Ventilatory responses to hypercapnia during wakefulness and sleep in obese adolescents with and without obstructive sleep apnea syndrome

The role of sleep state and time of day in modulating breathing in epilepsy: implications for sudden unexpected death in epilepsy

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death among patients with refractory epilepsy. While the exact etiology of SUDEP is unknown, mounting evidence implicates respiratory dysfunction as a precipitating factor in cases of seizure-induced death. Dysregulation of breathing can occur in epilepsy patients during and after seizures as well as interictally, with many epilepsy patients exhibiting sleep-disordered breathing (SDB), such as obstructive sleep apnea (OSA). The majority of SUDEP cases occur during the night, with the victim found prone in or near a bed. As breathing is modulated in both a time-of-day and sleep state-dependent manner, it is relevant to examine the added burden of nocturnal seizures on respiratory function. This review explores the current state of understanding of the relationship between respiratory function, sleep state and time of day, and epilepsy. We highlight sleep as a particularly vulnerable period for individuals with epilepsy and press that this topic warrants further investigation in order to develop therapeutic interventions to mitigate the risk of SUDEP.

Awake Hypercapnic Ventilatory Response in Obstructive Sleep Apnea Syndrome

Background and Objective Decreased ventilatory response to carbon dioxide or hypercapnic ventilatory response (HCVR) is a feature of pediatric obstructive sleep apnea (OSA) and is also known to diminish during sleep in obese adolescents (age, 12–16 years) with OSA. It reduces minute ventilation, air flow, and tidal volume during inspiration, as well as upper airway obstruction. The purpose of this study was to investigate awake HCVR in adult patients with OSA and to elucidate its association with sleep apnea.Methods HCVR was measured before performing polysomnography (PSG). PSG is performed as the evaluation method during sleep, and the severity of apnea is evaluated by apnea hypopnea index. Patient background, PSG data and HCVR were examined.Results Awake HCVR was greater in patients with severe OSA than in patients with mild and moderate OSA, and in severe OSA patients, the HCVR during awaking was higher in patients with larger changes in saturation of percutaneous oxygen during sleep. Awake HCVR did not differ by age, but it was greater in morbidly obese patients with OSA than in thin patients with OSA. The most frequent apnea pattern of OSA was obstructive, regardless of severity; although with an increasing severity of OSA, the central pattern decreased and the mixed pattern increased in frequency. The appearance of the mixed pattern increased in the augmented HCVR group.Conclusions This study suggested that awake HCVR could be used as an index of progression and a factor to determine the effects of treatment in patients with OSA.

Cerebral Erythropoietin Prevents Sex-Dependent Disruption of Respiratory Control Induced by Early Life Stress

Injuries that occur early in life are often at the root of adult illness. Neonatal maternal separation (NMS) is a form of early life stress that has persistent and sex-specific effects on the development of neural networks, including those that regulate breathing. The release of stress hormones during a critical period of development contributes to the deleterious consequences of NMS, but the role of increased corticosterone (CORT) in NMS-induced respiratory disturbance is unknown. Because erythropoietin (EPO) is a potent neuroprotectant that prevents conditions associated with hyperactivation of the stress neuroaxis in a sex-specific manner, we hypothesized that EPO reduces the sex-specific alteration of respiratory regulation induced by NMS in adult mice. Animals were either raised under standard conditions (controls) or exposed to NMS 3 h/day from postnatal days 3–12. We tested the efficacy of EPO in preventing the effects of NMS by comparing wild-type mice with transgenic mice that overexpress EPO only in the brain (Tg21). In 7-days-old pups, NMS augmented CORT levels ~2.5-fold by comparison with controls but only in males; this response was reduced in Tg21 mice. Respiratory function was assessed using whole-body plethysmography. Apneas were detected during sleep; the responsiveness to stimuli was measured by exposing mice to hypoxia (10% O₂; 15 min) and hypercapnia (5% CO₂; 10 min). In wild-type, NMS increased the number of apneas and the hypercapnic ventilatory response (HcVR) only in males; with no effect on Tg21. In wild-type males, the incidence of apneas was positively correlated with HcVR and inversely related to the tachypneic response to hypoxia. We conclude that neural EPO reduces early life stress-induced respiratory disturbances observed in males.

Hypoxemia and pulmonary hypertension in patients with concomitant restrictive ventilatory defect and sleep apnea: the overlap syndrome

BACKGROUND

To investigate the severity of hypoxemia and prevalence of pulmonary hypertension (PHTN) in patients with the overlap syndrome (OS) of restrictive ventilatory defect (RVD) and sleep apnea (SA).

