The obstructive sleep apnoea endotypes are similar in elderly trauma-exposed veterans with and without diagnosed PTSD

BACKGROUND

Approximately 60% of veterans living with posttraumatic stress disorder (PTSD) experience obstructive sleep apnoea (OSA). Why OSA is so prevalent in individuals with PTSD remains unknown, though PTSD may influence the underlying endotypes known to cause OSA. We examined whether these endotypes (upper airway collapsibility, muscle compensation, loop gain, and the arousal threshold) differ between those with comorbid OSA and PTSD relative to their counterparts with OSA-only.

METHODS

Using the ventilatory flow pattern from diagnostic polysomnography, the OSA endotypes were measured in a retrospective cohort of 21 OSA patients with PTSD and 27 OSA-only patients. All participants were trauma exposed elderly male Australian Vietnam War veterans with mild-to-severe OSA (median Apnoea-Hypopnea index: 20.2 vs. 23.6 events/h). Age and BMI were similar between groups (70.7 vs. 71.7 years, and 28.4 vs. 28.4 kg/m2).

RESULTS

There were no significant differences in the OSA endotype traits between PTSD + OSA and OSA-only patients for upper airway collapsibility (76.68 [71.53-83.56] vs. 78.35 [72.81-83.82] %Veupnea, median [IQR]), muscle compensation (4.27 [0.34-9.18] vs. 5.41 [1.83-7.21] %Veupnea), loop gain (0.56(0.17) vs. 0.60(0.14)), and arousal threshold (135.76 [126.59-147.54] vs. 146.95 [128.64-151.28] %Veupnea).

CONCLUSION

The OSA endotypes in veterans with PTSD were similar to their trauma exposed OSA-only counterparts. PTSD appears to exert little influence on the OSA endotypes beyond the effect that age and trauma exposure may have. The aetiology of increased prevalence of OSA in PTSD remains unclear. Further work examining OSA endotypes using larger and more diverse samples is needed before robust conclusions can be made.

Combination pharmacological therapy targeting multiple mechanisms of sleep apnoea: a randomised controlled cross-over trial

RATIONALE

Acetazolamide and atomoxetine-plus-oxybutynin ('AtoOxy') can improve obstructive sleep apnoea (OSA) by stabilising ventilatory control and improving dilator muscle responsiveness respectively. Given the different pathophysiological mechanisms targeted by each intervention, we tested whether AtoOxy-plus-acetazolamide would be more efficacious than AtoOxy alone.

METHODS

In a multicentre randomised crossover trial, 19 patients with moderate-to-severe OSA received AtoOxy (80/5 mg), acetazolamide (500 mg), combined AtoOxy-plus-acetazolamide or placebo at bedtime for three nights (half doses on first night) with a 4-day washout between conditions. Outcomes were assessed at baseline and night 3 of each treatment period. Mixed model analysis compared the reduction in Apnoea-Hypopnoea Index (AHI) from baseline between AtoOxy-plus-acetazolamide and AtoOxy (primary outcome). Secondary outcomes included hypoxic burden and arousal index.

RESULTS

Although AtoOxy lowered AHI by 49 (33, 62)%baseline (estimate (95% CI)) vs placebo, and acetazolamide lowered AHI by+34 (14, 50)%baseline vs placebo, AtoOxy-plus-acetazolamide was not superior to AtoOxy alone (difference: -2 (-18, 11)%baseline, primary outcome p=0.8). Likewise, the hypoxic burden was lowered with AtoOxy (+58 (37, 71)%baseline) and acetazolamide (+37 (5, 58)%baseline), but no added benefit versus AtoOxy occurred when combined (difference: -13 (-5, 39)%baseline). Arousal index was also modestly reduced with each intervention (11%baseline-16%baseline). Mechanistic analyses revealed that similar traits (ie, higher baseline compensation, lower loop gain) were associated with both AtoOxy and acetazolamide efficacy.

CONCLUSIONS

While AtoOxy halved AHI, and acetazolamide lowered AHI by a third, the combination of these leading experimental interventions provided no greater efficacy than AtoOxy alone. Failure of acetazolamide to further increase efficacy suggests overlapping physiological mechanisms.

TRIAL REGISTRATION NUMBER

NCT03892772.

A review of supine position related obstructive sleep apnea: Classification, epidemiology, pathogenesis and treatment

Supine related obstructive sleep apnea (OSA) is the most common clinical and physiological phenotype of OSA. This condition is recognizable by patients, their families and through polysomnographic recordings. Commonly used definitions distinguish the presence of supine related OSA when respiratory events occur at twice the frequency when the patient lies in the supine compared to non-supine sleeping positions. Recent physiology studies have demonstrated that airway obstruction arises more commonly in the supine position particularly at the level of the soft palate and epiglottis. Increased airway collapsibility is reliability observed supine relative to lateral position. To a lesser extent, changes in control of breathing favour less stable ventilation when the supine sleeping posture is adopted. Many treatments have been developed and trialled to help patients avoid sleeping on their back. The last 10 years has seen the emergence of vibrotactile warning devices that are worn on the patients' neck or chest. High quality randomized controlled trial data is accumulating on the efficacy and common pitfalls of the application of these treatments.

Obstructive Sleep Apnea Is a Distinct Physiological Endotype in Individuals with Comorbid Insomnia and Sleep Apnea

Rationale: With up to 40% of individuals with either insomnia or obstructive sleep apnea (OSA) demonstrating clinically significant symptoms of the other disorder, the high degree of comorbidity among the two most common sleep disorders suggests a bidirectional relationship and/or shared underpinnings. Although the presence of insomnia disorder is believed to influence the underlying pathophysiology of OSA, this influence is yet to be examined directly. Objectives: To investigate whether the four OSA endotypes (upper airway collapsibility, muscle compensation, loop gain, and the arousal threshold) are different in patients with OSA with and without comorbid insomnia disorder. Methods: Using the ventilatory flow pattern captured from routine polysomnography, the four OSA endotypes were measured in 34 patients with OSA who met the diagnostic criteria for insomnia disorder (COMISA) and 34 patients with OSA without insomnia (OSA only). Patients demonstrated mild-to-severe OSA (apnea-hypopnea index, 25.8 ± 2.0 events/h) and were individually matched according to age (50.2 ± 1.5 yr), sex (42 male: 26 female), and body mass index (29.3 ± 0.6 kg/m2). Results: Compared with patients with OSA without comorbid insomnia, patients with COMISA demonstrated significantly lower respiratory arousal thresholds (128.9 [118.1 to 137.1] vs. 147.7 [132.3 to 165.0] % eupneic ventilation ([Formula: see text]); U = 261; 95% confidence interval [CI], -38.3 to -13.9; d = 1.1; P < 0.001), less collapsible upper airways (88.2 [85.5 to 94.6] vs. 72.9 [64.7 to 79.2] %[Formula: see text]; U = 1081; 95% CI, 14.0 to 26.7; d = 2.3; P < 0.001), and more stable ventilatory control (i.e., lower loop gain: 0.51 [0.44 to 0.56] vs. 0.58 [0.49 to 0.70]; U = 402; 95% CI, -0.2 to -0.01; d = 0.05; P = 0.03). Muscle compensation was similar between groups. Moderated linear regression revealed that the arousal threshold moderated the relationship between collapsibility and OSA severity in patients with COMISA but not in patients with OSA only. Conclusions: A low arousal threshold is an overrepresented endotypic trait in individuals with COMISA and may exhibit a greater relative contribution to OSA pathogenesis in these patients. Contrastingly, the prevalence of a highly collapsible upper airway in COMISA was low, suggesting that anatomical predisposition may contribute less to OSA development in COMISA. Based on our findings, we theorize that conditioned hyperarousal perpetuating insomnia may translate to a reduced arousal threshold to respiratory events, thereby increasing the risk or severity of OSA. Therapies that target increased nocturnal hyperarousal (e.g., through cognitive behavior therapy for insomnia) may be effective in individuals with COMISA. Clinical trial registered with the Australian and New Zealand Clinical Trial Registry (ACTRN12616000586415).

