Intermittent hypoxia, cardiovascular disease and obstructive sleep apnoea

Biological sex-related differences in the postprandial triglyceride response to intermittent hypoxaemia in young adults: a randomized crossover trial

Obstructive sleep apnoea is characterized by chronic intermittent hypoxaemia and is independently associated with an increased risk of metabolic comorbidities (e.g. type II diabetes and ischaemic heart disease). These comorbidities could be attributable to hypoxaemia-induced alterations in blood lipid profiles. However, it remains unclear whether intermittent hypoxaemia alters triglyceridaemia differently between biological sexes. Therefore, we used a randomized crossover design to examine whether 6 h of moderate intermittent hypoxaemia (15 hypoxaemic cycles/h, 85% oxyhaemoglobin saturation) alters plasma triglyceride levels differently between men and women after a high-fat meal. Relative to men, women displayed lower levels of total triglycerides, in addition to denser triglyceride-rich lipoprotein triglycerides (TRL-TG; mainly very low-density lipoprotein triglycerides and chylomicron remnant triglycerides) and buoyant TRL-TG (mainly chylomicron triglycerides) during normoxia (ambient air) and intermittent hypoxaemia (sex × time: all P ≤ 0.008). Intermittent hypoxaemia led to higher triglyceride levels (condition: all P ≤ 0.016); however, this effect was observed only in men (sex × condition: all P ≤ 0.002). Compared with normoxia, glucose levels were higher in men and lower in women during intermittent hypoxaemia (sex × condition: P < 0.001). The different postprandial responses between biological sexes occurred despite similar reductions in mean oxyhaemoglobin saturation and similar elevations in insulin levels, non-esterified fatty acid levels and mean heart rate (sex × condition: all P ≥ 0.185). These results support growing evidence showing that intermittent hypoxaemia impacts men and women differently, and they might help to explain biological sex-related discrepancies in the rate of certain comorbidities associated with intermittent hypoxaemia. KEY POINTS: Intermittent hypoxaemia is a key characteristic of obstructive sleep apnoea and alters lipid metabolism in multiple tissues, resulting in increased circulating triglyceride levels, an important risk factor for cardiometabolic diseases. Circulating triglyceride levels are regulated differently between biological sexes, with women typically displaying much lower fasting and postprandial triglyceride levels than men, partly explaining why women of all ages experience lower mortality rates from cardiometabolic diseases. In this study, healthy young men and women consumed a high-fat meal and were then exposed to 6 h of intermittent hypoxaemia or ambient air. We show that postprandial triglyceride levels are significantly lower in women compared with men and that intermittent hypoxaemia leads to higher postprandial triglyceride levels in men only. These results might help us to understand better why women living with obstructive sleep apnoea experience lower rates of cardiometabolic diseases (e.g. type II diabetes and ischaemic heart disease) than men living with obstructive sleep apnoea.

Prognostic value of hypoxaemic burden from overnight oximetry in heart failure with preserved ejection fraction

AIMS

Nocturnal hypoxaemic burden, quantified as time spent with oxygen saturation below 90% (T90), is an established independent predictor of mortality in heart failure (HF) with reduced ejection fraction. The prognostic value of T90 in HF with preserved ejection fraction (HFpEF) is unknown. This study aims to determine the association of T90 with adverse outcomes in HFpEF.

METHODS AND RESULTS

One hundred twenty-six patients prospectively included from our specialised HFpEF outpatient clinic underwent ambulatory home sleep monitoring to obtain oximetry data, including T90. We investigated the association between T90 and a composite endpoint of HF hospitalisations or all-cause mortality. Nocturnal hypoxaemic burden in this HFpEF population was high, with a median T90 of 13.7 min. In only 10 patients (7.9%), oxygen saturation was at no time point below 90%. After median 34 months [IQR 18.4-52.0] of follow-up, 32 patients (25%) reached the composite endpoint. T90 was significantly associated with the composite endpoint, also after adjusting for potential confounders (HR 1.004 (95% CI 1.001-1.007, P = 0.019) per 1 min T90 increase or HR 1.265 (95% CI 1.061-1.488) per 1 h T90 increase). Patients with HFpEF in the highest T90 tertile (T90 ≥ 31.4 min) had a significantly higher event rate compared to patients in the lowest two T90 tertiles, with 19 (45%) versus 13 (15%) events, respectively (P < 0.001).

CONCLUSIONS

Nocturnal hypoxaemic burden is an independent prognostic marker for the composite of HF hospitalisations or all-cause mortality in HFpEF. Whether reduction of T90 improves the prognosis of patients with HFpEF warrants further research.

The relationships between intermittent hypoxia and oxidative stress in patients with sleep apnea syndrome

Intermittent hypoxia in sleep apnea syndrome (SAS) patients increases the oxidative stress and can cause serious cardiovascular diseases such as hypertension or atherosclerotic diseases through endothelial dysfunction. The evaluation of risk caused by oxidative stress, however, is not easy in a clinical setting. Thus, we intended to evaluate the changes in oxidative stress by SAS treatment using a simple method that can be easily used in the clinical testing. We enrolled 42 consecutive newly diagnosed severe SAS patients (30 men). Reactive oxygen species metabolites (d-ROMs) for oxidative stress and biological antioxidant (BAP) in blood samples were estimated using FREE Carrio Duo® before and 3 months after continuous positive airway pressure (CPAP) treatment. SAS parameters were obtained by polysomnography before CPAP and endothelial function was measured twice as well. The body mass index and apnea hypopnea index (AHI) were 29.1 ± 5.3 and 57.9 ± 19.7/h. The d-ROMs and BAP were 317.4 ± 71.8 CARR U and 2121.2 ± 299.6 μmol/L. Although no significant correlation was found between hypoxia parameters and d-ROMs or BAP before CPAP treatment, we found a significant negative correlation between basal AHI or basal oxygen desaturation index representing intermittent hypoxia and the change in d-ROMs (r = - 0.31, p = 0.046/r = - 0.33, p = 0.03) and between the change in SpO2 < 90% duration (min) representing continuous hypoxia and the change in BAP (r = - 0.35, p = 0.03) after CPAP treatment. The changes in d-ROM and BAP might reflect the different kind of reduction of oxidative stress by CPAP treatment and, thus, can be used as handy indicators of the treatment effect.

Impact of obstructive sleep apnoea on postoperative outcomes of patients undergoing coronary artery bypass grafting: a systematic review and meta-analysis

OBJECTIVE

To assess the association between obstructive sleep apnoea (OSA) and postoperative complications in patients after coronary artery bypass graft (CABG).

METHODS

PubMed, Embase, Web of Science and Scopus databases were explored to identify relevant observational studies that reported incidences of OSA in CABG patients, and assessed OSA using standard objective methods such as polysomnography (PSG). The primary outcomes of interest were risk of major adverse cardiac and cerebrovascular events (MACCE) and all-cause mortality. Pooled effect sizes were reported as odds ratio (OR) with 95% confidence intervals.

RESULTS

Twelve studies were included. All studies, except one, had a prospective cohort design. CABG patients with OSA had increased risk of MACCE (OR 1.71, 95% CI: 1.16, 2.53), myocardial infarction (MI) (OR 2.21, 95% CI: 1.19, 4.13), pulmonary complications (OR 1.86, 95% CI: 1.03, 3.38), renal complications (OR 8.14, 95% CI: 2.07, 32.1), heart failure (OR 1.86, 95% CI: 1.19, 2.89) and need for revascularization (OR 2.80, 95% CI: 1.01, 7.75). However, risk of all-cause mortality (OR 1.63, 95% CI: 0.75, 3.52) was comparable in all patients.

CONCLUSION

This study showed that OSA significantly correlates with the increased risk of major adverse events. Our results indicate that recognizing and managing OSA in CABG patients is crucial for mitigating associated risks.

