gms | German Medical Science

GMS Current Topics in Otorhinolaryngology - Head and Neck Surgery

Deutsche Gesellschaft für Hals-Nasen-Ohren-Heilkunde, Kopf- und Hals-Chirurgie e.V. (DGHNOKHC)

ISSN 1865-1011

Current diagnostic trends in sleep disordered breathing

Review Article

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  • corresponding author Joachim T. Maurer - Sleep Disorders Centre, University Dept. of Otorhinolaryngology, Head and Neck Surgery Mannheim, Faculty for Clinical Medicine Mannheim at the Ruprecht-Karls-University Heidelberg, Mannheim, Germany

GMS Curr Top Otorhinolaryngol Head Neck Surg 2006;5:Doc02

Die elektronische Version dieses Artikels ist vollständig und ist verfügbar unter:

Veröffentlicht: 5. Oktober 2006

© 2006 Maurer.
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Over the past two decades, various methods of sophisticated diagnostics of the upper airway have been tested in patients with sleep disordered breathing (SDB). In this context, endoscopic techniques and pharyngeal pressure recordings are of special interest for the otorhinolaryngologist.

Whereas the basic otorhinolaryngological examination is able to detect anatomical pathologies which need to and can be corrected, the Müller-Manoeuvre seems to help exclude patients from uvulopalatopharyngoplasty.

To a large extent, videoendoscopy during natural sleep has been replaced by videoendoscopy under sedation. Despite good methodological preparation and impressive presentability of the obstructions, there is not sufficent evidence to demonstrate that videoendoscopy under sedation improves the success rate of surgery in SDB. However, in assessing the impact of the epiglottis on upper airway obstructions in the individual patient, videoendoscopy is the only existing option.

Multi-channel pressure recordings permit analysing the entire sleep period and are well tolerated. They can be used to determine the Apnea-Hypopnea-Index as well as to quantify obstructive events in the upper and lower pharyngeal segment. On the other hand, obstructions of the tongue base cannot be distinguished from obstructions related to the epiglottis.

According to the data available so far, the benefit of sophisticated diagnostics of the upper airway still has to be judged with caution. Therefore, the promising approaches of both videoendoscopy under sedation and multi-channel pressure recordings deserve further intensive research. According to the personal estimation of the author, they will nevertheless become valuable tools for otorhinolaryngologists in the near future, thus complementing the basic ENT-examination and improving the treatment of patients.

Keywords: sleep disordered breathing, sleep apnoea syndrome, primary snoring, diagnostics, Müller-Manoeuvre, videoendoscopy, multi-channel pressure recordings

1. Introduction

In 1965, the French researchers Gastaut, Tasnari and Duron [1] and the Germans Jung and Kuhlo [2] simultaneously described obstructive sleep apnoea (OSA) for the first time. They were relying on the use of many different singular instruments in order to assess sleep, respiration and circulation. All analogue signals were amplified and recorded on paper. Every night hundreds of pages accumulated. Only a few patients could be recorded and anlaysed. Following the publication of the clinical symptoms of OSA [3] and the recognition that excessive daytime sleepiness was a major symptom in many other diseases [4], the number of patients admitted to the few existing sleep disorder centers increased during the second half of the seventies. During that period the first clinical sleep laboratories were founded in Germany, mainly in the context of psychiatry and neurology departments. Patients suffering from sleep apnoea were rarely presented there because a tracheotomy was the only existing treatment option for OSA [5]. In 1981 tracheotomy was supplemented by another surgical and conservative therapy: In Australia, Sullivan invented nasal ventilation with continuous positive airway pressure (CPAP) [6] and in America Fujita established uvulopalatopharyngoplasty (UPPP) [7]. Both treatments restricted patients' quality of life considerably less than tracheotomy. Sleep laboratories in pulmonary and otorhinolaryngologic departments sprung up. Yet at the end of the eighties patients still had to wait for more than a year in order to be examined in a sleep laboratory. The waiting period could not be reduced by the improvement of computers because the number of patients seeking help increased rapidly. Questionnaires were developed in order to help estimate the urgency of a sleep recording. Devices measuring only a few cardiorespiratory parameters were invented aiming to confirm or exclude the presence of sleep disordered breathing (SDB).These screening-recordings entered the outpatient sector in 1991. Yet in general, they were reserved for pulmonologists. Today the necessary steps in diagnosing SDB are clearly defined by the guidelines of the Federal Committee for the evaluation of diagnostic and therapeutic procedures, issued in November 2004. Now general practicioners, otorhinolaryngologists, internists, pulmonologists, neurologists and psychiatrists are allowed to execute cardiorespiratory polygraphic recordings, thereby increasing the accessibility to preclinical diagnostics.

Nowadays a timely investigation can be ensured virtually throughout the Federal Republic of Germany. After taking down the history (supported by standardized questionnaires), a clinical examination and several additional tests (e.g. lung function, blood gas analysis, rhinomanometry, allergy testing, Holter monitoring) are administered. Finally, a cardiorespiratory polygraphy is recorded. A complete polysomnography (PSG) is only called for in unclear cases or if a nasal ventilation therapy has to be initiated. Parallel to the optimisation of the general diagnostic procedures new therapies emerged. Several ventilation modes, oral devices and numerous operations were tested in primary snorers and sleep apnoea patients. Nasal CPAP-ventilation has established itself as the gold standard therapy.With increasing numbers of diagnosed sleep apnoea patients, there are more and more patients who cannot tolerate CPAP-therapy and therefore need alternative treatment. This constitutes a new therapeutical challenge for the medical community involved in the treatment.