Body composition changes and their relationship with obstructive sleep apnoea symptoms, severity: The Sleeping Well Trial

BACKGROUND & AIMS

Obstructive sleep apnoea (OSA) and obesity share a complex bi-directional relationship as location of body fat and changes in regional body composition may be more important for OSA improvement than changes in total body weight only. The aim of this study was to evaluate the impact of a 6-month weight loss intervention for adults newly diagnosed with moderate-severe OSA and obesity on regional body composition. The secondary aims evaluated the relationship between changes in OSA symptoms and severity and anthropometry and regional body composition during the first 12-months after commencing CPAP and explored differences in outcomes between males and females.

METHODS

Participants (n = 59) received CPAP overnight at home alongside a 6-month modified fasting intervention with 12-months follow up. Regional body composition was measured by Dual X-ray absorptiometry, (DXA) and anthropometry before and after the lifestyle intervention. OSA severity was measured using the apnoea hypopnea index via overnight polysomnography and OSA symptoms were measured using the Epworth Sleepiness scale.

RESULTS

Forty-seven adults (74% male) had complete measures available with a mean age of 50.0 y (SD 11.0) and BMI 34.1 kg/m2 (SD 5.0). Following the intervention average fat mass changed by -5.27 kg (5.36), p < 0.001) and visceral adipose tissue (-0.63 kg (0.67), p < 0.001) significantly decreased in males only with a maintenance of fat-free mass (mean -0.41 kg (1.80), p = 0.18). Females (n = 12) had significant decreases in waist circumference (mean -3.36 cm (3.18) p < 0.01), android lean (-0.12 kg (0.04), p < 0.05) and android total mass (-0.28 kg (0.39), p < 0.05) only. Regional body composition changes in males were positively associated with improvements in OSA severity (p < 0.01) but not OSA symptoms.

CONCLUSION

Improvements in regional body composition were seen in males only which were related to improvements in OSA severity but not OSA symptoms. Females may exhibit different OSA pathophysiology and may require different treatment approaches.

TRIAL REGISTRATION

https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=369975&isReview=trueAACTRN12616000203459 ACTRN12616000203459.

Oronasal vs Nasal Masks: The Impact of Mask Type on CPAP Requirement, Pharyngeal Critical Closing Pressure (Pcrit), and Upper Airway Cross-Sectional Areas in Patients With OSA

BACKGROUND

CPAP delivered via an oronasal mask is associated with lower adherence, higher residual apnea-hypopnea index (AHI), and increased CPAP therapeutic pressure compared with nasal masks. However, the mechanisms underlying the increased pressure requirements are not well understood.

RESEARCH QUESTION

How do oronasal masks affect upper airway anatomy and collapsibility?

STUDY DESIGN AND METHODS

Fourteen patients with OSA underwent a sleep study with both a nasal and oronasal mask, each for one-half of the night (order randomized). CPAP was manually titrated to determine therapeutic pressure. Upper airway collapsibility was assessed using the pharyngeal critical closing pressure (Pcrit) technique. Cine MRI was done to dynamically assess the cross-sectional area of the retroglossal and retropalatal airway throughout the respiratory cycle with each mask interface. Scans were repeated at 4 cm H2O and at the nasal and oronasal therapeutic pressures.

RESULTS

The oronasal mask was associated with higher therapeutic pressure requirements (ΔM ± SEM; +2.6 ± 0.5; P < .001) and higher Pcrit (+2.4 ± 0.5 cm H2O; P = .001) compared with the nasal mask. The change in therapeutic pressure between masks was strongly correlated with the change in Pcrit (r2 = 0.73; P = .003). Increasing CPAP increased both the retroglossal and retropalatal airway dimensions across both masks. After controlling for pressure and breath phase, the retropalatal cross-sectional area was moderately larger when using a nasal vs an oronasal mask (+17.2 mm2; 95% CI, 6.2-28.2, P < .001) while nasal breathing.

INTERPRETATION

Oronasal masks are associated with a more collapsible airway than nasal masks, which likely contributes to the need for a higher therapeutic pressure.

Quantitative and Qualitative Changes in Peripheral Chemoreceptor Activity in Preterm Infants

Rationale: Preterm infants are at risk for ventilatory control instability that may be due to aberrant peripheral chemoreceptor activity. Although term infants have increasing peripheral chemoreceptor contribution to overall ventilatory drive with increasing postnatal age, how peripheral chemoreceptor contribution changes in preterm infants with increasing postmenstrual age is not known. Objectives: To evaluate peripheral chemoreceptor activity between 32 and 52 weeks postmenstrual age in preterm infants, using both quantitative and qualitative measures. Methods: Fifty-five infants born between 24 weeks, 0 days gestation and 28 weeks, 6 days gestation underwent hyperoxic testing at one to four time points between 32 and 52 weeks postmenstrual age. Quantitative [Formula: see text] decreases were calculated, and qualitative responses were categorized as apnea, continued breathing with a clear reduction in [Formula: see text], sigh breaths, and no response. Measurements and Main Results: A total of 280 hyperoxic tests were analyzed (2.2 ± 0.3 tests per infant at each time point). Mean peripheral chemoreceptor contribution to ventilatory drive was 85.2 ± 20.0% at 32 weeks and 64.1 ± 22.0% at 52 weeks. Apneic responses were more frequent at earlier postmenstrual ages. Conclusions: Among preterm infants, the peripheral chemoreceptor contribution to ventilatory drive was greater at earlier postmenstrual ages. Apnea was a frequent response to hyperoxic testing at earlier postmenstrual ages, suggesting high peripheral chemoreceptor activity. A clearer description of how peripheral chemoreceptor activity changes over time in preterm infants may help explain how ventilatory control instability contributes to apnea and sleep-disordered breathing later in childhood. Clinical trial registered with www.clinicaltrials.gov (NCT03464396).

