Endotyping, phenotyping and personalised therapy in obstructive sleep apnoea: are we there yet?

Obstructive sleep apnoea (OSA) was traditionally thought to be mainly caused by obesity and upper airway crowding, and hence OSA management was not personalised according to particular characteristics, with most symptomatic patients receiving continuous positive airway pressure therapy. Recent advances in our understanding have identified additional potential and distinct causes of OSA (endotypes), and subgroups of patients (phenotypes) with increased risk of cardiovascular complications. In this review, we discuss the evidence to date as to whether there are distinct clinically useful endotypes and phenotypes of OSA, and the challenges to the field in moving towards delivering personalised therapy in OSA.

Effect of obstructive sleep apnoea on retinal microvascular function: a randomised controlled trial.

PURPOSE: Retinal microvascular endothelial dysfunction is thought to be of importance in the development of ocular vascular diseases. Obstructive sleep apnoea (OSA) causes macrovascular endothelial dysfunction, but the effect of OSA on retinal microvascular endothelial function is not known. We aimed to determine the effect of OSA on retinal microvascular function. METHODS: We conducted a multi-centre, double-blind, randomised, parallel, controlled trial in patients with known moderate-to-severe OSA, established on continuous positive airway pressure (CPAP). Participants were randomised to 14 nights of either continued CPAP or sham CPAP to generate a return of OSA. Retinal vascular responses to flickering light were measured using dynamic vessel analysis both at baseline and after 14 nights of intervention. The primary outcome was the change from baseline to follow-up in the area under the curve of the arteriolar response to flickering light, sham CPAP versus continued CPAP. RESULTS: Nineteen patients were randomised to sham CPAP, and 18 patients were randomised to continued CPAP. There was no significant effect of CPAP withdrawal and return of OSA on retinal responses, with a change in the area under the curve of the arteriole response to flickering light of + 3.8 arbitrary units (95% CI - 10.6 to + 18.2, p = 0.59), sham CPAP versus continued CPAP. CONCLUSIONS: CPAP withdrawal and a return of OSA had no significant effect on retinal microvascular responses. This contrasts with the effect of CPAP withdrawal on macrovascular endothelial function and suggests that OSA has different effects on macrovascular and microvascular endothelial function. ISRCTN 78082983, 23/10/2014, Prospectively registered.

Obstructive sleep apnoea and the progression of thoracic aortic aneurysm: a prospective cohort study.

BACKGROUND: Obstructive sleep apnoea (OSA) is associated with an increased prevalence of aortic aneurysms and it has also been suggested that severe OSA furthers aneurysm expansion in the abdomen. We evaluated whether OSA is a risk factor for the progression of ascending thoracic aortic aneurysm (TAA). METHODS: Patients with TAA underwent yearly standardised echocardiographic measurements of the ascending aorta over 3 years and two level III sleep studies. The primary outcome was the expansion rate of TAA in relation to the apnoea-hypopnoea index (AHI). Secondary outcomes included surveillance for aortic events (composite end-points of rupture/dissection, elective surgery or death). RESULTS: Between July 2014 and March 2020, 230 patients (median age 70 years, 83.5% male) participated in the cohort. At baseline, 34.8% of patients had AHI ≥15 events·h-1. There was no association between TAA diameter and AHI at baseline. After 3 years, mean±sd expansion rates were 0.55±1.25 mm at the aortic sinus and 0.60±1.12 mm at the ascending aorta. In the regression analysis, after controlling for baseline diameter and cardiovascular risk factors, there was strong evidence for a positive association of TAA expansion with AHI (aortic sinus estimate 0.025 mm, 95% CI 0.009-0.040 mm; p<0.001 and ascending aorta estimate 0.026 mm, 95% CI 0.011-0.041 mm; p=0.001). 20 participants (8%) experienced an aortic event; however, there was no association with OSA severity. CONCLUSION: OSA may be a modest but independent risk factor for faster TAA expansion and thus potentially contributes to life-threatening complications in aortic disease.

