Clinical Use of Loop Gain Measures to Determine Continuous Positive Airway Pressure Efficacy in Patients with Complex Sleep Apnea. A Pilot Study

Treatment-emergent central sleep apnea resolves with lower inspiratory pressure

STUDY OBJECTIVES

Treatment-emergent central sleep apnea (TECSA) is an important problem during therapy with continuous positive airway pressure (CPAP) in patients with obstructive sleep apnea. We tested a device designed to improve CPAP comfort through reducing inspiratory positive airway pressure (IPAP; V ˙ -Com ) to determine whether such a reduction in IPAP could eliminate central apneas in patients with TECSA. Because increasing tidal volume (potentially via IPAP increments) has been suggested as a possible mechanism contributing to TECSA onset, our hypothesis was that reducing IPAP would yield a drop in the central apnea index.

METHODS

The addition of a known resistance (V ˙ -Com device) that reduces IPAP was implemented into the CPAP circuit during the second half of CPAP titrations in a cohort of community-dwelling patients who developed TECSA during a split-night CPAP titration. Central apnea index was quantified from the sleep periods without and with V ˙ -Com in place.

RESULTS

A total of 1,613 patients underwent CPAP titration, with 19 of them developing TECSA during the titration. The addition of V ˙ -Com resulted in complete resolution of TECSA in all patients with adequate sleep data under all conditions (n = 13), yielding a significant reduction in the central apnea index (17.3 ± 11.0 vs 1.5 ± 1.7 events/h without and with V ˙ -Com , respectively; P < .001).

CONCLUSIONS

V ˙ -Com virtually resolved all instances of TECSA, suggesting that reducing IPAP could be an effective strategy for managing the occurrence of central respiratory events in patients with obstructive sleep apnea using CPAP.

CITATION

Noah WH, Messineo L, Hete B, et al. Treatment-emergent central sleep apnea resolves with lower inspiratory pressure. J Clin Sleep Med. 2025;21(3):559-564.

Obstructive Sleep Apnea Endophenotypes

Obstructive sleep apnea (OSA) is a common disorder with major neurocognitive and cardiometabolic consequences. It is now recognized as a heterogeneous disease with multiple different underlying mechanisms (endotypes) as well as variable clinical expression of disease (phenotypes). The importance of this variability is emphasized since one variable in isolation typically explains only a fraction of the variance in OSA occurrence. This review provides an update of what is known regarding OSA heterogeneity. The importance of OSA endotypes is discussed in the context of how mechanism might affect disease management and/or design of subsequent randomized trials. Further research is recommended to provide further validation of OSA endophenotypes and how this information may influence clinical management in the future.

Deciphering loop gain complexity: a primer for understanding a pathophysiological trait of obstructive sleep apnea patients

Loop Gain (LG), a concept borrowed from engineering used to describe the stability of electrical circuits under negative feedback, has emerged as a crucial pathophysiological trait in sleep respiratory disorders. In simple terms, LG measures how the respiratory control system reacts to changes in breathing. A high LG suggests that minor disturbances in breathing prompt exaggerated responses, potentially leading to instability and oscillations in respiratory patterns. Conversely, a low LG implies that the system responds more gently to disturbances, resulting in stable and well-regulated breathing. However, understanding the concept of loop gain presents challenges due to its dynamic nature across various sleep respiratory disorders, sleep stages, positions, and interactions with other pathophysiological traits. Recent efforts have aimed to identify a non-invasive method for assessing LG, with some evidence suggesting that information regarding pathophysiological traits can be extracted from polysomnography. There exists a clinical imperative for physician to unravel the intricacies of LG when managing Obstructive Sleep Apnea (OSA) patients, because LG abnormalities delineate a distinct pathophysiological phenotype of OSA. Specifically, certain patients exhibit a high LG as the primary factor driving sleep apnea, influencing treatment outcomes. For instance, individuals with high LG may respond differently to therapies such as continuous positive airway pressure (CPAP) or oral appliances compared to those with normal LG, or they can be treated with specific drugs or combination therapies. Thus, understanding LG becomes paramount for precise assessment of OSA patients and is fundamental for optimizing a personalized and effective treatment approach.

Novel physiologic predictors of positive airway pressure effectiveness (NICEPAP) study: rationale, design and methods

PURPOSE

Continuous positive airway pressure (CPAP) is the primary therapy for obstructive sleep apnea (OSA); however the effectiveness of CPAP remains suboptimal. We describe the Novel PhysIologiC prEdictors of Positive Airway Pressure Effectiveness (NICEPAP) study. Its purpose is to determine whether physiological traits of OSA contribute to CPAP effectiveness.

METHODS

NICEPAP (NCT05067088) is a prospective, observational cohort study conducted at an academic sleep center. Adults newly diagnosed with OSA (n = 267) are assessed for OSA traits of loop gain, arousal threshold, pharyngeal collapsibility, and muscle compensation from baseline polysomnography. We perform a comprehensive assessment of covariates relevant to CPAP adherence, efficacy, and patient-centered outcomes. Participants are followed for 12 months. Primary outcomes include (1) CPAP adherence (hours/night), (2) CPAP efficacy (apneas-hypopneas/hour), and (3) quality of life at six months measured by objective CPAP data and Functional Outcomes of Sleep Questionnaire. Secondary outcomes include sleep quality, sleepiness, insomnia, and neurocognitive function.

RESULTS

Data on covariates, including demographics, sleep symptoms, medical history, medications, sleep quality, OSA and treatment self-efficacy, decisional balance, and socio-economic and social and partner support, are collected using validated instruments. The analysis for primary outcomes includes a generalized linear mixed model for an outcome (e.g., CPAP adherence) with OSA traits as exposures followed by the addition of relevant covariates.

