Definition of POSAS

Definition of POSAS

Two to four percent of the Western population suffers from Obstructive Sleep Apnea Syndrome (OSAS)1. OSAS comes hand-in-hand with excessive tiredness during the day, heavy snoring and an increased risk of developing heart and vascular disorders. It further reduces your quality of life2,3. The gold standard treatment for severe OSAS is Continuous Positive Airway Pressure (CPAP).

Half of OSAS patients suffer from positional OSAS

Scientific research has shown that many OSAS patients experience increased airway obstruction during sleep when lying on their backs than when lying on their sides4. When an individual experiences an increased level of airway obstruction when lying on their back as compared to any other position, it is known as Positional OSAS (POSAS). POSAS is defined as OSAS whose Apnea Hypopnea Index (AHI) level is at least twice as high when lying on their back (supine) than in any other position (AHI supine > 2 x AHI other positions).
A study of over 600 patients conducted in The Netherlands and Israel has shown that roughly half (56%) of the light and moderate OSAS patients indeed have POSAS5,6. On top of this, 30% of patients have a higher AHI when supine than in any other position, only not twice as high5,6. The incidence of POSAS is much higher among light and medium OSAS (5 ≤ AHI < 30) than by severe OSAS (AHI > 30)7.


A typical POSAS patient (whose supine AHI > 2x AHI in any other position) is also easily identified in the visual representation of a polysomnography

Easily calculate POSAS online

Almost all equipment used in The Netherlands as sleep diagnostic tools also measure sleep position. To determine whether someone has positional apnea, the supine AHI must be at least twice as large as the AHI in any other position. This seems easy to calculate however often on a PSG or PG report only the total AHI and the supine AHI is shown. The % of sleep time spent supine thus plays a role in the calculation of AHI in any other position, which is used to determine whether the apnea is positional or not.

Below you can quickly determine if your patient has positional apnea using the total AHI, supine AHI and the percentage of time spent supine values. It also informs you which AHI will remain after treatment using position therapy on the basis of the PG and PSG data.


  1. Young TT, Peppard PE, Palta M, 1997. Population-based study of sleep-disordered breathing as a risk factor for hypertension. Arch Intern Med. 1997;157.
  2. Young T, Finn L, Peppard PE, Szklo-Coxe M, Austin D, Nieto FJ, Stubbs R, Hla KM (2008) Sleep disordered breathing and mortality: eighteen-year follow-up of the Wisconsin sleep cohort. Sleep 31:1071-8.
  3. Redline S, Yenokyan G, Gottlieb DJ, Shahar E, O’Connor GT, Resnick HE, Diener-West M, Sanders MH, Wolf PA, Geraghty EM, Ali T, Lebowitz M, Punjabi NM (2010) Obstructive sleep apnea-hypopnea and incident of stroke: the sleep heart health study. Am J Respir Crit Care Med. 182:269-77.
  4. Cartwright RD (1984) Effect of sleep position on sleep apnea severity. Sleep 7:110-4.
  5. Oksenberg A, Arons E, Greenberg-Dotan S, Nasser K, Radwan H (2009) The significance of body posture on breathing abnormalities during sleep: data analysis of 2077 obstructive sleep apnea patients. Harefuah 148:304-9.
  6. Richard W, Kox D, den Herder C, Laman M, van Tinteren H, de Vries N (2006) The role of sleeping position in obstructive sleep apnea. Eur Arch Otorhinolaryngol 263:946-50.
  7. Mador MJ, Kufel TJ, Magalang UJ, Rajesh SK, WatweV, Grant BJB (2005) Prevalence of positional sleep apnea in patients undergoing polysomnography. Chest 128:2130-2137.