The effect of supplemental oxygen and continuous positive airway pressure withdrawal on endocan levels

PURPOSE

Endocan is a biomarker of endothelial dysfunction, which is a precursor to cardiovascular disease. Obstructive sleep apnoea (OSA) is associated with elevated endocan levels but the effects of treatment on endocan levels in OSA are not fully established. We aimed to determine whether endocan levels could be detected by immunoassay and to determine the effect of supplemental oxygen during continuous positive airway pressure (CPAP) withdrawal on circulating endocan levels.

METHODS

We conducted an exploratory analysis from a randomised controlled crossover study which included participants with OSA. Participants stopped their CPAP therapy and were randomised to receive either supplemental oxygen or sham for 14 nights before crossing over. Supplemental oxygen blocked the rise in blood pressure seen in the sham group. We analysed plasma endocan levels by immunoassay at baseline and after 14 nights of intervention in both groups.

RESULTS

Twenty-five participants were included, with a total of 100 samples. Endocan levels were detectable at all time points in 22 participants (88%), and in 93 (93%) samples. Supplemental oxygen had no effect on endocan levels compared to sham (+ 0.52 ng/ml, 95%CI -0.21 to + 1.25, p = 0.16), and there was no significant difference in endocan levels from baseline to follow-up in either the sham (-0.30 ng/ml, 95%CI -0.89 to + 0.30, p = 0.31) or supplemental oxygen (+ 0.22 ng/ml, 95%CI 0.00 to + 0.44, p = 0.05) arm.

CONCLUSIONS

We have shown that endocan levels are detectable before and after CPAP withdrawal. However, we found no effect of supplemental oxygen following CPAP withdrawal on circulating endocan levels.

TRIAL REGISTRATION AND DATE

ISRCTN 17,987,510 19/02/2015.

Prolonged intermittent hypoxia differentially regulates phrenic motor neuron serotonin receptor expression in rats following chronic cervical spinal cord injury

Low-dose (< 2 h/day), acute intermittent hypoxia (AIH) elicits multiple forms of serotonin-dependent phrenic motor plasticity and is emerging as a promising therapeutic strategy to restore respiratory and non-respiratory motor function after spinal cord injury (SCI). In contrast, high-dose (> 8 h/day), chronic intermittent hypoxia (CIH) undermines some forms of serotonin-dependent phrenic motor plasticity and elicits pathology. CIH is a hallmark of sleep disordered breathing, which is highly prevalent in individuals with cervical SCI. Interestingly, AIH and CIH preconditioning differentially impact phrenic motor plasticity. Although mechanisms of AIH-induced plasticity in the phrenic motor system are well-described in naïve rats, we know little concerning how these mechanisms are affected by chronic SCI or intermittent hypoxia preconditioning. Thus, in a rat model of chronic, incomplete cervical SCI (lateral spinal hemisection at C2 (C2Hx), we assessed serotonin type 2A, 2B and 7 receptor expression in and near phrenic motor neurons and compared: 1) intact vs. chronically injured rats; and 2) the impact of preconditioning with varied "doses" of intermittent hypoxia (IH). While there were no effects of chronic injury or intermittent hypoxia alone, CIH affected multiple receptors in rats with chronic C2Hx. Specifically, CIH preconditioning (8 h/day; 28 days) increased serotonin 2A and 7 receptor expression exclusively in rats with chronic C2Hx. Understanding the complex, context-specific interactions between chronic SCI and CIH and how this ultimately impacts phrenic motor plasticity is important as we leverage AIH-induced motor plasticity to restore breathing and other non-respiratory motor functions in people with chronic SCI.

Obstructive sleep apnea, coronary calcification and arterial stiffness in patients with diabetic kidney disease

BACKGROUND AND AIMS

Obstructive sleep apnea (OSA) may accelerate arterial calcification, but the relation remains unexplored in diabetic kidney disease (DKD). We examined the associations between OSA, coronary calcification and large artery stiffness in patients with DKD and reduced renal function.

METHODS

Patients with type 2 diabetes, estimated glomerular filtration rate (eGFR) < 60 ml/min/1.73 m2 and urine albumin-creatinine ratio (UACR) > 30 mg/g were tested for OSA quantified by the apnea-hypopnea index (AHI, events/hour). Patients without OSA (AHI< 5) were compared to patients with moderate (AHI 15-29) or severe (AHI ≥30) OSA and underwent computed tomography angiography with coronary Agatston scoring (CAS) to quantify coronary calcification. Arterial stiffness was determined as carotid-femoral pulse wave velocity (PWV).

RESULTS

Among 114 patients with acceptable AHI recordings had 43 no OSA, 33 mild OSA and 38 moderate-severe OSA. Mean age of the 74 patients completing the study was 71.5 ± 9.4 years (73% males), eGFR 32.2 ± 12.3 ml/min/1.73 m2 and UACR 533 (192-1707) mg/g. CAS (ln-transformed) was significantly higher in patients with OSA compared to patients without (6.6 ± 1.7 vs. 5.6 ± 2.4, p = 0.04), and the same was observed for PWV (11.9 ± 2.7 vs. 10.5 ± 2.2 m/s, p = 0.02). In multivariable linear regression analyses adjusted for sex, age, body mass index, UACR, and mean arterial pressure, moderate-severe OSA remained significantly associated with PWV but not with CAS. Dominance analysis revealed OSA as the third and second most important factor relative to CAS and PWV respectively.

CONCLUSIONS

In DKD patients, moderate-severe OSA is a significant predictor of arterial stiffness but is not independently associated with coronary calcification.

[Obstructive sleep apnea in cardiology clinical practice. Epidemiology, diagnosis, and treatment. Observational, cross-sectional, retrospective study]

Objective

To determine the clinical-epidemiological characteristics, diagnostic feasibility of home respiratory polygraphy and treatment of patients with suspected obstructive sleep apnea (OSA) at cardiovascular risk.

Methods

An observational, cross-sectional, descriptive study was conducted in patients seen in a cardiology outpatient service with suspected OSA, from January 2015 to December 2019. The information was obtained from medical records, and a descriptive statistical analysis was applied to this information.

Results

138 files were reviewed; only 8% of the home respiratory polygraphs were discarded, because they did not meet the required quality standards. It was demonstrated that 89% suffered from OSA, 60% moderate to severe; in men after 50 years of age. The main cardiovascular risk factors was hypertension (89%). The most prevalent heart disease was hypertension (52%). Cardiovascular pharmacological treatment was improved in 82% of the cases. Cardiac rehabilitation in 30%, noninvasive mechanical ventilation 41%, fixed modality 33%, and self-adjustable 9%, all with telemetry.

Conclusions

The prevalence and severity of OSA is higher in the presence of risk or established cardiovascular disease. In the presence of clinical suspicion, it is feasible to confirm the diagnosis with home respiratory poligrafy due to the level of precision and the lower infrastructure required. Greater involvement of the cardiologist in the diagnosis and treatment of this disorder is necessary due to the significant risk of cardiovascular disease it represents.

Nocturnal oxygen saturation is associated with all-cause mortality: a community-based study

STUDY OBJECTIVES

Observational studies have demonstrated the association between the single-point measurement of oxygen saturation (SpO2) level and mortality in the general population. This study aimed to evaluate whether nocturnal SpO2 level could predict all-cause mortality in a community-based population.

METHODS

The study samples were obtained from the Sleep Heart Health Study, which included 2,280 men and 2,606 women (mean age, 63.8 ± 11.1 years). A pulse oximeter based on overnight in-home polysomnography was used to monitor SpO2 levels during total sleep time (SpO2-TOTAL). Multivariable Cox proportional hazards analysis was performed to examine the association between nocturnal SpO2 and all-cause mortality.

