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Sleep apnea, pathophysiology, signs and symptoms

Obstructive sleep apnea is the most frequent problem of breathing disorders related to sleep. It is a known fact that snoring is one of the first symptoms of apnea. 20% to 25% of snorers (1 out of 4) are reported to suffer from obstructive sleep apnea as well.

A consultation in sleep medicine is strongly recommended for people who snore and who present daytime sleepiness, sleep interruptions (insomnia), hypertension or other cardiovascular problems, a lack of restorative sleep or a lack of concentration (similar to attention deficit disorder).

Loud and intermittent snoring with periods of silence of more than 10 seconds long should suggest an apnea problem.


Obstructive apnea

Obstructive apnea

• Reduction of respiratory amplitude of more than 90% (≥ 90%) during episodes of 10 seconds or more (≥ 10 s).



• Reduction of respiratory amplitude of 50% (≥ 50%) for more than 10 seconds in duration with a 3% or greater (≥ 3%) desaturation in oxygen or presence of microarousals.

Upper airway resistance syndrome (UARS)

Upper airway resistance syndrome

• Increase in the effort to breathe or flattening of the nasal pressure wave of 10 seconds or more in duration and presence of microarousals, increase in heart rate of 5 heart beats or more per minute.


Central apnea

Central apnea

• More than 3 consecutive cycles of crescendo and decrescendo changes in respiratory amplitude AND 5 or more episodes of central apnea or hypopnea per hour OR crescendo or decrescendo changes for 10 consecutive minutes or more.

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Symptoms associated with apnea

Symptoms associated with sleep apnea are:

• Night-time arousal

• Diaphoresis or night-time sweating

• Choking sensation during the night

• Lack of restorative sleep

• Enuresis (night-time urination in bed) or nocturia (waking up often to urinate at night)

• Abnormal motor activity of legs and arms during sleep

• Daytime sleepiness

• Cephalgia in the morning when waking up (morning headache)

• Poor concentration

• Memory loss

• Anxiety and depression

• Gastroesophageal reflux disease

• Impotence


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Signs of apnea

Signs of sleep apnea are:

• Obesity

All patients suffering from apnea are not necessarily obese. However, we can assume, due to epidemiological studies, that 90% of obese patients suffer from apnea.

• Increase in neck circumference

Fat deposits in the neck compress airways in the same way as if we clamp a hose. Less air goes through and the pressure has to be increased to overcome the resistance caused by the narrowing of the airway and obtain the same throughput. The increase in parapharyngeal fat reduces airways.

• Increase in waist circumference

Obesity is associated with a high body mass index (BMI). Among the people who consult in sleep clinics for apnea, 28% have a BMI greater than 30 and 47% have a BMI between 26 and 30. A normal BMI is between 20 and 25.

• Retrognathia (recessed jaw or jaw shifted backward)

Retrognathia can affect the upper jaw only (retrusive maxilla), the lower jaw (mandibular retrognathia) or both jaws.

• Maxillary constriction (palate too narrow)

Lack of width in the maxilla can be explained by the fact that an individual who does not breathe through the nose necessarily breathes through the mouth. Yet, to breathe through the mouth, the tongue must be lowered and must not be in contact with the palate, otherwise air would not pass through. Small child, small tongue, big child, bigger tongue. In a growing patient, the tongue thus lowered almost permanently to facilitate mouth breathing does not participate in the development in width of the palate as the child grows up. Indeed, if a patient breathes normally through the nose and maintains the mouth closed during breathing, chances are that the tongue is in contact with the palate most of the time. As the child grows up, his/her tongue grows and the palate gets wider to adapt to the development of the tongue.

• Overjet and overbite (horizontal and vertical distances between the upper and lower teeth greater than normal)

• Tonsil hyperplasia

• Macroglossia (large tongue)

Airways obstruction area

• Narrow oropharynx

Airways restriction areas can be located in the nasopharynx, oropharynx or laryngopharynx.


