Aging is associated with increased propensity for central apnea during NREM sleep

The enigma of sleep: Implications of sleep neuroscience for the dental clinician and patient

BACKGROUND

Sleep disturbances have been shown to result in considerable morbidity and mortality. It is important for dental clinicians to understand the neuroscience behind sleep disorders.

TYPES OF STUDIES REVIEWED

The authors conducted a search of the literature published from January 1990 through March 2024 of sleep medicine-related articles, with a focus on neuroscience. The authors prioritized articles about the science of sleep as related to dental medicine.

RESULTS

The authors found a proliferation of articles related to sleep neuroscience along with its implications in dental medicine. The authors also found that the intricate neuroscientific principles of sleep medicine are being investigated robustly. The salient features of, and the differences between, central and obstructive sleep apneas have been elucidated. Sleep genes, such as CRY, PER1, PER2, and CLOCK, and their relationship to cancer and neurodegeneration are also additions to this rapidly developing science.

CONCLUSIONS AND PRACTICAL IMPLICATIONS

The dental clinician has the potential to be the first to screen patients for possible sleep disorders and make prompt referrals to the appropriate medical professionals. This can be lifesaving as well as minimize potential future morbidity for the patient.

Predictors of Initial CPAP Prescription and Subsequent Course with CPAP in Patients with Central Sleep Apneas at a Single Center

PURPOSE

Guidelines recommend considering an initial trial of continuous positive airway pressure (CPAP) to treat central sleep apnea (CSA). However, practice patterns vary widely. This study investigated predictors for an initial trial of CPAP in patients with central apneas and whether those factors predict adequate treatment response in patients receiving an initial CPAP trial.

METHODS

Charts of patients receiving a diagnostic code for CSA following a sleep study during 2016-2018 at a single center were reviewed. Patient factors, initial treatment prescriptions, and subsequent changes to therapy were extracted from electronic health records. Regression models were used to estimate factors associated with an initial CPAP prescription and the likelihood of an adequate CPAP response (no subsequent therapy change and no discontinuation of therapy) among patients prescribed CPAP.

RESULTS

429/588 (73%) patients with central apneas received an initial trial of CPAP. Younger age, diagnosis by home sleep testing, non-opiate etiology of central apneas, and a lower proportion of central apneas at diagnosis were independently associated with a higher likelihood of an initial CPAP trial. A lower proportion of central apneas was associated with a higher probability of adequate response, while current smoking and opiate-related central apneas predicted an unsuccessful CPAP trial. A new finding was that older age predicted a lower likelihood of an initial CPAP prescription but did not predict an unsatisfactory response to CPAP.

CONCLUSION

Clinicians may incorrectly weigh certain clinical and sleep study characteristics when deciding whether to trial CPAP for patients with central apneas.

REM-OSA as a Tool to Understand Both the Architecture of Sleep and Pathogenesis of Sleep Apnea-Literature Review

Sleep is a complex physiological state, which can be divided into the non-rapid eye movement (NREM) phase and the REM phase. Both have some unique features and functions. This difference is best visible in electroencephalography recordings, respiratory system activity, arousals, autonomic nervous system activity, or metabolism. Obstructive sleep apnea (OSA) is a common condition characterized by recurrent episodes of pauses in breathing during sleep caused by blockage of the upper airways. This common condition has multifactorial ethiopathogenesis (e.g., anatomical predisposition, sex, obesity, and age). Within this heterogenous syndrome, some distinctive phenotypes sharing similar clinical features can be recognized, one of them being REM sleep predominant OSA (REM-OSA). The aim of this review was to describe the pathomechanism of REM-OSA phenotype, its specific clinical presentation, and its consequences. Available data suggest that in this group of patients, the severity of specific cardiovascular and metabolic complications is increased. Due to the impact of apneas and hypopneas predominance during REM sleep, patients are more prone to develop hypertension or glucose metabolism impairment. Additionally, due to the specific function of REM sleep, which is predominantly fragmented in the REM-OSA, this group presents with decreased neurocognitive performance, reflected in memory deterioration, and mood changes including depression. REM-OSA clinical diagnosis and treatment can alleviate these outcomes, surpassing the traditional treatment and focusing on a more personalized approach, such as using longer therapy of continuous positive airway pressure or oral appliance use.

