An Australian study found for the first time that poor blood oxygenation during sleep, independent of sleep apnea, increased the risk of heart-related death by up to 59% in elderly men.
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 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 Linz. "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 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 Baumert.
"Approximately 20% of the time that oxygen saturation was below 90% could not be attributed to episodic desaturations traditionally related to sleep-disordered breathing."
"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 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 programme," says Baumert.
Abstract
Aims: To investigate the composition of nocturnal hypoxaemic burden and its prognostic value for cardiovascular (CV) mortality in community-dwelling older men.
Methods and results: We analysed overnight oximetry data from polysomnograms obtained in 2840 men from the Outcomes of Sleep Disorders in Older Men (MrOS Sleep) study (ClinicalTrials.gov Identifier: NCT00070681) 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. After 8.8 ± 2.7 years follow-up, 185 men (6.5%) died from CV disease. T90 [hazard ratio (HR) 1.21, P < 0.001], but not ODI (HR 1.13, P = 0.06), was significantly associated with CV death in univariate analysis. T90 remained significant when adjusting for potential confounders (HR 1.16, P = 0.004). Men with T90 > 12 min were at an elevated risk of CV mortality (HR 1.59; P = 0.006). Approximately 20.7 (5.7–48.5) percent of the variation in T90 could be attributed to non-specific drifts in oxygen saturation. T90desaturation and T90non-specific were individually associated with CV death but combining both variables did not improve the prediction.
Conclusion: In community-dwelling older men, T90 is an independent predictor of CV mortality. T90 is not only a consequence of frank desaturations, but also reflects non-specific drifts in oxygen saturation, both contributing towards the association with CV death. Whether T90 can be used as a risk marker in the clinical setting and whether its reduction may constitute a treatment target warrants further study.
Authors
Mathias Baumert, Sarah A Immanuel, Katie L Stone, Stephanie Litwack Harrison, Susan Redline, Sara Mariani, Prashanthan Sanders, R Doug McEvoy, Dominik Linz
[link url="https://www.adelaide.edu.au/news/news104422.html"]University of Adelaide material[/link]
[link url="https://academic.oup.com/eurheartj/advance-article-abstract/doi/10.1093/eurheartj/ehy838/5255631?redirectedFrom=fulltext"]European Heart Journal abstract[/link]