Respiratory Testing
Track breathing changes and plan support
Review status: Waiting for team review. An AI editorial check was completed on 2026-08-14 by claude-opus-5. It checks clarity, attribution and scope against the sources, and it is not a Compass team or clinical sign-off. Waiting for clinical review. Last updated 2026-08-14.
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Planning 3
- Arrange baseline respiratory testingBook breathing tests through your care team so there is a starting point.Why it matters: A first set of results is what every later test is compared against, so having one early is worth more than any single reading.
- Track breathing symptomsNote breathlessness, morning headaches, poor sleep, or a weak cough.Why it matters: Symptoms can change between appointments, and your own notes are the part no clinic can reconstruct later.
- Ask how often this should be repeatedClarify what the results mean and when retesting is needed.Why it matters: Knowing the interval turns testing into something predictable instead of something you have to chase.
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ALS/MND can gradually weaken the muscles used for breathing. This includes the diaphragm, the main muscle below the lungs. Because this often happens slowly, regular checks help your team notice changes early, while there is time to plan support calmly rather than during a crisis.
Monitoring is not about expecting the worst. It is a routine part of care that helps make sure any support you might want is ready when, and if, it is needed.
Your team is mainly watching for signs that the breathing muscles are working less strongly, which can show up as:
- breathlessness, especially with activity or when lying flat
- broken or unrefreshing sleep, or waking through the night
- morning headaches
- daytime tiredness or low energy
- a weaker cough, or more frequent chest infections
These changes often appear at night first, before they affect the day. Monitoring usually combines simple breathing tests with how you are actually feeling and sleeping, and it is repeated over time so your team can see the trend rather than a single snapshot.
The related cards cover what the results might lead to, such as a conversation about breathing support. The aim of monitoring itself is simply to keep a clear, up-to-date picture so decisions can be made with good information and without rush.
Explained: what this word meansEvidence for this answer
The sources the Compass team used to write this answer. Highlighted phrases in the answer above correspond to the statements below.
Statement 1 of 2. Breathing is checked regularly so that changes are picked up early, often before the person notices anything.
Adds context. NICE MND guideline — NICE · Clinical guideline
Recommends monitoring respiratory function and symptoms as routine MND care, and sets a usual testing interval of every 2 to 3 months. It establishes that checks are regular, not that they catch changes early.
“Assess and monitor the person's respiratory function and symptoms.”
1.13.1Link checked August 2026
Statement 2 of 2. Weak breathing muscles affect gas exchange at night before they show up in the day.
Supports this. Guidelines for the physiotherapy management of MND — Irish Motor Neurone Disease Association · Clinical guideline · 2014
Its section on medical management says weak breathing muscles impair gas exchange particularly at night, and that the carbon dioxide building up then shows itself as disturbed sleep, morning headaches and fatigue. Its fatigue section calls night-time under-breathing a common symptom of MND.
“Nocturnal hypoventilation is a common symptom of MND and is thought to contribute significantly to impaired sleep.”
Section 3.4e.2 Evidence (Fatigue Management)Link checked August 2026
Used across the whole answer
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Breathing tests are a way of keeping an eye on how well your breathing muscles are working over time. Most are quick, painless and done in a clinic chair, and they are usually repeated at intervals so your team can see how things are changing rather than relying on a single snapshot. You may not have all of these. Which tests are used, and how often, varies between teams and from person to person.
Lung function tests (including FVC)
These measure how much air your lungs can move. The most common is FVC (forced vital capacity). You take a deep breath in and blow out as hard and fully as you can into a mouthpiece. FVC is often measured both sitting up and lying down, because the diaphragm has to work against the weight of the abdomen when you are flat, so weakness tends to show up more in that position. This can sometimes happen before you notice anything in daily life.
Breathing-muscle strength tests
These check the strength of the muscles you breathe with, and for some people changes show up here earlier than on other tests.
- Sniff test (often called SNIP). You sniff in sharply through your nose with a small soft probe in one nostril.
