week 4

Title : Obstructive Sleep Apnoea (OSA)

Figure 1: Diagrammatic an open airway during sleep

Figure 2 : A blocked airway

The blockage shown is caused by the soft tissue at the base of the tongue collapsing and preventing the flow of air.

During sleep, the OSA sufferer cycles through a series of events:

• The airway becomes blocked and the sufferer does not breathe,

• Blood oxygenation saturation (SaO2) decreases, causing the heart to pump faster,

• The sleeper arouses to open their airway and breathe,

• The sufferer falls asleep again.

Diagnosing OSA

The gold standard in diagnosis of OSA is polysomnography. Originally developed by Dr. Nathaniel Kleitman at the University of Chicago in the 1950s, polysomnography takes multiple physiological measurements of the patient being studied. This combined data is used in the diagnosis of apnoea events. The physiological measurements recorded can include:

•              Electroencephalogram EEG (brain electrical activity)

•              Electroculogram EOG (eye movement)

•              Electromyogram EMG (jaw muscle movement)

•              Leg muscle movement

•              Airflow

•              Respiratory effort (chest and abdominal excursion)

•              Electrocardiogram ECG

•              Oxygen saturation SaO2

•              Audio and visual recording of nocturnal sounds and movements

Stage 0 (or preclinical)	Sporadic obstructive apnoeas
Stage I (or initial)	Obstructive apnoeas persisting during light (stage 1-2) and REM sleep
Stage II (or overt)	Obstructive apnoeas persisting for the whole length of sleep
Stage III (or complicated)	Alveolar hypoventilation persisting during wakefulness.

Table 1. Four stage scale of snoring noises proposed by Lugaresi et el.

Treatment of OSA

It was between 1960 – 1980 that OSA was clearly defined as a clinical disease and the only clinical treatment was surgical intervention (3). In 1981 a device was described that kept the airway open by passing a continuous stream of air through the airway, which is known as Continuous Positive Airway Pressure (CPAP) (5). This device is the method of choice for prevention of airway blockage for sufferers of OSA.

 

Snoring Detector

One simple method to screen a person for potential OSA in their own home is the analysis of their snore sounds. The basic premise behind these studies was to determine whether the snoring sound generated was related to OSA status.