METHODS

Patients referred for both sleep test and spirometry for suspected SA and ventilatory disorders were recruited prospectively from January 2019 to January 2020. SA was determined by an apnea-hypopnea index ≥ 5/h; average oxygen saturation during sleep (meanSaO₂) and percentage of total sleep time with saturation < 90% (T90) were calculated. RVD was diagnosed in the presence of forced expiratory volume in the first second/forced vital capacity (FVC) > 0.7 and FVC < 80% predicted value. PHTN was defined by tricuspid regurgitation peak velocity ≥ 3.4 m/s, documented by noninvasive transthoracic echocardiography.

RESULTS

Patients with OS had significantly lower meanSaO₂ but higher T90 than subjects with isolated SA and isolated RVD. Patients with OS vs. those with isolated SA had higher odds of PHTN in multivariable analysis with age, sex, and body mass index adjusted for (OR 2.96, 95%CI 1.05-8.91, p = 0.040). Patients with meanSaO₂ < 92% vs. meanSaO₂ ≥ 92% had significantly higher odds of being diagnosed with PHTN (OR 5.40, 95%CI 2.01-15.7, p < 0.001). Similarly, T90 (≥ 4.5% versus < 4.5%) was also independently associated with the prevalence of PHTN (OR 7.21, 95%CI 2.54-23.67, p < 0.001).

CONCLUSION

Patients with OS of RVD and SA had severe hypoxemia, which is associated with the prevalence of PHTN. Further investigation is needed to discern whether therapeutic strategies toward OS might mitigate PHTN in this cohort.

TRIAL REGISTRATION

Clinical Trial Registration No. ChiCTR1900027294 on 1 October 2019.

Pulmonary hypertension and chronic hypoventilation in ROHHAD syndrome treated with average-volume assured pressure support

INTRODUCTION

Rapid-onset obesity with hypothalamic dysfunction, hypoventilation, and autonomic dysregulation (ROHHAD) syndrome is an exceptionally rare clinical entity with significant morbidity and high mortality with challenging-to-treat hypoventilation.

CASE PRESENTATION

An 11-year-old morbidly obese Chinese female presented with a putative diagnosis of ROHHAD associated with a left psoas ganglioneuroma. Initial polysomnography showed severe obstructive sleep apnea and hypoventilation. She was not adherent to prescribed non-invasive positive pressure ventilation (NIPPV). Echocardiography demonstrated evidence of pulmonary hypertension, likely secondary to chronic hypoventilation. With behavioral modification and trial of average volume-assured pressure support (AVAPS), adherence improved with eventual improvement of her pulmonary hypertension.

CONCLUSION

AVAPS may improve ventilation and NIPPV adherence in central hypoventilation disorders such as ROHHAD, reducing risk of morbidity and mortality.

Inherent vs. Induced Loop Gain Abnormalities in Obstructive Sleep Apnea

Unstable ventilatory chemoreflex control, quantified as loop gain, is recognized as one of four key pathophysiological traits that contribute to cause obstructive sleep apnea (OSA). Novel treatments aimed at reducing loop gain are being investigated, with the intention that future OSA treatment may be tailored to the individual's specific cause of apnea. However, few studies have evaluated loop gain in OSA and non-OSA controls and those that have provide little evidence to support an inherent abnormality in either overall chemical loop gain in OSA patients vs. non-OSA controls, or its components (controller and plant gain). However, intermittent hypoxia may induce high controller gain through neuroplastic changes to chemoreflex control, and may also decrease plant gain via oxidative stress induced inflammation and reduced lung function. The inherent difficulties and limitations with loop gain measurements are discussed and areas where further research are required are highlighted, as only by understanding the mechanisms underlying OSA are new therapeutic approaches likely to emerge in OSA.

Obstructive sleep apnea in refractory epilepsy: A pilot study investigating frequency, clinical features, and association with risk of sudden unexpected death in epilepsy

OBJECTIVE

We aimed to determine the frequency of probable obstructive sleep apnea (pOSA) in refractory epilepsy monitoring unit inpatients and clinical features associated with pOSA, including risk for sudden unexpected death in epilepsy (SUDEP).

