cardiovascular risk factors of obstructive sleep apnea patients
Neşe DURSUNOĞLU1,2, Dursun DURSUNOĞLU3, Sibel ÖZKURT2, Göksel KİTER2, Fatma EVYAPAN2
1 Sahlgrenska Üniversitesi Hastanesi, Uyku Laboratuvarı, Göteborg, İsveç,
2 Pamukkale Üniversitesi Tıp Fakültesi, Göğüs Hastalıkları Anabilim Dalı,
3Pamukkale Üniversitesi Tıp Fakültesi, Kardiyoloji Anabilim Dalı, Denizli.
ÖZET
Obstrüktif uyku apne hastalarının global kardiyovasküler risk faktörlerinde cinsiyet farkları
Obstrüktif uyku apne (OSA)’nin morbidite ve mortalitesi daha çok kardiyovasküler komplikasyonlar ile ilişkilidir. Metabo- lik sendrom (MBS)’un kardiyovasküler hastalık riskini arttırdığı kabul edilmektedir. Bu çalışmada, ciddi OSA tanısını ön- görmede, MBS’nin tanısal değerini incelemeyi amaçladık. Kalp ve akciğer hastalığı olmayan 87 hasta (54 erkek, 33 kadın) OSA açısından sorgulandı ve polisomnografik çalışmaya alındı. MBS tanısı “National Cholesterol Education Program (NCEP)” kriterine göre konuldu. Apne hipopne indeksi (AHİ)’ne göre hastalar iki gruba ayrıldı: Ciddi OSA (AHİ ≥ 30, 26 erkek, 15 kadın) ve ciddi olmayan OSA (AHİ < 30, 28 erkek, 18 kadın). Her iki cins için iki grupta da yaşlar benzerdi. Cid- di OSA grubunda MBS’li hastaların sayısı (13 kadın %86.6, 19 erkek %73), ciddi olmayan OSA grubundakinden (6 kadın
%33, 9 erkek %32) özellikle kadınlarda olmak üzere daha fazlaydı. MBS tanı kriterlerinin ortalama değerleri her iki cinste de ciddi OSA grubunda, ciddi olmayan OSA grubundan anlamlı olarak daha yüksekti. Ciddi OSA tanısını öngörmede MBS’nin tanısal değeri (kriter ≥ 3 varlığı) analiz edildiğinde, erkek ve kadınlarda sırasıyla %73 ve %86.6 duyarlılık, %67.8 ve %94.4 özgüllük, %67.9 ve %86.7 pozitif prediktif değer, %73 ve %85.7 negatif prediktif değerleri saptandı. Uyku kliniğine başvuran hastalarda, özellikle kadınlarda, MBS kriterlerinin değerlendirilmesi, ciddi OSA tanısını öngörmede yüksek du- yarlılık ve negatif prediktif değer ile önemli bir rol üstlenebilir. Ayrıca, OSA hastalarında MBS varlığı kardiyovasküler komplikasyon riskini arttırabilir.
Anahtar Kelimeler: Obstrüktif uyku apne sendromu, metabolik sendrom, kardiyovasküler risk.
Yazışma Adresi (Address for Correspondence):
Dr. Neşe DURSUNOĞLU, Sleep Laboratory Bla Straket 5 Sahlgrenska University Hospital, 41345 GÖTEBORG - SWEDEN
e-mail: ndursunoglu@yahoo.com
Cardiovascular disturbances are the most seri- ous complications of obstructive sleep apnea (OSA) (1,2). These complications include vent- ricular dysfunction, acute myocardial infarction, arrhythmias, systemic and pulmonary hyperten- sion (3-10). All these cardiovascular complica- tions increase morbidity and mortality of OSA.
Increased sympathetic nerve activity and also endothelial dysfunction which are the results of hypoxia, have important roles in vascular comp- lications of OSA. Nowadays, sleep apnea is ac- cepted as one of the identifiable causes of hypertension in JNC 7 report (11). Also, OSA is closely associated with obesity and aging (12,13). Severity of OSA is described according to total number of apneas and hypopneas per hour of sleep which is named as apnea hypop- nea index (AHI).
Metabolic syndrome (MBS), dysmetabolic syndrome or insulin-resistance syndrome or syndrome X as it was initially designated, which is closely linked to insulin resistance, is a condi- tion which is recognized as raising the risk of
cardiovascular disease (14-16). It was originally described by Reaven as a quartet of hypertensi- on, glucose intolerance and dyslipidemia [high triglyceride, low high-density lipoprotein-choles- terol (HDL-C)], with insulin resistance or hype- rinsulinemia. Central obesity is often associated (16,17). The new National Cholesterol Educati- on Program (NCEP) guidelines [Adult Treatment Panel (ATP) III] recognized MBS as a secondary target of risk-reduction therapy and selected to define MBS when three or more of certain five risk determinants are present (18).
