Changes in tongue morphology predict responses in pharyngeal patency to selective hypoglossal nerve stimulation

STUDY OBJECTIVES

The major goal of the study was to determine whether changes in tongue morphology under selective hypoglossal nerve therapy for obstructive sleep apnea were associated with alterations in airway patency during sleep when specific portions of the hypoglossal nerve were stimulated.

METHODS

This case series was conducted at the Johns Hopkins Sleep Disorders Center at Johns Hopkins Bayview Medical Center. Twelve patients with apnea implanted with a multichannel targeted hypoglossal nerve-stimulating system underwent midsagittal ultrasound tongue imaging during wakefulness. Changes in tongue shape were characterized by measuring the vertical height and polar dimensions between tongue surface and genioglossi origin in the mandible. Changes in patency were characterized by comparing airflow responses between stimulated and adjacent unstimulated breaths during non-rapid eye movement sleep.

RESULTS

Two distinct morphologic responses were observed. Anterior tongue base and hyoid-bone movement (5.4 [0.4] to 4.1 [1.0] cm (median and [interquartile range]) with concomitant increases in tongue height (5.0 [0.9] to 5.6 [0.7] cm) were associated with decreases in airflow during stimulation. In contrast, comparable anterior hyoid movement (tongue protrusion from 5.8 [0.5] to 4.5 [0.9] cm) without significant increases in height (5.2 [1.6] to 4.6 [0.8] cm) were associated with marked increases in airflow during sleep.

CONCLUSIONS

Tongue protrusion with preservation of tongue shape predicted increases in patency, whereas anterior movement with concomitant increases in height were associated with decreased pharyngeal patency. These findings suggest that pharyngeal patency can be best stabilized by stimulating lingual muscles that maintain tongue shape while protruding the tongue, thereby preventing it from prolapsing posteriorly during sleep.

CITATION

Fleury Curado T, Pham L, Otvos T, et al. Changes in tongue morphology predict responses in pharyngeal patency to selective hypoglossal nerve stimulation. J Clin Sleep Med. 2023;19(5):947-955.

PSUN111 Rationale and Design of the Dinner Time 2 Trial: A Randomized, Crossover Trial to Compare the Effects of Delayed Eating vs Delayed Sleeping on Overnight Metabolism in Healthy Volunteers

Background

Obesity and its associated metabolic complications are leading causes of morbidity and mortality worldwide. Recent studies suggest that the timing of meals may be critically important for weight control and metabolic health. Consuming calories later in the day is associated with greater risks of obesity and metabolic syndrome. Interventional diet studies show more weight loss with early, rather than later, eating. Our team conducted a randomized, crossover study ("Dinner Time Study") that compared the metabolic effects of routine dinner (6pm) vs late dinner (10pm) with a fixed sleep period (11pm-7am) in young, healthy adults. We found that late dinner caused an 18% increase in post-prandial glucose and a 10% decrease in dietary fat oxidation. These metabolic consequences in the long term may lead to the development of obesity and type 2 diabetes. However, it remains unclear whether the adverse metabolic effects of late dinner are mediated by circadian misalignment (eating at the "wrong" time relative to the body's central circadian clock) or mediated by sleep (eating too close to bedtime, coinciding with the fall in metabolic rate induced by sleep). To address this question, we aim to examine the metabolic effects of early dinner, late dinner, and late dinner followed by delayed sleep, in healthy adults.

