Plasminogen Activator Inhibitor-1 in Obstructive Sleep Apnea Patients with and without Hypertension

Association Between the Severity of Obstructive Sleep Apnea and the Risk Stratification of Acute Pulmonary Embolism

Obstructive sleep apnea (OSA) has been associated with the initiation and progression of cardiovascular disease. This study aimed to explore the relationship between the severity of OSA and the risk stratification of acute pulmonary embolism (PE). In this single-center cohort study, patients diagnosed with PE were evaluated for OSA via polygraphy monitoring. The simplified PE severity index (sPESI) and the number of patients requiring systemic thrombolysis were used to determine the severity of the disease. Echocardiography was performed on all participants. All patients were divided into 2 groups (OSA group and non-OSA group), and the patients in OSA group were then divided into 3 groups based on the severity of OSA. Patients with severe OSA had a significantly higher number of patients with sPESI ≥ 1 (P = .005). A higher proportion of patients with severe OSA require systemic thrombolysis (P = .010). Patients with apnea-hypopnea index (AHI) > 30/h had a much higher fibrinogen (P = .004) and D-dimer (P = .040) level than those in the non-OSA group. The levels of creatinine were significantly higher in patients with OSA (P = .040). Echocardiography showed a significant difference in left ventricular ejection fraction (LVEF) between patients in non-OSA and severe OSA groups (P = .035). And brain natriuretic peptide (BNP) also exhibited a progressive worsening related to the deepest desaturation and oxygen desaturation index. OSA, especially with AHI > 30/h, is correlated with the severity and prognosis of acute PE. This might be attributed to the prothrombotic effect, renal impairment, and cardiac dysfunction in patients with severe OSA.

Obstructive sleep apnoea and venous thromboembolism: pathophysiological links and clinical implications

Obstructive sleep apnoea (OSA) and pulmonary embolism (PE) remain major health issues worldwide. Data from pathophysiological studies suggest that both intermittent hypoxia and sleep fragmentation are associated with increased blood coagulability, endothelial dysfunction and venous stasis. There is growing evidence that OSA is potentially prevalent in and a risk factor for PE. Conversely, patients with acute PE have two to four times greater risk of moderate-to-severe OSA. The role of continuous positive airway pressure (CPAP) treatment in improving clinically meaningful outcomes in PE patients remains unclear, although some authors have suggested that CPAP could improve the hypercoagulability state and normalise circadian alterations in some of the coagulation molecules, as observed in patients with OSA. Emerging research highlights the complex interdependent relationships between OSA and PE, emphasising the need for rigorous, well-powered trials that address the impact of OSA and its treatment on the prevention and management of PE. Undoubtedly, these will require closer collaboration between the sleep medicine and clinical/venous thromboembolism communities.

Feasibility Testing of a Self-Management Program Book to Improve Adherence to PAP in Persons Newly Diagnosed With Sleep Apnea

OBJECTIVES

To obtain feasibility data on a self-management program to improve adherence with positive airway pressure (PAP) in individuals with newly diagnosed obstructive sleep apnea.

METHODS

A mixed-methods design assessed program effectiveness and participants' opinions on program ease-of-use. Structured interviews with the treatment group occurred one week and one month after initiation of PAP therapy.

RESULTS

Participants (n = 14) completing the study demonstrated 64% adherence versus 58% of the controls. Ease of use was demonstrated.

CONCLUSIONS

The PAP self-management program demonstrated ease of use and was found somewhat effective in improving PAP adherence.

PRACTICE IMPLICATIONS

The book was useful in assisting participants by validating information obtained from their providers and developing an understanding of the consequences of not using PAP.

Impaired plasma clot lysis and its determinants in patients with obstructive sleep apnea syndrome