The association of OSA with some diseases, ha- ving endothelial dysfunction in their physiopat- hology, such as hypertension, diabetes mellitus, obesity, coronary artery diseases, stroke and heart failure is common. So, it’s very important to evaluate cardiovascular global risk assess- ment in OSA patients to prevent the high poten- tial cardiovascular morbidity and mortality.
In this study, we analysied the diagnostic value of MBS to predict the diagnosis of severe OSA.
SUMMARY
Gender differences in global cardiovascular risk factors of obstructive sleep apnea patients
Neşe DURSUNOĞLU1,2, Dursun DURSUNOĞLU3, Sibel ÖZKURT2, Göksel KİTER2, Fatma EVYAPAN2
1 Sahlgrenska University Hospital Sleep Laboratory, Göteborg, Sweden,
2 Departments of Chest Disease, Faculty of Medicine, Pamukkale University, Denizli, Turkey,
3 Departments of Cardiology, Faculty of Medicine, Pamukkale University, Denizli, Turkey.
The morbidity and mortality of obstructive sleep apnea (OSA) are related principally to its cardiovascular complications.
Metabolic syndrome (MBS) is recognized as raising the risk of cardiovascular disease. In this study, we analysied the diag- nostic value of MBS to predict the diagnosis of severe OSA. Eight-seven subjects (54 males and 33 females) without any cardiac or pulmonary disease referred for evaluation of OSA, had overnight polysomnography. MBS were diagnosed ac- cording to NCEP criteria. According to apnea-hypopnea index (AHI), subjects were divided into two groups: severe OSA (AHI ≥ 30, 26 males, 15 females) and non-severe OSA (AHI < 30, 28 males, 18 females). Ages were similar in both OSA gro- ups for both genders. In the severe OSA group, number of patients with MBS was especially higher (in females n= 13, 86.6%; in males n= 19, 73%) than non-severe OSA (in females 6, 33%, in males 9, 32%). The mean values of the five diag- nostic criteria of MBS were significantly higher in severe OSA than non-severe groups in both genders. Analysis of diag- nostic value (criteria ≥ 3) of MBS for predicting the diagnosis of severe OSA in males and females revealed the sensitivity 73% and 86.6%, the specificity 67.8% and 94.4%, positive predictive value 67.9% and 86.7%, negative predictive value 73%
and 85.7% respectively. Especially in female patients referred to the sleep clinics, evaluation of MBS criteria may play an important role in predicting severe OSA with high sensitivity and negative predictivity. Furthermore, the presence of MBS in OSA patients might increase cardiovascular complications.
Key Words: Obstructive sleep apnea syndrome, metabolic syndrome, cardiovascular risk.
MATERIALS and METHODS a. Study Population
Eighty-seven patients (54 males and 33 fema- les) referred for evaluation of OSA, had over- night polysomnography. A detailed sleep and cardiovascular anamnesis of the patients were recorded. Sleep cycle, nutritional status, medi- cations, alcohol usage and family anamnesis were also questioned. Epworth sleepiness scale (ESS) was questioned to all patients, and pati- ents having high scores (ESS ≥ 10) were taken into the sleep study (19). Pulmonary function tests (Sensor medics 2400, Netherlands), arteri- al blood gas analysis (ABL 30, Kopenhag) were performed to all patients at rest.
All of the subjects had no heart and pulmonary diseases based on physical examination. A 12- lead surface electrocardiogram (ECG) was ta- ken from every subject, and all of them were in sinus rhythm. In addition, all of subjects under- went a treadmill exercise test for myocardial isc- hemia, and the test was normal for each subject.
b. Polysomnography
Polysomnography was applied to all subjects at the diagnostic night (20). The portable, limited sleep study performed with the Embletta device, consisted of the following (21):
1. Nasal pressure detector using nasal cannu- lae/pressure transducer system, recording the square root of pressure as an index of flow, 2. Thoraco-abdominal movement detection through two piezoelectric belts,
3. Finger pulse oximeter, and 4. Body position detection.
Apnea was defined as total obstruction of orona- sal airflow ≥ 10 seconds, an hypopnea was defi- ned as decrease of airflow by at least 50%, and desaturations were defined as ≥ 4% decrease in oxygen saturation (22). Desaturation index (DI) was identified as number of oxygen desaturation events per hour of sleep. Subjects with AHI ≥ 5 were diagnosed as OSA (23). According AHI, subjects were divided into two groups: severe
OSA (AHI ≥ 30, 26 males, 15 females) and non- severe OSA (AHI < 30, 28 males, 18 females).
