Saurabh Thosar, PhD, MS

Credit: Oregon Health & Science University

New research presented during the SLEEP 2023 conference in Indianapolis shows how patients with obstructive sleep apnea (OSA) have certain characteristics in their circadian rhythms.

A team, led by Saurabh Thosar, Oregon Health & Science University, tested whether circadian rhythms in systolic blood pressure during rested wakefulness and in response to a standardized mild exercise are disturbed in patients with OSA compared to healthy individuals.

OSA and Cardiovascular Events

OSA can be linked to an increased risk of major adverse cardiovascular events, including sudden cardiac death. These events occur more frequently in the morning for the general population but occur more frequently in the middle of the night for patients with OSA.

However, it is not currently known whether these differences are linked to changes in circadian rhythms of blood pressure regulation.

In the study, the investigators examined 39 individuals, 14 of which had OSA and 25 healthy control participants. The mean age of the control group was 52.8 years and the mean age of the OSA group was 50.6 years.

The Study

Each participant was looked at during 10 identical recurring 5 hour 20 minute behavioral cycles in dim light and in an environment free of time cues.

The investigators measured systolic blood pressure in the supine position during rested wakefulness followed by seated at rest and during mild-intensity exercise, where the heart rate was at 50% heat rate reserve using the Karvonen formula, on a static cycle ergometer.

They also determined circadian phases relative to the dim-light melatonin onset and performed mixed-model cosigner analyses to test whether the groups differed in their systolic blood pressure rhythms during rested wakefulness and in their blood pressure responses to exercise.

The results show melatonin levels or phases relative to clock time were not different between the 2 groups (P = 0.17). This likely means there is similar timing of central circadian clock outputs.

The investigators also found an overall rhythm (P <0.001) and a trend to group x circadian phase interaction for resting systolic blood pressure (P = 0.10).

In another group analysis, the team found a significant circadian rhythm in systolic blood pressure in the healthy control group (P <0.001). There was also a peak in the evening, but the results did not show evident circadian rhythm in patients with OSA (P = 0.17).

Finally, there was no circadian phase x exercise reactivity interaction between the 2 groups, but exercise reactivity of systolic blood pressure was significantly higher in the OSA group (+4 mmHg; P = 0.001).

“OSA is characterized by a blunted circadian rhythm in resting blood pressure and an exaggerated blood pressure reactivity to exercise,” the authors wrote. “Mechanisms for these rhythm changes should be investigated further.”

References:

Thosar S, Bowles N, Butler M, McHill A, Emens J et al. OBSTRUCTIVE SLEEP APNEA IS ASSOCIATED WITH ALTERED CIRCADIAN RHYTHMS IN SYSTOLIC BLOOD PRESSURE AT REST AND DURING EXERCISE. Abstract presented at the Sleep 2023 Annual Meeting. Indianapolis, IN June 3-7, 2023.