CONCLUSION

The findings of the NICEPAP study will inform research aimed to enhance CPAP effectiveness. Understanding the role of physiological OSA traits in CPAP effectiveness is a crucial step toward a precision medicine approach to OSA.

The prevalence and polysomnographic characteristics of treatment-emergent central sleep apnea with obstructive sleep apnea

PURPOSE

To investigate the prevalence of treatment-emergent central sleep apnea (TECSA) in individuals with obstructive sleep apnea syndrome (OSAS) during continuous positive airway pressure (CPAP) titration and assess their polysomnographic characteristics.

METHODS

A total of 116 patients with OSAS who underwent full-night CPAP titration at the Sleep Laboratory of Adana City Research and Education Hospital from September 2017 to January 2018 were recruited for the study. The patients' polysomnographic data related to respiratory events and sleep stages were reviewed in a retrospective manner.

RESULTS

While on CPAP titration, 20 of the 116 patients developed central sleep apnea (CSA). The prevalence of TECSA in the patients with OSAS was 17.2%, being separately determined as 16.3% and 2.2% for the male and female patients, respectively. In the baseline PSG, the groups did not statistically significantly differ in relation to the apnea hypopnea index (AHI), central apnea index (CAI), arousal index (AI), or oxygen desaturation index (ODI). However, the TECSA group had a significantly higher mean oxygen saturation value compared to the non-TECSA group (p = 0.01). The total AHI, CAI, and AI values of the TECSA group were significantly higher during the whole CPAP titration compared to the non-TECSA group. No significant difference was observed in the comparison of the two groups in relation to the titration pressure and ODI.

CONCLUSION

TECSA is a phenomenon that can occur with obstructive sleep apnea treatment and mostly regress spontaneously following appropriate CPAP treatment. TECSA is observed at different rates of prevalence. In this study, the prevalence of TECSA was higher than previously reported.

The Present and Future of the Clinical Use of Physiological Traits for the Treatment of Patients with OSA: A Narrative Review

People with obstructive sleep apnea (OSA) are a heterogeneous group. While many succeed in the treatment of their OSA, many others struggle with therapy. Herein, we discuss how anatomical and physiological factors that cause sleep apnea (OSA traits) impact treatment response and may offer an avenue for more precise care. These OSA traits, including anatomical (upper-airway collapsibility) and physiological (loop gain, airway muscle responsiveness, and arousal threshold) factors, may help determine who can succeed with continuous positive airway pressure, oral appliances, hypoglossal nerve stimulation, or pharmacotherapy. In the future, identifying OSA traits before initiating treatment may help guide the selection of the most effective and tolerable therapy modalities for each individual.

Continuous positive airway pressure and adherence in patients with different endotypes of obstructive sleep apnea

Determining the endotypes of obstructive sleep apnea (OSA) has potential implications for precision interventions. Here we assessed whether continuous positive airway pressure (CPAP) treatment outcomes differ across endotypic subgroups. We conducted a retrospective analysis of data obtained from 225 patients with moderate-to-severe OSA from a single sleep centre. Polysomnographic and CPAP titration study data were collected between May 2020 and January 2022. One-month CPAP treatment adherence was followed. Obstructive sleep apnea endotypes, namely arousal threshold, collapsibility, loop gain, and upper airway gain were estimated from polysomnography and dichotomised as high versus low. We examined associations between endotypic subgroups and (1) optimal CPAP titration pressure, (2) CPAP-related improvements in sleep architecture (proportions of slow-wave and rapid eye movement (REM) sleep), and (3) CPAP adherence. We observed that patients with high collapsibility required a higher CPAP pressure than those with low collapsibility (∆ = 0.4 cmH2 O, 95% confidence interval [CI] = 0.3-1.7). A larger increase in slow-wave sleep and in REM sleep proportions after CPAP treatment were observed in patients with a high arousal threshold, high collapsibility, high loop gain, or high upper airway gain than in those with low levels of endotypes. High loop gain and high collapsibility were independently associated with longer CPAP use hours per night (∆ = 0.6 h, 95% CI = 0.2-1.5 and ∆ = 0.3 h, 95% CI = 0.03-1.5, respectively). In conclusion, different endotypic subgroups of OSA exhibit a difference in outcomes of CPAP treatment. Knowledge of endotypes may help clinicians to understand which patients are expected to benefit most from CPAP therapy prior to its administration.

The prevalence of treatment-emergent central sleep apnea with mandibular advancement device therapy

STUDY OBJECTIVES

Treatment-emergent central sleep apnea (TECSA) describes the appearance or persistence of central sleep apnea while undergoing treatment for obstructive sleep apnea. TECSA is well studied in continuous positive airway pressure therapy with an estimated prevalence of 8%. Based on a few case reports, mandibular advancement devices (MAD) may also provoke TECSA. This study aims to gain insight into the prevalence of TECSA with MAD therapy.

METHODS

This retrospective study includes a total of 129 patients with moderate to severe obstructive sleep apnea who were treated with a custom-made titratable MAD. Baseline and follow-up sleep studies were compared to identify patients with TECSA. Since different diagnostic criteria to define TECSA are used in literature, prevalence was calculated according to three definitions (TECSA-1, -2, and -3). Demographics, MAD treatment variables, and findings of the diagnostic polysomnography were compared between TECSA and non-TECSA patients to identify possible predictors.

RESULTS

Depending on the definition used, TECSA was found in 3.1%-7.8% of patients undergoing MAD therapy. TECSA patients had a higher apnea index (9.2 vs 2.0 events/h, P = .042), central apnea-hypopnea index (4.1 vs 0.2 events/h, P = .045) and oxygen desaturation index (23.9 vs 16.3 events/h, P = .018) at baseline compared to non-TECSA patients. No differences were found in demographics and treatment variables.