RESULTS

During the follow-up period of 10.7 ± 3.0 years, 1,110 (22.7%) people died. After adjusting for confounding factors, multivariable Cox regression analysis showed that the average SpO2-TOTAL (hazard ratio [HR] 0.93; 95% confidence interval [CI] 0.90-0.96, P < .001) was associated with all-cause mortality. These findings remained stable in individuals with low and high apnea-hypopnea index levels. Additionally, maximum SpO2-TOTAL (HR, 0.91; 95% CI, 0.87-0.96; P = .001) and minimum SpO2-TOTAL (HR, 0.98; 95% CI, 0.97-0.99; P = .001) could predict all-cause mortality. A significant association between nocturnal hypoxemia and all-cause mortality was also observed.

CONCLUSIONS

Our findings highlight the importance of monitoring nocturnal SpO2 level and improving hypoxemia in the general populations.

CITATION

Yan B, Gao Y, Zhang Z, Shi T, Chen Q. Nocturnal oxygen saturation is associated with all-cause mortality: a community-based study. J Clin Sleep Med. 2024;20(2):229-235.

Acute Effect of Positive Airway Pressure on Heart Rate Variability in Obstructive Sleep Apnea

Autonomic dysregulation is associated with cardiovascular consequences in obstructive sleep apnea (OSA). This study aimed to investigate the effect of acute continuous positive airway pressure (CPAP) treatment on autonomic activity and to identify factors contributing to heart rate variability (HRV) changes in OSA. Frequency domain HRV parameters were calculated and compared between the baseline polysomnography and during the CPAP titration in 402 patients with moderate to severe OSA. There were significant reductions in total power, very low-frequency band power, low-frequency band power, and high-frequency band power during the CPAP titration as compared to the baseline polysomnography. This tendency was pronounced in male patients with severe OSA. Multivariate analysis found that changes in the apnea-hypopnea index and oxygen saturation were significantly associated with changes in sympathetic and parasympathetic activity, respectively. This study demonstrated that HRV parameters significantly changed during the CPAP titration, indicating a beneficial effect of CPAP in the restoration of sympathetic and parasympathetic hyperactivity in OSA. Prospective longitudinal studies should determine whether long-term CPAP treatment aids in maintaining the long-lasting improvement of the autonomic functions, thereby contributing to the prevention of cardiovascular and cerebrovascular diseases in patients with OSA.

Microglia dynamic response and phenotype heterogeneity in neural regeneration following hypoxic-ischemic brain injury

Hypoxic-ischemic brain injury poses a significant threat to the neural niche within the central nervous system. In response to this pathological process, microglia, as innate immune cells in the central nervous system, undergo rapid morphological, molecular and functional changes. Here, we comprehensively review these dynamic changes in microglial response to hypoxic-ischemic brain injury under pathological conditions, including stroke, chronic intermittent hypoxia and neonatal hypoxic-ischemic brain injury. We focus on the regulation of signaling pathways under hypoxic-ischemic brain injury and further describe the process of microenvironment remodeling and neural tissue regeneration mediated by microglia after hypoxic-ischemic injury.

Association Between Arterial Stiffness and Measures of Autonomic Dysfunction in People With Chronic Kidney Disease

Background

Autonomic nervous system (ANS) dysfunction and vascular stiffness increase cardiovascular risk in people with chronic kidney disease (CKD). Chronic elevations in sympathetic activity can lead to increased arterial stiffness; however, the relationship between these variables is unknown in CKD.

Objective

To explore the association between measures of autonomic function and arterial stiffness in patients with moderate-to-severe CKD.

Methods

This study was a prespecified secondary analysis of a randomized controlled trial. This included the following measures: 24-hour ambulatory blood pressure (BP), carotid-femoral and carotid-radial pulse wave velocity (PWV), and postexercise heart rate recovery (HRR). We used mixed effect linear regression models with Bayesian information criteria (BIC) to assess the contribution of ANS measurements.

Results

Forty-four patients were included in the analysis. Mean carotid-femoral and carotid-radial PWV were 7.12 m/s (95% CI 6.13, 8.12) and 8.51 m/s (7.90, 9.11), respectively. Mean systolic dipping, calculated as percentage change in mean systolic readings from day to night, was 10.0% (95% CI 7.79, 12.18). Systolic dipping was independently associated with carotid-radial PWV, MD -0.09 m/s (95% CI -0.15, -0.02) and had the lowest BIC.

Conclusions

Systolic dipping was associated with carotid-radial PWV in people with moderate-to-severe CKD; however, there was no association with carotid-femoral PWV. Systolic dipping may be a feasible surrogate of ANS function, as the association with carotid-radial PWV was consistent with the minimal clinically important difference (MCID). Future studies are needed to define the relationship between ANS function, arterial stiffness, and CV events over time in people with CKD.

Loss of heme oxygenase 2 causes reduced expression of genes in cardiac muscle development and contractility and leads to cardiomyopathy in mice

Obstructive sleep apnea (OSA) is a common breathing disorder that affects a significant portion of the adult population. In addition to causing excessive daytime sleepiness and neurocognitive effects, OSA is an independent risk factor for cardiovascular disease; however, the underlying mechanisms are not completely understood. Using exposure to intermittent hypoxia (IH) to mimic OSA, we have recently reported that mice exposed to IH exhibit endothelial cell (EC) activation, which is an early process preceding the development of cardiovascular disease. Although widely used, IH models have several limitations such as the severity of hypoxia, which does not occur in most patients with OSA. Recent studies reported that mice with deletion of hemeoxygenase 2 (Hmox2-/-), which plays a key role in oxygen sensing in the carotid body, exhibit spontaneous apneas during sleep and elevated levels of catecholamines. Here, using RNA-sequencing we investigated the transcriptomic changes in aortic ECs and heart tissue to understand the changes that occur in Hmox2-/- mice. In addition, we evaluated cardiac structure, function, and electrical properties by using echocardiogram and electrocardiogram in these mice. We found that Hmox2-/- mice exhibited aortic EC activation. Transcriptomic analysis in aortic ECs showed differentially expressed genes enriched in blood coagulation, cell adhesion, cellular respiration and cardiac muscle development and contraction. Similarly, transcriptomic analysis in heart tissue showed a differentially expressed gene set enriched in mitochondrial translation, oxidative phosphorylation and cardiac muscle development. Analysis of transcriptomic data from aortic ECs and heart tissue showed loss of Hmox2 gene might have common cellular network footprints on aortic endothelial cells and heart tissue. Echocardiographic evaluation showed that Hmox2-/- mice develop progressive dilated cardiomyopathy and conduction abnormalities compared to Hmox2+/+ mice. In conclusion, we found that Hmox2-/- mice, which spontaneously develop apneas exhibit EC activation and transcriptomic and functional changes consistent with heart failure.

No impact of a high-fat meal coupled with intermittent hypoxemia on acute kidney injury biomarkers in adults with and without obstructive sleep apnea

Obstructive sleep apnea (OSA) is characterized by chronic intermittent hypoxemia, which is associated with progressive loss of kidney function, where postprandial fluctuations in renal physiology may further compromise oxygen supply and kidney function. Therefore, we measured biomarkers of acute kidney injury (AKI) following a high-fat meal with and without intermittent hypoxemia. Eighteen healthy young men (mean age [SD]: 22.7 years [3.1]) and seven middle-aged to older individuals with OSA (54.4 years [6.4]) consumed a high-fat meal during normoxia or intermittent hypoxemia (~15 hypoxic cycles per hour, ~85% oxyhemoglobin saturation) for 6 h. We observed no changes in estimated glomerular filtration rate and plasma concentrations of creatinine, neutrophil gelatinase-associated lipocalin (NGAL), and kidney injury molecule-1 (KIM-1) at any measured time points. In both groups, plasma concentrations of interleukin-18 (IL-18) increased after 6 h during normoxia only (p = 0.033, ηp 2  = 0.122), and plasma concentrations of liver-type fatty acid-binding protein (L-FABP) transiently decreased after 3 h in both conditions (p = 0.008, ηp 2  = 0.152). These findings indicate that AKI biomarkers are not acutely elevated during the postprandial state with or without intermittent hypoxemia, suggesting that other mechanisms may play more important roles in the progression of kidney disease in OSA.