Otorhinolaryngologists see two groups of patients: First those who have had a CPAP trial and either rejected a continuous treatment directly afterwards or discontinued it some time later. Second those with mild to moderate OSA not yet requiring nasal ventilation and presenting snoring as their major complaint but not suffering from excessive daytime symptoms. Profound knowledge of the general aspects of diagnostics in sleep medicine and of the specific airway examinations are the prerequisites to care adequately for these patients.

In this context, otorhinolaryngologists are utmost engaged in identifying the essential pathomechanism and the anatomic correlates of snoring and sleep apneoa as well as searching for innovative surgical concepts with improved success rates. Taking both aspects into account, the soft palate, the tongue base and the epiglottis are the major anatomical sites addressed (Figure 1 [Fig. 1]). In particular, new techniques for the assessment of the upper airway function during sleep are being constantly developed. These new techniques need to be evaluated systematically in order to define their diagnostic value (Figure 2 [Fig. 2]).

The objective of this work is to present the status quo and the trends of the ENT-specific diagnostic procedures in suspicion of SDB. Their impact on selecting the appropriate operation and improving its outcome will be a main focus. Imaging procedures [8], [9], [10] acoustic pharyngometry [11], [12], [13], [14], [15], [16] and snoring sound analysis [17], [18], [19] will not be addressed because they are procedures which are not performed by otorhinolaryngologists, are no longer available, or are still too unclear in terms of their methodology.

2. Examination of the upper airway during wakefulness

2.1. Basic clinical-endoscopical examination

Endoscopy of the upper airway during wakefulness constitutes the foundation of the otorhinolaryngological examination in snorers and sleep apnoea patients [20]. Already in the early publications, failures of in sleep apnoea patients were reported [7]. In order to improve the success rate, anatomic and static findings were the first parameters to be evaluated [7], [21]. The impact of enlarged palatine tonsils came to the fore due to the experiences made in children. If performed simultaneously, tonsillectomy was described by most authors as a positive predictive factor for a successful UPPP [22], [23], [24], [25], [26], [27], [28] (Table 1 [Tab. 1]): The larger the tonsils the higher the success rate [29]. After UPPP, Anand found a non-significant reduction of the apnoea index (AI) from 48 to 38/h in patients after previous tonsillectomy. If UPPP could be combined with tonsillectomy, the AI dropped significantly from 55 to 13/h [23]. A success rate of 78.6% after solitary tonsillectomy [30] yielded further evidence that UPPP should always include removing the tonsils if still present. All the other anatomic parameters such as the size of the uvula, the existence of longitudinal pharyngeal folds and so forth did not show any relationship to the success rate of UPPP if evaluated separately [31]. Clinical findings during wakefulness were not suited to detect patients with tongue base obstruction in cases , where these obstructions could be successfully assessed during sleep, using manometry or videoendoscopy. Woodson only found hints that the oropharynx was normal in cases with retrolingual obstruction [32].

Aware of this dilemma, Friedman et al. developed a clinical four degree staging system incorporating the tonsil size, the position of the soft palate/tongue size and the body mass index (BMI) [33], [34], [35]. They reported a success rate of 80% after a solitary UPPP with tonsillectomy in patients with large tonsils, visible posterior pharyngeal wall and a BMI below 40 kg/m² (stage 1). According to our own experience these patients are rarely found among the group of typical sleep apnoea patients. If the tonsils were small or missing, the tongue rather large and the BMI below 40 kg/m² (stage 3) they achieved a success rate of only 8% which could be improved by the concomitant radiofrequency treatment of the tongue base in addition to UPPP [35]. By means of this staging systems it could be shown shown for the first time that an operation at the tongue base level can improve the success rate of UPPP if certain anatomic findings are given. One can argue that an isolated radiofrequency treatment of the tongue base reaches succes rates of 35 - 40% [36], [37]. It has not been evaluated yet whether predictive anatomic parameters exist for other surgeries. Publications dealing with this question always include the Müller Manoeuvre [38].

The subjectivity of the assessment and the variability of the nomenclature of the clinical findings hamper their comparison. However, it has been shown that this variability can be reduced by using pictograms [39].

2.1.1. Summary

a) The clinical-endoscopical basic examination can be performed by every otolaryngologist.

b) Tonsillar hyperplasia and tonsillectomy are positive predictive parameters for a successful UPPP.

c) There is some evidence that the combination of various anatomic parameters can facilitate the indication for different operations.

2.2. Müller-Manoeuvre

Snoring as well as apnoeas are based upon a dynamic process and can be simulated by most people. Thus snoring simulations and the Müller-Manoeuvre were used prior to sleep apnoea operations [38], [40], [41], [42] in order to improve patient selection. In addition the Müller-Manoeuvre was performed to assess postoperative changes of the upper airway [8], [43], [44]. In Germany the value of this simple examination has been questioned again and again. Until today it is widely used throughout the United States although Victor Hoffstein [45] wrote in the standard English textbook"]in the year 2000: "Simulating snoring or performing Müller's maneuver during endoscopic evaluation is not useful for determining the site of obstruction and predicting surgical success." However, the author does not provide references for his hypothesis.

2.2.1. Reliability of the Müller-Manoeuvre

In order to be able to compare results between different investigators and patients as well as intraindividually (before and after an operation), these manoeuvres have to be performed in a standardised way and have to be classified concisely. There are no literature reports concerning a standardization of snoring simulations. For the Müller-Manoeuvre the awake patient is sitting or lying and inspiring maximally with nose and mouth closed while the pharynx is examined via the fibrescope [25], [46], [47], [48], [49]. The endoscope is placed at the level of the supraglottis, the uvula tip and the nasopharynx.

