Upper airway collapsibility: the importance of gender and adiposity

Long-term trends in body mass index throughout upper airway stimulation treatment: does body mass index matter?

STUDY OBJECTIVES

Upper airway stimulation is a surgical option for patients with obstructive sleep apnea who fail other forms of noninvasive treatment. Current guidelines recommend a baseline body mass index (BMI) below 32 kg/m2 for eligibility. In this study, we identify trends in BMI before and after upper airway stimulation to characterize the influence of BMI on treatment success.

METHODS

Patients underwent upper airway stimulation implantation between 2016 and 2021. Sleep study data were collected from preoperative and most recent postoperative sleep study. BMI data were collected and compared across the following time points: preoperative sleep study (BMI-1), initial surgeon consultation (BMI-2), surgery (BMI-3), titration polysomnogram (BMI-4), and second postoperative sleep study (BMI-5). Patients were categorized into groups (BMI ≥32 [BMI32], 25 ≤ BMI <32 [BMI25], BMI <25 [BMI18]) based BMI-1, and clinical outcomes were compared.

RESULTS

253 patients were included. The BMI32 group showed a significant decrease in BMI between BMI-1 and BMI-3 (33.9 vs 32.2; P < .001) and a significant increase in BMI between BMI-3 and BMI-5 (32.2 vs 33.0; P = .047). Apnea-hypopnea index improvement and treatment success rate were not significantly different between groups. On univariate and multivariable logistic regression, a lower BMI-5 was significantly predictive of treatment success (odds ratio: 0.88; 95% confidence interval: 0.79-0.97; P = .016). BMI-5 was also significantly associated with improvement in apnea-hypopnea index (P = .002). Other BMI time points were not associated with measures of treatment success.

CONCLUSIONS

Reduced BMI after upper airway stimulation implantation, as opposed to baseline BMI, predicted treatment success. These findings may guide patient counseling, with implications for long-term adherence and therapy success.

CITATION

Renslo B, Virgen CG, Sawaf T, et al. Long-term trends in body mass index throughout upper airway stimulation treatment: does body mass index matter? J Clin Sleep Med. 2023;19(6):1061-1071.

Effect of Gender on Chronic Intermittent Hypoxic Fosb Expression in Cardiorespiratory-Related Brain Structures in Mice

We aimed to delineate sex-based differences in neuroplasticity that may be associated with previously reported sex-based differences in physiological alterations caused by repetitive succession of hypoxemia-reoxygenation encountered during obstructive sleep apnea (OSA). We examined long-term changes in the activity of brainstem and diencephalic cardiorespiratory neuronal populations induced by chronic intermittent hypoxia (CIH) in male and female mice by analyzing Fosb expression. Whereas the overall baseline and CIH-induced Fosb expression in females was higher than in males, possibly reflecting different neuroplastic dynamics, in contrast, structures responded to CIH by Fosb upregulation in males only. There was a sex-based difference at the level of the rostral ventrolateral reticular nucleus of the medulla, with an increase in the number of FOSB/ΔFOSB-positive cells induced by CIH in males but not females. This structure contains neurons that generate the sympathetic tone and which are involved in CIH-induced sustained hypertension during waking hours. We suggest that the sex-based difference in neuroplasticity of this structure contributes to the reported sex-based difference in CIH-induced hypertension. Moreover, we highlighted a sex-based dimorphic phenomenon in serotoninergic systems induced by CIH, with increased serotoninergic immunoreactivity in the hypoglossal nucleus and a decreased number of serotoninergic cells in the dorsal raphe nucleus in male but not female mice. We suggest that this dimorphism in the neuroplasticity of serotoninergic systems predisposes males to a greater alteration of neuronal control of the upper respiratory tract associated with the greater collapsibility of upper airways described in male OSA subjects.