A 12-month weight loss intervention in adults with obstructive sleep apnoea: is timing important? A step wedge randomised trial

BACKGROUND/OBJECTIVES

Continuous positive airway pressure (CPAP) concomitant with weight loss is a recommended treatment approach for adults with moderate-severe obstructive sleep apnoea (OSA) and obesity. This requires multiple synchronous behaviour changes. The aim of this study was to examine the effectiveness of a 6-month lifestyle intervention and to determine whether the timing of starting a weight loss attempt affects weight change and trajectory after 12 months in adults newly diagnosed with moderate-severe OSA and treated at home with overnight CPAP.

METHODS

Using a stepped-wedge design, participants were randomised to commence a six-month lifestyle intervention between one and six-months post-enrolment, with a 12-month overall follow-up. Adults (n = 60, 75% males, mean age 49.4 SD 10.74 years) newly diagnosed with moderate-severe OSA and above a healthy weight (mean BMI 34.1 SD 4.8) were recruited.

RESULTS

After 12 months, exposure to the intervention (CPAP and lifestyle) resulted in a 3.7 (95% CI: 2.6 to 4.8, p < 0.001) kg loss of weight compared to the control condition (CPAP alone). Timing of the weight loss attempt made no difference to outcomes at 12 months. When exposed to CPAP only (control period) there was no change in body weight (Coef, [95% CI] 0.03, [-0.3 to 0.36], p = 0.86).

CONCLUSIONS

The lifestyle intervention resulted in a modest reduction in body weight, while timing of commencement did not impact the degree of weight loss at 12 months. These findings support the recommendation of adjunctive weight-loss interventions within six-months of starting CPAP.

Examining the impact of multilevel upper airway surgery on the obstructive sleep apnoea endotypes and their utility in predicting surgical outcomes

BACKGROUND AND OBJECTIVE

Upper airway surgery for obstructive sleep apnoea (OSA) is an alternative treatment for patients who are intolerant of continuous positive airway pressure (CPAP). However, upper airway surgery has variable treatment efficacy with no reliable predictors of response. While we now know that there are several endotypes contributing to OSA (i.e., upper airway collapsibility, airway muscle response/compensation, respiratory arousal threshold and loop gain), no study to date has examined: (i) how upper airway surgery affects all four OSA endotypes, (ii) whether knowledge of baseline OSA endotypes predicts response to surgery and (iii) whether there are any differences when OSA endotypes are measured using the CPAP dial-down or clinical polysomnographic (PSG) methods.

METHODS

We prospectively studied 23 OSA patients before and ≥3 months after multilevel upper airway surgery. Participants underwent clinical and research PSG to measure OSA severity (apnoea-hypopnoea index [AHI]) and endotypes (measured in supine non-rapid eye movement [NREM]). Values are presented as mean ± SD or median (interquartile range).

RESULTS

Surgery reduced the AHI_Total (38.7 [23.4 to 79.2] vs. 22.0 [13.3 to 53.5] events/h; p = 0.009). There were no significant changes in OSA endotypes, however, large but variable improvements in collapsibility were observed (CPAP dial-down method: ∆1.9 ± 4.9 L/min, p = 0.09, n = 21; PSG method: ∆3.4 [-2.8 to 49.0]%V_eupnoea , p = 0.06, n = 20). Improvement in collapsibility strongly correlated with improvement in AHI (%∆AHI_SupineNREM vs. ∆collapsibility: p < 0.005; R²  = 0.46-0.48). None of the baseline OSA endotypes predicted response to surgery.

CONCLUSION

Surgery unpredictably alters upper airway collapsibility but does not alter the non-anatomical endotypes. There are no baseline predictors of response to surgery.

Body position during laboratory and home polysomnography compared to habitual sleeping position at home

STUDY OBJECTIVES

Supine-predominant obstructive sleep apnea (OSA) is highly prevalent. The proportion of time spent in the supine position may be overrepresented during polysomnography, which would impact on the apnea-hypopnea index (AHI) and have important clinical implications. We aimed to investigate the difference in body position during laboratory or home polysomnography compared to habitual sleep and estimate its effect on OSA severity. Secondary aims were to evaluate the consistency of habitual sleeping position and accuracy of self-reported sleeping position.

METHODS

Patients undergoing diagnostic laboratory or home polysomnography were recruited. Body position was recorded using a neck-worn device. Habitual sleeping position was the average time spent supine over 3 consecutive nights at home. Primary outcomes were the proportion of sleep time spent supine (% time supine) and AHI adjusted for habitual sleeping position.

RESULTS

Fifty-seven patients who underwent laboratory polysomnography and 56 who had home polysomnography were included. Compared to habitual sleep, % time supine was higher during laboratory polysomnography (mean difference 14.1% [95% confidence interval: 7.2-21.1]; P = .0002) and home polysomnography (7.1% [95% confidence interval 0.9-13.3]; P = .03). Among those with supine-predominant OSA, there was a trend toward lower adjusted AHI than polysomnography-derived AHI (P = .07), changing OSA severity in 31.6%. There was no significant between-night difference in % time supine during habitual sleep (P = .4). Self-reported % time supine was inaccurate (95% limits of agreement -49.2% to 53.9%).

CONCLUSIONS

More time was spent in the supine position during polysomnography compared to habitual sleep, which may overestimate OSA severity for almost one-third of patients with supine-predominant OSA.

CLINICAL TRIAL REGISTRATION

Registry: Australia and New Zealand Clinical Trials Registry (ANZCTR); Title: Sleeping position during sleep tests and at home; Identifier: ACTRN12618000628246; URL: https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=374873&isReview=true.

CITATION

Yo SW, Joosten SA, Wimaleswaran H, et al. Body position during laboratory and home polysomnography compared to habitual sleeping position at home. J Clin Sleep Med. 2022;18(9):2103-2111.

A single dose of noradrenergic/serotonergic reuptake inhibitors combined with an antimuscarinic does not improve obstructive sleep apnoea severity

Previous trials have demonstrated that the combination of noradrenergic reuptake inhibitors with an antimuscarinic can substantially reduce the apnoea-hypopnoea index (AHI) and improve airway collapsibility in patients with obstructive sleep apnoea (OSA). However, some studies have shown that when administered individually, neither noradrenergic or serotonergic agents have been effective at alleviating OSA. This raises the possibility that serotonergic agents (like noradrenergic agents) may also need to be delivered in combination to be efficacious. Therefore, we investigated the effect of an antimuscarinic (oxybutynin) on OSA severity when administered with either duloxetine or milnacipran, two dual noradrenergic/serotonergic reuptake inhibiters. A randomized, double-blind, 4 way cross-over, placebo-controlled trial in ten OSA patients was performed. Patients received each drug condition separately across four overnight in-lab polysomnography (PSG) studies ~1-week apart. The primary outcome measure was the AHI. In addition, the four key OSA endotypes (collapsibility, muscle compensation, arousal threshold, loop gain) were measured non-invasively from the PSGs using validated techniques. There was no significant effect of either drug combinations on reducing the total AHI or improving any of the key OSA endotypes. However, duloxetine+oxybutynin did significantly increase the fraction of hypopnoeas to apnoeas (F_Hypopnoea ) compared to placebo (p = 0.02; d = 0.54). In addition, duloxetine+oxybutynin reduced time in REM sleep (p = 0.009; d = 1.03) which was positively associated with a reduction in the total AHI (R²  = 0.62; p = 0.02). Neither drug combination significantly improved OSA severity or modified the key OSA endotypes when administered as a single dose to unselected OSA patients.

