Upper airway resistance syndrome 2018: non-hypoxic sleep-disordered breathing

Hypoxic burden - definitions, pathophysiological concepts, methods of evaluation, and clinical relevance

PURPOSE OF REVIEW

Obstructive sleep apnea (OSA) is a common chronic condition that affects over a billion people worldwide and is associated with adverse cardio- and cerebrovascular consequences. Currently, the go-to clinical measure that determines the presence and severity of OSA is the apnea-hypopnea index (AHI). The AHI captures the frequency of respiratory events due to changes in ventilation that are associated with either oxygen desaturations or arousal from sleep. The AHI is poorly correlated to adverse outcomes in OSA with poor prognostic ability. To overcome the limitations of AHI and perhaps driven by the ease of acquisition, several studies have suggested characterizing nocturnal hypoxia in OSA, termed as "hypoxic burden". The purpose of this review is to focus on the hypoxic burden in OSA, its various definitions, and its utility in moving OSA diagnosis beyond the AHI.

RECENT FINDINGS

Several measures and definitions of hypoxic burden have been proposed and studied that show promise in overcoming limitations of AHI and also have a greater prognostic ability than AHI. More recently, area-based measures that attempt to characterize the depth and duration of oxygen desaturations, i.e., nocturnal hypoxia in OSA, have been shown to better relate to incident cardiovascular disease than AHI. In this review, we delve into the evidence for these novel area-based metrics and also delve into the pathophysiological concepts underlying nocturnal hypoxia while cautioning the reader on interpretation of the recent findings relating hypoxic burden to adverse outcomes in OSA.

SUMMARY

In this review on hypoxic burden, we focus on the need that has driven the sudden influx of studies assessing hypoxic burden for various outcomes of OSA, its underlying pathophysiology, the various definitions, and clinical relevance. We hope that the reader can appreciate the nuances underlying hypoxic burden in OSA and suggest the need for a cohesive framework for moving beyond the AHI with hypoxic burden.

Flow Limitation Is Associated with Excessive Daytime Sleepiness in Individuals without Moderate or Severe Obstructive Sleep Apnea

Rationale: Moderate-severe obstructive sleep apnea (OSA) (apnea-hypopnea index [AHI], >15 events/h) disturbs sleep through frequent bouts of apnea and is associated with daytime sleepiness. However, many individuals without moderate-severe OSA (i.e., AHI <15 events/h) also report sleepiness. Objectives: To test the hypothesis that sleepiness in the AHI <15 events/h group is a consequence of substantial flow limitation in the absence of overt reductions in airflow (i.e., apnea/hypopnea). Methods: A total of 1,886 participants from the MESA sleep cohort were analyzed for frequency of flow limitation from polysomnogram-recorded nasal airflow signal. Excessive daytime sleepiness (EDS) was defined by an Epworth Sleepiness Scale score ⩾11. Covariate-adjusted logistic regression assessed the association between EDS (binary dependent variable) and frequency of flow limitation (continuous) in individuals with an AHI <15 events/h. Results: A total of 772 individuals with an AHI <15 events/h were included in the primary analysis. Flow limitation was associated with EDS (odds ratio, 2.04; 95% confidence interval, 1.17-3.54; per 2-standard deviation increase in flow limitation frequency) after adjusting for age, sex, body mass index, race/ethnicity, and sleep duration. This effect size did not appreciably change after also adjusting for AHI. Conclusions: In individuals with an AHI <15 events/h, increasing flow limitation frequency by 2 standard deviations is associated with a twofold increase in the risk of EDS. Future studies should investigate addressing flow limitation in low-AHI individuals as a potential mechanism for ameliorating sleepiness.

Obstructive Sleep Apnea

OBJECTIVE

Obstructive sleep apnea (OSA) is the most common type of sleep-disordered breathing. This article describes advances in the diagnosis, testing, treatment, and monitoring of OSA.

LATEST DEVELOPMENTS

Home sleep apnea testing and in-laboratory polysomnography are the most commonly used diagnostic tools in the identification and monitoring of OSA, but new methods for diagnosis and at-home monitoring of treatment response are being developed and validated. While the apnea-hypopnea index is regularly used to define OSA severity, recognition is increasing of its inability to risk-stratify patients. Other sleep study data including arousal threshold, hypoxic burden, and pulse rate variability as well as clinical characteristics can help with risk stratification. The most effective treatment is continuous positive airway pressure (CPAP), which can be limited by adherence and tolerance in some patients. Newer masks and comfort features including heated tubing and expiratory pressure relief may improve tolerance to positive airway pressure (PAP) therapy. Additional treatment options include other PAP modalities, mandibular advancement devices, tongue stimulation therapy, negative inspiratory pressure, nasal expiratory pressure valves, nasal congestion treatments, upper airway surgeries including hypoglossal nerve stimulation, and medications.