Due to its simplicity the classification according to Sher has been widely used. He divides the collapse into four degrees ranging from minimal to complete occlusion. The degree of collapse found in the velar and retrolingual region is classified and any obstruction linked to the epiglottis is described [50]. Catalfumo et al. quantified the epiglottic collapse which they found in 11.5% of UPPP-failures being examined with the Müller-Manoeuvre in the sitting position (Table 2 [Tab. 2]) [51]. Fujita (Table 3 [Tab. 3]) scored the single airway evaluations obtained in one patient and defined an isolated palatal (type 1), isolated retrolingual (type 2) or combined obstruction (type 3) according to their predominance [52]. The distribution of the major sites of obstruction using the Fujita classification is shown in Table 4 [Tab. 4]. Terris's study group integrated the collapse of the lateral pharyngeal walls [53]. He compared his own results of airway evaluation using the Müller-Manoeuvre with the results obtained by one of his residents. They found the same degree of collapse in one third of the patients. Allowing for the difference of one degree according to Sher's classification [50], both investigators agreed upon the classification in 80% of their patients. However, they found a difference of three degrees in some cases. There was no systematic error between resident and specialist. Faber and Grymer, both experienced specialists, examined the same 40 patients and compared their results of the Müller-Manoeuvre with each other. They only agreed in 16 cases, being exactly the agreement obtainable by random distribution [13]. They could even show that the subjective grading of identical videosequences differed. Two blinded investigators agreed in only 64% of the cases [11]. Only Jäger et al. found a significant correlation of more than 0.8 between the degree of obstruction obtained by Müller-Manoeuvre and MRI [54]. Recently, the problem of interinvestigator variability could be eliminated by the quantitative, computer-assisted analysis of digitalized endoscopic recordings of the manoeuvre [55], [56], [57]. Nevertheless, taking all the available data into account, the reliability of the Müller-Manoeuvre cannot be assumed.

2.2.2. Transferability of the results to sleep

Up to now, no evidence exists that the sites of obstruction detected when using the Müller-Manoeuvre relate to what happens during sleep. This could be demonstrated through a comparison to videoendoscopy [32], [58], multi-channel pressure recordings [59] and to functional MRI during sleep [60]. Furthermore, there were several different sites of obstruction during sleep which could not been recognized with the Müller-Manoeuvre [59]. The impact of body position on the transferability of the Müller-Manoeuvre also remains unclear [46], [57], [61]. Some of our staff are able to produce varying mechanisms and levels of obstruction. This active component of the Müller-Manoeuvre is confirmed further by investigations concerning the critical closing pressure which is between -10 and -17 mbar in healthy adults during sleep [62]. When being subjected to the Müller-Manoeuvre, healthy persons produce negative pressures of -80 mbar without any signs of pharyngeal collapse [57]. This behaviour of the upper airway demonstrates the different collapsibility in wakefulness and sleep. All the data given do not support the transfer of results obtained by the Müller-Manoeuvre to natural sleep.

2.2.3. Predictability of success of an operation

It has to be questioned to what extent the Müller-Manoeuvre can predict surgical outcome (Table 1 [Tab. 1]). Several research groups were not able to better predict the success rate of UPPP when using the Müller-Manoeuvre [25], [46], [47], [63].

Abboussouan et al. and Sher considered an additional retrolingual collapse during the Müller-Manoeuvre as an exclusion criterion for a UPPP because their success rate was only 5% in such cases [48], [64]. There is only one Chinese study showing the same success rate for UPPP whether topodiagnosis was performed with Müller-Manoeuvre or sleep endoscopy [65]. Surgery of the epiglottis was always looked at and done separately if it was the site of obstruction during the Müller-Manoeuvre. Catalfumo could reduce the apnea index significantly from 42 to 8/h by partial resection of the epiglottis in 9 patients after UPPP failure [51].

Only Riley et al. report about the efficacy of selection criteria for the combination of different surgical procedures. In phase 1 of their protocol an isolated UPP was only performed if Müller-Manoeuvre as well as cephalometry revealed an isolated retrolpalatal collapse. In case of an isolated retrolingual collapse in both examinations, the group performed a hyoid suspension and a genioglossal advancement. If there was a combined collapse, all four surgical steps were done simultaneously. According to their selection criteria the authors found an isolated palatal collapse in 10 and an isolated retrolingual collapse in 6 patients. The remaining 223 patients (93%) had a combined collapse. The success rate of this protocol averaged out at 61% which is higher than Sher found in his meta-analysis of isolated UPPP, with definition of the major site of obstruction either by Müller-Manoeuvre, somnofluoroscopy or cephalometry (52%) or without (45%) [38], [64]. Riley's group does not compare their results with those they obtained without using their selection criteria. Even though they included mainly patients with moderate to severe sleep apnoea, the clinical relevance of such a selection may be questioned especially because patients with an isolated collapse of either palate or tongue base seem to be rare.

2.2.4. Summary

a) The Müller-Manoeuvre is easily performed and exerts only a minor strain on the patient.

b) The reliability of the Müller-Manoeuvre is not established. It may improve with the implementation of computer-aided evaluation tools.

c) The results of the Müller-Manoeuvre cannot be transfered to natural sleep.

d) A hypopharyngeal collapse indicates the exclusion of patients from UPPP, thus indirectly improving surgical success rate.

e) The Müller-Manoeuvre does not facilitate the indication for the varying surgical interventions used in OSA patients.