Predictors of Initial CPAP Prescription and Subsequent Course with CPAP in Patients with Central Sleep Apneas

Purpose

Guidelines recommend considering an initial trial of continuous positive airway pressure (CPAP) to treat central sleep apnea (CSA). However, practice patterns vary widely. This study investigated predictors for an initial trial of CPAP in patients with central apneas and whether those factors predict adequate treatment response in patients receiving an initial CPAP trial.

Methods

Charts of patients receiving a diagnostic code for CSA following a sleep study during 2016-2018 at a single center were reviewed. Patient factors, initial treatment prescriptions, and subsequent changes to therapy were extracted from electronic health records. Regression models were used to estimate factors associated with an initial CPAP prescription and the likelihood of an adequate CPAP response (no subsequent therapy change or nonadherence) among patients prescribed CPAP.

Results

429/588 (73%) patients with central apneas received an initial trial of CPAP. Younger age, diagnosis by home sleep testing, non-opiate etiology of central apneas, and a lower proportion of central apneas at diagnosis were independently associated with a higher likelihood of an initial CPAP trial. A lower proportion of central apneas was associated with a higher probability of adequate response, while current smoking and opiate-related central apneas predicted an unsuccessful CPAP trial. A new finding was that older age predicted a lower likelihood of an initial CPAP prescription but did not predict a suboptimal response to CPAP.

Conclusion

Clinicians may incorrectly weigh certain clinical and sleep study characteristics when deciding whether to trial CPAP for patients with central apneas.

Central Apneic Event Prevalence in REM and NREM Sleep in OSA Patients: A Retrospective, Exploratory Study

Patients with sleep-disordered breathing show a combination of different respiratory events (central, obstructive, mixed), with one type being predominant. We observed a reduced prevalence of central apneic events (CAEs) during REM sleep compared to NREM sleep in patients with predominant obstructive sleep apnea (OSA). The aim of this retrospective, exploratory study was to describe this finding and to suggest pathophysiological explanations. The polysomnography (PSG) data of 141 OSA patients were assessed for the prevalence of CAEs during REM and NREM sleep. On the basis of the apnea-hypopnea index (AHI), patients were divided into three OSA severity groups (mild: AHI < 15/h; moderate: AHI = 15-30/h; severe: AHI > 30/h). We compared the frequency of CAEs adjusted for the relative length of REM and NREM sleep time, and a significantly increased frequency of CAEs in NREM was found only in severely affected OSA patients. Given that the emergence of CAEs is strongly associated with the chemosensitivity of the brainstem nuclei regulating breathing mechanics in humans, a sleep-stage-dependent chemosensitivity is proposed. REM-sleep-associated neuronal circuits in humans may act protectively against the emergence of CAEs, possibly by reducing chemosensitivity. On the contrary, a significant increase in the chemosensitivity of the brainstem nuclei during NREM sleep is suggested.

Sleep apnoea in the elderly: a great challenge for the future

Due in part to overall improvements in health, the population of elderly individuals is increasing rapidly. Similarly, obstructive sleep apnoea (OSA) is both gaining increased recognition and also increasing due to the worldwide obesity epidemic. The overlap of OSA and ageing is large, but there is strong plausibility for causation in both directions: OSA is associated with pathological processes that may accelerate ageing and ageing-related processes; ageing may cause physical and neurological changes that predispose to obstructive (and central) apnoea. In addition, the common symptoms (e.g. excessive daytime sleepiness, and defects in memory and cognition), possible physiological consequences of OSA (e.g. accelerated cardiovascular and cerebrovascular atherosclerosis), and changes in metabolic and inflammatory markers overlap with the symptoms and associated conditions seen in ageing. There is also the possibility of synergy in the effects of these symptoms and conditions on quality of life, as well as a need to separate treatable consequences of OSA from age-related complaints. Taken together, the aforementioned considerations make it essential to review the interaction of OSA and ageing, both proven and suspected. The present review examines some aspects of what is known and points to the need for further investigation of the relationships, given the large number of potentially affected subjects.