Methods

Dinner Time 2 Study is a randomized crossover trial with 3 treatment arms with a 3-4-week washout period: (1) early dinner + routine sleep; (2) late dinner + routine sleep; (3) late dinner + late sleep. Dinner times and bedtimes will be customized to each participant's central circadian rhythm (assessed by dim light melatonin onset, DLMO). The primary objectives of this study are to (1) examine the metabolic effects of early dinner (DLMO-3h) vs late dinner (DLMO+1h) with a fixed routine bedtime (DLMO+2h); (2) examine the metabolic effects of routine bedtime (DLMO+2h) vs delayed bedtime (DLMO+6h) with a fixed late dinner time (DLMO+1h). We will examine 24-h profiles of glucose, insulin, free fatty acids, triglycerides, and dietary fat oxidation using serial blood sampling and an ingested stable isotope ([²H31] palmitate) tracer. We aim to recruit 20 healthy adults, age 18-30 years old, with a BMI 18-29.9 kg/m². Participants who perform night shift work or have any sleep disorders or metabolic diseases including diabetes are ineligible. Each participant will have 4 overnight admissions to our Clinical Research Unit (1 DLMO visit and 3 metabolic visits). A total of 3 participants have successfully completed the protocol since recruitment started in 2021.

Conclusion

Dinner Time 2 will greatly advance our understanding of the interactions between meal timing, sleep timing, and metabolism, which could inform the design and implementation of future studies that leverage chronobiology to combat diabetes and obesity.

Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.

0167 Obesity-Induced Breathing Variability During Sleep Is Not Entirely Attributed to Apneas and Sleep Fragmentation

Introduction

Obesity is a major cause of sleep-disordered breathing (SDB). Conventional metrics of SDB can be confounded by the effects of obesity on oxygenation and lack of standard definitions. Sleep fragmentation is frequently observed in obese individuals, but whether it occurs independently of SDB remains unknown. Quantitative analysis of ventilation may delineate the effects of obesity on breathing patterns and sleep fragmentation. We aimed to examine the effects of obesity on respiratory patterns during sleep and the relationship between obesity-related respiratory variability and sleep fragmentation.

Methods

Sleep recordings were performed in 15 lean C57BL/6J and 17 diet-induced obese (DIO) mice on the same genetic background. We applied Poincaré analysis of minute ventilation (VE) during sleep to estimate the breathing variability. Arousals were classified as respiratory when associated with ≥30% drops in VE from baseline.

Results

Breathing variability was significantly higher in DIO mice during NREM sleep, but not during REM sleep. Obesity-induced breathing variability could not be entirely attributed to apneas or arousals. Sleep fragmentation was 45% greater in DIO mice. Respiratory arousals comprised 15% of the arousals in both strains. Breathing variability was inversely associated with sleep fragmentation regardless of obesity.

Conclusion

Obesity increased respiratory variability during NREM sleep, which was not fully attributed to apneas and macro-sleep architecture. Obesity caused sleep fragmentation that was not entirely explained by SDB severity. Our quantitative analysis of VE identified differences in breathing variability in obesity that were not captured by traditional SDB metrics, which may be applicable for human SDB.

Support (If Any)

NHLBI NIH R01 HL135483, 2R01 HL133100-05, R01 HL128970, and R01 HL13892; NINDS NIH R01 NS112266; American Academy of Sleep Medicine Foundation 238-BS-20; American Thoracic Society Unrestricted Award; Johns Hopkins Blaustein Pain Research Grant; American Heart Association Postdoctoral Fellowship Award 828142.

D-dimer in Marfan syndrome: effect of obstructive sleep apnea induced blood pressure surges

