|
CPAP
Introduction and Overview
(cpaps, bipaps, autos, bilevels, etc: )
Copyright Notice:
This document was written by and is the copyright of DSM at
www.internetage.com 18th
October 2006. (dsm@internetage.com)
Anyone is free
to download and use this document as long as the copyright notice is left
intact. (### Update #4 - 14 May 2007 ###).
_________________________________________________________________________________________
This document is to provide a simple
and concise summary of Sleep Apnea (SA), some of
the terminology, and the CPAP equipment used to treat it. The document
seeks to provide enough basic detail so the reader can do further research
based on their own particular interest. The report includes descriptions of
the various types of CPAP gear used in the treatment of Sleep Apnea. It attempts to do this in basic non-medical
language. The document starts off
with a high level overview of Sleep Apnea and
then moves on to include an overview of the different types of CPAP
equipment including CPAP machines and CPAP masks. This report also mentions the benefits of
using Pulse Oximetry equipment to determine pulse and blood oxygen
saturation readings for those serious about self monitoring.
Notes:
In this report uses the common spelling
of ‘Apnea’ in preference to the alternative but
more correct ‘Apnoea’.
_________________________________________________________________________________________
Report Index
______________________________________________. 2
Sleep Apnea, Sleep Disordered Breathing (SA, SDB). 2
1. Obstructive Sleep Apnea (OSA). 2
What is OSA. 3
OSA Symptoms. 3
OSA and Blood Oxygen Saturation (SpO2). 3
Causes of OSA. 3
Sleeping Position and OSA. 3
2. Central Apnea (CA). 4
3. Mixed Apnea and Complex Apnea. 4
4. Other contributors to Apneas. 4
Cheynes-Stokes Breathing/Respiration (CSB CSR). 4
______________________________________________. 5
Measuring Sleep Apneas. 5
Apnea Index (AI), Hypopnea Index(HI). 5
Sleep Apnea Severity Levels. 5
Apnea Types Summary. 5
______________________________________________. 6
Categories of CPAP Equipment. 6
1. CPAP Machines. 6
Summary of CPAP Machines. 6
What do CPAP Machines actually Do ?. 6
Measuring Airflow Pressure (CMS). 6
The Machine Types. 7
Ventilator machine vs CPAP machine. 7
CPAP Machines and the law. 7
A. Basic CPAP Machines. 8
B. AUTO Cpap Machines. 8
C. BiLevel CPAP Machines (BiPap, Vpap). 8
D. Humidifiers for CPAP Machines. 9
CPAP Machine Manufacturers. 9
What machine is best for who?. 9
Where can I buy CPAP Machines at best prices ?. 10
2. CPAP Masks. 10
Mask Problems. 10
Nasal Masks (cover the nose). 10
Nasal Pillows / Prongs (feed the air into the
nostrils). 10
Full Face Masks ( cover the nose and mouth). 10
Mouth Masks (feed air in via the mouth). 10
Hybrid Masks (a combination of mouth and nasal
pillows/prongs). 11
Masks fixed leak rates (vents) 11
Mask Deadspace – what is it why does it matter 11
Where can I buy Masks at best prices ?. 11
3 Pulse Oximeters and Oxygen Generators. 12
What is a Pulse Oximeter ?. 12
How do they work. 12
The benefit of a recording Pulse Oximeter. 12
Supplemental Oxygen and Oxygen generators. 12
Where can I buy Pulse Oximeters at best prices ?. 13
______________________________________________. 13
Issues of CPAP compliance. 13
______________________________________________. 13
Other good reference links to help start your own
research. 13
______________________________________________. 14
Some online cpap sales links. 14
______________________________________________. 14
Notes: 14
Sleep Apnea, Sleep
Disordered Breathing (SA, SDB).
