Effects of 12 Months Continuous Positive Airway Pressure on Sympathetic Activity Related Brainstem Function and Structure in Obstructive Sleep Apnea

Association between Obstructive Sleep Apnea and Heart Failure in Adults-A Systematic Review

BACKGROUND

Heart failure (HF) patients commonly experience obstructive sleep apnea (OSA), which may worsen their condition. We reviewed a diverse range of studies to investigate the prevalence of OSA in HF patients, the effects of positive airway pressure (PAP) treatment, and the potential impact of sodium-glucose cotransporter-2 inhibitors (SGLT2i) and sacubitril/valsartan on OSA outcomes.

METHODS

We analyzed case-control, observational studies, and randomized controlled trials. Prevalence rates, PAP treatment, and HF pharmacotherapy were assessed.

RESULTS

Numerous studies revealed a high prevalence of OSA in HF patients, particularly with preserved ejection fraction. PAP treatment consistently improved an apnea-hypopnea index, left ventricular ejection fraction, oxygen saturation, and overall quality of life. Emerging evidence suggests that SGLT2i and sacubitril/valsartan might influence OSA outcomes through weight loss, improved metabolic profiles, and potential direct effects on upper airway muscles.

CONCLUSIONS

The complex interplay between OSA and HF necessitates a multifaceted approach. PAP treatment has shown promising results in improving OSA symptoms and HF parameters. Additionally, recent investigations into the effects of HF pharmacotherapy on OSA suggest their potential as adjunctive therapy. This review provides insights for clinicians and researchers, highlighting the importance of addressing OSA and HF in patient management strategies.

Changes in Functional Connectivity of Hippocampal Subregions in Patients with Obstructive Sleep Apnea after Six Months of Continuous Positive Airway Pressure Treatment

Previous studies have shown that the structural and functional impairments of hippocampal subregions in patients with obstructive sleep apnea (OSA) are related to cognitive impairment. Continuous positive airway pressure (CPAP) treatment can improve the clinical symptoms of OSA. Therefore, this study aimed to investigate functional connectivity (FC) changes in hippocampal subregions of patients with OSA after six months of CPAP treatment (post-CPAP) and its relationship with neurocognitive function. We collected and analyzed baseline (pre-CPAP) and post-CPAP data from 20 patients with OSA, including sleep monitoring, clinical evaluation, and resting-state functional magnetic resonance imaging. The results showed that compared with pre-CPAP OSA patients, the FC between the right anterior hippocampal gyrus and multiple brain regions, and between the left anterior hippocampal gyrus and posterior central gyrus were reduced in post-CPAP OSA patients. By contrast, the FC between the left middle hippocampus and the left precentral gyrus was increased. The changes in FC in these brain regions were closely related to cognitive dysfunction. Therefore, our findings suggest that CPAP treatment can effectively change the FC patterns of hippocampal subregions in patients with OSA, facilitating a better understanding of the neural mechanisms of cognitive function improvement, and emphasizing the importance of early diagnosis and timely treatment of OSA.

Influence of Obstructive Sleep Apnea Severity on Muscle Sympathetic Nerve Activity and Blood Pressure: a Systematic Review and Meta-Analysis

BACKGROUND

We conducted meta-analyses to identify relationships between obstructive sleep apnea (OSA) severity, muscle sympathetic nerve activity (MSNA), and blood pressure (BP). We quantified the effect of OSA treatment on MSNA.

METHODS

Structured searches of electronic databases were performed until June 2021. All observational designs (except reviews) were included: population (individuals with OSA); exposures (OSA diagnosis and direct measures of MSNA); comparator (individuals without OSA or different severity of OSA); outcomes (MSNA, BP, and heart rate).

RESULTS

Fifty-six studies (N=1872) were included. MSNA burst frequency was higher in OSA (27 studies; n=542) versus controls (n=488; mean differences [MDs], +15.95 bursts/min [95% CI, 12.6-17.6 bursts/min]; I²=86%). As was burst incidence (20 studies; n=357 OSA, n=312 Controls; MD, +22.23 bursts/100 hbs [95% CI, 18.49-25.97 bursts/100 hbs]; I²=67%). Meta-regressions indicated relationships between MSNA and OSA severity (burst frequency, R²=0.489; P<0.001; burst incidence, R²=0.573; P<0.001). MSNA burst frequency was related to systolic pressure (R²=0.308; P=0.016). OSA treatment with continuous positive airway pressure reduced MSNA burst frequency (MD, 11.91 bursts/min [95% CI, 9.36-14.47 bursts/min] I²=15%) and systolic (n=49; MD, 10.3 mm Hg [95% CI, 3.5-17.2 mm Hg]; I²=42%) and diastolic (MD, 6.9 mm Hg [95% CI, 2.3-11.6 mm Hg]; I²=37%) BP.

CONCLUSIONS

MSNA is higher in individuals with OSA and related to severity. This sympathoexcitation is also related to BP in patients with OSA. Treatment effectively reduces MSNA and BP, but limited data prevents an assessment of the link between these reductions. These data are clinically important for understanding cardiovascular disease risk in patients with OSA.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: CRD42021285159.

Baroreflex sensitivity during rest and pressor challenges in obstructive sleep apnea patients with and without CPAP

INTRODUCTION

Obstructive sleep apnea (OSA) increases sympathetic vasoconstrictor drive and reduces baroreflex sensitivity (BRS), the degree to which blood pressure changes modify cardiac output. Whether nighttime continuous positive airway pressure (CPAP) corrects BRS in the awake state in OSA remains unclear. We assessed spontaneous BRS using non-invasive continuous BP and ECG recordings at rest and during handgrip and Valsalva challenges, maneuvers that increase vasoconstrictor drive with progressively higher BP, in untreated OSA (unOSA), CPAP-treated OSA (cpOSA) and healthy (CON) participants.

