Effect of intensified diuretic therapy on overnight rostral fluid shift and obstructive sleep apnoea in patients with uncontrolled hypertension

Acetazolamide Reduces Blood Pressure and Sleep-Disordered Breathing in Patients With Hypertension and Obstructive Sleep Apnea: A Randomized Controlled Trial

STUDY OBJECTIVES

The carbonic anhydrase inhibitor acetazolamide (AZT) modulates blood pressure at high altitude and reduces sleep-disordered breathing in patients with obstructive sleep apnea (OSA). We aimed to investigate the treatment effect of AZT and in combination with continuous positive airway pressure (CPAP) on blood pressure in patients with hypertension and OSA.

METHODS

In a prospective, randomized, three-way crossover study, 13 male patients with hypertension and moderate to severe OSA (age 64 ± 7 years, body mass index 29 ± 4 kg/m², and mean apnea-hypopnea index 37 ± 23 events/h) received AZT, CPAP, or AZT plus CPAP for 2-week periods. Antihypertensive medication was washed out. Office and 24-hour blood pressure, arterial stiffness, polygraphic sleep study data, and blood chemistry were compared.

RESULTS

AZT alone and AZT plus CPAP, but not CPAP alone, reduced office mean arterial pressure compared to baseline (-7 [95% CI -11 to -4], -7 [95% CI -11 to -4] and -1 [95% CI -5 to 4] mmHg, respectively; repeated- measures analysis of variance (RM-ANOVA; P = .015). Aortic systolic pressure and augmentation index, assessed by radial artery oscillatory tonometry, were unaffected by CPAP but decreased after AZT and AZT plus CPAP (RM-ANOVA P = .030 and .031, respectively). The apnea-hypopnea index was significantly reduced in all three treatment arms, most prominently by AZT plus CPAP (RM-ANOVA P = .003). The reduction of venous bicarbonate concentration following AZT was correlated with the change of apnea-hypopnea index (r = 0.66, P = .013).

CONCLUSIONS

AZT reduced blood pressure, vascular stiffness, and sleep-disordered breathing in patients with OSA and comorbid hypertension. Carbonic anhydrase inhibition may constitute a potential target for drug therapy in patients with sleep apnea and comorbid hypertension.

CLINICAL TRIAL REGISTRATION

Registry: ClinicalTrials.gov; Identifier: NCT02220803; Title: A Short Term Open, Randomized Cross-over Trial Exploring the Effect of Carbonic Anhydrase Inhibition by Acetazolamide on Sleep Apnea Associated Hypertension and Vascular Dysfunction; URL: https://clinicaltrials.gov/ct2/show/NCT02220803 and Registry: EU Clinical Trials Register; EudraCT Number: 2013-004866-33; Title: A short term open, randomized cross over trial exploring the effect of carbonic anhydrase inhibition by acetazolamide on sleep apnea associated hypertension; URL: https://www.clinicaltrialsregister.eu/ctr-search/search?query=2013-004866-33.

Neuroendocrine and Inflammatory Responses to Losartan and Continuous Positive Airway Pressure in Patients with Hypertension and Obstructive Sleep Apnea. A Randomized Controlled Trial

RATIONALE

Blood pressure reduction in response to antihypertensive agents is less for patients with obstructive sleep apnea (OSA). Increased sympathetic and inflammatory activity, as well as alterations in the renin-angiotensin-aldosterone system, may play a role in this context.

OBJECTIVES

To address the cardiovascular mechanisms involved in response to an angiotensin II receptor antagonist, losartan, and continuous positive airway pressure (CPAP) as add-on treatment for hypertension and OSA.

METHODS

Newly diagnosed hypertensive patients with or without OSA (allocated in a 2:1 ratio for OSA vs. no OSA) were treated with losartan 50 mg daily during a 6-week two-center, open-label, prospective, case-control, parallel-design study. In the second 6-week, sex-stratified, open-label, randomized, parallel-design study, all subjects with OSA continued to receive losartan and were randomly assigned to either CPAP as add-on therapy or to no CPAP (1:1 ratio for CPAP vs. no CPAP). Study subjects without OSA were followed in parallel while they continued to take losartan. Blood samples were collected at baseline, after 6 weeks, and after 12 weeks for analysis of renin, aldosterone, noradrenaline, adrenaline, and inflammatory markers.

