Blood pressure variability in obstructive sleep apnea: role of sympathetic nervous activity and effect of continuous positive airway pressure

The association between sleep disturbances and blood pressure variability: a review of the literature

STUDY OBJECTIVES

Sleep disturbances are an underrecognized public health issue that results in various adverse outcomes and disturbed quality of life. Blood pressure variability (BPV) is an emerging entity in assessing cardiovascular disease risk and accumulating evidence suggests that BPV is closely associated with end-organ damage. This review aims to explore the association between sleep disturbances and BPV.

METHODS

A comprehensive systematic literature search was conducted electronically using Web of Science, Ovid MEDLINE, , and SCOPUS. The electronic search was restricted to relevant English-language studies published between 1985 and August 2020. Most studies were prospective cohorts in design. After applying eligibility criteria, 29 articles were included for synthesis.

RESULTS

This review shows that sleep disturbances are linked to short-term, midterm, and long-term BPV. Restless legs syndrome, shift work, insomnia, short sleep, long sleep, obstructive sleep apnea, and sleep deprivation were all positively associated with systolic blood pressure or diastolic blood pressure fluctuations.

CONCLUSIONS

Given the prognostic implications of BPV and sleep disturbances on cardiovascular mortality, recognizing and treating both disorders is essential. More research is needed to examine the impact of sleep disorder treatment on BPV and cardiovascular mortality.

CITATION

Al Haddad N, Costanian C, Zibara V, et al. The association between sleep disturbances and blood pressure variability: a review of the literature. J Clin Sleep Med. 2023;19(8):1533-1544.

Pathophysiology of the Nondipping Blood Pressure Pattern

The nondipping blood pressure (BP) pattern corresponds to a disruption in the circadian BP rhythm with an insufficient decrease in BP levels during nighttime sleep as observed using 24-hour ambulatory BP monitoring. Patients with nondipping BP pattern have poorer renal and cardiovascular outcomes, independent of their average 24-hour BP levels. The pathophysiology of nondipping BP is complex and involves numerous mechanisms: perturbations of (1) the circadian rhythm, (2) the autonomic nervous system, and (3) water and sodium regulation. This review provides an outline of the pathways potentially involved in the nondipping BP profile in different conditions. A recent hypothesis is also discussed involving the role of gut microbiota in the dipping/nondipping patterns, via the fecal diet-derived short chain fatty acids.

Comparative effects of CPAP and mandibular advancement splint therapy on blood pressure variability in moderate to severe obstructive sleep apnoea

BACKGROUND

Obstructive sleep apnoea (OSA) is associated with increased blood pressure variability (BPV) and are risk factors for cardiovascular disease. We aimed to assess the comparative effects of two OSA therapies, continuous positive airway pressure (CPAP) and mandibular advancement splint (MAS), on BPV.

METHODS

This is a secondary analysis of data collected as part of a previously published randomised crossover trial of one month each of CPAP and MAS therapy. BPV was determined from 24-h-ambulatory blood pressure recordings in 92 patients with moderate to severe OSA at baseline and after one month of optimised treatment with each modality. BPV was assessed by three measures: Standard deviation of the mean (SD), Coefficient of variation (CoV), and the Average Real Variability (ARV) index.

RESULTS

Neither CPAP nor MAS therapy improved BPV, with no difference between treatments. BPV did not change in hypertensive OSA patients, however, there was a reduction in ARV of diastolic blood pressure in the effectively treated compared to ineffectively treated CPAP patients, Δ ARV 24-h-DBP (mmHg), -0.72 ± 2.14, 0.34 ± 1.52, P = 0.02, respectively. There was no difference between effective versus ineffective MAS treatment, Δ ARV 24-h-DBP (mmHg), -0.04 ± 2.4, 0.02 ± 1.9, P = 1.00, respectively.

CONCLUSIONS

One month of optimised CPAP or MAS therapy did not improve short term BPV in patients with moderate to severe OSA. The subgroup of patients on effective CPAP showed some improvement in BPV with CPAP but not MAS. Further work on the effect of OSA therapy on BPV following long-term therapy is needed.