METHODS

In a cross-sectional study of 104 participants, 34 unOSA (age mean±std, 50.6±14.1years; Respiratory Event Index [REI] 21.0±15.3 events/hour; 22male), 31 cpOSA (49.6±14.5years; REI 23.0±14.2 events/hour; 22male; self-report 4+hours/night,5+days/week,6months), and 39 CON (42.2±15.0years; 17male), we calculated BRS at rest and during handgrip and Valsalva. Additionally, we correlated BP variability (BPV) with BRS during these protocols.

RESULTS

BRS in unOSA, cpOSA and CON was, respectively (mean±sdv in ms/mmHg), at rest: 14.8±11.8, 15.8±17.0, 16.1±11.3; during handgrip 13.3±7.6, 12.7±8.4, 16.4±8.7; and during Valsalva 12.7±8.0, 11.5±6.6, 15.1±8.9. BRS was lower in cpOSA than CON for handgrip (p=0.04) and Valsalva (p=0.03). BRS was negatively correlated with BPV in unOSA during Valsalva and handgrip for cpOSA, both R=-0.4 (p=0.02). BRS was negatively correlated with OSA severity (levels: none, mild, moderate, severe) at R=-0.2 (p=0.04,n=104).

CONCLUSIONS

As expected, BRS was lower and BPV higher in OSA during the pressor challenges, and disease severity negatively correlated with BRS. In this cross-sectional study, both CPAP-treated (self-reported) and untreated OSA showed reduced BRS, leaving open whether within-person CPAP improves BRS.

Breathing rate variability in obstructive sleep apnea during wakefulness

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is defined by pauses in breathing during sleep, but daytime breathing dysregulation may also be present. Sleep may unmask breathing instability in OSA that is usually masked by behavioral influences during wakefulness. A breath-hold (BH) challenge has been used to demonstrate breathing instability. One measure of breathing stability is breathing rate variability (BRV). We aimed to assess BRV during rest and in response to BH in OSA.

METHODS

We studied 62 participants (31 with untreated OSA: respiratory event index [mean ± SD] 20 ± 15 events/h, 12 females, age 51 ± 14 years, body mass index [BMI] 32 ± 8 kg/m²; 31 controls: 17 females, age 47 ± 13 years; BMI 26 ± 4 kg/m²). Breathing movements were collected using a chest belt for 5 minutes of rest and during a BH protocol (60 seconds baseline, 30 seconds BH, 90 seconds recovery, 3 repeats). From the breathing movements, we calculated median breathing rate (BR) and interquartile BRV at rest. We calculated change in BRV during BH recovery from baseline. Group comparisons of OSA vs control were conducted using analysis of covariance with age, sex, and BMI as covariates.

RESULTS

We found 10% higher BRV in OSA vs controls (P < .05) during rest. In response to BH, BRV increased 7% in OSA vs 1% in controls (P < .001). Resting BR was not significantly different in OSA and controls, and sex and age did not have any significant interaction effects. BMI was associated with BR at rest (P < .05) and change in BRV with BH (P < .001), but no significant BMI-by-group interaction effect was observed.

CONCLUSIONS

The findings suggest breathing instability as reflected by BRV is high in OSA during wakefulness, both at rest and in response to a stimulus. Breathing instability together with high blood pressure variability in OSA may reflect a compromised cardiorespiratory consequence in OSA during wakefulness.

CITATION

Pal A, Martinez F, Akey MA, et al. Breathing rate variability in obstructive sleep apnea during wakefulness. J Clin Sleep Med. 2022;18(3):825-833.

Sympathetic neural responses to sleep disorders and insufficiencies

Short sleep duration and poor sleep quality are associated with cardiovascular risk, and sympathetic nervous system (SNS) dysfunction appears to be a key contributor. The present review will characterize sympathetic function across several sleep disorders and insufficiencies in humans, including sleep deprivation, insomnia, narcolepsy, and obstructive sleep apnea (OSA). We will focus on direct assessments of sympathetic activation, e.g., plasma norepinephrine and muscle sympathetic nerve activity, but include heart rate variability (HRV) when direct assessments are lacking. The review also highlights sex as a key biological variable. Experimental models of total sleep deprivation and sleep restriction are converging to support several epidemiological studies reporting an association between short sleep duration and hypertension, especially in women. A systemic increase of SNS activity via plasma norepinephrine is present with insomnia and has also been confirmed with direct, regionally specific evidence from microneurographic studies. Narcolepsy is characterized by autonomic dysfunction via both HRV and microneurographic studies but with opposing conclusions regarding SNS activation. Robust sympathoexcitation is well documented in OSA and is related to baroreflex and chemoreflex dysfunction. Treatment of OSA with continuous positive airway pressure results in sympathoinhibition. In summary, sleep disorders and insufficiencies are often characterized by sympathoexcitation and/or sympathetic/baroreflex dysfunction, with several studies suggesting women may be at heightened risk.

Six Months of Inspiratory Muscle Training to Lower Blood Pressure and Improve Endothelial Function in Middle-Aged and Older Adults With Above-Normal Blood Pressure and Obstructive Sleep Apnea: Protocol for the CHART Clinical Trial

Background: Cardiovascular disease is a major global health concern and prevalence is high in adults with obstructive sleep apnea (OSA). Lowering blood pressure (BP) can greatly reduce cardiovascular disease risk and physical activity is routinely prescribed to achieve this goal. Unfortunately, many adults with OSA suffer from fatigue, daytime sleepiness, and exercise intolerance—due to poor sleep quality and nocturnal hypoxemia—and have difficulty initiating and maintaining an exercise program. High-resistance inspiratory muscle strength training (IMST) is a simple, time-efficient breathing exercise consistently reported to reduce BP in small, selective groups of both healthy and at-risk adults. Herein we present the study protocol for a randomized clinical trial to determine the long-term efficacy of IMST performed regularly for 24 weeks in middle-aged and older adults with OSA. The primary outcome is casual systolic BP. Secondary outcomes are 24-h systolic BP and circulating plasma norepinephrine concentration. Other outcomes include vascular endothelial function (endothelial-dependent and -independent dilation), aortic stiffness, casual and 24-h diastolic BP, and the influence of circulating factors on endothelial cell nitric oxide and reactive oxygen species production. Overall, this trial will establish efficacy of high-resistance IMST for lowering BP and improving cardiovascular health in middle-aged and older adults with OSA.

