Dogs trained to detect PTSD stress in human breath

Man’s best friend aren’t simply loveable companions, as assistance dogs their sensitive noses are used to sniff out the early warning signs of many potentially dangerous medical conditions – like impending seizures or high blood sugar levels.

Now, a new proof-of-concept study indicates that assistance dogs might even be able to detect an oncoming PTSD flashback.

Post-traumatic stress disorder, or PTSD, is a psychiatric disorder which can occur in people who have been exposed to a traumatic event, series of events, or set of circumstances. Their symptoms can include re-experiencing the event, hyperarousal, avoiding reminders, and cognitive or mood changes.

“PTSD service dogs are already trained to assist people during episodes of distress,” says Laura Kiiroja of Dalhousie University in Canada, first author of the paper in Frontiers in Allergy.

“However, dogs are currently trained to respond to behavioural and physical cues. Our study showed that at least some dogs can also detect these episodes via breath.”

Previous research has indicated that dogs might be capable of detecting the volatile organic compounds (VOCs) – molecules emitted by the body in secretions like sweat and urine – linked to human stress. However, this is the first study to investigate whether dogs can learn to detect VOCs associated with PTSD symptoms.

If PTSD assistance dogs could be trained to respond to these markers, they could potentially interrupt episodes earlier and make intervention more effective.

The team recruited 26 human participants – 14 of whom met the diagnostic requirements for PTSD –to attend sessions where they were reminded of their traumatic experiences while wearing a facemask. Participants also provided one facemask worn while calm as a control breath sample.

The scientists also recruited 25 pet dogs to train in scent detection, though ultimately only 2 dogs – Ivy and Callie – were skilled and motivated enough to complete the study.

They were trained to recognise the stressed odour from pieces of the facemasks and could tell the difference between a stressed and non-stressed sample with 90% accuracy. Then, when they were presented with one sample at a time, Ivy could still detect the stress VOCs with 74% accuracy, while Callie achieved 81% accuracy.

Participants had also completed questionnaires about their emotions during the experiment. Comparing the dogs’ successful identifications against these self-reported emotions revealed interesting correlations – Ivy’s identifications were associated with anxiety, whereas Callie’s were associated with feelings of shame.

“Although both dogs performed at very high accuracy, they seemed to have a slightly different idea of what they considered a ‘stressed’ breath sample,” says Kiiroja.

“We speculated that Ivy was attuned to sympathetic-adreno-medullar axis hormones (like adrenaline) and Callie was oriented to the hypothalamo-pituitary-adrenal axis hormones (like cortisol),” says Kiiroja.

“This is important knowledge for training service dogs, as alerting to early-onset PTSD symptoms requires sensitivity to sympathetic-adreno-medullar axis hormones.”

The team plans to carry out further experiments to confirm the sympathetic-adreno-medullar axis is indeed involved. Kiiroja cautions that their study, with 40 sample sets, needs to be validated by studies with larger sample sizes.

“In addition to enrolling more participants, validation studies should collect samples from a higher number of stressful events to confirm dogs’ ability to reliably detect stress VOCs in the breath of one human across different contexts.”

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