Aortic dissection and rupture are the major causes of premature death in persons with Marfan syndrome (MFS), a rare genetic disorder featuring cardiovascular, skeletal, and ocular impairments. We and others have found that obstructive sleep apnea (OSA) confers significant vascular stress in this population and may accelerate aortic disease progression. We hypothesized that D-dimer, a diagnostic biomarker for several types of vascular injury that is also elevated in persons with MFS with aortic enlargement, may be sensitive to cardiovascular stresses caused by OSA. To test this concept, we recruited 16 persons with MFS without aortic dissection and randomized them to two nights of polysomnography, without (baseline) and with OSA treatment: continuous positive airway pressure (CPAP). In addition to scoring OSA by the apnea-hypopnea index (AHI), beat-by-beat systolic BP (SBP) and pulse-pressure (PP) fluctuations were quantified. Morning blood samples were also assayed for D-dimer levels. In this cohort (male:female, 10:6; age, 36 ± 13 yr; aortic diameter, 4 ± 1 cm), CPAP eliminated OSA (AHI: 20 ± 17 vs. 3 ± 2 events/h, P = 0.001) and decreased fluctuations in SBP (13 ± 4 vs. 9 ± 3 mmHg, P = 0.011) and PP (7 ± 2 vs. 5 ± 2 mmHg, P = 0.013). CPAP also reduced D-dimer levels from 1,108 ± 656 to 882 ± 532 ng/mL (P = 0.023). Linear regression revealed a positive association between the maximum PP during OSA and D-dimer in both the unadjusted (r = 0.523, P = 0.038) and a model adjusted for contemporaneous aortic root diameter (r = 0.733, P = 0.028). Our study revealed that overnight CPAP reduces D-dimer levels commensurate with the elimination of OSA and concomitant hemodynamic fluctuations. Morning D-dimer measurements together with OSA screening might serve as predictors of vascular injury in MFS.NEW & NOTEWORTHY What is New? Surges in blood pressure caused by obstructive sleep apnea during sleep increase vascular stress and D-dimer levels in Marfan syndrome. Elevations in D-dimer can be lowered with CPAP. What is Noteworthy? D-dimer levels might serve as a marker for determining the significance of obstructive sleep apnea in persons with Marfan syndrome. D-dimer or obstructive sleep apnea screening is a potential method to identify persons with Marfan syndrome at risk for adverse cardiovascular events.

003 Treatment of Sleep Disordered Breathing with Leptin Loaded Exosomes

Introduction

Obstructive sleep apnea (OSA) is characterized by recurrent periods of upper airway obstruction. The prevalence of OSA exceeds 50% in obese individuals and in 10–20% of obese patients OSA coexists with obesity hypoventilation syndrome (OHS) defined as daytime hypercapnia and hypoventilation during sleep attributed to the depressed control of breathing. There is no effective pharmacotherapy for OSA and OHS. Leptin is a potent respiratory stimulant and a potential therapeutic candidate. However, diet-induced obesity (DIO) results in reduced permeability of the blood-brain barrier (BBB) for leptin. Previous studies have shown that the BBB can be penetrated by exosomes, natural nanoparticles that can be used as drug delivery vehicles. In this study, we aimed to determine if exosomes overcome the BBB and treat OSA and OHS in DIO mice.

Methods

o examine the ability of exosomes to cross the BBB, male, lean (n=5) and DIO (n=5) C57BL/6J mice were injected with fluorescent exosomes or saline into the lateral tail vein. After 4h fluorescent exosomes biodistribution was evaluated by an in vitro imaging system (IVIS). Saline injected mice images were used for background adjustment. A separate subgroup of male, DIO (n=10) and lean (n=10) mice were headmounted with EEG and nuchal EMG leads. Sleep studies were performed in a plethysmography chamber and mice received saline, empty exosomes, free leptin, or leptin-loaded exosomes in a crossover manner.

Results

Exosomes were successfully delivered to the brain and the transport across the BBB was more efficient in DIO mice with 2-times greater relative fluorescence units measured in DIO when compared to lean mice (p<0.005). In DIO mice, exosomal leptin induced dramatic 1.7-2.2-fold increases in minute ventilation and 1.5-2.0-fold increases in maximal inspiratory flow during both flow-limited (upper airway/sleep apnea) and non-flow limited breathing (control of breathing) (p<0.05). In contrast, free leptin had no effect. Lean mice did not present significant sleep disordered breathing and no differences were observed between groups.

Conclusion

We demonstrated that exosomes overcome the BBB and that leptin-loaded exosomes treat OSA and OHS in DIO mice.