Methods: This is a single-site, double-blind, randomized clinical trial. A minimum of 92 and maximum of 122 male and female adults aged 50–80 years with OSA and above-normal BP will be enrolled. After completion of baseline assessments, subjects will be randomized in a 1:1 ratio to participate in either high-resistance or sham (low-resistance) control IMST, performed at home, 5 min/day, 5 days/week, for 24 weeks. Repeat assessments will be taken after the 24-week intervention, and after 4 and 12 weeks of free living.

Discussion: This study is designed to assess the effects of 24 weeks of IMST on BP and vascular function. The results will characterize the extent to which IMST can reduce BP when performed over longer periods (i.e., 6 months) than have been assessed previously. Additionally, this study will help to determine underlying mechanisms driving IMST-induced BP reductions that have been reported previously.

Clinical Trial Registration: This trial is registered with ClinicalTrials.gov (Registration Number: NCT04932447; Date of registration June 21, 2021).

Obstructive sleep apnoea and 12-month weight loss in adults with class 3 obesity attending a multidisciplinary weight management program

BACKGROUND

Although there is a strong association between obesity and obstructive sleep apnoea (OSA), the effects of OSA and CPAP therapy on weight loss are less well known. The aim of this study in adults with class 3 obesity attending a multidisciplinary weight management program was to assess the relationship between OSA and CPAP usage, and 12-month weight change.

METHODS

A retrospective cohort study of all patients commencing an intensive multidisciplinary publicly funded weight management program in Sydney, Australia, between March 2018 and March 2019. OSA was diagnosed using laboratory overnight sleep studies. Demographic and clinical data, and use of CPAP therapy was collected at baseline and 12 months. CPAP use was confirmed if used ≥4 h on average per night on download.

RESULTS

Of the 178 patients who joined the program, 111 (62.4 %) completed 12 months in the program. At baseline, 63.1 % (n=70) of patients had OSA, of whom 54.3 % (n=38) were using CPAP. The non-OSA group had more females compared to the OSA with CPAP group and OSA without CPAP group (90.2 % vs. 57.9 % and 62.5 %, respectively; p=0.003), but there were no significant baseline differences in BMI (50.4±9.3 vs. 52.1±8.7 and 50.3±9.5 kg/m², respectively; p=0.636). There was significant weight loss across all three groups at 12 months. However, there were no statistically significant differences across groups in the percentage of body weight loss (OSA with CPAP: 6.3±5.6 %, OSA without CPAP: 6.8±6.9 %, non-OSA: 7.2±6.5 %; p=0.844), or the proportion of patients who achieved ≥5 % body weight loss (OSA with CPAP: 57.9 %, OSA without CPAP: 59.4 %, non-OSA: 65.9 %; p=0.743). In patients with T2DM, there was a significant reduction in HbA1c from baseline to 12 months (7.8±1.7 % to 7.3±1.4 %, p=0.03), with no difference between groups (p=0.997).

CONCLUSIONS

This multidisciplinary weight management program resulted in significant weight loss at 12 months, regardless of OSA diagnosis or CPAP use in adults with class 3 obesity. Larger studies are needed to further investigate the effects of severity of OSA status and CPAP use in weight management programs. Until completed, this study suggests that the focus should remain on implementing lifestyle changes and weight management regardless of OSA status.

Neuroadrenergic activation in obstructive sleep apnea syndrome: a systematic review and meta-analysis

BACKGROUND

Neuroadrenergic overdrive occurs in obstructive sleep apnea syndrome (OSAS). However, the small sample size of the microneurographic studies, heterogeneity of the patients examined, presence of comorbidities, represented major weaknesses not allowing to precisely define the main features of the phenomenon, particularly in nonobese patients.

OBJECTIVE

This meta-analysis evaluated 850 participants recruited in 26 microneurographic studies, based on muscle sympathetic nerve activity (MSNA) quantification in uncomplicated OSAS of different clinical severity.

METHODS

The evaluation was extended to the relationships of MSNA with heart rate (HR), anthropometric and blood pressure (BP) values, metabolic variables, apnea-hypopnea index (AHI) and oxygen saturation.

RESULTS

MSNA is activated markedly and almost homogeneously between studies, showing a progressive increase from the healthy state to mild, moderate and severe OSAS (41.6, 48.3, 65.5 and 70.7 bursts/100 heart beats, respectively, P < 0.01). Of special interest are the findings that first, MSNA is significantly related to the AHI, a marker of OSAS severity (r = 0.55, P < 0.02) and O2 saturation but not to body weight and BMI, as it occurs in OSAS associated with obesity; and second, HR is significantly and directly related to MSNA and AHI (r = 0.56 and 0.46, P < 0.03 for both), thus representing a surrogate marker of the sympathetic overdrive.

CONCLUSION

OSAS, even when uncomplicated by other cardiometabolic disease, displays a marked sympathetic activation, reflected by the MSNA and HR behavior, becoming a target of therapeutic interventions aimed at exerting sympathomoderating effects, such as continuous positive airway pressure.

Beat-to-beat blood pressure variability in patients with obstructive sleep apnea

STUDY OBJECTIVES

Cardiovascular comorbidities in obstructive sleep apnea (OSA) are difficult to treat, perhaps due to autonomic dysfunction. We assessed beat-to-beat blood pressure (BP) variability (BPV) in OSA while considering other markers derived from electrocardiogram and continuous BP signals.