Evidence indicates that hypercoagulability and impaired fibrinolysis have been observed in patients with obstructive sleep apnea syndrome (OSAS). It is unclear which factors determine prolonged fibrin clot lysis in OSAS. One hundred and sixty-five consecutive patients suspected of OSAS underwent overnight polysomnography. Prior to polysomnography, we determined plasma clot lysis time (CLT), plasminogen activator inhibitor (PAI)-1 antigen, activated thrombin-activatable fibrinolysis inhibitor (TAFIa), plasmin, and antiplasmin. OSAS was diagnosed in 110 (66.7%) patients, including 35 (31.8%) with severe OSAS, 26 (23.6%) with moderate OSAS, and 49 (44.6%) mild OSAS. Compared with 55 (33.3%) individuals in whom OSAS was not confirmed, OSAS patients had prolonged CLT (+12.8%), associated with higher PAI-1 antigen (+18.1%) (after adjustment for age, diabetes, and body mass index; both P < 0.01) and similar levels of TAFIa, plasmin, or antiplasmin. PAI-1, TAFIa, and CLT correlated positively with apnea/hypopnea index, which reflects the severity of OSAS (R = 0.66, P < 0.001; R = 0.29, P = 0.002; R = 0.55, P = 0.001, respectively), and with other polysomnography parameters, with the most potent correlations observed for desaturation index. Regression analysis adjusted for potential confounders showed that in OSAS, CLT was independently predicted by apnea/hypopnea index (B = 0.29, P = 0.002), PAI-1 (B = 0.42, P < 0.001), and TAFIa (B = 0.81, P = 0.044), whereas both PAI-1 and TAFIa were predicted only by desaturation index (B = 0.24, P = 0.002; and B = 0.14, P = 0.001, respectively). The severity of OSAS is closely associated with hypofibrinolysis measured in a global plasma-based assay, driven largely by PAI-1. Attenuated fibrinolysis might contribute to high risk of thromboembolic events in this disease.

The effect of acute aerobic exercise on hemostasis in obstructive sleep apnea

PURPOSE

Individuals with obstructive sleep apnea (OSA) have an altered hemostatic balance; however, the exercise response is less described. The purpose of this study is to determine the hemostatic response after acute aerobic exercise in obstructive sleep apnea.

METHODS

Eighteen males (nine OSA vs. nine controls) were recruited from the university and local community. Individuals with evidence of cardiovascular, pulmonary, or metabolic disease were excluded. An apnea-hypopnea index (AHI) of >5 was a criterion for OSA. Subjects performed a treadmill exercise test at 35 and 70% predicted VO₂ reserve during the morning hours. Pre-exercise blood samples were obtained after 15 min supine rest and within 2 min following exercise. Repeated measures ANOVA were performed for factor VIII antigen, tissue plasminogen activator (tPA) antigen, tPA activity, and PAI-1 activity. Correlational analysis compared resting and post-exercise hemostatic factors with age, BMI, and AHI.

RESULTS

Mean AHI was 13.00 ± 12.6. No exercise × condition interactions were observed for hemostatic markers. There was a main effect for exercise in factor VIII, tPA antigen, and tPA activity in both groups. PAI-1 activity tended to be elevated in OSA (145%) compared to controls which remained after exercise (205%) (P = 0.05). Post-exercise FVIII/Ag correlated with BMI (r = 0.52), while resting tPA/Ag correlated with AHI (r = 0.49) and age (r = 0.50).

CONCLUSION

The hemostatic response after acute aerobic exercise is unaffected in mild OSA, although PAI-1 activity seems to be elevated, reducing fibrinolytic potential. BMI seems to correlate with FVIII/Ag, while tPA/Ag is associated with AHI and age.

Sleep apnea in total joint arthroplasty patients and the role for cardiac biomarkers for risk stratification: an exploration of feasibility

Obstructive sleep apnea (OSA) is highly prevalent in patients undergoing total joint arthroplasty (TJA) and is a major risk factor for postoperative cardiovascular complications and death. Recognizing this, the American Society of Anesthesiologists urges clinicians to implement special considerations in the perioperative care of OSA patients. However, as the volume of patients presenting for TJA increases, resources to implement these recommendations are limited. This necessitates mechanisms to efficiently risk stratify patients having OSA who may be susceptible to post-TJA cardiovascular complications. We explore the role of perioperative measurement of cardiac troponins (cTns) and brain natriuretic peptides (BNPs) in helping determine which OSA patients are at increased risk for post-TJA cardiovascular-related morbidity.

Evaluation of Fibrinolytic Inhibitors: Alpha-2-Antiplasmin and Plasminogen Activator Inhibitor 1 in Patients with Obstructive Sleep Apnoea