Markers of adipose tissue hypoxia are elevated in subcutaneous adipose tissue of severely obese patients with obesity hypoventilation syndrome but not in the moderately obese.

It has been suggested that metabolic dysfunction in obesity is at least in part driven by adipose tissue (AT) hypoxia. However, studies on AT hypoxia in humans have shown conflicting data. Therefore we aimed to investigate if markers of AT hypoxia were present in the subcutaneous AT of severly obese individuals (class III obesity) with and without hypoventilation syndrome (OHS) in comparison to moderately obese (class I obesity) and lean controls. To provide a proof-of-concept study, we quantified AT hypoxia by hypoxia inducible factor 1 A (HIF1A) protein abundance in human participants ranging from lean to severly obese (class III obesity). On top of that nightly arterial O2 saturation in individuals with obesity OHS was assessed. Subjects with class III obesity (BMI > 40 kg/m2) and OHS exhibited significantly higher adipose HIF1A protein levels versus those with class I obesity (BMI 30-34.9 kg/m2) and lean controls whereas those with class III obesity without OHS showed an intermediate response. HIF1A gene expression was not well correlated with protein abundance. Although these data demonstrate genuine AT hypoxia in the expected pathophysiological context of OHS, we did not observe a hypoxia signal in lesser degrees of obesity suggesting that adipose dysfunction may not be driven by hypoxia in moderate obesity.

Effects of suboptimal adherence of CPAP therapy on symptoms of obstructive sleep apnoea: a randomised, double-blind, controlled trial.

INTRODUCTION: Continuous positive airway pressure (CPAP) is currently the treatment of choice for sleepiness in patients with obstructive sleep apnoea (OSA); however, adherence is often thought to be suboptimal. We investigated the effects of suboptimal CPAP usage on objective and subjective sleepiness parameters in patients with OSA. MATERIAL AND METHODS: In this 2-week, parallel, double-blind, randomised controlled trial we enrolled moderate-to-severe OSA patients with excessive pre-treatment daytime sleepiness (Epworth sleepiness scale (ESS) score >10 points) who had suboptimal CPAP adherence over ≥12 months (mean nightly usage time 3-4 h). Patients were allocated through minimisation to either subtherapeutic CPAP ("sham CPAP") or continuation of CPAP ("therapeutic CPAP"). A Bayesian analysis with historical priors calculated the posterior probability of superiority. RESULTS: Between May, 2016 and November, 2018, 57 patients (aged 60±8 years, 79% male, 93% Caucasian) were allocated in total, and 52 who completed the study (50% in each arm) were included in the final analysis. The unadjusted ESS score increase was 2.4 points (95% CI 0.6-4.2, p=0.01) in the sham-CPAP group when compared to continuing therapeutic CPAP. The probability of superiority of therapeutic CPAP over sham CPAP was 90.4% for ESS, 90.1% for systolic blood pressure and 80.3% for diastolic blood pressure. CONCLUSIONS: Patients with moderate-to-severe OSA and daytime sleepiness are still getting a substantial benefit from suboptimal CPAP adherence, albeit not as much as they might get if they adhered more. Whether a similar statement can be made for even lower adherence levels remains to be established in future trials.

Effect of Supplemental Oxygen on Blood Pressure in Obstructive Sleep Apnea (SOX). A Randomized Continuous Positive Airway Pressure Withdrawal Trial.

