Reduced respiratory-related evoked activity in subjects with obstructive sleep apnea syndrome

Impaired pharyngeal reflex responses to negative pressure: A novel cause of sleep apnea in multiple sclerosis

Obstructive sleep apnea (OSA) is common in people with multiple sclerosis (MS). However, people with MS often do not have 'typical' anatomical risk factors (i.e. non-obese and female predominance). Accordingly, non-anatomical factors such as impaired upper airway muscle function may be particularly important for OSA pathogenesis in MS. Therefore, this study aimed to investigate genioglossus (largest upper-airway dilator muscle) reflex responses to brief pulses of upper airway negative pressure in people with OSA and MS. 11 people with MS and OSA and 10 OSA controls without MS matched for age, sex and OSA severity were fitted with a nasal mask, pneumotachograph, choanal and epiglottic pressure sensors and intramuscular electrodes into genioglossus. Approximately 60 brief (250ms) negative pressure pulses (~-12cmH₂O mask pressure) were delivered every 2-6 breaths at random during quiet nasal breathing during wakefulness to determine genioglossus EMG reflex responses (timing, amplitude and morphology). Where available, recent clinical MRI brain scans were evaluated for the number, size and location of brainstem lesions in the MS group. When present, genioglossus reflex excitation responses were similar between MS participants and controls (e.g. peak excitation amplitude 229±85 vs. 282±98 % baseline, p=0.17). However, ~30% of people with MS had either an abnormal (predominantly inhibition) or no protective excitation reflex. Participants with MS without a reflex had multiple brainstem lesions including in the hypoglossal motor nucleus which may impair sensory processing and/or efferent output. Impaired pharyngeal reflex function may be an important contributor to OSA pathogenesis for a proportion of people with MS.

Muscles of Breathing: Development, Function, and Patterns of Activation

This review is a comprehensive description of all muscles that assist lung inflation or deflation in any way. The developmental origin, anatomical orientation, mechanical action, innervation, and pattern of activation are described for each respiratory muscle fulfilling this broad definition. In addition, the circumstances in which each muscle is called upon to assist ventilation are discussed. The number of "respiratory" muscles is large, and the coordination of respiratory muscles with "nonrespiratory" muscles and in nonrespiratory activities is complex-commensurate with the diversity of activities that humans pursue, including sleep (8.27). The capacity for speech and adoption of the bipedal posture in human evolution has resulted in patterns of respiratory muscle activation that differ significantly from most other animals. A disproportionate number of respiratory muscles affect the nose, mouth, pharynx, and larynx, reflecting the vital importance of coordinated muscle activity to control upper airway patency during both wakefulness and sleep. The upright posture has freed the hands from locomotor functions, but the evolutionary history and ontogeny of forelimb muscles pervades the patterns of activation and the forces generated by these muscles during breathing. The distinction between respiratory and nonrespiratory muscles is artificial, as many "nonrespiratory" muscles can augment breathing under conditions of high ventilator demand. Understanding the ontogeny, innervation, activation patterns, and functions of respiratory muscles is clinically useful, particularly in sleep medicine. Detailed explorations of how the nervous system controls the multiple muscles required for successful completion of respiratory behaviors will continue to be a fruitful area of investigation. © 2019 American Physiological Society. Compr Physiol 9:1025-1080, 2019.

Effects of morphine on respiratory load detection, load magnitude perception, and tactile sensation in obstructive sleep apnea