Sleep Apnea
and Sleep Disordered Breathing, are terms used to
describe a range of problems to do with sleep and breathing disorders. It
is being experienced by a very large segment of the world population. In
the US and western nations, it is estimated that the prevalence of Sleep Disordered Breathing (SDB) is 25%
of males and 9% of women while among the middle aged in the workforce, it
is estimated that 4% of males and 2% of females, meet the minimal diagnostic
criteria for the presence of SDB. Obstructive Sleep Apnea
is the most common form of SDB. http://www.lungusa.org/site/pp.asp?c=dvLUK9O0E&b=35771
This on-line link contains a very
helpful glossary of respiratory terminology and as such is a helpful
reference whilst reading this report.
http://www.sleepcompliance.com/html/glossary.htm
OSA is a condition that occurs when a
sleeping person’s airway in the area near the soft palate, closes
(collapses) on itself while the sleeper is trying to breathe in. The effect of this closure is that the
chest muscles are working hard to suck air into the lungs but can’t do so
because the airway is blocked.
Eventually the person becomes aroused from sleep (arousal) and will
shift or change position thus freeing up the airway and their breathing resumes,
often accompanied by gasps and panting. If this situation repeats itself
too often, the person’s health can over time, begin suffer seriously. The
bad effects include the risk of increased heart complications as well as
potential brain damage.
OSA Symptoms.
Symptoms associated with OSA can
include constant tiredness, low energy levels, falling asleep while
driving, ‘foggy headedness’, sluggish thinking, slow mental responses (can
be at work or in other social situations), depression. Then there is
Pulmonary Hypertension (this is high blood pressure in the arteries that
supply the lungs which is further manifested as tiredness, dizziness and
shortness of breath).
OSA and Blood Oxygen Saturation (SpO2).
The result of constant sleep arousals is
poor sleep. An added result if blockages are severe and prolonged is that a
person’s blood-oxygen saturation (called SpO2) may drop to alarmingly low
levels. Repeated nights at low SpO2 levels can do irreversible harm to the
person, particularly the brain. Most
people’s SpO2 level is going to be around 95%-96%. It can vary as low as
90%. For people with normal lung function and who have normal blood oxygen
absorption, SpO2 can be as high as 97%-99%.
When measuring blood oxygen saturation, there is a term used to
describe it when the saturation drops too much, this term
is ‘desaturation’. It occurs when
the % SpO2 has dropped by 4% in 10 seconds (some clinics may use slight
variations of this such as 3% in 10 secs).
Patients in intensive care often have
their SpO2 adjusted up to 99-100% by blending a small percent of oxygen into the
air they are breathing. Generally, the higher the SpO2 % reading, the
quicker they are going to heal. Use of supplemental Oxygen can be done for
people on CPAP therapy but it is not all that common a practice.
Causes of OSA.
There really are three core causes of
OSA, These are …
1) physiological causes (a persons neck
throat structure)
2) aging and lifestyle
3) being
overweight and lifestyle.
The lifestyle part really means things
like food intake, alcohol intake, smoking, the amount of exercise someone
does, a persons general state of fitness, etc:. Aging combined with being overweight and
not exercising and consuming regular amounts of alcohol are a great way to
bring on OSA and allowing it to get worse. The physiological causes relate
to if the person has a physical build such that their throat and neck are
predisposed to cause breathing obstructions.
Sleeping Position and OSA.
It is accepted that people sleeping on
their sides, will generally suffer less OSA events in the night, than
people sleeping on their back. In fact, when doing a sleep clinic study
they will usually ask you to sleep on your back so as to create the worst
case scenario particularly when the person being studied is just drifting
off to sleep.
There is one other type of apnea that can occur in some people. This is called
‘central apnea’ (CA). CA occurs when the person ceases
breathing not because of an airway block but because their brain stops
sending the ‘breathe’ message to the muscles used to control
breathing. Central Apneas can be a complex aspect of Sleep Apnea and may require special attention. Not all forms
of Central Apnea lend themselves to being managed
by CPAP machines. Some may require medication or the more sophisticated
ventilator type respiratory machines. But, there are some special models of
cpap machines that try to assist some types of CA
sufferers. CA can also show up in
people that have particular types of heart problems or are being treated for
some types of heart disorders. CA is often linked to people having Cheynes-Stokes breathing patterns (often associated
with CHF – Chronic Heart Failure).