Influence of obstructive sleep apnea syndrome on the contralateral optic nerve in patients with unilateral nonarteritic anterior ischemic optic neuropathy

STUDY OBJECTIVES

The aim was to quantitatively evaluate the influence of obstructive sleep apnea syndrome (OSAS) on the morphology and function of the contralateral optic nerve in patients with unilateral nonarteritic anterior ischemic optic neuropathy (NAION).

METHODS

Fifty patients with unilateral NAION were divided into non-OSAS (n = 16), mild OSAS (n = 15), and moderate-severe OSAS (n = 19) groups based on their apnea-hypopnea index (AHI) scores. Systemic and ocular characteristics were compared between these groups. Spearman correlation and multiple linear regression analyses were used to determine the independent factors that most influenced the thickness of the peripapillary retinal nerve fiber layer (pRNFL).

RESULTS

Body mass index and hypertension occurrence were higher in the moderate-severe OSAS group than in the non-OSAS group. Temporal pRNFL was thinner in the moderate-severe group than in the mild and non-OSAS groups, whereas no difference was found between the mild and non-OSAS groups. Spearman correlation showed that the AHI (r = -.469, P = .001) and the percentage of total sleep time with oxygen saturation < 90% (T90%; r = -.477, P = .001) correlated with temporal pRNFL thickness. Multiple linear regression showed that the AHI was negatively associated with temporal pRNFL thickness (β = -0.573, P = .003).

CONCLUSIONS

OSAS may cause subclinical temporal pRNFL thinning in the contralateral optic nerve among patients with unilateral NAION without any significant change in visual function. Advanced optic nerve observation and intervention may be warranted in patients with moderate-severe OSAS.

CITATION

Li X, Zhang Y, Guo T, et al. Influence of obstructive sleep apnea syndrome on the contralateral optic nerve in patients with unilateral nonarteritic anterior ischemic optic neuropathy. J Clin Sleep Med. 2023;19(2):347-353.

Neurotrophins in the Neuropathophysiology, Course, and Complications of Obstructive Sleep Apnea-A Narrative Review

Obstructive sleep apnea (OSA) is a disorder characterized by chronic intermittent hypoxia and sleep fragmentation due to recurring airway collapse during sleep. It is highly prevalent in modern societies, and due to its pleiotropic influence on the organism and numerous sequelae, it burdens patients and physicians. Neurotrophins (NTs), proteins that modulate the functioning and development of the central nervous system, such as brain-derived neurotrophic factor (BDNF), have been associated with OSA, primarily due to their probable involvement in offsetting the decline in cognitive functions which accompanies OSA. However, NTs influence multiple aspects of biological functioning, such as immunity. Thus, extensive evaluation of their role in OSA might enlighten the mechanism behind some of its elusive features, such as the increased risk of developing an immune-mediated disease or the association of OSA with cardiovascular diseases. In this review, we examine the interactions between NTs and OSA and discuss their contribution to OSA pathophysiology, complications, as well as comorbidities.

Combined Airway and Bariatric Surgery (CABS) for Obstructive Sleep Apnea Patients with Morbid Obesity: A Comprehensive Alternative Preliminary Study

Although continuous positive airway pressure is the gold standard for obstructive sleep apnea (OSA), it does not improve obesity. By contrast, bariatric surgery significantly improves obesity but with sustained OSA in the majority of patients. This study proposes a comprehensive technique—combined airway and bariatric surgery (CABS)—to improve both obesity and OSA. The aims of the study are to evaluate the feasibility, safety and efficacy of CABS in morbidly obese OSA patients. The retrospective study enrolled 20 morbidly obese OSA patients (13 males; median age, 44 years; median apnea−hypopnea index (AHI), 63.2 event/h; median body mass index (BMI), 41.4 kg/m2). The study population was divided into two groups based on patients’ volition after shared decision making. The bariatric surgery (BS) group included laparoscopic sleeve gastrectomy (LSG, n = 8) and laparoscopic Roux-en-Y gastric bypass (LRYGB, n = 2). CABS involved bariatric surgery—LSG (n = 8) and LRYGB (n = 2) in conjunction with airway surgery (concurrent nasal/palatal/lingual surgery [n = 8], concurrent palatal/lingual surgery [n = 2]). Patients received a home sleep apnea test at baseline and one year after surgery. The two patient groups were not different in age, sex, preoperative AHI or preoperative BMI. There was no airway compromise, wound bleeding or infection throughout the postoperative period. One year after surgery, patients in both groups achieved significant improvement in AHI and BMI. Furthermore, the improvement in AHI was significantly higher (p = 0.04) in the CABS group than in the BS group despite the insignificant change in BMI reduction (p = 0.63) between the two groups. In the CABS group, the BMI dropped from 40.4 to 28.4 kg/m2 (p < 0.0001) and the AHI decreased from 75.1 to 4.5 event/h (p = 0.0004). The classic success rate for OSA was 90% and the cure rate was 60% in the CABS group. A perioperative assessment of CABS group patients also revealed a significant improvement in the Epworth sleepiness scale, minimal O2 saturation, snoring index and heart rate. CABS is feasible and safe in treating OSA with morbid obesity. CABS achieves more reduction in AHI than BS alone with high success and cure rates for OSA. CABS can also significantly improve quality of life and general health and offers a comprehensive alternative for morbidly obese OSA patients.

Temporal changes in coronary artery function and flow velocity reserve in mice exposed to chronic intermittent hypoxia

Study Objectives

Obstructive sleep apnea (OSA) is a chronic condition characterized by intermittent hypoxia (IH) that is implicated in an increased risk of cardiovascular disease (i.e., coronary heart disease, CHD) and associated with increased overall and cardiac-specific mortality. Accordingly, we tested the hypothesis that experimental IH progressively impairs coronary vascular function and in vivo coronary flow reserve.

Methods

Male C57BL/6J mice (8-week-old) were exposed to IH (FiO2 21% 90 s–6% 90 s) or room air (RA; 21%) 12 h/day during the light cycle for 2, 6, 16, and 28 weeks. Coronary artery flow velocity reserve (CFVR) was measured at each time point using a Doppler system. After euthanasia, coronary arteries were micro-dissected and mounted on wire myograph to assess reactivity to acetylcholine (ACh) and sodium nitroprusside (SNP).

Results

Endothelium-dependent coronary relaxation to ACh was preserved after 2 weeks of IH (80.6 ± 7.8%) compared to RA (87.8 ± 7.8%, p = 0.23), but was significantly impaired after 6 weeks of IH (58.7 ± 16.2%, p = 0.02). Compared to ACh responses at 6 weeks, endothelial dysfunction was more pronounced in mice exposed to 16 weeks (48.2 ± 5.3%) but did not worsen following 28 weeks of IH (44.8 ± 11.6%). A 2-week normoxic recovery after a 6-week IH exposure reversed the ACh abnormalities. CFVR was significantly reduced after 6 (p = 0.0006) and 28 weeks (p &lt; 0.0001) of IH when compared to controls.