Support (if any)

R01HL 128970, R01HL 138932, R61 HL156240, U18 DA052301, FAPESP 2018/08758-3

Inflammation in sleep apnea: an update

Obstructive sleep apnea (OSA) is a common disorder associated with cardiovascular disease (CVD). One theory to explain this relationship proposes that OSA can induce systemic inflammation, thereby inducing CVD. This theory is based on the premise that obesity is a pro-inflammatory state, and that physiological derangements during sleep in subjects with OSA further aggravate inflammation. In support of this theory, some clinical studies have shown elevated inflammatory biomarkers in OSA subjects, or improvement in these markers following treatment of OSA. However, the data are inconsistent and often confounded by the effects of comorbid obesity. Animal models of OSA have been developed, which involve exposure of rodents or cells to intermittent hypoxia, a hallmark feature of OSA. Several of these experiments demonstrate that intermittent hypoxia can stimulate inflammatory pathways and lead to cardiovascular or metabolic pathology. In this review, we review relationships between OSA and inflammation, with particular attention to studies published within the last year.

Effects of leptin and obesity on the upper airway function

Obesity is associated with alterations in upper airway collapsibility during sleep. Obese, leptin-deficient mice demonstrate blunted ventilatory control, leading us to hypothesize that (1) obesity and leptin deficiency would predispose to worsening neuromechanical upper airway function and that (2) leptin replacement would acutely reverse neuromuscular defects in the absence of weight loss. In age-matched, anesthetized, spontaneously breathing C57BL/6J (BL6) and ob(-)/ob(-) mice, we characterized upper airway pressure-flow dynamics during ramp decreases in nasal pressure (P(N)) to determine the passive expiratory critical pressure (P(CRIT)) and active responses to reductions in P(N), including the percentage of ramps showing inspiratory flow limitation (IFL; frequency), the P(N) threshold at which IFL developed, maximum inspiratory airflow (Vi(max)), and genioglossus electromyographic (EMG(GG)) activity. Elevations in body weight were associated with progressive elevations in P(CRIT) (0.1 ± 0.02 cmH(2)O/g), independent of mouse strain. P(CRIT) was also elevated in ob(-)/ob(-) compared with BL6 mice (1.6 ± 0.1 cmH(2)O), independent of weight. Both obesity and leptin deficiency were associated with significantly higher IFL frequency and P(N) threshold and lower VI(max). Very obese ob(-)/ob(-) mice treated with leptin compared with nontreated mice showed a decrease in IFL frequency (from 63.5 ± 2.9 to 30.0 ± 8.6%) and P(N) threshold (from -0.8 ± 1.1 to -5.6 ± 0.8 cmH(2)O) and increase in VI(max) (from 354.1 ± 25.3 to 659.0 ± 71.8 μl/s). Nevertheless, passive P(CRIT) in leptin-treated mice did not differ significantly from that seen in nontreated ob(-)/ob(-) mice. The findings suggest that weight and leptin deficiency produced defects in upper airway neuromechanical control and that leptin reversed defects in active neuromuscular responses acutely without reducing mechanical loads.

Effect of age and weight on upper airway function in a mouse model

Defects in pharyngeal mechanical and neuromuscular control are required for the development of obstructive sleep apnea. Obesity and age are known sleep apnea risk factors, leading us to hypothesize that specific defects in upper airway neuromechanical control are associated with weight and age in a mouse model. In anesthetized, spontaneously breathing young and old wild-type C57BL/6J mice, genioglossus electromyographic activity (EMG(GG)) was monitored and upper airway pressure-flow dynamics were characterized during ramp decreases in nasal pressure (Pn, cmH₂O). Specific body weights were targeted by controlling caloric intake. The passive critical pressure (Pcrit) was derived from pressure-flow relationships during expiration. The Pn threshold at which inspiratory flow limitation (IFL) developed and tonic and phasic EMG(GG) activity during IFL were quantified to assess the phasic modulation of pharyngeal patency. The passive Pcrit increased progressively with increasing body weight and increased more in the old than young mice. Tonic EMG(GG) decreased and phasic EMG(GG) increased significantly with obesity. During ramp decreases in Pn, IFL developed at a higher (less negative) Pn threshold in the obese than lean mice, although the frequency of IFL decreased with age and weight. The findings suggest that weight imposes mechanical loads on the upper airway that are greater in the old than young mice. The susceptibility to upper airway obstruction increases with age and weight as tonic neuromuscular activity falls. IFL can elicit phasic responses in normal mice that mitigate or eliminate the obstruction altogether.