Obstructive sleep apnoea (OSA) induces thrombophilia and reduces fibrinolysis. Alpha-2-antiplasmin (a-2-AP) and plasminogen activator inhibitor 1 (PAI-1) are major inhibitors of the fibrinolytic system. Increased concentrations of these factors are associated with a higher risk of cardiovascular diseases. The aim of this study was to assess plasma a-2-AP and PAI-1 in patients with OSA and evaluate correlations with the polysomnographic record and selected risk factors of cardiovascular diseases. The study group comprised 45 patients with OSA, and the control group consisted of 19 patients who did not meet the diagnostic criteria of OSA. Plasma a-2-AP and PAI-1 concentrations were assessed by enzyme-linked immunosorbent assay (ELISA). In the study group, the median value of plasma a-2-AP was higher than that of the control group (157.34 vs. 11.89 pg/ml, respectively, P<0.0001). A-2-AP concentration increased proportionally to the severity of OSA. The concentration of a-2-AP was positively correlated with the apnoea-hypopnoea index (AHI), apnoea index (AI), respiratory disturbances time (RDT), and desaturaion index (DI), and negatively correlated with mean and minimal oxygen saturation (SpO2 mean, SpO2 min, respectively). The median value of PAI-1 was higher in the study group than the control group (12.55 vs. 5.40 ng/ml, respectively, P = 0.006) and increased along with OSA severity. PAI-1 concentration was positively correlated with AHI, AI, RDT, DI, and body mass index (BMI) and negatively correlated with SpO2 mean and SpO2 min. Higher plasma concentrations of a-2-AP and PAI-1 in patients with OSA indicated that these patients had increased prothrombotic activity. OSA increases the risk of cardiovascular complications as it enhances prothrombotic activity.

Diagnostic capability of biological markers in assessment of obstructive sleep apnea: a systematic review and meta-analysis

OBJECTIVE

The purpose of this systematic review is to evaluate the diagnostic value of biological markers (exhaled breath condensate, blood, salivary and urinary) in the diagnosis of OSA in comparison to the gold standard of nocturnal PSG.

METHODS

Studies that differentiated OSA from controls based on PSG results, without age restriction, were eligible for inclusion. The sample of selected studies could include studies in obese patients and with known cardiac disease. A detailed individual search strategy for each of the following bibliographic databases was developed: Cochrane, EMBASE, MEDLINE, PubMed, and LILACS. The references cited in these articles were also crosschecked and a partial grey literature search was undertaken using Google Scholar. The methodology of selected studies was evaluated using the 14-item Quality Assessment Tool for Diagnostic Accuracy Studies.

RESULTS

After a two-step selection process, nine articles were identified and subjected to qualitative and quantitative analyses. Among them, only one study conducted in children and one in adults found biomarkers that exhibit sufficiently satisfactory diagnostic accuracy that enables application as a diagnostic method for OSA.

CONCLUSION

Kallikrein-1, uromodulin, urocotin-3, and orosomucoid-1 when combined have enough accuracy to be an OSA diagnostic test in children. IL-6 and IL-10 plasma levels have potential to be good biomarkers in identifying or excluding the presence of OSA in adults.

Biomarkers associated with obstructive sleep apnea: A scoping review

The overall validity of biomarkers in the diagnosis of obstructive sleep apnea (OSA) remains unclear. We conducted a scoping review to provide assessments of biomarkers characteristics in the context of obstructive sleep apnea (OSA) and to identify gaps in the literature. A scoping review of studies in humans without age restriction that evaluated the potential diagnostic value of biological markers (blood, exhaled breath condensate, salivary, and urinary) in the OSA diagnosis was undertaken. Retained articles were those focused on the identification of biomarkers in subjects with OSA, the latter being confirmed with a full overnight or home-based polysomnography (PSG). Search strategies for six different databases were developed. The methodology of selected studies was classified using an adaptation of the evidence quality criteria from the American Academy of Pediatrics. Additionally the biomarkers were classified according to their potential clinical application. We identified 572 relevant studies, of which 117 met the inclusion criteria. Eighty-two studies were conducted in adults, 34 studies involved children, and one study had a sample composed of both adults and children. Most of the studies evaluated blood biomarkers. Potential diagnostic biomarkers were found in nine pediatric studies and in 58 adults studies. Only nine studies reported sensitivity and specificity, which varied substantially from 43% to 100%, and from 45% to 100%, respectively. Studies in adults have focused on the investigation of IL-6, TNF-α and hsCRP. There was no specific biomarker that was tested by a majority of authors in pediatric studies, and combinatorial urine biomarker approaches have shown preliminary promising results. In adults IL-6 and IL-10 seem to have a favorable potential to become a good biomarker to identify OSA.

The association between sleep characteristics and prothrombotic markers in a population-based sample: Chicago Area Sleep Study

BACKGROUND AND AIM

Short sleep duration and poor quality sleep are associated with coronary heart disease (CHD) mortality; however, the underlying pathophysiologic process remains unclear. Sleep apnea may confound the association because of its relationship with formation of thrombi, the vascular occlusive process in CHD. We tested whether sleep duration and quality were associated with prothrombotic biomarkers in adults with a low probability of apnea.

