By Natasha Baker

TOKYO (Reuters) - Want to reduce stress and improve mental focus? A new app that promotes slow breathing may help.

Called MyCalmBeat, the app uses a heart rate monitor that attaches to the ear to detect a person's optimal breathing rate, or resonant frequency, which is unique to each person.

At this breathing rate, the company says the user can increase the variability of their heart rate to lower stress levels.

"People don't realize the profound impact that slow breathing can have until they actually sit down and do it for 10 minutes and then they feel completely different," said Savannah DeVarney, vice president of product marketing for MyBrainSolutions, the creators of the app.

After finding their ideal breathing rate, animated exercises show users how to breathe at that rate, while the heart monitor provides feedback about the variability of their heart rate.

"Normally people think of 65 beats per minute as a good resting heart rate. But we're not necessarily looking at heart rate -- we're looking at the degree to which the space between consecutive heart beats varies," DeVarney explained.

When a person is stressed their heart rate becomes consistent and variability is minimized. But when relaxed, variability is maximized, slowing down as you breathe out and speeding up as you breathe in.

"We know that for most people their resonant frequency is between 7.5 and 4.5 breaths per minute. The software maps your heart rate variability through each of those rates to find the breathing rate where it becomes maximized," said DeVarney.

This frequency remains consistent throughout adult life, and usually only varies during childhood or pregnancy.

DeVarney said the company collaborated with Dr Richard Gevirtz, a professor at the Alliant International University in San Diego, California, who conducts research in heart rate variability.

She said in people who meditate for hours increased heart rate variability is one of the characteristics of being in a highly relaxed state.

"Meditators will find their resonant frequency naturally through trial and error, so we know that there's something in that."

Other biofeedback-based heart rate monitor apps include Instant Heart Rate which uses the iPhone's camera to detect a user's heart rate, rather than an external ear clip.

The company recommends training ten minutes a day, three times a week.

The app is available for iPhone, Android and Blackberry.