RATIONALE: Obstructive sleep apnea (OSA) is associated with systemic hypertension. Either overnight intermittent hypoxia, or the recurrent arousals that occur in OSA, could cause the daytime increases in blood pressure (BP). OBJECTIVES: To establish the role of intermittent hypoxia in the increased morning BP in patients with OSA. METHODS: Randomized, double-blinded, crossover trial assessing the effects of overnight supplemental oxygen versus air (sham) on morning BP, after continuous positive airway pressure (CPAP) withdrawal in patients with moderate to severe OSA. The primary outcome was the change in home morning BP after CPAP withdrawal for 14 nights, oxygen versus air. Secondary outcomes included oxygen desaturation index (ODI), apnea-hypopnea index (AHI), subjective sleepiness (Epworth Sleepiness Scale score), and objective sleepiness (Oxford Sleep Resistance Test). MEASUREMENTS AND MAIN RESULTS: Supplemental oxygen virtually abolished the BP rise after CPAP withdrawal and, compared with air, significantly reduced the rise in mean systolic BP (-6.6 mm Hg; 95% confidence interval [CI], -11.3 to -1.9; P = 0.008), mean diastolic BP (-4.6 mm Hg; 95% CI, -7.8 to -1.5; P = 0.006), and median ODI (-23.8/h; interquartile range, -31.0 to -16.3; P < 0.001) after CPAP withdrawal. There was no significant difference, oxygen versus air, in AHI, subjective sleepiness, or objective sleepiness. CONCLUSIONS: Supplemental oxygen virtually abolished the rise in morning BP during CPAP withdrawal. Supplemental oxygen substantially reduced intermittent hypoxia, but had a minimal effect on markers of arousal (including AHI), subjective sleepiness, or objective sleepiness. Therefore intermittent hypoxia, and not recurrent arousals, appears to be the dominant cause of daytime increases in BP in OSA.

Minimum important difference of the Epworth Sleepiness Scale in obstructive sleep apnoea: estimation from three randomised controlled trials.

BACKGROUND: The Epworth Sleepiness Scale (ESS) is a widely used tool for assessing sleepiness in patients with obstructive sleep apnoea (OSA). We aimed to estimate the minimal important difference (MID) in patients with OSA. METHODS: We used individual data from three randomised controlled trials (RCTs) in patients with OSA where the preintervention to postintervention change in ESS was used as a primary outcome. We used anchor-based linear regression and responder analysis approaches to estimate the MID. For anchors, we used the change in domains of the Functional Outcomes of Sleep Questionnaire and 36-Item Short Form Health Survey. We also used the distribution-based approaches Cohen's effect size, SE of measurement and empirical rule effect size to support the anchor-based estimates. The final MID was determined by triangulating all estimates to a single MID. FINDINGS: A total of 639 patients with OSA were included in our analyses across the three RCTs with a median (IQR) baseline ESS score of 10 (6-13). The median (IQR) ESS change score overall was -2 (-5 to 1). The anchor-based estimates of the MID were between -1.74 and -4.21 points and estimates from the responder analysis were between -1 and -3 points. Distribution-based estimates were smaller, ranging from -1.46 to -2.36. INTERPRETATION: We propose an MID for the ESS of 2 points in patients with OSA with a disease severity from mild to severe. This estimate provides the means to plan trials and interpret the clinical relevance of changes in ESS. TRIAL REGISTRATION NUMBER: Provent, NCT01332175; autoCPAP trial, NCT00280800; MOSAIC,ISRCTN (3416388).

Effects of short-term continuous positive airway pressure withdrawal on cerebral vascular reactivity measured by blood oxygen level-dependent magnetic resonance imaging in obstructive sleep apnoea: a randomised controlled trial.

Impaired cerebral vascular reactivity (CVR) increases long-term stroke risk. Obstructive sleep apnoea (OSA) is associated with peripheral vascular dysfunction and vascular events. The aim of this trial was to evaluate the effect of continuous positive airway pressure (CPAP) withdrawal on CVR.41 OSA patients (88% male, mean age 57±10 years) were randomised to either subtherapeutic or continuation of therapeutic CPAP. At baseline and after 2 weeks, patients underwent a sleep study and magnetic resonance imaging (MRI). CVR was estimated by quantifying the blood oxygen level-dependent (BOLD) MRI response to breathing stimuli.OSA did recur in the subtherapeutic CPAP group (mean treatment effect apnoea-hypopnoea index +38.0 events·h-1, 95% CI 24.2-52.0; p<0.001) but remained controlled in the therapeutic group. Although there was a significant increase in blood pressure upon CPAP withdrawal (mean treatment effect +9.37 mmHg, 95% CI 1.36-17.39; p=0.023), there was no significant effect of CPAP withdrawal on CVR assessed via BOLD MRI under either hyperoxic or hypercapnic conditions.Short-term CPAP withdrawal did not result in statistically significant changes in CVR as assessed by functional MRI, despite the recurrence of OSA. We thus conclude that, unlike peripheral endothelial function, CVR is not affected by short-term CPAP withdrawal.

