Using insertable cardiac monitors to test determinants of heart rate and activity in captive baboons

Insertable cardiac monitors (ICMs) provide fine-grained, continuous data on cardiac activity. These data have great potential to reveal individual physiology, energetics, and stress responses, with implications for animal health, cognition, welfare, and conservation. However, these devices must be tested for safety, accuracy, and biological validity before being deployed in new species. Here we do so for the Reveal LINQ^™ ICM (Medtronic, Minneapolis, MN USA) over an 8-month period in 10 adult female baboons (Papio anubis and P. cynocephalus) at the Kenya Institute of Primate Research in Kenya. We also report data on heart rate, physical activity, and body temperature in unrestrained, conscious, captive baboons during their normal activities. Finally, we test how heart rate and activity levels are predicted by baboon species, body mass, time of day, ambient temperature, social dominance rank, and ovarian cycle phase.

The baboons had no adverse reactions to the Reveal LINQ^™ ICM. Their mean daytime heart rates (HRs) ranged from 89.6 to 128.0 beats per minute (bpm), and their resting HRs ranged from 74.4 to 98.2 bpm. The fastest observed R-wave interval validated by electrocardiogram (ECG) was 230 milliseconds (ms) (260 bpm), and the slowest was 1270 ms (47.4 bpm). In terms of predictors of HR and activity, HR was highly individualized, while activity level was not: baboon identity explained 41% of the variation in HR, but identity only explained 2% of variation in activity levels. HR was positively correlated with physical activity and HR was highest during daylight hours when the baboons were more active. Dominant baboons had higher HRs controlling for activity and were more active than low ranking individuals. In terms of ovarian cycle phase, HR was higher when individuals were in the periovulatory and luteal phases of the ovarian cycle compared to the follicular phase.

Our findings support the future use of ICMs to investigate physiological responses in baboons. These devices' safety and validity represent the plausibility of understanding inter-individual and inter-species variation in heart rate and activity in response to variation in the external environment and in individual internal state.