Respiratory modulation of lingual muscle activity across sleep-wake states in rats

In obstructive sleep apnea (OSA) patients, inspiratory activation (IA) of lingual muscles protects the upper airway from collapse. We aimed to determine when rats' lingual muscles exhibit IA. In 5 Sprague-Dawley and 3 Wistar rats, we monitored cortical EEG and lingual, diaphragmatic and nuchal electromyograms (EMGs), and identified segments of records when lingual EMG exhibited IA. Individual segments lasted 2.4-269 s (median: 14.5 s), most (89%) occurred during slow-wave sleep (SWS), and they collectively occupied 0.3-6.1% of the total recording time. IA usually started to increase with a delay after SWS onset and ended with an arousal, or declined prior to rapid eye movement sleep. IA of lingual EMG was not accompanied by increased diaphragmatic activity or respiratory rate changes, but occurred when cortical EEG power was particularly low in a low beta-1 frequency range (12.5-16.4 Hz). A deep SWS-related activation of upper airway muscles may be an endogenous phenomenon designed to protect the upper airway against collapse.

Influence of gender and anthropometric measures on severity of obstructive sleep apnea

PURPOSE

Gender differences influence upper airway anatomy and physiology. The purpose of our study was to evaluate the influence of gender as well as anthropometric measures on severity of obstructive sleep apnea (OSA).

METHODS

A retrospective review of patients referred to our sleep laboratory for evaluation of OSA was done. Patients with a diagnosis of OSA (Respiratory Disturbance Index (RDI) > 5) were included in the study. Anthropometric measurements were available for all the patients included in the study. Measurements of subjects' height, weight, neck size, and waist and hip sizes were used in the study; waist-hip ratio and neck-to-height ratio were calculated.

RESULTS

Three hundred eighty-six females and 661 males were included. Women were older than men and had a higher body mass index (BMI) and waist-to-hip ratio; men had a thicker neck circumference and a higher neck-to-height ratio. The severity of OSA was significantly higher in males (RDI 41.2 ± 27.9 in men vs. 30.0 ± 26.7 in women, p < 0.0001) despite a lower BMI and age in the men. Severity of OSA, as measured by RDI, varied significantly with changes in anthropometric measures such as neck circumference, and waist and hip sizes in both genders. Waist-to-hip ratio was associated with severity of OSA in men but not in women (p = 0.19 and 0.0001 in women and men, respectively). However, no single anthropometric value was found to be strongly predictive of OSA severity.

CONCLUSION

Despite having a higher mean BMI and age, women have lower RDI compared with men. Waist-to-hip ratio is more predictive of severity of OSA in men than in women. However, the correlation of anthropometric measures with severity of OSA was weak in our subjects.

Electromyographic activity at the base and tip of the tongue across sleep-wake states in rats

Obstructive sleep apnea (OSA) patients have elevated tonic and phasic inspiratory activity in the genioglossus and other upper airway muscles during wakefulness; this protects their upper airway from collapse. In this group, sleep-related decrements of upper airway motor tone result in sleep-related upper airway obstructions. We previously reported that in the rat, a species widely used to study the neural mechanisms of both sleep and breathing, lingual electromyographic activity (EMG) is minimal or absent during slow-wave sleep (SWS) and then gradually increases after the onset of rapid eye movement sleep (REMS) due to the appearance of large phasic bursts. Here, we investigated whether sleep-wake patterns and respiratory modulation of lingual EMG depend on the site of EMG recording within the tongue. In nine chronically instrumented rats, we recorded from 17 sites within the tongue and from the diaphragm across sleep-wake states. We quantified lingual EMG in successive 10s intervals of continuous 2h recordings (1-3 p.m.). We found that sleep-wake patterns of lingual EMG did not differ between the base and tip of the tongue, and that respiratory modulation was extremely rare regardless of the recording site. We also determined that the often rhythmic lingual bursts during REMS do not occur with respiratory rhythmicity. This pattern differs from that in OSA subjects who, unlike rats, have collapsible upper airway, exhibit prominent respiratory modulation of upper airway motor tone during quiet wakefulness, retain considerable tonic and inspiratory phasic activity during SWS, and show nadirs of activity during REMS.

Does obesity play a major role in the pathogenesis of sleep apnoea and its associated manifestations via inflammation, visceral adiposity, and insulin resistance?