- Mouth pressure tests. You breathe in or out firmly against a small handheld device.
Both are simple, take only a moment, and do not involve needles. The sniff test can be useful if making a tight seal on a mouthpiece is difficult, because you breathe in through your nose instead.
Checking your breathing overnight
Because breathing can be affected during sleep before it is noticeable in the day, some checks are done overnight, often at home.
- Overnight oximetry. A small sensor, usually on a fingertip, records your oxygen levels while you sleep.
- Carbon dioxide (CO2) checks. Weakened breathing can let CO2 build up overnight. This can usually be measured without a needle, for example with a small sensor on the skin or a soft tube at the nose. Which method is used varies between teams.
The occasional needle test
Sometimes a precise reading of the oxygen and CO2 in your blood is needed. An arterial blood gas is a one-off blood sample taken with a needle, usually from the wrist. It is used less often than the tests above, and your team will explain it beforehand if it is needed.
What the results are for
No single result decides anything on its own. Your team puts the numbers together with how you are actually feeling and sleeping to build a picture over time, and the checks are usually repeated. It is always fine to ask your team to talk you through what your own results mean.
Explained: what this word meansEvidence for this answer
The sources the Compass team used to write this answer. Highlighted phrases in the answer above correspond to the statements below.
Statement 1 of 3. Breathing tests are repeated at intervals so the team can follow the direction of travel rather than judge a single reading.
Supports this. NICE MND guideline — NICE · Clinical guideline
Recommends that respiratory function tests are performed about every 2 to 3 months, more or less often depending on symptoms and signs, how fast MND is progressing, and what the person prefers. Repeating the tests is the recommendation, not an option.
Link checked August 2026
Statement 2 of 3. Weak breathing muscles affect gas exchange during sleep before the problem is obvious in the daytime.
Supports this. Guidelines for the physiotherapy management of MND — Irish Motor Neurone Disease Association · Clinical guideline · 2014
Its section on medical management says weak breathing muscles impair gas exchange particularly at night, and that the carbon dioxide building up then shows itself as disturbed sleep, morning headaches and fatigue. Its fatigue section calls night-time under-breathing a common symptom of MND.
“Nocturnal hypoventilation is a common symptom of MND and is thought to contribute significantly to impaired sleep.”
Section 3.4e.2 Evidence (Fatigue Management)Link checked August 2026
Statement 3 of 3. A blood gas test is done only when particular conditions are met, not as one of the routinely repeated checks.
Supports this. NICE MND guideline — NICE · Clinical guideline
Treats blood gas analysis as conditional rather than routine: it is done when oxygen saturation measured at rest on room air falls to or below 92 per cent for someone with known lung disease, or 94 per cent for someone without. The tests repeated every 2 to 3 months are the lung function and muscle strength ones.
Link checked August 2026
Used across the whole answer
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There is no single schedule that fits everyone. How often your breathing is checked depends on your situation. Your team considers how your breathing is doing now, whether it is changing, and what they are watching for.
For many people, breathing is checked at regular clinic reviews, often alongside other parts of their care, even when things feel stable. Clinical guidelines commonly suggest checking about every two to three months, more or less often depending on your symptoms, how quickly things are changing, and what you prefer. This is because changes can happen gradually, and a routine check helps catch them early. If your breathing or symptoms are changing, your team may suggest checking more often for a while.
It is also reasonable to ask for a check sooner if something new comes up between appointments. Examples include more breathlessness, poorer sleep, morning headaches, or a chest infection that is slow to clear.
The aim is to keep the picture up to date so that, if a conversation about support is needed, it happens with current information and without rush. Your team can tell you what interval they suggest for you and why, and it is fine to ask.
Evidence for this answer
The sources the Compass team used to write this answer. Highlighted phrases in the answer above correspond to the statements below.
Statement 1 of 2. How often breathing is checked varies from person to person, rather than following one fixed schedule for everyone.
