Editor's Note: Commentary based on Trimer R, Cabidu R, Sampaio LLM, et al. Heart rate variability and cardiorespiratory coupling in obstructive sleep apnea: elderly compared with young. Sleep Med 2014;15:1324-31.

Background

Aging is known to be a major contributing factor to the increased risk of obstructive sleep apnea (OSA). Aging especially impacts breathing pattern during sleep by increasing the prevalence of apnea events, which affects heart rate variability (HRV) and cardiorespiratory coupling (CRC). This study was performed to evaluate the different patterns of HRV and CRC changes during wakefulness and sleep between young and elderly patients with and without OSA and determine whether or not the presence of OSA in young and elderly patients has a different impact on HRV and CRC during sleep.

Methods

One hundred subjects, 50 young (mean age, 27 ± 9; 20 normal and 30 OSA) and 50 elderly (mean age, 65 ± 7; 20 normal and 30 OSA), underwent polysomnography. Spectral, cross-spectrum, and HRV parameters were analyzed during wakefulness and sleep. Exclusion criteria for selection of all subjects were atrial fibrillation and other cardiac arrhythmias; history of myocardial ischemia, cardiomyopathy, or myocardial infarction; cardiac pacemaker; sleep disorders such as periodic limb movement disorder; treatment with antiarrhythmic medications; and diabetes and/or uncontrolled hypertension. Patients with OSA were defined as those with an apnea–hypopnea index (AHI) ≥5 events/hour.

Results

The spectral analysis indicated that age affected HRV, with higher values of low frequency (P <0.05) in elderly subjects during wakefulness and an interaction between the presence of OSA and age. OSA influenced HRV during sleep with lower lower-frequency (LF)/higher-frequency (HF) ratios during stage 2 (S2) and rapid eye movement (REM) sleep (P < 0.05); with an interaction between the presence of OSA and age in REM sleep. Elderly patients had significant impairment in CRC during wakefulness (P < 0.05), and OSA led to similar impairment in CRC during stage S2 of sleep.

Conclusion

Age and OSA have an unfavorable impact on HRV, with reduced autonomic modulation during wakefulness, S2, and REM sleep. Age affects CRC during wakefulness and the presence of OSA affects CRC during sleep.

Commentary/Perspective

Aging is associated with significant increase in the risk of sleep-disordered breathing and OSA. There are many mechanisms that can explain this relationship, including the change in body habitus associated with aging and especially the increased prevalence of obesity in elderly patients.¹ Aging is also associated with a potential damage to the autonomic cardiovascular regulation.² This pattern was noticed in patients with OSA.³ However, whether or not this pattern is uniformly present in all age groups is uncertain.

To assess autonomic dysfunction, two modalities can be used (HRV and/or CRC). HRV is reported in a spectrum that is reported in LF and HF range. The ratio between these two spectrums varies with the change of sympathetic tone. CRC can be assessed by observing the relationship of the HF band of HRV signal with the respiratory rhythm.⁴

Healthy elderly individuals without OSA had lower HRV during the day and at night when compared to subjects in the young control group.⁵ Similarly, a comparison of HRV indices between young and elderly subjects without OSA during wakefulness and different sleep stages found that elderly subjects showed higher values of HRV and lower HF power during non-REM sleep when compared with young subjects, suggesting that aging affects cardiac vagal activity during the night. They also observed that young individuals without OSA showed higher values of HF in non-REM sleep and that elderly subjects did not show the same behavior.⁶ In young healthy subjects, the CRC is represented by a pattern in which the coherence between the tachogram and respirogram in the HF band increases progressively with synchronization of sleep and decreases in REM sleep.^4,7 This pattern is impaired in healthy elderly patients even during wakefulness.

During sleep, the repeated episodes of OSA led to intermittent periods of hypoxia and hypercapnia. This lead to activation of chemoreceptor reflexes and other mechanisms, which lead in turn to a significant increase in sympathetic activation. However, this impact of OSA on sympathetic activation is not universal across all age groups. It was noticed significantly in young patients representing as an increase in both night and day LF/HF ratio when compared to healthy young control patient; however; this was not the case in older patients as inversely this ratio was significantly reduced in this group.

The impact of aging on CRC is prominent as well, while the normal pattern is noticed in young OSA patients during wakefulness with impaired CRC in S2 stage. CRC was also impaired in both wakefulness and S2 stage. These results may be explained by a lower synchronization between breathing and heartbeat during wakefulness, suggesting that aging leads to impaired cardiorespiratory synchronization, even during wakefulness, and that OSA has a negative impact on cardiorespiratory coordination during sleep.

This study should be praised for showing the impact that both age and OSA have on autonomic regulation. The presence of OSA influenced HRV in young and elderly individuals, with reduced autonomic modulation during wakefulness and REM sleep. Age per se appeared to influence HRV during wakefulness and REM sleep in elderly subjects. The presence of OSA and age had an unfavorable impact on CRC during wakefulness and sleep. Thus, whereas OSA has negative effects on HRV and CRC across the lifespan, there seems to be an age-dependent influence with respect to how these negative effects manifest. The impact of this result on clinical course and management of OSA in different age group is yet to determined.

Keywords: Apnea, Atrial Fibrillation, Cardiomyopathies, Control Groups, Diabetes Mellitus, Healthy Volunteers, Heart Rate, Hypercapnia, Hypertension, Myocardial Infarction, Myocardial Ischemia, Nocturnal Myoclonus Syndrome, Obesity, Polysomnography, Prevalence, Sleep Apnea Syndromes, Sleep Apnea, Obstructive, Sleep Wake Disorders, Sleep Stages, Sleep, REM, Wakefulness

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