Discriminating the severity of pharyngeal collapsibility in men using anthropometric and polysomnographic indices

Sleep apnea endotypes and their implications for clinical practise

Obstructive sleep apnea (OSA) is now recognized to be a multifactorial disorder caused by several endotypes that differ between individuals and patient populations. In order to understand the current clinical implications of OSA endotypes, this review aims to examine the current state of play in endotype measurements, endotype modification and their impact on clinical outcomes/prognosis. In summary, the field has developed multiple techniques to measure the endotypes over the last few decades. There is now good proof-of-concept evidence that a priori knowledge of an individual's OSA endotype traits may be useful in helping to guide treatment decisions. However, in order to truly deliver a personalized medicine approach to the treatment of OSA, we need to address critical gaps in: understanding OSA endotype treatment thresholds, and the impact of OSA modification on patient centred outcomes and hard clinical endpoints. Such efforts will benefit from a united, collaborative approach that involve partnerships between academics and consumers (i.e. patients, healthcare providers, industry).

Sex-specific age-related worsening of pathological endotypic traits in patients with obstructive sleep apnea

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is more prevalent in men and older adults. Few studies have explored variations in pathological endotypic traits by age and sex using a large patient sample, offering insights into the development of the disease. Our study aims to examine how endotype characteristics of OSA vary across ages in different sex.

METHODS

A cross-sectional study was conducted, enrolling 2296 adult patients referred for in-laboratory diagnostic polysomnography at a single sleep center in Taiwan. Among them, 1374 had an apnea-hypopnea index ≥5. Using the "Phenotyping Using Polysomnography" method, we estimated four endotypic traits-arousal threshold, upper airway collapsibility, loop gain, and upper airway muscle compensation. Demographic and polysomnographic characteristics were compared between sexes and age groups. Generalized linear regression and generalized additive models were employed to explore the associations of sex and age with endotypic traits.

RESULTS

Men with OSA exhibited higher collapsibility and lower compensation than women (difference: 4.32 %eupnea and 4.49 %eupnea, respectively). Younger patients with OSA had a higher prevalence of obesity, more snoring symptoms, and lower loop gain compared to older patients. For men, age was correlated with increased collapsibility, increased loop gain, and decreased arousal threshold after 37 years old. Whereas in women, endotypic traits were not associated with age, except for an increase in loop gain with advancing age.

CONCLUSIONS

Personalized treatment options for OSA should take into consideration age and sex. Reducing loop gain could be a treatment objective for older patients with OSA.

[From vibration trauma to pharyngeal muscle instability: A self-sustaining pathophysiological process (circulus vitiosus) in obstructive sleep apnea]

Pharyngeal stability is ensured by both anatomical and non-anatomical factors. In addition to the anatomical width, functional factors are also significant in determining the degree of obstruction of the upper airway. The functionality of the pharyngeal muscles depends on an undisturbed sensorimotor system. In patients with rhonchopathy or obstructive sleep apnea (OSA), sensorimotor function and muscle morphology change progressively. It is hypothesised that long-term snoring leads to vibration-induced sensorimotor neuropathy, resulting in the loss of function and structure of the pharyngeal muscles. Pharyngeal mechanoreceptors lose their sensitivity, and due to neural damage, information can no longer be adequately translated into motor responses. This raises the question of the timeframe within which irreversible vibration-induced receptor damage occurs due to snoring.

Comparison of awake respiratory control versus sleep obstructive sleep apnea endotypes

Most approaches to advance simplified physiology-based precision medicine strategies for obstructive sleep apnea (OSA) focus on sleep parameters (i.e., OSA endotypes). However, wakefulness physiology measures can also provide prediction insight for certain OSA therapies, yet their relationship with sleep parameters has not been extensively investigated. This study aimed to investigate potential relationships between awake ventilatory control parameters and sleep OSA endotypes and their potential to predict changes in OSA severity with morphine. Data were acquired from a randomized, crossover trial that investigated the effects of morphine versus placebo on OSA severity and underlying mechanisms. Here, awake ventilatory chemoreflex testing before overnight polysomnography was compared with direct measures of sleep respiratory control (e.g., hypercapnic ventilatory responses and loop gain) and OSA endotypes during a separate overnight physiology study [pharyngeal critical closure pressure (Pcrit), muscle responsiveness via genioglossus intramuscular electromyography, and arousal threshold via epiglottic pressure catheter to transient continuous positive airway pressure reductions]. Twenty-one men with OSA completed both study arms. During placebo, 1) awake chemosensitivity correlated with Pcrit (r = 0.726, P = 0.001), 2) arousal threshold correlated with awake CO2 ventilatory response threshold (r = -0.467, P = 0.047) and basal ventilation (r = -0.500, P = 0.029). Awake chemosensitivity and Pcrit also correlated with the apnea-hypopnea index (P < 0.001) during placebo. Awake chemosensitivity was predictive of changes in OSA severity with morphine (r = -0.535, P = 0.013). In conclusion, awake measures of respiratory control are related to physiological endotypes, such as airway collapsibility and arousal threshold during sleep and OSA severity. Awake ventilatory chemosensitivity has the best potential to predict changes in OSA severity with morphine.NEW & NOTEWORTHY Both awake ventilatory control measures and OSA endotypes measured during sleep have reported potentials in endotyping/phenotyping OSA, although no randomized, controlled trial has compared/linked between the two techniques. From a double-blind, randomized placebo-controlled crossover trial, we found that awake measures of respiratory control are related to physiological endotypes such as airway collapsibility and arousal threshold during sleep and OSA severity. Awake ventilatory chemosensitivity has the best potential to predict changes in OSA severity with morphine.

