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What does hypoventilation mean?
In medicine, hypo means below and ventilation means breathing. So hypoventilation means "under-breathing". This occurs when breathing is insufficient to bring in enough oxygen to the lungs and breathe out sufficient of the waste gas, carbon dioxide (carbon dioxide levels above normal, or dependency on a ventilator).
Hypoventilation can be caused by diseases of the muscles, lungs, upper airways and the brain, particularly in the deep brain structures (so called brainstem).


What is Central Hypoventilation?
Central hypoventilation means that the hypoventilation is due to a disorder in the bottom of the brain, just above the back of the neck.
If central hypoventilation has either a finding of a specific genetic mutation (PHOX2B) or the absence of any other diagnosed disorder of the brain, nerves, muscles or metabolism or other genetic syndrome, this is called central hypoventilation syndrome.


What is Congenital Central Hypoventilation Syndrome?
Congenital means that you are born with the condition. Symptoms are either present immediately or soon after birth, or the genetic abnormality is present but may not show itself for many months or years due to a milder version of the condition. If the symptoms appear after the first month of life or later, the disease is sometimes called late-onset CCHS (LO-CCHS).


Are there other types of central hypoventilation syndromes?
Hypoventilation that appears later in childhood and is associated with a rapid weight gain and hormonal disorders is called Rapid-Onset Obesity with Hypothalamic and Autonomic Dysfunction (ROHHAD).


How does CHS present?
Hypoventilation may occur only during deep sleep with normal breathing when awake. In other cases, breathing stops completely during sleep with severe hypoventilation during wakefulness. The ways this presents are as follows:

  • Needing mechanical (assisted) ventilation from birth
    Blue episodes or pale / grey episodes
    Apparent life-threatening events
    Severe chest infections
    Poor weight gain or growth
    Slow development
    Heart failure
    Seizures (fits or convulsions)


In children, we would also consider CHS if they have:

  • Rapid onset obesity
    Behavioural disorders
    Excessive thirst
    Hormonal disorders


CHS should also be considered in children and adults who have:

  • Severe sleep apnoea
    Bad reactions to anaesthesia
    Severe chest infections needing prolonged ventilation


What is the cause of hypoventilation in patients with CHS?
Patients with CHS do not react to changes in oxygen and carbon dioxide in the blood. This is because sensors in blood vessels in the neck and brain do not send messages to the brainstem correctly. The brainstem does not respond with an increase in breathing when needed. The affected individual does not recognise, either consciously or unconsciously, that their breathing is inadequate. He or she then has shallow breathing and does not take in enough oxygen or breathe out enough carbon dioxide.


Do patients with CHS suffer from other symptoms than hypoventilation?
CCHS and LO-CCHS (but not ROHHAD) are genetic disorders caused by mutations in PHOX2B gene. This gene is important for the normal development of the autonomic nervous system which controls many organs and muscles within the body. The PHOX2B mutations affect therefore many body functions.
Approximately 20% of patients suffer from an absence of nerves in the large intestine (Hirschsprung disease). Others experience feeding difficulty with acid reflux, indigestion and difficulty swallowing solids. Some patients with CHS are at risk to develop cancer in the nerve tissue (neuroblastoma) in the adrenal glands (above the kidneys), neck, chest or spinal cord. Among other symptoms are abnormal reactions of pupils to light, sporadic profuse sweating episodes, thirst and abnormal regulation of blood pressure, heart rhythm and body temperature.

update: 11/01/2012


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