MEASUREMENTS AND MAIN RESULTS

Fifty-four patients with OSA and 35 without OSA were included in the first 6-week study. Losartan significantly increased renin levels and reduced aldosterone levels in the group without OSA. There was no significant decrease in aldosterone levels among patients with OSA. Add-on CPAP treatment tended to lower aldosterone levels, but reductions were more pronounced in measures of sympathetic activity. No significant changes in inflammatory markers were observed following treatment with losartan and CPAP.

CONCLUSIONS

Hypertensive patients with OSA responded to losartan treatment with smaller reductions in aldosterone compared with hypertensive patients without OSA. Sympathetic system activity seemed to respond primarily to add-on CPAP treatment in patients with newly discovered hypertension and OSA. Clinical trial registered with www.clinicaltrials.gov (NCT00701428).

Which place of pharmacological approaches beyond continuous positive airway pressure to treat vascular disease related to obstructive sleep apnea?

Obstructive sleep apnea (OSA) is characterized by recurrent episodes of partial or complete upper airway obstruction, occurring during sleep, leading to chronic intermittent hypoxia (IH), which harms the cardiovascular system. OSA is associated with both functional and structural vascular alterations that contribute to an increased prevalence of fatal and non-fatal cardiovascular events. OSA is a heterogeneous disease with respect to the severity of hypoxia, the presence of daytime symptoms, obesity, and cardiovascular comorbidities. Various clusters of OSA phenotypes have been described leading to more highly personalized treatment. The aim of this review is to describe the various therapeutic strategies including continuous positive airway pressure (CPAP), oral appliances, surgery, weight loss, and especially pharmacological interventions that have been evaluated to reduce vascular alterations in both OSA patients and preclinical animal models. Conventional therapies, predominantly CPAP, have a limited impact on vascular alterations in the presence of co-morbidities. A better knowledge of pharmacological therapies targeting IH-induced vascular alterations will facilitate the use of combined therapies and is crucial for designing clinical trials in well-defined OSA phenotypes.

Reduced Baseline Airway Caliber Relates to Larger Airway Sensitivity to Rostral Fluid Shift in Asthma

Background: We have previously shown that when asthmatics go supine, fluid shifts out of the legs, accumulates in the thorax, and exacerbates lower airway narrowing. In the retrospective analysis of our previous work presented here, we test the hypothesis that the sensitivity of this process relates inversely to baseline caliber of the lower airways.

Methods: Eighteen healthy (six women) and sixteen asthmatic subjects (nine women) sat for 30 min, and then lay supine for 30 min. While supine, lower body positive pressure (LBPP, 40 mm Hg) was applied to displace fluid from the legs similar in amount to the overnight fluid shift. Respiratory resistance and reactance at 5 Hz (R5 and X5) and leg and thoracic fluid volumes (LFV and TFV) were measured at the beginning and end of the supine period.

Results: With LBPP, healthy, and asthmatic subjects had similar changes in the LFV and TFV (p = 0.3 and 0.1, respectively). Sensitivity to fluid shift, defined by ΔR5/ΔTFV, was larger in the asthmatics than in the healthy subjects (p = 0.0001), and correlated with baseline R5 in the supine position in the asthmatics (p = 0.7, p = 0.003). No such association was observed in the healthy subjects (p = 0.6). In the asthmatics, women showed a greater reduction in X5 than men with LBPP (p = 0.009).

Conclusions: Smaller baseline airway caliber, as assessed by larger R5, was associated with increased sensitivity to fluid shift in the supine position. We conclude that asthmatics with narrower small airways such as obese asthma patients, women with asthma and those with severe asthma may be more sensitive to the effects fluid shift while supine as during sleep.

A novel approach for acoustic estimation of neck fluid volume between men and women

Obstructive Sleep apnea can be caused by fluid shift from the legs to the neck that narrows the upper airway (UA) and contributes to changes in tracheal sound. Tracheal sound is generated from the turbulent airflow in the pharynx and respiratory airways and it has recently been used to estimate increases in neck fluid volume (NFV). However, tracheal sound is also highly variable among people, especially across the sexes. In this paper, a novel method is proposed to select tracheal sound features towards estimating NFV in men and women separately. To validate this method, it was applied to the tracheal sound data of 28 healthy individuals. Our proposed feature selection algorithm is based on sparse representations and incorporates NFV to maximize the relevance of selected features. This feature selection eliminates the dependence of the previous methods on calibrating the model for every individual. Two models, regression and Kalman filters, are then used to estimate NFV from selected features. Kalman filter obtains the highest performance, estimating NFV with more than 90% accuracy in both men and women. This algorithm can be used to develop non-invasive acoustic technologies to investigate the effects of fluid on UA anatomy in general applications. These results could be used to develop convenient devices to monitor the neck edema and its contribution to sleep apnea severity in fluid retaining patients such as heart or renal failure.