ESSENTIAL POINTS

OSA is a common disorder that causes sleep and daytime symptoms and increases the risk of neurologic and medical complications. Neurologists should be aware of atypical presentations and understand the diagnostic and treatment options.

Treatment of obstructive sleep apnea in high risk pregnancy: a multicenter randomized controlled trial

BACKGROUND

Obstructive sleep apnea (OSA) during pregnancy is a risk factor for preeclampsia possibly through a link to placental physiology. This study evaluates the efficacy of continuous positive airway pressure (CPAP) on the modulation of blood pressure and the reduction in preeclampsia in women with high-risk pregnancy and OSA.

METHODS

A multicenter open-label, randomized controlled trial comparing CPAP treatment versus usual antenatal care was conducted in three academic hospitals in Bangkok, Thailand. Participants included singleton pregnant women aged older than 18 years with any high-risk condition (i.e., chronic hypertension, obesity, history of preeclampsia or gestational diabetes in the previous pregnancy, or diabetes), and OSA (respiratory disturbance index 5-29.99 events/hour by polysomnography), who presented either in the first trimester (gestational age, GA 0-16 weeks) or subsequently developed OSA during the 2nd trimester (GA 24-28 weeks). The primary endpoint was blood pressure during antenatal care. Secondary endpoints included the incidence of preeclampsia. An intention-to-treat analysis was performed with additional per-protocol and counterfactual analyses for handling of nonadherence.

RESULTS

Of 340 participants, 96.5% were recruited during the first trimester. Thirty participants were later excluded leaving 153 and 157 participants in the CPAP and usual-care groups for the modified-intention-to-treat analysis. CPAP adherence rate was 32.7% with average use of 2.5 h/night. Overall, CPAP treatment significantly lowered diastolic blood pressure (DBP) by - 2.2 mmHg [95% CI (- 3.9, - 0.4), p = 0.014], representing approximately - 0.5 mmHg per hour of CPAP use [95%CI (- 0.89, - 0.10), p = 0.013]. CPAP treatment also altered the blood pressure trajectory by continuously lowering DBP throughout pregnancy with mean differences (95% CI) of - 3.09 (- 5.34, - 0.93), - 3.49 (- 5.67, - 1.31) and - 3.03 (- 5.20, - 0.85) mmHg at GA 18-20, 24-28, and 32-34 weeks, respectively compared to 0-16 weeks. Preeclampsia rate was 13.1% (20/153 participants) in the CPAP and 22.3% (35/157 participants) in the usual-care group with a risk difference (95% CI) of - 9% (- 18%, - 1%, p-value = 0.032) and a number-needed-to-treat (95% CI) of 11 (1, 21).

CONCLUSIONS

CPAP treatment in women with even mild-to-moderate OSA and high-risk pregnancy demonstrated reductions in both DBP and the incidence of preeclampsia. CPAP treatment also demonstrated a sustained reduction in DBP throughout gestation. Trial registration ClinicalTrial.GovNCT03356106, retrospectively registered November 29, 2017.

Effect of tonsillectomy in a child with obesity and obstructive sleep apnea: A case report and review of the literature

Obstructive sleep apnea (OSA) is an increasingly recognized disorder in children. Adenotonsillectomy is the primary surgical treatment for OSA in children with adenotonsillar hypertrophy (ATH). We present the case of an obese 4-year-old boy hospitalized for severe desaturation during sleep and severe ATH. Nasal steroid therapy proved ineffective with persistent symptoms. Polygraphy documented severe OSA with an apnea-hypopnea index (AHI) equal to 11. Tonsillectomy resulted in prompt symptom improvement and a substantial reduction of the AHI (2.2). In this case, tonsillectomy alone resulted effective in treating OSA, despite obesity. We concluded that the presence of obesity should not postpone/exclude surgical treatment of preschool children for whom ATH is the most important cause of OSA.

Obstructive sleep apnea is common in patients with high-impact chronic pain - an exploratory study from an interdisciplinary pain center

OBJECTIVES

Sleep disturbances are increasingly recognized as a major part of chronic pain pathology. Obstructive sleep apnea (OSA) is a common occurrence in patients with chronic pain attending specialized pain clinics, yet its prevalence remains unclear. Using screening tools such as the Berlin and STOP-BANG questionnaires may aid in early identification of OSA and improve clinical care. This study i) examined the frequency of OSA based on objective sleep monitoring in patients with high-impact chronic pain, ii) explored potential differences in self-reported pain and sleep characteristics between patients with and without OSA, and iii) tested the agreement between OSA classification based on objective assessment and two OSA screening questionnaires.

