target animals and that there are risks associated with anesthesia during installation. This study explores the application of heartbeat measurement techniques using millimeter-wave radar, primarily developed for humans, as a remote and noninvasive method for measuring the heart rate of nonhuman primates. Through a measurement test conducted on two chimpanzees, we observed a remarkable correspondence between the peak frequency spectrum of heart rate estimated using millimeter-wave radar and the mean value obtained from electrocardiograph data, thereby validating the accuracy of the method. To the best of our knowledge, this is the first demonstration of the precise measurement of great apes' heart rate using millimeter-wave radar technology. Compared to heart rate measurement using video analysis, the method using millimeter-wave radar has the advantage that it is less susceptible to weather and lighting conditions and that measurement techniques for multiple individuals have been developed for human subjects, while its disadvantage is that validation of measurement from long distances has not been completed. Another disadvantage common to both methods is that measurement becomes difficult when the movement of the target individual is large. The possibility of noncontact measurement of heart rate in wild and captive primates will undoubtedly open up a new research area while taking animal welfare into consideration.

Measuring heart rate in captive chimpanzees without anesthesia

Heart rate measurements can be useful for the monitoring of both physical and mental condition in humans and nonhuman animals. Yet, information about heart rates in chimpanzees, who are phylogenetically the closest species to humans, is scarce. Existing data on chimpanzee heart rates have mainly been collected from chimpanzees under anesthesia. To address this issue, we conducted electrocardiogram recordings in captive chimpanzees under normal conditions without anesthesia based on positive reinforcement training. We obtained a total of 771 recordings from 35 individuals (22 males and 13 females, 14-53 years old) with no cardiac problems. The females had a higher heart rate than the male chimpanzees, and heart rate decreased as a function of age. In addition, heart rate was lower in the morning and increased during the day. Overall, the mean heart rate of adult males was 86.5 beats/min, and that of female chimpanzees 106.4 beats/min. Our data could serve as a reference point for future research and health-based monitoring of chimpanzee heart rates.

A System for Monitoring Animals Based on Behavioral Information and Internal State Information

Managing the risk of injury or illness is an important consideration when keeping pets. This risk can be minimized if pets are monitored on a regular basis, but this can be difficult and time-consuming. However, because only the external behavior of the animal can be observed and the internal condition cannot be assessed, the animal's state can easily be misjudged. Additionally, although some systems use heartbeat measurement to determine a state of tension, or use rest to assess the internal state, because an increase in heart rate can also occur as a result of exercise, it is desirable to use this measurement in combination with behavioral information. In the current study, we proposed a monitoring system for animals using video image analysis. The proposed system first extracts features related to behavioral information and the animal's internal state via mask R-CNN using video images taken from the top of the cage. These features are used to detect typical daily activities and anomalous activities. This method produces an alert when the hamster behaves in an unusual way. In our experiment, the daily behavior of a hamster was measured and analyzed using the proposed system. The results showed that the features of the hamster's behavior were successfully detected. When loud sounds were presented from outside the cage, the system was able to discriminate between the behavioral and internal changes of the hamster. In future research, we plan to improve the accuracy of the measurement of small movements and develop a more accurate system.