Sleep-Disordered Breathing in Heart Failure - A Therapeutic Dilemma

Sleep-disordered breathing (SDB) occurs in approximately 50% of patients with reduced left ventricular ejection fraction receiving contemporary heart failure (HF) therapies. Obstructive (OSA) and central sleep apneas (CSA) interrupt breathing by different mechanisms but impose qualitatively similar autonomic, chemical, mechanical, and inflammatory burdens on the heart and circulation. Because contemporary evidence-based drug and device HF therapies have little or no mitigating effect on the acute or long-term consequences of such stimuli, there is a sound mechanistic rationale for targeting SDB to reduce cardiovascular event rates and prolong life. However, the promise of observational studies and randomized trials of small size and duration describing a beneficial effect of treating SDB in HF via positive airway pressure was not realized in 2 recent randomized outcome-driven trials: SAVE, which evaluated the cardiovascular effect of treating OSA in a cohort without HF, and SERVE-HF, which reported the results of a strategy of random allocation of minute-ventilation-triggered adaptive servo-ventilation (ASV) for HF patients with CSA. Whether effective treatment of either OSA or CSA improves the HF trajectory by reducing cardiovascular morbidity or mortality has yet to be definitively established. ADVENT-HF, designed to determine the effect of treating both CSA and non-sleepy OSA HF patients with a peak-airflow triggered ASV algorithm, could resolve this present clinical equipoise concerning the treatment of SDB.

Treatment of primary aldosteronism is associated with a reduction in the severity of obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is known to commonly co-exist with primary aldosteronism (PA), but it is unknown if treatment of PA improves sleep apnoea parameters in these patients. We therefore aimed to determine whether specific medical or surgical treatment of PA improves OSA, as measured by the apnoea-hypopnoea index (AHI). We recruited patients undergoing diagnostic workup for PA if they had symptoms suggestive of OSA. Patients with confirmed PA underwent polysomnography (PSG) at baseline and again at least 3 months after specific treatment for PA. Of 34 patients with PA, 7 (21%) had no evidence of OSA (AHI <5), 9 (26%) had mild (AHI ⩾5 and <15), 8 (24%) moderate (AHI ⩾15 and <30) and 10 (29%) severe OSA (AHI ⩾30). Body mass index tertile, neck circumference and 24 h urinary sodium correlated with the AHI. Twenty patients had repeat PSG performed after treatment for PA (mineralocorticoid receptor antagonists in 13 with bilateral PA and adrenalectomy in 7 with unilateral PA). In this group the median (s.d.) AHI reduced from 22.5 (14.7) to 12.3 (12.1) (P=0.02). Neck circumference reduced with PA treatment (41.6 vs 41.2 cm, P=0.012). OSA is common in patients with primary aldosteronism and may improve with specific therapy for this disease. Aldosterone and sodium-mediated fluid retention in the upper airways and neck region may be a potential mechanism for this relationship.

The effect of sitting and calf activity on leg fluid and snoring

Prolonged sitting may promote leg fluid retention that redistributes to the neck during sleep and contributes to snoring. This could be attenuated by calf activity while sitting. In 16 healthy non-obese subjects we measured leg fluid volume (LFV) below the knees using bioelectrical impedance while sitting for 4h, snoring using a portable BresoDx™ device, and Mallampati grade. Using a double cross-over study design, subjects were randomized to one of two arms and crossed-over one week later: control arm - no calf exercise while sitting; intervention arm - calf contraction against a pedal resistance while sitting. The effects of sitting±calf activity on LFV and snoring were compared. We found that LFV increased by 216±101.0ml (p<0.0001) after sitting. Calf activity while sitting attenuated LFV by 53.8ml (p<0.0001) and, in all five subjects with severe upper airway narrowing (Mallampati grade IV), reduced snoring duration (from 357±132.9 to 116.2±72.1s/h, p=0.02) suggesting reduced overnight rostral fluid shift to the neck.