Qualifies this. NICE MND guideline — NICE · Clinical guideline
Agrees that the interval varies, and names the three things it varies with: whether there are symptoms and signs of breathing problems, how fast MND is progressing, and the person's own preference and circumstances. It also gives a usual starting point of every 2 to 3 months, which this answer does not mention.
Link checked August 2026
Statement 2 of 2. Guidelines put the usual interval for respiratory function tests at about every 2 to 3 months, varied according to symptoms and signs, how fast MND is progressing, and the person's own preference.
Supports this. NICE MND guideline — NICE · Clinical guideline
Recommends the tests every 2 to 3 months and names the three things that move the interval: symptoms and signs of respiratory impairment, the rate of progression, and the person's preference and circumstances.
“perform the respiratory function tests every 2 to 3 months, although tests may be performed more or less often”
1.15.10Link checked August 2026
Used across the whole answer
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Breathing results are best understood as one part of the picture, not a verdict on their own. A single number rarely decides anything. Your team reads the results alongside how you are actually feeling, including your energy, your sleep and your breathlessness. They also look at the trend over time rather than any one reading.
If results stay steady, monitoring usually just continues as before. For most results, a change is a prompt for a conversation rather than an automatic step. Depending on what is found, your team might:
- suggest checking your breathing a little more often
- talk through symptoms you can watch for at home
- offer a referral to a respiratory ventilation service for a fuller assessment
- raise the option of breathing support to think about. What that involves, and whether and when it might help, is covered on the breathing-support cards rather than decided here
Some results do lead to a set next step rather than a discussion. If a blood test shows a raised carbon dioxide level, NICE guidance tells your team to refer you urgently to a respiratory ventilation service, to be seen within a week, and to explain why. That is a defined part of the pathway rather than a sign that something has gone wrong suddenly, and it is worth taking up that appointment.
It is normal to find numbers worrying, especially if they move in the "wrong" direction. It can help to remember that results guide planning and give you more time to consider options, rather than forcing a decision. If a result concerns you, it is always reasonable to ask your team what it means for you specifically and what, if anything, it changes.
Evidence for this answer
The sources the Compass team used to write this answer. Highlighted phrases in the answer above correspond to the statements below.
Statement 1 of 3. A breathing result is interpreted together with the person's symptoms, not on its own.
Supports this. NICE MND guideline — NICE · Clinical guideline
Builds symptoms into the thresholds themselves. A lung function result that is not low enough to act on alone still counts once there are symptoms or signs of breathing problems, particularly breathlessness lying flat, and a normal carbon dioxide level with symptoms still leads to an overnight study.
Link checked August 2026
Statement 2 of 3. When a lung function or breathing-muscle strength result reaches a level NICE lists, the recommended next step is a discussion of the respiratory impairment, the treatment options and possible referral for further assessment.
Supports this. NICE MND guideline — NICE · Clinical guideline
At 1.15.15 the trigger is the table 2 results: lung function (FVC or VC) and breathing-muscle strength (SNIP or MIP). There the instruction is to discuss the respiratory impairment, treatment options and possible referral, guided by the person's wishes. It covers those results only. Other thresholds are not discussions: 1.15.13 requires an urgent referral if carbon dioxide is raised.
“If any of the results listed in table 2 is obtained, discuss with the person and (if appropriate) their family and carers”
1.15.15Link checked August 2026
Statement 3 of 3. If arterial carbon dioxide is above 6 kPa, NICE tells the team to refer the person urgently to a respiratory ventilation service, to be seen within one week, and to explain the reasons for the urgency.
Supports this. NICE MND guideline — NICE · Clinical guideline
Sets this out as a defined, time-limited step rather than something to weigh up: above 6 kPa the referral is urgent and the person should be seen within a week, and the team must explain the reasons for it and what it means.