3. Mixed Apnea and Complex Apnea.
Some people can suffer both Obstructive
Apneas (OA) and Central Apneas
(CA) these people may be afflicted by Mixed Apnea or Complex Apnea.
One type of Mixed Apnea
is when an apnea that starts off as a central apnea (sleeper stops breathing – initially has no
airway blockage) then an obstruction develops because their airway closes
or flops shut during a central apnea, the result
is that the apnea starts off as a ‘central’ but
ends as an ‘obstructive’ apnea. So mixed apnea can be taken to mean that the sufferer
experiences both Obstructive Apneas and Central Apneas. Not every professional may agree with this
definition.
Complex Apnea
is a recently established type of Apnea (Mayo
Clinic) that is considered to be resistant to CPAP treatment. In fact a person my
appear to have Obstructive Apnea but when
prescribed CPAP therapy and are using a CPAP machine, their Obstructive Apnea becomes Central and Obstructive Apnea. Central Apnea does not
respond well to straight CPAP therapy. A CPAP machine holding their airway
open doesn’t make a person breathe.
One other form of Central Apnea worth mentioning, is
what is called ‘pressure induced’ central apnea.
This where the pressure from a cpap machine is
perhaps too high, and results in the user stopping breathing for a short
period. This condition can be difficult to detect unless the user
recognises the condition or in explaining their sleep, the respiratory
therapists recognises the symptoms from the user’s description.
Cheynes-Stokes
Breathing/Respiration (CSB CSR).
CSB breathing is usually associated
with people suffering from some types of chronic heart failure/disease
(CHF). CSB is characterised by the person going through repeated cycles of
fast breathing followed by slow deep breathing. In this pattern, during the
slow breathing part of the cycle the person suffers apneas
& hypopneas and in the fast breathing part of the cycle the person is
hyperventilating. The hyperventilation part of the cycle tends to then
trigger the slow breathing and Central Apneas.
The cycle manifests itself as a gradual
increase in breathing depth and frequency followed by a gradual decrease in
the same. It is a form of breathing that really needs immediate and special
treatment.
Resmed Corporation recently released a machine called the VPAP Adapt
SV that uses an Adaptive Servo Ventilation approach. The machine was
originally designed for patients with: Centrals (CA), Mixed Apnea and particularly Cheynes-Stokes
Breathing (CSB).
However!, sometimes it is considered
normal for people to slow their breathing and to even stop breathing
momentarily if this happens at start of sleep onset or just before waking,
or after being momentarily woken, it can be normal if the person’s SpO2 %
(blood oxygen level) is not dropping at the same time. Sleep onset and post-arousal ‘centrals’ are
no particular cause for any concern, just a natural part of a normal sleep
cycle.
______________________________________________
Measuring Sleep Apneas.
Apnea Index (AI), Hypopnea Index(HI).
In their simplest form, SA events are
divided into two types. One is called an Apnea
event and the other is called a Hypopnea event. The first is measured using
an index called the AI (apnea index) and the
second is measured by the HI (hypopnea index). When added together they are
called the AHI (apnea hypopnea index) and this is
usually what a sleep study clinic will quote to you if you go in for a
sleep study. A regular AHI of over 5 is usually regarded as beginning
to require treatment. 5 or under is acceptable.
Apneas are actual airflow
stoppages while Hypopneas are
loosely defined as a 50% reduction in airflow that lasts for at least 10
seconds. Some respiratory specialist
will further add that to be true hypopneas, they also requires
a blood oxygen ‘desaturation’ to occur. It is normal for hypopnea events to
precede apnea events. As previously mentioned, a blood oxygen
desaturation is usually measured as the SpO2 percent dropping by 4%.
There have been many debates about the
usefulness of the AHI measurement as a useful measure of
a persons Sleep Apnea. However, it is
better than no measurement and also is best used in relation to one brand
of CPAP machine. The AHI numbers
from one brand may appear to be almost unrelated to the numbers off another
brand. This is especially so with hypopnea measurements. For example, Resmed machines tend to score higher hypopnea (HI)
levels than a Respironics brand cpap. The respironics is
likely to score higher apneas (AI). This may have
to do with how each brand tracks mask leaks, as they both take quite different
approaches.