Conclusion

Chronic IH emulating the hypoxia-re-oxygenation cycles of moderate-to-severe OSA promotes coronary artery endothelial dysfunction and CFVR reductions in mice, which progressively worsen until reaching asymptote between 16 and 28 weeks. Normoxic recovery after 6 weeks exposure reverses the vascular abnormalities.

Associations of the Severity of Obstructive Sleep Apnea With Age-Related Comorbidities: A Population-Based Study

Aging is accompanied by changes in the quantity and quality of sleep. Obstructive sleep apnea (OSA) is also more prevalent in the older population. Although severe OSA has been linked to a higher risk of cardiovascular disease regardless of adult age, clinical consequences of mild-to-moderate OSA in the older adults are still uncertain.

Objectives

To investigate the relationships between severity and metabolic, cognitive, and functional characteristics in community-dwelling older adults from a representative sample of the city of São Paulo.

Methods

In total, 199 participants of the first follow-up of the São Paulo Epidemiologic Sleep Study (EPISONO, São Paulo, Brazil) &gt;60 years were cross-sectionally assessed through questionnaires, physical evaluations, laboratory tests, and full in-lab polysomnography (PSG). Three groups according to the OSA severity were compared according to sociodemographic characteristics, anthropometric measures, PSG parameters, the frequency of comorbidities, and the use of medications.

Results

Participants' age ranged from 60 to 87 years with a mean of 70.02 ± 7.31, 59.8% female. In the univariate analysis, body mass index (BMI, kg/m2) (p = 0.049) and waist circumference (p = 0.005) were significantly higher in the participants with moderate OSA, but not among those with severe OSA. Participants with severe OSA had a higher arousal index (p = 0.007). Multivariate analysis showed that severe OSA was significantly associated with hypertension (p = 0.005), heart diseases (p = 0.025), and the use of two or more medications (p = 0.035).

Conclusion

In a population-based study, severe, but not mild-to-moderate, OSA in older adults was associated with hypertension and the use of more medications. As age advances, anthropometric indicators of obesity may not increase the risk of severe OSA.

Relationships Between Cardinal Features of Obstructive Sleep Apnea and Blood Pressure: A Retrospective Study

BACKGROUND

Obstructive sleep apnea (OSA) is associated with hypertension; however, the associations between cardinal features of OSA, such as intermittent hypoxia (IH) and sleep fragmentation (SF), and blood pressure remain unclear. We performed this study to address this issue.

METHOD

We investigated 335 subjects with the polysomnography (PSG) tests. Data, including basic characteristics, PSG parameters, and blood pressure, were collected. We calculated p-values for linear trends of blood pressure across oxygen-desaturation index (ODI)/microarousal index (MAI) quartiles. Logistic regressions were used to determine the risk factors for abnormal blood pressure and to detect the multiplicative interaction between ODI and MAI with blood pressure.

RESULTS

After adjusting for multiple variables, compared with subjects with lower ODI quartiles, those with higher ODI quartiles had significant higher systolic blood pressure (SBP) and diastolic blood pressure (DBP) (p for trend = 0.010 and 0.018, respectively). And compared with subjects with lower ODI quartiles, those with higher ODI quartiles were also more likely to have abnormal DBP and hypertension after adjusting for multiple variables. Similarly, compared with subjects with lower MAI quartiles, those with higher MAI quartiles had significant higher SBP and DBP, and were more likely to have abnormal DBP and hypertension. No significant multiplicative interactions between ODI and MAI with blood pressure were detected.

CONCLUSION

Subjects with more severe IH/SF had significant higher blood pressure and were more likely to have abnormal DBP and hypertension than those with less severe IH/SF. No interaction between IH and SF on the relationship with blood pressure was shown.

Influence of nocturnal hypoxemia on follow-up course after type B acute aortic syndrome

Introduction

Association between sleep nocturnal breathing disorders and acute aortic syndrome (AAS) has been described but mid-term data are scarce.

Objectives

We assessed the prognostic value of sleep apnea parameters and their relationship with aortic morphology after the onset of a type B AAS.

Methods

Between January 2010 and January 2018, sleep apnea screening in post type B AAS was prospectively performed. The association of sleep apnea parameters with aortic morphology and aortic expansion during follow-up was studied.

Results

Over the 8-year-study period, 103 patients were included, with a mean age of 57.8 ± 12.1 years old. Median follow-up was 25.0 months (11.0–51.0). Thirty-two patients (31%) required aortic stenting during the acute phase. In patients treated by aortic stenting, the descending thoracic aortic diameter was positively associated with a higher percentage of nocturnal time of saturation ≤ 90% after adjustment (p = 0.016). During follow-up, the nocturnal time of saturation ≤ 90% in patients treated by medical therapy was the only parameter associated with significant aortic expansion rate (r = 0.26, p = 0.04). Thirty-eight patients started and sustained nocturnal ventilation during follow-up. The association between aortic expansion rate and nocturnal time of saturation ≤ 90% did not persist during follow-up after adjustment on nocturnal ventilation initiation (r = 0.25, p = 0.056).

Conclusions

Nocturnal hypoxemia parameters are positively associated with the max onset aortic diameter and significant aortic growth after type B AAS. Nocturnal ventilation seems to mitigate aortic expansion during follow-up.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-021-01778-y.

Intermittent Hypoxemia in Preterm Infants: A Potential Proinflammatory Process

OBJECTIVE

A major consequence of prematurity is intermittent hypoxemia (IH). Data from both adult studies and neonatal animal models suggest that IH is proinflammatory; however, there is limited data in preterm infants. Here, we assess the relationship between IH and systemic inflammation, namely, serum C-reactive protein (CRP) in preterm infants.

STUDY DESIGN

Serum CRP was measured at 30 days of life, at the time of peak IH frequency. IH measures (e.g., per cent time in hypoxemia, frequency, duration) were calculated the week prior to CRP collection. Statistical analyses were based on Spearman's correlation.

RESULTS

A total of 26 infants were included. Median gestational age and birth weight were 27^4/7 weeks and 980 g, respectively. There were positive correlations between primary IH measures and CRP levels, especially for events longer than 1-minute duration (r range: 0.56-0.74, all p < 0.01).

CONCLUSION

We demonstrate that IH is associated with increased CRP for the first time in preterm infants. Our findings are consistent with studies from adults and neonatal animal models suggesting that IH is a proinflammatory process.

KEY POINTS

· IH events are common.. · IH is associated with elevated C-reactive protein.. · Longer IH events (>1 min) are of most significance..

Aryl Hydrocarbon Receptor and Cysteine Redox Dynamics Underlie (Mal)adaptive Mechanisms to Chronic Intermittent Hypoxia in Kidney Cortex

We hypothesized that an interplay between aryl hydrocarbon receptor (AhR) and cysteine-related thiolome at the kidney cortex underlies the mechanisms of (mal)adaptation to chronic intermittent hypoxia (CIH), promoting arterial hypertension (HTN). Using a rat model of CIH-HTN, we investigated the impact of short-term (1 and 7 days), mid-term (14 and 21 days, pre-HTN), and long-term intermittent hypoxia (IH) (up to 60 days, established HTN) on CYP1A1 protein level (a sensitive hallmark of AhR activation) and cysteine-related thiol pools. We found that acute and chronic IH had opposite effects on CYP1A1 and the thiolome. While short-term IH decreased CYP1A1 and increased protein-S-thiolation, long-term IH increased CYP1A1 and free oxidized cysteine. In addition, an in vitro administration of cystine, but not cysteine, to human endothelial cells increased Cyp1a1 expression, supporting cystine as a putative AhR activator. This study supports CYP1A1 as a biomarker of obstructive sleep apnea (OSA) severity and oxidized pools of cysteine as risk indicator of OSA-HTN. This work contributes to a better understanding of the mechanisms underlying the phenotype of OSA-HTN, mimicked by this model, which is in line with precision medicine challenges in OSA.