METHODS

A consecutive cohort of 90 patients (71 women and 19 men; mean age: 47.1 ± 11.0 years) referred for interdisciplinary pain treatment, underwent one night of sleep monitoring using portable respiratory polygraphy (RP), and suspected OSA was confirmed with polysomnography (PSG). Self-reported data on clinical pain (severity, pain drawings and health-related quality of life), sleep characteristics (sleep quality insomnia, sleepiness), and risk of OSA (Berlin and STOP-BANG questionnaires) were collected the day before RP assessment.

RESULTS

Forty-six (51.1%) patients were classified with OSA according to RP and verified with PSG. Twenty-eight patients (31.1%) had moderate or severe OSA (apnea-hypopnea index [AHI] >15). Patients with OSA reported lower sleep quality compared with patients without OSA. Scores on pain severity, disability, quality of life, insomnia and sleepiness were comparable between patients with and without OSA. Sensitivity and specificity were 78.6 and 45.2% respectively for the Berlin questionnaire, and 71.4 and 58.1% respectively for the STOP-BANG questionnaire. The agreement for both questionnaires with objective assessment was poor-to-fair. Both questionnaires had acceptable negative predictive values but low positive predictive values reducing the clinical utility to identify patients with low OSA-risk in this sample.

CONCLUSIONS

The current study demonstrates a high prevalence of OSA in patients with high-impact chronic pain referred to specialized pain treatment, however the clinical pain profiles were similar in patients with and without OSA. The Berlin and STOP-BANG questionnaires have poor specificity and low-to-fair agreement with RP/PSG questioning their clinical utility in identifying OSA in this sample.

Altered K-complex morphology during sustained inspiratory airflow limitation is associated with next-day lapses in vigilance in obstructive sleep apnea

STUDY OBJECTIVES

Determine if changes in K-complexes associated with sustained inspiratory airflow limitation (SIFL) during N2 sleep are associated with next-day vigilance and objective sleepiness.

METHODS

Data from thirty subjects with moderate-to-severe obstructive sleep apnea who completed three in-lab polysomnograms: diagnostic, on therapeutic continuous positive airway pressure (CPAP), and on suboptimal CPAP (4 cmH2O below optimal titrated CPAP level) were analyzed. Four 20-min psychomotor vigilance tests (PVT) were performed after each PSG, every 2 h. Changes in the proportion of spontaneous K-complexes and spectral characteristics surrounding K-complexes were evaluated for K-complexes associated with both delta (∆SWAK), alpha (∆αK) frequencies.

RESULTS

Suboptimal CPAP induced SIFL (14.7 (20.9) vs 2.9 (9.2); %total sleep time, p < 0.001) with a small increase in apnea-hypopnea index (AHI3A: 6.5 (7.7) vs 1.9 (2.3); p < 0.01) versus optimal CPAP. K-complex density (num./min of stage N2) was higher on suboptimal CPAP (0.97 ± 0.7 vs 0.65±0.5, #/min, mean ± SD, p < 0.01) above and beyond the effect of age, sex, AHI3A, and duration of SIFL. A decrease in ∆SWAK with suboptimal CPAP was associated with increased PVT lapses and explained 17% of additional variance in PVT lapses. Within-night during suboptimal CPAP K-complexes appeared to alternate between promoting sleep and as arousal surrogates. Electroencephalographic changes were not associated with objective sleepiness.

CONCLUSIONS

Sustained inspiratory airflow limitation is associated with altered K-complex morphology including the increased occurrence of K-complexes with bursts of alpha as arousal surrogates. These findings suggest that sustained inspiratory flow limitation may be associated with nonvisible sleep fragmentation and contribute to increased lapses in vigilance.

A validation study of an esophageal probe-based polygraph against polysomnography in obstructive sleep apnea

STUDY OBJECTIVES

The aim of this study was to validate the automatically scored results of an esophageal probe-based polygraph system (ApneaGraph® Spiro) against manually scored polysomnography (Nox A1, PSG) results. We compared the apnea-hypopnea index, oxygen saturation index, and respiratory disturbance index of the devices.