Cardiovascular aspects in obstructive sleep apnea syndrome--molecular issues, hypoxia and cytokine profiles

Obstructive sleep apnea syndrome (OSAS), which is a highly prevalent breathing disorder in sleep, is an independent risk factor for cardiovascular morbidity and mortality. Results from clinical studies as well as animal models and cell culture studies utilizing intermittent hypoxia implicate oxidative stress and inflammation in the pathogenesis of OSAS. However, the underlying mechanisms are not entirely understood. Both oxidative stress and inflammation are major components in the initiation and development of endothelial dysfunction and consequently atherosclerosis. Yet, these fundamental mechanisms are associated with obesity and with components of the metabolic syndrome that also cluster with OSAS. Accumulated evidence indicates that inflammatory cytokines such as TNF-α that are under the control of nuclear factor ĸB actively participate in endothelial damage. The current review highlights some of the recent findings on oxidative stress and inflammation in OSAS with specific emphasis on the role of inflammatory pathway activation and expression of cytokines and their possible role in OSAS-related cardiovascular morbidity. In light of the new findings in the field of cytokines, their potential involvement in endothelial dysfunction and cardiovascular morbidity in OSAS is discussed.

Behavioral and respiratory characteristics during sleep in neonatal DBA/2J and A/J mice

The ventilatory response to hypoxia depends on the carotid body function and sleep-wake states. Therefore, the response must be measured in a consistent sleep-wake state. In mice, EMG with behavioral indices (coordinated movements, CMs; myoclonic twitches, MTs) has been used to assess sleep-wake states. However, in neonatal mice EMG instrumentation could induce stress, altering their behavior and ventilation. Accordingly, we examined: (1) if EMG can be eliminated for assessing sleep-wake states; and (2) behavioral characteristics and carotid body-mediated respiratory control during sleep with EMG (EMG+) or without EMG (EMG-). Seven-day-old DBA/2J and A/J mice were divided into EMG+ and EMG- groups. In both strains, CMs occurred when EMG was high; MTs were present during silent/low EMG activity. The durations of high EMG activity and of CMs were statistically indifferent. Thus, CMs can be used to indicate wake state without EMG. The stress caused by EMG instrumentation may be distinctively manifested based on genetic background. Prolonged agitation was observed in some EMG+ DBA/2J (5 of 13), but not in A/J mice. The sleep time and MT counts were indifferent between the groups in DBA/2J mice. The EMG+ A/J group showed longer sleep time and less MT counts than the EMG- A/J group. Mean respiratory variables (baseline, hyperoxic/hypoxic responses) were not severely influenced by EMG+ in either strain. Individual values were more variable in EMG+ mice. Carotid body-mediated respiratory responses (decreased ventilation upon hyperoxia and increased ventilation upon mild hypoxia) during sleep were clearly observed in these neonatal mice with or without EMG instrumentation.