3. Examination of the upper airway during sleep and under sedation

3.1. Videoendoscopy during sleep

As early as 1978 the first report about videoendoscopic recording of the pharynx and larynx during sleep was published. In 10 patients Borowiecki and colleagues described a palatopharyngeal collaps at the end of exspiration and directly before inspiration. They observed a varying extension of the obstruction, caudally often combined with a medialisation of the lateral pharyngeal walls. Snoring sounds during the observed arousals were attributed to the soft palate and the lateral pharyngeal walls [66]. At that time there was no other treatment possibility than tracheotomy for sleep apnoea patients [67]. Patient selection did not possess any importance. Today ENT-surgeons hope to better select the proper candidates for surgery by videoendoscopy during sleep. Videoendoscopy during natural sleep can also be performed while a polysomnography is recorded [68], [69], [70], [71], [72], [73], [74], [75], enabling the assessment of the upper airway in relation to sleep stages. Therefore it may be considered superior to videoendoscopy under sedation. In the same way Becker and colleagues investigated the impact of CPAP-therapy on the upper airway [76]. However, sleep videoendoscopy is scarcely performed as it puts additional strain on both patient and doctor.

3.2. Videoendoscopy under sedation

3.2.1. Impact of videoendoscopy on sleep and breathing

Videoendoscopy under sedation is also supposed to visualize the site and mechanism of snoring and pharyngeal obstruction. For this purpose it is mandatory that snoring as well as pharyngeal obstruction can be provoked in affected patients under sedation. Furthermore, the inserted endoscope may neither disturb the patients' sleep nor prevent snoring. It is claimed that surgery can be indicated more precisely when using videoendoscopy under sedation. This implies that recommendations made according to endoscopy under sedation are different from those based on the examination during wakefulness alone. As a result an improved success rate is anticipated. At first videoendoscopy was described in children by Pringle and Croft using Midazolam sedation [77], one year later it was described in adults [78]. In comparison to natural sleep Sadaoka and colleagues could show that during a 3-hour videoendoscopy under sedation (with Midazolam) only the longest apnoea and the portion of REM-sleep became significantly longer compared to PSG in natural sleep [79]. During REM-sleep a significant increase of the RDI from 22.5 ± 19.2 auf 24.2 ± 21.6 was found, which is of no clinical relevance. All other respiratory and sleep parameters remained unchanged. This indicates that the sleep breathing disorder can be mimicked by sedation in spite of a fibroscope; therefore, videoendoscopy during natural sleep is not necessary. It has to be mentioned that the examination under sedation usually lasts only 10 to 15 minutes due to practical considerations (see below).

3.2.2. Procedure of videoendoscopy under sedation

For videoendoscopy under sedation only those drugs are suitable which meet the following demands: Their half-life must be sufficiently short and they must be available for intravenous administration in order to ensure a well-controlled sedation. Additionally, breathing drive and muscle tone ought to be affected as little as possible. In the ideal case one can achieve a sleep-like state under sedation. In practice it is attempted to keep the patient in the sleep-like state for at least 10 to 15 minutes in order to have enough time for the transnasal fibreoptic endoscopy. Midazolam and Propofol meet these demands sufficiently and therefore have prevailed for the induction of artificial sleep. For both drugs a careful cardiorespiratory monitoring is required. For otorhinolaryngologists, Midazolam has the advantage that it can be administered without the presence of an anaesthesiologist [80]. Its disadvantages are a half-life of more than one hour and a muscle relaxing as well as breath suppressing effect.

In their first publication presenting this method, Croft and Pringle indicated that they administered repetitive doses of 2.5 mg Midazolam in 5 to 10 minute intervals until the patients had fallen asleep [78]. Other colleagues proceed similarly [79], [81], [82], [83]. Propofol is titrated by repetitive boluses or manually adjusted perfusors until the patient falls asleep [84], [85], [86], [87], [88]. The mean dose required is 1.5 mg/kg KG Propofol. Saunders and colleagues used Midazolam as basic sedative and added Propofol in a titration protocol in order to maintain sedation [18]. To better address the problem of keeping sedation stable, Roblin et al. introduced a computer-controlled infusion system which is able to achieve and maintain precise plasma levels of Propofol [89].

All investigators put the patients on their back during the examination, only Hessel and de Vries report on the extension to the lateral recumbent position [82]. It is regarded in different ways whether or not one may decongest and anaesthetise one nasal cavitiy. In our department we perform videoendoscopy while the patient is in the supine position. We decongest one nasal cavity and put some xylocaine jelly on the fibrescope itself. Sedation is initiated with 0.03 mg/kg KG of Midazolam and is increased by a bolus of 1mg in 5-minutes intervals until a maximum dosage of 0.1 mg/kg KG is achieved.

3.2.3. Initiation of snoring and obstructions

The method is only suitable for clinical routine if snoring and obstructions can be initiated in a large percentage of the patients examined. According to our own experience this is not always possible. According to the literature snoring and obstructions, respectively, could be initiated in 79 - 95% of the manually sedated patients [78], [81], [84], [90]. In a cohort study using propofol, Marais detected snoring sounds in 45% of the 126 healthy controls. He described the sound being less intense but displaying the same pattern as found in the snorers [90]. When titrating propofol with target-controlled infusion, all 53 patients snored reliably at a plasma level of 8 mg/ml whereas not a single control person did at the same plasma level, amounting to a sensitivity and specificity of 100% [91]. Therefore, target-controlled infusion with propofol is clearly superior to manual titration.