Pharyngeal and respiratory sensation is impaired in obstructive sleep apnea (OSA). Opioids may further diminish respiratory sensation. Thus protective pharyngeal neuromuscular and arousal responses to airway occlusion that rely on respiratory sensation could be impaired with opioids to worsen OSA severity. However, little is known about the effects of opioids on upper airway and respiratory sensation in people with OSA. This study was designed to determine the effects of 40 mg of MS-Contin on tactile sensation, respiratory load detection, and respiratory magnitude perception in people with OSA during wakefulness. A double-blind, randomized, crossover design (1 wk washout) was used. Twenty-one men with untreated OSA (apnea/hypopnea index = 26 ± 17 events/h) recruited from a larger clinical study completed the protocol. Tactile sensation using von Frey filaments on the back of the hand, internal mucosa of the cheek, uvula, and posterior pharyngeal wall were not different between placebo and morphine [e.g., median (interquartile range) posterior wall = 0.16 (0.16, 0.4) vs. 0.4 (0.14, 1.8) g, P = 0.261]. Similarly, compared with placebo, morphine did not alter respiratory load detection thresholds for nadir mask pressure detected = −2.05 (−3.37, −1.55) vs. −2.19 (−3.36, −1.41) cmH2O, P = 0.767], or respiratory load magnitude perception [mean ± SD Borg scores during a 5 resistive load (range: 5–126 cmH2O·l−1·s−1) protocol = 4.5 ± 1.6 vs. 4.2 ± 1.2, P = 0.347] but did reduce minute ventilation during quiet breathing (11.4 ± 3.3 vs. 10.7 ± 2.6 l/min, P < 0.01). These findings indicate that 40 mg of MS-Contin does not systematically impair tactile or respiratory sensation in men with mild to moderate, untreated OSA. This suggests that altered respiratory sensation to acute mechanical stimuli is not likely to be a mechanism that contributes to worsening of OSA with a moderate dose of morphine.

NEW & NOTEWORTHY Forty milligrams of MS-Contin does not alter upper airway tactile sensation, respiratory load detection thresholds, or respiratory load magnitude perception in people with obstructive sleep apnea but does decrease breathing compared with placebo during wakefulness. Despite increasing concerns of harm with opioids, the current findings suggest that impaired respiratory sensation to acute mechanical stimuli with this dose of MS-Contin is unlikely to be a direct mechanism contributing to worsening sleep apnea severity in people with mild-to-moderate disease.

Neuromuscular function of the soft palate and uvula in snoring and obstructive sleep apnea: A systematic review

OBJECTIVE

A collapsible upper airway is a common cause of obstructive sleep apnea. The exact pathophysiology leading to a more collapsible airway is not well understood. A progressive neuropathy of the soft palate and pharyngeal dilators may be associated with the progression of snoring to OSA. The purpose of this study is to systematically review the international literature investigating the neurophysiologic changes in the soft palate and uvula that contribute to progression from snoring to OSA.

METHODS

PubMed/MEDLINE and 4 other databases were systematically searched through July 4, 2017. Eligibility: (1) Patients: controls, snoring or OSA patients (2) Intervention: neuromuscular evaluation of the palate and/or uvula (3) Comparison: differences between controls, snoring and OSA patients (4) Outcomes: neuromuscular outcomes (5) Study design: Peer reviewed publications of any design.

RESULTS

845 studies were screened, 76 were downloaded in full text form and thirty-one studies met criteria. Histological studies of the soft palate demonstrated diffuse inflammatory changes, muscular changes consistent with neuropathy, and neural aberrancies. Sensory testing studies provided heterogeneous outcomes though the majority favored neuronal dysfunction. Studies have consistently demonstrated that increasing severity of snoring and sleep apnea is associated with worsening sensory nerve function of the palate in association with atrophic histological changes to the nerves and muscle fibers of the soft palate and uvula.

CONCLUSIONS

Recent evidence highlighted in this systematic review implicates the role of neurogenic pathology underlying the loss of soft palate and/or uvular tone in the progression of snoring to sleep apnea.

Effect of chronic intermittent hypoxia on the reflex recruitment of the genioglossus during airway obstruction in the anesthetized rat