Despite the early recognition of the strong association between obstructive sleep apnoea (OSA) and obesity, and OSA and cardiovascular problems, sleep apnoea has been treated as a "local abnormality" of the respiratory track rather than as a "systemic illness". In 1997, we first reported that the pro-inflammatory cytokines interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNFalpha) were elevated in patients with disorders of excessive daytime sleepiness (EDS) and proposed that these cytokines were mediators of daytime sleepiness. In subsequent studies, it was shown that IL-6, TNFalpha, and insulin levels were elevated in sleep apnoea independently of obesity and that visceral fat was the primary parameter linked with sleep apnoea. Further studies showed that women with the polycystic ovary syndrome (PCOS) were much more likely than controls to have sleep-disordered breathing (SDB) and daytime sleepiness, suggesting a pathogenetic role of insulin resistance in OSA. Additional accumulated evidence that supports the role of obesity and the associated metabolic aberrations in the pathogenesis of sleep apnoea and related symptoms include: obesity without sleep apnoea is associated with daytime sleepiness; the protective role of gonadal hormones as suggested by the increased prevalence of sleep apnoea in post-menopausal women and the significantly reduced risk for OSA in women on hormonal therapy; partial effects of continuous positive airway pressure (CPAP) in obese patients with apnoea on hypercytokinemia, insulin resistance indices, and visceral fat; and that the prevalence of the metabolic syndrome in the U.S. population from the Third National Health and Nutrition Examination Survey (1988-1994) parallels the prevalence of symptomatic sleep apnoea in general random samples. Furthermore, the beneficial effect of a cytokine antagonist on EDS and apnoea in obese, male apnoeics and that of exercise and weight loss on SDB and EDS in general random or clinical samples, supports the hypothesis that cytokines and insulin resistance are mediators of EDS and sleep apnoea in humans. Finally, our recent finding that in obese, hypothalamic CRH neuron is hypoactive, provides additional evidence on the potential central neural mechanisms for depressed ventilation and consequent development of sleep apnoea in obese individuals. In conclusion, accumulating evidence provides support to our thesis that obesity via inflammation, insulin resistance, visceral adiposity, and central neural mechanisms, e.g. hypofunctioning hypothalamic CRH, play a major role in the pathogenesis of sleep apnoea, sleepiness, and the associated cardiovascular co-morbidities.

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.

Donepezil improves obstructive sleep apnea in Alzheimer disease: a double-blind, placebo-controlled study

BACKGROUND

There is an association between Alzheimer disease and sleep-disordered breathing. Donepezil is the drug most frequently used to treat cognitive symptoms in Alzheimer disease. This study evaluates the effects of donepezil on obstructive sleep apnea in patients with Alzheimer disease.

METHODS

Randomized, double-blind, placebo-controlled design. Twenty-three patients with mild-to-moderate Alzheimer disease and apnea-hypopnea index (AHI) > 5/h were allocated to two groups: donepezil treated (n = 11) and placebo treated (n = 12). Polysomnography and cognitive evaluation using Alzheimer disease assessment scale-cognitive (ADAS-cog) subscale were performed at baseline and after 3 months. Cognitive and sleep data were analyzed using analysis of variance.

RESULTS

AHI and oxygen saturation improved significantly after donepezil treatment compared to baseline and placebo (p < 0.05). Rapid eye movement (REM) sleep duration increased after donepezil treatment (p < 0.05). ADAS-cog scores improved after donepezil treatment, although they did not correlate with REM sleep increase and sleep apnea improvement (p < 0.01).

CONCLUSIONS

Donepezil treatment improved AHI and oxygen saturation in patients with Alzheimer disease. Treatment also increased REM sleep duration and reduced ADAS-cog scores.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00480870.

Testosterone therapy and obstructive sleep apnea: is there a real connection?

INTRODUCTION

With the recent increased recognition and treatment of hypogonadism in men, a caution has been given that testosterone replacement therapy (TRT) may cause or aggravate obstructive sleep apnea syndrome (OSA).

AIM

To evaluate the scientific data behind the cautionary statements about TRT and OSA.

MAIN OUTCOME MEASURES

Methodology and criteria for such studies and evaluation of documents and results based on methodology, duration, and outcome of treatment.

METHODS

A review of the literature on the subject of TRT and OSA was performed. The possible mechanisms of action of TRT, on breathing and respiration during sleep were explored.