METHODS

We studied 66 participants (33 participants with OSA: respiratory event index [mean ± SEM]: 21.1 ± 2.7 events/h; 12 females, aged 51.5 ± 2.4 years; body mass index: 32.8 ± 1.4 kg/m²; 33 healthy controls: 20 females; aged 45.3 ± 2.4 years; body mass index: 26.3 ± 0.7 kg/m²). We collected 5-minute resting noninvasive beat-to-beat BP and electrocardiogram values. From BP, we derived systolic, diastolic, and mean BP values, and calculated variability as standard deviations (systolic BPV, diastolic BPV, BPV). We also calculated diastole-to-systole time (time to peak). From the electrocardiogram, we derived QRS markers and calculated heart rate and heart rate variability. We performed a multivariate analysis of variance based on sex and group (OSA vs control), with Bonferroni-corrected post hoc comparisons (P ≤ .05) between groups. We calculated correlations of BPV with biological variables.

RESULTS

Multivariate analysis of variance showed effects of diastolic BPV and BPV in OSA; post hoc comparisons revealed high diastolic BPV and BPV only in female participants with OSA vs controls. QRS duration was higher in OSA, with post hoc comparisons showing the effect only in males. BPV correlated positively with heart rate variability in controls but not in participants with OSA. BPV correlated positively with time to peak in females with OSA and OSA combined, whereas there was no BPV-time-to-peak correlation in healthy participants.

CONCLUSIONS

The findings show sex-specific autonomic dysfunction reflected in beat-to-beat BP in OSA. The higher BPV may reflect poor baroreflex control or vascular damage in OSA, which are potential precursors to cardiovascular complications.

Functional organization of the insula in men and women with obstructive sleep apnea during Valsalva

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) patients show impaired autonomic regulation, perhaps related to functional reorganization of the insula, which in healthy individuals shows sex-specific anterior and right dominance during sympathetic activation. We examined insular organization of responses to a Valsalva maneuver in OSA with functional magnetic resonance imaging (fMRI).

METHODS

We studied 43 newly diagnosed OSA (age mean ± SD: 46.8 ± 8.7 years; apnea-hypopnea index (AHI) ± SD: 32.1 ± 20.1 events/hour; 34 males) and 63 healthy (47.2 ± 8.8 years; 40 males) participants. Participants performed four 18-second Valsalva maneuvers (1-minute intervals, pressure ≥ 30 mmHg) during scanning. fMRI time trends from five insular gyri-anterior short (ASG); mid short (MSG); posterior short (PSG); anterior long (ALG); and posterior long (PLG)-were assessed for within-group responses and between-group differences with repeated measures ANOVA (p < 0.05); age and resting heart rate (HR) influences were also assessed.

RESULTS

Right and anterior fMRI signal dominance appeared in OSA and controls, with no between-group differences. Separation by sex revealed group differences. Left ASG anterior signal dominance was lower in OSA versus control males. Left ASG and ALG anterior dominance was higher in OSA versus control females. In all right gyri, only OSA females showed greater anterior dominance than controls. Right dominance was apparent in PSG and ALG in all groups; females showed right dominance in MSG and PLG. OSA males did not show PLG right dominance. Responses were influenced substantially by HR but modestly by age.

CONCLUSIONS

Anterior and right insular fMRI dominance appears similar in OSA versus control participants during the sympathetic phase of the Valsalva maneuver. OSA and control similarities were present in just males, but not necessarily females, which may reflect sex-specific neural injury.

Frequency‑Specific Regional Homogeneity Alterations and Cognitive Function in Obstructive Sleep Apnea Before and After Short-Term Continuous Positive Airway Pressure Treatment

PURPOSE

Previous studies have demonstrated abnormal local spontaneous brain activity in the conventional frequency bands (0.01-0.08 Hz) in obstructive sleep apnea (OSA). However, it is not clear whether these abnormalities are associated with the specific frequency band of low-frequency oscillations or whether it can be improved with a continuous positive airway pressure (CPAP) treatment. This study aimed to investigate the regional homogeneity (ReHo) in specific frequency at baseline (pre-CPAP) and after one month of CPAP adherence treatment (post-CPAP) in OSA patients.

METHODS

Twenty-one patients with moderate-to-severe OSA and 21 age- and sex-matched healthy controls (HCs) were included in the final analysis. ReHo was calculated in three different frequency bands (typical frequency band: 0.01-0.1 Hz; slow-5 band: 0.01-0.027 Hz; slow-4 band: 0.027-0.073 Hz), respectively. A partial correlational analysis was performed to assess the relationship between altered ReHo and clinical evaluation.

RESULTS

OSA patients revealed increased ReHo in the brainstem, bilateral inferior temporal gyrus (ITG)/fusiform, and right-cerebellum posterior lobe (CPL), and decreased ReHo in the bilateral inferior parietal lobule (IPL), right superior temporal gyrus (STG), and left precentral gyrus (PG) compared to HC groups in different frequency bands. Significantly changed ReHo in the bilateral middle temporal gyrus (MTG), PG, medial frontal gyrus (MFG), supplementary motor area (SMA), CPL, IPL, left superior frontal gyrus (SFG), ITG, MTG, and right STG were observed between post-CPAP and pre-CPAP OSA patients, which was associated with specific frequency bands. The altered ReHo in specific frequency bands was correlated with Montreal cognitive assessment score, Epworth sleepiness scale, and apnea hypopnea index in pre-CPAP OSA patients.

CONCLUSION

These findings indicate that OSA has frequency-related abnormalities of spontaneous neural activity before and after short-term CPAP treatment, which might contribute to a better understanding of local neural psychopathology and may serve as potential biomarkers for clinical CPAP treatment.