CONCLUSIONS

These findings demonstrate that TECSA also occurs in patients starting MAD treatment. Patients with TECSA had a higher apnea index, central apnea-hypopnea index, and oxygen desaturation index at baseline compared to non-TECSA patients.

CITATION

Hellemans S, Van de Perck E, Braem MJ, Verbraecken J, Dieltjens M, Vanderveken OM. The prevalence of treatment-emergent central sleep apnea with mandibular advancement device therapy. J Clin Sleep Med. 2023;19(12):2035-2041.

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.

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.

Acute and long-term effects of acetazolamide in presumed high loop gain sleep apnea

BACKGROUND

The acute effect during positive pressure titration and long term efficacy of acetazolamide (AZT) in high loop gain sleep apnea (HLGSA) is inadequately assessed. We predicted that AZT may improve HLGSA in both conditions.

METHODS

A retrospective analysis of polysomnograms from patients with presumed HLGSA and residual respiratory instability administered AZT (125 or 250 mg) about 3 h into an initially drug-free positive pressure titration. A responder was defined as ≥ 50% reduction of the apnea hypopnea index(AHI 3% or arousal) before and after AZT. A multivariable logistic regression model estimated responder predictors. Long term efficacy of AZT was assessed by comparing both auto-machine (aREI_FLOW) and manually scored respiratory events (sREI_FLOW) extracted from the ventilator, prior to and after 3 months of AZT, in a subset.

RESULTS

Of the 231 participants (median age of 61[51-68] years) and 184 (80%) males in the acute effect testing: 77 and 154 patients were given 125 mg and 250 mg AZT. Compared to PAP alone, PAP plus AZT was associated with a lower breathing related arousal index (8 [3-16] vs. 5 [2-10], p < 0.001), and AHI3% (19 [7-37] vs. 11 [5-21], p < 0.001); 98 patients were responders. The non-rapid eye movement sleep (NREM) AHI3% (OR 1.031, 95%CI [1.016-1.046], p < 0.001) was a strong predictor for responder status with AZT exposure. In the 109 participants with 3-month data, both aREI_FLOW and sREI_FLOWwere significantly reduced after AZT.

CONCLUSIONS

AZT acutely and chronically reduced residual sleep apnea in presumed HLGSA; NREM AHI3% is a response predictor. AZT was well tolerated and beneficial for at least 3 months.

Central sleep apnea: pathophysiologic classification

Central sleep apnea is not a single disorder; it can present as an isolated disorder or as a part of other clinical syndromes. In some conditions, such as heart failure, central apneic events are due to transient inhibition of ventilatory motor output during sleep, owing to the overlapping influences of sleep and hypocapnia. Specifically, the sleep state is associated with removal of wakefulness drive to breathe; thus, rendering ventilatory motor output dependent on the metabolic ventilatory control system, principally PaCO2. Accordingly, central apnea occurs when PaCO2 is reduced below the "apneic threshold". Our understanding of the pathophysiology of central sleep apnea has evolved appreciably over the past decade; accordingly, in disorders such as heart failure, central apnea is viewed as a form of breathing instability, manifesting as recurrent cycles of apnea/hypopnea, alternating with hyperpnea. In other words, ventilatory control operates as a negative-feedback closed-loop system to maintain homeostasis of blood gas tensions within a relatively narrow physiologic range, principally PaCO2. Therefore, many authors have adopted the engineering concept of "loop gain" (LG) as a measure of ventilatory instability and susceptibility to central apnea. Increased LG promotes breathing instabilities in a number of medical disorders. In some other conditions, such as with use of opioids, central apnea occurs due to inhibition of rhythm generation within the brainstem. This review will address the pathogenesis, pathophysiologic classification, and the multitude of clinical conditions that are associated with central apnea, and highlight areas of uncertainty.

Predictors and consequences of residual apnea during positive airway pressure therapy

STUDY OBJECTIVES

Determine the risk factors for, and consequences of, residual apnea during long-term positive airway pressure (PAP) therapy for obstructive sleep apnea (OSA).

METHODS

A prospective cohort study of 195 subjects after a split-night polysomnogram. Estimation of residual respiratory events on PAP were done by both automated and manual scoring of data in EncoreAnywhere™. Clinical and polysomnographic predictors of residual apnea were estimated.

RESULTS

There were 166 and 101 patients still on PAP at the 3 and 12 months, respectively. Seventy four (44.6%) and 46 (45.5%) had a residual scored respiratory event index-flow (sREI_FLOW) ≥ 15/hour of use and 46 (45.5%) at the 3rd and 12th month, respectively. Treatment phase central apnea hypopnea index (TCAHI), a surrogate of high loop gain, was the main predictor for residual sREI_FLOW (β = 0.345, p: 0.025) at the 3rd and 12th month (β = 0.147, p: 0.020). TCAHI also predicted unstable breathing (U) %. The body mass index (hazard ratio [HR] 1.034, 95% CI 1.008-1.062, p: 0.012) and effective sREI_FLOW>15/hour in the first month (HR 2.477, 95% CI 1.510-4.065, p < 0.001) were the key predictors for drop out of PAP use at the 12th month. Effective sREI_FLOW>15/hour in the first month was also a predictor for median usage duration >4 h for 70% of the night at both the 3rd month (odds ratio [OR] 0.947, 95% CI 0.909-0.986, p: 0.008) and 12th month (OR 0.973, 95% CI 0.951-0.994, p: 0.014).

CONCLUSIONS

Treatment-phase CAHI predicts long-term residual apnea on PAP. High residual disease adversely impacts adherence.