• Soft palate erythema and edema

• Nasal obstruction (deviated nasal septum, turbinate and nasal mucosa hypertrophy following chronic allergies)

• Hypertension

Comorbidities associated with apnea are hypertension, cardiovascular diseases, infarction and thyroid problems.

Alcohol intake increases the risk of apnea by increasing the nasal and pharyngeal resistance to the passage of air. This is explained by the effect of alcohol on muscular motor function (it is a known fact that muscles of a drunk person are weaker…). The pharynx collapses more easily, which increases the resistance to the passage of air and thus reduces the throughput of inhaled and exhaled air.

Smoking is a risk factor for apnea. Sleep is unstable by the decrease of nicotine level in the blood during the night. Smokers have 3 times more risks of suffering from apnea than non-smokers.

The prevalence of apnea is from 4% to 9% of middle-aged men and from 1% to 2% of middle-aged women. The highest prevalence is among men of 40 to 65 years of age.

The prevalence in children from 2 to 8 years of age is 2%, but consequences can include hypertension, enuresis, growth delay, hyperactivity and cognitive impairment.

Pediatric apnea

Just listen to this baby and you will feel like choking.


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Apnea screening questionnaire


An apnea diagnosis cannot be made by a clinical examination only. The presence of symptoms and clinical signs associated with it must be detected. An evaluation questionnaire must allow the assessment of the probability to suffer from apnea.


Here is how to conduct a self-assessment.

Write down your neck circumference in cm:__________

If your neck is larger than 49 cm, write down 49 cm as a result.

If you suffer from arterial hypertension, add 4 cm to your neck circumference.

If you snore, add an additional 3 cm to your neck circumference.

If someone noticed that you stopped breathing during your sleep, add 3 cm.

Screening table:

Circumference Hypertension + 4 cm Snorer + 3cm Respiratory pauses + 3 cm TOTAL
 . .  .  . .

1- Sleep habits

1- I got to bed at:__________ hour(s)           I wake up at:______________hour(s)

2- I fall asleep quickly:                            Yes __             No __

3- I wake up easily:                          Yes __              No __

4- I frequently wake up at night:           Yes __             No __

5- I wake up tired in the morning:                   Yes __              No __

                        since how long:___________________________

6- Globally, do you consider that you sleep:

       __ Very well                 __ Well             __ Bad                 __ Very bad

7- Do you snore?:       Yes __              No __

                        since how long:___________________________

                        socially disturbing:          Yes _              No _

                        severe:  _                    moderate:  _                  light: _

                        more important when you sleep on your back:        Yes _              No _

                        regularly:              Yes _              No _

                        explosive:                      Yes _              No _

                        is your snoring worsened by:

                                   _ alcohol intake       _ tiredness

8- Do you have respiratory pauses during your sleep which are noted by an external person?:

                                    Yes _              No _

            If yes, does it happen: _ rarely     _ often        _ every night

9- Did you ever wake up with a choking sensation?:            Yes _             No _

2- Epworth sleepiness scale

10- Are you sleepy during the day?:       Yes _             No _

Last week, what was your probability of drowsing (letting yourself fall asleep slowly; being half asleep) during the following situations? Even if you have not recently been in one of these situations, try to imagine how this situation could have affected you. To answer, use the following scale by choosing the appropriate number for each situation:

No drowsiness:  0

Small chance of drowsiness:  1

Moderate chance of drowsiness:  2

High chance of drowsiness:  3

Situations: Answer each of the statements below:


Sitting down reading ____

Sitting down watching television ____

Sitting down inactive in a public place (movies, theater (play), meeting) ____

Sitting down as a passenger in a car (or in a public transport) for more than one hour without interruption ____

Resting laid down in the afternoon when circumstances allow it ____

Sitting down talking to someone ____

Sitting down calmly after lunch without alcohol ____

Sitting down in a car that is stuck in traffic for a few minutes ____

Total: ____

11- Do you feel the need to move your legs irresistibly?:   Yes _              No _

12- Do you suffer from headaches in the morning when you wake up?:            Yes _              No _

