from glasgo conference Detecting respiratory problems during...

from glasgo conference Detecting respiratory problems during sleep:
two simple new techniques
presented to Glasgow Congress

Costly polysomnography may no longer be needed


The Australian AirwayClear system and its German counterpart microMESAM, the validation of which has been announced in two scientific communications to the 14th Annual Congress of the European Respiratory Society, could provide an economical replacement for polysomnographic recording, the generally-accepted gold standard, in initial screening of sleep-related respiratory problems. It should become much easier to distinguish everyday snorers from sleep apnoea sufferers using these two portable devices that can be operated in the home without the presence of doctors or technicians.


Given the increasingly evident risks affecting obstructive sleep apnoea sufferers (increased hypertension, risk of cardiovascular disease, a higher death rate among affected stroke victims and, more mundanely, a greater number of traffic accidents because of excessive daytime sleepiness), there is more and more concern about the need to screen for the condition.

Readers will recall that apnoea involves repeated interruptions to breathing during sleep, leading to collapse of the upper airways as a result of a loss of pharyngeal muscle tone.
Obstructive sleep apnoeas are generally characterised by initial snoring, followed by a more or less lengthy silence and then various snorts as the reflex forces the subject to start breathing again.
In severe cases, such episodes can occur more than 200 times per night, causing such fragmentation of sleep that it ceases to be refreshing. The most obvious consequence is a loss of daytime performance, sometimes coupled with an irresistible urge to sleep that can cause the subject literally to fall asleep in the middle of an activity.


Eight-week waiting lists

Hence the increasing efforts being made to screen the broader population for apnoea. While this is certainly praiseworthy, there is, however, a major obstacle that is difficult to overcome. While up to 20% of the population suffers, to a varying degree, from respiratory problems or apnoea during sleep, it is impossible to provide polysomnography (the standard examination for the condition) for all subjects. Not only because the test, which involves simultaneous measurement of respiratory, cardiac, brain and blood parameters over the course of at least one night in a sleep laboratory, costs several hundred euros, but, above all, because it requires premises, equipment and staff, and as a result waiting lists are a problem almost everywhere.

“In our hospital”, the Congress was told by Thomas E. Wessendorf, of the RuhrlandKlinik in Essen during his presentation of the microMESAM, “we have a waiting list of about eight weeks for polysomnography. So it would be impossible to provide it as a standard screening for obstructive sleep apnoea syndrome, which probably affects several million people in Germany.”

Hence the interest in various types of simpler device that allow an initial triage of patients, such as the one validated by the team working under Wessendorf and Helmut Teschler, or the AirwayClear system, also presented at the 14th ERS Congress, which was developed by an Australian team led by Philip Berger, of the Monash Medical Centre in Clayton (Victoria).

“MicroMESAM is based on the famous MESAM monitor, one of the long-recognised standards for polygraphic investigations”, Wessendorf informed the Congress. “This device uses a simple nasal cannula that detects variations in respiratory flow during sleep. The flow signals are recorded and then interpreted using an algorithm that automatically checks for apnoea, hypopnoea (spells of shallow breathing) and snoring.”


Major savings

Indeed, the device is extremely simple to use: the subject has merely to attach the recording apparatus on his chest using a strap, put the two ends of the nasal cannula in his nostrils and press a button when he goes to bed. Like in a classical Holter cardiological test, the device begins to record and store data, registering apnoea, hypopnoea and snoring.
Its performance, as described in Glasgow, appears perfect for screening, since it allows identification of the greatest possible number of individuals with apnoea proper (true positives) while screening out the subjects who do not have the syndrome (false positives).

The results of the validation presented to the 14th Congress show that, in a test on 50 subjects, microMESAM correctly identified 100% of individuals whose nocturnal breathing presented at least ten anomalies per hour, which corresponds to a mild form of the condition, and correctly eliminated, in 87.5% of cases, patients who did not have apnoea.

“Personally, I think this tool could be particularly useful with snorers who are not aware of whether they have apnoea”, said Wessendorf in Glasgow. “In these subjects, a negative test would remove the need for further investigations, allowing major savings. A positive test, on the other hand, should lead to polysomnography, whose cost would then be justified.”


Polysomnography far from perfect

A similarly simple and inexpensive device, which operates, however, on an entirely different principle, was presented to the 14th Congress by Philip Berger and his Australian team.
AirwayClear, which is designed specifically to detect obstructive sleep apnoea, allows continuous monitoring of whether the upper airways are open or blocked.
A barely audible sound is sent into the subject’s nostrils, while a microphone at the base of the neck detects whether or not the sound has passed through the airways. When there is an obstruction, the sound fails to pass and apnoea can be diagnosed.

As Berger explained in Glasgow, validation of the device on fifteen adults allowed detection of 421 obstructions, against only 383 in the parallel polysomnographic test. AirwayClear further showed that, while 82% of the obstructions diagnosed by polysomnography were correct, in 18% of cases the upper airways were either completely clear or partially obstructed. “What’s more, our results show that, in diagnosing hypopnoea, polysomnography gets it wrong in 48% of cases”, Berger explained to the Congress.

While there is no doubt that many will still consider polysomnography as the “gold standard” for a precise diagnosis, simple techniques like those presented to the 14th Annual Congress of the European Respiratory Society will certainly allow substantial savings. Above all, they should facilitate and accelerate screening of sleep-related respiratory problems in the public at large.