Some respiratory experts believe the
AHI measurement is inadequate in determining how effective CPAP therapy is
for a given person but until a better way of measuring is agreed upon AHI
is the accepted way.
Sleep Apnea
Severity Levels.
These numbers are very
generalised and it is highly likely that different organisations will have
their own differing versions of these severity levels. The different levels
of severity of events in this report are :-
-
30+ events per hour
(severe)
-
15-30 events per hour
(moderate)
-
5-15 events per hour (mild)
Apnea
Types Summary.
- Obstructive
(OSA):
>
Apnea where airflow is blocked
while trying to breath in
>
Hypopnea a flow reduction where airflow drops
50% for more than 10 secs
- Central
Apnea. person ceases breathing but
without there being a blockage
- Mixed
Apnea. combination of the above (often
seen as a central that becomes OSA)
- Complex
Apnea, combination of the above but
doesn’t respond to plain CPAP.
(plus as part of SDB …)
- Cheynes-Stokes Breathing. A disorder associated with Chronic Heart
Failure (CHF)
Categories of CPAP Equipment.
Put simply, there are three categories
of CPAP, and CPAP related equipment that are worth
including in this report. These are
1)
CPAP Machines
2)
CPAP Masks
3)
Pulse Oximeter Machines
(measure pulse and blood oxygen saturation)
Each of these categories has distinct
sub-categories. These are all covered in the following paragraphs.
Summary of CPAP Machines.
There are really three principal types
of CPAP machine. Each evolved over
time, in response to different needs and based on the cost and complexity
of the various designs. CPAP technology
has advanced a great deal recently and many of the original reasons for why
there are different types of machine are being lost as cost and complexity
of these different types, merges. In fact it is possible to buy some models
of CPAP machine that can do in one machine what was previously done in the
three different types of machines. Newer designs now emerging can offer all
functions.
Most modern CPAP, AutoCPAP
and BiLevel machines now have a computer
processor and software programs that run in them. The programs analyse the
data gathered from pressure transducers and air-flow detectors plus detect
things like snoring (which causes detectable air-flow vibrations) and
volume of air flowing.
CPAP machines are often referred to as
‘flow generators’. A basic CPAP
machine will deliver a flow of air at a constant preset pressure along an
air hose that is typically 6 foot long with an approx ¾ inch diameter, to a
mask that is strapped onto the user’s face. Normally the airflow is
delivered via the nose. There are other mask types that can deliver the air
to either mouth or nose, and one other design that delivers airflow just
only via the mouth. The nasal types are the most popular. The full face
masks appear to be the second most popular.
The airflow causes the users airway to
be inflated like a sausage balloon thus holding the airway open all the
time. In respiratory care the term commonly used to describe this holding
the airway open is, that the pressure ‘splints’ the airway open.
The pressure of airflow coming from a
CPAP machine is usually referred to as the ‘CMS’ setting. The pressure is actually a measurement of
how much air pressure it takes to push water up a tubular column a
particular distance. Thus a CMS of 15 is then, the pressure of air from a CPAP
machine that is needed to push a column of water up by 15 centimetres from
rest. This pressure setting will
vary depending on altitude. It is normal for people on CPAP to describe
their machine’s setting as “x cms”
where x is typically a number between 6 and 20. Some machines can go higher (30 CMS).But,
at 30 CMS, it is hard to keep the mask strapped to one’s face, it starts to
act like a hovercraft and is not very comfortable.
Most users of CPAP find that in certain
climates and times of the year, they need various levels of humidification
of the air. If the air is not
humidified, users can experience dry mouths and other discomfort. On the other hand, excessive humidification
can cause some users to suffer congestion and stuffiness. Most modern CPAP
machines offer optional integrated heated humidifiers.
The Machine Types.
This report only looks at the common
types of CPAP machine and doesn’t try to delve into the emerging or
specialised types such as Resmed’s new Adaptive Servo Ventilation’ (ASV)
machine (also called the Vpap Adapt CS(USA) or
the AutosetCS2(Aust)), or the Respironics BipapSV (their response to Resmed’s
Vpap Adapt CS).