The Triad of Sleep Apnea, Hypertension, and Chronic Kidney Disease: A Spectrum of Common Pathology

Obstructive sleep apnea (OSA), hypertension, and chronic kidney disease (CKD) are different entities and are generally managed individually most of the time. However, CKD, OSA, and hypertension share many common risk factors and it is not uncommon to see this complex triad together. In fact, they share similar pathophysiology and have been interlinked with each other. The common pathophysiology includes chronic volume overload, hyperaldosteronism, increased sympathetic activity, endothelial dysfunction, and increased inflammatory markers. The combination of this triad has significant negative impact on the cardiovascular health, and increases the mortality and morbidity in this complicated group of patients. On one hand, progression of CKD can lead to the worsening of OSA and hypertension; similarly, worsening sleep apnea can make the hypertension difficult to treat and enhance the progression of CKD. This review article highlights the bidirectional interlink among these apparently different disease processes which share common pathophysiological mechanisms and emphasizes the importance of treating them collectively to improve outcomes.

Relationship of Fluid Accumulation in the Neck to Sleep Structure in Men during Daytime Sleep

STUDY OBJECTIVES

Induction of fluid overload during sleep in older men causes fluid accumulation in the neck, worsens obstructive sleep apnea (OSA), and reduces sleep efficiency and slow wave sleep. However, it is not clear whether disrupted sleep structure was related to age, fluid accumulation, or to OSA severity as assessed by the apnea-hypopnea index (AHI). We hypothesize that fluid accumulation in the neck is a significant contributor to the sleep structure.

METHODS

Twenty non-obese men, 46 ± 11 years, underwent a daytime sleep study following a night of sleep deprivation. Before and after sleep, neck circumference (NC), upper airway cross-sectional area, and neck fluid volume (NFV) were assessed. Stepwise regression analyses were used to determine factors that contributed to sleep structure, AHI, and arousal frequency. Independent factors were age, NC, ΔNC, ΔNFV, and AHI (excluded for AHI and arousal).

RESULTS

Subjects slept for 145 ± 44 minutes with a mean AHI of 26 ± 25. After sleep, NC and NFV increased and the upper airway narrowed (all: p < 0.001). ΔNC and ΔNFV correlated directly with %N2 and inversely with %N3 sleep. Regression analyses revealed that only ΔNC correlated directly with %N2 sleep (r² = 0.44, p = 0.001). ΔNC, ΔNFV, and pre-sleep NC correlated inversely with %N3 sleep (r² = 0.76, p < 0.001). Pre-sleep NC and ΔNC correlated directly with AHI and arousal frequency.

CONCLUSIONS

Fluid accumulation in the neck and larger neck circumference are related to impaired sleep structure with reduced %N3 sleep. Fluid accumulation in the neck had stronger contribution to sleep structure than AHI or age.

Effect of Antihypertensive Medications on the Severity of Obstructive Sleep Apnea: A Systematic Review and Meta-Analysis

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is an independent risk factor for hypertension (HTN). Increasing evidence from animal and human studies suggests that HTN exacerbates OSA. We performed a systematic review and meta-analysis of studies evaluating the effect of anti-hypertensive medications on the severity of OSA.

METHODS

A literature search of PubMed and Embase was done using search concepts of OSA, HTN, and drug classes used to treat HTN. Studies that reported changes in the severity of OSA objectively by using apnea-hypopnea index (AHI) or respiratory disturbance index (RDI) were included. Pooled mean difference estimates were calculated. Tests for heterogeneity, publication bias, and subgroup sensitivity analysis were conducted.

RESULTS

Of 27,376 studies screened, only 11 met inclusion criteria, including 5 randomized controlled trials and 6 single-arm prospective trials. The pooled mean difference estimate (95% confidence interval [CI]), based on a random-effects model, was -5.69 (95% CI -10.74 to -0.65), consistent with an overall decrease in AHI or RDI attributable to antihypertensive medications. The effect size was even more pronounced, -14.52 (95% CI -25.65 to -3.39), when only studies using diuretics were analyzed. There was no significant heterogeneity or publication bias among the studies. Meta-regression indicated neither age, baseline AHI, nor change in systolic/diastolic blood pressure influenced the results.

