Cerebral hemodynamics is altered in patients with sleep apnea/hypopnea syndrome

Walking the fine line between OSA and aging

Obstructive Sleep Apnea (OSA) is the most common sleep- related breathing disorder. In recent years, evidence have shown that patients with OSA may have this disorder for different reasons, with different symptoms and comorbidities. Therefore, treatment should be individualized [1]. This has led to a growing interest in the characterization of the disease into phenotypes. OSA in elderly patients is often a challenge for clinician in terms of diagnosis, as symptoms may be masked, but also for treatment in terms of efficacy and adherence. However, aging is a pathophysiological factor that predisposes to obstructive sleep apnea, and the two conditions share symptoms and comorbidities to such an extent that it becomes very difficult to establish a casual link between the two. We summarize the recent evidence in OSA elderly patients, particularly in terms of pathophysiology, symptoms and main comorbidities.

Retinal microcirculation characteristics in obstructive sleep apnea/hypopnea syndrome evaluated by OCT-angiography: a literature review

PURPOSE

The retina may provide a window to estimate systemic vascular status; therefore, there has been interest in identifying microcirculation characteristics that possibly reflect hypoxic alterations in obstructive sleep apnea/hypopnea syndrome (OSAS). Emerging evidence has suggested that retinal microvasculature investigation holds the potential to characterize the pathophysiology involved in ocular manifestations of OSAS. The advent of optical coherence tomography angiography (OCT-A) has attracted significant attention as this technique offers detailed analysis of the retinal capillary plexus.

METHODS

A detailed literature search was performed in PubMed database until December 2021. We identified and reviewed all papers referring to the alterations of the retinal capillary plexus in OSAS using OCT-A.

RESULTS

A comprehensive update indicates that microcirculation alterations of the retinal capillary plexus utilizing OCT-A may differ with severity of OSAS and imply the potential underlying pathophysiology of ocular manifestations. The reviewed series have revealed variability concerning microvasculature characteristics at the macular and the peripapillary area. Further studies are warranted to establish the OCT-A parameters as biomarkers regarding the evaluation of OSAS in clinical practice.

CONCLUSION

Retinal capillary plexus characteristics as seen on OCT-A reflect microvasculature alterations, potentially leading to concomitant ocular comorbidity in the context of OSAS. The reviewed literature may confirm the diagnostic and prognostic value of OCT-A in the assessment of the pathophysiology of ocular manifestations in OSAS and highlight unmet needs to be addressed by future research.

EVALUATİON OF THE EFFECT OF OBSTRUCTİVE SLEEP APNEA SYNDROME ON RETİNAL MİCROVASCULARİTY BY OPTİCAL COHERENCE TOMOGRAPHY ANGİOGRAPHY

PURPOSE

Using optical coherence tomography angiography (OCTA), we sought to determine whether there are retinal microvascular changes in patients with obstructive sleep apnea syndrome (OSAS).

METHOD

The study included 56 patients diagnosed with OSAS by polysomnography [21 patients with mild OSAS (group 1), 14 with moderate OSAS (group 2) and 21 with severe OSAS (group 3)], and 26 healthy individuals as a control group (group 4). The vascular densities of the superficial capillary plexus and deep capillary plexus of the retinal segmentations, together with the foveal avascular zone (FAZ) width, were measured for all participants, using OCTA.

RESULT

Compared with the control group, vascular densitiy in whole image of superficial capillary plexus were found to be significantly lower in group 2. In addition, vascular densitiy in fovea region of superficial capillary plexus was significantly lower in group 1 than the control group. In deep capillary plexus, vascular densitiy of whole image, superior hemi and nasal regions were found to be significantly lower in group 2 and group 3 compared with the control group. Parafoveal region in group 3 had significantly lower vascular densities than the controls. A significantly larger FAZ was also found in group 1 and group 3 in the deep capillary plexus, compared with the controls.

CONCLUSION

We detected smaller vascular densities in both the superficial capillary plexus and deep capillary plexus and a larger deep capillary plexus FAZ in OSAS patients. Therefore, OCTA may be useful as a non-invasive method to understand the systemic effects of OSAS.