We sought to test the hypothesis that chronic intermittent hypoxia (CIH)-a feature of sleep-disordered breathing in humans-impairs reflex recruitment of the genioglossus (GG, pharyngeal dilator) during obstructive airway events. Adult male Wistar rats were exposed to 20 cycles of normoxia and hypoxia (5% O2 at nadir) per hour, 8h a day for 7 days (CIH, N=7). The sham group (N=7) were exposed to normoxia in parallel. Following gas treatments, rats were anesthetized with an i.p. injection of urethane (1.5g/kg; 20%, w/v). Fine concentric needle electrodes were inserted into the GG and the costal diaphragm. Discriminated GG motor unit potentials and whole electromyograph (EMG), together with arterial blood pressure and arterial O2 saturation, were recorded during quiet basal breathing and during nasal airway occlusion. Airway occlusion significantly increased GG EMG activity in all animals; but there was no difference in the reflex response to airway occlusion between sham and CIH-treated animals (+105±22% vs. +105±17%, mean±SEM for area under the curve of integrated GG EMG, % increase from baseline, p=0.99). Occluded breaths were characterized by a significant increase in the firing frequency of phasically active units and the recruitment of large motor units that were quiescent under basal conditions. Though there are reports of impaired control of the upper airway following CIH in the rat, we conclude that reflexly evoked motor discharge to the GG is not affected by 7 days of CIH, a paradigm that we have shown increases apnea index in sleeping rats.

Functional role of neural injury in obstructive sleep apnea

The causes of obstructive sleep apnea (OSA) are multifactorial. Neural injury affecting the upper airway muscles due to repetitive exposure to intermittent hypoxia and/or mechanical strain resulting from snoring and recurrent upper airway closure have been proposed to contribute to OSA disease progression. Multiple studies have demonstrated altered sensory and motor function in patients with OSA using a variety of neurophysiological and histological approaches. However, the extent to which the alterations contribute to impairments in upper airway muscle function, and thus OSA disease progression, remains uncertain. This brief review, primarily focused on data in humans, summarizes: (1) the evidence for upper airway sensorimotor injury in OSA and (2) current understanding of how these changes affect upper airway function and their potential to change OSA progression. Some unresolved questions including possible treatment targets are noted.

Sensorimotor function of the upper-airway muscles and respiratory sensory processing in untreated obstructive sleep apnea

Numerous studies have demonstrated upper-airway neuromuscular abnormalities during wakefulness in snorers and obstructive sleep apnea (OSA) patients. However, the functional role of sensorimotor impairment in OSA pathogenesis/disease progression and its potential effects on protective upper-airway reflexes, measures of respiratory sensory processing, and force characteristics remain unclear. This study aimed to gain physiological insight into the potential role of sensorimotor impairment in OSA pathogenesis/disease progression by comparing sensory processing properties (respiratory-related evoked potentials; RREP), functionally important protective reflexes (genioglossus and tensor palatini) across a range of negative pressures (brief pulses and entrained iron lung ventilation), and tongue force and time to task failure characteristics between 12 untreated OSA patients and 13 controls. We hypothesized that abnormalities in these measures would be present in OSA patients. Upper-airway reflexes (e.g., genioglossus onset latency, 20 ± 1 vs. 19 ± 2 ms, P = 0.82), early RREP components (e.g., P1 latency 25 ± 2 vs. 25 ± 1 ms, P = 0.78), and the slope of epiglottic pressure vs. genioglossus activity during iron lung ventilation (-0.68 ± 1.0 vs. -0.80 ± 2.0 cmH(2)O/%max, P = 0.59) were not different between patients and controls. Maximal tongue protrusion force was greater in OSA patients vs. controls (35 ± 2 vs. 27 ± 2 N, P < 0.01), but task failure occurred more rapidly (149 ± 24 vs. 254 ± 23 s, P < 0.01). Upper-airway protective reflexes across a range of negative pressures as measured by electromyography and the early P1 component of the RREP are preserved in OSA patients during wakefulness. Consistent with an adaptive training effect, tongue protrusion force is increased, not decreased, in untreated OSA patients. However, OSA patients may be vulnerable to fatigue of upper-airway dilator muscles, which could contribute to disease progression.

Blunted respiratory-related evoked potential in awake obstructive sleep apnoea subjects: a NEP technique study

OBJECTIVE

Respiratory-related evoked potentials (RREP) elicited by transmural pressure in obstructive sleep apnoea (OSA) subjects have reported conflicting data. Different features of pressure stimuli and/or in the timing of stimuli application seem to account for these contradictory results. The negative expiratory pressure (NEP) technique, highly reproducible in terms of rise time and pressure values, allows to minimize the methodological confounding factors. We determined whether the afferent activity from the upper airway (UA) is altered in OSA subjects.