Inspiratory muscle strength training lowers blood pressure and sympathetic activity in older adults with OSA: a randomized controlled pilot trial

Previous work has shown lowered casual blood pressure after just 6 wk of inspiratory muscle strength training (IMST), suggesting IMST as a potential therapeutic in the prevention/treatment of hypertension. In this study, we assessed the effects of IMST on cardiovascular parameters in older, overweight adults diagnosed with moderate and severe obstructive sleep apnea (OSA). Subjects were randomly assigned to one of two interventions 1) high-intensity IMST (n = 15, 75% maximal inspiratory pressure), or 2) a control intervention (n = 10, 15% maximum inspiratory pressure). Subjects in both groups trained at home completing 30 training breaths/day, 5 days/wk for 6 wk. Pre- and posttraining measures included maximal inspiratory pressure, casual and ambulatory blood pressures, spontaneous cardiac baroreflex sensitivity, and muscle sympathetic nerve activity. Men and women in the high-intensity IMST group exhibited reductions in casual systolic (SBP), diastolic (DBP), and mean arterial blood pressures (MAP) [SBP: -8.82 ± 4.98 mmHg; DBP: -4.69 ± 2.81 mmHg; and MAP: -6.06 ± 1.03 mmHg; P < 0.002] and nighttime SBP (pre: -12.00 ± 8.20 mmHg; P < 0.01). Muscle sympathetic nerve activities also were lower (-6.97 ± 2.29 bursts/min^-1; P = 0.01 and -9.55 ± 2.42 bursts/100 heartbeats; P = 0.002) by week 6. Conversely, subjects allocated to the control group showed no change in casual blood pressure or muscle sympathetic nerve activity and a trend toward higher overnight blood pressures. A short course of high-intensity IMST may offer significant respiratory and cardiovascular benefits for older, overweight adults with OSA. For Clinical Trial Registration, see https://www.clinicaltrials.gov (Identifier: NCT02709941).NEW & NOTEWORTHY Older, obese adults with moderate-severe obstructive sleep apnea who perform 5 min/day high-intensity inspiratory muscle strength training (IMST) exhibit lowered casual and nighttime systolic blood pressure and sympathetic nervous outflow. In contrast, adults assigned to a control (low-intensity) intervention exhibit no change in casual blood pressure or muscle sympathetic nerve activity and a trend toward increased overnight blood pressure. Remarkably, adherence to IMST even among sleep-deprived and exercise-intolerant adults is high (96%).

Effects of CPAP on Blood Pressure and Sympathetic Activity in Patients With Diabetes Mellitus, Chronic Kidney Disease, and Resistant Hypertension

Background

Patients with obstructive sleep apnea (OSA) have increased sympathetic activity and frequently also have resistant hypertension (HTN). Treatment of OSA with continuous positive airway pressure (CPAP) decreases awake and sleep blood pressure (BP) and sympathetic activity. This study was designed to assess the effect of treatment of OSA with CPAP on sympathetic activity and BP in patients with diabetes mellitus (DM), chronic kidney disease (CKD), and resistant HTN.

Methods

This was a randomized, double-blind, sham-controlled trial. Patients with DM, CKD, and resistant HTN were randomized to treatment with a therapeutic or subtherapeutic CPAP for 6 weeks. They underwent 24-hour ambulatory BP monitoring and assessment of muscle sympathetic nerve activity before and after 6 weeks on treatment.

Results

Treatment with therapeutic CPAP caused significant decreases in awake systolic and diastolic BP from 144 to 136 mm Hg (P = 0.004) and from 79 to 74 mm Hg (P = 0.004) and in sleep BP from 135 to 119 mm Hg (P = 0.045) and from 75 to 65 mm Hg (P = 0.015) compared with treatment with subtherapeutic CPAP. In contrast, treatment with therapeutic CPAP did not decrease sympathetic activity as assessed from muscle sympathetic nerve activity.

Conclusions

Decrease in BP by treatment with CPAP in patients with DM, CKD, and OSA indicates the contribution of OSA to severity of HTN in this clinical scenario. Decrease in BP in the absence of changes in sympathetic activity is suggestive that other mechanisms induced by OSA play a larger role in the maintenance of HTN in these patients.

Changes in Serum Leptin Level After Multilevel Surgery in Patients with Obstructive Sleep Apnea

OBJECTIVE

Leptin hormone plays an important role in metabolic control and is elevated in obstructive sleep apnea (OSA). The aim of this study was to assess the hypothesis that surgical treatment will reduce leptin levels in OSA patients.

STUDY DESIGN

Prospective study.

SUBJECTS AND METHODS

Twenty-three patients with multilevel OSA underwent modified genioglossus muscle advancement with anterolateral advancement pharyngoplasty between April 2018 and September 2019. Serum leptin level was measured preoperatively and 3 months postoperatively for all patients and 18 control subjects. All patients were evaluated before and 3 months after surgery by history taking, clinical examination, polysomnography, cephalometry, and Epworth Sleepiness Scale.

RESULTS

Preoperatively, patients with OSA had a higher Leptin level (18.46 ± 4.73 ng/mL) than did control subjects (7.07 ± 1.26 ng/mL) (P < .001). Surgery resulted in a significant reduction in the level of leptin from 18.46 ± 4.73 ng/mL to 8.03 ± 2.22 ng/mL (P < .001). Reductions in leptin level was correlated with changes in apnea hypopnea index (AHI) (r = 0.61, P = .002) and minimum oxygen saturation (SaO2) (r = -0.54, P = .008).

CONCLUSION

Effective multilevel surgery in the form of modified genioglossus muscle advancement with anterolateral advancement pharyngoplasty could significantly reduce leptin level in OSA patients and this reduction is correlated with the degree of OSA improvement in term of AHI and SaO2.

LEVEL OF EVIDENCE

4 Laryngoscope, 131:E665-E670, 2021.

Different prognosis between severe and very severe obstructive sleep apnea patients; Five year outcomes

BACKGROUND

Obstructive sleep apnea (OSA) is characterized by augmented sympathetic nerve activity. In our previous study, patients with OSA and an apnea-hyperpnea index (AHI)>55events/h showed increased single-unit muscle sympathetic nerve activity compared to patients with OSA and AHI of 30-55events/h. However, the prognostic impact in these patients remains unclear.

METHODS

Ninety-one OSA patients were included. All patients who had indication for continuous positive airway pressure (CPAP) were treated with CPAP. Patients were divided into three groups: mild/moderate OSA (S), AHI<30events/h (n=44); severe OSA (SS), AHI 30-55events/h (n=29); and very severe OSA (VSS), AHI>55events/h (n=18). The primary endpoint was a composite outcome composed of death, cardiovascular events, stroke, and heart failure with hospitalization.