METHODS

We included adults aged 35-64 years recruited from the community and who had an apnea hypopnea index <15 after one night of screening (n=506). Sleep duration and maintenance were determined from 7 days of wrist actigraphy; daytime sleepiness was estimated using the Epworth Sleepiness Scale. Factor VIII (FVIII), von Willebrand factor (vWF), thrombin antithrombin (TAT) complexes, and plasminogen activator inhibitor-1 (PAI-1) were measured in fasting blood.

RESULTS

Sleep duration, maintenance, and daytime sleepiness were not associated with FVIII, vWf, or TAT. Sleep maintenance was modestly inversely associated with higher levels of log-transformed PAI-1 (β = -0.07, standard error (SE)=0.03 per 4.8%, p=0.04) following adjustment for demographic characteristics, cardiovascular risk factors, and body mass index (BMI).

CONCLUSIONS

Mild impairment in sleep was modestly associated with activation of coagulation; further study is needed to evaluate the role of fibrinolytic factors in sleep-mediated coronary thrombosis.

Circadian variability of fibrinolytic markers and endothelial function in patients with obstructive sleep apnea

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is strongly associated with cardiovascular disease, including stroke and acute coronary syndromes. Plasminogen activator inhibitor-1 (PAI-1), the principal inhibitor of tissue-type plasminogen activator (t-PA), has a pronounced circadian rhythm and is elevated in both OSA and cardiovascular disease and may be an important link between the two conditions. Endothelial dysfunction is one of the underlying pathophysiological mechanisms of cardiovascular disease, and may be altered in OSA. Our primary aim was to compare circadian variability of PAI-1 and t-PA in patients with OSA and normal controls by determining the amplitude (peak level) and mesor (rhythm adjusted mean) of PAI-1 and t-PA in serial blood samples over a 24-h period. The secondary aim was to measure markers of endothelial function (brachial and radial artery flow) in patients with OSA compared with normal controls.

SETTING

Cross-sectional cohort study.

PATIENTS OR PARTICIPANTS

Subjects age 18 y or older, with a body mass index of 25-45 kg/m(2), with or without evidence of untreated OSA.

INTERVENTIONS

Plasma samples were collected every 2 h, in OSA patients and matched controls, over a 24-h period. PAI-1 and t-PA antigen and activity were measured. The presence or absence of OSA (apnea-hypopnea index of 5 or greater) was confirmed by overnight polysomnography. Endothelial function was measured via brachial artery flow mediated vasodilatation and computerized arterial pulse waveform analysis.

MEASUREMENTS AND RESULTS

The rhythm-adjusted mean levels of PAI-1 antigen levels in the OSA group (21.8 ng/mL, 95% confidence level [CI], 18 to 25.7) were significantly higher as compared to the non-OSA group (16 ng/mL, 95% CI, 12.2 to 19.8; P = 0.03). The rhythm-adjusted mean levels of PAI-1 activity levels in the OSA group (23.9 IU/mL, 95% CI, 21.4 to 26.5) were also significantly higher than in the non-OSA group (17.2 IU/ mL, 95% CI, 14.6 to 19.9; P < 0.001).There were strong correlations between amplitude of PAI-1 activity and severity of OSA as measured by AHI (P = 0.02), and minimum oxygen levels during sleep (P = 0.04). Endothelial function parameters did not differ significantly between the two groups.

CONCLUSION

The presence of obstructive sleep apnea adversely affects circadian fibrinolytic balance with higher mean plasminogen activator inhibitor-1 activity and antigen, and significantly lower mean tissue-type plasminogen activator activity compared with controls. This perturbation may be an important mechanism for increased cardiovascular events in patients with obstructive sleep apnea. Intermittent hypoxia and changes in circadian clock gene activity in obstructive sleep apnea may be responsible for these findings and warrant further study. Favorable changes in fibrinolytic balance may underlie the reduction in cardiovascular events observed with the treatment of obstructive sleep apnea.

Pathophysiologic mechanisms of cardiovascular disease in obstructive sleep apnea syndrome