3.2.4. Description of findings

The patterns of snoring and obstruction which can be observed during videoendoscopy under sedation are quite manifold. Pringle and Croft were the first to standardise the findings according to the data obtained in 90 patients (Table 5 [Tab. 5]) [92]. Currently, different classifications coexist. Ultimately, none of them are feasible. They distinguish either between an isolated obstruction at the level of the soft palate, tongue base or a multisegmental obstruction, respectively (Table 5 [Tab. 5]) [82], or they are modifications of the classification according to Pringle and Croft comprising the epiglottis [87], [90]. The classification according to Catalfumo [51] which describes the position of the epiglottis during the Müller-Manoevre was transferred to sleep videoendoscopy by Golz et al. [93]. All the remaining authors do not classify their findings but enumerate the various mechanisms and anatomical sites of snoring and obstruction [81], [83], [85], [88]. The obstructive patterns are decribed as circular, antero-posterior and latero-lateral at the level of the soft palate, tonsils, tongue base and epiglottis. An involvement of the latter is found in less than 1% up to 40% [81], [83], [84], [90], [93]. Abdullah mentioned a combination of as many as 5 different concomitant sites of obstruction in primary snorers (soft palate, tonsils, tongue base, posterior pharyngeal wall and epiglottis in 1/30 patients = 3%) and even 6 in sleep apnoea patients (soft palate, tonsils, tongue base, lateral pharyngeal wall, hypopharynx and epiglottis in 11/89 patients = 12%) an. Furthermore, he found an isolated collaps only in 15% of the sleep apnoea patients [83]. Steinhart et al. and Hohenhorst et al. showed concordantly an increase of the extent of tongue base obstruction with increasing AHI; furthermore, twice as many sleep apnoea patients than snorers had a combined obstruction at soft palate and tongue base [84], [88]. Hessel and de Vries are the only group asserting nasal obstruction, which they found to be the sole site of obstruction in 11% of their patients, as an own entity [82]. This is astonishing as the nose is not the relevant site of obstruction during sleep since it can be bypassed at any time by opening the mouth.The various patterns of obstruction and their frequency are summarized in Table 4 [Tab. 4].

3.2.5. Impact on the therapeutical concept

Even if a sleep-like status can be achieved, if snoring sounds and obstructions can be initiated reliably and documented in detail during videoendoscopy under sedation, the additional time and effort are only justified under the condition that the success rate of surgery for OSA and primary snoring can be improved. In fact, the outcome can only be improved if - compared to the examination during wakefulness - the therapeutical concept is changed due to the results of videoendoscopy under sedation. Based on the latter examination Hessel and de Vries have established a flow-chart for the therapeutical proceedings, yet limiting it to the enumeration of all the various operations available at the site of major obstruction [82]. In clinical routine a large tongue - defined by a modified Mallampati-score of 3 or 4 [33] - is usually considered as a negative predictive parameter for a successful UPPP. However, den Herder and co-workers did not find any correlation between videoendoscopy under sedation and Mallampati index [94]. This missing correlation supports the possibility of changing the therapeutical concept based on videoendoscopy without giving evidence of its superiority over the Mallampati index because outcome data are not given. This aspect is emphasized because the use of the Mallampati index is only recommended for patient selection in conjunction with other parameters (BMI > 30kg/m², no tonsils) [33]. It has not been compared with videoendoscopy under sedation.

Pringle and Croft compared their results of the Müller-Manoeuvre using Sher's classification to those obtained by videoendoscopy under sedation in the same 50 patients [50]. Due to the Müller-manoeuvre 25 patients would have been selected for UPPP. However, 11 (44%) of those patients had a substantial hyppopharyngeal collapse under sedation which would have meant excluding them from UPPP. Vice versa 8 of 25 (32%) patients who were excluded from UPPP due to the Müller-Manoeuvre had isolated palatal vibrations or obstructions under sedation; therefore, UPPP could have been indicated [95]. In this regard Steinhart and colleagues examined 324 patients with suspected OSAS in a waking state with Müller-Manoeuvre as well as under sedation with propofol. They found a significant increase of the mean airway collapse under propofol at the palate (64.3 vs. 80%) and tongue base (32.3 vs. 59.7%). Among the pool of patients who did not have a relevant obstruction, neither at the palate nor at the tongue base while awake (n = 78), isolated obstructions were found at the palate in one third, at the tongue base in 14% and at both levels in 50% of the patients when under sedation with propofol [85]. In many patients, videoendoscopy under sedation seems to be able to provoke obstructions which the Müller-Manoeuvre failed to initiate. In such cases one may assume a change of the therapeutical plan. On the other hand, videoendoscopic results seem to differ significantly between primary snorers and sleep apnoea patients. While a combined collapse is found in almost 75% of sleep apnoeics this finding is much less present in primary snorers.

3.2.6. Impact on the success rate

Only Camilleri reports about changing the indication he made in light of the basic clinical-endoscopical examination. Videoendoscopy under sedation then revealed a tongue base collaps in 4 of 27 patients who subsequently were excluded from the scheduled UPPP [96]. In spite of excluding those 4 patients considered less suitable, the success rate of the remaining patients was identical to a historical control group consisting of patients treated before the implementation of videoendoscopy under sedation (Table 1 [Tab. 1]). Yet an improved success rate was found in those patients who did not even show the slightest involvement of structures other than the palate. Hessel and de Vries retrospectively reviewed 48 snorers and 88 sleep apnoea patients after UPPP where during preoperative sedation-videoendoscopy the soft palate was at least involved in the collapse. There was no change of success rate if the hypopharynx contributed to the obstruction [97]. In a retrospective analysis of 55 sleep apnoea patients after UPPP, the same investigators did not find significantly different success rates depending on the sites of obstruction as revealed by videoendoscopy under sedation. But they achieved a doubling of the success rate if a tonsillectomy was included in UPPP. Because in this study success is defined less strictly than usual the results cannot be generalised [28].

