Cardiovascular Benefit of CPAP May Be Greater in High-Risk Obstructive Sleep Apnoea

Background

Obstructive sleep apnoea (OSA) is a common sleep disorder in which the upper airway repeatedly collapses during sleep, causing breathing pauses, fragmented sleep, and drops in blood oxygen levels. These repeated events place strain on the heart and blood vessels. OSA is strongly linked with hypertension, coronary artery disease, stroke, heart failure, and other cardiovascular problems.

Continuous positive airway pressure, or CPAP, is the standard treatment for moderate to severe OSA. It works by delivering a steady stream of air through a mask to keep the airway open during sleep. CPAP improves breathing and sleep quality, but large randomized trials in patients with cardiovascular disease have generally not shown a clear reduction in major cardiovascular events overall. That has raised an important question: could CPAP help some patients more than others?

This multi-trial analysis addressed that question by testing whether people with high-risk OSA derive greater cardiovascular benefit from CPAP than those with lower-risk OSA. The study focused on two biological features of OSA that may signal greater cardiovascular stress: a stronger heart rate surge after breathing events and a larger hypoxic burden, meaning a greater cumulative load of oxygen deprivation during the night.

Why This Study Matters

Not all OSA is the same. Two people may have similar numbers of apnoeas and hypopnoeas, yet one may experience much more intense oxygen drops or stronger autonomic stress responses. These differences may help explain why CPAP has shown mixed results in cardiovascular outcome trials.

The investigators hypothesized that CPAP would be more effective in patients whose OSA creates greater physiological stress, especially those with:
– a heart rate response after respiratory events greater than 9.4 beats per minute, or
– a hypoxic burden above 87.1 percent minutes per hour.

These thresholds defined “high-risk OSA” in the analysis.

Study Design

The researchers performed a post hoc pooled analysis of three randomized trials:
– Randomized Intervention with Continuous Positive Airway Pressure in Coronary Artery Disease and Obstructive Sleep Apnoea
– Impact of Continuous Positive Airway Pressure on Patients with Acute Coronary Syndrome and Nonsleepy Obstructive Sleep Apnoea
– Sleep Apnoea Cardiovascular Endpoints Study

Together, these trials included 3,549 participants with OSA and cardiovascular disease. Participants were assigned to either CPAP treatment or usual care.

The main outcome was major adverse cardiovascular and cerebrovascular events, or MACCE, which included cardiovascular death, myocardial infarction, and stroke. The analysis compared CPAP versus usual care within the high-risk OSA group and also tested whether the treatment effect differed from that in the low-risk OSA group.

The investigators also examined two clinically important subgroups:
– participants without excessive sleepiness, defined as an Epworth Sleepiness Scale score below 11
– participants without increased blood pressure, defined as systolic/diastolic blood pressure below 140/90 mmHg

These subgroup analyses matter because many patients with cardiovascular disease and OSA do not complain of major daytime sleepiness, and many do not have marked hypertension.

Key Findings

Overall, 16.6% of participants in the CPAP group and 16.3% in the usual care group reached the MACCE endpoint. At first glance, this confirms what earlier trials have suggested: CPAP does not clearly lower cardiovascular event rates across all patients with OSA and cardiovascular disease.

However, the picture changed when the researchers looked at OSA risk phenotype.

Among participants with high-risk OSA, CPAP had a significantly greater beneficial effect than it did in those without high-risk OSA. The interaction hazard ratio was 0.69, with a 95% confidence interval of 0.50 to 0.95, and the interaction P value was .024. In plain language, this means that the cardiovascular benefit of CPAP was meaningfully stronger in the high-risk group.

The effect was even more pronounced in the subgroup analyses:
– In participants without excessive sleepiness, the interaction hazard ratio was 0.59, 95% CI 0.41 to 0.84.
– In participants without increased blood pressure, the interaction hazard ratio was 0.54, 95% CI 0.36 to 0.81.

These results suggest that CPAP may be most useful for patients whose OSA is biologically severe, even if they do not feel very sleepy or have obvious hypertension.

The study also reported that CPAP benefits in high-risk OSA were seen alongside harm in low-risk OSA, meaning the net effect may reflect a balance between benefit in a vulnerable subgroup and little benefit, or possible adverse effects, in others.

How to Interpret the Results

The study does not mean that CPAP should only be used in high-risk OSA. CPAP remains the standard therapy for symptomatic OSA, for moderate to severe disease, and for many patients in whom improving breathing and sleep quality is clinically important.

What the study does suggest is that cardiovascular outcome benefits are not uniform. Rather than using apnoea counts alone, clinicians may eventually need to consider OSA phenotypes that capture the true biological burden of disease. Two patients with similar apnea-hypopnea index values may have very different cardiovascular risks depending on how much oxygen deprivation they experience and how strongly their cardiovascular system reacts.

This helps explain why previous CPAP trials have often been disappointing in broad populations. If many enrolled patients had relatively mild physiological stress, the average benefit of treatment would be diluted.

Clinical Implications

This analysis points toward a more personalized approach to sleep apnea care. Potential future steps may include:
– measuring hypoxic burden rather than relying only on apnea-hypopnea index
– considering autonomic responses, such as heart rate surges after respiratory events
– identifying patients with cardiovascular disease who are more likely to benefit from CPAP in terms of hard outcomes like heart attack and stroke

In practical terms, this may help clinicians better select patients for CPAP when the primary goal is cardiovascular risk reduction. It may also help researchers design future trials that focus on patients most likely to benefit.

For patients, the results reinforce an important message: OSA severity is more than just the number of breathing interruptions per hour. The depth and duration of oxygen drops, along with the body’s stress response to these events, may be just as important.

Strengths and Limitations

A major strength of this study is its large pooled sample from three randomized trials, which improves statistical power. Another strength is the use of biologically meaningful OSA risk markers rather than relying solely on traditional severity metrics.

There are also important limitations. Because this was a post hoc analysis, the high-risk definitions were tested after the original trials were completed. That means the findings are hypothesis-generating and should be confirmed in future prospective studies. In addition, CPAP adherence, patient selection, and differences across trials may influence the results.

The study also cannot prove that CPAP directly causes the observed subgroup differences with absolute certainty. It does, however, provide a strong signal that some OSA phenotypes are more likely to benefit than others.

Bottom Line

This multi-trial analysis suggests that continuous positive airway pressure may preferentially reduce cardiovascular events in patients with high-risk obstructive sleep apnoea, defined by stronger heart rate responses or greater hypoxic burden. In lower-risk OSA, the cardiovascular benefit may be absent or offset by harm.

The findings support a shift toward precision medicine in sleep apnea, where treatment decisions are guided not only by the presence of OSA but also by its physiological impact on the body. For clinicians, that means looking beyond the apnea-hypopnea index. For researchers, it offers a promising pathway to identify which patients are most likely to gain cardiovascular protection from CPAP.