“refer them urgently to a respiratory ventilation service (to be seen within 1 week)”
1.15.13Link checked August 2026
Used across the whole answer
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Breathing changes in ALS/MND often show up as everyday symptoms, so what you notice is genuinely useful information for your team. It is worth mentioning these between appointments rather than waiting for the next review:
- breathlessness that is new or worse, with activity, or when lying flat
- difficulty lying flat, or needing more pillows to sleep
- broken or unrefreshing sleep, or waking often
- morning headaches
- daytime sleepiness, fatigue or low energy
- a weaker cough, more mucus, or trouble clearing it
- repeated or slow-to-clear chest infections
Noticing one of these come on gradually does not usually mean something is suddenly wrong. They are signs worth sharing so your team can check whether anything needs attention.
Sudden or rapidly worsening breathlessness is different. Seek medical attention immediately, by calling emergency services or going to an emergency department, rather than waiting to reach your MND team. The cause may be something other than ALS/MND, such as a clot on the lung, and that needs treating quickly.
Separately, a chest infection that is not improving, or feeling unusually unwell with your breathing, is worth raising promptly rather than waiting for the next review. A chest infection in particular is worth seeing a doctor about as soon as possible. Ask your team now who to contact and how, so you already know before you need it.
Keeping a simple note of what you notice, and when, can make these conversations easier. It is always fine to raise something even if you are not sure it matters.
Explained: what this word meansEvidence for this answer
The sources the Compass team used to write this answer. Highlighted phrases in the answer above correspond to the statements below.
Statement 1 of 3. Breathing problems in MND announce themselves as ordinary day-to-day symptoms, and monitoring for those symptoms is part of standard care.
Supports this. NICE MND guideline — NICE · Clinical guideline
Sets out a table of the symptoms and signs to monitor for, and it is close to this answer's list: breathlessness, breathlessness lying flat, recurrent chest infections, disturbed and unrefreshing sleep, daytime sleepiness, morning headaches, fatigue and a weak cough.
“Monitor the symptoms and signs listed in table 1 to detect potential respiratory impairment.”
1.15.7Link checked August 2026
Statement 2 of 3. Sudden shortness of breath needs immediate medical attention, not a call to the MND team, because the cause may be something other than ALS/MND, such as a clot on the lung.
Supports this. ALS Respiratory Support — Your ALS Guide · Practical guide
Treats sudden shortness of breath as an emergency in its own right, separate from the gradual breathing changes of ALS/MND, and gives the reason: the cause may be something else, such as a clot on the lung.
“If you develop sudden shortness of breath, it is important to seek immediate medical attention, as the cause could be something other than ALS, such as a blood clot in the lungs.”
Shortness of BreathLink checked August 2026
Statement 3 of 3. A chest infection that is not clearing, or feeling unusually unwell with your breathing, should be raised with the team promptly rather than saved for the next appointment.
Supports this. ALS Respiratory Support — Your ALS Guide · Practical guide
Says an infection should be seen about as soon as possible rather than left, and that the person's usual doctor stays involved alongside the ALS team.
“If you get the flu, a cold, or an infection, it is especially important to see your doctor as soon as possible to get it cleared up.”
Keep Your Primary DoctorLink checked August 2026
Adds context. NICE MND guideline — NICE · Clinical guideline
Explains why an infection matters so much here. It instructs teams to look for and treat reversible causes such as chest infections first, before treating worsening breathing as progression.
“Treat people with MND and worsening respiratory impairment for reversible causes (for example, respiratory tract infections or secretion problems) before considering other treatments.”
1.13.1Link checked August 2026
Used across the whole answer
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Breathing tests can feel abstract, so it helps to bring a few questions and to ask your team to explain results in plain language. You do not need to ask all of these. Pick what matters most to you.
Understanding my results
- What do my results actually mean for me right now?
- Are they steady, or have they changed since last time?
- What would you be looking for as a sign that something needs attention?
The plan
- How often do you suggest checking my breathing, and why?
- What would change the plan, or lead to a conversation about support?
- Which symptoms should make me get in touch sooner?
Practical
- Who do I contact if my breathing changes between appointments?
- Is there anything I can do that helps my breathing or sleep in the meantime?