3.2.7. Epiglottis and videoendoscopy

According to our own experience videoendoscopy under sedation or in sleep is particularly useful for recognizing or excluding a possible glottic or supraglottic obstruction. Such patterns of obstruction have never been described as a finding during the basic clinical-endoscopical examination. They are solely documented during the Müller-Manoeuvre which has so far not been validated for sleep. Most often a posterior movement of the epiglottis during inspiration is described [51]. The so called "floppy epiglottis" closes the glottis like a valve, causing attacks of dyspnoea with absolute blocking of inspiration. They typically appear in the supine position or when dozing off. They can be interrupted by rapid and vigorous expiration. In adults laryngeal obstructive sleep apnoea has been reported with laryngomalacia-like findings [98], after radiation [99], surgery and trauma [100] and in the context of natural aging [101], [102]. Nasal ventilation may even increase the valve mechanism, which can worsen OSAS or render it impossible to fall asleep. Partial epiglottectomy as well as hyoid suspension have been published as successful treatment possibilities [71], [75], [102]. In 27 adult patients with epiglottic collapse during sleep videoendoscopy, Golz et al. found a reduction of the AHI from 45/h to 14/h after partial epiglottectomy [93]. The publication does not reveal whether the same result could have been achieved by basic clinical-endoscopic examination or Müller-Manoeuvre.

According to the estimation of the author videoendoscopy under sedation or during sleep is therefore reserved for those rare cases suspected of laryngeal collapse and therapy failures of standard therapy.

3.2.8. Summary

a) Videoendoscopy under sedation is able to initiate snoring and upper airway obstruction during a short period, especially in the supine position.

b) The severity of sleep disordered breathing during videoendoscopy under sedation seems to be comparable to natural sleep. Limitation is the short examination time.

c) The classification of findings can be condensed to an isolated obstruction at the palate, tongue base or epiglottis or combinations of these.

d) There are subtle hints that videoendoscopy under sedation may change the indication for certain operations. Currently, there is not enough evidence that this improves the outcome of snoring and sleep apnoea surgery.

e) Videoendoscopy under sedation or during sleep is able to detect laryngeal sleep apnoea. Those patients can be treated with procedures familiar from surgery for laryngomala.

3.3. Multi-channel pressure recordings

Inspiratory pressure swings which occur during obstructive events in the entire upper airway can be measured with catheters. For this purpose several measuring points are needed from the nasopharynx to the oro- and hypopharynx down to the esophagus. Initially they were mainly used to investigate the mechanism of the pathogenesis of obstructive apnoeas; nowadays, research is focussing on their predictive value for the outcome of sleep apnoea surgery.

Apart from the general validity criteria Figure 2 [Fig. 2]), the catheters must be tolerated during the total bed time without significantly disturbing sleep or breathing. Furthermore, the position of the measuring points has to be reliable because the site of obstruction can only be localised indirectly without visual control. Otherwise, malpositioning before or position changes during the recording might falsify the results. Furthermore, reproducibility as well as validity should be comparable to other methods of topodiagnosis.

3.3.1. Tolerability of the pressure catheters

First pressure recordings investigating SDB were performed with balloon and open catheters [103]. Chaban et al. used stationary balloon catheters for the oesophagus (10 cm long!) and the nasopharynx but added a catheter with a built-in pressure transducer (micro-tip catheter) to be slowly pulled through the whole upper airway. He recorded pressure changes during single apneas at each different site [104]. Oesophageal balloons massively irritated the patient, leading to an increase of alpha waves and thus objectively destroying the microstructure of sleep [105]. This fact was not so important in the beginning because only patients with severe sleep apnoea syndrome were investigated who could easily sleep despite this disturbance. The reliability of micro-tip catheters was shown during wakefulness and sleep for the oesophagus by Panizza and Finucane and for the pharynx by Tvinnereim [106], [107]. Chervin et al. and Skatvedt et al. presented well-designed studies demonstrating that catheters with not more than 2 mm of diameter did not significantly disturb the sleep structure of patients suspected of SDB. The degree of SDB was not influenced either [108], [109]. Överland et al. asked 799 patients by questionnaire how they tolerated the catheter. 3% rejected the assessment and 1% interrupted it during the night, amounting to a compliance rate of 96%. Only patients with nasal obstruction indicated a significantly higher level of discomfort [110]. Having experimented with many of the available microtip-catheters, we estimate the two catheters developed by Skatvedt and Tvinnereim to be of least discomfort for the patients due to the smallest diameter and softest material.

3.3.2. Reliability of measuring points

All multi-channel pressure catheters require a reliable positioning of the single measuring points in order to attribute the site of obstruction found by manometry to the anatomically defined airway segment. Verse et al. showed by means of cephalonetry that the distance of the probe from the nostril to the vertebral bodies, the epiglottic tip and the hyoid bone varied interindividually more than 3 cm. Positioning the zero point at the level of the mandibular plane reduced the range of the distances marginally. The authors concluded that measuring points in multi-channel pressure sensors cannot reliably be attributed to the different levels of obstruction if fixed. This would severely limit the predictive value of pharyngeal manometry with fixed measuring points [111], [112]. On the other hand most investigators choose the oropharyngeal sensor as a reference to be placed under visual control at the free edge of the soft palate. Skatvedt reported that the sensor was found exactly where it had been placed the evening before [113]. One can at least distinguish an isolated obstruction at the palate ("upper") from a lower one ("lower"). This is sufficient for most of the patients. An isolated collapse at the level of the epiglottis cannot be distinguished by this method. Today the monitoring devices only evaluate and report on "upper" and "lower" obstructions.