c. Identification of Metabolic Syndrome (MBS) Systolic (SBP) and diastolic (DBP) blood pres- sures were measured in the sitting position on the right arm using an aneroid sphygmomano- meter (Erka, Germany), after at least 5 min of rest. First appearance and disappearance (pha- se V) of Korotkoff’s sounds were used to define the pressures. Readings were recorded to the nearest even number, and the mean of two re- cordings 3 min apart was computed. Heart rate per minute (HR) was measured in the sitting po- sition. Waist circumference (WC) was measured with the subject standing and wearing only un- derwear, at the level midway between the lower rib margin and the iliac crest, while that of the hip was measured at the level of the greater trochanters. Body mass index (BMI) was calcu- lated by a computer as weight divided by height squared (kg/m2). After an overnight fasting (at least 12 hours) blood glucose (FBG), total cho- lesterol, triglycerides (TRG), high-density lipop- rotein cholesterol (HDL-C) were analysed with commercial kits (Abbott, USA) by an autoanaly- ser (Aeroset, USA).
Identification of MBS confirmed to the definition used by the NCEP (ATP III) (18), namely when three or more of the following five risk determi- nants were present: WC (in men > 102 cm, in women > 88 cm), TRG ≥ 150 mg/dL, HDL-C (in men < 40, in women < 50 mg/dL), blood pres- sure (≥ 130/≥ 85 mmHg or taking antihyperten- sive medication), and FBG ≥ 110 mg/dL (or pre- sence of diabetes mellitus) (Table 1).
d. Statistical Analysis
Statistics were performed by Statistical Package for Social Sciences version 10.0 (SPSS-10.0) for windows statistic packet program. Results were given as mean ± standard deviation, differences between measurements were assessed using in- dependent t-test. Correlations between variables were tested assuming a linear relationship. A p- value < 0.05 was considered significant.
RESULTS
Basic measurements of male and female pati- ents with OSA in two groups of AHI were shown in Table 2 and Table 3 respectively. Ages were si- milar in both OSA groups for both genders.
Number of patients with MBS was higher (espe- cially in females) in the severe OSA group (n=
13, 86.6%, in males 9, 73%) than non-severe OSA (n= 6, 33%, in males 9, 32%). The mean va- lues of the five diagnostic criteria of MBS were significantly higher in severe OSA than non-se- vere groups in both gender. Analysis of diagnos- tic value (criteria ≥ 3) of MBS for predicting the diagnosis of severe OSA in males and females revealed the sensitivity 73% and 86.6%, the spe- cificity 67.8% and 94.4%, positive predictive va- lue 67.9% and 86.7%, negative predictive value 73% and 85.7% respectively (Table 4).
In female patients with OSA and MBS, the seve- rity of OSA (AHI) was significantly correlated with WC (r= 0.594, p= 0.01) and BMI (r= 0.522, p= 0.006), serum TRG (r= 0.547, p= 0.04) and serum HDL-C (r= -0.595, p= 0.001) negatively, SBP (r= 0.673, p= 0.0001) and DBP (r= 0.551, p= 0.004) (Figure 1-3). On the other hand, in male patients with OSA and MBS, AHI was only significantly correlated with WC (r= 0.517, p=
0.01) and BMI (r= 0.515, p= 0.01) (Figure 4).
Table 2. Basic measurements of 54 male patients with obstructive sleep apnea (OSA) in two groups of apnea hypopnea index (AHI).