CONCLUSIONS

Collectively, findings from these relatively small, short-term studies tend to support the contention that treatment with antihypertensive agents confers a statistically significant, albeit small, reduction in the severity of OSA, which may be more pronounced with the use of diuretics.

Factors predisposing to worsening of sleep apnea in response to fluid overload in men

OBJECTIVES

Obstructive sleep apnea (OSA) is highly prevalent in patients with fluid-retaining conditions. Using bioimpedance measurements, previous studies have shown that the greater the amount of fluid redistributed from the legs to the neck overnight, the greater the severity of OSA. Our objective was to investigate factors that predispose the development or worsening of OSA in response to experimental fluid overload.

METHODS

Fifteen normotensive and non-obese adult men with and without OSA underwent polysomnography (PSG) during which normal saline was infused intravenously at a minimal rate to keep the vein open (control) or as a bolus of 22 ml/kg body weight (approximately 2 L) in a random order and crossed over after a week.

RESULTS AND CONCLUSIONS

Before and after sleep, neck circumference and bioimpedance were measured to calculate neck resistance, reactance, phase angle, and fluid volume. Subjects who experienced more than a twofold increase in apnea-hypopnea index (AHI) or obstructive AHI from control to intervention and had an AHI>10 during intervention were considered susceptible to the development or worsening of OSA. Baseline neck circumference and phase angle before saline infusion were independently associated with increased susceptibility to developing or worsening OSA in response to saline infusion. In non-obese men, a larger neck circumference and bioimpedance phase angle of the neck, which may be associated with larger pharyngeal tissue content, is associated with increased susceptibility for worsening of OSA in response to fluid overloading.

Hypervolemia and Sleep Apnea in Kidney Disease

In end-stage renal disease (ESRD) and heart failure, conditions characterized by fluid overload, both obstructive sleep apnea (OSA) and central sleep apnea (CSA) are highly prevalent. This observation suggests that fluid overload may be a unifying mechanism in the pathogenesis of both OSA and CSA in these conditions. An overnight rostral fluid shift from the legs to the neck and lungs has been shown to contribute to the pathogenesis of OSA and CSA, respectively, in various different patient populations. This article reviews the evidence that supports a role for fluid overload and overnight fluid shift in the pathogenesis of sleep apnea in ESRD. The diagnosis, epidemiology, and clinical features of sleep apnea in patients with ESRD also are considered.

Effects of exercise training on sleep apnoea in patients with coronary artery disease: a randomised trial

Overnight fluid shift from the legs to the neck and lungs may contribute to the pathogenesis of obstructive sleep apnoea (OSA) and central sleep apnoea (CSA). We hypothesised that exercise training will decrease the severity of OSA and CSA in patients with coronary artery disease (CAD) by decreasing daytime leg fluid accumulation and overnight rostral fluid shift.Patients with CAD and OSA or CSA (apnoea-hypopnoea index >15 events per h) were randomised to 4 weeks of aerobic exercise training or to a control group. Polysomnography, with measurement of leg, thoracic and neck fluid volumes and upper-airway cross-sectional area (UA-XSA) before and after sleep, was performed at baseline and follow-up.17 patients per group completed the study. Apnoea-hypopnoea index decreased significantly more in the exercise group than in the control group (31.1±12.9 to 20.5±9.4 versus 28.1±13.5 to 27.0±15.1 events per h, p=0.047), in association with a greater reduction in the overnight change in leg fluid volume (579±222 to 466±163 versus 453±164 to 434±141 mL, p=0.04) and by a significantly greater increase in the overnight change in UA-XSA in the exercise group (p=0.04).In patients with CAD and sleep apnoea, exercise training decreases sleep apnoea severity via attenuation of overnight fluid shift and an increase in UA-XSA.

Pathogenesis of drug-resistant hypertension

More is known about the epidemiology of drug-resistant hypertension than particular pathogenic factors and pathways. Several recurring themes, however, seem evident on using insight from epidemiology and general knowledge of the pathophysiology of hypertension. Specifically, 4 main pathways converge on drug resistance including sodium handling, sympathetic nervous system activation, endothelial dysfunction, and arterial stiffness. These factors, and the various pathways and elements contributing to them, are reviewed. In addition to describing how these factors exert their individual influences on resistant hypertension, several examples of how interactions between these factors, particularly in the case of chronic kidney disease, are included. At the conclusion of this review some thoughts are offered on additional mechanisms and areas for potential research.