Systemic hypertension in obstructive sleep apnea

There is consistent epidemiological evidence that sleep disordered breathing and systemic arterial hypertension are deeply associated, being linked through a bidirectional complex interaction among multiple mechanisms including autonomic nervous system alterations, inflammation, hormonal and hemodynamic components, sleep alterations. However there are several unanswered questions not only from a pathophysiological perspective, but also regarding the effects of obstructive sleep apnea (OSA) treatment on arterial blood pressure values. At present, while many studies have supported the possibility to obtain at least a small blood pressure reduction with OSA treatment, in particular in hypertensive patients, large trials have not clearly confirmed a significant anti-hypertensive effect, nor a beneficial effect of this intervention on cardiovascular endpoints including cardiovascular mortality. Aim of the present review article is to address the relationship between OSA and hypertension in the light of the latest evidence in the field. Moreover we will discuss research topics which need to be investigated in the future, in order to better clarify still pending issues with the aim of obtaining an early diagnosis, a more suitable phenotyping including comorbidities, and better strategies to improve patients' compliance and adherence to treatment.

Blood-pressure variability in patients with obstructive sleep apnea: current perspectives

Obstructive sleep apnea (OSA) is often associated with hypertension and other cardiovascular diseases. Blood pressure (BP) variability is part of the assessment of cardiovascular risk. In OSA, BP variability has been studied mainly as very short-term (beat-by-beat) and short-term (24-hour BP profile) variability. BP measured on consecutive heartbeats has been demonstrated to be highly variable, due to repeated peaks during sleep, so that an accurate assessment of nocturnal BP levels in OSA may require peculiar methodologies. In 24-hour recordings, BP frequently features a "nondipping" profile, ie, <10% fall from day to night, which may increase cardiovascular risk and occurrence of major cardiovascular events in the nocturnal hours. Also, BP tends to show a large "morning BP surge", a still controversial negative prognostic sign. Increased very short-term BP variability, high morning BP, and nondipping BP profile appear related to the severity of OSA. Treatment of OSA slightly reduces mean 24-hour BP levels and nocturnal beat-by-beat BP variability by abolishing nocturnal BP peaks. In some patients OSA treatment turns a nondipping into a dipping BP profile. Treatment of arterial hypertension in OSA usually requires both antihypertensive pharmacological therapy and treatment of apnea. Addressing BP variability could help improve the management of OSA and reduce cardiovascular risk. Possibly, drug administration at an appropriate time would ensure a dipping-BP profile.

Influences of obstructive sleep apnea on blood pressure variability might not be limited only nocturnally in middle-aged hypertensive males

PURPOSE

In this cross-sectional study, we analyzed the potential association between sleep measures and blood pressure variability.

METHODS

Ninety-three middle-aged hypertensive males, who underwent polysomnography and 24-h ambulatory blood pressure monitoring, were enrolled. Blood pressure variability was assessed by blood pressure standard deviation. Obstructive sleep apnea (apnea hypopnea index ≥ 15) was diagnosed in 52 (55.91%) patients. Mean body mass index and age were 27.77 ± 3.11 kg/m² and 44.05 ± 8.07 years, respectively.

RESULTS

Hypertensive males with obstructive sleep apnea showed significantly higher 24-h, diurnal, and nocturnal diastolic blood pressure variability, compared to those without obstructive sleep apnea. While total cohort was further divided into two groups using the median of oxygen desaturation index, another indicator for severity of OSA, significant differences were also observed in 24-h, diurnal, and nocturnal diastolic blood pressure variability between two groups with higher and lower oxygen desaturation index. While subjects were also divided into two groups via the mean of sleep stage 1, hypertensive males with sleep stage 1 ≥ 8.1% showed significantly higher diurnal diastolic blood pressure variability than those with sleep stage 1 < 8.1%. Apnea hypopnea index was independently associated with 24-h and nocturnal diastolic blood pressure variability; oxygen desaturation index of 3% with 24-h diastolic, diurnal, and nocturnal diastolic blood pressure; and sleep stage 1 was with 24-h and with diurnal diastolic blood pressure variability in all study subjects.

CONCLUSION

Effects of obstructive sleep apnea on blood pressure variability may not be limited nocturnally.

