- Arousal burden (AB) quantifies the percentage of total sleep time affected by cortical arousals.
- AB combines the frequency and duration of arousals during sleep, measured via overnight polysomnography (PSG).
- Arousal index (AI) measures only the frequency of arousals
Metrics and Measurements: https://doi.org/10.1093/eurheartj/ehab151
- AB is expressed as a percentage of total sleep time affected by arousals:AB=(∑duration of all arousals/total sleep time (TST))×100%
- The arousal index (AI) measures the frequency of arousals per hour but does not account for duration, making AB a more comprehensive metric.
Findings in Cohorts: https://doi.org/10.1093/eurheartj/ehab151
- Men with AB >8.5% and women with AB >6.5% were in the highest quartile and showed significantly higher risks of CV and all-cause mortality.
- AB correlated weakly with total sleep time, suggesting that sleep fragmentation impacts outcomes beyond simple reductions in sleep duration.
Arousal Burden Quartile Ranges (https://doi.org/10.1093/eurheartj/ehab151)
Research studies have used the following quartile ranges for AB-
Men:
- 1st Quartile (Q1): ≤4.5%
- 2nd Quartile (Q2): >4.5% to ≤6.5%
- 3rd Quartile (Q3): >6.5% to ≤8.5%
- 4th Quartile (Q4): >8.5%
Women:
- 1st Quartile (Q1): ≤3.5%
- 2nd Quartile (Q2): >3.5% to ≤5.0%
- 3rd Quartile (Q3): >5.0% to ≤6.5%
- 4th Quartile (Q4): >6.5%
These quartile ranges were used to stratify participants in the study and evaluate the association of arousal burden with cardiovascular and all-cause mortality. The main findings from the latest study which studies impact of AB in men and women are- https://doi.org/10.1093/eurheartj/ehab151
- Arousal burden (AB) is strongly associated with long-term cardiovascular (CV) and all-cause mortality, with a more pronounced effect in women than in men.
- Women experienced fewer arousals than men but had stronger correlations between higher AB and mortality risks.
Mechanisms of Impact:
- AB contributes to autonomic nervous system activation, circadian rhythm disruption, and metabolic dysregulation, which elevate CV disease risks.
- Frequent arousals lead to sleep fragmentation, increasing nocturnal blood pressure, heart rate, and stress hormone levels.
Nonlinear Mortality Risk:
- Mortality risk was lowest in the 2nd AB quartile, indicating a potential nonlinear relationship between AB and mortality.
- Extremely low or high arousal rates may both pose risks, possibly due to elevated arousal thresholds in the lower range and excessive fragmentation in the higher range.
Gender Differences:
- Despite lower arousal rates, women were more susceptible to the adverse consequences of high AB.
- This suggests that gender-specific physiological or hormonal factors may amplify the impact of AB on mortality in women.
Clinical Implications:
- AB could serve as a novel marker for risk stratification, especially in populations with high CV mortality risks.
- Integrating AB assessment into routine clinical practice requires accessible and scalable tools, such as actigraphy, for monitoring sleep and arousals.
Study Strengths:
- Large cohort size with robust follow-up durations.
- Use of rigorously scored polysomnography (PSG) data blinded to other clinical data.
- Comprehensive adjustment for confounders, including age, sleep duration, CV history, and other sleep metrics.
Limitations:
- Study populations primarily included older, white individuals, limiting generalizability to other age groups and races.
- AB assessment relied on single-night PSG, which may not account for night-to-night variability.
- The study did not distinguish between different causes or types of arousals.
Future Directions:
- Research is needed to explore the potential of AB as a modifiable risk factor.
- Prospective studies should evaluate interventions to reduce AB and assess their impact on CV and all-cause mortality.
- Development of more accessible tools for measuring AB could enhance its clinical utility.