Longitudinal changes in regional cerebral blood flow in late middle-aged and older adults with treated and untreated obstructive sleep apnea

Obstructive sleep apnea (OSA) is associated with abnormal cerebral perfusion at wakefulness, but whether these anomalies evolve over time is unknown. Here, we examined longitudinal changes in regional cerebral blood flow (rCBF) distribution in late middle‐aged and older adults with treated or untreated OSA. Twelve controls (64.8 ± 8.0 years) and 23 participants with newly diagnosed OSA (67.8 ± 6.2 years) were evaluated with polysomnography and cerebral ^99mTc‐HMPAO single‐photon emission computed tomography during wakeful rest. OSA participants were referred to a sleep apnea clinic and 13 of them decided to start continuous positive airway pressure (CPAP). Participants were tested again after 18 months. Voxel‐based analysis and extracted relative rCBF values were used to assess longitudinal changes. Untreated OSA participants showed decreased relative rCBF in the left hippocampus and the right parahippocampal gyrus over time, while treated participants showed trends for increased relative rCBF in the left hippocampus and the right parahippocampal gyrus. No changes were found over time in controls. Untreated OSA is associated with worsening relative rCBF in specific brain areas over time, while treated OSA shows the opposite. Considering that OSA possibly accelerates cognitive decline in older adults, CPAP treatment could help reduce risk for cognitive impairment.

Retinal vascular impairment in patients newly diagnosed with obstructive sleep apnea syndrome

Background

To evaluate retinal morphological and vascular parameters in patients recently diagnosed with obstructive sleep apnea syndrome (OSAS) and determine the correlation between retinal vascular density and the severity of OSAS.

Methods

We performed a retrospective study on the retinal vasculature of patients with OSAS and age-match healthy controls. OSAS was confirmed by full-night cardiorespiratory polygraphy. Patients were divided into three groups according to disease severity given by apnea-hypopnea index (AHI) i.e., mild, moderate or severe. Retinal thicknesses and vascular density were compared among groups, for both the macula and optic disc. Correlation between vascular density and clinical features were also assessed.

Results

The study included 30 eyes of patients with OSAS and 12 controls. No differences were found regarding retinal thickness in both the macula and the optic disc between OSAS patients and controls. In contrast, significant differences were found in the peripapillary vessel density between groups versus control patients. The greatest difference being between severe OSAS and controls (49.4% ± 2.1 versus 40.4% ± 4.2 respectively, p=0.01). Peripapillary vessel density was found to significantly and negatively correlate with AHI (p=0.02; r= -0.74) and directly correlate with the lowest percutaneous oxygen saturation (p=0.02; r= 0.58).

Conclusions

This study indicates that OSAS is associated with retinal microvasculature impairment, that seems to mainly affect the optic disc. This suggests that microvascular damage increases with the increasing severity of OSAS. As such, prospective trials are needed to clarify if this vascular peripapillary damage precedes glaucomatous optic neuropathy in OSAS patients.

Association Between Sleep Apnea Risk Score and Retinal Microvasculature Using Optical Coherence Tomography Angiography

PURPOSE

To investigate the retinal vessel changes at peripapillary and parafoveal regions using optical coherence tomography angiography in patients with varying obstructive sleep apnea syndrome (OSAS) risk, identified by the STOP-BANG questionnaire.

DESIGN

Prospective, hospital-based cross-sectional study.

METHODS

Participants were divided into 3 groups based on the OSAS risk score. Flow areas and vessel densities were calculated at peripapillary and parafoveal regions using optical coherence tomography angiography. Microvasculature changes between the 3 groups and correlation between OSAS risk score and vascular changes were calculated.

RESULTS

Six hundred and six eyes of 303 patients were included in groups 1 (n = 96), 2 (n = 135), and 3 (n = 72). In patients with high OSAS risk, an increase in flow areas (P = .011) and vessel densities (P = .002) in superficial capillary plexus was noted. In contrast, flow areas (P = .003) and vessel densities (P < .000) in deep capillary plexus were reduced. Positive correlation was noted between sleep scores and vessel densities in superficial capillary plexus (P = .04). Negative correlation was noted between sleep scores and flow areas (P = .003) and vessel densities (P ≤ .001) in deep capillary plexus.

CONCLUSION

The sleep apnea questionnaire is an easy method of identifying the disease severity stage, but polysomnography still remains the definitive gold standard. Optical coherence tomography angiography shows some associations with disease severity, but it cannot be used unambiguously to distinguish the severity of sleep apnea.

Prevalence of Sleep Apnea in Patients with Carotid Artery Stenosis

Obstructive sleep apnea (OSA) is a common disease affecting about 13% of men and 6% of women, usually having severe cardiovascular sequalae. OSA is responsible for the systemic inflammatory response and oxidative stress and results in endothelial injury being a risk factor for atherosclerosis. The aim of this study was to estimate the prevalence of OSA among patients with severe carotid artery stenosis. Fifty-five patients (F/M-24/31, mean age 70 ± 7 years, body mass index 28.3 ± 6.3 kg/m²) were enrolled into the study. The patients were qualified for elective surgical treatment of carotid artery stenosis. Polysomnography was performed in all patients the night before surgery. Thirty-six patients underwent surgical endarterectomy and nineteen patients underwent carotid artery stenting. Sleep apnea was diagnosed in 44 (80%) of all patients. The mean apnea-hypopnea index (AHI) was 14.5 ± 12.9. The OSA severity distribution was as follows: 22 mild, 16 moderate, and 6 severe cases. We found that the percentage of carotid endarterectomies was the greatest in mild and moderate OSA. It was approximately twofold greater than that in non-OSA patients. Carotid artery stenting was performed in nearly half of the patients in each of these groups. We conclude that OSA is highly prevalent in patients with carotid artery stenosis scheduled for carotid surgery. Nonetheless, the exact pathogenetic mechanisms underlying mutual interaction between OSA and vascular wall damage remain elusive. OSA is not routinely diagnosed among patients with advanced atherosclerosis. The study results might be an argument for performing polysomnography in patients with carotid artery stenosis.