Nocturnal cerebral hypoxia in obstructive sleep apnoea: a randomised controlled trial.

Cerebral hypoxia may promote cerebral damage in patients with obstructive sleep apnoea (OSA). We investigated whether OSA patients experience nocturnal cerebral hypoxia that is prevented by continuous positive airway pressure (CPAP).OSA patients using CPAP underwent sleep studies including pulse oximetry (arterial oxygen saturation (SpO2 )) and near-infrared spectroscopy to monitor cerebral tissue oxygenation (CTO) at baseline and after 2 weeks on either subtherapeutic or therapeutic CPAP according to randomised allocation. Changes in oxygenation at end of the 2-week intervention were compared between groups.Among 21 patients (mean apnoea/hypopnoea index 50.3 events·h-1), OSA recurred in all nine patients using subtherapeutic CPAP and in none of the patients using therapeutic CPAP: mean (95% CI) between-group differences in changes of oxygen desaturation index from baseline to 2 weeks +40.7 (31.1-50.4) events·h-1 for SpO2 and +37.0 (25.3-48.7) events·h-1 for CTO (both p<0.001). Mean nocturnal SpO2 and CTO decreased more in patients using subtherapeutic versus therapeutic CPAP: -2.4 (-3.4--1.1)% and -3.8 (-7.4--0.1)%, respectively; both p<0.03. Severe CTO drops ≥13% associated with cerebral dysfunction in previous studies occurred in four out of nine patients using subtherapeutic CPAP, but in none out of 12 patients using therapeutic CPAP (p=0.01).In patients with OSA, CPAP withdrawal resulted in nocturnal cerebral deoxygenation, suggesting a role of cerebral hypoxia in predisposing untreated OSA patients to cerebral damage.

Continuous positive airway pressure effect on visual acuity in patients with type 2 diabetes and obstructive sleep apnoea: a multicentre randomised controlled trial.

We sought to establish whether continuous positive airway pressure (CPAP) for obstructive sleep apnoea (OSA) in people with type 2 diabetes and diabetic macular oedema (DMO) improved visual acuity.We randomly assigned 131 eligible patients aged 30-85 years from 23 UK centres with significant DMO causing visual impairment (LogMAR letters identified ≥39 and ≤78, score 0.92-0.14) plus severe OSA on screening to either usual ophthalmology care (n=67) or usual ophthalmology care plus CPAP (n=64) for 12 months.Mean age of participants was 64 years, 73% male, mean body mass index 35.0 kg·m- 2 Mean 4% oxygen desaturation index was 36 events·h-1 There was no significant difference in the visual acuity at 12 months between the CPAP group and the control group (mean LogMAR 0.33 (95% CI 0.29-0.37) versus 0.31 (95% CI 0.27-0.35); p=0.39), and no significant correlation between change in LogMAR and average CPAP use. The median±sd (range) daily CPAP use was 3.33±2.25 (0-7.93) h at 3 months, 3.19±2.54 (0-8.07) h at 6 months and 3.21±2.70 (0-7.98) h at 12 months.CPAP therapy for OSA did not improve visual acuity in people with type 2 diabetes and DMO compared with usual care alone over 12 months.

Night-to-night variability of obstructive sleep apnea.

