sleep apnoea Model for investigating snorers with suspected subwts were obtained during polysomnography

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1 Thorx 1993;48: Model for investigting snorers with suspected sleep pnoe 275 Pulmonry Deprtment, Krnkenhus Linz, A-1130 Vienn, Austri H Ruscher W Popp H Zwick Reprint requests to: Dr H Ruscher Received 19 Februry 1992 Returned to uthors 8 My 1992 Revised version received 26 My 1992 Accepted 9 July 1992 Helmuth Ruscher, Wolfgng Popp, Hrtmut Zwick Abstrct Bckground Overnight polysomnogrphy is expensive nd time consuming. An pproch bsed on logistic regression model nd overnight pulse oximetry hs been developed to determine which of the snorers referred to our sleep lbortory need polysomnogrphy. Methods The vribles entered in the regression model were derived from questionnires completed by 95 hbitul snorers nd 89 ptients with obstructive sleep pnoe. The resulting regression eqution included weight, height, sex, witnessed episodes of pnoe, nd reports of flling sleep when reding. This prediction eqution ws pplied to smple of 116 consecutive ptients referred for investigtion of hevy snoring. Pjlse oximetry dt on the 116 test subwts were obtined during polysomnogrphy nd nlysed seprtely. Pulse oximetry ws judged to indicte obstructive sleep pnoe when it showed cyclic oscilltions of oxyhemoglobin sturtion or hert rte, or both, for more thn 30 minutes during the study night. Results A cut off probbility of 0-31 gve the prediction model sensitivity of 94% to predict n pnoe-hypopnoe index bove 10, with specificity of 45%. When this cutoff point ws used to predict n pnoe-hypopnoe index of over 20 sensitivity ws 95% nd specificity 41%. Combined with oximetry our regression model hd sensitivity of 100% for predicting n pnoe-hypopnoe index of more thn 10. On the other hnd, ll ptients with negtive results from oximetry nd probbility vlue below 0'31 hd n pnoe-hypopnoe index lower thn 10 ccording to polysomnogrphy. Conclusions It is concluded tht snorers with negtive results from oximetry clssified s not hving obstructive sleep pnoe ccording to this model do not need polysomnogrphy. (Thorx 1993;48: ) Obstructive sleep pnoe is common problem mong middle ged obese snorers."2 Although complints bout loud snoring, dytime sleepiness, nd psychomentl impirment re chrcteristic fetures of obstructive sleep pnoe, these symptoms lso occur in hbitul snorers without sleep pnoe.34 As the development from snoring to obstructive sleep pnoe is grdul, even pnoe reported by the bed prtner does not clerly differentite between snorers with nd without cliniclly relevnt obstructive sleep pnoe. Incresing wreness of the risks ssocited with obstructive sleep pnoe in regrd to morbidity nd mortlity5-8 hs led to rpid rise in the number of referrls to sleep lbortories. Thus severl ttempts hve been mde to identify those ptients in need of sleep study mong the lrge number of snorers seeking medicl help for their problem. Wheres scoring system bsed on self reporting9 detected obstructive sleep pnoe in round 80% of cses, recently published regression model' bsed on ge, weight, height, blood pressure, nd reported episodes of pnoe predicted more thn 15 disturbed brething events per hour of sleep with sensitivity of 92% nd specificity of 51%. Becuse of the low specificity, however, such models re of limited vlue in reducing the number of polysomnogrphic studies in snorers without obstructive sleep pnoe. Furthermore, relying completely on such prediction model crries the risk of missing some ptients with obstructive sleep pnoe. To compenste for the shortcomings of prediction model we hve combined it with pulse oximetry. As most episodes of pnoe re ssocited with cyclic oscilltions of oxyhemoglobin sturtion (So2) nd pulse rte"i 12 typicl obstructive sleep pnoe is esily recognisble from overnight pulse oximetry.1' 14 The sensitivity of oximetry my, however, be poor in ptients with obstructive sleep pnoe who hve short episodes of pnoe nd only minor desturtions' -'6 nd in snorers with incomplete upper irwy obstruction tht is not ssocited with pnoe or desturtion but my led to severe frgmenttion of sleep.3 As both conditions usully cuse dytime sleepiness these ptients should be detectble from prediction model tht includes some feture of excessive dytime sleepiness. We report series of snorers referred to sleep lbortory becuse of suspected obstructive sleep pnoe on which these ides hve been tested. Methods To develop the regression model we used dt from 95 hbitul snorers with n pnoe-hypopnoe index below 10 nd from 89 ptients with obstructive sleep pnoe Thorx: first published s /thx on 1 Mrch Downloded from on 27 April 2018 by guest. Protected by copyright.