The Relationship Between Volume Overload in End-Stage Renal Disease and Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is common, underdiagnosed, and undertreated among patients with end-stage renal disease (ESRD). As in all cases, pathogenesis of OSA is related to repeated upper airway (UA) occlusion or narrowing, but in ESRD, additional contributory factors likely include uremic destabilization of central respiratory control and anatomic changes in the UA related to fluid status. Pulmonary congestion is common in acute and chronic kidney failure and is a consequence of cardiomyopathy and fluid overload, two potentially reversible risk factors. Emerging evidence suggests that volume overload also reduces the UA caliber. The diminution in UA area as well as destabilization of ventilatory control in ESRD have been postulated as causes of increased OSA prevalence and severity in these patients, and creates a vicious cycle wherein OSA exacerbates fluid overload disorders such as in congestive heart failure (CHF) and ESRD, which then further worsen OSA. Dialysis modalities may differ in their effects on volume status, the accumulation of uremic toxins, and acid-base status, and as a consequence, on the emergence and severity of OSA. Given the contribution of excess fluid to both the severity of nocturnal hypoxia and UA narrowing, establishing and maintaining dry weight is of particular importance when managing OSA in ESRD. Clinical trials to determine the extent to which more aggressive fluid removal in ESRD patients may alleviate OSA are needed.

Effect of diuretics and sodium-restricted diet on sleep apnea severity: study protocol for a randomized controlled trial

Background

Obstructive sleep apnea occurs as a result of increased collapsibility of the upper airway. Overnight fluid displacement from the legs to the neck causes pharyngeal narrowing and increased apnea severity. Sodium intake is associated with apnea severity. We hypothesized that interventions that decrease bodily fluid content might reduce the severity of sleep apnea.

Methods/design

This is a randomized clinical trial including men with an apnea-hypopnea index greater than 30 events/hour, previously diagnosed by full-night in-laboratory polysomnography. A total of 54 men will be included and randomly assigned to three groups: Diuretic (n = 18), sodium-restricted diet (n = 18), and control (n = 18). The intervention will last one week. Intention-to-treat and per-protocol analyses will be performed. The diuretic group will receive combined spironolactone 100 mg plus furosemide 20 mg daily, taken in the morning. The diet group will receive a regimen with a maximum intake of 3 g of sodium per day. The control group will receive a placebo pill and will maintain all eating habits while keeping a recall diary of their dietary behavior. The primary outcome measure will be change in apnea-hypopnea index. The secondary outcome measures will be variations of: anthropometric and bioelectrical impedance variables, office blood pressure, respiratory variables from in-home level III polysomnography, excessive daytime sleepiness, glycolipid profile, C-reactive protein, 24 h urinary variables, and adverse events.

Discussion

Despite the high efficacy of continuous positive airway pressure to reverse upper airway obstruction in sleep apnea, partial adherence to this form of treatment reduces its efficiency. Thus, additional forms of treating apnea need to be investigated. If the results of this proof-of-concept trial show that decreases in bodily fluid content, either by diuretic or dietary intervention, reduces the severity of sleep apnea, further investigation will be necessary before these results can be translated and adopted as an adjunct apnea therapy.

Trial registration

clinicaltrials.gov NCT01945801.

Heart Failure and Sleep Apnea

Obstructive and central sleep apnea are far more common in heart failure patients than in the general population and their presence might contribute to the progression of heart failure by exposing the heart to intermittent hypoxia, increased preload and afterload, sympathetic nervous system activation, and vascular endothelial dysfunction. There is now substantial evidence that supports a role for fluid overload and nocturnal rostral fluid shift from the legs as unifying mechanisms in the pathogenesis of obstructive and central sleep apnea in heart failure patients, such that the predominant type of sleep apnea is related to the relative distribution of fluid from the leg to the neck and chest. Despite advances in therapies for heart failure, mortality rates remain high. Accordingly, the identification and treatment of sleep apnea in patients with heart failure might offer a novel therapeutic target to modulate this increased risk. In heart failure patients with obstructive or central sleep apnea, continuous positive airway pressure has been shown to improve cardiovascular function in short-term trials but this has not translated to improved mortality or reduced hospital admissions in long-term randomized trials. Other forms of positive airway pressure such as adaptive servoventilation have shown promising results in terms of attenuation of sleep apnea and improvement in cardiovascular function in short-term trials. Large scale, randomized trials are required to determine whether treating sleep apnea with various interventions can reduce morbidity and mortality.

