How the presence of a dog and types of interaction affect physiological responses to experimental heat pain induction in healthy humans - a randomized controlled study

It has become increasingly popular to include dogs as a complement to regular therapy, with the expectation that they offer, among other benefits, pain-relieving effects. Meanwhile, studies covering the topic of painful situations within the field of animal-assisted interventions (AAI) present conflicting results and rarely consider the type and duration of interaction with the dog. Thus, the impact of human-dog interactions on physiological measurements during painful situations is largely unknown. Basic research is needed on the effects of interacting with a dog, using commonly applied immediate physiological measurements in healthy humans during experimental pain induction to fill this gap in the literature.

The present study investigated how AAI influences physiological measurements when healthy humans are subjected to experimental heat pain induction. Simultaneously, the study explored how the duration of different types of interaction with a human companion or a dog as well as dog behavior during experimental heat pain induction affected physiological measurements.

Fifty-eight healthy participants (14 men, 44 women, age: 18-66 years) were randomly assigned to one of two intervention groups: 1) a dog and a human companion or 2) a human companion only. Both intervention groups underwent two test conditions in a balanced order: an active test condition with their allocated intervention and a control test condition without their allocated intervention. The participants were exposed to a 5-minute heat pain induction trial in both test conditions with a 20-minute break between trials. Heart rate (HR), heart rate variability (HRV) and skin conductance (SC), analyzed as tonic level (SCL) and peak counts (SCR), were continuously recorded. Blood pressure (BP) and salivary cortisol (s-cortisol) were collected as pre- and post-measurements for each test condition. Behavioral interactions between the participant, dog and human companion as well as behavior of the dog were recorded and the influence of the behavioral interactions on each physiological measure was analyzed. Linear Mixed Models were applied.

HR was higher for the intervention group with a dog and a human companion compared to a human companion only (p=0.013). Additionally, within-subject comparison showed an increased HR during the active condition compared to the control condition in both intervention groups (dog and human companion: p<0.001 and human companion only: p=0.025). None of the other physiological measurements were influenced by the mere presence of a dog in either the between- nor within-subject comparisons. Within the human companion only group, SCL and SCR were higher during the active condition compared to the control (both p<0.001). The duration of the behavioral interaction between the participant and human companion variously influenced HRV, SBP, s-cortisol and SCL during the active condition in both intervention groups. Further, the duration of the behavioral interactions with the dog and dog behavior variously influenced HR, HRV, s-cortisol and SCL during the active condition in the human companion and the dog intervention group.

In conclusion, this study shows that the presence of a dog in addition to a human companion during experimental heat pain induction results in an increased HR compared to the presence of a human companion only. Thus, despite previously reported pain-relieving effects of the presence of a dog, this study suggests that dog presence may also induce a certain level of arousal and further studies are needed to explore the causal mechanisms. Interactions with a dog or a human companion influenced several physiological measurements and it is therefore important to quantify the type and duration of human-animal interaction in AAI-studies.