Association of alternative polysomnographic features with patient outcomes in obstructive sleep apnea: a systematic review

STUDY OBJECTIVES

Polysomnograms (PSGs) collect a plethora of physiologic signals across the night. However, few of these PSG data are incorporated into standard reports, and hence, ultimately, under-utilized in clinical decision making. Recently, there has been substantial interest regarding novel alternative PSG metrics that may help to predict obstructive sleep apnea (OSA)-related outcomes better than standard PSG metrics such as the apnea-hypopnea index. We systematically review the recent literature for studies that examined the use of alternative PSG metrics in the context of OSA and their association with health outcomes.

METHODS

We systematically searched EMBASE, MEDLINE, and the Cochrane Database of Systematic Reviews for studies published between 2000 and 2022 for those that reported alternative metrics derived from PSG in adults and related them to OSA-related outcomes.

RESULTS

Of the 186 initial studies identified by the original search, data from 31 studies were ultimately included in the final analysis. Numerous metrics were identified that were significantly related to a broad range of outcomes. We categorized the outcomes into 2 main subgroups: (1) cardiovascular/metabolic outcomes and mortality and (2) cognitive function- and vigilance-related outcomes. Four general categories of alternative metrics were identified based on signals analyzed: autonomic/hemodynamic metrics, electroencephalographic metrics, oximetric metrics, and respiratory event-related metrics.

CONCLUSIONS

We have summarized the current landscape of literature for alternative PSG metrics relating to risk prediction in OSA. Although promising, further prospective observational studies are needed to verify findings from other cohorts, and to assess the clinical utility of these metrics.

CITATION

Hajipour M, Baumann B, Azarbarzin A, et al. Association of alternative polysomnographic features with patient outcomes in obstructive sleep apnea: a systematic review. J Clin Sleep Med. 2023;19(2):225-242.

Factors Associated With Residual Apnea-Hypopnea Index Variability During CPAP Treatment

BACKGROUND

CPAP is the first-line therapy for OSA. A high or variable residual apnea-hypopnea index (rAHI) reflects treatment failure and potentially is triggered by exacerbation of cardiovascular comorbidities. Previous studies showed that high rAHI and large rAHI variability are associated with underlying comorbidities, OSA characteristics at diagnosis, and CPAP equipment, including mask type and settings.

RESEARCH QUESTION

What factors are associated with predefined groups with low to high rAHI variability?

STUDY DESIGN AND METHODS

This registry-based study included patients with a diagnosis of OSA who were receiving CPAP treatment with at least 90 days of CPAP remote monitoring. We applied the hidden Markov model to analyze the day-to-day trajectories of rAHI variability using telemonitoring data. An ordinal logistic regression analysis identified factors associated with a risk of having a higher and more variable rAHI with CPAP treatment.

RESULTS

The 1,126 included patients were middle-aged (median age, 66 years; interquartile range [IQR], 57-73 years), predominantly male (n = 791 [70.3%]), and obese (median BMI, 30.6 kg/m² (IQR, 26.8-35.2 kg/m²). Three distinct groups of rAHI trajectories were identified using hidden Markov modeling: low rAHI variability (n = 393 [35%]), moderate rAHI variability group (n = 420 [37%]), and high rAHI variability group (n = 313 [28%]). In multivariate analysis, factors associated with high rAHI variability were age, OSA severity at diagnosis, heart failure, opioids and alcohol consumption, mental and behavioral disorders, transient ischemic attack and stroke, an oronasal mask, and level of leaks when using CPAP.

INTERPRETATION

Identifying phenotypic traits and factors associated with high rAHI variability will allow early intervention and the development of personalized follow-up pathways for CPAP treatment.

Point-of-care prediction model of loop gain in patients with obstructive sleep apnea: development and validation

Background

High loop gain (unstable ventilatory control) is an important—but difficult to measure—contributor to obstructive sleep apnea (OSA) pathogenesis, predicting OSA sequelae and/or treatment response. Our objective was to develop and validate a clinical prediction tool of loop gain.

Methods

A retrospective cohort of consecutive adults with OSA (apnea–hypopnea index, AHI > 5/hour) based on in-laboratory polysomnography 01/2017–12/2018 was randomly split into a training and test-set (3:1-ratio). Using a customized algorithm (“reference standard”) loop gain was quantified from raw polysomnography signals on a continuous scale and additionally dichotomized (high > 0.7). Candidate predictors included general patient characteristics and routine polysomnography data. The model was developed (training-set) using linear regression with backward selection (tenfold cross-validated mean square errors); the predicted loop gain of the final linear regression model was used to predict loop gain class. More complex, alternative models including lasso regression or random forests were considered but did not meet pre-specified superiority-criteria. Final model performance was validated on the test-set.

Results

The total cohort included 1055 patients (33% high loop gain). Based on the final model, higher AHI (beta = 0.0016; P < .001) and lower hypopnea-percentage (beta = −0.0019; P < .001) predicted higher loop gain values. The predicted loop gain showed moderate-to-high correlation with the reference loop gain (r = 0.48; 95% CI 0.38–0.57) and moderate discrimination of patients with high versus low loop gain (area under the curve = 0.73; 95% CI 0.67–0.80).

Conclusion

To our knowledge this is the first prediction model of loop gain based on readily-available clinical data, which may facilitate retrospective analyses of existing datasets, better patient selection for clinical trials and eventually clinical practice.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-022-01950-y.

A longitudinal study of the accuracy of positive pressure therapy machine-detected apnea-hypopnea events

STUDY OBJECTIVES

During positive airway pressure (PAP) therapy for sleep apnea syndromes, the machine detected respiratory event index (REI_FLOW) is an important method for clinicians to evaluate the beneficial effects of PAP. There are concerns about the accuracy of this detection, which also confounds a related question-how common and severe are residual events on PAP.

