For a long time, strong emphasis was laid on the importance of the topodiagnosis of the collapse site(s) in the upper airway, especially before choosing an adequate surgical treat- ment method [463, 465]. An initial classifica- tion stems from Fujita, who differentiated the patient pool into three types in accordance with retrovelar, retrolingual, or a combined collapse site [159]. However, CT investigations during sleep have demonstrated that this classification oversimplifies the dynamic processes occurring in the pharynx [231].
Some studies still advocate a rigorous preop- erative topodiagnosis [368], but this postulate can no longer be held without reservations because the pharyngeal obstruction site is not determined once and for all. It can change first between wakefulness and sleep, second between the different sleep stages, third post- operatively after upper airway surgery, and fourth depending on a person’s age (overview in [127, 540]). Nevertheless, as our colleagues may still request some of these diagnostic procedures, the most important techniques of topodiagnosis will be discussed here censori- ously.
3.1 Pressure Measurements Increased respiratory effort in both children and adults can be recognized with the help of simple esophagus pressure measurements [516]. If these measurements are combined with the registration of the oro-nasal air flow, it is then possible to differentiate between
central, mixed, and obstructive respiratory events [521]. Together with the demonstration of frequent arousals in polysomnography, the esophageal pressure probe provides the es- sential tool in the verification of an upper air- way resistance syndrome (UARS) [487].
Initially, single flexible pressure sensors were employed in order to identify a pharyn- geal collapse site [221]. As this method turned out to be too time-consuming, multi-pressure sensors with up to six sensors were devel- oped. With these sensors it is also possible to identify several collapse sites. Only one study recommends pressure probes in the selection of patients for laser-assisted uvulopala- topharyngoplasty (LAUP) [477]. Other study groups are more cautious in regards to the predictive value, because postoperative shifts of the collapse site into a different pharynx level, towards both cranial and caudal, have been observed [220, 331, 463, 479].
Several possible reasons have been dis- cussed for the failure of topodiagnosis with pressure measurements in regards to the se- lection of patients for palatal surgery. On the one hand, pressure probes are incapable of recognizing segments that are already severe- ly constricted but not yet totally collapsed [581]. Suratt et al. [502] observed a shift of the obstruction site during a single apnea phase towards caudal. Furthermore, other authors have registered such a high number of retrolingual obstructions that they recom- mend the inclusion of the tongue base into the surgery concept along the lines of so- called multi-level surgery [478, 578].
Identifying the Site of Obstruction 3
3.2 Flexible Endoscopy
A fiberoptic endoscopy of the upper airway can be administered without difficulty on the awake patient in sitting and supine positions.
However, the results do not correlate with those gained in the supine position during sleep [216]. Sleep videoendoscopy is a very sophisticated procedure and has to be re- stricted to specific indications [43, 392, 428].
Disadvantages of the method include the re- duction of the cross-section of the airway by the endoscope, arousal reactions due to the mechanic stimulus, visual obstruction by the phlegm, the simultaneous assessment of only one level of the airway, and the personnel-in- tense aspects of the procedure [216]. The Müller maneuver consists in the endoscopic observation of the upper airway during in- tensified inspiratory respiration with closed nose and closed mouth. While older studies considered the Müller maneuver as an identi- fication method for the velar collapse type, and therefore recommended it as a selection criterion for a successful uvulopalatopharyn- goplasty (UPPP) [466], nowadays this investi- gation is no longer regarded to have that val- ue [42, 574].
The flexible endoscopic assessment of the upper airway during pharmacologically in- duced sleep was first suggested for children [94], and later also for adults [93]. In addition to the disadvantages of an endoscopy during sleep mentioned above, the employment of this procedure is further restricted by the fact that pharmacologically induced sleep cannot simply be equated with natural sleep [96, 308, 404]. Differences in collapse sites according to different sleep phases have already been mentioned. Nonetheless, sleep endoscopy continues to be recommended for preopera- tive topodiagnosis [202]. But we do not know of any study that was able to demonstrate that the surgical success, regardless of the method, can actually be improved by virtue of such a preoperative diagnosis.