RESULT

Historically, the first such caution came in 1978. Since then, a few similar incidence reports have been cited. The total number of patients in such reports was very small, very disproportional to the millions of patients treated with TRT. Also, there was a lack of consistent findings connecting TRT to OSA. In addition, different results may occur with physiologic replacement vs. supraphysiologic doses in regard to breathing and OSA. The studies showing the effect of TRT on OSA and breathing were all case studies with small numbers of subjects and showed little effect of TRT on OSA in the majority of case reports. Only one study using supraphysiologic doses was a double-blind, placebo-controlled study, which showed a development of OSA in healthy pooled subjects. The other reports were case studies with limited numbers of subjects, suggesting an inconsistent effect of supraphysiologic TRT on OSA and breathing.

CONCLUSION

Cautionary statements about TRT in OSA appear frequently in the TRT literature and guidelines, despite lack of convincing evidence that TRT causes and/or aggravates OSA. Also, there is a lack of consistency in the findings connecting TRT to OSA. It is evident that the link between TRT and OSA is weak, based on methodological issues in many of the studies, and most studies involved small numbers of men. Further studies in this area are needed.

Neuromechanical control of upper airway patency during sleep

Obstructive sleep apnea is caused by pharyngeal occlusion due to alterations in upper airway mechanical properties and/or disturbances in neuromuscular control. The objective of the study was to determine the relative contribution of mechanical loads and dynamic neuromuscular responses to pharyngeal collapse during sleep. Sixteen obstructive sleep apnea patients and sixteen normal subjects were matched on age, sex, and body mass index. Pharyngeal collapsibility, defined by the critical pressure, was measured during sleep. The critical pressure was partitioned between its passive mechanical properties (passive critical pressure) and active dynamic responses to upper airway obstruction (active critical pressure). Compared with normal subjects, sleep apnea patients demonstrated elevated mechanical loads as demonstrated by higher passive critical pressures [-0.05 (SD 2.4) vs. -4.5 cmH2O (SD 3.0), P = 0.0003]. Dynamic responses were depressed in sleep apnea patients, as suggested by failure to lower their active critical pressures [-1.6 (SD 3.5) vs. -11.1 cmH2O (SD 5.3), P < 0.0001] in response to upper airway obstruction. Moreover, elevated mechanical loads placed some normal individuals at risk for sleep apnea. In this subset, dynamic responses to upper airway obstruction compensated for mechanical loads and maintained airway patency by lowering the active critical pressure. The present study suggests that increased mechanical loads and blunted neuromuscular responses are both required for the development of obstructive sleep apnea.

Respiratory control stability and upper airway collapsibility in men and women with obstructive sleep apnea

Obstructive sleep apnea (OSA) is two to three times more common in men as in women. The mechanisms leading to this difference are currently unclear but could include gender differences in respiratory stability [loop gain (LG)] or upper airway collapsibility [pharyngeal critical closing pressure (Pcrit)]. The aim of this study was to compare LG and Pcrit between men and women with OSA to determine whether the factors contributing to apnea are similar between genders. The first group of 11 men and 11 women were matched for OSA severity (mean +/- SE apnea-hypopnea index = 43.8 +/- 6.1 and 44.1 +/- 6.6 events/h). The second group of 12 men and 12 women were matched for body mass index (BMI; 31.6 +/- 1.9 and 31.3 +/- 1.8 kg/m2, respectively). All measurements were made during stable supine non-rapid eye movement sleep. LG was determined using a proportional assist ventilator. Pcrit was measured by progressively dropping the continuous positive airway pressure level for three to five breaths until airway collapse. Apnea-hypopnea index-matched women had a higher BMI than men (38.0 +/- 2.4 vs. 30.0 +/- 1.9 kg/m2; P = 0.03), but LG and Pcrit were similar between men and women (LG: 0.37 +/- 0.02 and 0.37 +/- 0.02, respectively, P = 0.92; Pcrit: 0.35 +/- 0.62 and -0.18 +/- 0.87, respectively, P = 0.63). In the BMI-matched subgroup, women had less severe OSA during non-rapid eye movement sleep (30.9 +/- 7.4 vs. 52.5 +/- 8.1 events/h; P = 0.04) and lower Pcrit (-2.01 +/- 0.62 vs. 1.16 +/- 0.83 cmH2O; P = 0.005). However, LG was not significantly different between genders (0.38 +/- 0.02 vs. 0.33 +/- 0.03; P = 0.14). These results suggest that women may be protected from developing OSA by having a less collapsible upper airway for any given degree of obesity.

