Imagine someone undergoing treatment by a psychiatrist. How do we know the treatment is really working or should be modified?
To assess whether the patient’s condition is objectively improving, the doctor could ask him or her to take home a heart rate monitor and wear it continuously for 24 hours. An app connected to the monitor could then track how much the patient’s heart rate varies over time and how much the patient moves.
MD/PhD student Erik Reinertsen is the first author on two papers in Physiological Measurement advancing this approach, working under the supervision of Gari Clifford, interim chair of Emory’s Department of Biomedical Informatics.
Clifford’s team has been evaluating heart rate variability and activity as a tool for monitoring both PTSD (post-traumatic stress disorder) and schizophrenia. Clifford says his team’s research is expanding to look at treatment-resistant depression and other mental health issues.
For clinical applications, Clifford emphasizes that his plans focus on tracking disease severity for patients who are already diagnosed, rather than screening for new diagnoses. His team is involved in much larger studies in which heart rate data is being combined with physical activity data from smart watches, body patches, and clinical questionnaires, as well as other behavioral and exposure data collected through smartphone usage patterns.
Intuitively, heart rate variability makes sense for monitoring PTSD, because one of the core symptoms is hyperarousal, along with flashbacks and avoidance or numbness. However, it turns out that the time that provides the most information is when heart rate is lowest and study participants are most likely asleep, or at their lowest ebb during the night.
Home sleep tests generate a ton of information, which can be mined. This approach also fits into a trend for wearable medical technology, recently highlighted in STAT by Max Blau (subscription needed).
The research on PTSD monitoring grows out of work by cardiologists Amit Shah and Viola Vaccarino on heart rate variability in PTSD-discordant twin veterans (2013 Biological Psychiatry paper). Shah and Vaccarino had found that low frequency heart rate variability is much less (49 percent less) in the twin with PTSD. Genetics influences heart rate variability quite a bit, so studying twins allows those factors to be accounted for.
To develop their algorithm, Clifford’s team studied 23 male veterans with confirmed PTSD and 25 controls. With the 24 hour heart rate data they obtained, they were able to build a “classifer” that distinguished study participants with PTSD from controls with a sensitivity of 0.71 and specificity of 0.94.
“Our novel approach of segmenting heart rate data into quiescent segments improves the AUC [a measure of discriminatory power] of our classifier to 0.86,” Reinertsen writes, and adds:
“The features used in the classification algorithm are associated with alterations in autonomic nervous system (ANS) function. One could hypothesize the magnitude of these alterations correlate with symptomatic severity. If this is true, then the probability of PTSD classification would likely correlate with disease severity.”
Shah says future studies will be in multiple populations, including both veterans and civilians: “We are expanding our twin database with more twins, longer follow up, and additional monitoring for movement in addition to heart rate over several days.”
This research was supported in part by Medibio Limited, an Australian medical technology company that has licensed the technology.
For the paper on schizophrenia, the researchers used longer time periods (2 to 8 days) and combined heart rate variability data with patterns of physical activity, yielding an AUC of 0.96 for eight days and 0.91 for two.
The schizophrenia patients were all being treated with anti-psychotic medications, so the results may not apply to non-medicated schizophrenia patients. The patients came from Zucker Hillside Hospital in New York, as part of a collaboration with psychiatrist John Kane at Hofstra Northwell School of Medicine. Clifford has previously published work on a similar type of approach while on faculty at Oxford.
Disclosure: As inventors and licensees, Clifford, Shah and Emory are eligible to benefit financially from the PTSD evaluation technology. This relationship has been reviewed and is managed by Emory University through its conflict of interest office.