Use of continuous positive airway pressure for sleep apnea in the treatment of hypertension

PURPOSE OF REVIEW

Obstructive sleep apnea (OSA) and hypertension are highly prevalent and treatable conditions that often coexist and both contribute to an increased cardiovascular risk. The ability of continuous positive airway pressure (CPAP) to improve blood pressure in hypertensive patients with OSA is debated. This review highlights findings from recent studies that have investigated the impact of CPAP on blood pressure in patients with OSA.

RECENT FINDINGS

Comparing the results of various studies is complicated by important methodological differences among them. In hypertensive patients with OSA, treatment with CPAP improves blood pressure to a smaller degree than that derived from antihypertensive medication. Patients with more severe OSA and with greater adherence to CPAP are likely to gain the most benefit from the therapy.

SUMMARY

CPAP should be used in combination with antihypertensive medications in hypertensive patients with OSA. CPAP has the additional benefits of restoring nocturnal dipping and improving arterial stiffness, thus potentially influencing cardiovascular morbidity in these high-risk patients.

Overnight fluid shifts in subjects with and without obstructive sleep apnea

OBJECTIVE

To investigate the characteristics of baseline body fluid content and overnight fluid shifts between non-obstructive sleep apnea (non-OSA) and obstructive sleep apnea (OSA) subjects.

METHODS

A case-controlled study was performed between February 2013 and January 2014, with 36 (18 OSA and 18 non-OSA) outpatients enrolled in this study. Polysomnographic parameters and results of body fluid were compared between the two groups.

RESULTS

There were no differences in age, weight, and body mass index (BMI) between groups. Compared with the non-OSA group, OSA group had significantly higher neck circumference (NC) and fluid volume shift in the legs. OSA patients had higher left and right leg fluid indices than non-OSA subjects. There were significant correlations between apnoea-hypopnoea index and baseline fluid indices in both legs as well as the reduction in overnight change in both legs fluid volume. The increase in NC was also significantly correlated with the reduction in overnight change in both legs fluid volume, but not with the change in head and neck fluid volume. There were significant correlations between change in NC and increased fluid shifts in head and neck volume.

CONCLUSIONS

OSA patients had a higher baseline fluid content in both legs as compared with non-OSA subjects, which may be the basic factor with regards to fluid shifts in OSA patients. The increase in head and neck fluid shift volume did not directly correlate with the severity of OSA.

Night-to-night variability in obstructive sleep apnea severity: relationship to overnight rostral fluid shift

STUDY OBJECTIVES

Overnight rostral fluid shift from the legs to the neck may narrow the pharynx and contribute to obstructive sleep apnea (OSA) pathogenesis. We hypothesized that night-to-night changes in the apnea-hypopnea index (AHI) would be associated with changes in overnight rostral fluid shift.

METHODS

Twenty-six patients with OSA (AHI ≥10) underwent two polysomnograms 14 days apart with measurement of neck and leg fluid volumes (LFV), neck circumference and upper-airway cross-sectional area before and after sleep.

RESULTS

Although mean AHI did not differ between polysomnograms, 35% of patients had a difference in AHI >10, indicating significant intra-individual variability. There were direct correlations between change in non-rapid-eye movement (NREM), but not REM AHI and change in evening LFV between polysomnograms (r = 0.440, p = 0.036 and r = 0.005, p = 0.982, respectively) and between change in supine, but not non-supine AHI and change in evening LFV (r = 0.483, p = 0.020 and r = 0.269, p = 0.280, respectively). An increase in evening LFV between polysomnograms was associated with a greater overnight decrease in LFV (r = 0.560, p = 0.005) and a greater overnight increase in neck fluid volume (r = 0.498, p = 0.016). Additionally, a greater overnight increase in neck circumference was associated with a greater overnight increase in neck fluid volume between polysomnograms (r = 0.453, p = 0.020) and a greater overnight decrease in upper-airway cross-sectional area (r = -0.587, p = 0.005).

CONCLUSION

Intra-individual variability in OSA severity may be partly explained by day-to-day changes in evening leg fluid volume and overnight rostral fluid shift, which may be most important in the pathogenesis of OSA during NREM and supine sleep.