2 276 Ruscher, Popp, Zwick Tble 1 Anthropometric dt (men (SD) vlues) on 89 ptients with obstructive sleep pnoe (OSA) nd 95 hbitul snorers used to develop the regression model Hbitul snorers OSA Age (y) 49 0 (11 7) 50-6 (10-2) Body mss index 4 (3-1) 31-8 (5 3)* Mle: femle 63:32 75:14 *p<oooo1. with n pnoe-hypopnoe index bove 20. These 184 subjects were prt of popultion of 222 snorers referred to our sleep lbortory for investigtion of suspected obstructive sleep pnoe during the course of one yer. The 38 subjects mong this popultion with n pnoe-hypopnoe index of were excluded so tht we would hve two clerly distinct groups-one with obstructive sleep pnoe nd one with hevy snoring only. Anthropometric dt on the study popultion re given in tble 1. Most of our ptients (63%) were self referred becuse they hd red bout snoring nd sleep pnoe; the others were referred by their er, nose, nd throt specilist (17%), their generl prctitioner (14%), or other specilist (6%). All ptients underwent ll night polysomnogrphy, including electroencephlogrphy, electro-oculogrphy, submentl electromyogrphy, electrocrdiogrphy, mesurement of irflow t the nose nd mouth nd of the movements of rib cge nd bdomen, nd oximetry (Minolt Pulsox 7). These vribles were recorded by computer using the Respisomnogrphe hrdwre nd softwre (SEFAM, Vndoeuvre-Les-Nncy, Frnce) nd were mnully scored ccording to stndrd criteri.'7 An episode of pnoe ws defined s cesstion of irflow t the nose nd mouth for longer thn 10 seconds. Hypopnoe ws defined s reduction in rib cge nd bdominl movements to 50% or less of those recorded during the preceding five breths for longer thn 10 seconds, ccompnied by fll in So2 to 92% or lower if bseline ws 94% or more or by fll in So2 of 3% or more if bseline ws 93% or less. The totl number of episodes of pnoe nd hypopnoe per hour of sleep represented the pnoe-hypopnoe index. The symptoms nd complints of ll ptients were recorded by self dministered questionnire with 36 items, most of them requiring simple "yes or no" decisions. The frequencies of positive nd negtive nswers given by the two groups were compred by x2 test nd significnt difference ws ssumed t p vlues below Ordered ccording to decresing X2 vlue, ll items with significnt differences were entered in stepwise logistic regression nlysis using the BMDP sttisticl softwre pckge for microcomputers."8 The vribles entering the model did not chnge when we lso included the dt on the 38 ptients with n pnoe-hypopnoe index of The resulting regression eqution ws then pplied to nother smple- 116 consecutive ptients (95 men, 21 women) referred for investigtion of hevy snoring. According to polysomnogrphy 47 of them hd n pnoehypopnoe index bove 10 nd 38 bove 20. The pulse oximetry dt for these subjects were nlysed seprted from polysomnogrphy by n investigtor blinded to the ptient's symptoms nd the polysomnogrphy results. For scoring of pulse oximetry the full outprints of our Sleepox softwre'9 were used, where intervls of 30 minutes re displyed on 13 cm width of print (theoreticlly this would represent pper speed of 6-5 cm/h on conventionl chrt recorder). The pulse oximetry dt were considered positive for obstructive sleep pnoe if the sum of ll intervls during the study night showing cyclic oscilltions of So2 or pulse rte exceeded 30 minutes. Scoring ws bsed solely on pttern recognition without definition of limits for the mplitudes of oscilltions in So2 nd pulse rte. Results The symptoms nd complints of the two ptient groups used to develop the model re Tble 2 Symptoms nd complints of the 89 ptients with obstructive sleep pnoe (OSA) nd 95 hbitul snorers (HS) used to develop the regression model nd the 47 subjects with n pnoe-hypopnoe index (AHI) bove 10 nd 69 subjects with n AHI lower thn 10 used to test the model Reported episodes of pnoe >20% overweight Hypertension Flling sleep when driving Flling sleep fter nocturnl wkenings within 10 min Nocturi Mle gender Flling sleep when reding Flling sleep when tlking Flling sleep when wtching TV Restless sleep Wking up choking Flling sleep t bedtime within 10 min Poor mentl performnce Feeling sleepy during dytime Hering own snoring on wkening *p<0.05; **p<0-01; ***p<0.005; ****p< OSA HS (Go) (Go)) x **** 14-9**** 9.6*** 9.2*** 8-2*** 8-1** 7-9** 7.8*** 5-1* 4-5* 4-1* AHI > I 0 (G/o) <1 0(Y.) x2 10-5*** 4.3* 4.1* 7.5* 6-8* 6-0* * *** Thorx: first published s /thx on 1 Mrch Downloded from on 27 April 2018 by guest. Protected by copyright.

