Scientists from Israel and Germany say that it is possible to monitor sleep, and potentially diagnose sleep disorders, just by recording a person's heart rate.
People suffering from disturbed sleep have an increased risk of heart attack, stroke, hypertension, obesity, depression, and accidents.
However, diagnosing sleep disorders is not necessarily easy-in standard "sleep studies", people spend one or more nights at hospitals or other inpatient centres, sleeping while sensors and electrodes attached to the head and torso record breathing, brain waves, heart rate, and other vital signs.
The new method, however, does away with all such problems. It relies on using a mathematical technique to analyse these recordings and tease out information related to the synchronization between heartbeat and breathing.
The synchronization between heartbeat and breathing might be a measure of fitness of the cardio-respiratory system.
The new method may help clinicians diagnose sleep disorders more easily, and determine optimal treatments for people with congestive heart failure.
Athletes might also be able analyse their own recordings to optimise workouts.
In the new study, the researchers showed that the synchronization between the heartbeat and breathing pattern is significantly enhanced during certain stages of sleep.
By mathematically analysing someone's heart rate throughout the night, they could gain information on that person's breathing and sleep stage.
Also, they looked at data from the European project SIESTA, which keeps a database of sleep data recorded in seven countries from 295 people, about half of whom have sleep disorders.
They then analysed just the heart data for the 150 people in the SIESTA study who have no known sleep disorders.
By using the heartbeats to reconstruct the breathing patterns, the researchers showed that the reconstructions were completely in sync with the actual recorded breathing data collected in sleep labs.
The researchers are now planning to extend their study to people with sleep disorders to determine whether their technique can accurately diagnose these disorders.
By analysing the heartbeat through the new technique, scientists could find information about cardiorespiratory capacity, which may lead to diagnostic markers of cardiac diseases and ways to determine optimal treatments for people with congestive heart failure.
Monitoring cardiorespiratory capacity may also help atheletes optimise their workout routines.
The study appears in a special focus issue of the journal Chaos, which is published by the American Institute of Physics (AIP).