[The upper airway in obstructive sleep apnea patients is pathological even when awake]

Obstructive sleep apnea (OSA) is characterized by partial or complete obstruction of the pharyngeal airway. Anatomical factors can be distinguished from non-anatomical factors. Age and obesity are the main risk factors for OSA; however, approximately 50% of patients are not obese. In older patients (>60 years), the importance of obesity decreases. There is an increased prevalence of OSA among patients with normal weight. The effects of chronic intermittent hypoxemia, low-grade inflammation, increased sympathetic tone and mechanical stress contribute to a transformation of muscle fibers in the upper airway, resulting in reduced muscle mass and strength. Less frequently encountered non-anatomical factors include decreased muscle tone, increased arousal threshold, and altered sensitivity of CO2 chemoreceptors.

Sleep and Breathing Conference highlights 2023: a summary by ERS Assembly 4

This paper presents some of the highlights of the Sleep and Breathing Conference 2023 https://bit.ly/46MxJml.

Clinical polysomnographic methods for estimating pharyngeal collapsibility in obstructive sleep apnea

STUDY OBJECTIVES

Obstructive sleep apnea has major health consequences but is challenging to treat. For many therapies, efficacy is determined by the severity of underlying pharyngeal collapsibility, yet there is no accepted clinical means to measure it. Here, we provide insight into which polysomnographic surrogate measures of collapsibility are valid, applicable across the population, and predictive of therapeutic outcomes.

METHODS

Seven promising polysomnography-derived surrogate collapsibility candidates were evaluated: Vpassive (flow at eupneic ventilatory drive), Vmin (ventilation at nadir drive), event depth (depth of the average respiratory event), oxygen desaturation slope and mean oxygen desaturation (events-related averages), Fhypopneas (fraction of events scored as hypopneas), and apnea index. Evaluation included (1) validation by comparison to physiological gold-standard collapsibility values (critical closing pressure, Pcrit), (2) capacity to detect increased collapsibility with older age, male sex, and obesity in a large community-based cohort (Multi-Ethnic Study of Atherosclerosis, MESA), and (3) prediction of treatment efficacy (oral appliances and pharmacological pharyngeal muscle stimulation using atomoxetine-plus-oxybutynin).

RESULTS

Pcrit was significantly correlated with Vmin (r = -0.54), event depth (r = 0.49), Vpassive (r = -0.38), Fhypopneas (r = -0.46), and apnea index (r = -0.46; all p < .01) but not others. All measures detected greater collapsibility with male sex, age, and obesity, except Fhypopneas and apnea index which were not associated with obesity. Fhypopneas and apnea index were associated with oral appliance and atomoxetine-plus-oxybutynin efficacy (both p < .05).

CONCLUSIONS

Among several candidates, event depth, Fhypopneas, and apnea index were identified as preferred pharyngeal collapsibility surrogates for use in the clinical arena.

Fraction of apnea is associated with the required continuous positive airway pressure level and reflects upper airway collapsibility in patients with obstructive sleep apnea

STUDY OBJECTIVES

We aimed to determine whether the fraction of apnea (Fapnea) could be used as an alternative index to reflect upper airway (UA) collapsibility.

METHODS

We retrospectively recruited 161 patients (16 women, mean age 47.8 years, body mass index [BMI] 28.0 kg/m², and apnea-hypopnea index [AHI] 46.4/h) with moderate to severe obstructive sleep apnea (OSA) who underwent nasal continuous positive airway pressure (CPAP) titration. The Fapnea was defined as the percentage of apneic events over the total apneic and hypopneic events during sleep in a supine position on diagnostic polysomnography. We randomly split the data (70/30) into the development and validation datasets. In the development dataset, we conducted a multiple regression analysis to assess the association of variables, including the age, sex, BMI, rapid eye movement (REM) supine AHI, and apnea with the CPAP level during supine REM sleep (REM_CPAP). Moreover, we developed an equation for predicting the CPAP level. Thereafter, we evaluated the correlation between the actual CPAP level and the value calculated using the model.