Quantitative Retinal Vascular Changes in Obstructive Sleep Apnea

PURPOSE

To examine the relationship between both static and dynamic retinal vascular caliber and the severity of obstructive sleep apnea (OSA).

DESIGN

Prospective cross-sectional study.

METHODS

Adult patients undergoing diagnostic polysomnography studies at a private Australian university teaching hospital were recruited. OSA severity was defined by the apnea-hypopnea index (AHI): severe >30, moderate >15-30, mild 5-15, and controls <5. Of 115 patients recruited (73 male; mean age 58 ± 13 years), there were 41 severe, 35 moderate, and 25 mild OSA patients and 14 controls. Static retinal vascular caliber was measured as the average diameter of retinal arterioles (CRAE) and venules (CRVE), and summarized as the arteriovenous ratio (AVR). Dynamic retinal vascular caliber was evaluated as the average pulsation amplitude of retinal arterioles (SRAP) and venules (SRVP). Comparisons across groups were performed using multivariate linear regression analysis. All results were adjusted for age, body mass index, and mean arterial pressure.

RESULTS

Increasing AHI was significantly associated with decreasing AVR (P = .008) and CRAE (P = .016). A significant relationship was demonstrated between increasing AHI and attenuated retinal vascular pulsation amplitude (arterioles P = .028; venules P < .0001).

CONCLUSIONS

Increasing OSA severity is independently associated with retinal arteriolar narrowing and attenuated vascular pulsation amplitude. The retinal vasculature is easily imaged, and may be a surrogate biomarker of cerebral and systemic vascular risk in patients with OSA requiring further comprehensive investigation.

The sympathetic nervous system and catecholamines metabolism in obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is the most common sleep disorder of breathing in middle-aged and overweight subjects. It features recurrent episodes of upper airway total (apnoea) o partial (hypopnea) collapse during sleep, which are associated with a reduction in blood oxygen saturation and with arousal from sleep to re-establish airway patency. An association of OSA with dysregulation of the autonomous nervous system (ANS) and altered catecholamines (CAs) metabolism has been contended for years. However, the pathophysiology mechanisms underlying these alterations remain to be fully clarified. Nonetheless, these alterations are deemed to play a key pathogenic role in the established association of OSA with several conditions besides arterial hypertension (HT), including coronary artery disease, stroke, and, more in general, with increased risk of cardiovascular (CV) events. Hence, in this review we will analyse the relationship between the sleep disturbances associated with OSA and the altered function of the ANS, including CAs metabolism.

Sleep-disordered Breathing in Heart Failure

Sleep-disordered breathing affects over half of patients with heart failure (HF) and is associated with a poor prognosis. It is an under-diagnosed condition and may be a missed therapeutic target. Obstructive sleep apnoea is caused by collapse of the pharynx, exacerbated by rostral fluid shift during sleep. The consequent negative intrathoracic pressure, hypoxaemia, sympathetic nervous system activation and arousals have deleterious cardiovascular effects. Treatment with continuous positive airway pressure may confer symptomatic and prognostic benefit in this group. In central sleep apnoea, the abnormality is with regulation of breathing in the brainstem, often causing a waxing-waning Cheyne Stokes respiration pattern. Non-invasive ventilation has not been shown to improve prognosis in these patients and the recently published SERVE-HF trial found increased mortality in those treated with adaptive servoventilation. The management of sleep-disordered breathing in patients with HF is evolving rapidly with significant implications for clinicians involved in their care.

The complex relationship between CKD and ambulatory blood pressure patterns

Hypertension and CKD frequently coexist, and both are risk factors for cardiovascular events and mortality. Among people with hypertension, the loss of the normal fall in night-time BP, called nondipping, can only be diagnosed by ambulatory BP monitoring (ABPM) and is a risk factor for cardiovascular events. The pathophysiology of nondipping is complex, and CKD is an independent risk factor for nondipping. In fact, nondipping can be seen in as many as 80% of people with CKD. However, the evidence for nondipping as an independent risk factor or causal agent for adverse outcomes in CKD remains mixed. ABPM has been shown to be superior to clinical BP measurement for correlating with end-organ damage and prognosis in CKD. This review covers the evidence for the use of ABPM in CKD, the evidence linking ABPM patterns to outcome in CKD and the evidence for treatment of nondipping in CKD.

