London, Sep 12 (IANS): For the first time, researchers and clinicians have revealed that measuring changes in the heart rate for 24 hours can reliably indicate whether or not someone is depressed.

In practical terms, this may give clinicians an objective "early warning" of potential depression, as well as a rapid indication whether or not treatment is working, so opening the way to more rapid and responsive treatment.

"Our pilot study suggests that by just measuring your heart rate for 24 hours, we can tell with 90 per cent accuracy if a person is currently depressed or not," said the study's lead author Carmen Schiweck from the Goethe University in Germany.

According to the study, presented at the ECNP virtual congress, scientists have known that heart rate is linked to depression, but until now they have been unable to understand exactly how one is related to the other.

Two innovative elements in this study were the continuous registration of heart rate for several days and nights, and the use of the new antidepressant ketamine, which can lift depression more or less instantly.

"This allowed us to see that average resting heart rate may change quite suddenly to reflect the change in mood," said Schiweck.

In the past researchers had shown that depressed patients had consistently higher heart rates and lower heart rate variability, but because of the time, it takes to treat depression it had been difficult to follow up and relate any improvement to heart rate.

"But when we realized that ketamine leads to a rapid improvement in mood, we knew that we might be able to use it to understand the link between depression and heart rate," Schiweck said.

For the results, the team research team worked with a small sample of 16 patients with Major Depressive Disorder, none of who had responded to normal treatment, and 16 healthy controls.

They measured their heart rates for four days and three nights, and then the volunteers with depression were given either ketamine treatment or a placebo.

"We found that those with depression had both a higher baseline heart rate, and a lower heart rate variation, as we expected. On average we saw that depressed patients had a heart rate which was roughly 10 to 15 beats per minutes higher than in controls," the authors wrote.

"After treatment, we again measured the heart rates and found that both the rate and the heart rate fluctuation of the previously depressed patients had changed to be closer to those found in the controls."

The most striking finding was that the scientists were able to use 24-hour heart rate as a "biomarker" for depression.

Heart rates were measured using a wearable mini-ECG. The data was fed to an Artificial Intelligence programme, which was able to classify nearly all controls and patients correctly as being depressed or healthy.