Obstructive sleep apnea syndrome (OSAS) is a highly prevalent sleep disorder, characterized by repeated disruptions of breathing during sleep. This disease has many potential consequences including excessive daytime sleepiness, neurocognitive deterioration, endocrinologic and metabolic effects, and decreased quality of life. Patients with OSAS experience repetitive episodes of hypoxia and reoxygenation during transient cessation of breathing that provoke systemic effects. Furthermore, there may be increased levels of biomarkers linked to endocrine-metabolic and cardiovascular alterations. Epidemiological studies have identified OSAS as an independent comorbid factor in cardiovascular and cerebrovascular diseases, and physiopathological links may exist with onset and progression of heart failure. In addition, OSAS is associated with other disorders and comorbidities which worsen cardiovascular consequences, such as obesity, diabetes, and metabolic syndrome. Metabolic syndrome is an emerging public health problem that represents a constellation of cardiovascular risk factors. Both OSAS and metabolic syndrome may exert negative synergistic effects on the cardiovascular system through multiple mechanisms (e.g., hypoxemia, sleep disruption, activation of the sympathetic nervous system, and inflammatory activation). It has been found that CPAP therapy for OSAS provides an objective improvement in symptoms and cardiac function, decreases cardiovascular risk, improves insulin sensitivity, and normalises biomarkers. OSAS contributes to the pathogenesis of cardiovascular disease independently and by interaction with comorbidities. The present review focuses on indirect and direct evidence regarding mechanisms implicated in cardiovascular disease among OSAS patients.

Effect of continuous positive airway pressure on day/night rhythm of prothrombotic markers in obstructive sleep apnea

OBJECTIVE

Obstructive sleep apnea (OSA) has been associated with an increased risk of atherothrombotic events. A prothrombotic state might partially explain this link. This study investigated OSA patients' day/night rhythm of several prothrombotic markers and their potential changes with therapeutic continuous positive airway pressure (CPAP).

METHODS

The study included 51 OSA patients [apnea hypopnea index (AHI) ⩾10] and 24 non-OSA controls (AHI<10). Of the 51 OSA patients, 25 were randomized to CPAP and 26 to placebo-CPAP. Twelve blood samples were collected over a 24h period to measure prothrombotic markers. For the apneic patients these samples were collected before treatment and after 3weeks of treatment with either CPAP or placebo-CPAP. Day/night variation in prothrombotic markers was examined using a cosinor analysis.

RESULTS

Compared with controls, OSA patients showed lower mesor (mean) and amplitude (difference between maximum and minimum activity) of D-dimer. In unadjusted (but not in adjusted) analysis, patients showed higher mesor of plasminogen activator inhibitor-1 (p<0.05 in all cases). No significant group differences were seen in mesor and amplitude for either soluble tissue factor or von Willebrand factor, or the acrophase (time of the peak) and periodic pattern for any prothrombotic markers. There were no significant differences in changes of periodic pattern and in day/night rhythm parameters of prothrombotic markers pre- to post-treatment between the CPAP and placebo condition.

CONCLUSIONS

There may be altered day/night rhythm of some prothrombotic markers in OSA patients compared with controls. CPAP treatment for 3weeks did not affect day/night rhythm of prothrombotic markers in OSA patients differently from placebo-CPAP.

Coagulability in obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) is a common disorder that affects both quality of life and cardiovascular health. The causal link between OSA and cardiovascular morbidity⁄mortality remains elusive. One possible explanation is that repeated episodes of nocturnal hypoxia lead to a hypercoagulable state that predisposes patients to thrombotic events. There is evidence supporting a wide array of hematological changes that affect hemostasis (eg, increased hematocrit, blood viscosity, platelet activation, clotting factors and decreased fibrinolytic activity).

OBJECTIVE

To provide a comprehensive review of the current evidence associating OSA with increased coagulability, and to highlight areas for future research.

METHODS

Keyword searches in Ovid Medline were used to identify relevant articles; all references in the articles were searched for relevant titles. The Web of Science was used to identify articles citing the relevant articles found using the Ovid Medline search. All original peer-reviewed articles, meta-analyses and systematic reviews regarding the pertinent topics between 1990 and present were selected for review.

RESULTS

Hematocrit, blood viscosity, certain clotting factors, tissue factor, platelet activity and whole blood coagulability are increased in patients with OSA, while fibrinolysis is impaired.

CONCLUSION

There is considerable evidence that OSA is associated with a procoagulant state. Several factors are involved in the procoagulant state associated with OSA. There is a need for adequately powered clinical studies involving well-matched control groups to address potential confounding variables, and to accurately delineate the individual factors involved in the procoagulant state associated with OSA and their response to treatment.

Sleep apnea and risk of deep vein thrombosis: a non-randomized, pair-matched cohort study

BACKGROUND

Patients with sleep apnea have been reported to be associated with increased prevalence of deep vein thrombosis (DVT) in some papers, which were criticized for either a small sample size or lack of a prospective control. Our study strived to explore the relationship of sleep apnea and the subsequent development of DVT using a nationwide, population-based database.

METHODS

From 2000 to 2007, we identified a study cohort consisting of newly diagnosed sleep apnea cases in the National Health Insurance Research Database. A control cohort without sleep apnea, matched for age, sex, comorbidities, major operation, and fractures, was selected for comparison. The 2 cohorts were followed-up, and we observed the occurrence of DVT by registry of DVT diagnosis.