METHODS

RREP potentials were examined in 10 OSA and in 12 non-apnoeic awake subjects by means of the NEP technique.

RESULTS

All controls showed a cortical response to all pressure stimuli. All OSA subjects showed responses to -5 and -10 cmH(2)O whereas six of them showed no responses to -1 cmH(2)O. The amplitude of the P22, N45 and P85 components of the RREP was significantly reduced in OSA with respect to the controls in response to both the -5 and -10 cmH(2)O stimuli. We found no significant differences in latencies.

CONCLUSIONS

Awake OSA subjects had a raised threshold to pressure stimuli and blunted respiratory-related evoked potentials.

SIGNIFICANCE

These data indicate a deficit in afferent activity in the UA.

Alcohol alters sensory processing to respiratory stimuli in healthy men and women during wakefulness

STUDY OBJECTIVES

Alcohol can cause sleep-disordered breathing in healthy men, increase O2 desaturation in men who snore, and worsen obstructive sleep apnea (OSA) severity in men with OSA. These findings are less consistent among women, and the underlying mechanisms are incompletely understood. Respiratory-load sensory processing, which underpins upper-airway and respiratory responses to increased breathing load, is potentially impaired by alcohol. Using respiratory-related evoked potentials (RREPs) during wakefulness, this study aimed to test the hypothesis that alcohol impairs respiratory-load sensory processing and to explore potential sex differences.

DESIGN

Within-subjects cross-over design in men versus women.

SETTING

Sleep physiology laboratory.

PARTICIPANTS

Twenty healthy individuals (9 women) aged 18 to 38 years.

INTERVENTIONS

Within each subject, RREP waveform components were generated by approximately 60 brief early-inspiratory negative-pressure pulses (-13 cm H2O mask pressure, 200 ms) before and after acute alcohol administration (1.5 mL/kg body weight). Choanal and epiglottic pressures were recorded to monitor stimulus magnitude and upper-airway resistance.

MEASUREMENTS AND RESULTS

The latency of several RREP waveform components increased after the administration of alcohol (deltaN1 = 11 +/- 5 ms, deltaN2 = 6 +/- 3 ms, deltaP3 = 26 +/- 10 ms), and P2 amplitude decreased (3.4 +/- 1.5 microV vs 1.2 +/- 0.8 microV). There were no changes in P1 latency or amplitude. During relaxed breathing, nasal resistance increased after alcohol ingestion (1.38 +/- 0.16 vs 1.86 +/- 0.18 cm H2O x l(-1) x s(-1)), but pharyngeal and supraglottic resistances remained unchanged. RREP waveform components and upper-airway resistance measures were not different in men versus women before or after alcohol ingestion.

CONCLUSIONS

These data demonstrate that alcohol alters sensory processing of respiratory neural information, but not early neural transmission (P1), to a similar extent in healthy men and women. Altered sensory processing to respiratory stimuli, as well as nasal congestion, may be important mechanisms contributing to alcohol-related sleep disordered breathing.

Abnormal respiratory-related evoked potentials in untreated awake patients with severe obstructive sleep apnoea syndrome

AIM

Obstructive sleep apnoeas generate an intense afferent traffic leading to arousal and apnoea termination. Yet a decrease in the sensitivity of the afferents has been described in patients with obstructive sleep apnoea, and could be a determinant of disease severity. How mechanical changes within the respiratory system are processed in the brain can be studied through the analysis of airway occlusion-related respiratory-related evoked potentials. Respiratory-related evoked potentials have been found altered during sleep in mild and moderate obstructive sleep apnoea syndrome, with contradictory results during wake. We hypothesized that respiratory-related evoked potentials' alterations during wake, if indeed a feature of the obstructive sleep apnoea syndrome, should be present in untreated severe patients.

METHODS

Ten untreated patients with severe obstructive sleep apnoea syndrome and eight matched controls were studied. Respiratory-related evoked potentials were recorded in Cz-C3 and Cz-C4, and described in terms of the amplitudes and latencies of their components P1, N1, P2 and N2.