One night of a sleep study is the standard for diagnosis and exclusion of obstructive sleep apnea. Single testing requires high sensitivity of the test method and a stable disease of interest to warrant a low rate of false-negative tests. Obstructive sleep apnea is diagnosed and graded by conventional thresholds of apneas and hypopneas per hour of sleep, and treatment is usually initiated in the presence of symptoms. The aim of this study was to assess night-to-night variability of obstructive sleep apnea to reassess the current practice. Seventy-seven patients previously diagnosed with obstructive sleep apnea, randomised to continuous positive airway pressure withdrawal within four trials, performed nightly pulse-oximetry over 2 weeks while off continuous positive airway pressure. The main outcome of interest was the coefficient of variation of the oxygen desaturation index marking night-to-night variability in obstructive sleep apnea. Obstructive sleep apnea was categorised according to conventional thresholds using oxygen desaturation index (no obstructive sleep apnea: <5 per h; mild: 5-15 per h; moderate: 15-30 per h; and severe: >30 per h). High night-to-night variability of obstructive sleep apnea was evidenced by a coefficient of variation of oxygen desaturation index of 31.1% (SD 16.5). Differences in oxygen desaturation index of >10 per h between nights were found in 84.4% and shifts in obstructive sleep apnea severity category in 77.9% of patients. The probability of missing moderate obstructive sleep apnea was up to 60%. Variability was higher in less severe obstructive sleep apnea. Obstructive sleep apnea shows a considerable night-to-night variability. Single-night diagnostic sleep studies are prone to miscategorise obstructive sleep apnea if arbitrary thresholds are used. Thus, treatment decisions should be based less on the conventional derivatives from sleep studies, especially in patients with less severe obstructive sleep apnea. CLINICAL TRIAL REGISTRATION: www.controlled-trials.com (ISRCTN 93153804, ISRCTN 73047833) and www.clinicaltrials.gov (NCT01332175 & NCT02050425).

Effect of OSA on hypoxic and inflammatory markers during CPAP withdrawal: Further evidence from three randomized control trials.

BACKGROUND AND OBJECTIVE: Obstructive sleep apnoea (OSA) is associated with cardiovascular disease. Intermittent hypoxia, endothelial dysfunction and adipose tissue-mediated inflammation have all been linked to cardiovascular disease in OSA. We therefore explored the effect of OSA on relevant associated blood markers: adrenomedullin (ADM), endocan, endothelin-1 (ET-1), resistin and vascular endothelial growth factor (VEGF). METHODS: Patients with OSA, established on and compliant with continuous positive airways pressure (CPAP) therapy for >1 year were included from three randomized controlled trials, conducted at two centres. Patients were randomized to either continued therapeutic CPAP or sham CPAP (CPAP withdrawal) for 2 weeks. Blood markers were measured at baseline and at 14 days and the treatment effect between sham CPAP and therapeutic CPAP was analysed. RESULTS: A total of 109 patients were studied (therapeutic CPAP n = 54, sham CPAP n = 55). Sham CPAP was associated with a return of OSA (between-group difference in oxygen desaturation index (ODI) 36.0/h, 95% CI 29.9-42.2, P < 0.001). Sham CPAP was associated with a reduction in ADM levels at 14 days (-26.0 pg/mL, 95% CI -47.8 to -4.3, P = 0.02), compared to therapeutic CPAP. Return of OSA was not associated with changes in endocan, ET-1, resistin or VEGF. CONCLUSION: Whilst CPAP withdrawal was associated with return of OSA, it was associated with an unexpected significant reduction in the vasodilator ADM and not with expected increases in hypoxia-induced markers, markers of endothelial function or resistin. We propose that the vascular effects occurring in OSA may be brought about by other mechanisms, perhaps partly through a reduction in ADM.

Blood Pressure Variability in Obstructive Sleep Apnoea: Data from 4 Randomised Controlled CPAP Withdrawal Trials.