Neuromechanical control of the isolated upper airway of mice

We characterized the passive structural and active neuromuscular control of pharyngeal collapsibility in mice and hypothesized that pharyngeal collapsibility, which is elevated by anatomic loads, is reduced by active neuromuscular responses to airflow obstruction. To address this hypothesis, we examined the dynamic control of upper airway function in the isolated upper airway of anesthetized C57BL/6J mice. Pressures were lowered downstream and upstream to the upper airway to induce inspiratory airflow limitation and critical closure of the upper airway, respectively. After hyperventilating the mice to central apnea, we demonstrated a critical closing pressure (Pcrit) of -6.2 +/- 1.1 cmH(2)O under passive conditions that was unaltered by the state of lung inflation. After a period of central apnea, lower airway occlusion led to progressive increases in phasic genioglossal electromyographic activity (EMG(GG)), and in maximal inspiratory airflow (Vi(max)) through the isolated upper airway, particularly as the nasal pressure was lowered toward the passive Pcrit level. Moreover, the active Pcrit fell during inspiration by 8.2 +/- 1.4 cmH(2)O relative to the passive condition (P < 0.0005). We conclude that upper airway collapsibility (passive Pcrit) in the C57BL/6J mouse is similar to that in the anesthetized canine, feline, and sleeping human upper airway, and that collapsibility falls markedly under active conditions. Active EMG(GG) and Vi(max) responses dissociated at higher upstream pressure levels, suggesting a decrease in the mechanical efficiency of upper airway dilators. Our findings in mice imply that anatomic and neuromuscular factors interact dynamically to modulate upper airway function, and provide a novel approach to modeling the impact of genetic and environmental factors in inbred murine strains.

Obesity and obstructive sleep apnea: pathogenic mechanisms and therapeutic approaches

Obstructive sleep apnea is a common disorder whose prevalence is linked to an epidemic of obesity in Western society. Sleep apnea is due to recurrent episodes of upper airway obstruction during sleep that are caused by elevations in upper airway collapsibility during sleep. Collapsibility can be increased by underlying anatomic alterations and/or disturbances in upper airway neuromuscular control, both of which play key roles in the pathogenesis of obstructive sleep apnea. Obesity and particularly central adiposity are potent risk factors for sleep apnea. They can increase pharyngeal collapsibility through mechanical effects on pharyngeal soft tissues and lung volume, and through central nervous system-acting signaling proteins (adipokines) that may affect airway neuromuscular control. Specific molecular signaling pathways encode differences in the distribution and metabolic activity of adipose tissue. These differences can produce alterations in the mechanical and neural control of upper airway collapsibility, which determine sleep apnea susceptibility. Although weight loss reduces upper airway collapsibility during sleep, it is not known whether its effects are mediated primarily by improvement in upper airway mechanical properties or neuromuscular control. A variety of behavioral, pharmacologic, and surgical approaches to weight loss may be of benefit to patients with sleep apnea, through distinct effects on the mass and activity of regional adipose stores. Examining responses to specific weight loss strategies will provide critical insight into mechanisms linking obesity and sleep apnea, and will help to elucidate the humoral and molecular predictors of weight loss responses.

Basis for substrate specificity of the Toxoplasma gondii nucleoside triphosphate hydrolase

The Toxoplasma gondii nucleoside triphosphate hydrolase is the most active E-type ATPase yet identified, and was the first member of this new gene family to be cloned (Bermudes D, Peck KR, Afifi-Afifi M, Beckers CJM, Joiner KA. J Biol Chem 1994;269:29252-29260. Previous work also identified two isoforms of the enzyme in the virulent RH strain, and demonstrated that internal fragments of the genes encoding these isoforms were found differentially in virulent versus avirulent organisms (Asai T, Miura S, Sibley D, Okabayashi H, Tsutomu T, J Biol Chem 1995;270:11391-11397). We now show that the NTPase 1 isoform is expressed in avirulent strains, whereas virulent strains express both the NTPase 1 and NTPase 3 isoforms. The avirulent PLK strain lacks the gene for NTPase 3, explaining the absence of expression. Despite the fact that NTPase 1 and NTPase 3 are 97% identical at the amino acid level, recombinant NTPase 1 is a true apyrase, whereas recombinant NTPase 3 cleaves predominantly nucleotide triphosphates. Furthermore, native and recombinant NTPase 3 but neither native nor recombinant NTPase 1 bind to ATP-agarose, further distinguishing the two isoforms. Using chimeras between the NTP1 and NTP3 genes, we show that a block of twelve residues at the C-terminus dictates substrate specificity. These residues lie outside the regions conserved among other E-ATPases, and therefore provide new insight into substrate recognition by this class of enzymes.