Choroidal Thickening in Patients with Sleep Apnea Syndrome

Sleep apnoea syndrome (SAS) is characterised by repetitive episodes of cessation of breathing during sleep, resulting in hypoxaemia and hypercapnia. Ophthalmological consequences such as glaucoma, non-arteritic anterior ischaemic neuropathy and papilloedema are relevant to hypoxaemia. The choroid is a vascular structure that performs several regulatory functions for the retina. Defects in this structure contribute to degenerative, inflammatory, and neovascular changes in the retina. The authors examined the choroidal thickness (CT) in sleep apnoea patients using optical coherence tomograpy (OCT). The sleep apnoea patients were divided into subgroups according to their apnoea-hypopnoea index (AHI) scores, and statistical analysis was performed using the AHI and minimal arterial oxygen saturation (min. Spo₂) values. There was a medium-high negative correlation between CT and AHI (Spearman rho: r = -0.744, p = 0.000), and a positive correlation between CT and min. Spo₂ values (Pearson correlation: r = 0.308, p = 0.000).

Black tea lowers the rate of blood pressure variation: a randomized controlled trial

BACKGROUND

Measures of blood pressure variation have been associated with cardiovascular disease and related outcomes. The regular consumption of black tea can lower blood pressure, but its effects on blood pressure variation have yet to be investigated.

OBJECTIVE

We aimed to assess the effects of black tea consumption on the rate of ambulatory blood pressure variation.

DESIGN

Men and women (n = 111) with systolic blood pressure between 115 and 150 mm Hg at screening were recruited in a randomized, controlled, double-blind, 6-mo parallel-designed trial designed primarily to assess effects on blood pressure. Participants consumed 3 cups/d of either powdered black tea solids (tea) or a flavonoid-free caffeine-matched beverage (control). The 24-h ambulatory blood pressure level and rate of measurement-to-measurement blood pressure variation were assessed at baseline, day 1, and 3 and 6 mo.

RESULTS

Across the 3 time points, tea, compared with the control, resulted in lower rates of systolic (P = 0.0045) and diastolic (P = 0.016) blood pressure variation by ~10% during nighttime (2200-0600). These effects, which were immediate at day 1 and sustained over 6 mo, were independent of the level of blood pressure and heart rate. The rate of blood pressure variation was not significantly altered during daytime (0800-2000).

CONCLUSIONS

These findings indicate that a component of black tea solids, other than caffeine, can influence the rate of blood pressure variation during nighttime. Thus, small dietary changes have the potential to significantly influence the rate of blood pressure variation. This trial was registered at the Australian New Zealand Clinical Trials Registry as ACTR12607000543482.

Sympathetic and catecholaminergic alterations in sleep apnea with particular emphasis on children

Sleep is involved in the regulation of major organ functions in the human body, and disruption of sleep potentially can elicit organ dysfunction. Obstructive sleep apnea (OSA) is the most prevalent sleep disorder of breathing in adults and children, and its manifestations reflect the interactions between intermittent hypoxia, intermittent hypercapnia, increased intra-thoracic pressure swings, and sleep fragmentation, as elicited by the episodic changes in upper airway resistance during sleep. The sympathetic nervous system is an important modulator of the cardiovascular, immune, endocrine and metabolic systems, and alterations in autonomic activity may lead to metabolic imbalance and organ dysfunction. Here we review how OSA and its constitutive components can lead to perturbation of the autonomic nervous system in general, and to altered regulation of catecholamines, both of which then playing an important role in some of the mechanisms underlying OSA-induced morbidities.

Non-synonymous polymorphism in the neuropeptide S precursor gene and sleep apnea

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) is a complex disease with a strong genetic basis. One of the primary molecular domains affected by OSAS is sympathetic activity. Neuropeptide S (NPS) plays an important role in the regulation of the sleep-wakefulness cycle, anxiety states, and daytime sleepiness. It is important to study neuropeptides related to sympathetic activity regulation and how their function could be modified by genetic variants affecting the expression of these molecules.

OBJECTIVES

We investigated the association of the non-synonymous polymorphism rs4751440 in the NPS precursor gene with OSAS and certain variables related to OSAS (daytime sleepiness, body mass index (BMI), insulin resistance, and blood pressure). This polymorphism causes an amino acid substitution in exon 3 of the human NPS precursor gene.