BACKGROUND: Increased daytime blood pressure variability (BPV) is associated with cardiovascular risk. Preliminary data suggest that obstructive sleep apnoea (OSA) might contribute to increased daytime BPV. OBJECTIVE: The aim of this study was to evaluate the effect of continuous positive airway pressure (CPAP) therapy withdrawal on daytime BPV. METHODS: A total of 183 patients previously diagnosed with OSA and treated with CPAP were randomised to either continue or withdraw from CPAP within 4 trials. Office morning BP was measured in triplicate at baseline and at follow-up (day 14). In addition, the participants performed BP measurements at home on a daily basis (days 1-13). The main outcome of interest was the treatment effect on within-visit BPV expressed as the standard deviation (SD) of the triplicate measurements. Additional outcomes included morning home BPV and day-to-day home BPV. RESULTS: Within-visit variability in systolic BP significantly increased in response to recurrence of OSA in the CPAP withdrawal group (difference between groups in SD of systolic BPV, +1.14 mm Hg, 95% CI +0.20/+2.09, p = 0.02). There was no statistically significant effect on within-visit variability in diastolic BP (p = 0.38) or heart rate (p = 0.07). Neither morning home BP variability (systolic BPV, p = 0.81; diastolic BPV, p = 0.46) nor day-to-day variability in home BP measurements (systolic BPV, p = 0.61; diastolic BPV, p = 0.58) differed significantly between the groups. CONCLUSION: CPAP withdrawal results in a minor increase in within-visit variability in office systolic BP, but it has no effect on home BPV or day-to-day BPV. Although the treatment effect may be blunted by antihypertensives, it is unlikely that OSA contributes to cardiovascular risk via elevated daytime BPV.

Effect of Home Noninvasive Ventilation With Oxygen Therapy vs Oxygen Therapy Alone on Hospital Readmission or Death After an Acute COPD Exacerbation: A Randomized Clinical Trial.

Importance: Outcomes after exacerbations of chronic obstructive pulmonary disease (COPD) requiring acute noninvasive ventilation (NIV) are poor and there are few treatments to prevent hospital readmission and death. Objective: To investigate the effect of home NIV plus oxygen on time to readmission or death in patients with persistent hypercapnia after an acute COPD exacerbation. Design, Setting, and Participants: A randomized clinical trial of patients with persistent hypercapnia (Paco2 >53 mm Hg) 2 weeks to 4 weeks after resolution of respiratory acidemia, who were recruited from 13 UK centers between 2010 and 2015. Exclusion criteria included obesity (body mass index [BMI] >35), obstructive sleep apnea syndrome, or other causes of respiratory failure. Of 2021 patients screened, 124 were eligible. Interventions: There were 59 patients randomized to home oxygen alone (median oxygen flow rate, 1.0 L/min [interquartile range {IQR}, 0.5-2.0 L/min]) and 57 patients to home oxygen plus home NIV (median oxygen flow rate, 1.0 L/min [IQR, 0.5-1.5 L/min]). The median home ventilator settings were an inspiratory positive airway pressure of 24 (IQR, 22-26) cm H2O, an expiratory positive airway pressure of 4 (IQR, 4-5) cm H2O, and a backup rate of 14 (IQR, 14-16) breaths/minute. Main Outcomes and Measures: Time to readmission or death within 12 months adjusted for the number of previous COPD admissions, previous use of long-term oxygen, age, and BMI. Results: A total of 116 patients (mean [SD] age of 67 [10] years, 53% female, mean BMI of 21.6 [IQR, 18.2-26.1], mean [SD] forced expiratory volume in the first second of expiration of 0.6 L [0.2 L], and mean [SD] Paco2 while breathing room air of 59 [7] mm Hg) were randomized. Sixty-four patients (28 in home oxygen alone and 36 in home oxygen plus home NIV) completed the 12-month study period. The median time to readmission or death was 4.3 months (IQR, 1.3-13.8 months) in the home oxygen plus home NIV group vs 1.4 months (IQR, 0.5-3.9 months) in the home oxygen alone group, adjusted hazard ratio of 0.49 (95% CI, 0.31-0.77; P = .002). The 12-month risk of readmission or death was 63.4% in the home oxygen plus home NIV group vs 80.4% in the home oxygen alone group, absolute risk reduction of 17.0% (95% CI, 0.1%-34.0%). At 12 months, 16 patients had died in the home oxygen plus home NIV group vs 19 in the home oxygen alone group. Conclusions and Relevance: Among patients with persistent hypercapnia following an acute exacerbation of COPD, adding home noninvasive ventilation to home oxygen therapy prolonged the time to readmission or death within 12 months. Trial Registration: clinicaltrials.gov Identifier: NCT00990132.