Patients with OSA AHI < 30 AHI ≥ 30
(n= 28) (n= 26) p
Age (year) 47.3 ± 7.7 50.7 ± 5.9 NS
Metabolic syndrome (n, %) 9 (32) 19 (73) 0.001
Hypertension (n, %) 6 (21.4) 13 (50) 0.01
Diabetes mellitus (n, %) 1 (3.5) 2 (7.7) 0.02
BMI (kg/m2) 29.1 ± 2.3 31.7 ± 3.9 0.04
WC (cm) 107.4 ± 8.3 117 ± 10.4 0.002
Systolic BP (mmHg) 128.6 ± 21.5 138.8 ± 14.4 0.06
Diastolic BP (mmHg) 83.2 ± 10.2 88.9 ± 10.3 0.06
FBT (mg/dL) 145.6 ± 55.8 188.8 ± 59.6 0.02
HDL-C (mg/dL) 47.5 ± 11.1 41.3 ± 11.1 0.04
FBG (mg/dL) 94.5 ± 9.1 99.0 ± 12.1 0.03
TC (mg/dL) 200.0 ± 32.9 209.1 ± 53.8 NS
AHI (per hour) 19.8 ± 10.8 43.4 ± 12.4 0.0001
DI (per hour) 19.9 ± 16.0 37.5 ± 19.6 0.001
MinSatO2 (%) 79.4 ± 6.3 72.9 ± 5.9 0.01
BMI: Body mass index, WC: Waist circumference, BP: Blood pressure, FBT: Fasting blood triglyceride, HDL-C: High density lipoprotein-choles- terol, FBG: Fasting blood glucose, TC: Total cholesterol, AHI: Apnea hypopnea index, DI: Desaturation index, MinSatO2: Minimum saturation of arterial oxygen, NS: Not significant.
Table 1. Diagnosis of metabolic syndrome accor- ding to NCEP ATP III criteria (in the presence of
≥ 3 of the following five risk determinants).
1. Blood pressure ≥ 130/≥ 85 mmHg, or hypertension 2. Abdominal obesity
Waist circumference > 102 cm in men,
> 88 cm in women
3. Fasting blood triglyceride ≥ 150 mg/dL 4. High density lipoprotein-cholesterol (HDL-C)
< 40 mg/dL in men, < 50 mg/dL in women 5. Fasting blood glucose ≥ 110 mg/dL, or diabetes mellitus
DISCUSSION
It is well known that important cardiovascular risk factors, such as hypertension, glucose into- lerance, hyperinsulinemia, dyslipidemia, and obesity, often cluster in the same individuals.
The importance of the MBS lies in its associati- on with cardiovascular morbidity and mortality.
Reaven who has determined MBS firstly in 1988,
proposed that the coexistence of some of these disorders was not by chance but rather compri- sed what he termed “syndrome X” (16). He was even able to hypothesize a direction of causality, citing data that suggested the following: that obesity, sedentary lifestyle, and genetic propen- sity can cause insulin resistance; and insulin re- sistance results in hyperinsulinemia; and hype- rinsulinemia can provoke catecholamine excess and renal retention of salt and water, either or both of which can raise blood pressure, and hyperinsulinemia results in elevated hepatic very low-density lipoprotein (VLDL) triglyceride secretion and inversely correlates with HDL-C concentrations; and impaired glucose tolerance, hypertension, and elevated VLDL triglyceri- de/reduced HDL-C are all associated with incre- ased atherogenesis and cardiovascular risk.
The metabolic syndrome has not escaped from the interest of the sleep medicine community OSA is usually associated with conditions known to increase insulin resistance and cardi- Table 3. Basic measurements of 33 female patients with obstructive sleep apnea (OSA) in two groups of apnea hypopnea index (AHI).
Patients with OSA AHI < 30 AHI ≥ 30
(n= 18) (n= 15) p
Age (year) 45.0 ± 5.7 49.1 ± 8.3 NS
Metabolic syndrome (n, %) 6 (33) 13 (86.6) 0.0001
Hypertension (n, %) 2 (11) 6 (40) 0.01
Diabetes mellitus (n, %) 0 (0) 1 (6.6) 0.02
BMI (kg/m2) 27.9 ± 2.4 31.9 ± 4.0 0.003
WC (cm) 93.5 ± 8.5 108.1 ± 11.3 0.003
Systolic BP (mmHg) 114.4 ± 17.5 135.0 ± 12.9 0.006
Diastolic BP (mmHg) 75.6 ± 14.2 88.5 ± 7.1 0.004
FBT (mg/dL) 134.9 ± 24.0 179.5 ± 44.2 0.003
HDL-C (mg/dL) 52.8 ± 9.1 42.6 ± 8.9 0.005
FBG (mg/dL) 88.7 ± 11.0 99.4 ± 9.9 0.03
TC (mg/dL) 229.8 ± 42.6 217.4 ± 53.8 NS
AHI (per hour) 16.4 ± 11.1 59.3 ± 12.7 0.0001
DI (per hour) 15.1 ± 18.1 47.8 ± 22.5 0.0001
MinSatO2 (%) 87.0 ± 7.4 70.5 ± 7.0 0.004
BMI: Body mass index, WC: Waist circumference, BP: Blood pressure, FBT: Fasting blood triglyceride, HDL-C: High density lipoprotein-choles- terol, FBG: Fasting blood glucose, TC: Total cholesterol, AHI: Apnea hypopnea index, DI: Desaturation index, MinSatO2: Minimum saturation of arterial oxygen, NS: Not significant.