PATIENTS AND METHODS

We included 253 OSAS patients and 70 healthy subjects. Genotyping was done by polymerase chain reaction using specific flanking primers and agarose gel electrophoresis. Daytime sleepiness, BMI, plasma levels of high-density lipoprotein, glucose, total cholesterol, insulin, triglycerides, and the homeostasis model assessment index were also determined.

RESULTS

A similar genotypic and allelic distribution was found in OSAS patients and controls. The risk of OSAS was not associated with the rs4751440 polymorphism. There was no significant interaction between daytime sleepiness or metabolic variables and the rs4751440 polymorphism.

CONCLUSION

Genotypic and allelic frequency distribution of the rs4751440 polymorphism was similar in OSAS patients and controls. In this population-based study, we could not show a significant association between rs4751440 polymorphism and susceptibility to OSAS or certain phenotypes related to OSAS (daytime sleepiness, BMI, systolic blood pressure, and insulin resistance) with the exception of diastolic blood pressure.

Regulation of circadian blood pressure: from mice to astronauts

PURPOSE OF REVIEW

Circadian variation is commonly seen in healthy people; aberration in these biological rhythms is an early sign of disease. Impaired circadian variation of blood pressure (BP) has been shown to be associated with greater target organ damage and with an elevated risk of cardiovascular events independent of the BP load. The purpose of this review is to examine the physiology of circadian BP variation and propose a tripartite model that explains the regulation of circadian BP.

RECENT FINDINGS

The time-keeper in mammals resides centrally in the suprachiasmatic nucleus. Apart from this central clock, molecular clocks exist in most peripheral tissues including vascular tissue and the kidney. These molecular clocks regulate sodium balance, sympathetic function and vascular tone. A physiological model is proposed that integrates our understanding of molecular clocks in mice with the circadian BP variation among humans. The master regulator in this proposed model is the sleep-activity cycle. The equivalents of peripheral clocks are endothelial and adrenergic functions. Thus, in the proposed model, the variation in circadian BP is dependent upon three major factors: physical activity, autonomic function, and sodium sensitivity.

SUMMARY

The integrated consideration of physical activity, autonomic function, and sodium sensitivity appears to explain the physiology of circadian BP variation and the pathophysiology of disrupted BP rhythms in various conditions and disease states. Our understanding of molecular clocks in mice may help to explain the provenance of blunted circadian BP variation even among astronauts.

Causes and mechanisms of nondipping hypertension

Growing evidence indicates that nondippers have worsened cardiovascular outcomes than dippers. Ambulatory blood pressure monitoring with a lack of nocturnal BP fall (nondipping) have also been shown to be more closely associated with target organ damage and worsened cardiovascular outcome than in patients with essential hypertension with dipping pattern. The underlying pathogenetic mechanisms potentially linking nondipping with cardiovascular disease are not fully understood. There are multiple possible underlying pathophysiologic mechanisms in the impaired BP decline during the night. Extrinsic and intrinsic factors including abnormal neurohormonal regulation, lack of physical activity, nutritional factors such as increased dietary sodium intake, and smoking of tobacco have been implicated for blunted circadian rhythm of BP. Certain diseases such as diabetes and chronic renal diseases also affect the circadian BP rhythm. Currently, the clinical importance of nondipping is known well; however, the relationship between certain disease states and nondipping has not been fully explained yet. This paper will attempt to address to clarify the underlying basis for nondipping and the specific associations with various disease states.

Circadian blood pressure: Clinical implications based on the pathophysiology of its variability

The circadian blood pressure (BP) rhythm is associated with worsened cardiovascular outcomes in patients who have an excessive morning BP surge and in those who lack the normal nocturnal BP fall (non-dippers). There are multiple pathophysiologic mechanisms underlying abnormalities in circadian BP, most importantly abnormalities in sympathetic nervous system activity, salt and volume balance, and activation of the renin-angiotensin system. Several of these factors can be modified by clinical interventions, either related to lifestyle changes and/or antihypertensive drug therapy. The timing of drug administration or specific drug delivery systems that lead to a greater effect at night and/or mitigate the early morning BP surge can correct abnormal circadian rhythms. Although these strategies have not yet been shown to alter clinical outcomes, it is reasonable to understand their biologic basis and take them into consideration when designing antihypertensive therapy.