Microbiota Modulates Cardiac Transcriptional Responses to Intermittent Hypoxia and Hypercapnia

The microbiota plays a critical role in regulating organismal health and response to environmental stresses. Intermittent hypoxia and hypercapnia, a condition that represents the main hallmark of obstructive sleep apnea in humans, is known to induce significant alterations in the gut microbiome and metabolism, and promotes the progression of atherosclerosis in mouse models. To further understand the role of the microbiome in the cardiovascular response to intermittent hypoxia and hypercapnia, we developed a new rodent cage system that allows exposure of mice to controlled levels of O₂ and CO₂ under gnotobiotic conditions. Using this experimental setup, we determined the impact of the microbiome on the transcriptional response to intermittent hypoxia and hypercapnia in the left ventricle of the mouse heart. We identified significant changes in gene expression in both conventionally reared and germ-free mice. Following intermittent hypoxia and hypercapnia exposure, we detected 192 significant changes in conventionally reared mice (96 upregulated and 96 downregulated) and 161 significant changes (70 upregulated and 91 downregulated) in germ-free mice. Only 19 of these differentially expressed transcripts (∼10%) were common to conventionally reared and germ-free mice. Such distinct transcriptional responses imply that the host microbiota plays an important role in regulating the host transcriptional response to intermittent hypoxia and hypercapnia in the mouse heart.

Cell-Selective Altered Cargo Properties of Extracellular Vesicles Following In Vitro Exposures to Intermittent Hypoxia

Intermittent hypoxia (IH), a hallmark of obstructive sleep apnea (OSA), is associated with cardiovascular and metabolic dysfunction. However, the mechanisms underlying these morbidities remain poorly delineated. Extracellular vesicles (EVs) mediate intercellular communications, play pivotal roles in a multitude of physiological and pathological processes, and could mediate IH-induced cellular effects. Here, the effects of IH on human primary cells and the release of EVs were examined. Microvascular endothelial cells (HMVEC-d), THP1 monocytes, THP1 macrophages M0, THP1 macrophages M1, THP1 macrophages M2, pre-adipocytes, and differentiated adipocytes (HAd) were exposed to either room air (RA) or IH for 24 h. Secreted EVs were isolated and characterized using transmission electron microscopy, nanoparticle tracking analysis, and Western blotting. The effects of each of the cell-derived EVs on endothelial cell (EC) monolayer barrier integrity, on naïve THP1 macrophage polarity, and on adipocyte insulin sensitivity were also evaluated. IH did not alter EVs cell quantal release, but IH-EVs derived from HMVEC-d (p < 0.01), THP1 M0 (p < 0.01) and HAd (p < 0.05) significantly disrupted HMVEC-d monolayer integrity, particularly after H₂O₂ pre-conditioning. IH-EVs from HMVEC-d and THP1 M0 elicited M2-polarity changes did not alter insulin sensitivity responses. IH induces cell-selective changes in EVs cargo, which primarily seem to target the emergence of endothelial dysfunction. Thus, changes in EVs cargo from selected cell sources in vivo may play causal roles in some of the adverse outcomes associated with OSA.

VE-cadherin cleavage in sleep apnoea: new insights into intermittent hypoxia-related endothelial permeability

BACKGROUND

Obstructive sleep apnoea (OSA) causes intermittent hypoxia that in turn induces endothelial dysfunction and atherosclerosis progression. We hypothesised that VE-cadherin cleavage, detected by its released extracellular fragment solubilised in the blood (sVE), may be an early indicator of emergent abnormal endothelial permeability. Our aim was to assess VE-cadherin cleavage in OSA patients and in in vivo and in vitro intermittent hypoxia models to decipher the cellular mechanisms and consequences.

METHODS

Sera from seven healthy volunteers exposed to 14 nights of intermittent hypoxia, 43 OSA patients and 31 healthy control subjects were analysed for their sVE content. Human aortic endothelial cells (HAECs) were exposed to 6 h of intermittent hypoxia in vitro, with or without an antioxidant or inhibitors of hypoxia-inducible factor (HIF)-1, tyrosine kinases or vascular endothelial growth factor (VEGF) pathways. VE-cadherin cleavage and phosphorylation were evaluated, and endothelial permeability was assessed by measuring transendothelial electrical resistance (TEER) and fluorescein isothiocyanate (FITC)-dextran flux.

RESULTS

sVE was significantly elevated in sera from healthy volunteers submitted to intermittent hypoxia and OSA patients before treatment, but conversely decreased in OSA patients after 6 months of continuous positive airway pressure treatment. OSA was the main factor accounting for sVE variations in a multivariate analysis. In in vitro experiments, cleavage and expression of VE-cadherin increased upon HAEC exposure to intermittent hypoxia. TEER decreased and FITC-dextran flux increased. These effects were reversed by all of the pharmacological inhibitors tested.

CONCLUSIONS

We suggest that in OSA, intermittent hypoxia increases endothelial permeability in OSA by inducing VE-cadherin cleavage through reactive oxygen species production, and activation of HIF-1, VEGF and tyrosine kinase pathways.

Angiopoietin-like proteins 8 knockout reduces intermittent hypoxia-induced vascular remodeling in a murine model of obstructive sleep apnea

OBJECTIVE

Obstructive sleep apnea (OSA) is a major risk factor for cardiovascular mortality. Apnea-induced chronic intermittent hypoxia (CIH) is a primary pathophysiological manifestation of OSA that promotes various cardiovascular alterations, such as aortic vascular remodeling. In this study, we investigated the association between angiopoietin-like proteins 8 (ANGPTL8) and CIH-induced aortic vascular remodeling in mice.

METHODS

C57BL/6J male mice were divided into four groups: Normoxia group, ANGPTL8^-/- group, CIH group, CIH + ANGPTL8^-/- group. Mice in the normoxia group and ANGPTL8^-/- group received no treatment, while mice in the CIH and CIH + ANGPTL8^-/- group were subjected to CIH (21%-5% O₂, 180 s/cycle, 10 h/day) for 6 weeks. At the end of the experiments, intima-media thickness (IMT), elastin disorganization, and aortic wall collagen abundance were assessed in vivo. Immunohistochemistry and Western-blot were used to detect endoplasmic reticulum stress (ERS) and aortic vascular smooth muscle cell proliferation. ANGPTL8 shRNA and ANGPL8 overexpression were used in aortic vascular smooth muscle cells to investigate the mechanism of ANGPTL8 in CIH.

RESULTS

Compared to the control group, CIH exposure significantly increased intima-media thickness (IMT), elastic fibers disorganization, and aortic wall collagen abundance. CIH also significantly increased blood pressure, induced hyperlipidemia, as well as the expression of ERS protein activating transcription factor-6 (ATF6) and aortic vascular smooth muscle cell proliferation. Contrary, ANGPTL8^-/- significantly mitigated the CIH-induced vascular remodeling; ANGPTL8^-/- decreased CIH-induced hypertension and hyperlipidemia, inhibited the protein expression of ATF6, and aortic vascular smooth muscle cell proliferation. Moreover, our in vitro study suggested that CIH could induce ANGPTL8 expression via hypoxia-inducible factor (HIF-1α); ANGPTL8 induced proliferation of aortic vascular smooth muscle cells via the ERS pathway.

CONCLUSION

ANGPTL8^-/- can prevent CIH-induced aortic vascular remodeling, probably through the inhibition of the ERS pathway. Therefore, ANGPTL8 might be a potential target in CIH-induced aortic vascular remodeling.