Table 4. Analysis of diagnostic value (criteria ≥ 3) of metabolic syndrome for predicting the diag- nosis of severe obstructive sleep apnea syndrome (apnea hypopnea index ≥ 30) in both genders.
Male Female
(%) (%)
Sensitivity 73.0 86.6
Specificity 67.8 94.4
Positive predictive value 67.9 86.7 Negative predictive value 73.0 85.7
ovascular risk, such as hypertension, obesity, and diabetes. Early reports by Davies et al. and Stoohs et al. documented an increased preva- lence of insulin resistance in small groups of
subjects with OSA, but differences in BMI acco- unted for the entire relationship (24,25). Simi- larly, Levinson and colleagues published a small study in 1994 that failed to detect a relationship Figure 1. Correlations betwen AHI and WC and BMI in female patients with sleep apnea and metabolic syndrome (for WC r= 0.594, p= 0.001 and for BMI r= 0.522, p= 0.006).
Apnea hypopnea index (AHI)
0 20 40 60 80
140
120
100
80
60
40
20
BMI (kg/m2) AHI
WC (cm) AHI
Figure 2. Correlations between AHI and plasma TRG and HDL-C in female patients with sleep apnea and meta- bolic syndrome (for TRG r= 0.547, p= 0.004 and for HDL-C r= -0.595, p= 0.001).
Apnea hypopnea index (AHI)
0 20 40 60 80
300
200
100
0
HDL-C AHI
TRG AHI
Waist circumference (WC) and body-mass index (BMI)Plasma tryglyceride (TRG) and HDL-C levels (mg/dL)
between central obesity using waist-to-hip ratio (WHR) and severity of OSA, although patients did tend to have higher WHR when compared to normative values (26).
In our study, number of patients with MBS was higher in the severe OSA group than non-severe OSA. Also, the mean values of the five diagnos- tic criteria of MBS were significantly higher in se- Figure 3. Correlations between AHI and SBP and DBP in female patients with sleep apnea and metabolic syndro- me (for SBP r= 0.673, p= 0.0001 and for DBP r= 0.551, p= 0.004).
Apnea hypopnea index (AHI)
0 20 40 60 80
160
140
120
100
80
60
40
DBP (mmHg) AHI
SBP (mmHg) AHI
Systolic (SBP)/diastolic (DBP) blood pressures (mmHg)
Figure 4. Correlations of AHI and WC and BMI in male patients with sleep apnea and metabolic syndrome (for WC r= 0.517, p= 0.01 and for BMI r= 0.515, p= 0.01).
Apnea hypopnea index (AHI)
0 20 40 60 80
140
120
100
80
60
40
20
BMI (kg/m2) AHI
WC (cm) AHI
Waist circumference (WC) and body-mass index (BMI)
vere OSA than non-severe groups in both gen- der. Analysis of diagnostic value (criteria ≥ 3) of MBS for predicting the diagnosis of severe OSA in males and females revealed the sensitivity 73% and 86.6%, the specificity 67.8% and 94.4%, positive predictive value 67.9% and 86.7%, nega- tive predictive value 73% and 85.7% respectively.
In our study, we established that the presence of MBS was a useful predictor to diagnose a severe OSA in the patients, especially among females with sleep related breathing disorders. However, our sleep clinic population may not reflect the findings in the general community.
The prevalence and the excess coronary heart disease (CHD) risk of the MBS and its compo- nents were investigated in the Turkish Adult Risk Factor Study by Onat A et al (27). Prospective analysis was based on 2398 men and women (mean age at baseline 49.1±13 years) and 27%
of men and 38.6% of women were found to ha- ve MBS at baseline examination. It was estima- ted that MBS was the culprit in just over half the cases of CHD in Turkey. It was shown that MBS was the major determinant of CHD risk in a po- pulation having generally low levels of HDL-C and LDL-C in middle-aged and elderly adults, extending to three out of every eight adults, and imposing an overall excess CHD risk of approxi- mately 70%. In contrast to men, a substantial re- sidual coronary risk is retained in Turkish wo- men after controlling for five MBS components.