METHODS

We prospectively recruited 49 consecutive adult patients admitted to the Mayo Clinic Epilepsy Monitoring Unit with focal, generalized, or unclassified epilepsy syndromes. pOSA was identified using oximetric oxyhemoglobin desaturation index (ODI) and the Sleep Apnea-Sleep Disorders Questionnaire (SA-SDQ) and STOP-BAG screening tools. Revised SUDEP Risk Inventory (rSUDEP-7) scores were calculated, and epilepsy patients with and without pOSA were compared with Wilcoxon signed-rank tests. Correlation and regression analyses were utilized to determine relationships between pOSA and rSUDEP-7 scores.

RESULTS

Thirty-five percent of patients had pOSA, with a mean ODI of 11.3 ± 5.1/h (range = 5.1-22.8). Patients with pOSA were older and heavier, and more frequently had a focal epilepsy syndrome and longer epilepsy duration, with higher SA-SDQ and STOP-BAG scores (all P < 0.05). Median rSUDEP-7 score was 3 ± 1.4 (range = 0-6). Higher rSUDEP-7 scores were positively correlated with higher ODI (P = 0.036). rSUDEP-7 score ≥ 5 was associated with pOSA by ODI, SA-SDQ, and STOP-BAG questionnaire criteria (P < 0.05).

SIGNIFICANCE

Our pilot study identified a high frequency of pOSA in refractory epilepsy monitoring patients, finding that pOSA patients were older and heavier, with higher screening symptoms for sleep apnea and more frequent focal seizures with a longer epilepsy duration. We also found a possible association between OSA and SUDEP risk. Identification and treatment of OSA in patients with epilepsy could conceivably provide a novel approach toward preventing the risk of SUDEP. Future studies with polysomnography are needed to confirm predictive features for OSA in epilepsy populations, and to determine whether OSA is associated with SUDEP risk.

Obstructive sleep apnea as an independent predictor of postoperative delirium and pain: protocol for an observational study of a surgical cohort

Introduction: Postoperative delirium and pain are common complications in adults, and are difficult both to prevent and treat. Obstructive sleep apnea (OSA) is prevalent in surgical patients, and has been suggested to be a risk factor for postoperative delirium and pain. OSA also might impact pain perception, and alter pain medication requirements. This protocol describes an observational study, with the primary aim of testing whether OSA is an independent predictor of postoperative complications, focusing on (i) postoperative incident delirium and (ii) acute postoperative pain severity. We secondarily hypothesize that compliance with prescribed treatment for OSA (typically continuous positive airway pressure or CPAP) might decrease the risk of delirium and the severity of pain. Methods and analysis: We will include data from patients who have been enrolled into three prospective studies: ENGAGES, PODCAST, and SATISFY-SOS. All participants underwent general anesthesia for a non-neurosurgical inpatient operation, and had a postoperative hospital stay of at least one day at Barnes Jewish Hospital in St. Louis, Missouri, from February 2013 to May 2018.  Patients included in this study have been assessed for postoperative delirium and pain severity as part of the parent studies. In the current study, determination of delirium diagnosis will be based on the Confusion Assessment Method, and the Visual Analogue Pain Scale will be used for pain severity. Data on OSA diagnosis, OSA risk and compliance with treatment will be obtained from the preoperative assessment record. Other variables that are candidate risk factors for delirium and pain will also be extracted from this record. We will use logistic regression to test whether OSA independently predicts postoperative delirium and linear regression to assess OSAs relationship to acute pain severity. We will conduct secondary analyses with subgroups to explore whether these relationships are modified by compliance with OSA treatment.

Upper Airway Vibration Perception in School-Aged Children with Obstructive Sleep Apnea

STUDY OBJECTIVES

Children with the obstructive sleep apnea (OSA) have impaired upper airway two-point discrimination compared to controls. In addition, blunted vibration threshold detection (VT) in the palate has been recognized in adults with OSA, but has not been studied in children. Both findings are indicative of a defect in the afferent limb of the upper airway dilator reflex that could prevent upper airway dilation secondary to airway loading, resulting in airway collapse. We hypothesized that children with OSA have impaired palate VT compared to controls, and that this improves after OSA treatment.

METHODS

Case-control study. Children with OSA and healthy non-snoring controls underwent polysomnography and palate VT measurements. Children with OSA were retested after adenotonsillectomy.