Effects of CPAP therapy withdrawal on exhaled breath pattern in obstructive sleep apnoea.

BACKGROUND: Obstructive sleep apnoea (OSA) is highly prevalent and associated with cardiovascular and metabolic changes. OSA is usually diagnosed by polysomnography which is time-consuming and provides little information on the patient's phenotype thus limiting a personalised treatment approach. Exhaled breath contains information on metabolism which can be analysed by mass spectrometry within minutes. The objective of this study was to identify a breath profile in OSA recurrence by use of secondary-electrospray-ionization-mass spectrometry (SESI-MS). METHODS: Patients with OSA effectively treated with CPAP were randomised to either withdraw treatment (subtherapeutic CPAP) or continue therapeutic CPAP for 2 weeks. Exhaled breath analysis by untargeted SESI-MS was performed at baseline and 2 weeks after randomisation. The primary outcome was the change in exhaled molecular breath pattern. RESULTS: 30 patients with OSA were randomised and 26 completed the trial according to the protocol. CPAP withdrawal led to a recurrence of OSA (mean difference in change of oxygen desaturation index between groups +30.3/h; 95% CI 19.8/h,40.7/h, p<0.001) which was accompanied by a significant change in 62 exhaled features (16 metabolites identified). The panel of discriminating mass-spectral features allowed differentiation between treated and untreated OSA with a sensitivity of 92.9% and a specificity of 84.6%. CONCLUSION: Exhaled breath analysis by SESI-MS allows rapid and accurate detection of OSA recurrence. The technique has the potential to characterise an individual's metabolic response to OSA and thus makes a comprehensible phenotyping of OSA possible. TRIAL REGISTRATION NUMBER: NCT02050425 (registered at ClinicalTrials.gov).

Intrathoracic pressure swings induced by simulated obstructive sleep apnoea promote arrhythmias in paroxysmal atrial fibrillation.

AIMS: There is preliminary evidence for a link between obstructive sleep apnoea (OSA) and arrhythmias such as paroxysmal atrial fibrillation (PAF) and sudden cardiac death but underlying mechanisms remain largely unknown. METHODS AND RESULTS: In this interventional crossover study, we evaluated whether intrathoracic pressure changes, induced by simulated OSA, trigger premature cardiac beats, and alter measures of ventricular repolarization [QTc and Tpeak-to-Tend (TpTec) intervals] in patients with PAF. 12-Lead-electrocardiograms were recorded continuously in 44 patients, while simulating obstructive apnoea (Mueller manoeuvre, MM), obstructive hypopnoea (inspiration through a threshold load, ITH), end-expiratory central apnoea (AP), and during normal breathing (NB) in randomized order. The prevalence of OSA in these 44 patients was assessed by a sleep study. Atrial premature beats (APBs) occurred more frequently during MM (55% of patients) and ITH (32%), but not during AP (14%), compared with NB (9%) (P < 0.001, P = 0.006 and P = 0.688, respectively). Mueller manoeuvre led to a significant prolongation of QTc and TpTec intervals (+17.3 ms, P < 0.001 and +4.3 ms, P = 0.005). Inspiration through a threshold load significantly increased QTc (+9.6 ms, P < 0.001) but not TpTec. End-expiratory central apnoea did not alter QTc and TpTec intervals. According to the sleep study, 56% of patients had OSA (apnoea hypopnoea index ≥5). CONCLUSION: Simulated OSA induces APBs which may be important in patients with PAF, because the majority of episodes of PAF has been shown to be triggered by APBs. Simulated OSA leads to a significant prolongation of ventricular repolarization.