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.

OUP accepted manuscript

Background

Healthcare workers (HCWs) are at risk from aerosol transmission of severe acute respiratory syndrome coronavirus 2. The aims of this study were to (1) quantify the protection provided by masks (surgical, fit-test_FAILED N95, fit-test_PASSED N95) and personal protective equipment (PPE), and (2) determine if a portable high-efficiency particulate air (HEPA) filter can enhance the benefit of PPE.

Methods

Virus aerosol exposure experiments using bacteriophage PhiX174 were performed. An HCW wearing PPE (mask, gloves, gown, face shield) was exposed to nebulized viruses (10⁸ copies/mL) for 40 minutes in a sealed clinical room. Virus exposure was quantified via skin swabs applied to the face, nostrils, forearms, neck, and forehead. Experiments were repeated with a HEPA filter (13.4 volume-filtrations/hour).

Results

Significant virus counts were detected on the face while the participants were wearing either surgical or N95 masks. Only the fit-test_PASSED N95 resulted in lower virus counts compared to control (P = .007). Nasal swabs demonstrated high virus exposure, which was not mitigated by the surgical/fit-test_FAILED N95 masks, although there was a trend for the fit-test_PASSED N95 mask to reduce virus counts (P = .058). HEPA filtration reduced virus to near-zero levels when combined with fit-test_PASSED N95 mask, gloves, gown, and face shield.

Conclusions

N95 masks that have passed a quantitative fit-test combined with HEPA filtration protects against high virus aerosol loads at close range and for prolonged periods of time.

Pathogenesis of obstructive sleep apnea in people living with HIV

Obstructive sleep apnea (OSA) is highly prevalent in people living with human immunodeficiency virus (HIV) (PLWH), and it might contribute to frequently reported symptoms and comorbidities. Traditional risk factors for OSA are often absent in PLWH, suggesting that HIV or HIV medications might predispose to OSA. Therefore, we measured the anatomical and nonanatomical traits important for OSA pathogenesis in those with and without HIV. We recruited virally suppressed PLWH who had been previously diagnosed with OSA (PLWH + OSA) adherent to positive airway pressure (PAP) therapy, along with age-, sex-, and body mass index (BMI)-matched OSA controls. All participants underwent a baseline polysomnogram to assess OSA severity and a second overnight research sleep study during which the airway pressure was adjusted slowly or rapidly to measure the OSA traits. Seventeen PLWH + OSA and 17 OSA control participants were studied [median age = 58 (IQR = 54-65) yr, BMI = 30.7 (28.4-31.8) kg/m², apnea-hypopnea index = 46 (24-74)/h]. The groups were similar, although PLWH + OSA demonstrated greater sleepiness (despite PAP) and worse sleep efficiency on baseline polysomnography. On physiological testing during sleep, there were no statistically significant differences in OSA traits (including V_eupnea, V_arousal, V_passive, V_active, and loop gain) between PLWH + OSA and OSA controls, using mixed-effects modeling to account for age, sex, and BMI and incorporating each repeated measurement (range = 72-334 measures/trait). Our data suggest that well-treated HIV does not substantially impact the pathogenesis of OSA. Given similar underlying physiology, existing available therapeutic approaches are likely to be adequate to manage OSA in PLWH, which might improve symptoms and comorbidities.NEW & NOTEWORTHY Clinical data suggest an increased risk of obstructive sleep apnea (OSA) in people living with HIV (PLWH), while OSA might account for chronic health issues in this population. We characterized the anatomical and nonanatomical OSA traits in PLWH + OSA compared with OSA controls, using detailed physiological measurements obtained during sleep. Our data suggest against a major impact of HIV on OSA pathogenesis. Available OSA management strategies should be effective to address this potentially important comorbidity in PLWH.

Effects of acetazolamide on control of breathing in sleep apnea patients: Mechanistic insights using meta-analyses and physiological model simulations

Obstructive and central sleep apnea affects ~1 billion people globally and may lead to serious cardiovascular and neurocognitive consequences, but treatment options are limited. High loop gain (ventilatory instability) is a major pathophysiological mechanism underlying both types of sleep apnea and can be lowered pharmacologically with acetazolamide, thereby improving sleep apnea severity. However, individual responses vary and are strongly correlated with the loop gain reduction achieved by acetazolamide. To aid with patient selection for long-term trials and clinical care, our goal was to understand better the factors that determine the change in loop gain following acetazolamide in human subjects with sleep apnea. Thus, we (i) performed several meta-analyses to clarify how acetazolamide affects ventilatory control and loop gain (including its primary components controller/plant gain), and based on these results, we (ii) performed physiological model simulations to assess how different baseline conditions affect the change in loop gain. Our results suggest that (i) acetazolamide primarily causes a left shift of the chemosensitivity line thus lowering plant gain without substantially affecting controller gain; and (ii) higher controller gain, higher paCO2 at eupneic ventilation, and lower CO2 production at baseline result in a more pronounced loop gain reduction with acetazolamide. In summary, the combination of mechanistic meta-analyses with model simulations provides a unified framework of acetazolamide's effects on ventilatory control and revealed physiological predictors of response, which are consistent with empirical observations of acetazolamide's effects in different sleep apnea subgroups. Prospective studies are needed to validate these predictors and assess their value for patient selection.

A Pilot Randomized Controlled Trial of Effect of Genioglossus Muscle Strengthening on Obstructive Sleep Apnea Outcomes

The genioglossus is a major upper airway dilator muscle. Our goal was to assess the efficacy of upper airway muscle training on Obstructive Sleep Apnea (OSA) as an adjunct treatment. Sixty-eight participants with OSA (AHI > 10/h) were recruited from our clinic. They fall into the following categories: (a) Treated with Automatic Positive Airway Pressure (APAP), (n = 21), (b) Previously failed APAP therapy (Untreated), (n = 25), (c) Treated with Mandibular Advancement Splint (MAS), (n = 22). All subjects were given a custom-made tongue strengthening device. We conducted a prospective, randomized, controlled study examining the effect of upper airway muscle training. In each subgroup, subjects were randomized to muscle training (volitional protrusion against resistance) or sham group (negligible resistance), with a 1:1 ratio over 3 months of treatment. In the baseline and the final visit, subjects completed home sleep apnea testing, Epworth Sleepiness Scale (ESS), Pittsburgh Sleep Quality Index (PSQI), SF-36 (36-Item Short Form Survey), and Psychomotor Vigilance Test (PVT). Intervention (muscle training) did not affect the AHI (Apnea-Hypopnea Index), (p-values > 0.05). Based on PSQI, ESS, SF-36 scores, and PVT parameters, the changes between the intervention and sham groups were not significant, and the changes were not associated with the type of treatment (p-value > 0.05). The effectiveness of upper airway muscle training exercise as an adjunct treatment requires further study.