METHODS

Consenting patients, referred for obstructive sleep apnea workup, were tested simultaneously with the ApneaGraph® Spiro and Nox A1® polysomnograph. Each participant made one set of simultaneous registrations for one night. PSG results were scored independently. Apnea-hypopnea index, oxygen desaturation index, and respiratory disturbance index were compared using Pearson's correlation and scatter plots. Sensitivity, specificity, and positive likelihood ratio of all indices at 5, 15, and 30 were calculated.

RESULTS

A total of 83 participants had successful registrations. The apnea-hypopnea index showed sensitivity of 0.83, specificity of 0.95, and a positive likelihood ratio of 5.11 at an index cutoff of 15. At a cutoff of 30, the positive likelihood ratio rose to 31.43. The respiratory disturbance index showed high sensitivity (> 0.9) at all cutoffs, but specificity was below 0.5 at all cutoffs. Scatterplots revealed overestimation in mild OSA and underestimation in severe OSA for all three indices.

CONCLUSIONS

The ApneaGraph® Spiro performed acceptably when OSA was defined by an AHI of 15. The equipment overestimated mild OSA and underestimated severe OSA, compared to the PSG.

Cardiovascular and somatic comorbidities and sleep measures using three hypopnea criteria in mild obstructive sleep-disordered breathing: sex, age, and body mass index differences in a retrospective sleep clinic cohort

STUDY OBJECTIVES

To describe sex, age, and body mass index (BMI) differences in comorbidities and polysomnography measures, categorized using 3 different apnea-hypopnea index (AHI) criteria in sleep clinic patients with mild obstructive sleep-disordered breathing.

METHODS

A retrospective cohort of 305 (64% female) adult sleep clinic patients who underwent full-night in-laboratory polysomnography having been diagnosed with mild sleep-disordered breathing and prescribed positive airway pressure. Effects of sex, age, and BMI on comorbidities and polysomnography measures, including rates of AHI defined by ≥ 3% desaturations (AHI_3%), with arousals (AHI_3%A), by ≥ 4% desaturations (AHI_4%), and by respiratory disturbance index, were evaluated.

RESULTS

Sixty-nine (23%), 116 (38%), 258 (85%), and 267 (88%) patients had AHI_4%, AHI_3%, AHI_3%A, and respiratory disturbance index ≥ 5 events/h, respectively. Ninety-day positive airway pressure adherence rates were 45.9% overall and higher in women > 50-years-old (51.2%, P = 0.013) and men (54.5%, P = 0.024) with no difference whether AHI_4% or AHI_3%A was < 5 or ≥ 5 events/h. Men and women had similar rates of daytime sleepiness (43.3%), anxiety (44.9%), and hypertension (44.9%). Women were more likely to have obesity, anemia, asthma, depression, diabetes, fibromyalgia, hypothyroidism, migraine, and lower rates of coronary artery disease. More patients with AHI_4% < 5 events/h had depression, migraines, and anemia, and more patients with AHI_4% ≥ 5 events/h had congestive heart failure. Women were more likely to have higher sleep maintenance and efficiency, shorter average obstructive apnea and hypopnea durations, and less supine-dominant pattern. Average obstructive apnea and hypopnea duration decreased with increasing BMI, and average hypopnea duration increased with age. Obstructive apnea duration and obstructive hypopnea with arousal duration decreased with increasing BMI. More women had AHI_4% < 5 (81.5% vs 69.1%), AHI_3% < 5 (68.7% vs 49.1%), and AHI_3%A < 5 events/h (18.5% vs 10.0%). Greater age and higher BMI were associated with higher AHI.

CONCLUSIONS

Current AHI criteria do not predict comorbidities or adherence in mild sleep-disordered breathing patients. In this hypothesis-generating descriptive analysis, sex, BMI, and age may all be factors that should be accounted for in future research of mild sleep-disordered breathing patients. Different sleep study measures may weigh differently in calculations of risk for cardiovascular versus somatic comorbidities.

Comorbid Insomnia and Sleep Apnea: mechanisms and implications of an underrecognized and misinterpreted sleep disorder

Sleep-disordered breathing (SDB) and insomnia have long been recognized as important sleep disrupters often associated with increased morbidity and mortality. Although they are often seen as divergent conditions, mainly because their cardinal symptoms (excessive daytime sleepiness, and sleep loss) differ, these two sleep disorders present with many common symptoms, which may hinder diagnosis and treatment. In addition to possible bidirectional pathways between SDB and insomnia, other factors such as circadian timing may play a role. In this paper, we review the mechanisms, differential clinical aspects, and implications of Comorbid Insomnia and Sleep Apnea, sometimes termed COMISA.