Hyperbaric
oxygenation is a treatment that supplies a high level of oxygen through the
lungs which is then dissolved in the blood and supplied to the tissues of the
body. Pure oxygen is
provided at a pressure greater than atmospheric in a hyperbaric chamber.
To
understand why more oxygen may help some children with cerebral palsy it is
necessary to explain the background to the condition. There are some obvious
questions to be answered:
Ultrasonic
scanning of the brain has shown that the events which cause the development of
cerebral palsy almost certainly occur at the time of birth, although it is
usually many months before spasticity develops.
The
areas affected are in the middle of the brain and one side or both sides may
be involved. These critical
areas, called the internal capsules, are where the fibres from the controlling
nerve cells in the grey matter of the brain pass down on their way to the
spinal cord. In the spinal cord
they interconnect with the nerve cells whose fibres finally activate the
muscles of the legs and arms.
Unfortunately,
the internal capsules have a poor
blood supply, which is shown by the frequent occurrence of damage to these
areas (shown by Magnetic Resonance Imaging (MRI) in younger patients with
multiple sclerosis and in strokes in the elderly). When an event causes lack of oxygen, the blood vessels leak
and the tissues become swollen. The
increased water content, reduces the transport of oxygen.
These changes apply to any tissue but a sufficient quantity of oxygen
is vital both to the function and, in children, for the development of the
brain.
What
causes paralysis and spasticity to develop?
When
the, controlling nerve cells in the brain are disconnected from the spinal
cord, the signals to the arms and legs cannot pass and the ability to move is
lost. Eventually, because the
nerve cells in the spinal cord are separated from the control of the brain,
they send an excess of signals to the muscles, causing the uncontrolled
contractions known as spasticity. The
areas carrying the controlling nerve fibres to the legs are the closest to the
centre of the brain where blood
supply is poorest so the legs are the most commonly affected.
This
is a crucial question that is, at present, not adequately explained.
Children who develop spacticity often appear to develop normally for
several months and then lose function gradually. Because in children there is
voluntary movement for a time after birth, the nerve connections from the
brain to the spinal cord must be intact.
Why then are they lost allowing spasticity to develop?
The answer almost certainly is due to the failure of the coverings of
the nerve fibres, known as myelin sheaths, to develop. The evidence for this
has come from MRI. Myelin sheaths
envelop the nerve fibres like a swiss roll in order to increase the speed with
which impulses can be transmitted. Myelination
normally begins about a month before birth and progresses to completion by the
age of two. If there is tissue swelling in the mid-brain the delicate cells
that form myelin die and the nerve fibres are left exposed and slowly
deteriorate with the development of spasticity.
Loss
of function in the brain can be either due to tissue swelling, which is
reversible, or tissue destruction, which is not reversible.
The recoverable areas can now he identified by a technique called SPECT
imaging. It can demonstrate the levels of blood flow to the brain which is, of
course, directly related to oxygen availability. By giving oxygen at the high dosages possible under
hyperbaric conditions, the areas which are not "dead but
sleeping" can be
reactivated and identified. This
phenomenon has been discussed for many years in stroke patients and
authorities have even stated that the critical parameter is oxygen delivery. Under normal circumstances blood flow and oxygen delivery are
inextricably coupled but the use of hyperbaric conditions can change this
situation. Tissue swelling may
persist in many tissues for years and SPECT imaging has now revealed that this
is true in the brain. Suggesting
that oxygen supplied under hyperbaric conditions may be of value generates
further questions:
It
means a pressure greater than normal sea-level atmospheric pressure.
A hyerbaric chamber allows much more oxygen to be dissolved in the
blood plasma. Breathing pure
oxygen at, for example, twice atmospheric pressure reduces the workload of the
heart by 20% which is an indication of the increased efficiency of the
distribution of oxygen in the body. Infact so much can be dissolved that a
person can be kept alive for a short time without blood flow.
How
can cerebral palsy children be helped?
There
has been much research carried out in the treatment of physical and
neurological disorders using hyperbaric oxygen therapy. Clearly the
appropriate time to use oxygen therapy is at the start of a disease, not after
a delay of months or years. Nevertheless,
a course of oxygen therapy sessions at increased pressure has been shown to
resolve tissue swelling after the lapse of years.
It works by narrowing blood vessels and interrupting the cycle where
lack of oxygen leads to tissue swelling which then leads to further oxygen
deficiency. A pilot study of a
small number of cerebral palsy children has shown improvement.
In children the brain is still developing and therefore the prospects
for improvement are much greater. Recovery
of brain damage in children as a result of cardiac surgery improving blood
flow, and hence oxygen supply, has been documented using x-ray scanning.
Will
oxygen therapy cure cerebral palsy?
Hyperbaric
oxygen therapy is not a miracle cure for children with cerebral palsy.
It is simply a way of ensuring the most complete recovery possible, It
must be used with exercise programmes because lack of use in muscles and
joints leads to changes that can only be reversed by exercise.