RESULTS

29 children with OSA (median [interquartile range] age = 9.5 [7.5-12.6] years, obstructive apnea-hypopnea index [OAHI] = 11.3 [5.7-19.5] events/h, BMI z = 1.8 [1.3-2.1]) and 32 controls (age = 11.2 [9.3-13.5] years, P = 0.1; OAHI = 0.5 [0.1-0.7] events/h, P < 0.001; BMI z = 1 [0.3-1.7], P = 0.004) were tested. OSA palate VT (1.0 [0.8-1.5] vibration units) was similar to that of controls (1 [0.8-1.3], P = 0.37). 20 children with OSA were retested 4.4 (3.2-7.1) months after treatment. OAHI decreased from 13.1 (5.8-19) to 0.6 (0.2-2.5) events per hour (P < 0.001) postoperatively, but palate VT did not change (before = 1 [0.7-1.5], after = 1.2 [0.8-1.4], P = 0.37).

CONCLUSIONS

Children with OSA and controls have similar palate VT. Unlike in adults, palate VT does not seem to be affected by childhood OSA.

Cerebral Blood Flow Response to Hypercapnia in Children with Obstructive Sleep Apnea Syndrome

STUDY OBJECTIVES

Children with obstructive sleep apnea syndrome (OSAS) often experience periods of hypercapnia during sleep, a potent stimulator of cerebral blood flow (CBF). Considering this hypercapnia exposure during sleep, it is possible that children with OSAS have abnormal CBF responses to hypercapnia even during wakefulness. Therefore, we hypothesized that children with OSAS have blunted CBF response to hypercapnia during wakefulness, compared to snorers and controls.

METHODS

CBF changes during hypercapnic ventilatory response (HCVR) were tested in children with OSAS, snorers, and healthy controls using diffuse correlation spectroscopy (DCS). Peak CBF changes with respect to pre-hypercapnic baseline were measured for each group. The study was conducted at an academic pediatric sleep center.

RESULTS

Twelve children with OSAS (aged 10.1 ± 2.5 [mean ± standard deviation] y, obstructive apnea hypopnea index [AHI] = 9.4 [5.1-15.4] [median, interquartile range] events/hour), eight snorers (11 ± 3 y, 0.5 [0-1.3] events/hour), and 10 controls (11.4 ± 2.6 y, 0.3 [0.2-0.4] events/hour) were studied. The fractional CBF change during hypercapnia, normalized to the change in end-tidal carbon dioxide, was significantly higher in controls (9 ± 1.8 %/mmHg) compared to OSAS (7.1 ± 1.5, P = 0.023) and snorers (6.7 ± 1.9, P = 0.025).

CONCLUSIONS

Children with OSAS and snorers have blunted CBF response to hypercapnia during wakefulness compared to controls. Noninvasive DCS blood flow measurements of hypercapnic reactivity offer insights into physiopathology of OSAS in children, which could lead to further understanding about the central nervous system complications of OSAS.

Understanding the anatomic basis for obstructive sleep apnea syndrome in adolescents

RATIONALE

Structural risk factors for obstructive sleep apnea syndrome (OSAS) in adolescents have not been well characterized. Because many adolescents with OSAS are obese, we hypothesized that the anatomic OSAS risk factors would be more similar to those in adults than those in children.

OBJECTIVES

To investigate the anatomic risk factors in adolescents with OSAS compared with obese and lean control subjects using magnetic resonance imaging (MRI).

METHODS

Three groups of adolescents (age range: 12-16 yr) underwent MRI: obese individuals with OSAS (n = 49), obese control subjects (n = 38), and lean control subjects (n = 50).

MEASUREMENTS AND MAIN RESULTS

We studied 137 subjects and found that (1) obese adolescents with OSAS had increased adenotonsillar tissue compared with obese and lean control subjects; (2) obese OSAS adolescents had a smaller nasopharyngeal airway than control subjects; (3) the size of other upper airway soft tissue structures (volume of the tongue, parapharyngeal fat pads, lateral walls, and soft palate) was similar between subjects with OSAS and obese control subjects; (4) although there were no major craniofacial abnormalities in most of the adolescents with OSAS, the ratio of soft tissue to craniofacial space surrounding the airway was increased; and (5) there were sex differences in the pattern of lymphoid proliferation.

CONCLUSIONS

Increased size of the pharyngeal lymphoid tissue, rather than enlargement of the upper airway soft tissue structures, is the primary anatomic risk factor for OSAS in obese adolescents. These results are important for clinical decision making and suggest that adenotonsillectomy should be considered as the initial treatment for OSAS in obese adolescents, a group that has poor continuous positive airway pressure adherence and difficulty in achieving weight loss.