RESULTS

Of the 10,185 sampled patients (5680 sleep apnea patients vs. 4505 control), 40 (0.39%) cases developed DVT during a mean follow-up period of 3.56 years, including 30 (0.53%) from the sleep apnea cohort and 10 (0.22 %) from the control group. Subjects with sleep apnea experienced a 3.113-fold (95% confidence interval, 1.516-6.390; P=.002) increase in incident DVT, which was independent of age, sex, and comorbidities. Kaplan-Meier analysis also revealed the tendency of sleep apnea patients toward DVT development (log-rank test, P=.001). The risk of DVT was even higher in sleep apnea cases who needed continuous positive airway pressure treatment (hazard ratio 9.575; 95% confidence interval, 3.181-28.818; P <.001).

CONCLUSION

Sleep apnea may be an independent risk factor for DVT.

Circulating levels of vascular endothelial markers in obstructive sleep apnoea syndrome. Effects of nasal continuous positive airway pressure

INTRODUCTION

Obstructive sleep apnoea syndrome (OSAS) is an important risk factor in cardiovascular disorders. Although the exact mechanism remains to be elucidated, the endothelial dysfunction process seems to be implicated.

MATERIAL AND METHODS

In order to test this hypothesis, blood circulating levels of endothelial markers were measured at baseline and 1 year after treatment with continuous positive airway pressure (CPAP). We studied 37 males using polysomnography: 20 subjects with OSAS and a 17-subject control group. An OSAS-validated sleep questionnaire covering the most important cardiovascular risk factors was applied to all subjects. Furthermore, patients received a complete general physical examination and biochemistry test with lipid profile. The specific markers measured were intercellular cell adhesion molecule-1 (ICAM-1), E-selectin, endothelin-1, von Willebrand factor (vWF) and plasminogen activator inhibitor-1 (PAI-1).

RESULTS

Obstructive sleep apnoea syndrome patients presented higher circulating levels of ICAM-1, endothelin-1 and PAI-1 than the control group. On the other hand, no differences were found in E-selectin and vWF. After 1 year of CPAP treatment, there was a significant decrease in circulating levels of ICAM-1 and PAI-1. On the other hand, no differences were found in endothelin-1, E-selectin and vWF.

CONCLUSIONS

Obstructive sleep apnoea syndrome is associated with elevated levels of ICAM-1 and PAI-1 and these levels normalize after treatment with CPAP.

Cardiovascular consequences of sleep apnea

Sleep apnea is a common health concern that is characterized by repetitive episodes of asphyxia. This condition has been linked to serious long-term adverse effects such as hypertension, metabolic dysregulation, and cardiovascular disease. Although the mechanism for the initiation and aggravation of cardiovascular disease has not been fully elucidated, oxidative stress and subsequent endothelial dysfunction play major roles. Animal models, which have the advantage of being free of comorbidities and/or behavioral variables (that commonly occur in humans), allow invasive measurements under well-controlled experimental conditions, and as such are useful tools in the study of the pathophysiological mechanisms of sleep apnea. This review summarizes currently available information on the cardiovascular consequences of sleep apnea and briefly describes common experimental approaches useful to sleep apnea in different animal models.

Obstructive sleep apnea, stroke, and cardiovascular diseases

BACKGROUND

Obstructive sleep apnea (OSA) is gaining recognition as a cardiovascular and cerebrovascular risk factor. Sleep apnea is now implicated in the etiopathogenesis of stroke, coronary artery disease, hypertension, and congestive heart failure.

REVIEW SUMMARY

OSA exerts its negative cardiovascular consequences through its unique pattern of intermittent hypoxia and arousals. The putative mechanisms involved in the pathogenesis of cardiovascular disease in OSA include fibrinolytic imbalance, endothelial dysfunction, oxidative stress, and inflammation. This study discusses the known cellular and molecular processes that promote atherogenesis and vascular dysfunction in patients with OSA, and their implications for cardiovascular disease and prevention in that patient population.

CONCLUSION

Neurologists should familiarize themselves with the symptoms and signs of OSA and the pathophysiology of the association between untreated OSA and cardiovascular disease, including stroke. OSA should be ruled out in patients with cardiovascular disease and be regarded as an important modifiable risk factor. Knowledge of this association is of prime public health importance and can result in primary and secondary prevention of cardiovascular events. This study will also help neurologists in providing patient education and treatment.