Hypercapnia-induced vasodilation in the cerebral circulation is reduced in older adults with sleep-disordered breathing

The prevalence of sleep-disordered breathing (SDB) is higher in older adults compared with younger individuals. The increased propensity for ventilatory control instability in older adults may contribute to the increased prevalence of central apneas. Reductions in the cerebral vascular response to CO₂ may exacerbate ventilatory overshoots and undershoots during sleep. Thus, we hypothesized that hypercapnia-induced cerebral vasodilation (HCVD) will be reduced in older compared with younger adults. In 11 older and 10 younger adults with SDB, blood flow velocity in the middle cerebral artery (MCAV) was measured using Doppler transcranial ultrasonography during multiple steady-state hyperoxic hypercapnic breathing trials while awake, interspersed with room air breathing. Changes in ventilation, MCAV, and mean arterial pressure (MAP) via finger plethysmography during the trials were compared with baseline eupneic values. For each hyperoxic hypercapnic trial, the change (Δ) in MCAV for a corresponding change in end-tidal CO₂ and the HCVD or the change in cerebral vascular conductance (MCAV divided by MAP) for a corresponding change in end-tidal CO₂ was determined. The hypercapnic ventilatory response was similar between the age groups, as was ΔMCAV/Δ[Formula: see text]. However, compared with young, older adults had a significantly smaller HCVD (1.3 ± 0.7 vs. 2.1 ± 0.6 units/mmHg, P = 0.004). Multivariable analyses demonstrated that age and nadir oxygen saturation during nocturnal polysomnography were significant predictors of HCVD. Thus, our data indicate that older age and SDB-related hypoxia are associated with diminished HCVD. We hypothesize that this impairment in vascular function may contribute to breathing instability during sleep in these individuals.NEW & NOTEWORTHY This study demonstrates, for the first time, in individuals with sleep-disordered breathing (SDB) that aging is associated with decreased hypercapnia-induced cerebral vasodilation (HCVD). In addition to advanced age, the magnitude of nocturnal oxygen desaturation due to SDB is an equal independent predictor of HCVD.

Central sleep apnea

Central apnea syndrome is a disorder with protean manifestations and concomitant conditions. It can occur as a distinct clinical entity or as part of another clinical syndrome. The pathogenesis of central sleep apnea (CSA) varies depending on the clinical condition. Sleep-related withdrawal of the ventilatory drive to breathe is the common denominator among all cases of central apnea, whereas hypocapnia is the final common pathway leading to apnea in the majority of central apnea. Medical conditions most closely associated with CSA include heart failure, stroke, spinal cord injury, and opioid use, among others. Nocturnal polysomnography is the standard diagnostic method, including measurement of sleep and respiration. The latter includes detection of flow, measurement of oxyhemoglobin saturation and detection of respiratory effort. Management strategy incorporates clinical presentation, associated conditions, and the polysomnographic findings in an individualized manner. The pathophysiologic heterogeneity may explain the protean clinical manifestations and the lack of a single effective therapy for all patients. While research has enhanced our understanding of the pathogenesis of central apnea, treatment options are extrapolated from treatment of obstructive sleep apnea. Co-morbid conditions and concomitant obstructive sleep apnea influence therapeutic approach significantly. Therapeutic options include positive pressure therapy, pharmacologic therapy, and supplemental Oxygen. Continuous positive airway pressure (CPAP) is the initial standard of care, although the utility of other modes of positive pressure therapy, as well as pharmacotherapy and device-based therapies, are currently being investigated.

Research Priorities for Patients with Heart Failure and Central Sleep Apnea. An Official American Thoracic Society Research Statement

Background: Central sleep apnea (CSA) is common among patients with heart failure and has been strongly linked to adverse outcomes. However, progress toward improving outcomes for such patients has been limited. The purpose of this official statement from the American Thoracic Society is to identify key areas to prioritize for future research regarding CSA in heart failure.