3 Modelfor investigting snorers with suspected sleep pnoe 2 to 0~ F_ 09 f * O. Tble 3 Distribution of the 116 test subjects in groups with probbility vlues (p) for obstructive sleep pnoe (OSA) bove nd below the cutoffpoint of 0 31 ccording to pnoe-hypopnoe index (AHI) nd gender p<031 p > 031 AHI M F Totl M F Totl < > < > given in tble 2. Of the 11 items found to hve different frequencies in the two groups, only four contributed significntly to the logistic regression model. Thus the eqution found to estimte probbility of obstructive sleep pnoe in hevy snorers ws: = ek ProbbilitY 1 + ek' where k= ( b c + 1-3d) nd = 0 if mle nd 1 if femle, b = weight in kg x 100/height in cm - 100, c = 1 if flling sleep when reding is reported nd 0 if not, d = 1 if episodes of pnoe re reported nd 0 if not. Although cut off probbility of 0-56 hd the highest efficcy (= true positive predictions plus true negtive predictions divided by totl number of study subjects), with 77% of the ptients clssified correctly, the sensitivity in predicting n pnoe-hypopnoe index of 10 or more ws too poor for clinicl use. Thus we chose cut off point of 0-31 s the on 0O *2 0. sto o n *1.1. ~~~~ * n- f 0 1 i I Apnoe-hypopnoe index Probbility vlues clcultedfrom the regression modelfor 116 snorers s function of the pnoe-hypopnoe index. Full squres indicte subjects with overnight oximetry giving results positive for obstructive sleep pnoe nd open squres those with negtive results best compromise between high sensitivity nd reltively well preserved specificity. The sensitivity of our model for the detection of obstructive sleep pnoe ws defined s the number of true positive predictions divided by the number of ptients with n pnoe-hypopnoe index of 10 or more or 20 or more. Specificity ws defined s the number of true negtive predictions divided by the number of ptients with n pnoe-hypopnoe index below 10 or 20. With our eqution pplied to the 116 test subjects (tble 3), this cut off point gve the model sensitivity of 94% for predicting n index of 10 or more (three flse negtives out of 47) with specificity of 45% (31 true negtives out of 69). When we used this cut off point to predict n pnoe-hypopnoe index of 20 or more sensitivity ws 95% nd specificity 41%. The negtive predictive vlue (=true negtive predictions divided by totl negtive predictions) of probbility below 0-31 ws 91% for n pnoe-hypopnoe index of 10 or less nd 94% for one of 20 or less. As cn be seen from tble 3, the model performed better for men thn for women, the sensitivity for predicting n pnoe-hypopnoe index of 20 or more in men being 100%. The symptoms nd complints of these 116 test subjects re lso given in tble 2. Three ptients with more thn 10 episodes of pnoe per hour of sleep were missed by our model. The first ws 30 yer old womn with body mss index of 20-9, who reported hevy snoring nd excessive dytime sleepiness but hd no witnessed episodes of pnoe. The pnoe-hypopnoe index from polysomnogrphy ws 22-7 nd er, nose, nd throt exmintion showed enlrged tonsils nd n bnormlly long soft plte with lrge uvul. The polysomnogrm obtined two months fter surgery showed complete disppernce of sleep disordered brething. The second ptient ws 77 yer old womn of norml weight with n pnoe-hypopnoe index of Although she reported episodes of pnoe nd sleepiness the probbility clculted from our model ws only The third cse missed by our model ws 26 yer old mn with body mss index of 24-1, who complined bout dytime sleepiness but hd no witnessed episodes of pnoe. Wheres his probbility vlue ws 0 3, polysomnogrphy yielded n pnoehypopnoe index of 15. Pthologicl results from oximetry, ccording to our definition, were found in 70 ptients, in 26 of whom simultneous polysomnogrphy showed n pnoe-hypopnoe index lower thn 10. Only three ptients with n pnoe-hypopnoe index of 10 or more hd negtive results from oximetry. Thus sensitivity for detecting obstructive sleep pnoe from more thn 30 minutes of cyclic oscilltions in So, or pulse rte during the night ws 94% nd specificity 62%. As shown in the figure, t'-e three ptients considered s not hving obstructive sleep pnoe on the bsis of oximetry were in the high probbility group, nd the three ptients Thorx: first published s /thx on 1 Mrch Downloded from on 27 April 2018 by guest. Protected by copyright.