A newer development is the digital analy- sis of fixated endoscopic images of the soft palate with the help of appropriate software.
In an initial study, morphological differences were described in a pool of 121 primary snor- ers, 79 patients after LAUP, and 51 healthy control subjects [409]. It remains to be seen whether this concept will foster a viable method for the clinical routine.
3.3 Analysis of the Respiratory Sounds During Sleep
In principle, retropalatal and retrolingual col- lapse sites can be differentiated with the help of a recording of the respiratory sounds dur- ing sleep using fast Fourier transfer (FFT) analyses [447]. It was possible to raise the on- target rate of the UPPP from 52.6 % [465] to approximately 75 % [447]. In the USA, such a diagnostic option for the clinical routine ex- ists in the form of the so-called SNAP proce- dure [547]. The investigator has the possibility to send in an audio cassette with snoring sounds for both an FFT analysis and an acoustic evaluation by an experienced listener.
In Europe, the working group of Osman et al.
developed the so-called Glan Clwyd snore box, an instrument to differentiate between palatal and non-palatal snoring [368, 371].
3.4 Further Imaging Procedures Many studies have attempted to establish the collapse site with the help of somnofluo- roscopy, radiocephalometry, computer to- mography and magnetic resonance imaging.
Overall, these imaging procedures are of only limited use in predicting the surgical success of a UPPP [26]. Body mass and apnea hypop- nea index (AHI) continue to be decisive pa- rameters.
Radiocephalometry is more successful in determining a retrolingual than a retropalatal collapse site [376, 415]. Accordingly, in the case of therapy failures after UPPP, it is possi- ble to determine a more constricted retrolin- gual airway and a hyoid bone situated lower in relation to the mandible [416]. Both pa- rameters also influence the success rate of nasal surgery in regards to the AHI in pa-
10 Chapter 3 Identifying the Site of Obstruction
tients with mild obstructive sleep apnea (OSA) [459]. While radiocephalometry can- not in general be recommended as a routine form of diagnosis, it is certainly of use in pa- tients with malocclusion or suspected retrolingual collapse site, and in patients who need to undergo surgery. An absolute indica- tion is given before a planned maxillo- mandibular osteotomy [26, 205].
Fluoroscopy, rapid computer tomography and functional magnetic resonance tomogra- phy have not become part of the clinical rou- tine, as they are too cost-intensive and cover too short a period of sleep.
A relatively new instrument in this context is acoustic reflectometry. A probe generates a noise signal and measures the reflecting
sound using a microphone [126].As the probe is flexible it already has proven feasibility in sleeping sleep apneics [128]. This so-called flextube reflectometry seems to be a promis- ing tool for routine use.
These procedures remain reserved for spe- cific lines of research [392].
Table 3.1 summarizes the advantages and disadvantages of the diagnostic procedures described above. For our daily routine, we have essentially made the decision that in ad- dition to the otorhinolaryngological evalua- tion, we only perform an endoscopy in the waking state and sometimes a radiocephalo- gram. All the other procedures outlined above are available in our center, but require a specific indication.
3.4 Further Imaging Procedures 11
Table 3.1. Techniques for objective localization of upper airway narrowing
Technique During Quanti- Disadvantages Clinical
sleep fication routine
Pressure measurements in the upper airway + + SE, limited life-span of the expensive probes +
Flexible nasopharyngoscopy + (+) SE, mom +
Analysis of the respiratory sounds + + SE (+)
Cinefluoroscopy + + rad, mom –
Rapid CT scans + + rad, mom –
Radiocephalometry – + rad, mom +
Acoustic reflexions + + SE (+)
Rapid MRI scans + + Mom (up to 1 hour) –
SE special expert knowledge necessary, mom detects only short periods of sleep, rad exposure to radiation.