The three most common types are the
straight CPAP, the AutoCPAP and Bilevel (BiPap, Vpap) machines.
- CPAP – machines that deliver one constant pressure for
inhale and exhale
- AUTO – machines that auto adjust between a max and a min
pressure. An Auto tries to hold to the lowest pressure it feels is
keeping the user breathing
- BILEVEL – machines that have one pressure setting for
inhale and a lower pressure setting for exhale.
Among the Bilevel
machines one will see three brandings, these are BiPap
(a trade name of Respironics), Vpap (a trade name of ResMed),
and the name Bilevel itself. The other vendors will usually label
their Bilevel machines ‘Bilevel’
or some label that includes the word ‘Ventilator’.
Ventilator machine vs
CPAP machine.
In respiratory circles, the word
‘Ventilator’ is usually applied to machines that can or do attempt to
control the breathing or ventilation of a patient. That is, the machine attempts to control
the users breathing by pushing and pulling the airflow to the patient. Some special models of CPAP machine try
to do this by switching between an inhale pressure and exhale pressure at a
normal breathing rate. Only some models of Bilevel
are actually able do this. These models typically have the letters S/T or
A/C after the model name. Examples are ‘Bipap
S/T, VpapIII S/T’, PB330 A/C etc:.
An intensive care unit of a hospital
will normally use a plain Ventilator for controlling breathing. CPAP machines are
normally used in Sleep Clinics or in the home and are called ‘Flow
Generators’ and not Ventilators because other than the S/T or A/C models, cpap machines don’t actually control the user’s
breathing.
CPAP Machines and the law.
In the US, CPAP machines (not the
masks), can only be sold to a purchaser who has a doctor’s prescription for
one. If the machine is a straight
CPAP machine or is a non-auto BiLevel machine,
then the doctor must
write the pressure setting(s) into the prescription. If the CPAP machine is an AutoCPAP of any type, then the doctor is expected to
specify the low/high range the pressure is to be set to. It is technically
illegal in some US
states, to alter a CPAP machine’s pressure settings without a prescription, but, many
people do so. Many people monitor and tune their therapy.
The standard CPAP machine is capable of
being set to a fixed air pressure on which it stays. For example, if your sleep study
indicated you require 13CMS pressure setting, your doctor will write a
prescription for a CPAP machine and will state the pressure it is to be set
to 13 CMS. The DME/RT* who provides you with the machine is responsible for
setting the pressure as per the prescription.
*(DME = Distributor of Medical
Equipment, RT = Respiratory Therapist)
B. AUTO Cpap Machines.
AutoCPAPs were introduced for several reasons.
- to allow clinics to let the machine try to find the best
pressure for the user
- to allow home users to start with a lower pressure and if
the machine senses the need to increase pressure, then it will do so
as required
AutoCPAP machines tend to be more expensive than standard CPAP machines
but are growing in popularity. There
is even a brand of BiLevel Auto on the market.
AutoCPAP machines became popular because of their added sophistication.
They were the first home CPAP machines able to record various types of data
related to each night’s performance and then save this detail for later
download by either a cable to a PC or via a datacard
that can be removed from the machine and read in a datacard
reader. Many people are buying the
software used to monitor these machines so they can read the machine / datacard themselves at home. This enables many people to monitor their
own progress.
Concerns with AutoCPAP
machines include that each brand has its own algorithms for analysing the
input and feedback from users. Today, these differences are enough that
different brands of AutoCPAP machine,
will often produce different results. Doctors tend to feel very
uncomfortable about this. Pressure is being exerted on CPAP manufacturers
to publish their Auto algorithms. To date, none have other than in obscure
wording in their patent applications.
C. BiLevel CPAP Machines (BiPap, Vpap).
BiLevel machines were an early development that occurred before the
development of AutoCPAP machines. The intention of having two pressure
settings was that the higher pressure would be applied while the user breathes
in and a lower pressure applied when the user breathes out. The input (breathe in - inhale) pressure
is called the IPAP value and the output (breathe out - exhale) pressure is
the EPAP value.