4 278 Ruscher, Popp, Zwick from the low probbility group with n pnoe-hypopnoe index of 10 or more hd positive results from oximetry. Thus the combintion of oximetry with our regression model hd sensitivity of 100% for predicting n pnoe-hypopnoe index of 10 or more. On the other hnd, ll ptients with negtive results from oximetry in the low probbility group hd n pnoe-hypopnoe index below 10. Thus, despite the low overll specificity for obstructive sleep pnoe, our pproch mkes possible reduction of negtive polysomnogrms of 29% (49 insted of 69) without the risk of missing ptients with obstructive sleep pnoe. Discussion The purpose of this study ws to develop n pproch to the investigtion of snorers referred to sleep lbortory with possible obstructive sleep pnoe. Our gol ws to reduce the number of polysomnogrphy studies with negtive result in those who only snore-without missing ptients with cliniclly relevnt sleep disordered brething. As we think it inpproprite to refuse sleep study-for exmple, in snorer with witnessed episodes of pnoe-solely becuse of the lck of relevnt clinicl symptoms, we chose pulse oximetry s simple nd widely vilble screening test for obstructive sleep pnoe s our first step. The decision bout further investigtion could then be bsed on the results of oximetry nd the probbility of obstructive sleep pnoe clculted from logistic regression model. The vribles entering our prediction model were weight, height, sex, witnessed pnoe, nd the positive or negtive nswer to the question: "Do you frequently fll sleep during the dy when reding books or newsppers?" sing our regression eqution with cut off probbility vlue of 0-31, we were ble to predict n pnoe-hypopnoe index of 10 or more with sensitivity of 94% in 116 unselected hevy snorers. Only three of the 47 subjects with n pnoe-hypopnoe index of 10 or more were misclssified by our regression eqution. These ptients were rther different from the typicl ptient with obstructive sleep pnoe, for whom our prediction model worked very well, nd ll of them hd pthologicl results from pulse oximetry ccording to our definition. In contrst to recently published pproch for predicting sleep pnoe from clinicl symptoms,10 our model included vrible indicting excessive dytime sleepiness but did not include ge or hypertension. Although hypertension ws more frequently found in ptients with obstructive sleep pnoe thn in hbitul snorers, its prevlence ws not correlted with severity of sleep disordered brething nd ws influenced only by obesity nd mle gender-both included in our model. The reson for not including ge ws tht we found neither n increse in pnoe-hypopnoe index with ge (r = 0 02) nor higher prevlence of obstructive sleep pnoe in older ge groups, which my be due to the high percentge of self referrls mong our study popultion, resulting in n overrepresenttion of young ptients with severe obstructive sleep pnoe by comprison with the generl popultion. Surprisingly, questions bout typicl fetures of obstructive sleep pnoe, such s short sleep ltency, restless sleep, wkenings with choking, or difficulty in stying wke in situtions other thn reding, did not enter the model by stepwise logistic regression nlysis. As our model is thought to estimte the probbility of obstructive sleep pnoe in snorers nd not to discover ptients with obstructive sleep pnoe mong the generl popultion, snoring is not included in the eqution. Snoring, however, is the most common finding in ptients with obstructive sleep pnoe, so ptient's complint of loud snoring mens tht obstructive sleep pnoe should be excluded. Our pproch should be helpful in predicting 10 or more sleep disordered brething events per hour of sleep, which is well below the pnoe index ssocited with incresed mortlity.5 How generlly pplicble our model is remins to be estblished. The method of collecting dt-tht is, type of questionnire or questionnire versus interview-my influence the frequency with which subjective complints re elicited. For clinicl purposes our eqution cn be recommended only when used with pulse oximetry, whose shortcomings3 14 it overcomes. From our results we conclude tht ptients in the low probbility group clssified