Frequency of flow limitation using airflow shape

STUDY OBJECTIVES

The presence of flow limitation during sleep is associated with adverse health consequences independent of obstructive sleep apnea (OSA) severity (apnea-hypopnea index, AHI), but remains extremely challenging to quantify. Here we present a unique library and an accompanying automated method that we apply to investigate flow limitation during sleep.

METHODS

A library of 117,871 breaths (N=40 participants) were visually classified (certain flow limitation, possible flow limitation, normal) using airflow shape and physiological signals (ventilatory drive per intra-esophageal diaphragm EMG). An ordinal regression model was developed to quantify flow limitation certainty using flow-shape features (e.g. flattening, scooping); breath-by-breath agreement (Cohen's ƙ) and overnight flow limitation frequency (R 2, %breaths in certain or possible categories during sleep) were compared against visual scoring. Subsequent application examined flow limitation frequency during arousals and stable breathing, and associations with ventilatory drive.

RESULTS

The model (23 features) assessed flow limitation with good agreement (breath-by-breath ƙ=0.572, p<0.001) and minimal error (overnight flow limitation frequency R 2=0.86, error=7.2%). Flow limitation frequency was largely independent of AHI (R 2=0.16) and varied widely within individuals with OSA (74[32-95]%breaths, mean[range], AHI>15/hr, N=22). Flow limitation was unexpectedly frequent but variable during arousals (40[5-85]%breaths) and stable breathing (58[12-91]%breaths), and was associated with elevated ventilatory drive (R 2=0.26-0.29; R 2<0.01 AHI v. drive).

CONCLUSIONS

Our method enables quantification of flow limitation frequency, a key aspect of obstructive sleep-disordered breathing that is independent of the AHI and often unavailable. Flow limitation frequency varies widely between individuals, is prevalent during arousals and stable breathing, and reveals elevated ventilatory drive.

Viable virus aerosol propagation by positive airway pressure circuit leak and mitigation with a ventilated patient hood

INTRODUCTION

Nosocomial transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been a major feature of the COVID-19 pandemic. Evidence suggests patients can auto-emit aerosols containing viable viruses; these aerosols could be further propagated when patients undergo certain treatments, including continuous positive airway pressure (PAP) therapy. Our aim was to assess 1) the degree of viable virus propagated from PAP circuit mask leak and 2) the efficacy of a ventilated plastic canopy to mitigate virus propagation.

METHODS

Bacteriophage phiX174 (10⁸ copies·mL^-1) was nebulised into a custom PAP circuit. Mask leak was systematically varied at the mask interface. Plates containing Escherichia coli host quantified viable virus (via plaque forming unit) settling on surfaces around the room. The efficacy of a low-cost ventilated headboard created from a tarpaulin hood and a high-efficiency particulate air (HEPA) filter was tested.

RESULTS

Mask leak was associated with virus contamination in a dose-dependent manner (χ²=58.24, df=4, p<0.001). Moderate mask leak (≥21 L·min^-1) was associated with virus counts equivalent to using PAP with a vented mask. The highest frequency of viruses was detected on surfaces <1 m away; however, viable viruses were recorded up to 3.86 m from the source. A plastic hood with HEPA filtration significantly reduced viable viruses on all plates. HEPA exchange rates ≥170 m³·h^-1 eradicated all evidence of virus contamination.

CONCLUSIONS

Mask leak from PAP may be a major source of environmental contamination and nosocomial spread of infectious respiratory diseases. Subclinical mask leak levels should be treated as an infectious risk. Low-cost patient hoods with HEPA filtration are an effective countermeasure.

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

STUDY OBJECTIVES

Although obstructive sleep apnea results from the combination of different pathophysiologic mechanisms, the degree of anatomical compromise remains the main responsible factor. The passive pharyngeal critical closing pressure (Pcrit) is a technique used to assess the collapsibility of the upper airway and is often used as a surrogate measure of this anatomical compromise. Patients with a low Pcrit (ie, less collapsible airway) are potential candidates for non-continuous positive airway pressure therapies. However, Pcrit determination is a technically complex method not available in clinical practice. We hypothesized that the discrimination between low and high Pcrit can be estimated from simple anthropometric and polysomnographic indices.

METHODS

Men with and without obstructive sleep apnea underwent Pcrit determination and full polysomnography. Receiver operating characteristics analysis was performed to select the best cutoff of each variable to predict a high Pcrit (Pcrit ≥ 2.5 cmH₂O). Multiple logistic regression analysis was performed to create a clinical score to predict a high Pcrit.

RESULTS

We studied 81 men, 48 ± 13 years of age, with an apnea-hypopnea index of 32 [14-60], range 1-96 events/h), and Pcrit of -0.7 ± 3.1 (range, -9.1 to +7.2 cmH₂O). A high and low Pcrit could be accurately identified by polysomnographic and anthropometric indices. A score to discriminate Pcrit showed good performance (area under the curve = 0.96; 95% confidence interval, 0.91-1.00) and included waist circumference, non-rapid eye movement obstructive apnea index/apnea-hypopnea index, mean obstructive apnea duration, and rapid eye movement apnea-hypopnea index.

CONCLUSIONS

A low Pcrit (less collapsible) can be estimated from a simple clinical score. This approach may identify candidates more likely to respond to non-continuous positive airway pressure therapies for obstructive sleep apnea.

Side effects of acetazolamide: a systematic review and meta-analysis assessing overall risk and dose dependence

Introduction

Acetazolamide (AZM) is used for various conditions (eg, altitude sickness, sleep apnoea, glaucoma), but therapy is often limited by its side effect profile. Our objective was to estimate the risk of commonly reported side effects based on meta-analyses. We hypothesised that these risks are dose-dependent.

Methods

We queried MEDLINE/EMBASE (Medical Literature Analysis and Retrieval System Online/Excerpta Medica dataBASE) up until 04/10/2019, including any randomised placebo-controlled trial in which adults received oral AZM versus placebo reporting side effects. Eligibility assessment was performed by two independent reviewers. Data were abstracted by one reviewer who verified key entries at a second time point. For side effects reported by >3 studies a pooled effect estimate was calculated, and heterogeneity assessed via I²; for outcomes reported by >5 studies effect modification by total daily dose (EMbyTDD; <400 mg/d, 400–600 mg/d, >600 mg/d) was assessed via meta-regression. For pre-specified, primary outcomes (paraesthesias, taste disturbances, polyuria and fatigue) additional subgroup analyses were performed using demographics, intervention details, laboratory changes and risk of bias.