Effects of changing in the neck circumference during sleep on snoring sound characteristics

Rostral fluid shift during sleep from the lower body part into the neck can increase neck circumference (NC) and narrow the upper airway. Such narrowing in the upper airway may increase turbulence of airflow passing through the upper airway; thus, induce snoring. The objective of this study was to investigate the effects of changes in NC during sleep on snoring sound characteristics. Fifteen non-obese men slept supine, and their sleep was monitored by a regular polysomnography. Snoring sounds were recorded with a microphone attached to the neck. NC was measured before and after sleep with a measuring tape. Snoring sounds' average power was calculated in different frequency ranges of 100 - 4000 Hz, 100 - 150 Hz, 150 - 450 Hz, 450 - 600 Hz, 600 - 1200 Hz, 1200 - 1800 Hz, 1800 - 2500 Hz and 2500 - 4000 Hz. Statistical analysis showed that increases in NC after sleep were strongly correlated with higher average power of the snoring sounds in the frequency ranges of 100-4000 Hz (r=0.74, P=0.004), 100-150 Hz (r=0.70, P=0.008), 150-450 Hz (r=0.73, P=0.005), and 450 - 600 Hz (r= 0.65, P=0.025). These results encourage the use of snoring sound analysis for monitoring the effects of fluid accumulation in the neck in relation to sleep apnea.

Effect of below-the-knee compression stockings on severity of obstructive sleep apnea

BACKGROUND

Overnight fluid shift from the legs to the neck may narrow the upper airway and contribute to obstructive sleep apnea (OSA) pathogenesis. We hypothesized that below-the-knee compression stockings will decrease OSA severity in a general OSA population by decreasing daytime leg fluid accumulation and overnight fluid shift and increasing upper-airway size.

METHODS

Patients with OSA (apnea-hypopnea index ≥ 10) were randomized to wear compression stockings during the daytime or to a control group for 2 weeks. Overnight polysomnography with measurement of leg and neck fluid volumes and upper-airway cross-sectional area before and after sleep was performed at baseline and follow-up. The primary outcome was change in the apnea-hypopnea index.

RESULTS

Twenty-two patients randomized to compression stockings and 23 to control completed the study. The apnea-hypopnea index decreased significantly more in the compression stockings than in the control group (from 32.4 ± 20.0 to 23.8 ± 15.5 vs. from 31.2 ± 25.0 to 30.3 ± 23.8, p = 0.042), in association with a significantly greater reduction in the overnight decrease in leg fluid volume (p = 0.028), and a significantly greater increase in morning upper-airway cross-sectional area (p = 0.006). Overnight change in neck fluid volume was unchanged.

CONCLUSION

These observations suggest that in, a general OSA population, below-the-knee compression stockings decrease OSA severity modestly via attenuation of overnight fluid shift and consequent upper-airway dilatation.

A randomized, double crossover study to investigate the influence of saline infusion on sleep apnea severity in men

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is commoner in patients with fluid-retaining states than in those without fluid retention, in men than in women, and worsens with aging. In men, OSA severity is related to the amount of fluid shifting out of the legs overnight, but a cause-effect relationship is not established. Our objective was to test the hypothesis that mimicking fluid overload during sleep would increase severity of OSA more in older (≥ 40 years) than in younger men (< 40 years).

DESIGN

Randomized, single-blind, double crossover study.

SETTING

Research sleep laboratory.

PATIENTS OR PARTICIPANTS

Seven older and 10 younger men with non-severe or no sleep apnea, matched for body mass index.

INTERVENTIONS

During the control arm, normal saline was infused to keep the vein open. During intervention, subjects received an intravenous bolus of normal saline (22 mL/kg body weight) after sleep onset while they were wearing compression stockings to prevent fluid accumulation in the legs.

MEASUREMENTS AND RESULTS

Compared to younger men, infusion of similar amounts of saline in older men caused a greater increase in neck circumference (P < 0.05) and in the AHI (32.2 ± 22.1 vs. 2.2 ± 7.1, P = 0.002).

CONCLUSIONS

Older men are more susceptible to the adverse effects of intravenous fluid loading on obstructive sleep apnea severity than younger men. This may be due to age-related differences in the amount of fluid accumulating in the neck or upper airway collapsibility in response to intravenous fluid loading. These possibilities remain to be tested in future studies.