Doctors have long known that continuous positive airway pressure (CPAP) therapy can modestly lower blood pressure in people with obstructive sleep apnea (OSA). A study published online July 31 in the journal CHEST suggests that benefit is not evenly distributed — and that patients who also have insomnia may be the ones getting most of it.
Researchers led by Shuang Li, MD, at Beijing Anzhen Hospital, Capital Medical University, followed 71 adults with obstructive sleep apnea and elevated blood pressure through four weeks of auto-CPAP therapy. Twenty-two of the patients met criteria for COMISA — comorbid insomnia and obstructive sleep apnea — while the remaining 49 had sleep apnea without significant insomnia symptoms.
A 20-Fold Difference in Blood Pressure Response
The results, reported by Healio, were striking. Twenty-four-hour systolic blood pressure fell by 6 mmHg in the COMISA group after four weeks of CPAP use, compared with just 0.3 mmHg in the OSA-only group — a statistically significant difference (P = .002). Among the subset of patients with the best CPAP adherence, the gap widened further, with COMISA patients seeing a 6.8 mmHg reduction versus 1.5 mmHg for OSA alone.
A 6 mmHg drop in systolic blood pressure is not a trivial number in cardiovascular terms — reductions of that size, sustained over time, are associated in outcomes research with meaningfully lower rates of stroke and heart attack. That the effect concentrated almost entirely in the COMISA group suggests something specific about the biology of overlapping insomnia and sleep apnea, rather than a general CPAP effect that simply varies by chance.
Why Insomnia Might Change the Picture
The researchers propose that the mechanism runs through sleep fragmentation. Insomnia symptoms — particularly trouble staying asleep — compound the sleep disruption already caused by repeated respiratory events in OSA, driving greater nighttime sympathetic nervous system activation and blood pressure surges. When CPAP resolves the breathing-related fragmentation, it may be undoing a larger share of the total sleep disturbance in COMISA patients than in those whose sleep is disrupted primarily by breathing pauses alone, in the authors' hypothesis.
This lines up with a growing body of research on COMISA, a pattern in which the two disorders' cardiovascular effects appear to compound rather than simply add together. But most prior COMISA research has focused on documenting elevated risk. This study is notable for pointing toward a treatment implication: that the presence of insomnia symptoms in an OSA patient with hypertension might actually predict a better response to CPAP, not a worse one.
What This Means for Patients
If confirmed in larger trials, this finding could reshape how clinicians counsel patients on CPAP's expected benefits. Patients are sometimes discouraged from starting or sticking with CPAP therapy when the blood pressure improvements seem underwhelming — a common frustration in sleep clinics. This research suggests that whether a patient also reports insomnia symptoms, such as difficulty falling or staying asleep, may be a meaningful piece of information for predicting how much cardiovascular benefit to expect.
For patients who have been diagnosed with obstructive sleep apnea and also struggle with insomnia, the takeaway is not to expect less from treatment — it may be the opposite. Discussing both conditions openly with a sleep specialist, rather than treating insomnia symptoms as a separate or secondary complaint, could help clinicians set more accurate expectations and monitor blood pressure response more closely during the early weeks of CPAP therapy.