Results

We included 42 studies in the meta-analyses (N_subjects=1274/1211 in AZM/placebo groups). AZM increased the risk of all primary outcomes (p<0.01, I² ≤16% and low-to-moderate quality of evidence for all)—the numbers needed to harm (95% CI; n_Studies) for each were: paraesthesias 2.3 (95% CI 2 to 2.7; n=39), dysgeusia 18 (95% CI 10 to 38, n=22), polyuria 17 (95% CI 9 to 49; n=22), fatigue 11 (95% CI 6 to 24; n=14). The risk for paraesthesias (beta=1.8 (95% CI 1.1 to 2.9); P_EMbyTDD=0.01) and dysgeusia (beta=3.1 (95% CI 1.2 to 8.2); P_EMbyTDD=0.02) increased with higher AZM doses; the risk of fatigue also increased with higher dose but non-significantly (beta=2.6 (95% CI 0.7 to 9.4); P_EMbyTDD=0.14).

Discussion

This comprehensive meta-analysis of low-to-moderate quality evidence defines risk of common AZM side effects and corroborates dose dependence of some side effects. These results may inform clinical decision making and support efforts to establish the lowest effective dose of AZM for various conditions.

Predicting sleep apnea responses to oral appliance therapy using polysomnographic airflow

STUDY OBJECTIVES

Oral appliance therapy is an increasingly common option for treating obstructive sleep apnea (OSA) in patients who are intolerant to continuous positive airway pressure (CPAP). Clinically applicable tools to identify patients who could respond to oral appliance therapy are limited.

METHODS

Data from three studies (N = 81) were compiled, which included two sleep study nights, on and off oral appliance treatment. Along with clinical variables, airflow features were computed that included the average drop in airflow during respiratory events (event depth) and flow shape features, which, from previous work, indicates the mechanism of pharyngeal collapse. A model was developed to predict oral appliance treatment response (>50% reduction in apnea-hypopnea index [AHI] from baseline plus a treatment AHI <10 events/h). Model performance was quantified using (1) accuracy and (2) the difference in oral appliance treatment efficacy (percent reduction in AHI) and treatment AHI between predicted responders and nonresponders.

RESULTS

In addition to age and body mass index (BMI), event depth and expiratory "pinching" (validated to reflect palatal prolapse) were the airflow features selected by the model. Nonresponders had deeper events, "pinched" expiratory flow shape (i.e. associated with palatal collapse), were older, and had a higher BMI. Prediction accuracy was 74% and treatment AHI was lower in predicted responders compared to nonresponders by a clinically meaningful margin (8.0 [5.1 to 11.6] vs. 20.0 [12.2 to 29.5] events/h, p < 0.001).

CONCLUSIONS

A model developed with airflow features calculated from routine polysomnography, combined with age and BMI, identified oral appliance treatment responders from nonresponders. This research represents an important application of phenotyping to identify alternative treatments for personalized OSA management.

A randomized controlled trial of oxygen therapy for patients who do not respond to upper airway surgery for obstructive sleep apnea

STUDY OBJECTIVES

We aimed to determine whether patients diagnosed with obstructive sleep apnea (OSA) who fail to respond to upper airway surgery may be successfully treated with supplemental oxygen and whether we could identify baseline physiologic endotypes (ie, collapsibility, loop gain, arousal threshold, and muscle compensation) that predict response to oxygen therapy.

METHODS

We conducted a single night, randomized double-blinded cross over trial in which patients with OSA who failed to respond to upper airway surgery were treated on separate nights with oxygen therapy (4 L/min) or placebo (medical air). Effect of oxygen/air on OSA on key polysomnography outcomes were assessed: apnea-hypopnea index (AHI), AHI without desaturation (ie, flow-based AHI), arousal index, and morning blood pressure. OSA endotypes were estimated from the polysomnography signals to determine whether baseline OSA physiology could be used to predict response to oxygen therapy.

RESULTS

There was a statistically significant reduction in AHI and flow-based AHI on oxygen vs placebo (flow-based AHI: 42.4 ± 21.5 vs 30.5 ± 17.1 events/h, P = .008). Arousal index was also reduced on oxygen vs placebo (41.1 ± 19.5 vs 33.0 ± 15.3 events/h, P = .006). There was no significant difference in morning blood pressure between oxygen and placebo. Although 7 of 20 individuals experienced a 50% reduction or greater in flow-based AHI on oxygen (responders), there was no difference in the baseline OSA endotypes (or clinical characteristics) between responders and nonresponders.

CONCLUSIONS

Our findings demonstrate that a proportion of patients who fail to respond to upper airway surgery for OSA respond acutely to treatment with supplemental oxygen.

CLINICAL TRIAL REGISTRATION

Registry: Australian New Zealand Clinical Trials Registry; Name: Oxygen therapy for treating patients with residual obstructive sleep apnea following upper airway surgery; URL: https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=373566; Identifier: ACTRN12617001361392.

Considering the Role of Adherence in New and Emerging Sleep Treatments

There are several novel and emerging treatments for obstructive sleep apnea (OSA), including new devices and pharmacotherapies. Long-term efficacy and adherence data for these interventions in the sleep context are lacking. Future studies exploring the long-term adherence and efficacy in novel and emerging treatments of OSA are required to fully understand the place of these treatments in treatment hierarchies. Such research also should aim to evaluate the use of these novel therapies in real-world clinical settings, because many of the studies performed to date have been done under closely monitored research populations and relatively small sample sizes.

Interstitial lung disease and obstructive sleep apnea

Obstructive sleep apnea (OSA) is one of the most common comorbidities in patients with interstitial lung disease (ILD). Growing evidence highlights the significance of sleep disturbance on health outcomes in this population. The relationships between ILD and OSA are complex and possibly bidirectional, with multiple mechanisms postulated for the pathogenic and physiologic links. This review synthesizes current evidence and hypotheses regarding different aspects of the relationships between ILD and OSA, emphasizing the interactions between epidemiology, pathogenesis, and pathophysiology.

Children with down syndrome and sleep disordered breathing display impairments in ventilatory control

OBJECTIVES

To investigate the role of ventilatory control instability (i.e. loop gain) in children with Down syndrome and sleep disordered breathing.

METHODS

Children (3-19 years) with Down syndrome and sleep disordered breathing (n = 14) were compared with typically developing children (n = 14) matched for age, sex and sleep disordered breathing severity. All children underwent overnight polysomnography. Spontaneous sighs were identified and a 180s analysis window (60s pre-sigh to 120s post-sigh) containing flow measurements and oxygen saturation were created. Loop gain, a measure of the sensitivity of the negative feedback loop that controls ventilation, was estimated by fitting a mathematical model of ventilatory control to the post-sigh ventilatory pattern. Results; Loop gain was significantly higher in children with Down syndrome compared to matched typically developing children (median loop gain [interquartile range]: 0.36 [0.33, 0.55] vs 0.32 [0.24, 0.38]; P = 0.0395). While children with Down syndrome also had significantly lower average oxygen saturation associated within each analysis window compared to typically developing children (mean ± standard deviation: 96.9 ± 1.3% vs 98.0 ± 1.0%; P = 0.0155), loop gain was not related to polysomnographic measures of hypoxia.