RESULTS

Components amplitudes were similar in both groups. There was no significant difference in P1 latencies. This was also the case for N1 in Cz-C3. In contrast, N1 latencies in Cz-C4 were significantly longer in patients with obstructive sleep apnoea syndrome [median 98 ms (interquartile range 16.00) versus 79.5 ms (5.98), P = 0.015]. P2 and N2 were also significantly delayed, on both sides.

CONCLUSIONS

The cortical processing of airway occlusion-related afferents seems abnormal in untreated patients with severe obstructive sleep apnoea syndrome. This could be either a severity marker and/or an aggravating factor.

Pathophysiology of adult obstructive sleep apnea

Obstructive sleep apnea (OSA) is a common disorder characterized by repetitive narrowing or collapse of the pharyngeal airway during sleep. The disorder is associated with major comorbidities including excessive daytime sleepiness and increased risk of cardiovascular disease. The underlying pathophysiology is multifactorial and may vary considerably between individuals. Important risk factors include obesity, male sex, and aging. However, the physiological mechanisms underlying these risk factors are not clearly understood. This brief review summarizes the current understanding of OSA pathophysiology in adults and highlights the potential mechanisms underlying the principal risk factors. In addition, some of the pathophysiological characteristics associated with OSA that may modulate disease severity are illustrated. Finally, the potential for novel treatment strategies, based on an improved understanding of the underlying pathophysiology, is also discussed with the ultimate aim of stimulating research ideas in areas where knowledge is lacking.

Respiratory-related evoked potentials in children with asthma

AIMS OF THE STUDY

Respiratory-related evoked potentials (RREPs) are a method of recording brain activities in response to respiratory stimuli. Although data in childhood are scarce, the absence of the early P1 component of RREPs has been reported in children with a history of life-threatening asthma. This study was focused on the presence, latencies, and amplitudes of the P1, N1, P2, and N2 components of the RREPs in a paediatric series of asthmatic patients.

PATIENTS AND METHODS

RREPs were recorded in 21 patients with stable asthma, age range 8-17 years, 11 healthy children, age range 6-16 years, and 24 healthy adults, age range 20-28 years. The signals from left (C3-Cz) and right (C4-Cz) central (rolandic) location were recorded separately, using surface electrodes. Evoked responses to two series of 80 consecutive mid-inspiratory occlusions were averaged. Recordings were analysed manually.

RESULTS

All 4 RREPs components were significantly more often absent in asthmatic children than in healthy children and adults (P1, p=0.01; N1, p=0.008; P2, p=0.008, N2, p=0.01). The latencies and amplitudes of the four components were similar in patients and healthy subjects.

CONCLUSION

RREPs components were less frequently present in children with asthma than in healthy subjects. This finding should promote the recording of RREPs in other acute and chronic respiratory diseases in children in order to search for possible electroclinical correlations.

An Adaptive Detector of Genioglossus EMG Reflex Using Berkner Transform for Time Latency Measurement in OSA Pathophysiological Studies

To investigate obstructive sleep apnea syndrome mechanisms, we developed a device to measure the surface electromyogram (EMG) time latency reflex of the genioglossus muscle stimulated by time and amplitude calibrated negative pharyngeal pressure drops. The reflex signals were found to be disturbed by transient signals that generate false alarms. Thus, to reduce false alarm occurrences we designed an adaptive multiscale method. Continuous wavelet transform (CWT) is widely used in biomedical signal event detection processes. The Berkner transform is an approximation of a CWT that is based on a hierarchical scheme similar to discrete wavelet transform. We used the Berkner transform to build a multiscale detector because it offers the possibility of maxima coefficients linkage that leads to good accuracy in reflex onset localization. As a contribution to this novel approach we used a reconstruction formula to develop an adaptive method for scale range determination in our surface EMG reflex detector. Finally, we characterized our detector in terms of accuracy and robustness, first on synthesized signals and second, on signals acquired on apneic patients and healthy subjects. Preliminary results showed a significant difference (p < 0.01) between the two populations regarding the genioglossus muscle mean latency time. These physiological findings may partly explain why the upper airway protective reflex occurring when a negative pressure is applied to the upper airway is ineffective in OSA patients, leading to pharyngeal collapse.