The benefits were that this pressure
change helped overcome the discomfort of trying to breathe out while a
machine is at full bore trying to push air in, particularly when the user
has been prescribed a higher pressure (15 CMS to 20+ CMS). The other side benefits were that
lowering the exhale pressure also helped reduce mask leaks and other mask
problems. Also, BiLevels can act as ventilators
if the pressure gap between IPAP and EPAP is high enough. When used in
ventilator mode, a gap of 8 CMS between IPAP and EPAP is not uncommon but
if the user only wants pressure relief then a safe IPAP EPAP gap can be 3
to 4 CMS. Setting pressures above a gap of 4 CMS is a job for specialists
as it is easy for big gap settings to cause complications such as pressure
induced centrals.
A typical example of how a BiLevel may be set for a user without COPD or other
complications is …
IPAP = 14 CMS, EPAP = 10 CMS. There are other parameters that can be
set for these machines
In 2006, Respironics
Corp introduced a new type of BiLevel that in
fact is both a Bilevel (Bipap)
machine and an Auto. The lower
pressure can be given a range and the upper pressure can be given a
different range. Another parameter is the maximum gap that is allowed
between the upper & lower pressures.
This machine will then sample the user’s breathing during both the
inhale (IPAP) and exhale cycles (EPAP) and adjust either pressure as
required based on the algorithms built into the software running the
machine.
Most modern CPAP machines now offer
optional heated humidifiers. Years
back there were a variety of ways to humidify the air being sent from a CPAP machine to the
user. The earliest approaches used the ‘passover’
method. A large tray was constructed
such that air entering an input port, would be forced to ‘snake’ over
channels back and forth and exit the far corner having picked up moisture
along the way.
Later developments included adding a
heating element and a pan so that the warm water was picked up much more
easily and the humidifier could be built smaller. Almost all modern brands
of CPAP now offer an optional small integrated heated humidifier. Most people need them.
CPAP Machine Manufacturers.
The two leading CPAP machine
manufacturers are
Other well known companies include
(among others) :-
Most doctors tend to regard straight
CPAP machines as the simplest and best solution for the normal SA OSA
sufferer. They are not recommended for CA (Central Apnea)
sufferers.
AutoCPAP machines are good for people who are willing to explore and try
to improve their CPAP therapy.
Almost all brands of Auto can function as straight CPAP machines as
well as be set to work in Auto mode.
BiLevel machines fulfil two roles.
A Standard BiLevel (no timed control mode)
offers a very high level of exhalation relief which can be a big help to
people who find it difficult breathing out against higher pressures.
The 2nd role for BiLevels is when they have timed control. This enables
them to act like a ventilator that tries to manage the user’s
breathing. This then means they can
be used for some types of Central Apnea. But they are also used where the person
has other types of respiratory difficulty.
Try http://www.cpap.com/ cpap.com who are very competitive.
Masks have come a mighty long way since
the days when Dr Colin Sullivan used to hand craft them and seal them onto
his patient’s faces with liquid rubber. But, as advanced as masks are, they
still represent the Achilles heel of CPAP therapy in that lack of
compliance with therapy is probably more due to mask problems that any
other type of therapy problem.
The most common problem with today’s
range of masks is getting a comfortable fit.
Unfortunately people’s faces come in a
wide variety of shapes and patterns and trying to design a general mask to
fit all is a massive challenge.
Other problems include …
- Masks leaking the air. More so at higher pressures.
- Masks making noises while they leak. Can wake the wearer
and partner.
- Individuals breathing preferences – nose breathing, mouth
breathing, both.
- When using nasal masks, having air escape from the mouth (a
big issue).
- The effort it takes to set the mask up each night.
- The effort involved in cleaning and maintaining masks.
This type of mask is strapped over the
nose without touching any part of the nose itself. Air is breathed in by
the user through the nose from the cavity created.
This type of mask uses either pillows
or prongs to place the airflow directly into the nostrils by resting on or
in the person’s nares.
This type of mask covers the nose and
mouth and allows the user to breathe through either. Many people find they like Nasal Masks
but can’t stop air escaping through their throats and out their mouth. This is a very uncomfortable experience.
It reduces the effectiveness of the therapy and creates dryness as well as
waking the user and often their partner.