RESULTS

In the 5-year follow-up, the primary event rate in the SS group [3 events (7%)] was the same as that in the S group [3 events (10%)]. However, the VSS group showed a significantly higher primary event rate among the three groups [6 events (33%), p<0.05]. In Cox regression analysis, the VSS group had the highest hazard ratio compared to other risk factors.

CONCLUSIONS

CPAP was effective for preventing cardiovascular disease in patients with severe OSA, however patients with very severe OSA still had a high event rate, indicating that CPAP treatment might be insufficient to reduce the OSA-related risk burden in patients with very severe OSA. Additional systemic medical treatment for CPAP might be needed in patients with very severe OSA.

Sex differences in sympathetic activity in obesity and its related hypertension

The prevalence of obesity is rapidly increasing in the United States, particularly among women. Approximately 60-70% of hypertension in adults may be directly attributed to obesity. In addition, maternal obesity is a major risk factor for hypertensive disorders during pregnancy. The underlying mechanisms for the association between obesity and cardiovascular risk are multifactorial, but activation of the sympathetic nervous system is one significant contributing factor. This brief review summarizes the current knowledge on sex differences in sympathetic activity in obesity and its related hypertension, with a focus on studies in humans. Evidence suggests that abdominal visceral fat, rather than subcutaneous fat, is related to augmented sympathetic activity regardless of sex. Race/ethnicity may affect the relationship between obesity and sympathetic activity. Obesity-related hypertension has an important neurogenic component, which is characterized by sympathetic overactivity. However, sex may influence the association between hypertension and sympathetic overactivity in obese people. Finally, both body weight and sympathetic overactivity seem to be involved in the development of gestational hypertensive disorders in women. Chronic hyperinsulinemia due to insulin resistance, high plasma levels of leptin, and/or obstructive sleep apnea may be responsible for sympathetic overactivity in obesity-related hypertension.

Novel Approach to Elucidate Human Baroreflex Regulation at the Brainstem Level: Pharmacological Testing During fMRI

Introduction: Brainstem nuclei govern the arterial baroreflex, which is crucial for heart rate and blood pressure control. Yet, brainstem function is difficult to explore in living humans and is therefore mostly studied using animal models or postmortem human anatomy studies. We developed a methodology to identify brainstem nuclei involved in baroreflex cardiovascular control in humans by combining pharmacological baroreflex testing with functional magnetic resonance imaging. Materials and Methods: In 11 healthy men, we applied eight repeated intravenous phenylephrine bolus doses of 25 and 75 μg followed by a saline flush using a remote-controlled injector during multiband functional magnetic resonance imaging (fMRI) acquisition of the whole brain including the brainstem. Continuous finger arterial blood pressure, respiration, and electrocardiogram (ECG) were monitored. fMRI data were preprocessed with a brainstem-specific pipeline and analyzed with a general linear model (GLM) to identify brainstem nuclei involved in central integration of the baroreceptor input. Results: Phenylephrine elicited a pressor response followed by a baroreflex-mediated lengthening of the RR interval (25 μg: 197 ± 15 ms; 75 μg: 221 ± 33 ms). By combining fMRI responses during both phenylephrine doses, we identified significant signal changes in the nucleus tractus solitarii (t = 5.97), caudal ventrolateral medulla (t = 4.59), rostral ventrolateral medulla (t = 7.11), nucleus ambiguus (t = 5.6), nucleus raphe obscurus (t = 6.45), and several other brainstem nuclei [p < 0.0005 family-wise error (few)-corr.]. Conclusion: Pharmacological baroreflex testing during fMRI allows characterizing central baroreflex regulation at the level of the brainstem in humans. Baroreflex-mediated activation and deactivation patterns are consistent with previous investigations in animal models. The methodology has the potential to elucidate human physiology and mechanisms of autonomic cardiovascular disease.

Continuous positive airway pressure alters brain microstructure and perfusion patterns in patients with obstructive sleep apnea

OBJECTIVES

To assess the effects of continuous positive airway pressure (CPAP) treatment on brain structure and function in patients with obstructive sleep apnea (OSA).

METHODS

A prospective study of seven OSA patients recruited from the sleep center at our institution was carried out. Patients were treated with six weeks of CPAP treatment. Pre-treatment and post-treatment magnetic resonance imaging (MRI) perfusion scans were obtained and compared to assess for treatment-induced changes. Microstructural changes were quantified using functional anistrophy (FA) and mean diffusivity (MD), and brain perfusion was quantified using cerebral blood flow (CBF) and cerebral blood volume (CBV).

RESULTS

Of the seven patients included the in study, six (85.7%) were male, and the mean age was 51 years (standard deviation = 13.14). Increased FA and decreased MD were found in the hippocampus, temporal lobes, fusiform gyrus, and occipital lobes. Decreased FA and increased MD were found in frontal regions for all patients (p < 0.05). Increased CBF and CBV were also observed following treatment (p < 0.05).

CONCLUSION

In addition to symptom resolution, CPAP treatment may allow for healing of OSA-induced brain damage as seen by restoration of brain structure and perfusion.

Cardiovascular outcomes of continuous positive airway pressure therapy for obstructive sleep apnea

Obstructive sleep apnea is a common disorder with increased risk for cardiovascular morbidity and mortality. The first choice of treatment of obstructive sleep apnea is continuous positive airway pressure, which reduces excessive daytime sleepiness and improves quality of life in sleep clinic cohorts. Nevertheless, the majority of patients with cardiovascular disease and concomitant obstructive sleep apnea do not report daytime sleepiness, and adherence to treatment is insufficient particularly in this group. The current article aims to give an updated overview of the impact of continuous positive airway pressure therapy on cardiovascular outcomes mainly based on the observational studies and the recent randomized controlled trials.