It is always fine to ask for results to be written down, to bring someone with you, or to ask the same question again if the answer was not clear. Understanding your own breathing picture helps you take part in decisions with confidence.
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It can be surprising, but in ALS/MND extra oxygen is often not the right treatment for breathing problems, and giving it without specialist advice can sometimes cause harm. It is worth understanding why, because it is the opposite of what many people expect.
The breathing difficulty in ALS/MND usually comes from weak breathing muscles, which make it harder to move air in and out and to clear out carbon dioxide. The main problem is often a build-up of carbon dioxide, not simply a lack of oxygen.
If oxygen is given on its own in this situation, it can mask the problem and let carbon dioxide rise further, which can make someone drowsy or confused. That is why care teams usually focus on supporting the breathing itself, for example with non-invasive ventilation (NIV), and on measuring carbon dioxide, rather than reaching for oxygen.
What this means in practice:
- A low reading on a home oxygen monitor does not, by itself, mean oxygen is the answer.
- Breathing support and the right assessment matter more than the oxygen number alone.
- Oxygen is used in ALS/MND only in specific situations and under specialist guidance.
So if a reading worries you, the safest step is to talk to your respiratory or MND team rather than start oxygen yourself. They can assess what is really going on and arrange the right support. The Non-Invasive Ventilation and Respiratory Consult cards cover breathing support in more detail.
Explained: what this word meansEvidence for this answer
The sources the Compass team used to write this answer. Highlighted phrases in the answer above correspond to the statements below.
Statement 1 of 3. Giving extra oxygen in ALS/MND without specialist assessment can do harm, because it can suppress the drive to breathe when carbon dioxide is already raised.
Supports this. Guidelines for the physiotherapy management of MND — Irish Motor Neurone Disease Association · Clinical guideline · 2014
Gives exactly this reason, and puts it more strongly than the answer does: oxygen is generally not prescribed in MND at all, because of the risk of suppressing the drive to breathe when carbon dioxide is already high.
“In general, oxygen is not prescribed so as not to risk inhibition of respiratory drive in the setting of elevated serum carbon dioxide levels.”
Section 2.3 Medical ManagementLink checked August 2026
Statement 2 of 3. In ALS/MND the breathing problem is often a build-up of carbon dioxide from weak breathing muscles, not simply a shortage of oxygen.
Supports this. Guidelines for the physiotherapy management of MND — Irish Motor Neurone Disease Association · Clinical guideline · 2014
Describes the problem as impaired gas exchange from weak breathing muscles, with carbon dioxide retention named as what produces the symptoms. It does not set carbon dioxide against oxygen: its own NIV criteria at Table 2.3.2 accept significant nocturnal desaturation on overnight oximetry as an alternative to a morning PCO2 above 6.5 kPa.
“Respiratory muscle dysfunction results in impaired gas exchange, particularly at night, with symptoms of carbon dioxide retention including sleep disturbance, morning headaches and fatigue common”
Section 2.3 Medical ManagementLink checked August 2026
Qualifies this. ALS Respiratory Support — Your ALS Guide · Practical guide
Agrees on the practical conclusion, that most people with ALS do not need extra oxygen and that a genuinely low oxygen level usually means a separate lung condition. It is less clear-cut on the mechanism: it says a weak diaphragm makes it harder both to take oxygen in and to breathe carbon dioxide out, rather than singling carbon dioxide out.
“If you are experiencing shortness of breath, it is likely the result of a weakened diaphragm muscle.”
Shortness of BreathLink checked August 2026
Statement 3 of 3. Extra oxygen is not part of routine breathing care in ALS/MND and is kept for particular circumstances.
Supports this. ALS Respiratory Support — Your ALS Guide · Practical guide
Says most people with ALS do not need supplemental oxygen, and names the exception as an oxygen level that is genuinely low, which usually comes from an underlying lung condition such as COPD or emphysema.
“Most people living with ALS do not need supplemental oxygen.”
Shortness of BreathLink checked August 2026
Used across the whole answer
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