Sleep apnea is a manifestation of the metabolic syndrome

Obstructive sleep apnea (OSA) is a prevalent disorder particularly among middle-aged, obese men, although its existence in women as well as in lean individuals is increasingly recognized. Despite the early recognition of the strong association between OSA and obesity, and OSA and cardiovascular problems, sleep apnea has been treated as a 'local abnormality' of the respiratory track rather than as a 'systemic illness.' In 1997, we first reported that the pro-inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNFalpha) were elevated in patients with disorders of excessive daytime sleepiness (EDS) and proposed that these cytokines were mediators of daytime sleepiness. Also, we reported a positive correlation between IL-6 or TNFalpha plasma levels and the body-mass-index (BMI). In subsequent studies, we showed that IL-6, TNFalpha, and insulin levels were elevated in sleep apnea independently of obesity and that visceral fat, was the primary parameter linked with sleep apnea. Furthermore, our findings that women with the polycystic ovary syndrome (PCOS) (a condition associated with hyperandrogenism and insulin resistance) were much more likely than controls to have sleep disordered breathing (SDB) and daytime sleepiness, suggests a pathogenetic role of insulin resistance in OSA. Other findings that support the view that sleep apnea and sleepiness in obese patients may be manifestations of the Metabolic Syndrome, include: obesity without sleep apnea is associated with daytime sleepiness; PCOS and diabetes type 2 are independently associated with EDS after controlling for SDB, obesity, and age; increased prevalence of sleep apnea in post-menopausal women, with hormonal replacement therapy associated with a significantly reduced risk for OSA; lack of effect of continuous positive airway pressure (CPAP) in obese patients with apnea on hypercytokinemia and insulin resistance indices; and that the prevalence of the metabolic syndrome in the US population from the Third National Health and Nutrition Examination Survey (1988-1994) parallels the prevalence of symptomatic sleep apnea in general random samples. Finally, the beneficial effect of a cytokine antagonist on EDS in obese, male apneics and that of exercise on SDB in a general random sample, supports the hypothesis that cytokines and insulin resistance are mediators of EDS and sleep apnea in humans. In conclusion, accumulating evidence provides support to our model of the bi-directional, feed forward, pernicious association between sleep apnea, sleepiness, inflammation, and insulin resistance, all promoting atherosclerosis and cardiovascular disease.

Reduction of sleep-disordered breathing after physostigmine

The cholinesterase inhibitor physostigmine (PHYS) was investigated in a double-blind, placebo-controlled, randomized, crossover trial of 10 male patients with moderate to severe obstructive sleep apnea. PHYS (0.12 microg/minute/kg, 7-hour infusion) reduced mean apnea/hypopnea index (AHI) by 13.6 (95% confidence interval [CI], 2.2-25.1) corresponding to 21.4% (95% CI, -5.5 to 47.9) and increased minimum SaO2 by 8.7% (95% CI, -0.3 to 17.7) corresponding to 23.2% (95% CI, 4.8-41.3). During the last third of the night, coinciding with predicted plasma concentration steady state, non-REM sleep AHI decreased by 19.2 (95% CI, 0.1-38.3) or 14.9% (95% CI, -43.6 to 77.7) and REM AHI by 33.8 (95% CI, 13.7-54.0) or 67.5% (95% CI, 49.7-85.3). Mean total sleep time was reduced by 74 minutes (95% CI, 33.9-114.9), but patients with the least pronounced sleep shortening had the largest reduction of AHI (r = 0.73, p < 0.02). The nocturnal decline in heart rate was reduced by PHYS. Moreover, resting (early-night placebo heart rate) was positively correlated with proportional reduction of REM apnea index (r = 0.69, p < 0.02). Body mass index was negatively correlated with reduction of REM AHI (r = 0.77, p < 0.02). This, predominantly REM-related, reduction of obstructive sleep apnea after PHYS may provide a new treatment option if the effects are maintained in long-term studies.

Surgery for sleep-disordered breathing in female patients

This article focuses on the female patient with sleep-disordered breathing. Sleep-disordered breathing has historically been considered a disease seen primarily in men, but it has become increasingly recognized in women. Recent studies of the general population suggest that almost one third of all obstructive sleep apnea syndrome cases exist in women. A review of current information focusing on the epidemiology, diagnosis, and treatment of the female patient is presented.