METHODS

Subjects with OSA who underwent a split night polysomnography were recruited prospectively. Those treated with PAP and tracked by the EncoreAnywhere system were analyzed. The ones who stopped PAP within one month were excluded for this analysis. Compliance, therapy data and waveform data were analyzed. Machine detected versus manually scored events were compared at the 1st, 3rd, 6th and 12th month from PAP initiation. Logistic regression was used to determine factors associated with a high REI_FLOW difference.

RESULTS

One hundred and seventy-nine patients with a mean age 59.06 ± 13.97 years old, median body mass index 33.60 (29.75-38.75) kg/m², and median baseline AHI 46.30 (31.50-65.90) times/hour were included. The difference between the machine detected REI_FLOW and manually scored REI_FLOW was 10.72 ±8.43 in the first month and remained stable for up to 12 months. Male sex and large leak ≥ 1.5% were more frequent in patients who had an REI_FLOW difference of ≥ 5 / hour of use. A titration arousal index ≥ 15/ hour of sleep, and higher ratio of unstable to stable breathing were also associated with an REI_FLOW difference ≥ 5 times/hour of use.

CONCLUSIONS

There is a substantial and sustained difference between manual and automated event estimates during PAP therapy, and some associated factors were identified.

Characterizing respiratory parameters, settings, and adherence in real-world patients using adaptive servo ventilation therapy: big data analysis

STUDY OBJECTIVES

There is minimal guidance around how to optimize inspiratory positive airway pressure (IPAP) levels during use of adaptive servo ventilation (ASV) in clinical practice. This real-world data analysis investigated the effects of IPAP and minimum pressure support settings on respiratory parameters and adherence in ASV-treated patients.

METHODS

A United States-based telemonitoring database was queried for patients starting ASV between August 1, 2014 and November 30, 2019. Patients meeting the following criteria were included: United States-based patients aged ≥ 18 years; AirCurve 10 device (ResMed); and ≥ 1 session with usage of ≥ 1 hour in the first 90 days. Key outcomes were mask leak and residual apnea-hypopnea index at different IPAP settings, adherence and therapy termination rates, and respiratory parameters at different minimum pressure support settings.

RESULTS

There were 63,996 patients included. Higher IPAP was associated with increased residual apnea-hypopnea index and mask leak but did not impact device usage per session (average > 6 h/day at all IPAP settings; 6.7 h/day at 95th percentile IPAP 25 cm H2O). There were no clinically relevant differences in respiratory rate, minute ventilation, leak, and residual apnea-hypopnea index across all possible minimum pressure support settings. Patients with a higher 95th percentile IPAP or with minimum pressure support of 3 cm H2O were most likely to remain on ASV therapy at 1 year.

CONCLUSIONS

Our findings showed robust levels of longer-term adherence to ASV therapy in a large group of real-world patients. There were no clinically important differences in respiratory parameters across a range of pressure and pressure support settings. Future work should focus on the different phenotypes of patients using ASV therapy.

CITATION

Malhotra A, Benjafield AV, Cistulli PA, et al. Characterizing respiratory parameters, settings, and adherence in real-world patients using adaptive servo ventilation therapy: big data analysis. J Clin Sleep Med. 2021;17(12):2355-2362.

Non-REM Apnea and Hypopnea Duration Varies across Population Groups and Physiologic Traits

Rationale: Symptoms and morbidities associated with obstructive sleep apnea (OSA) vary across individuals and are not predicted by the apnea-hypopnea index (AHI). Respiratory event duration is a heritable trait associated with mortality that may further characterize OSA.Objectives: We evaluated how hypopnea and apnea durations in non-REM (NREM) sleep vary across demographic groups and quantified their associations with physiological traits (loop gain, arousal threshold, circulatory delay, and pharyngeal collapsibility).Methods: Data were analyzed from 1,546 participants from the Multi-Ethnic Study of Atherosclerosis with an AHI ≥5. Physiological traits were derived using a validated model fit to the polysomnographic airflow signal. Multiple linear regression models were used to evaluate associations of event duration with demographic and physiological factors.Measurements and Main Results: Participants had a mean age ± SD of 68.9 ± 9.2 years, mean NREM hypopnea duration of 21.73 ± 5.60, and mean NREM apnea duration of 23.87 ± 7.44 seconds. In adjusted analyses, shorter events were associated with younger age, female sex, higher body mass index (P < 0.01, all), and Black race (P < 0.05). Longer events were associated with Asian race (P < 0.01). Shorter event durations were associated with lower circulatory delay (2.53 ± 0.13 s, P < 0.01), lower arousal threshold (1.39 ± 0.15 s, P < 0.01), reduced collapsibility (-0.71 ± 0.16 s, P < 0.01), and higher loop gain (-0.27 ± 0.11 s, P < 0.05) per SD change. Adjustment for physiological traits attenuated age, sex, and obesity associations and eliminated racial differences in event duration.Conclusions: Average event duration varies across population groups and provides information on ventilatory features and airway collapsibility not captured by the AHI.