s not hving obstructive sleep pnoe on the bsis of oximetry do not need polysomnogrphy. Firstly, they generlly hve only very mild or no symptoms nd, secondly, our definition of pthologicl oximetry results ws rther rigorous. A totl of 30 minutes of cyclic oscilltions of So2 or pulse rte mens tht, for exmple, for sleep time of six hours there would be n pnoe-hypopnoe index of bout 5-8. Thus even ptients with supine or sleep stge dependent obstructive sleep pnoe re unlikely to be missed. On the other hnd, this definition resulted in reltively high number of flse positive results from oximetry, which contrsts with studies using less rigorous definitions of bnormlity Our pln of investigtion should be cpble of reducing the number of polysomnogrphy studies with negtive result in snorers by bout one third (49 insted of 69 in our 1 16 ptients). nfortuntely, we cnnot recommend tht polysomnogrphy is withheld in ptients with negtive results from oximetry in the high probbility group, s symptomtic ptients with only minor oxygen desturtions would be missed. At the sme time, polysomnogrphy hs to be performed in ptients with positive results from oximetry in the low probbility group, to detect nerly symptomless ptients with sleep disordered brething tht could cuse crdiovsculr dmge. These ptients, however, my not ccept effective tretment.20 Thorx: first published s /thx on 1 Mrch Downloded from on 27 April 2018 by guest. Protected by copyright.

5 Modelfor investigting snorers with suspected sleep pnoe 279 Theoreticlly, ptients with positive results from oximetry hve to undergo polysomnogrphy regrdless of their probbility group. Ptients with full blown obstructive sleep pnoe, however, hve chrcteristic cyclicl oscilltions of So, nd pulse rte throughout the night. About one third of such ptients cn be identified from visul scoring of oximetry lone. 14 Our dt support this s polysomnogrphy would not hve been bsolutely necessry to confirm the dignosis of obstructive sleep pnoe in the 17 subjects with n pnoe-hypopnoe index bove 50. Consequently, totl of 79 polysomnogrphic exmintions would hve been sufficient to mnge our smple of 116 snorers, reduction in the number of polysomnogrphy studies of 32%. In the light of recent results'4 we might put forwrd the hypothesis tht most of the remining 79 polysomnogrphy studies could be replced by simplified sleep studies tht include exmintion of brething pttern nd detection of leg movements s well; but the vlidity nd cost effectiveness of this pproch needs to be tested. nfortuntely, we did not mesure neck circumference, which hs been shown to be sensitive nd highly specific predictor of obstructive sleep pnoe.' 22 We suspect, however, tht routine mesurement of neck circumference will not reduce the number of sleep studies in snorers s physicins my be unwilling to refuse investigtion on the bsis of norml neck circumference. Given the discrepncy between the limited number of sleep lbortories in Europe tody nd the lrge number of ptients referred for sleep study, ny ttempt to reduce the number of expensive nd time consuming polysomnogrphy studies in snorers is useful. We conclude tht snorers with negtive results from oximetry clssified s not hving obstructive sleep pnoe by our prediction model do not need polysomnogrphy. A further reduction of polysomnogrphy studies in snorers seems fesible-by not doing polysomnogrphy in ptients of the high probbility group with oximetric screening results unequivoclly typicl for obstructive sleep pnoe. In summry, such n pproch should be ble to reduce considerbly the number of polysomnogrphy studies in snorers without missing ptients who would benefit from tretment. 1 Lugresi E, Coccgn G, Fmeti P, Mntovni M, Cirignott F. Snoring. Electroencephlogr Clin Neurophysiol 1975;39: Perez-Pdill JR, West P, Kryger M. Snoring in norml young dults: prevlence in sleep stges nd ssocited chnges in oxygen sturtion, hert rte nd brething pttern. Sleep 1987;10: Guilleminult C, Stoohs R, Duncn S. Snoring (I)- Dytime sleepiness in regulr hevy snorers. Chest 1991 ;99: Hoffstein V, Mteik JH, Mteik MS. Snoring nd sleep rchitecture. 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