Elderly men who experience extended episodes of interrupted
breathing while asleep have a high risk of heart problems. Research shows for
the first time that poor blood oxygenation is a good indicator of the chance of
heart-related death, which cannot be attributed to sleep apnoea alone.
A team led by Associate Professor Dominik Linz and Associate Professor Mathias
Baumert of the University of Adelaide’s Medical School and School of Electrical
and Electronic Engineering has published their study in the European Heart Journal which examined patterns of
low blood oxygenation during sleep and the relation to heart-related deaths in
2840 men aged in their 70s and early 80s.
“Understanding underlying causes of low oxygen saturation during sleep is
important as this may assist in preventing deaths,” says Associate Professor
”The study shows for the first time that poor blood oxygenation during sleep
predicts the chance of heart-related death in elderly men. The study also
demonstrates that reduced blood oxygenation cannot be attributed to episodic
drops in oxygen alone.”
A healthy person normally has a 95-100% saturation during the day. Oxygen
saturation is slightly lower while a person sleeps due to shallower breathing.
Saturation below 90% is considered low resulting in hypoxia where oxygen flow
to the body is restricted.
The researchers analysed overnight oximetry data from
polysomnograms obtained in 2840 men from the Outcomes of Sleep Disorders in
Older Men (MrOS Sleep) study to determine the number of acute episodic desaturations
per hour (oxygen desaturation index, ODI) and time spent below 90% oxygen
saturation (T90) attributed to acute desaturations (T90desaturation) and to
non-specific drifts in oxygen saturation (T90non-specific), respectively, and
their relationship with CV mortality.
“The study showed that when the men had 12 or more minutes of sleep at low
oxygen saturation below 90% this increased the risk of heart-related death by
59%,” says Associate Professor Baumert.
“Approximately 20% of the time that oxygen saturation was below 90% could not
be attributed to episodic desaturations traditionally related to
“Screening for and treatment of risk factors beyond sleep-disordered breathing
and obesity might help to reduce nocturnal hypoxia in people who regularly
experience long periods of time during the night below 90% oxygen saturation,”
says Associate Professor Linz.
“Simple and affordable tools for overnight measurement of hypoxia levels are
readily available. Tests can be performed at home or aged care facilities as
part of a standard health check program,” says Associate Professor Baumert.
M, et al. Composition of nocturnal hypoxaemic burden and its prognostic value
for cardiovascular mortality in older community-dwelling men. European Heart Journal. Published 22