Central apnea and periodic breathing in children with underlying conditions

Central sleep apneas and periodic breathing are poorly described in childhood. The aim of the study was to describe the prevalence and characteristics of central sleep apnea and periodic breathing in children with associated medical conditions, and the therapeutic management. We retrospectively reviewed all poly(somno)graphies with a central apnea index ≥ 5 events per hr in children aged > 1 month performed in a paediatric sleep laboratory over a 6‐year period. Clinical data and follow‐up poly(somno)graphies were gathered. Ninety‐five out of 2,981 patients (3%) presented central sleep apnea: 40% were < 1 year, 41% aged 1–6 years, and 19% aged ≥ 6 years. Chiari malformation was the most common diagnosis (13%). Mean central apnea index was 20 ± 30 events per hr (range 5–177). Fifty‐eight (61%) children had an exclusive central pattern with < 5 obstructive events per hr. Periodic breathing was present in 79 (83%) patients, with a mean percentage of time with periodic breathing of 9 ± 16%. Among periodic breathing episodes, 40% appeared after a sigh, 8% after an obstructive event, 6% after breathing instability and 2% after bradypnea. The highest clinical apnea index and percentage of time with periodic breathing were observed in children with encephalopathy and/or epilepsy (68 ± 63 events per hr and 30 ± 34%). Clinical apnea index did not differ according to age, while periodic breathing duration was longer in children > 1 year old. Watchful waiting was performed in 22 (23%) patients with spontaneous improvement in 20. Other treatments (upper airway or neurosurgery, nocturnal oxygen therapy, continuous positive airway pressure, non‐invasive ventilation) were effective in selected patients. Central sleep apnea is rare in children and comprises heterogeneous conditions. Sleep studies are essential for the diagnosis, characterization and management of central sleep apnea.

Treatment-emergent central sleep apnea: a unique sleep-disordered breathing

Treatment-emergent central sleep apnea (TECSA) is a specific form of sleep-disordered breathing, characterized by the emergence or persistence of central apneas during treatment for obstructive sleep apnea. The purpose of this review was to summarize the definition, epidemiology, potential mechanisms, clinical characteristics, and treatment of TECSA. We searched for relevant articles up to January 31, 2020, in the PubMed database. The prevalence of TECSA varied widely in different studies. The potential mechanisms leading to TECSA included ventilatory control instability, low arousal threshold, activation of lung stretch receptors, and prolonged circulation time. TECSA may be a self-limited disorder in some patients and could be resolved spontaneously over time with ongoing treatment of continuous positive airway pressure (CPAP). However, central apneas persist even with the regular CPAP therapy in some patients, and new treatment approaches such as adaptive servo-ventilation may be necessary. We concluded that several questions regarding TECSA remain, despite the findings of many studies, and it is necessary to carry out large surveys with basic scientific design and clinical trials for TECSA to clarify these irregularities. Further, it will be vital to evaluate the baseline demographic and polysomnographic data of TECSA patients more carefully and comprehensively.

Endotypes and phenotypes in obstructive sleep apnea

PURPOSE OF REVIEW

The purpose of this review is to describe the variability of obstructive sleep apnea (OSA), both from a standpoint of underlying mechanisms and in terms of clinical manifestations.

RECENT FINDINGS

Recent data suggest that not all patients with sleep apnea get their disease for the same reason. As such, no one variable is effective at defining which patients do or do not have sleep apnea. Identifying the mechanism(s) underlying OSA for an individual is helpful as it can help to determine whether personalized therapy could be developed based on an individual's characteristics. In addition, these underlying mechanisms may be helpful in predicting response to therapy and prognosticating regarding future complications.

SUMMARY

OSA is a heterogeneous disease with highly varying underlying mechanisms. OSA has variable clinical manifestations with definable subsets having risk of particular complications. Future studies will be helpful to identify mechanisms underlying OSA using clinically accessible tools and then using these data to focus individualized treatment approaches.

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.

Effect of mild obstructive sleep apnea in mountaineers during the climb to Mount Aconcagua

OBJECTIVE

to compare mountaineers with and without asymptomatic sleep apnea (OSA) before the ascent and to study high altitude-related sleep disorders, its interaction with metabolic, neuroendocrine and immunological components.

MATERIAL AND METHODS

During an expedition to Mount Aconcagua, researchers assessed the respiratory polygraphy (RP), clinical condition and inflammatory parameters, and rhythm of cortisol secretion in mountaineers sleeping at different altitude camps.

RESULTS

8 athletes (4 women), 36 years old (25-51) participated. Baseline and final BMI were; 23.6 (20.9-28.7) and 22.77 (20.9-27.7), respectively: p<0.01. 40 valid RP recordings were analyzed. At 746 m.a.s.l. (baseline), only 2 mountaineers presented mild asymptomatic OSA. The OSA group presented baseline apnea-hypopnea index (AHI) values between 5-15 events per hour, which evidence a mild respiratory sleep disorder with AHI increased by altitude depending of central apneas and hypopneas (p<0.05) as high altitude periodic breathing pattern but no increase in obstructive apneas (p<0.01). The circadian rhythm of cortisol was maintained in all cases in which they had not received treatment with dexamethasone and their values increased with the altitude reached. Increased systolic blood pressure was observed in the OSA group.

CONCLUSION

In a context of hypobaric hypoxia, individuals with pre-existing asymptomatic OSA are prone to experiencing lower oxygen saturations and clinical deterioration.

More Than the Sum of the Respiratory Events: Personalized Medicine Approaches for Obstructive Sleep Apnea

Traditionally, the presence and severity of obstructive sleep apnea (OSA) have been defined by the apnea-hypopnea index (AHI). Continuous positive airway pressure is generally first-line therapy despite low adherence, because it reliably reduces the AHI when used, and the response to other therapies is variable. However, there is growing appreciation that the underlying etiology (i.e., endotype) and clinical manifestation (i.e., phenotype) of OSA in an individual are not well described by the AHI. We define and review the important progress made in understanding and measuring physiological mechanisms (or endotypes) that help define subtypes of OSA and identify the potential use of genetics to further refine disease classification. This more detailed understanding of OSA pathogenesis should influence clinical treatment decisions as well as help inform research priorities and clinical study design. In short, treatments could be individualized on the basis of the underlying cause of OSA; patients could better understand which symptoms and outcomes will respond to OSA treatment and by how much; and researchers could select populations most likely to benefit from specific treatment approaches for OSA.