Methods: An international multidisciplinary group with expertise in sleep medicine, pulmonary medicine, heart failure, clinical research, and health outcomes was convened. The group met at the American Thoracic Society 2019 International Conference to determine research priority areas. A statement summarizing the findings of the group was subsequently authored using input from all members.

Results: The workgroup identified 11 specific research priorities in several key areas: 1) control of breathing and pathophysiology leading to CSA, 2) variability across individuals and over time, 3) techniques to examine CSA pathogenesis and outcomes, 4) impact of device and pharmacological treatment, and 5) implementing CSA treatment for all individuals

Conclusions: Advancing care for patients with CSA in the context of heart failure will require progress in the arenas of translational (basic through clinical), epidemiological, and patient-centered outcome research. Given the increasing prevalence of heart failure and its associated substantial burden to individuals, society, and the healthcare system, targeted research to improve knowledge of CSA pathogenesis and treatment is a priority.

Treatment-Emergent Central Apnea: Physiologic Mechanisms Informing Clinical Practice

The purpose of this review was to describe our management approach to patients with treatment-emergent central sleep apnea (TECSA). The emergence of central sleep apnea during positive airway pressure therapy occurs in approximately 8% of titration studies for OSA, and it has been associated with several demographic, clinical, and polysomnographic factors, as well as factors related to the titration study itself. TECSA shares similar pathophysiology with central sleep apnea. In fact, central and OSA pathophysiologic mechanisms are inextricably intertwined, with ventilatory instability and upper airway narrowing occurring in both entities. TECSA is a "dynamic" process, with spontaneous resolution with ongoing positive airway pressure therapy in most patients, persistence in some, or appearing de novo in a minority of patients. Management strategy for TECSA aims to eliminate abnormal respiratory events, stabilize sleep architecture, and improve the underlying contributing medical comorbidities. CPAP therapy remains a standard therapy for TECSA. Expectant management is appropriate given its transient nature in most cases, whereas select patients would benefit from an early switch to an alternative positive airway pressure modality. Other treatment options include supplemental oxygen and pharmacologic therapy.

Natural History of REM-OSA in Children and Its Associations with Adverse Blood Pressure Outcomes: A Longitudinal Follow-Up Study

PURPOSE

Most respiratory events in childhood obstructive sleep apnea (OSA) take place during rapid-eye-movement (REM) sleep. This study aimed to describe the characteristics and natural history of childhood REM-OSA and to evaluate the associations between OSA subtypes and blood pressure (BP) outcomes.

PARTICIPANTS AND METHODS

This was a prospective 10-year follow-up study of a cohort established for a childhood OSA epidemiologic study. All subjects from the original cohort were invited to undergo a polysomnography (PSG) and 24-hour ambulatory blood pressure (ABP) monitoring. REM-OSA was defined with a ratio of obstructive apnea hypopnea index (OAHI) during REM sleep (OAHI_REM) to OAHI during non-REM sleep (OAHI_NREM) ≥ 2. Natural history was observed and linear mixed models were used to assess the associations between OSA subtypes and BP outcomes.

RESULTS

A total of 610 participants from baseline were included to study the epidemiology of REM-OSA in childhood. Among children with OSA, 65% had REM-OSA. At 10-year follow-up, 234 were included in the analysis. REM-OSA was more common at both baseline (58/92, 63%) and 10-year follow-up (34/58, 59%). For those with REM-OSA at baseline and persistent OSA at follow-up, the majority (72%) remained to have REM-OSA. Compared to those without OSA, subjects with REM-OSA had significantly higher nocturnal SBP (mean difference 2.19 mmHg, 95% confidence interval (CI): 0.12, 4.26; p = 0.039) and DBP (mean difference 1.58 mmHg, 95% confidence interval (CI): 0.11, 3.04; p = 0.035), and less nocturnal SBP dipping (mean difference -1.84%, 95% CI: -3.25, -0.43; p = 0.011), after adjusting for potential confounders. This significant association between REM-OSA and nocturnal SBP dipping was observed at baseline visit only.