Fisher & Paykel
offer a mask called the ‘Oracle’ model that fits into the mouth like a
scuba divers mouthpiece. Plugs are placed in the nostrils to block them and
the air is directed straight into the mouth via this mouth arrangement.
Very few people seem able to tolerate this type of mask.
A very recent development has been the
introduction of a new mask called the ‘Hybrid’. This mask combines the
prongs of a nasal mask and a cover that sits over the mouth such that the
user can breathe in either opening.
Nearly all CPAP masks no matter what type, have vent holes in the front that allow air to
escape from the mask at a fixed rate (usually measured in liters of air/min). Each mask should come with a chart
that explains this. The leak varies according to the pressure from the
machine. For example a Resmed Ultra Mirage FullFace mask at 10 CMS pressure from the CPAP machine,
will leak air through its vents at 37 litres/min then at 15 CMS it will
leak air at 46 litres/min and at 20 CMS it will leak air at 54 litres/min.
The purpose of these holes is to allow
the right amount of carbon dioxide to be breathed out on exhale. A side
effect of these holes is that a CPAP machine set at say 13 CMS pressure,
may deliver a different pressure because the mask leak rate varies the
effective pressure being delivered to the user. Some masks may allow as
little as say 25 litres/min air out through the
vents at say 15 CMS pressure while another type/brand may allow 54.9
litres/min at 15 CMS.
Many Respiratory physicians will now
want to have their patients do a sleep study with the mask they prefer to
use as this can change the recommended CMS setting.
Mask Deadspace – what is it why does
it matter
All masks have what is known as ‘deadspace’ this is where carbon dioxide and other used
air will accumulate and sit after exhale. Not all the used air is able to
be breathed out. As already mentioned, carbon dioxide needs to be flushed
out of the mask and tube each exhale. The vent holes attempt to allow this.
The actual placement of these vent holes is very important as it can alter
the effectiveness of the venting process. For most normal people, the
smaller the deadspace the better it is for them.
It is accepted that for proper
breathing, there needs to be a small component of carbon dioxide still
breathed in. The level of carbon dioxide in the blood is an important
component of each person breathing triggers. If it becomes too high the
person’s breathing system will raise the alarm to the brain and arouse the
sleeper. If there is too little carbon dioxide in the blood, some people
may not get the signal to breathe and a Central Apnea
occurs.
Some people with a form of Sleep
Disordered Breathing, will be affected by the
amount of carbon dioxide they breathe in. Some such patients on CPAP
therapy may even need to have the vent holes blocked and a special extra
tube added to their air circuit, that becomes an expanded ‘deadspace’ of
a required size. This allows more carbon dioxide to be accumulated &
then blended back in with the air breathed in. This type of modification is
usually only for people with abnormal respiratory conditions such as Cheynes-Stokes Breathing.
Try http://www.cpap.com/ cpap.com who are very competitive.
3 Pulse Oximeters and Oxygen Generators.
A pulse oximeter is used to monitor a
person’s heart rate (pulse) as well as their blood oxygen saturation which
is given as a %. The measurement of
saturation relates to the amount of oxygen picked up in the haemoglobin in
the blood, as it is pumped through the lungs.
Normal readings for people are in the
range of 94% to 97%. Someone with 99% has a very
high blood oxygen saturation. When
it regularly drops below 88%, doctors will start to be concerned.
The way a pulse oximeter works is that
the probe puts out two types of light, red and infra red. A sensor then
picks up the two lights. These two lights get absorbed differently
depending on the oxygen absorption in the blood. The differences are fed
into a built in computer in the PO that
then calculates the SpO2 percent.
The benefit of a recording Pulse Oximeter.
A recording Pulse Oximeter can record a
night’s data then allow it to be downloaded to a computer. PO units
that don’t record are really only good for spot checking & quickly
become boring. If you plan to buy a
PO to help manage your CPAP then make sure it is a recording PO. eBay has lots of Pulse Oximeters for sale. If you are
game enough to buy a PO off eBay, make certain it
has the extension cables and probe. These can sometimes cost more than a PO machine.