Sleep and Stroke: New Updates on Epidemiology, Pathophysiology, Assessment, and Treatment

PURPOSE OF REVIEW

This review aims to discuss the most recent data on sleep disorders and stroke, highlighting relevant findings for the practicing neurologist or health providers who encounter patients with sleep disorders and stroke.

RECENT FINDINGS

Sleep apnea and abnormal sleep duration have the strongest association with stroke risk. Possible mechanisms include non-dipping of blood pressure during sleep, hypoxemia or reoxygenation leading to sympathetic activation, hypertension, atrial fibrillation and impaired cerebral hemodynamics. Treatment studies suggest that continuous positive airway pressure (CPAP) for sleep apnea could improve primary prevention of stroke, but data is equivocal for secondary prevention. However, CPAP could improve functional outcomes after stroke.

SUMMARY

Sleep disorders present an opportunity to improve stroke risk and functional outcomes. However, new strategies are needed to determine the patients at high-risk who would most likely benefit from targeted care. Novel methods for phenotyping sleep disorders could provide personalized stroke care to improve clinical outcomes and public health strategies.

Evaluation of retinal vasculature before and after treatment of children with obstructive sleep apnea-hypopnea syndrome by optical coherence tomography angiography

PURPOSE

To evaluate the effect of adenoidectomy on the brains of children with obstructive sleep apnea-hypopnea syndrome (OSAS) through observation of the alteration of retinal perfusion by optical coherence tomography angiography (OCTA).

METHODS

Sixty-two children with OSAS (124 eyes; 5.94 ± 1.64 years old; 53.2% boys) were enrolled in this study. Their retinal vascular network density indices, including vascular diameter (VD), vascular area density (VAD), vessel skeleton density (VSD), vessel perimeter index (VPI) on the macular superficial/deep capillary plexus (SCP/DCP), and the size of the foveal avascular zone (FAZ) were analyzed by OCTA before treatment and at 1 month after the adenoidectomy.

RESULTS

After the adenoidectomy, the values of VD, VAD, VSD, and VPI in the SCP/DCP of the parafovea were significantly increased (p < 0.01). The FAZ was significantly diminished in the SCP (t = 4.50, p < 0.05) and increased in the DCP (t = - 4.43, p < 0.05). The peripapillary indices in the SCP/DCP were not significantly changed (p > 0.05).

CONCLUSION

By improvement of hypoxia, the response of the parafoveal vessels was more sensitive than that of the peripapillary region in children with OSAS. Therefore, OCTA may be an ideal method to evaluate the changes of the retinal vascular system, which could be an effective parameter for the early evaluation of adenoidectomy on cases of pediatric OSAS.

Human cerebral blood flow control during hypoxia: focus on chronic pulmonary obstructive disease and obstructive sleep apnea

The brain is a vital organ that relies on a constant and adequate blood flow to match oxygen and glucose delivery with the local metabolic demands of active neurons. Thus exquisite regulation of cerebral blood flow (CBF) is particularly important under hypoxic conditions to prevent a detrimental decrease in the partial pressure of oxygen within the brain tissues. Cerebrovascular sensitivity to hypoxia, assessed as the change in CBF during a hypoxic challenge, represents the capacity of cerebral vessels to respond to, and compensate for, a reduced oxygen supply, and has been shown to be impaired or blunted in a number of conditions. For instance, this is observed with aging, and in clinical conditions such as untreated obstructive sleep apnea (OSA) and in healthy humans exposed to intermittent hypoxia. This review will 1) provide a brief overview of cerebral blood flow regulation and results of pharmacological intervention studies which we have performed to better elucidate the basic mechanisms of cerebrovascular regulation in humans; and 2) present data from studies in clinical and healthy populations, using a translational physiology approach, to investigate human CBF control during hypoxia. Results from studies in patients with chronic obstructive pulmonary disease and OSA will be presented to identify the effects of the disease processes on cerebrovascular sensitivity to hypoxia. Data emerging from experimental human models of intermittent hypoxia during wakefulness will also be reviewed to highlight the effects of intermittent hypoxia on the brain.

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

NEW FINDINGS

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