Chronic sleep deprivation markedly reduces coagulation factor VII expression

Chronic sleep loss, a common feature of human life in industrialized countries, is associated to cardiovascular disorders. Variations in functional parameters of coagulation might contribute to explain this relationship. By exploiting the mouse model and a specifically designed protocol, we demonstrated that seven days of partial sleep deprivation significantly decreases (-30.5%) the thrombin generation potential in plasma evaluated upon extrinsic (TF/FVIIa pathway) but not intrinsic activation of coagulation. This variation was consistent with a decrease (-49.8%) in the plasma activity levels of factor VII (FVII), the crucial physiologicalal trigger of coagulation, which was even more pronounced at the liver mRNA level (-85.7%). The recovery in normal sleep conditions for three days completely restored thrombin generation and FVII activity in plasma. For the first time, we demonstrate that chronic sleep deprivation on its own reduces, in a reversible manner, the FVII expression levels, thus influencing the TF/FVIIa activation pathway efficiency.

Day/Night rhythm of hemostatic factors in obstructive sleep apnea

STUDY OBJECTIVES

To investigate the hypothesis that day/night patterns of prothrombotic activity differ between patients with obstructive sleep apnea (OSA) and individuals with no OSA.

DESIGN

Prothrombotic markers' day/night rhythms recorded over one 24-h period.

SETTING

General clinical research center.

PATIENTS

38 untreated OSA patients as verified by polysomnography (apnea-hypopnea index > or = 10/h sleep) and 22 non-OSA controls.

MEASUREMENTS AND RESULTS

Blood samples were collected every 2 h to measure plasma levels of fibrinolysis-inhibiting plasminogen activator inhibitor (PAI)-1 and the primary fibrin degradation product D-dimer. Day/night variation in hemostasis factors was examined using a cosinor analysis. Mesor (mean) PAI-1 over the 24-h period was higher (P = 0.015), and mesor of D-dimer was lower (P = 0.001) in patients with OSA than in the non-OSA controls. These group differences stayed significant when controlling for age and gender. After further adjustment for body mass index, mean arterial pressure, and smoking, the relationship between OSA and PAI-1 became non-significant, but the relationship between OSA and D-dimer continued to be significant (P = 0.006). In the fully adjusted analysis, the amplitude (peak) for D-dimer was lower in OSA patients than in non-OSA controls (P = 0.048). The acrophase (time of the peak) for PAI-1 and D-dimer did not significantly differ between groups.

CONCLUSIONS

The relatively higher average level of PAI-1 and lower average level of D-dimer across the 24-h in OSA patients might reflect decreased fibrinolytic capacity and fibrin degradation, respectively. The findings provide some evidence for a prothrombotic state in OSA, but were only partially independent of metabolic variables.

Repeated inspiratory occlusions in anesthetized rats acutely increase blood coagulability as assessed by thromboelastography

Many of the components contributing to coagulability are enhanced by repeated episodes of hypoxia, as occurs in obstructive sleep apnea, but no one has yet measured the global hemostatic properties of blood in an animal model of this disease. Using thromboelastography, a hemostatic assay, we measured hemostasis in six pentobarbital-anesthetized rats before and after 3h of repeated inspiratory occlusions lasting 30s applied every 2 min and compared the results to those in six identically prepared rats before and after 3h of resting breathing. Rats subjected to occlusions displayed faster onset of clotting (p<0.031) and more rapid coagulation (p<0.031). Thus, repeated inspiratory occlusions acutely cause hypercoagulability in rats. Thromboelastography, a simple test of hemostasis, may help evaluate the factors responsible for this increase and, in patients with obstructive sleep apnea, the risk of future cardiovascular disease.

Current world literature

This bibliography is compiled by clinicians from the journals listed at the end of this publication. It is based on literature entered into our database between 1 February 2008 and 31 January 2009 (articles are generally added to the database about two and a half months after publication). In addition, the bibliography contains every paper annotated by reviewers; these references were obtained from a variety of bibliographic databases and published between the beginning of the review period and the time of going to press. The bibliography has been grouped into topics that relate to the reviews in this issue.

Obstructive sleep apnea in patients admitted for acute myocardial infarction. Prevalence, predictors, and effect on microvascular perfusion

BACKGROUND

We investigated the prevalence and predictors of obstructive sleep apnea (OSA) in patients admitted to the hospital for acute myocardial infarction and whether OSA has any association with microvascular perfusion after primary percutaneous coronary intervention (PCI).