Good units include Nellcor
N200 and up. Ohmeda
3740 and up.
Blending oxygen into the airflow of a
CPAP machine is not very common but it is done. It is a practice that
applies to people on CPAP therapy who have other respiratory
complications. Also people
recovering from heart failure surgery are candidates.
Some CPAP masks such as the Resmed Ultra Mirage FullFace mask, have plugs with caps on that are there to allow
oxygen to be blended in. Using a Pulse Oximeter allows the user to confirm
the effect of blended oxygen.
The oxygen can be supplied out of oxygen
bottles or it can be generated by an Oxygen Generator.
Just as CPAP machines have become more
sophisticated and got smaller, so have oxygen generators.
There are a new generation of portable
oxygen generation machines that run on internal batteries and weigh less
than 12lbs. They are expensive costing over 3 to 4 thousand dollars. One
very interesting model is the Airsep LifeStyle http://www.airsep.com/medical/lifestyle.html
Non-portable units cost quite a bit
less (often under $US700) however these units, especially the 5 Litres per
Minute models, can be used to fill small oxygen bottles that can be carried
around or can be used at home to blend oxygen directly into the CPAP
airflow.
Try http://www.cpap.com/ cpap.com who are very competitive.
But failing that look on eBay using
Pulse Oximeter as the search argument.
Many people accept CPAP therapy
voluntarily based on the recommendation of their doctor. Some other people
are required to take on CPAP therapy in order to hold particular types of
jobs. In some states this requirement may be enacted in law.
No matter what reason someone has for
CPAP therapy, there is enormous interest in how effective CPAP therapy is.
The part of this interest that focuses on if a user sticks with the therapy
and to what extent they use it, is referred to as ‘compliance’. Compliance generally means how many hours
per day and, how many days per week, the user is
using the CPAP machine. Most modern
machines will now record this ‘compliance’ information. Doctors or RTs (Respiratory Therapists) can look at this data to
determine the extent of compliance for a given user. The data recorded will
show what time the user started the CPAP machine, any breaks, and what time
the user stopped using the machine.
As already mentioned, almost all modern
AutoCPAP machines, and many standard CPAP
machines (most brands do offer a basic model that will only record minimal
compliance data and not detailed nightly data) and some BiLevel
machines, can also record additional detailed data from each nights use.
The types of data each machine can record include …
- Basic model CPAP = compliance only
- Mid-range CPAP = compliance + pressure + leak rate + AI +
HI + AHI composite Index.
- Auto CPAP = compliance + pressures + leak rate + AI + HI +
AHI composite Index.
- BiLevel
Older = compliance + airflow + pressures + AHI summary for night.
- BiLevels
New = compliance + airflow + pressures + leak rate + AI + HI + AHI
composite Index.
Notes:
- airflow is
usually measured as litres of air / minute. Some machines show this reading
as ‘Minute Ventilation’
- pressures: on Autos the data is a
graph that varies up and down based on the pressure changes
- pressures: on Bilevels
(non Auto type) the graph will show IPAP pressure and EPAP pressure as they
change
- leak rate can be shown as litres of
air/second or litres of air/minute depending on the brand of machine
As always – The Best
http://en.wikipedia.org/wiki/Sleep_apnea
Sleep Apnea
Organisation
http://www.sleepapnea.org/info/index.html
Medicine Net
http://www.medicinenet.com/sleep_apnea/article.htm
Talk About Sleep – View a sleep study
http://www.talkaboutsleep.com/sleep-basics
Talk About Sleep – View a sleep study
http://www.talkaboutsleep.com/sleep-disorders/archives/viewasleepstudy.htm
http://www.cpap.com/ An excellent on-line CPAP sales site
offering excellent pricing options.
http://www.cpaptalk.com/ An interesting CPAP forum. This forum is
very good for getting personal assurance & advice in regard to using cpap machines and masks. It is generally a very good
site for new CPAP users and provides a wealth of helpful support and
information. This site is quite
unique as a self-help CPAP site.
http://www.cpapplus.com/ A reliable on-line supplier.
http://www.cpapsupplyusa.com/ Another reliable on-line supplier.
|