3.3.3. Determination of AHI using multi-channel pressure recordings

Pressure catheters also can be used to measure nasal and pharyngeal airflow. This implies that they are suitable to assess increased respiratory effort as well as the AHI. Tvinnereim et al. filtered the raw pressure signals, summated and integrated them, thus creating an enveloped curve. This processing allowed to accurately measure the absolute number of obstructive and mixed apnoeas during sleep with minimal deviation from the results obtained by PSG [114]. Even though the hypopnoea index measured by pressure sensor was significantly lower compared to PSG, the overall sensitivity, specifity and the negative predictive value reached 85-100% for the detection of the single apnoea and hypopnoea types [115]. In a blinded investigation Reda and co-workers realised a correlation of 0.97 between AHI as assessed by pressure sensors versus thermistors used for PSG. Patients with an AHI below 15/h and 40/h respectively could be detected with a sensitivity and specifity of 100% [116]. Overland added actimetry to manometry Figure 3 [Fig. 3]), helping to distinguish sleep and wake which improved the correlation (r=0.98) between AHI assessed by pressure catheter and PSG [117]. The data available indicate that multi-channel pressure recordings are suitable to assess the AHI correctly.

3.3.4. Determination of the sites of obstruction

Hudgel et al. were the first to describe the typical pattern of obstructions at different localisations with the help of one measuring point placed oesophageally, supralaryngeally, oropharyngeally and nasopharyngeally. They defined a palatal obstruction if intrathoracal pressure deflections extended to the supralaryngeal and oropharyngeal measuring point but not to the nasopharyngeal probe which instead showed ambient pressure (Figure 4 [Fig. 4]). A hypopharyngeal obstruction was defined in an analogous manner if during apnoeas ambient pressure was seen already at the oropharyngeal measuring point (Figure 5 [Fig. 5]). They pointed out that it was difficult to identify a combined collaps of hypo- and oropharynx [118]. Katsantonis postulated that a short segment obstruction displayed a high pressure gradient between two neighbouring sensors. In contrast a long segment obstruction would show pressure gradients extending over two or more sensors [119]. It has yet to be determined whether multi-channel pressure recordings during wakefulness predict the site of obstruction during sleep [120], [119].

Initially only single breaths could be examined [121]. Today it is possible to record pharyngeal pressures throughout the night and analyse them. Study groups from Norway may take credit for developing further whole-night recordings with multi-channel pressure sensors in order to investigate their feasiblity and capability as a tool in daily clinical routine. Skatvedt used a catheter with six sensors, placing the third at the free edge of the soft palate. He found a collaps extending over more than one segment in 13 of 20 patients with SDB . In one case the segments were not even neighbouring and in 7 of 20 patients the site of obstruction changed during the night. However, an exact distribution of the sites of obstruction is not given [113]. In another study he found a combined collaps of the upper and lower oropharynx in half of the patients [59]. At the same time, Tvinnereim and Miljeteig published their data using a 5-sensor-catheter, placing the second sensor at the free edge of the soft palate. They described pressure oscillations of high frequency being superimposed on the pressure swings of normal and obstructed breathing and suspected that those might be soft tissue vibrations due to snoring. Furthermore, they mentionned a cranio-caudal extension of the obstruction in some cases. In addition, Tvinnereim calculated a frequency distribution of every single obstructive event assessed during a 3-hour recording. Over 90% of the apneas originated from the middle oropharynx and the remaining events more caudally [119]. The frequency distribution of the major sites of obstruction is given in Table 4 [Tab. 4].

Rollheim and colleagues investigated whether the frequency distribution of the sites of obstruction depends on body weight. In 18 patients with an AI > 5/h all the obese patients had predominantly lower obstructions whereas one half of the patients with a BMI<30 kg/m² had predominantly upper obstructions and the other half lower obstructions, respectively [122]. They subdivided the patients according to the amount of upper (i.e. palatal) obstructions in another study (Table 6 [Tab. 6]) [123]. It has to be put into question whether both poles of this classification are appropriate because the authors themselves did not have a single patient in their study population with exclusively upper or lower obstruction.

3.3.5. Reliability of the determination of the sites of obstruction

Investigations concerning night-to-night variability of the distribution of the obstructive sites showed that the major site of obstruction could be reproduced during the second night in 72% of the cases. Results were best reproduced in patients with an AI above 5/h or with more than 75% palatal events [123]. Rollheim et al. compared the patterns of obstruction as obtained in the hospital with a recording at home. Although the mean AHI was significantly higher in the hospital than at home, the relative frequency of palatal obstructions did not differ between both recordings [124]. In patients who had less than 40% or more than 60% palatal obstructions in the first recording, this relationship was reproduced in 90% of the cases during the second recording.

3.3.6. Comparison with other methods of topodiagnosis

Skatvedt found that in 15 of 20 cases the site of obstruction assessed by Müller-Manoeuvre differed from the site obtained by multi-channel pressure sensors. In 12 cases the Müller-Manoeuvre missed a site of obstruction that was clearly detectable by manometry [59].

Multi-channel pressure sensors and videoendoscopy during sleep did not produce identical results. Woodson and Wooten examined 22 patients with severe sleep apnoea. They not only found clear differences between both methods but also diverging results when choosing varying assessment points during the respiratory cycle [32]. In another investigation 11 UPPP failures with persistent severe sleep apnoea had a tongue base obstruction in 67% of the cases as assessed by videoendoscopy versus 17% as assessed by manometry. Woodson concluded that multi-channel pressure sensors are not able to depict pharyngeal compliance so that the investigator may miss essential factors of apnoea generation; in contrast, these factors can be identified by sleep videoendoscopy [125]. It has to remain open which method - apart from MRI [54] which is not possible in daily routine - correctly represents the behaviour of the airway during natural sleep.