Postural and vestibular changes related to CPAP treatment in moderate-to-severe OSA patients: a 12-month longitudinal study

PURPOSE

To assess whether vestibulo-ocular reflex (VOR) gain, posturography parameters and related clinical outcomes can improve in OSA patients after 12 months of CPAP treatment, taking into consideration that a certain degree of vestibular dysfunction has been identified in these subjects.

METHODS

Vestibular, postural, clinical, and polygraphic parameters were assessed in 32 OSA patients before and after beneficial CPAP treatment by means of video head impulse test (vHIT), static posturography (SP), Dizziness Handicap Inventory (DHI), Epworth Sleepiness Scale (ESS), and Apnea-Hypopnea Index (AHI), respectively, and were compared by means of a "within-subject" ANOVA model and Spearman's rank correlation.

RESULTS

After the 12-month period of treatment, OSA patients demonstrated a significant reduction in AHI values, in both opened and closed eyes conditions of surface and length as well as in power spectra recorded in low, middle, and high frequency interval. Although a significant improvement was also recorded among DHI and ESS scores, VOR gain increase did not survive to post-hoc corrections. Finally, positive correlations between the differences between pre- and post-treatment AHI, ESS, and PS values were found.

CONCLUSIONS

The present work highlighted that postural instability and dizziness-related conditions due to OSA may improve after 12 months of CPAP treatment. Although VOR gain did not demonstrate significant improvement, this study might open future perspectives directed to assessing VOR gain changes after longer periods of CPAP treatment.

Effects of losartan and allopurinol on cardiorespiratory regulation in obstructive sleep apnoea

NEW FINDINGS

What is the central question of this study? In sleep apnoea, a putative link between intermittent hypoxia and hypertension is the generation of oxygen radicals by angiotensin II and xanthine oxidase within the chemoreflex arc and vasculature. We tested whether chemoreflex control of sympathetic outflow, hypoxic vasodilatation and blood pressure are altered by angiotensin blockade (losartan) and/or xanthine oxidase inhibition (allopurinol). What is the main finding and its importance? Both drugs lowered blood pressure without altering sympathetic outflow, reducing chemoreflex sensitivity or enhancing hypoxic vasodilatation. Losartan and allopurinol are effective therapies for achieving blood pressure control in sleep apnoea.

ABSTRACT

Chemoreflex sensitization produced by chronic intermittent hypoxia in rats is attenuated by angiotensin II type 1 receptor (AT₁ R) blockade. Both AT₁ R blockade and xanthine oxidase inhibition ameliorate chronic intermittent hypoxia-induced endothelial dysfunction. We hypothesized that treatment with losartan and allopurinol would reduce chemoreflex sensitivity and improve hypoxic vasodilatation in patients with obstructive sleep apnoea. Eighty-six hypertensive patients with apnoea-hypopnoea index ≥25 events h^-1 and no other cardiovascular, pulmonary, renal or metabolic disease were randomly assigned to receive allopurinol, losartan or placebo for 6 weeks. Treatment with other medications and/or continuous positive airway pressure remained unchanged. Tests of chemoreflex sensitivity and hypoxic vasodilatation were performed during wakefulness before and after treatment. Ventilation (pneumotachography), muscle sympathetic nerve activity (microneurography), heart rate (electrocardiography), arterial oxygen saturation (pulse oximetry), blood pressure (sphygmomanometry), forearm blood flow (venous occlusion plethysmography) and cerebral flow velocity (transcranial Doppler ultrasound) were measured during eupnoeic breathing and graded reductions in inspired O₂ tension. Losartan and allopurinol lowered arterial pressure measured during eupnoeic breathing and exposure to acute hypoxia. Neither drug altered the slopes of ventilatory, sympathetic or cardiovascular responses to acute hypoxia. We conclude that losartan and allopurinol are viable pharmacotherapeutic adjuncts for achieving blood pressure control in hypertensive obstructive sleep apnoea patients, even those who are adequately treated with continuous positive airway pressure.

Cardiorespiratory interaction with continuous positive airway pressure

The treatment of choice for obstructive sleep apnoea (OSA) is continuous positive airway pressure therapy (CPAP). Since its introduction in clinical practice, CPAP has been used in various clinical conditions with variable and heterogeneous outcomes. In addition to the well-known effects on the upper airway CPAP impacts on intrathoracic pressures, haemodynamics and blood pressure (BP) control. However, short- and long-term effects of CPAP therapy depend on multiple variables which include symptoms, underlying condition, pressure used, treatment acceptance, compliance and usage. CPAP can alter long-term cardiovascular risk in patients with cardiorespiratory conditions. Furthermore, the effect of CPAP on the awake patient differs from the effect on the patients while asleep, and this might contribute to discomfort and removal of the use interface. The purpose of this review is to highlight the physiological impact of CPAP on the cardiorespiratory system, including short-term benefits and long-term outcomes.

Obstructive sleep apnea is associated with altered midbrain chemical concentrations

Obstructive sleep apnea (OSA) is accompanied by altered structure and function in cortical, limbic, brainstem, and cerebellar regions. The midbrain is relatively unexamined, but contains many integrative nuclei which mediate physiological functions that are disrupted in OSA. We therefore assessed the chemistry of the midbrain in OSA in this exploratory study. We used a recently developed accelerated 2D magnetic resonance spectroscopy (2D-MRS) technique, compressed sensing-based 4D echo-planar J-resolved spectroscopic imaging (4D-EP-JRESI), to measure metabolites in the midbrain of 14 OSA (mean age±SD:54.6±10.6years; AHI:35.0±19.4; SAO2 min:83±7%) and 26 healthy control (50.7±8.5years) subjects. High-resolution T1-weighted scans allowed voxel localization. MRS data were processed with custom MATLAB-based software, and metabolite ratios calculated with respect to the creatine peak using a prior knowledge fitting (ProFit) algorithm. The midbrain in OSA showed decreased N-acetylaspartate (NAA; OSA:1.24±0.43, Control:1.47±0.41; p=0.03; independent samples t-test), a marker of neuronal viability. Increased levels in OSA over control subjects appeared in glutamate (Glu; OSA:1.23±0.57, Control:0.98±0.33; p=0.03), ascorbate (Asc; OSA:0.56±0.28, Control:0.42±0.20; (50.7±8.5years; p=0.03), and myo-inositol (mI; OSA:0.96±0.48, Control:0.72±0.35; p=0.03). No differences between groups appeared in γ-aminobutyric acid (GABA) or taurine. The midbrain in OSA patients shows decreased NAA, indicating neuronal injury or dysfunction. Higher Glu levels may reflect excitotoxic processes and astrocyte activation, and higher mI is also consistent with glial activation. Higher Asc levels may result from oxidative stress induced by intermittent hypoxia in OSA. Additionally, Asc and Glu are involved with glutamatergic processes, which are likely upregulated in the midbrain nuclei of OSA patients. The altered metabolite levels help explain dysfunction and structural deficits in the midbrain of OSA patients.