Quantifying statistical uncertainty in metrics of sleep disordered breathing

BACKGROUND

The apnea-hypopnea index (AHI) (or one of its derivatives) is the primary clinical metric for characterizing sleep disordered breathing-the value of which with respect to a threshold determines severity of diagnosis and eligibility for treatment reimbursement. The index value, however, is taken as a perfect point estimate, with no measure of statistical uncertainty. Thus, current practice does not robustly account for variability in diagnosis/eligibility due to chance. In this paper, we quantify the statistical uncertainty associated with respiratory event indices for sleep disordered breathing and the effect of uncertainty on treatment eligibility.

METHODS

We develop an empirical estimate of uncertainty using a non-parametric bootstrap on the interevent times, as well as a theoretical Poisson estimate reflecting the current formulation of the AHI. We then apply these methods to estimate AHI uncertainty for 2049 subjects (954/1095 M/F, age: mean 69 ± 9.1) from the Multi-Ethnic Study of Atherosclerosis (MESA).

RESULTS AND CONCLUSIONS

The mean 95% empirical confidence interval width was 11.500 ± 6.208 events per hour and the mean 95% theoretical Poisson confidence interval width was 5.998 ± 2.897 events per hour, suggesting that uncertainty is likely a major confounding factor within the current diagnostic framework. Of the 278 subjects in the symptomatic population (ESS>10), 27% (76/278) had uncertain diagnoses given the 95% empirical confidence interval. Of the 2049 subjects in the full population, 43% (880/2049) had uncertain diagnoses given the 95% empirical confidence interval. The inclusion of subjects with uncertain diagnoses increases the number of eligible patients by 21.3% for the symptomatic population and by 84.8% for the full population. The exclusion of subjects with uncertain diagnoses given the 95% empirical confidence interval decreases the number of eligible patients by 12.4% for the symptomatic population and by 34.8% for full population. Additional analyses suggest that it is practically infeasible to gain diagnostic statistical significance through additional testing for a broad range of borderline cases. Overall, these results suggest that AHI uncertainty is a vital additional piece of information that would greatly benefit clinical practice, and that the inclusion of uncertainty in epidemiological analysis might help improve the ability for researchers to robustly link AHI with co-morbidities and long-term outcomes.

Cycle length identifies obstructive sleep apnea and central sleep apnea in heart failure with reduced ejection fraction

AIM

To clarify whether unmasking of central sleep apnea during continuous positive airway pressure (CPAP) initiation can be identified from initial diagnostic polysomnography (PSG) in patients with heart failure with reduced ejection fraction (HFREF) and obstructive sleep apnea (OSA) MATERIALS AND METHODS: Forty-three consecutive patients with obstructive sleep apnea and central sleep apnea (OSA/CSA) in HFREF were matched with 43 HFREF patients with OSA and successful CPAP initiation. Obstructive apneas during diagnostic PSG were then analyzed for cycle length (CL), ventilation length (VL), apnea length (AL), time to peak ventilation (TTPV), and circulatory delay (CD). We calculated duty ratio (DR) as the ratio of VL/CL and mathematic loop gain (LG).

RESULTS

While AL was similar, CL, VL, TTPV, CD, and DR was significantly longer in patients with OSA/CSA compared to those with OSA, and LG was significantly higher. Receiver operator curves identified optimal cutoff values of 50.2 s for CL (area under the curve (AUC) 0.85, 29.2 s for VL (AUC 0.92), 11.5 s for TTPV (AUC 0.82), 26.4 s for CD (AUC 0.79), and 3.96 (AUC 0.78)) respectively for LG to identify OSA/CSA.

CONCLUSION

OSA/CSA in HFREF can be identified by longer CL, VL, TTPV, and CD from obstructive events in initial diagnostic PSG. The underlying mechanisms seem to be the presence of an increased LG.

Patient Engagement Using New Technology to Improve Adherence to Positive Airway Pressure Therapy: A Retrospective Analysis

BACKGROUND

Sleep apnea has major neurocognitive and cardiovascular and metabolic risks. Treatment of sleep apnea is suboptimal because of variable adherence to existing therapies.

METHODS

This trial compared positive airway pressure adherence among patients who were provided active patient engagement (APE) technology vs those who received usual care monitoring (UCM). The primary outcome was expressed by using the US Medicare definition of adherence. Adherence data from two cloud-based databases (AirView and myAir) were analyzed for patients with sleep apnea. Data were included if a patient's activation date in the APE tool was within 7 days of the therapy start date in the UCM database during a defined time window. Data were propensity matched in a 1:2 ratio (APE:UCM) based on baseline patient characteristics.

RESULTS

A total of 128,037 patients were analyzed. Baseline characteristics were typical of a sleep clinic cohort. APE was associated with more patients achieving adherence criteria (87.3%) compared with UCM patients (70.4%; P < .0001 for the difference). Average therapy usage was 5.9 h per night in the APE group vs 4.9 h per night in the matched UCM patients (P < .0001). Patients with sleep apnea "struggling" with therapy adherence had a 17.6% absolute improvement in adherence using APE compared with UCM.

CONCLUSIONS

Robust therapy adherence rates can be achieved by adding modern technology to usual care. Adopting advances in technology in care management may allow clinicians to more effectively and efficiently treat patients who have sleep apnea. Rigorous randomized controlled trials may be required before making strong clinical recommendations.

Ventilatory Cycle Measurements and Loop Gain in Central Apnea in Mining Drivers Exposed to Intermittent Altitude

STUDY OBJECTIVES

By measuring the apnea length, ventilatory phase, respiratory cycle length, and loop gain, we can further characterize the central apneas of high altitude (CAHA).

METHODS

Sixty-three drivers of all-terrain vehicles, working in a Peruvian mine located at 2,020 meters above sea level (MASL), were evaluated. A respiratory polygraph was performed in the first night they slept at high altitude. None of the subjects were exposed to oxygen during the test or acetazolamide in the preceding days of the test.