CONCLUSION

REM-OSA was found to be a stable phenotype through childhood to young adulthood, and REM-OSA was associated with higher nocturnal BP and a lesser degree of nocturnal SBP dipping in children.

Amelioration of sleep-disordered breathing with supplemental oxygen in older adults

Elderly adults demonstrate increased propensity for breathing instability during sleep compared with younger adults, and this may contribute to increased prevalence of sleep-disordered breathing (SDB) in this population. Hence, in older adults with SDB, we examined whether addition of supplemental oxygen (O₂) will stabilize breathing during sleep and alleviate SDB. We hypothesized that exposure to supplemental O₂ during non-rapid eye movement (NREM) sleep will stabilize breathing and will alleviate SDB by reducing ventilatory chemoresponsiveness and by widening the carbon dioxide (CO₂) reserve. We studied 10 older adults with mild-to-moderate SDB who were randomized to undergo noninvasive bilevel mechanical ventilation with exposure to room air or supplemental O₂ (Oxy) to determine the CO₂ reserve, apneic threshold (AT), and controller and plant gains. Supplemental O₂ was introduced during sleep to achieve a steady-state O₂ saturation ≥95% and fraction of inspired O₂ at 40%-50%. The CO₂ reserve increased significantly during Oxy versus room air (-4.2 ± 0.5 mmHg vs. -3.2 ± 0.5 mmHg, P = 0.03). Compared with room air, Oxy was associated with a significant decline in the controller gain (1.9 ± 0.4 L/min/mmHg vs. 2.5 ± 0.5 L/min/mmHg, P = 0.04), with reductions in the apnea-hypopnea index (11.8 ± 2.0/h vs. 24.4 ± 5.6/h, P = 0.006) and central apnea-hypopnea index (1.7 ± 0.6/h vs. 6.9 ± 3.9/h, P = 0.03). The AT and plant gain were unchanged. Thus, a reduced slope of CO₂ response resulted in an increased CO₂ reserve. In conclusion, supplemental O₂ reduced SDB in older adults during NREM sleep via reduction in chemoresponsiveness and central respiratory events.NEW & NOTEWORTHY This study demonstrates for the first time in elderly adults without heart disease that intervention with supplemental oxygen in the clinical range will ameliorate central apneas and hypopneas by decreasing the propensity to central apnea through decreased chemoreflex sensitivity, even in the absence of a reduction in the plant gain. Thus, the study provides physiological evidence for use of supplemental oxygen as therapy for mild-to-moderate SDB in this vulnerable population.

Central Sleep Apnea: a Brief Review

Purpose

The purpose of this review is to discuss the pathogenesis, clinical manifestations, diagnosis and treatment, including areas of controversy and uncertainty.

Recent Findings

Central apnea may be due to hypoventilation or to hypocapnia following hyperventilation. The occurrence of central apnea initiates a cascade of events that perpetuates breathing instability, recurrent central apnea and upper airway narrowing. In fact, breathing instability and upper airway narrowing are key elements of central and obstructive apnea. Clinically, central apnea is noted in association with obstructive sleep apnea, heart failure, atrial fibrillation, cerebrovascular accidents tetraplegia, and chronic opioid use.Management strategy for central apnea aim to eliminate abnormal respiratory events, stabilize sleep and alleviate the underlying clinical condition. Positive pressure therapy (PAP) remains a standard therapy for central as well as obstructive apnea. Other treatment options include adaptive-servo ventilation (ASV), supplemental oxygen, phrenic nerve stimulation, and pharmacologic therapy. However, ASV is contraindicated in patients with central sleep apnea who had heart failure with reduced ejection fraction, owing to increased mortality in this population.

Summary

There are several therapeutic options for central apnea. Randomized controlled studies are needed to ascertain the long-term effectiveness of individual, or combination, treatment modalities in different types of central apnea.