Impact of obstructive sleep apnoea and intermittent hypoxia on cardiovascular and cerebrovascular regulation

NEW FINDINGS

What is the topic of this review? This review examines the notion that obstructive sleep apnoea (OSA) and intermittent hypoxia (IH) have hormetic effects on vascular health. What advances does it highlight? Clinical (OSA patient) and experimental animal and human models report that IH is detrimental to vascular regulation. However, mild IH and, by extension, mild OSA also have physiological and clinical benefits. This review highlights clinical and experimental animal and human data linking OSA and IH to vascular disease and discusses how hormetic effects of OSA and IH relate to OSA severity, IH intensity and duration, and patient/subject age. Obstructive sleep apnoea (OSA) is associated with increased risk of cardiovascular and cerebrovascular disease, a consequence attributed in part to chronic intermittent hypoxia (IH) resulting from repetitive apnoeas during sleep. Although findings from experimental animal, and human, models have shown that IH is detrimental to vascular regulation, the severity of IH used in many of these animal studies [e.g. inspired fraction of oxygen (FI,O2) = 2-3%; oxygen desaturation index = 120 events h^-1 ] is considerably greater than that observed in the majority of patients with OSA. This may also explain disparities between animal and recently developed human models of IH, where IH severity is, by necessity, less severe (e.g. FI,O2 = 10-12%; oxygen desaturation index = 15-30 events h^-1 ). In this review, we highlight the current knowledge regarding the impact of OSA and IH on cardiovascular and cerebrovascular regulation. In addition, we critically discuss the recent notion that OSA and IH may have hormetic effects on vascular health depending on conditions such as OSA severity, IH intensity and duration, and age. In general, data support an independent causal link between OSA and vascular disease, particularly for patients with severe OSA. However, the data are equivocal for older OSA patients and patients with mild OSA, because advanced age and short-duration, low-intensity IH have been reported to provide a degree of protection against IH and ischaemic events such as myocardial infarction and stroke, respectively. Overall, additional studies are needed to investigate the beneficial/detrimental effects of mild OSA on the various vascular beds.

Effects of continuous positive airway pressure on neurocognitive architecture and function in patients with obstructive sleep apnoea: study protocol for a multicentre randomised controlled trial

OBJECTIVES

Many clinical studies have indicated that obstructive sleep apnoea (OSA), the most common chronic sleep disorder, may affect neurocognitive function, and that treatment for continuous positive airway pressure (CPAP) has some neurocognitive protective effects against the adverse effects of OSA. However, the effects of CPAP treatment on neurocognitive architecture and function remain unclear. Therefore, this multicentre trial was designed to investigate whether and when neurocognitive architecture and function in patients with OSA can be improved by CPAP treatment and to explore the role of gut microbiota in improving neurocognitive function during treatment.

METHODS/DESIGN

This study will be a multicentre, randomised, controlled trial with allocation concealment and assessor blinding. A total of 148 eligible patients with moderate to severe OSA will be enrolled from five sleep centres and randomised to receive CPAP with best supportive care (BSC) intervention or BSC intervention alone. Cognitive function, structure and function of brain regions, gut microbiota, metabolites, biochemical variables, electrocardiography, echocardiography, pulmonary function and arterial stiffness will be assessed at baseline before randomisation and at 3, 6 and 12 months.

ETHICS AND DISSEMINATION

This study has been approved by the Medical Ethics Committee of Shanghai Jiao Tong University Affiliated Sixth People's Hospital (approval number 2015-79). The results from this study will be published in peer-reviewed journals and at relevant conferences.

TRIAL REGISTRATION NUMBER

NCT02886156; pre-results.

The multi-level impact of chronic intermittent hypoxia on central auditory processing

During hypoxia, the tissues do not obtain adequate oxygen. Chronic hypoxia can lead to many health problems. A relatively common cause of chronic hypoxia is sleep apnea. Sleep apnea is a sleep breathing disorder that affects 3-7% of the population. During sleep, the patient's breathing starts and stops. This can lead to hypertension, attention deficits, and hearing disorders. In this study, we apply an established chronic intermittent hypoxemia (CIH) model of sleep apnea to study its impact on auditory processing. Adult rats were reared for seven days during sleeping hours in a gas chamber with oxygen level cycled between 10% and 21% (normal atmosphere) every 90s. During awake hours, the subjects were housed in standard conditions with normal atmosphere. CIH treatment significantly reduces arterial oxygen partial pressure and oxygen saturation during sleeping hours (relative to controls). After treatment, subjects underwent functional magnetic resonance imaging (fMRI) with broadband sound stimulation. Responses are observed in major auditory centers in all subjects, including the auditory cortex (AC) and auditory midbrain. fMRI signals from the AC are statistically significantly increased after CIH by 0.13% in the contralateral hemisphere and 0.10% in the ipsilateral hemisphere. In contrast, signals from the lateral lemniscus of the midbrain are significantly reduced by 0.39%. Signals from the neighboring inferior colliculus of the midbrain are relatively unaffected. Chronic hypoxia affects multiple levels of the auditory system and these changes are likely related to hearing disorders associated with sleep apnea.