Oxygen Therapy in Sleep-Disordered Breathing

Sleep-disordered breathing (SDB) is highly prevalent in adults and leads to significant cardiovascular and neurologic sequelae. Intermittent hypoxia during sleep is a direct consequence of SDB. Administration of nocturnal supplemental oxygen (NSO) has been used as a therapeutic alternative to positive airway pressure (PAP) in SDB. NSO significantly improves oxygen saturation in OSA but is inferior to PAP in terms of reducing apnea severity and may prolong the duration of obstructive apneas. The effect of NSO on daytime sleepiness remains unclear, but NSO may improve physical function-related quality of life in OSA. Its effects on BP reduction remain inconclusive. The effects of NSO vs PAP in OSA with comorbid COPD (overlap syndrome) are unknown. NSO is effective in reducing central sleep apnea related to congestive heart failure; however, its impact on mortality and cardiovascular clinical outcomes are being investigated in an ongoing clinical trial. In conclusion, studies are inconclusive or limited regarding clinical outcomes with oxygen therapy compared with sham or PAP therapy in patients with OSA and overlap syndrome. Oxygen does mitigate central sleep apnea. This review examines the crucial knowledge gaps and suggests future research priorities to clarify the effects of optimal dose and duration of NSO, alone or in combination with PAP, on cardiovascular, sleep, and cognitive outcomes.

Obstructive sleep apnoea, intermittent hypoxia and heart failure with a preserved ejection fraction

Obstructive sleep apnoea (OSA) is recognised to be a potent risk factor for hypertension, coronary heart disease, strokes and heart failure with a reduced ejection fraction. However, the association between OSA and heart failure with a preserved ejection fraction (HFpEF) is less well recognised. Both conditions are very common globally.It appears that there are many similarities between the pathological effects of OSA and other known aetiologies of HFpEF and its postulated pathophysiology. Intermittent hypoxia induced by OSA leads to widespread stimulation of the sympathetic nervous system, renin-angiotensin-aldosterone system and more importantly a systemic inflammatory state associated with oxidative stress. This is similar to the consequences of hypertension, diabetes, obesity and ageing that are the common precursors to HFpEF. The final common pathway is probably via the development of myocardial fibrosis and structural changes in collagen and myocardial titin that cause myocardial stiffening. Thus, considering the pathophysiology of OSA and HFpEF, OSA is likely to be a significant risk factor for HFpEF and further trials of preventive treatment should be considered.

Endothelial Dysfunction in a Cell Culture Model Exposed to Various Intermittent Hypoxia Modes

Wang, Juan, Jiahui Wang, Xin Li, Wanju Hou, Jie Cao, and Jing Feng. Endothelial dysfunction in a cell culture model exposed to various intermittent hypoxia modes. High Alt Med Biol. 21:388-395, 2020. Objective: To construct an in vitro model of endothelial cells exposed to various intermittent hypoxia (IH) modes, and determine whether different frequencies and degrees can cause different effects on endothelial cells. Methods: EA.hy926 cells were used to set up the cell model. A program-controlled gas delivery system was designed to regulate the flow of premixed air into the cell culture chamber. The cells were divided into eight groups exposed to various IH modes: standard cell culture group, intermittent normoxia (IN) group (21% O₂ 15 seconds/21% O₂ 3 minutes 45 seconds for 12 cycles/h), IH1 group (1.5% O₂ 15 seconds/21% O₂ 8 minutes 15 seconds for 6.32 cycles/h), IH2 group (1.5% O₂ 15 seconds/21% O₂ 5 minutes 15 seconds for 9.23 cycles/h), IH3 group (1.5% O₂ 15 seconds/21% O₂ 3 minutes 45 seconds for 12 cycles/h), IH4 group (1.5% O₂ 15 seconds/21% O₂ 1 minute 45 seconds for 20 cycles/h), IH5 group (1.5% O₂ 15 seconds/21% O₂ 15 seconds for 40 cycles/h), and IH6 group (10% O₂ 15 seconds/21% O₂ 3 minutes 45 seconds for 12 cycles/h). Results: Nuclear factor κB (NFκB) p65, c-fos, tumor necrosis factor-alpha (TNFα), malondialdehyde (MDA), and endothelin-1 (ET-1) were higher in the IH3 group or IH6 group than those in IN group, and they were much higher in IH3 group than those in IH6 group. Superoxide dismutase (SOD) and nitric oxide (NO) were the opposite results. In IH1, IH2, IH3, IH4, and IH5 groups, the frequencies increased gradually. NFκB p65, TNFα, and c-fos were the highest in IH3 group. MDA and ET-1 were the highest in IH2 group. SOD and NO were the lowest in IH2 group. Conclusions: Different IH frequencies and degrees could cause different effects on endothelial cells. The endothelial responses varied with the duration of reoxygenation. So, the duration of reoxygenation was the key phase for endothelial dysfunction.

Optimal Continuous Positive Airway Pressure Treatment of Obstructive Sleep Apnea Reduces Daytime Resting Heart Rate in Prediabetes: A Randomized Controlled Study

Background It has been widely recognized that obstructive sleep apnea (OSA) is linked to cardiovascular disease. Yet, randomized controlled studies failed to demonstrate a clear cardiovascular benefit from OSA treatment, mainly because of poor adherence to continuous positive airway pressure (CPAP). To date, no prior study has assessed the effect of CPAP treatment on daytime resting heart rate, a strong predictor of adverse cardiovascular outcomes and mortality. Methods and Results We conducted a randomized controlled study in 39 participants with OSA and prediabetes, who received either in-laboratory all-night (ie, optimal) CPAP or an oral placebo for 2 weeks. During daytime, participants continued daily activities outside the laboratory. Resting heart rate was continuously assessed over 19 consecutive days and nights using an ambulatory device consisting of a single-lead ECG and triaxis accelerometer. Compared with placebo, CPAP reduced daytime resting heart rate (treatment difference, -4.1 beats/min; 95% CI, -6.5 to -1.7 beats/min; P=0.002). The magnitude of reduction in daytime resting heart rate after treatment significantly correlated with the magnitude of decrease in plasma norepinephrine, a marker of sympathetic activity (r=0.44; P=0.02), and the magnitude of decrease in OSA severity (ie, apnea-hypopnea index [r=0.48; P=0.005], oxygen desaturation index [r=0.50; P=0.003], and microarousal index [r=0.57; P<0.001]). Conclusions This proof-of-concept randomized controlled study demonstrates, for the first time, that CPAP treatment, when optimally used at night, reduces resting heart rate during the day, and therefore has positive cardiovascular carry over effects. These findings suggest that better identification and treatment of OSA may have important clinical implications for cardiovascular disease prevention. Registration URL: https:/// www.clini​caltr​ials.gov; Unique identifier: NCT01156116.

Chronic intermittent hypoxia vs chronic continuous hypoxia: Effects on vascular endothelial function and myocardial contractility

BACKGROUND AND AIM

Both chronic intermittent hypoxia (CIH) and chronic continuous hypoxia (CCH) are risk factors for cardiovascular disease, which are associated with cardiac systolic function and associated with dysfunction of endothelia and coagulation-fibrinolysis system in the vasculature. However, the different effects of these two hypoxic models are not fully understood. In our study, we systemically compared the effects of CIH and CCH on cardiac function and related factor levels in serum using rat model.

METHODS

Forty-five male Sprague-Dawley rats were randomly divided into the normoxia control (NC), CIH and CCH groups. The rat CIH and CCH models were established, then the blood and tissue samples were collected to analyze the function of endothelium and the coagulation-fibrinolysis system. Also, the ultrasound cardiogram was performed to directly assess myocardial contractility.