CONCLUSIONS

Higher loop gain in children with Down syndrome and sleep disordered breathing indicates that these children have more unstable ventilatory control, compared to age, sex and sleep disordered breathing severity matched typically developing children. This may be due to an inherent impairment in ventilatory control in children with Down syndrome contributing to their increased risk of sleep disordered breathing which may inform alternative treatment options for this population.

An assessment of a simple clinical technique to estimate pharyngeal collapsibility in people with obstructive sleep apnea

Study Objectives

Quantification of upper airway collapsibility in obstructive sleep apnea (OSA) could help inform targeted therapy decisions. However, current techniques are clinically impractical. The primary aim of this study was to assess if a simple, novel technique could be implemented as part of a continuous positive airway pressure (CPAP) titration study to assess pharyngeal collapsibility.

Methods

A total of 35 participants (15 female) with OSA (mean ± SD apnea–hypopnea index = 35 ± 19 events/h) were studied. Participants first completed a simple clinical intervention during a routine CPAP titration, where CPAP was transiently turned off from the therapeutic pressure for ≤5 breaths/efforts on ≥5 occasions during stable non-rapid eye movement (non-REM) sleep for quantitative assessment of airflow responses (%peak inspiratory flow [PIF] from preceding 5 breaths). Participants then underwent an overnight physiology study to determine the pharyngeal critical closing pressure (Pcrit) and repeat transient drops to zero CPAP to assess airflow response reproducibility.

Results

Mean PIF of breaths 3–5 during zero CPAP on the simple clinical intervention versus the physiology night were similar (34 ± 29% vs. 28 ± 30% on therapeutic CPAP, p = 0.2; range 0%–90% vs. 0%–95%). Pcrit was −1.0 ± 2.5 cmH2O (range −6 to 5 cmH2O). Mean PIF during zero CPAP on the simple clinical intervention and the physiology night correlated with Pcrit (r = −0.7 and −0.9, respectively, p &lt; 0.0001). Receiver operating characteristic curve analysis indicated significant diagnostic utility for the simple intervention to predict Pcrit &lt; −2 and &lt; 0 cmH2O (AUC = 0.81 and 0.92), respectively.

Conclusions

A simple CPAP intervention can successfully discriminate between patients with and without mild to moderately collapsible pharyngeal airways. This scalable approach may help select individuals most likely to respond to non-CPAP therapies.

Role of ventilatory control instability in children with sleep-disordered breathing

BACKGROUND AND OBJECTIVE

The contribution of non-anatomical factors, such as ventilatory control instability (i.e. LG), to the pathogenesis of obstructive SDB in children is unclear. Therefore, we aimed to identify the relationship between LG and severity of SDB, demographic, anthropometric and anatomical characteristics in a clinically representative cohort of children.

METHODS

Children (aged 3-18 years) with various severities of SDB (n = 110) and non-snoring controls (n = 36) were studied. Children were grouped according to their OAHI. Anthropometric and upper airway anatomical characteristics were measured. Spontaneous sighs were identified on polysomnography and LG, a measure of the sensitivity of the negative feedback loop that controls ventilation, was estimated by fitting a mathematical model of ventilatory control to the post-sigh ventilatory pattern.

RESULTS

There was no difference in LG between controls and any of the SDB severity groups. However, LG was significantly lower in children with larger tonsils (tonsil grade 4) compared with children with smaller tonsils (tonsil grade 1) (median LG (range): 0.25 (0.20-0.42) vs 0.32 (0.25-0.44); P = 0.009) and in children with a modified Mallampati score of class III/IV compared with class I (0.28 (0.24-0.33) vs 0.37 (0.27-0.44); P = 0.009).

CONCLUSION

A direct relationship was not found between the severity of paediatric SDB and LG. However, an altered ventilatory control sensitivity may contribute to SDB in a subgroup of children depending on their degree of anatomical compromise of the airway.

Pathogenesis of obstructive sleep apnea in individuals with the COPD + OSA Overlap syndrome versus OSA alone

Overlap syndrome (OVS) is the concurrence of chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (OSA), and is associated with poor outcomes. We hypothesized that physiological changes in COPD may affect the pathogenesis of OSA in important ways. We therefore sought to measure the anatomical and nonanatomical OSA traits in individuals with OVS and compare to those with OSA alone. Patients with established OVS were recruited, along with age, gender, and BMI matched OSA only controls. Smoking and relevant comorbidities or medications were excluded. Subjects underwent baseline polysomnography followed by an overnight physiological research study to measure the OSA traits (Veupnea , Varousal , Vpassive , Vactive , and loop gain). Fifteen subjects with OVS and 15 matched controls with OSA alone were studied (overall 66 ± 8 years, 20% women, BMI 31 ± 4 kg/m2 , apnea-hypopnea index 49 ± 36/hr). Mixed-modeling was used to incorporate each measurement (range 52-270 measures/trait), and account for age, gender, and BMI. There were no significant differences in the traits between OVS and OSA subjects, although OVS subjects potentially tolerated a lower ventilation before arousal (i.e., harder to wake; p = .06). Worsened lung function was significantly associated with worsened upper airway response and more unstable breathing (p < .05 for all). Consistent differences in key OSA traits were not observed between OVS and OSA alone. However, worse lung function does appear to exert an influence on several OSA traits. These findings indicate that a diagnosis of OVS should not generally influence the approach to OSA, but that lung function might be considered if utilizing OSA trait-specific treatment.

Polysomnographic Endotyping to Select Patients with Obstructive Sleep Apnea for Oral Appliances

Rationale: Oral appliance therapy is efficacious in many patients with obstructive sleep apnea (OSA), but prediction of treatment outcome is challenging. Small, detailed physiological studies have identified key OSA endotypic traits (pharyngeal collapsibility and loop gain) as determinants of greater oral appliance efficacy.Objectives: We used a clinically applicable method to estimate OSA traits from routine polysomnography and identify an endotype-based subgroup of patients expected to show superior efficacy.Methods: In 93 patients (baseline apnea-hypopnea index [AHI], ≥20 events/h), we examined whether polysomnography-estimated OSA traits (pharyngeal: collapsibility and muscle compensation; nonpharyngeal: loop gain, arousal threshold, and ventilatory response to arousal) were associated with oral appliance efficacy (percentage reduction in AHI from baseline) and could predict responses to treatment. Multivariable regression (with interactions) defined endotype-based subgroups of "predicted" responders and nonresponders (based on 50% reduction in AHI). Treatment efficacy was compared between the predicted subgroups (with cross-validation).Results: Greater oral appliance efficacy was associated with favorable nonpharyngeal traits (lower loop gain, higher arousal threshold, and lower response to arousal), moderate (nonmild, nonsevere) pharyngeal collapsibility, and weaker muscle compensation (overall R2 = 0.30; adjusted R2 = 0.19; P = 0.003). Predicted responders (n = 54), compared with predicted nonresponders (n = 39), exhibited a greater reduction in AHI from baseline (mean [95% confidence interval], 73% [66-79] vs. 51% [38-61]; P < 0.0001) and a lower treatment AHI (8 [6-11] vs. 16 [12-20] events/h; P = 0.002). Differences persisted after adjusting for clinical covariates (including baseline AHI, body mass index, and neck circumference).Conclusions: Quantifying OSA traits using clinical polysomnography can identify an endotype-based subgroup of patients that is highly responsive to oral appliance therapy. Prospective validation is warranted.