13- Do you suffer from memory loss?:       Yes _              No _

14- Do you have poor concentration or difficulties focusing your attention?:   Yes _              No _

15- Do you get or have you ever gotten a treatment for the condition that brings you to consult today?:           Yes _              No _

            If yes, since how long:_________________________

16- Neck circumference:_____________mm

3- Symptoms that can be associated with sleep apnea

Daytime signs                                  Night-time signs
_ Headaches                                    _ Snoring
_ Hypersomnia                                 _ Agitated sleep
_ Lack of restorative sleep                 _ Night-time sweating
_ Memory loss                                 _ Arousals with choking sensation
_ Irritability                                       _ Apnea observed by relatives
_ Exhaustion                                    _ Getting out of bed regularly to urinate at night
_ Loss of libido

The presence of these symptoms indicates the possibility of suffering from sleep apnea or another sleep disorder.

4- Diagnosis

Predictive values:
Neck circumference: Yes __ No __
Respiratory pauses reported by the spouse: Yes __ No __
Choking sensation: Yes __ No __
Drowsiness: Yes __ No __
Mandibular and/or maxillary retrognathia: Yes __ No __
Arterial hypertension: Yes __ No __


Your risk of suffering from apnea is evaluated according to the score obtained by the evaluation of neck circumference, the score obtained on the Epworth sleepiness scale and the number of symptoms associated with sleep apnea. This allows the classification of the individual depending on a light, moderate or high probability rate and to take the decision to undergo more advanced evaluations with a polysomnography and search for sleep apnea therapy.

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When the probability of sleep apnea is moderate to high, that several symptoms associated with apnea are present or that the score on the Epworth sleepiness scale is 10 or more, it is indicated to proceed with a polysomnography. This examination can be done in the laboratory where there will be an electroencephalogram (EEG) or it can be done at home (outpatient polysomnography). An outpatient polysomnography is generally sufficient to make an apnea diagnosis.


Report of an outpatient polysomnography examination of a 29-year-old patient

This patient’s report indicates an average apnea-hypopnea index (AHI) of 18.9 events per hour. In dorsal position, the AHI is of 29 events per hour. In a non-dorsal position (on the side or on the stomach), the AHI is of 11 events per hour. The UARS index is of 1.9 events per hour. Anomalies are mainly obstructive as hypopnea, little have a central origin. The events are often associated with autonomous microarousals. The patient slept 43% of the night on the back.

To understand well what an AHI of 29/hr represents, imagine that you are in a pool and that you put your head under the water 29 times during 60 minutes, that is once every two minutes, and that you hold your breath for 18 to 22 seconds each time. Imagine now that you do that for 8 consecutive hours. Imagine that your rate increases to 50 or 60 immersions per hour. Would you be out of breath?



Obstructive sleep apnea and sleep hypopnea. Polysomnography report.

This outline coming from a polysomnography report shows a period of obstructive apnea of 16.13 seconds in duration (purple square). No breathing activity is observed during this period. The Effort #1 and Effort #2 curves shows a decrease in thoracic activity during the apnea respiratory pause. The rate of blood oxygen lowered by 3% (desaturation of 3%) as shown by the orange square at the bottom of the graph.

Two episodes of hypopnea of 14.68 and 18.76 seconds in duration respectively followed the period of apnea. Hypopnea is characterized by a drop in the amplitude of the wave of the breathing curve. The amplitude of thoracic efforts increased compared to the effort during apnea, but without being a normal amplitude. Snoring occurred right after the episode of apnea (little yellow rectangle on the first line of the outline).

Central sleep apnea

This outline shows 2 episodes of central apnea of 18 and 12 seconds respectively. Notice that there is no thoracic effort on the green and blue curves. It is as if the brain no longer told the thorax that it must move to breathe.

Central apnea and snoring

This graph shows important snoring followed by a respiratory pause of central apnea of 21.9 seconds followed by another snore. The oxygen rate lowered by 3% (desaturation) during 18.67 seconds.

Upper airway resistance syndrome

This portion of the graph shows an episode of increased upper airway resistance of 19.72 seconds in duration.

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