RESULTS

Both CIH and CCH significantly decreased the NO, eNOS, P-eNOS and AT-III levels in the rat serum but significantly increased the levels of ET-1, vWF, COX-2, NF-κB, FIB, FVIII and PAI-1 in the rat serum (P < 0.05). The expression of ET-1, VWF and ICAM-1 in CIH group were higher than CCH group (P < 0.05), however, the expression of CD62p was increased in CCH group but not in CIH group. The expression of t-PA in CIH group were lower than CCH group (P < 0.05), but there were no significant differences in CCH group and NC group (P > 0.05). Using transmission electron microscope, we found that the mitochondrial ultrastructure of thoracic aorta endothelial cells in CIH and CCH group were damaged. Moreover, the myocardial contractility in CIH and CCH group were significantly decreased compared with NC group.

CONCLUSION

Our results suggested that CIH and CCH could cause endothelial dysfunction, dysfunction of the coagulation-fibrinolysis system and decreasing of myocardial contractility. Compared with CCH, CIH has greater effect on vasoconstriction and adhesion of vascular endothelial cells, and stronger procoagulant effect.

Lipoprotein-associated phospholipase A2 predicted cardiovascular disease in obstructive sleep apnea syndrome

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) is an independent risk factor for cardiovascular disease (CVD). As a new inflammatory biomarker of CVD, rare attention has been paid to the roles of lipoprotein-associated phospholipase (Lp-PLA2) in OSAS studies. In this study, we aimed to investigate the correlation between Lp-PLA2 and concomitant CVD in OSAS patients.

METHODS

In this prospective study, 152 OSAS patients were further divided into mild, moderate, and severe OSAS subgroups. They presented heart failure, coronary artery disease, or arrhythmia were confirmed with CVD. Thirty-one subjects without OSAS were recruited for the control group. The relationship between Lp-PLA2 and concomitant CVD in OSAS patients was analyzed.

RESULTS

Serum Lp-PLA2 values were significantly higher in the severe and moderate OSAS group compared with mild OSAS and OSAS negative groups (P = 0.025). Significant increase was noticed in serum Lp-PLA2 levels in CVD patients compared with those without in severe-moderate-mild OSAS (P < 0.05). In logistic regression analysis, the level of Lp-PLA2 was proved as a significant independent predictor for CVD (OR = 1.117, P = 0.008). The ROC analysis indicated that the best cut-off value of Lp-PLA2 for predicting CVD in OSAS patients was 238.09 ng/ml. The positive and negative predictive values were 72.5% and 70.5%, respectively. The sensitivity was 46.8% and the specificity was 87.8%.

CONCLUSIONS

Lp-PLA2 might be associated with the severity of OSAS and the occurrence of CVD in OSAS patients. Lp-PLA2 is expected to be a promising biomarker candidate in predicting CVD in patients with OSAS due to test convenience.

Low oxygen microenvironment and cardiovascular remodeling: Role of dual L/N.type Ca2+ channel blocker

OBJECTIVE

Patients exposed to chronic sustained hypoxia frequently develop cardiovascular disease risk factors to ultimately succumb to adverse cardiovascular events. In this context, the present study intends to assess the role of cilnidipine (Cil), a unique calcium channel blocker that blocks both L-type and N-type calcium channels, on cardiovascular pathophysiology in face of chronic sustained hypoxia exposure.

MATERIALS AND METHODS

The study involved Wistar strain albino rats. The group-wise allocation of the experimental animals is as follows - Group 1, control (21% O₂); Group 2, chronic hypoxia (CH) (10% O₂, 90% N); Group 3, Cil + 21% O₂; and Group 4, CH (10% O₂, 90% N) + Cil (CH + Cil). Cardiovascular hemodynamics, heart rate variability, and endothelial functions (serum nitric oxide [NO], serum endothelial nitric oxide synthase [NOS3], and serum vascular endothelial growth factor [VEGF]) were assessed. Cardiovascular remodeling was studied by histopathological examination of the ventricular tissues, coronary artery (intramyocardial), and elastic and muscular arteries. Normalized wall index of the coronary artery was also calculated.

RESULTS AND CONCLUSION

The results demonstrated altered cardiovascular hemodynamics, disturbed cardiovascular autonomic balance, increased levels of VEGF and NOS3, and decreased bioavailability of NO on exposure to chronic sustained hypoxia. The histopathological examination further pointed toward cardiovascular remodeling. Treatment with Cil ameliorated the cardiovascular remodeling and endothelial dysfunction induced by CH exposure, which may be due to its blocking actions on L/N-type of calcium channels, indicating the possible therapeutic role of Cil against CH-induced cardiovascular pathophysiology.

Relationship between monocyte to HDL cholesterol ratio and concomitant cardiovascular disease in Chinese Han patients with obstructive sleep apnea

Background

Obstructive sleep apnea (OSA) is an independent risk factor for cardiovascular disease (CVD), which is attributed to chronic intermittent hypoxia (CIH) induced inflammation. As a new inflammatory biomarker of CVD, monocyte to high-density lipoprotein cholesterol ratio (MHR) has received little attention in OSA studies to date. Therefore, we aimed to investigate the correlation between MHR and concomitant CVD in Chinese Han patients with OSA.

Methods

A total of 657 Chinese Han subjects (169 controls, 145 mild, 94 moderate, and 249 severe OSA) of both genders were enrolled in this cross-sectional study, with an average BMI of 32.35±6.56 kg/m². The relationship between MHR and concomitant CVD in OSA patients was analyzed.

Results

The level of MHR was correlated positively with apnea-hypopnea index (AHI), while negatively with lowest SpO₂ (P<0.01). Moreover, the MHR values were higher in OSA patients with CVD than those without CVD (17.64±7.16 vs. 12.73±5.06, P<0.001). Logistic regression analysis demonstrated that MHR is an independent predictor of CVD (OR =1.190, P<0.001). The ROC analysis indicated that the best cut-off value of MHR for predicting CVD in OSA patients was 15.364 (sensitivity 65.0%, specificity 74.4%), while its cutoff value for identifying CVD in severe OSA patients was 15.362 (sensitivity 67.3%, specificity 80.1%).

Conclusions

MHR is strongly correlated with the severity of OSA and the occurrence of CVD in OSA patients. As an easy and available test, MHR is expected to be a promising biomarker candidate in predicting CVD in Chinese Han patients with OSA.

A dual blocker of endothelin A/B receptors mitigates hypertension but not renal dysfunction in a rat model of chronic kidney disease and sleep apnea

Obstructive sleep apnea is characterized by recurrent episodes of pharyngeal collapse during sleep, resulting in intermittent hypoxia (IH), and is associated with a high incidence of hypertension and accelerated renal failure. In rodents, endothelin (ET)-1 contributes to IH-induced hypertension, and ET-1 levels inversely correlate with glomerular filtration rate in patients with end-stage chronic kidney disease (CKD). Therefore, we hypothesized that a dual ET receptor antagonist, macitentan (Actelion Pharmaceuticals), will attenuate and reverse hypertension and renal dysfunction in a rat model of combined IH and CKD. Male Sprague-Dawley rats received one of three diets (control, 0.2% adenine, and 0.2% adenine + 30 mg·kg^-1·day^-1 macitentan) for 2 wk followed by 2 wk of recovery diet. Rats were then exposed for 4 wk to air or IH (20 short exposures/h to 5% O₂-5% CO₂ 7 h/day during sleep). Macitentan prevented the increases in mean arterial blood pressure caused by CKD, IH, and the combination of CKD + IH. However, macitentan did not improve kidney function, fibrosis, and inflammation. After CKD was established, rats were exposed to air or IH for 2 wk, and macitentan feeding continued for 2 more wk. Macitentan reversed the hypertension in IH, CKD, and CKD + IH groups without improving renal function. Our data suggest that macitentan could be an effective antihypertensive in patients with CKD and irreversible kidney damage as a way to protect the heart, brain, and eyes from elevated arterial pressure, but it does not reverse toxin-induced tubule atrophy.