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Yelda Turgut, Zeynep Atam, Melahat Uygun, Çağlar Çuhadaroğlu, Tunçalp Demir, Birsen Mutlu

The importance of measuring negative expiratory pressure (NEP) in the diagnosis of obstructive sleep apnoea syndrome (OSAS). Yelda Turgut, Zeynep Atam, Melahat Uygun, Çağlar Çuhadaroğlu, Tunçalp Demir, Birsen Mutlu. Diagnosis and Pathophysiology of OSAS.

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Yelda Turgut, Zeynep Atam, Melahat Uygun, Çağlar Çuhadaroğlu, Tunçalp Demir, Birsen Mutlu

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  1. The importance of measuring negative expiratory pressure (NEP) in the diagnosis of obstructive sleep apnoea syndrome (OSAS) Yelda Turgut, Zeynep Atam, Melahat Uygun, Çağlar Çuhadaroğlu, Tunçalp Demir, Birsen Mutlu

  2. Diagnosis and Pathophysiology of OSAS • The diagnosis is made when the PSG monitoring of the patients who have clinical characteristics of OSAS such as excessive daytime sleepiness, snoring and witnessed apnoea, as well as demonstration of AHI>5 and obstructive nature of hypopnoea in more than 50% of occasions. • There are three major factors causes upper airway (UA) obstruction and collapse, namely anatomical abnormalities of UA, negative pressure generated during inspiration and the loss of activity of pharyngeal muscles that dilate the airway during sleep.

  3. *Abnormal-narrow UA increases the resistance *Increased pharyngeal compliance -Pcrit is higher during inspiration *Muscles are hypotonic and response to negative pressure is decreased OBSTRUCTED UPPER AIRWAY DURING INSPIRATION

  4. Airway during expiratory phase Focus on expiration • The compliance of UA is higher during expiratory phase of patients who have increased OSAS • Marked narrowed UA is seen at the end of expiration in supine position in patients with OSAS. Expiratory positive airway pressure (EPAP) is required to maintain the UA patency. Schwab R. Am Rev Respir Dis 1993, Sanders MH. Chest 1990 • Studies suggest that both in loud snorers and OSAS patients, increased airway resistance, particularly in supine position, flow limitation (FL) and obstruction occur both during inspiration and expiration. Liistro G, J Appl Physiol 1990, Brown IG, Am Rev Respir Dis 1985, Tamisier Sleep 2004 Sanders MH. Am Rev Respir Dis 1983,.Morrell AJRCCM 1998,

  5. NEGATIVE EXPIRATORY PRESSURE (NEP) TECHNIQUE • NEP is a technique which is basically developed to detect the intrathorasic flow limitation during expiration. • NEP technique involves applying -3 or –5 cm H2O negative pressure on the mouth during tidal expiration and comparing the emerged expiratory ύ-V curve with the standard control expiration curve. Data analysis is made by visual analysis of the two ύ -V curves. • To simply the readings, limited expiratory flow is expressed as the percentage of the control tidal volume (VT%).

  6. Examples of NEP tracing of normal and flow limited patients

  7. A highly suggestive example of NEP tracing demonstrating increased upper airway resistance

  8. NEP in OSAS • The major drawback of NEP technique in detecting intrathoracic FL in snorers and patients with OSAS is the reflection of increased airway resistance to NEP measurement. • In the absence of any underlying cardiac-lung disease that can cause intrathoracic FL, this disadvantage was turned into an advantage by using the NEP technique in the diagnosis of OSAS patients. Unstable UAs with high compliance will respond with narrowing even if not with obstruction to negative pressure created during expiration, namely FL in the NEP trace during expiration FL that is expressed as the percentage of VT was found to be well-correlated with DI and AHI. Liistro G. Eur Respir J 1999, Verin E. Thorax 2002.

  9. The role of NEP technique in the diagnosis of OSAS ? The correlation between FL demonstrated by NEP technique and PFTs, the airway resistance (Raw) and AHI and DI derived by PSG? Aim of the study

  10. Material-Method & Statistical Analysis • 63 patients (43 male, 20 female) were subjected to overnight PSG in sleep laboratories • Extended PFTs by body pletsymography • FL detection by NEP technique at -5 cmH2O both in upright and supine position

  11. RESULTS-1 Table 1: Anthropometric characteristics of patients and parameters obtained from PSG

  12. RESULTS-2 Table 2: The classification of obesity according to BMI of the patients

  13. 63 Patients AHI<5 AHI≥30 15≤AHI<30 5≤AHI<15 7 Patients (%11.1) 13 Patients (%20.6) 17 Patients (%27) 26 Patients (%41,3) Primary snoring Mild OSAS Moderate OSAS Severe OSAS The severity of OSAS patients according to PSG

  14. RESULTS-4 Table 3: Significant correlations between all parameters and FL % both in supine and upright position

  15. RESULTS-5 Table 4: The correlations between the important parameters for OSAS and FL % both in upright and supine positions

  16. RESULTS-6 Table 5: The parameters significantly different between the patients with limited & unlimited flow while upright. Student’s t veya Mann whitney u

  17. RESULTS-7 Table 6: The parameters significantly different between the patients with limited & unlimited flow in supine position.

  18. RESULTS-8 Table 7: The differences of sleep parameters in the presence of FL in upright and supine positions.

  19. Table 8: The statistical characteristics of NEP technique in the diagnosis of OSAS RESULTS-9

  20. DISCUSSION-1 • The positive (+) PV of NEP technique when seated and supine were % 80 and % 89.3, respectively. This (+) PV strongly suggests that FL, that was found when seated and supine position in patients who are suspected for OSAS is due to OSAS. • No differences found between the patients who are flow limited and free of limitation in sleep parameters and no correlation found with the degree of FL that was shown by the previous studies.

  21. DISCUSSION-2 • The high value of BMI, the reduction in FEV1, VC, and TLC together in patients who are flow limited both in upright and supine positions suggest that obesity cause the restriction. • The increase of the degree of FL in correlation with the airway resistance and the significant elevation of these parameters in flow limited patients suggest that NEP technique may be used to indicate the increased UA resistance, and consequently the collapsibility of UA when intrathoracic obstruction is excluded.

  22. The role of NEP technique in the diagnosis of OSAS ? flow limited patients by NEP HIGH BMI Narrowed UA by fat deposition HIGH (+)PD The pathophysiological components of OSAS UA with high compliance HIGH RAW Decreaed response during sleep HIGH P 0,1

  23. DISCUSSION-4 • The widely accepted approach to patients who have clinically diagnosed as a possible OSAS is to perform limited PSG recording respiratory signals only. • In order to select the patients who will undergo the limited PSG, variety of scoring systems based on clinical and anthropometric properties were suggested. • However, the lack of correlation between the symptoms and AHI is well-known. NEP technique can be used as an aide in diagnosis. • NEP technique is a simple, non-invasive method which is performed daytime, therefore, it can be used as a screening test to select patients for limited PSG in patients who are suspected to have OSAS.

  24. THANK YOU FOR YOUR ATTENTION…

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