Most people with obstructive sleep apnea — a condition in which normal breathing is regularly interrupted during sleep — are prescribed a continuous positive airway pressure, or CPAP, machine as treatment. However, many people do not use their devices as often or for as long as recommended, reducing their effectiveness.
A new Yale study reveals that a person’s biological clock can affect how well they adhere to proper CPAP use. Specifically, “morning people,” or those who prefer to wake up earlier, are more likely than others to use their devices for longer periods of time while sleeping, the researchers found. This finding, they say, could help doctors anticipate adherence problems and proactively navigate them.
The study was published March 14 in the Annals of the American Thoracic Society.
Obstructive sleep apnea is common and affects one in seven people worldwide. When those with the condition fall asleep, the muscles in their throat relax and close their airways, interrupting normal breathing.
“As a result, oxygen can’t reach the rest of the body, specifically the brain,” said Andrey Zinchuk, assistant professor of pulmonary medicine, critical care and sleep medicine at Yale School of Medicine and senior author of the study. “So before they suffocate, their brain wakes them up. And this can happen anywhere from 10 to 15 times an hour to 100 times an hour for some people.
This repeated interruption of sleep has an immediate effect; heart rate and blood pressure increase and the body releases stress hormones such as cortisol. Untreated sleep apnea is also associated with long-term health consequences, such as high blood pressure, diabetes, stroke, neurocognitive dysfunction, and an increased risk of being involved in car crashes due to fatigue.
CPAP devices prevent airways from closing by opening them with air pressure. To be fully effective, Zinchuk said, the devices must be worn all night, every night.
“But a lot of people really struggle with it,” he said. “After one year, about half of patients will stop using their device.”
There are several behavioral and social factors associated with CPAP use, including readiness to change, resilience, socioeconomic status, and social support. But none of the factors studied so far can fully explain why a patient is more or less likely to use their device as directed.
For the new study, Zinchuk and colleagues examined whether chronotype — or a person’s tendency to sleep at a particular time — might contribute to CPAP adherence, using data from the Apnea Positive Pressure Long-term Efficacy Study, a long-term study of the health effects of CPAP devices in people with obstructive sleep apnea.
There are three types of chronotypes: morning chronotypes, or what would colloquially be called “early birds,” evening chronotypes, or “night owls,” and those that sit somewhere in between, called “intermediate” chronotypes.
The chronotype classification corresponds to a person’s biological clock. It is assessed by answering a questionnaire that asks when someone prefers to wake up and go to bed, what time of day they are tired and when during the day they feel at their best, among other questions.
In a sample of 469 CPAP users, the researchers found that most had a morning (44%) or intermediate (47%) chronotype, and a few (8%) had an evening chronotype. Because there were so few participants with an evening chronotype, the researchers compared CPAP use among those with a morning and intermediate chronotype.
They found that over a six-month period, people with morning chronotypes used their CPAP machines more than 40 minutes more each evening, on average, compared to those with intermediate chronotypes.
“Every additional half hour of CPAP use is clinically significant,” Zinchuk said. “It affects the patient’s quality of life. So 40 minutes is important.”
Zinchuk says more research is needed to determine what factors underlie this relationship between chronotype and CPAP adherence.
“It’s possible that a person’s biological clock can affect the type of sleep apnea they have,” he said. “Some types are more easily treated with CPAP, others with non-CPAP treatment. Or it may simply be that people with a morning chronotype are better suited to the accepted 9-to-5 patterns of life in our society.”
Regardless, chronotype may be a useful consideration when treating people with sleep apnea, Zinchuk said.
“So far, the findings suggest that chronotype may be something we should pay more attention to. If the patient is not a morning person, we might look more closely at their barriers to using CPAP,” he said. “This study also reiterates how important and influential our biological clocks are for all kinds of health factors, both biological and behavioral.”