METHODS

Recruited patients were scheduled to undergo an overnight sleep study between 2 and 5 days after primary PCI. An apnea-hypopnea index (AHI) of > or = 15 was considered diagnostic of OSA. Impaired microvascular perfusion after primary PCI was defined as an ST-segment resolution of < or = 70%, myocardial blush grade 0 or 1, or a corrected Thrombolysis in Myocardial Infarction (TIMI) [antegrade flow scale] frame count > 28.

RESULTS

Sleep study was performed in 120 patients and completed in 105 patients (study cohort, mean age 53 +/- 10 years, male 98%) with uncomplicated myocardial infarction. An AHI was > or = 15 in 69 patients (OSA-positive), giving a prevalence of 65.7%. Diabetes mellitus was found to be a significant risk factor for OSA (odds ratio, 2.86; 95% confidence interval, 1.06 to 8.24; p = 0.033). There were no differences between OSA-positive and OSA-negative groups with regard to the percentage of patients with < or = 70% ST-segment resolution (73% vs 64%, respectively; p = 0.411), myocardial blush grade 0 or 1 (39.1% vs 38.9%, respectively; p = 1.000), or corrected TIMI frame count > 28 (21.7% vs 25.0%, respectively; p = 0.807).

CONCLUSIONS

We found a high prevalence of previously undiagnosed OSA in patients admitted with acute myocardial infarction. Diabetes mellitus was independently associated with OSA. No evidence indicated that OSA is associated with impaired microvascular perfusion after primary PCI.

The coagulation and protein C pathways in patients with sleep apnea

Patients with obstructive sleep apnea (OSA) have a high frequency of cardiovascular diseases and hypercoagulability is believed to be involved in the mechanism of those vascular events. We evaluated whether there is a dysfunction in the protein C anticoagulant pathway in patients with obstructive sleep apnea. Two hundred ninety-three patients were enrolled. To confirm the diagnosis of OSA, all-night polysomnography, including determination of SpO(2), was carried out. The apnea-hypopnea index (AHI) was used for judging the presence of sleep-breathing disorder. The plasma levels of the thrombin-antithrombin complex were higher in patients with AHI > 5 than in those without OSA, defined as AHI < 5. However, there was no statistically significant difference in the plasma level of either activated protein C/alpha-antitrypsin complex or soluble thrombomodulin between patients with AHI > 5 and those with AHI < 5. The results of this study showed for the first time that markers of the protein C anticoagulant pathway are not affected in patients with OSA and that the protein C pathway is probably not involved in the mechanism of hypercoagulability in subjects with sleep-disordered breathing.

The impact of CPAP on cardiovascular biomarkers in minimally symptomatic patients with obstructive sleep apnea: a pilot feasibility randomized crossover trial

BACKGROUND

Previous, largely uncontrolled studies demonstrated the substantial effects of continuous positive airway pressure ventilation (CPAP) on a variety of physiologic and biochemical markers known to be risk factors for cardiovascular disease in patients with obstructive sleep apnea (OSA). In this pilot crossover study, we assessed (1) the feasibility of using CPAP in a group of minimally symptomatic patients with OSA, assessed through patient compliance and (2) CPAP therapy's effect on biomarkers in these patients.

METHODS

We studied patients with minimal daytime sleepiness who were referred to the University of British Columbia's Hospital Sleep Clinic with suspected OSA and an apnea-hypopnea index (AHI) > 15 events/h. Patients were randomized to either CPAP or no therapy for 4 weeks followed by a washout of 4 weeks, and then a crossover to the other intervention. Fasting morning blood and urine, 24-h blood pressure (BP) measurements, and endothelial function (peak flow-mediated dilation to nitroglycerin-mediated dilation ratio) were assessed before and after each study intervention.

RESULTS

Nine adult male and four female patients were studied. Mean (SD) age was 55 (7) years, mean AHI = 27.9/h, mean Epworth Sleepiness Score = 6.8 (11/13 had a score < 10), and mean BMI = 31.1 kg/m(2). Mean compliance with CPAP therapy was 5.53 h/night. Compared to no therapy, potential improvements were observed with CPAP for urinary microalbumin, norepinephrine, and epinephrine to creatinine ratios (decreased by 3.51 mg/mmol, 1.70 nmol/mmol, and 0.95 nmol/mmol, respectively); 24-h BP (systolic decreased by 3.60 mmHg, diastolic by 0.70 mmHg); homeostasis model for insulin resistance score (decreased by 1.11); and endothelial function (increased by 7.4%). However, none of the above differences was significant (p > 0.10).

CONCLUSION

In this pilot study there were potential improvements in a variety of cardiovascular biomarkers with CPAP. CPAP compliance was reasonably good even though patients were not particularly sleepy. Accordingly, larger randomized controlled trials in this area appear feasible and warranted.