Neurobehavioral functioning in adolescents with and without obesity and obstructive sleep apnea

STUDY OBJECTIVES

Children and adults with obstructive sleep apnea syndrome (OSAS) exhibit neurobehavioral abnormalities, but few studies have evaluated the transitional stage of adolescence. Obesity is also associated with neurobehavioral abnormalities, and many patients with OSAS are obese. However, the confounding effect of obesity on neurobehavioral abnormalities in adolescents with OSAS has not been evaluated. We hypothesized that obese adolescents with OSAS would exhibit more neurobehavioral abnormalities than obese and lean adolescents without OSAS.

DESIGN

Cross-sectional, case control.

SETTING

Sleep Center and community.

PARTICIPANTS

Obese adolescents with OSAS compared to (1) nonsnoring, obese controls without OSAS, and (2) nonobese, nonsnoring controls.

INTERVENTIONS

Neurobehavioral evaluation.

MEASUREMENTS AND RESULTS

Obese adolescents with OSAS had significantly worse executive function and attention compared to both obese (P < 0.001) and lean (P < 0.001) controls, and more depression (P = 0.004) and externalizing symptoms than lean controls (P = 0.008). A higher percentage of participants in the OSAS group scored in the clinically abnormal range on executive functioning, attention, sleepiness, and behavioral functioning than lean controls. Mediation analyses indicated that level of sleep apnea significantly mediated the effect of body mass on executive functioning, attention, and behavior.

CONCLUSIONS

Obese adolescents with OSAS show impaired executive and behavioral function compared to obese and lean controls, and are more likely to score in the clinically abnormal range on measures of neurobehavioral functioning. These results are especially concerning given that the frontal lobe is still developing during this critical age period. We speculate that untreated OSAS during adolescence may lead to significant neurobehavioral deficits in adulthood.

Effects of chronic sleep fragmentation on wake-active neurons and the hypercapnic arousal response

STUDY OBJECTIVES

Delayed hypercapnic arousals may occur in obstructive sleep apnea. The impaired arousal response is expected to promote more pronounced oxyhemoglobin desaturations. We hypothesized that long-term sleep fragmentation (SF) results in injury to or dysfunction of wake-active neurons that manifests, in part, as a delayed hypercapnic arousal response.

DESIGN

Adult male mice were implanted for behavioral state recordings and randomly assigned to 4 weeks of either orbital platform SF (SF4wk, 30 events/h) or control conditions (Ct4wk) prior to behavioral, histological, and locus coeruleus (LC) whole cell electrophysiological evaluations.

MEASUREMENTS AND RESULTS

SF was successfully achieved across the 4 week study, as evidenced by a persistently increased arousal index, P < 0.01 and shortened sleep bouts, P < 0.05, while total sleep/wake times and plasma corticosterone levels were unaffected. A multiple sleep latency test performed at the onset of the dark period showed a reduced latency to sleep in SF4wk mice (P < 0.05). The hypercapnic arousal latency was increased, Ct4wk 64 ± 5 sec vs. SF4wk 154 ± 6 sec, P < 0.001, and remained elevated after a 2 week recovery (101 ± 4 sec, P < 0.001). C-fos activation in noradrenergic, orexinergic, histaminergic, and cholinergic wake-active neurons was reduced in response to hypercapnia (P < 0.05-0.001). Catecholaminergic and orexinergic projections into the cingulate cortex were also reduced in SF4wk (P < 0.01). In addition, SF4wk resulted in impaired LC neuron excitability (P < 0.01).

CONCLUSIONS

Four weeks of sleep fragmentation (SF4wk) impairs arousal responses to hypercapnia, reduces wake neuron projections and locus coeruleus neuronal excitability, supporting the concepts that some effects of sleep fragmentation may contribute to impaired arousal responses in sleep apnea, which may not reverse immediately with therapy.

Physiological effects of obstructive sleep apnea syndrome in childhood

Sleep disordered breathing in children refers to a group of respiratory disorders that occur or are exacerbated during sleep. Obstructive sleep apnea syndrome (OSAS) is one of the most significant disorders in this group. OSAS can present in all age groups from early infancy to adolescent years. The cardinal feature of OSAS is limitation of inspiratory flow and volume during sleep resulting in abnormal gas exchange and/or alteration of sleep patterns. When OSAS is a chronic condition it often results in adverse physiological effects that impact on health and development. The present review discusses genesis of OSAS in children and consequent end organ injury with special emphasis on behavior and cognition, cardiovascular function, autonomic regulation, inflammation, endothelial function and metabolic syndrome.