Although each of the components of the MBS in- dividually have been identified as risk factors for cardiovascular disease, an individual with three or more components is at particularly high risk.
For instance, Wilson et al. have reported a pros- pective analysis of the Framingham Offspring Study looking for cardiovascular events in 2406 men and 2569 women between the ages of 18 to 74 years (28). Gender-specific quintiles for ba- seline values of HDL cholesterol, triglycerides, total cholesterol, BMI, systolic BP, and glucose were computed, and the lowest quintile for HDL cholesterol and highest quintiles for the other variables were used to compute the risk. Clus- ters of three or more risk factors occurred in 17% of the subjects. Fully 20% of the cardiovas- cular events in men and 48% of the events in
women could be attributed solely to the cluste- ring of three or more factors.
The prevalence of OSA is increased fourfold in patients with obesity (29). It’s well known that obesity plays a major part in the development of the metabolic syndrome, the prevalence of MBS in nonobese individuals is 10%, while in obese subjects it is more than 50% (30). It has been re- cognized that the type of regional fat distribution (abdominal-visceral vs gluteal-femoral) plays an important role in the development of the MBS (31,32). Not only increased body weight but fat distribution plays a major role in the develop- ment of OSA. Visceral (central) obesity has be- en recognized to be associated more often with OSA than other forms of obesity (33). The best surrogate of visceral adiposity across a wide age range is waist circumference, in a population in which MBS prevails.
In our study population, the mean values of the five diagnostic criteria of MBS were significantly higher in severe OSA than non-severe groups in both gender. In female patients with OSA and MBS, the severity of OSA (AHI) was significantly correlated with WC (r= 0.594, p= 0.01) and BMI (r= 0.522, p= 0.006), serum TRG (r= 0.547, p=
0.04) and serum HDL-C (r= -0.595, p= 0.001) negatively, SBP (r= 0.673, p= 0.0001) and DBP (r= 0.551, p= 0.004). However, in male patients with OSA and MBS, AHI was only significantly correlated with WC (r= 0.517, p= 0.01) and BMI (r= 0.515, p= 0.01).
Strohl et al. were able to demonstrate an associ- ation between hyperinsulinemia (as well as BP) and AHI independent of BMI in 386 men referred for polysomnography, and more recently, two relatively large prospective studies demonstra- ted a relationship between OSA severity and in- sulin resistance that was independent of BMI (34). Ip and colleagues studied 270 consecutive nondiabetic patients (73% men) who had been referred for evaluation of suspected OSA and fo- und such a quantitative relationship for both AHI and minimum oxyhemoglobin saturation with insulin resistance (35). Central obesity also was correlated with OSA severity. Not unexpectedly, given the previous discussion, hypertension was
significantly related to insulin resistance in their subjects.
Punjabi and associates recruited 150 men with no history of diabetes, cardiac disease, or pul- monary disease and subjected them to poly- somnography, oral glucose tolerance testing, and measurement of fasting insulin and lipid le- vels (36). They found a surprisingly high preva- lence of OSA, ranging from 40 to 60% depen- ding on the value of AHI score used to define a case. Impaired glucose tolerance and insulin re- sistance were associated with OSA severity, as represented by both AHI and the degree of oxy- hemoglobin desaturation. The WHR bore no re- lationship to the degree of OSA, but HDL cho- lesterol level decreased with increasing AHI.
Metabolic syndrome and also OSA may incre- ase cardiovascular morbidity and mortality. Re- cently in a study Peker Y et al. found that the risk of developing cardivascular disease was incre- ased in middle-aged OSA subjects indepen- dently of age, BMI, SBP, DBP, and smoking. In- sulin resistance could influence myocardial morphology and function in several ways, beca- use insulin resistance is associated with hyperin- sulinemia, which is known to induce growth of myocardial tissue in vitro (37,38). Also, an as- sociation between this insulin resistance syndro- me and left ventricular hypertrophy has been fo- und recently (39). Characteristically, cardiac hypertrophy is secondary to hypertension, but some degree of cardiac hypertrophy can also be found in normotensive obese subjects and in di- abetic patients (40).
As a conclusion, especially in female patients referred to the sleep clinics, evaluation of MBS criteria may play an important role in predicting severe OSA with high sensitivity and negative predictivity. Furthermore, the presence of MBS in OSA patients might increase cardiovascular complications.
Study Limitations
Small number of patients in our study populati- on is an important study limitation to evaluate MBS. Also, our sleep clinic population may not reflect the findings in the general community.
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