Sustained hypoxia depresses sensory processing of respiratory resistive loads

RATIONALE

The combination of acute hypoxia and increased respiratory load is encountered in several respiratory diseases including acute life-threatening asthma and sleep apnea. Hypoxia has been shown to inhibit respiratory load perception in healthy and asthmatic subjects, and could contribute to treatment delays and impaired function of protective reflexes.

OBJECTIVES

Using respiratory-related evoked potentials (RREPs) this study aimed to determine the sensory processes mediating hypoxia-induced suppression of respiratory load sensation.

METHODS

EEG was measured over the central and parietal cortical regions in 14 healthy subjects. RREPs were elicited by 500-ms midinspiratory resistive load stimuli during and after isocapnic normoxia or hypoxia (blood arterial O2 saturation approximately 80%). On a separate occasion, subjects rated the perceived magnitude of five externally applied inspiratory resistive loads (range, 8.6-43.7 cm H2O x L(-1) x s) under similar experimental conditions. In both experiments subjects voluntarily ventilated approximately 90% above baseline to match ventilatory output between gas conditions.

RESULTS

RREP stimulus was matched between gas conditions in 11 subjects (minimum mask pressure -9.7 +/- 0.6 versus -9.2 +/- 0.4 cm H2O). P1 and P2 amplitudes were reduced during isocapnic hypoxia compared with normoxia (maximal at Cz: P1, 2.5 +/- 1.1 versus 3.9 +/- 1.2 microv, p = 0.03; P2, 10.0 +/- 2.2 versus 12.4 +/- 2.1 microv, p < 0.01, respectively). Perceived magnitude of externally applied resistive loads was also reduced during hypoxia compared with normoxia (17.1 +/- 1.1 versus 19.0 +/- 1.1 au, p < 0.01).

CONCLUSIONS

These data confirm that isocapnic hypoxia suppresses respiratory load sensation. Decreased amplitude of the earlier (P1) RREP component suggests that this is mediated, at least in part, by suppression of respiratory afferent information before its arrival at the primary sensory cortex.

Mechanisms of arousal from sleep and their consequences

PURPOSE OF REVIEW

In recent years, understanding of the mechanisms by which sleep is maintained and the consequences of abnormal arousal from sleep has improved rapidly. This review describes the recent insights into the nature of sleep and arousal and the particular insights gained in common disease states such as sleep-disordered breathing.

RECENT FINDINGS

Expansion of the definitions of the classic stages of non-REM and REM sleep to include consideration of the role of cyclic alternating pattern sleep as a gating mechanism for arousal and maintenance of stable sleep has led to a significant advancement in understanding the nature of normal and pathologic arousals from sleep. In addition, the effect of arousals from sleep on cerebral cortical electrophysiology and autonomic activation has been further defined, with a potential effect on clinical practice.

SUMMARY

Arousal from sleep is dependent on wake-promoting influences overwhelming forces promoting sleep. Autonomic activation and cortical arousal can significantly affect and destabilize sleep homeostasis. The understanding of sleep-respiration interactions continues to evolve. The definition of the minimal arousal event is an important research goal. It will be important in clinical practice and research to consider sleep stability domains as a complement to sleep depth staging to allow better understanding of the relative stability and instability of the system and to consider all components of the consequences of arousal.

Recent advances in understanding the pathogenesis of obstructive sleep apnea

PURPOSE OF REVIEW

The pathogenesis of obstructive sleep apnea (OSA) is incompletely understood. Historically it was believed that patients with OSA have a small upper airway (often due to obesity) that is kept patent during wakefulness by the activity of upper airway dilating muscles. With the reduction in muscle tone at sleep onset, the airway collapses and causes apnea. While this appears to be the case for many patients with OSA, other patients show no major airway anatomic defects or minimal obesity.

RECENT FINDINGS

This has led to the concept that other factors such as unstable ventilatory control and changes in lung volume during sleep may be involved in the pathogenesis of OSA. Recently there have been several advances in our understanding of how these mechanisms are involved in OSA pathogenesis.

SUMMARY

A more complete understanding of apnea pathogenesis may improve therapeutic techniques and reduce the consequences of OSA.