Effect of CPAP Withdrawal on myocardial perfusion in OSA: A randomized controlled trial.

BACKGROUND AND OBJECTIVE: Obstructive sleep apnoea (OSA) is highly prevalent and associated with an increased incidence of cardiovascular events. Endothelial dysfunction is the proposed causative mechanism. Continuous positive airway pressure (CPAP) is presumed to improve cardiovascular outcome in OSA. CPAP withdrawal was recently shown to lead to peripheral endothelial dysfunction. However, it is not known whether short-term CPAP withdrawal reduces myocardial perfusion in OSA. METHODS: In this double-blind randomized controlled study, 45 patients with moderate to severe OSA previously adherent to CPAP were assigned to either subtherapeutic or continuing therapeutic CPAP for 2 weeks. The primary outcome was adenosine-induced myocardial blood flow (MBF) as a measure of endothelial function, assessed by (13) N-ammonia positron emission tomography. Secondary outcomes were measures of dermal and renal microvascular function, morning blood pressure (BP) and heart rate. RESULTS: Despite return of OSA associated with significant increases in BP (+9.1 mm Hg, 95% CI +4.9 to +13.4 mm Hg, P < 0.001) and heart rate (+9.6 bpm, 95% confidence interval (CI) +4.6 to +14.6 bpm, P < 0.001), CPAP withdrawal had no significant effect on maximal myocardial perfusion capacity (hyperaemic MBF -0.01 ml/min/g, 95% CI -0.33 to +0.24 ml/min/g, P = 0.91), nor renal and dermal microvascular function. CONCLUSION: In patients with OSA, a short-term CPAP withdrawal does not lead to detectable impairment of coronary endothelial function, as has been demonstrated in the brachial artery, despite a clinically relevant increase in BP of nearly 10 mm Hg. There was also no evidence of an impairment of renal or dermal microvascular function.

Does either obesity or OSA severity influence the response of autotitrating CPAP machines in very obese subjects?

PURPOSE: The pressures delivered by autotitrating continuous positive airways pressure (CPAP) devices not only treat obstructive sleep apnoea (OSA) effectively but also give potentially interesting physiological information about the forces impinging on the pharynx. In earlier work from this unit, we used correlations between autoCPAP pressure and both OSA severity and obesity, to construct an algorithm to estimate the fixed CPAP pressure a patient required for subsequent clinical use. We wished to discover if these relationships could be reliably extended to a much more obese group. METHODS: We performed a prospective cohort study in an obese population. Measurements of obesity were made, OSA severity was recorded, and the 95th centile autoCPAP pressure was recorded during 1 week of autoCPAP. Spearman's rank correlation was performed between measurements of obesity and autoCPAP pressure, and between OSA severity and autoCPAP pressure. RESULTS: Fifty-four obese individuals (median body mass index (BMI) 43.0 kg/m(2)), 52 % of whom had OSA (apnoea-hypopnoea index (AHI) ≥ 15), had a median 95th centile autoCPAP pressure of 11.8 cmH2O. We found no significant correlation between autoCPAP pressure and neck circumference, waist circumference or BMI. There was a moderate correlation between autoCPAP pressure and OSA severity (AHI r = 0.34, p = 0.02; oxygen desaturation index (ODI) r = 0.48, p < 0.001). CONCLUSIONS: In this population, neither BMI nor neck circumference nor waist circumference is predictive of autoCPAP pressure. Therefore, the previously derived algorithm does not adequately predict the fixed CPAP pressure for subsequent clinical use in these obese individuals. In addition, some subjects without OSA generated high autoCPAP pressures, and thus, the correlation between OSA severity and autoCPAP pressure was only moderate.