RESULTS

BMI and Fapnea were the only significant factors that predicted the REM_CPAP level (adjusted r=0.60, p<0.001) in the development dataset. The validation data revealed a significant correlation between the actual and predicted CPAP levels (r=0.69, p<0.0001). We observed similar associations during supine non-REM (NREM) sleep.

CONCLUSIONS

Fapnea could significantly predict the CPAP levels during both REM and NREM sleep, which likely reflects the UA collapsibility, independent of the BMI.

OSA Upper Airways Surgery: A Targeted Approach

Obstructive sleep apnea syndrome (OSA) is a multi-factorial disorder, with quite complex endotypes, consisting of anatomical and non-anatomical pathophysiological factors. Continuous positive airway pressure (CPAP) is recognized as the first-line standard treatment for OSA, whereas upper airway (UA) surgery is often recommended for treating OSA patients who have refused or cannot tolerate CPAP. The main results achievable by the surgery are UA expansion, and/or stabilization, and/or removal of the obstructive tissue to different UA levels. The site and pattern of UA collapse identification is of upmost importance in selecting the customized surgical procedure to perform, as well as the identification of the relation between anatomical and non-anatomical factors in each patient. Medical history, sleep studies, clinical examination, UA endoscopy in awake and drug-induced sedation, and imaging help the otorhinolaryngologist in selecting the surgical candidate, identifying OSA patients with mild UA collapsibility or tissue UA obstruction, which allow achievement of the best surgical outcomes. Literature data reported that the latest palatal surgical procedures, such as expansion sphincter palatoplasty or barbed reposition palatoplasty, which achieve soft palatal and lateral pharyngeal wall remodeling and stiffening, improved the Apnea Hypopnea Index, but the outcome analyses are still limited by methodological bias and the limited number of patients' in each study. Otherwise, the latest literature data have also demonstrated the role of UA surgery in the improvement of non-anatomical factors, confirming that a multidisciplinary and multimodality diagnostic and therapeutical approach to OSA patients could allow the best selection of customized treatment options and outcomes.

Non-continuous positive airway pressure treatment options in obstructive sleep apnoea: A pathophysiological perspective

The phenotyping of the pathophysiology of obstructive sleep apnoea (OSA) lies at the core of tailored treatments and it is one of the most debated topics in sleep medicine research. Recent sophisticated techniques have broadened the horizon for gaining insight into the variability of the endotypic traits in patients with OSA which account for the heterogeneity in the clinical presentation of the disease and consequently, in the outcome of treatment. However, the implementation of these concepts into clinical practice is still a major challenge for both researchers and clinicians in order to develop tailored therapies targeted to specific endotypic traits that contribute to OSA in each individual patient. This review summarizes available scientific evidence in order to point out the links between endotypic traits (pharyngeal airway collapsibility, upper airway neuromuscular compensation, loop gain and arousal threshold) and the most common non-continuous positive airway pressure (CPAP) treatment options for OSA (mandibular advancement device, upper airway surgery, medication therapy, positional therapy) and to clarify to what extent endotypic traits could help to better predict the success of these therapies. A narrative guide is provided; current design limitations and future avenues of research are discussed, with clinical and research perspectives.

Orofacial Myofunctional Therapy in Obstructive Sleep Apnea Syndrome: A Pathophysiological Perspective

Obstructive sleep apnea (OSA) syndrome is a multi-factorial disorder. Recently identified pathophysiological contributing factors include airway collapsibility, poor pharyngeal muscle responsiveness, a low arousal threshold, and a high loop gain. Understanding the pathophysiology is of pivotal importance to select the most effective treatment option. It is well documented that conventional treatments (continuous positive airway pressure (CPAP), upper airway surgery, and dental appliance) may not always be successful in the presence of non-anatomical traits, especially in mild to moderate OSA. Orofacial myofunctional therapy (OMT) consists of isotonic and isometric exercises targeted to oral and oropharyngeal structures, with the aim of increasing muscle tone, endurance, and coordinated movements of pharyngeal and peripharyngeal muscles. Recent studies have demonstrated the efficacy of OMT in reducing snoring, apnea-hypopnea index, and daytime sleepiness, and improving oxygen saturations and sleep quality. Myofunctional therapy helps to reposition the tongue, improve nasal breathing, and increase muscle tone in pediatric and adult OSA patients. Studies have shown that OMT prevents residual OSA in children after adenotonsillectomy and helps adherence in CPAP-treated OSA patients. Randomized multi-institutional studies will be necessary in the future to determine the effectiveness of OMT in a single or combined modality targeted approach in the treatment of OSA. In this narrative review, we present up-to-date literature data, focusing on the role of OSA pathophysiology concepts concerning pharyngeal anatomical collapsibility and muscle responsiveness, underlying the response to OMT in OSA patients.