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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.