Severe obstructive sleep apnea is associated with significant coronary artery plaque burden independent of traditional cardiovascular risk factors

Obstructive Sleep Apnea (OSA) is strongly associated with adverse cardiovascular events. In these patients, increased oxidative stress has been associated with accelerated coronary atherosclerosis. However, it is unclear if OSA is associated with significant coronary artery plaque burden. Our aim is to determine whether OSA and/or markers of hypoxemia are associated with coronary plaque burden (CPB). Patients who had coronary computed tomography angiography (CCTA) and a polysomnogram within 1 year of each other between 2011 and 2016 were analyzed. Apnea-Hypopnea Index (AHI) and hypoxemic burden (ODI3%, ODI4%, nadir SpO2, average spO₂ and time of spO₂ < 88%) were obtained from the polysomnogram. Total CPB was assessed using the prognostically validated CT-Leaman score (CT-LeSc). Significant CPB was defined as CT-LeSc ≥ 8.3. There were 119 patients with mean (± SD) age of 59 ± 12 years. Using logistical regression analysis; AHI, ODI4% and ODI3% were the only parameters associated with significant CPB. Severe OSA (AHI ≥ 30 events/h) was associated with significant CPB with adjusted OR of 3.21 (p = 0.010) independent of traditional cardiovascular risk factors. Mechanisms associated with apnea and hypopnea events (as measured by AHI, ODI3% and ODI4%), but not the severity of arterial desaturation (nadir SpO₂, burden of SpO₂ < 88%) were associated with significant CPB.

Assessing ventilatory instability using the response to spontaneous sighs during sleep in preterm infants

Study Objectives

Periodic breathing (PB) is common in newborns and is an obvious manifestation of ventilatory control instability. However, many infants without PB may still have important underlying ventilatory control instabilities that go unnoticed using standard clinical monitoring. Methods to detect infants with "subclinical" ventilatory control instability are therefore required. The current study aimed to assess the degree of ventilatory control instability using simple bedside recordings in preterm infants.

Methods

Respiratory inductance plethysmography (RIP) recordings were analyzed from ~20 minutes of quiet sleep in 20 preterm infants at 36 weeks post-menstrual age (median [range]: 36 [34-40]). The percentage time spent in PB was also calculated for each infant (%PB). Spontaneous sighs were identified and breath-by-breath measurements of (uncalibrated) ventilation were derived from RIP traces. Loop gain (LG, a measure of ventilatory control instability) was calculated by fitting a simple ventilatory control model (gain, time-constant, delay) to the post-sigh ventilatory pattern. For comparison, periodic inter-breath variability was also quantified using power spectral analysis (ventilatory oscillation magnitude index [VOMI]).

Results

%PB was strongly associated with LG (r2 = 0.77, p < 0.001) and moderately with the VOMI (r2 = 0.21, p = 0.047). LG (0.52 ± 0.05 vs. 0.30 ± 0.03; p = 0.0025) and the VOMI (-8.2 ± 1.1 dB vs. -11.8 ± 0.9 dB; p = 0.026) were both significantly higher in infants that displayed PB vs. those without.

Conclusions

LG and VOMI determined from the ventilatory responses to spontaneous sighs can provide a practical approach to assessing ventilatory control instability in preterm infants. Such simple techniques may help identify infants at particular risk for ventilatory instabilities with concomitant hypoxemia and its associated consequences.

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.

The physiological phenotype of obstructive sleep apnea differs between Caucasian and Chinese patients

Study Objectives

The mechanisms responsible for the development of obstructive sleep apnea (phenotypic “traits”) are known to differ between individuals and may differ across ethnicities. We aimed to examine whether loop gain, arousal threshold, pharyngeal collapsibility and muscle compensation differ between Chinese and Caucasian individuals with OSA.

Methods

We noninvasively determined the relative contribution of loop gain, arousal threshold, pharyngeal collapsibility, and muscle compensation from the ventilatory flow pattern recorded during a standard clinical polysomnography in a cohort of age and AHI matched Caucasian and Chinese patients with moderate-severe OSA (n = 90).

Results

Chinese participants had significantly more collapsible pharyngeal airways as indicated by a lower Vpassive (68.9 [51.5–75.2] vs. 74.0 [65.1–80.4] %Veupnea, U = 703, p = 0.012), but less ventilatory control instability as indicated by a lower loop gain (0.60 [0.50–0.67] vs. 0.63 [0.57–0.81], U = 762, p = 0.043) compared with Caucasian participants. Further, multiple logistic regression analyses demonstrated that the combined pharyngeal collapsibility (Vpassive) and loop gain traits help to better explain the differences between the groups beyond upper-airway collapsibility alone. No statistically significant group differences were found in muscle compensation or arousal threshold traits between groups.

Conclusion

Individuals of Chinese descent appear to have OSA that is driven much more by the relative contribution of their anatomical predisposition and to a lesser extent nonanatomical causes compared with Caucasians. Future research should focus on determining if Chinese versus Caucasian ethnicity is an important contributing factor to clinical outcomes and therapeutic responses in OSA.

Quantifying the Arousal Threshold Using Polysomnography in Obstructive Sleep Apnea

Study Objectives

Precision medicine for obstructive sleep apnea (OSA) requires noninvasive estimates of each patient's pathophysiological "traits." Here, we provide the first automated technique to quantify the respiratory arousal threshold-defined as the level of ventilatory drive triggering arousal from sleep-using diagnostic polysomnographic signals in patients with OSA.

Methods

Ventilatory drive preceding clinically scored arousals was estimated from polysomnographic studies by fitting a respiratory control model (Terrill et al.) to the pattern of ventilation during spontaneous respiratory events. Conceptually, the magnitude of the airflow signal immediately after arousal onset reveals information on the underlying ventilatory drive that triggered the arousal. Polysomnographic arousal threshold measures were compared with gold standard values taken from esophageal pressure and intraoesophageal diaphragm electromyography recorded simultaneously (N = 29). Comparisons were also made to arousal threshold measures using continuous positive airway pressure (CPAP) dial-downs (N = 28). The validity of using (linearized) nasal pressure rather than pneumotachograph ventilation was also assessed (N = 11).

Results

Polysomnographic arousal threshold values were correlated with those measured using esophageal pressure and diaphragm EMG (R = 0.79, p < .0001; R = 0.73, p = .0001), as well as CPAP manipulation (R = 0.73, p < .0001). Arousal threshold estimates were similar using nasal pressure and pneumotachograph ventilation (R = 0.96, p < .0001).

Conclusions

The arousal threshold in patients with OSA can be estimated using polysomnographic signals and may enable more personalized therapeutic interventions for patients with a low arousal threshold.