RESULTS

Sixty-three respiratory polygraphs were performed, and 59 were considered for analysis. Forty-six (78%) were normal, 6 (10%) had OSA, and 7 (12%) had CAHA. Key data from subjects include: residing altitude: 341 ± 828 MASL, Lake Louise scoring: 0.4 ± 0.8, Epworth score: 3.4 ± 2.7, apneahypopnea index: 35.7 ± 19.3, CA index: 13.4 ± 14.2, CA length: 14.4 ± 3.6 sec, ventilatory length: 13.5 ± 2.9 sec, cycle length: 26.5 ± 4.0 sec, ventilatory length/CA length ratio 0.9 ± 0.3 and circulatory delay 13.3 ± 2.9 sec. Duty ratio media [ventilatory duration/cycle duration] was 0.522 ± 0 0.128 [0.308-0.700] and loop gain was calculated from the duty ratio utilizing this formula: LG = 2π / [(2πDR-sin(2πDR)]. All subjects have a high loop gain media 2.415 ± 1.761 [1.175-6.260]. Multiple correlations were established with loop gain values, but the only significant correlation detected was between central apnea index and loop gain.

CONCLUSIONS

Twelve percent of the studied population had CAHA. Measurements of respiratory cycle in workers with CAHA are more similar to idiopathic central apneas rather than Hunter-Cheyne-Stokes respiration. Also, there was a high degree of correlation between severity of central apnea and the degree of loop gain. The abnormal breathing patterns in those subjects could affect the sleep quality and potentially increase the risk for work accidents.

Positive airway pressure adherence and subthreshold adherence in posttraumatic stress disorder patients with comorbid sleep apnea

STUDY OBJECTIVES

Patients with comorbid posttraumatic stress disorder (PTSD) and obstructive sleep apnea (OSA) manifest low adherence to continuous positive airway pressure (CPAP) due to fixed, pressure-induced expiratory pressure intolerance (EPI), a subjective symptom and objective sign aggravated by anxiety sensitivity and somatosensory amplification. As advanced PAP therapy modes (ie, auto-bilevel PAP [ABPAP] or adaptive servo-ventilation [ASV]) may address these side effects, we hypothesized such treatment would be associated with decreased expiratory intolerance and increased adherence in posttraumatic stress patients with co-occurring OSA.

METHODS

We reviewed charts of 147 consecutive adult patients with moderately severe posttraumatic stress symptoms and objectively diagnosed OSA. All patients failed or rejected CPAP and were manually titrated on auto-adjusting, dual-pressure ABPAP or ASV modes in the sleep laboratory, a technique to eliminate flow limitation breathing events while resolving EPI. Patients were then prescribed either mode of therapy. Follow-up encounters assessed patient use, and objective data downloads (ODDs) measured adherence.

RESULTS

Of 147 charts reviewed, 130 patients were deemed current PAP users, and 102 provided ODDs: 64 used ASV and 38 used ABPAP. ODDs yielded three groups: 59 adherent per insurance conventions, 19 subthreshold compliant partial users, and 24 noncompliant. Compliance based on available downloads was 58%, notably higher than recently reported rates in PTSD patients with OSA. Among the 19 partial users, 17 patients were minutes of PAP use or small percentages of nights removed from meeting insurance compliance criteria for PAP devices.

CONCLUSION

Research is warranted on advanced PAP modes in managing CPAP failure in PTSD patients with comorbid OSA. Subthreshold adherence constructs may inform clinical care in a patient-centric model distinct from insurance conventions. Speculatively, clinical application of this transitional zone ("subthreshold" number of hours) may increase PAP use and eventual adherence.

Control theory prediction of resolved Cheyne−Stokes respiration in heart failure

Cheyne–Stokes respiration (CSR) foretells deleterious outcomes in patients with heart failure. Currently, the size of therapeutic intervention is not guided by the patient's underlying pathophysiology. In theory, the intervention needed to resolve CSR, as a control system instability (loop gain >1), can be predicted knowing the baseline loop gain and how much it falls with therapy.

In 12 patients with heart failure, we administered an inspiratory carbon dioxide fraction of 1–3% during CSR (n=95 interventions) as a means to reduce loop gain. We estimated the loop gain on therapy (LGtherapy), using the baseline loop gain (using hyperpnoea length/cycle length) and its expected reduction (18% per 1% inspired carbon dioxide), and tested the specific hypothesis that LGtherapypredicts CSR persistence (LGtherapy>1)versusresolution (LGtherapy<1).

As predicted, when LGtherapy>1.0, CSR continued during therapy in 23 out of 25 (92%) trials. A borderline loop gain zone (0.8<LGtherapy<1) yielded an unpredictable outcome, while LGtherapy<0.8 consistently yielded CSR resolution (37 out of 37 trials). A threshold of LGtherapy=0.9 determined outcome in 76 out of 95 (80%) trials.

We establish proof-of-concept that control theory provides predictive insight into CSR resolution in heart failure. Thus, we now have a means to calculate the size of interventions needed to ameliorate CSR on a patient-by-patient basis.

New Approaches to Diagnosing Sleep-Disordered Breathing

Novel concepts and technological advances have the potential to change the landscape on which clinical sleep medicine is practiced. Screening for sleep apnea will take advantage of readily available mobile telephone technology (sound, accelerometers) to enable widespread recognition of sleep-disordered breathing. Advanced computer-assisted scoring algorithms will improve efficiency and reliability of sleep apnea diagnoses. As the field adopts a personalized approach to therapies, methods to determine the mechanisms of sleep apnea in individuals will be developed-utilizing simplified tests and available recordings-with the promise of predicting outcomes of novel therapies.