3.3.7. Impact on the success rate of surgery for sleep disordered breathing

Metes et al. were the first to publish concerning the impact of pharyngeal manometry on the success rate of surgery. They used a catheter with one measuring point only which was pulled through the pharynx and placed at several sites along the upper airway in order to record several obstructive events at each site. The obstruction they found in that way before UPPP persisted in 8 of 12 patients after the operation. The success rate of UPPP did not differ between patients with primarily palatal and tongue base obstruction [126]. The fact of having evaluated only a few obstructive events may have contributed to these bad results as well as having chosen patients with severe sleep apnoea who are more likely to have a combined obstruction and a more negative critical closing pressure. Skatvedt et al. selected 16 patients with SDB of different degree and predominantly palatal obstruction as detected by multi-channel manometry for laser-assisted uvulopalatoplasty. With this selection the AHI decreased from 18.6/h to 6.4/h. While the rate of upper apnoeas dropped from 90% to 8.8% of all apnoeas, the number of upper hypopnoeas was reduced to a minimal extent from 91.6% to 85.1%. This may indicate a shift from apnoeas to hypopnoeas in the palatal segment due to surgery [127]. Osnes et al. compared the efficacy of UPPP in patients with predominantly transpalatal and subpalatal obstructions. After UPPP, transpalatal apnoeas and hypopnoeas were reduced by 81% whereas subpalatal events only dropped by 42%. The success rate in patients with transpalatal obstruction was significantly higher than in subpalatal obstruction [128] (Table 1 [Tab. 1]). Multi-channel pressure recordings seem to be superior to single-channel pull-through techniques in predicting surgical success of soft palate surgery.

3.3.8. Summary

a) When using catheters with a diameter of not more than 2 mm one can obtain utilisable recordings in approximately 90% of the patients.

b) They neither worsen sleep architecture nor influence a persistent sleep breathing disorder.

c) The pressure curves allow a reliable detection of respiratory events.

d) Positioning of the measuring points by means of pharyngeal inspection seems to be sufficiently accurate for the evaluation of the palatal airway segment.

e) Upper and lower obstructions can be detected. In principle, combined obstructions are more difficult to recognise and are thererfore rarely mentioned.

f) Lower obstructions become more prevalent if the BMI increases.

g) There are no indications that obstructions at the hypopharrynx and the epiglottis can be discriminated reliably.

h) The frequency distribution of the single obstructions can be determined for the entire recording period. It seems to be reliable if less than 40% or more than 60% upper obstructions are detected in a patient.

i) There are indications that the success rate of soft palate surgery can be improved by multi-channel pressure recordings.

4. Conclusion

Otorhinolaryngologists often are the first contact points for patients with suspected SDB. Among the available possibilities to describe different aspects of upper airway obstruction, endoscopic techniques and the measurement of the predominant site of obstruction are of special interest.

The clinical-endoscopical examination of the morphology of the upper airway is the foundation of any further diagnostic procedure. It is suitable for detecting pathologic anatomy which needs to and can be corrected. In the future, staging systems considering various clinical parameters will probably prevail. They may facilitate the decision making process concerning surgery of the tongue base or multi-level surgery.

The Müller-Manoeuvre is the easiest functional evaluation of the upper airway. Even though it is proven to be neither reproducible nor transerable to sleep it seems to be helpful in excluding patients from a scheduled UPPP. It is not suitable to answer other questions. However, computer-aided anaylsis of the videosequences may increase its diagnostic value.

Videoendoscopy during sleep has mostly been abandonned due to the laborious execution and has to a large extent been replaced by videoendoscopy under sedation. Snoring sounds can be initiated rather reliably, vibrations and obstructions become visible and breathing during sedation corresponds to natural sleep. Nevertheless, there are no clear signs that videoendoscopy under sedation improves the success rate of surgery for sleep disordered breathing. If laryngeal OSA is suspected, this investigation very often reveals the answer. Furthermore, so far there is no alternative for this problem. Videoendoscopy under sedation is an attractive procedure for otorhinolaryngologists because it gives an impression of the individual pathogenesis, makes the patient understand the surgical plan and thus will probably increase patients' compliance and satisfaction. It has yet to be determined with well-designed ["well-designed"]studies whether videoendoscopy under sedation carries any real advantage for the patient.

Recording pharyngeal collapse with multi-channel pressure sensors has been used from the beginning of research on SDB. Systems available nowadays are well tolerated and allow the assessment of the AHI as well as a quantification of the distribution of all obstructive events at the upper - palatal - and lower - tongue base and epiglottis - airway segment during sleep. However, obstruction at the tongue base and the epiglottis cannot be discriminated. Currently, multi-channel pressure recordings are the only airway technique allowing an analysis of the entire sleep period. It is to be expected that the available clinical data will be extended and improved further. Then pressure recordings will likely serve not only as an ordinary screening tool for SDB but will also be of precious assistance when planning the surgical concept.

So far only a few studies have investigated the benefits of sophisticated airway diagnostics for other operations than UPPP or LAUP. The actual advantage of these costly examinations still has to be regarded rather critically. In particular, further studies are absolutely needed to verify the promising approaches made with videoendoscopy under sedation and multi-channel pressure recordings. However, in the author's estimation they will become important tools in the hands of otorhinolaryngologists in the future, supplementing the clinical-endoscopical basic examination to the advantage of our patients.


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