Impact of continuous positive airway pressure therapy on blood pressure in patients with obstructive sleep apnea hypopnea: a meta-analysis of randomized controlled trials

Patients with untreated obstructive sleep apnea hypopnea (OSAH) are predisposed to developing hypertension, and therapy with continuous positive airway pressure (CPAP) may reduce blood pressure (BP). The purpose of this study was to assess the impact of CPAP therapy on BP in patients with OSAH. We performed a comprehensive literature search up to July 2006 [Medline, PubMed, EMBASE, Cochrane Database of Systematic Reviews (CDSR), Cochrane controlled trials register (CCTR), and Database of Abstract and Reviews of Effect (DARE)] to identify clinical studies and systemic reviews that examined the impact of CPAP on BP. Studies were included if they (1) were randomized controlled trials with an appropriate control group, (2) included systolic and diastolic BP measurements before and after CPAP/control in patients with OSAH, and (3) contained adequate data to perform a meta-analysis. To calculate pooled results, studies were weighted by inverse variances, with either a fixed or a random effects model used depending on the presence of heterogeneity (assessed with Q test). Ten studies met our inclusion criteria (587 patients): three studies were crossover (149 patients) and seven were parallel in design. Seven studies (421 patients) used 24-h ambulatory BP and three used one-time measurements. Two studies were of patients with heart failure (41 patients). Overall, the effects of CPAP were modest and not statistically significant; CPAP (compared to control) reduced systolic BP (SBP) by 1.38 mmHg (95% CI: 3.6 to -0.88, p = 0.23) and diastolic BP (DBP) by 1.52 mmHg (CI: 3.1 to -0.07; p = 0.06). Six of the trials studied more severe OSAH (mean AHI > 30/h, 313 patients); in these six trials, CPAP reduced SBP by 3.03 mmHg (CI 6.7 to -0.61; p = 0.10) and DBP by 2.03 mmHg (CI: 4.1 to -0.002; p = 0.05). There was a trend for SBP reduction to be associated with CPAP compliance. In unselected patients with sleep apnea, CPAP has very modest effects on BP. However, we cannot exclude the possibility that certain subgroups of patients may have more robust responses-this may include patients with more severe OSAH or difficult-to-control hypertension. Future randomized controlled trials in this area should potentially concentrate on these subgroups of patients.

Continuous positive airway pressure reduces daytime sleepiness in mild to moderate obstructive sleep apnoea: a meta-analysis

BACKGROUND

Obstructive sleep apnoea syndrome (OSAS) affects an estimated 2-4% of the middle aged population. Meta-analyses of randomised controlled trials have shown that the severe presentation of the syndrome (apnoea hypopnoea index (AHI) >30/hour) is effectively treated with continuous positive airway pressure (CPAP). Until recently there have been insufficient data to determine whether CPAP improves sleepiness in the larger subgroup with mild to moderate OSAS (AHI 5-30/hour).

METHODS

A systematic search of Medline and a hand search identified seven randomised controlled trials where CPAP was compared with either a placebo or with conservative management in the treatment of mild to moderate OSAS (AHI 5-30/hour). All trials used the Epworth Sleepiness Scale (ESS), four used the Multiple Sleep Latency Test (MSLT), and three used the Maintenance of Wakefulness Test (MWT) to measure sleepiness.

RESULTS

Meta-analyses indicated that CPAP significantly reduced subjective daytime sleepiness (ESS) by 1.2 points (95% CI 0.5 to 1.9, p = 0.001), improved objective daytime wakefulness (MWT) by 2.1 minutes (95% CI 0.5 to 3.7, p = 0.011), but did not affect objective daytime sleepiness (MSLT, mean benefit -0.2 minutes, 95% CI -1.0 to 0.6, p = 0.6). The two significant effects were small (effect size <0.30).

CONCLUSIONS

CPAP elicits small improvements in subjective sleepiness and objective wakefulness in people with mild to moderate OSAS. However, the effects on sleepiness are of limited clinical significance.