Breathing and Muscular Dystrophy: Ventilation and Cough Assist

Breathing and muscular dystrophy: the numbers that trigger action

Respiratory management is where muscular dystrophy care has changed most, and it is the clearest example of something that sounds frightening being, in practice, the thing that keeps people well.

The diaphragm and the intercostal muscles are muscles, so in most muscular dystrophies they weaken. Left alone, that produces nocturnal under-breathing, then daytime carbon dioxide retention, then respiratory failure, and historically it was the commonest cause of death. Managed properly — with monitoring on a schedule, cough assist, and non-invasive ventilation started at defined thresholds — it becomes a chronic condition people live with for decades.

The Australian 50-year Duchenne cohort published in 2025 found that increasing use of respiratory support, alongside corticosteroids and cardiac medication, accompanied median survival rising from 18.2 to 24.0 years.

What makes this subject unusually tractable is that the international care considerations give actual numbers. Not “consider ventilation when appropriate,” but specific thresholds at which specific things should start. Those numbers are set out below, because a family who knows them can ask whether they have been reached — and in adult services, where the surveillance schedule is frequently not delivered automatically, asking is often what makes it happen.

What happens, and why the first signs are at night

The thing families and clinicians most commonly get wrong is expecting breathlessness.

Breathlessness comes eventually. But respiratory weakness in muscular dystrophy announces itself at night, as bad sleep, and the early symptoms are so unspecific that they get attributed to the condition generally, or to adolescence, or to depression.

What is actually happening. Lying flat, with reduced muscle tone during sleep, somebody with a weak diaphragm does not move enough air. Carbon dioxide accumulates overnight. That rising carbon dioxide produces the morning headache, the nausea and the exhaustion on waking, and it breaks sleep into pieces. The daytime exhaustion that follows gets blamed on the muscle disease — which does cause fatigue — so the most treatable symptom in the whole condition gets filed under “expected.”

The nocturnal signs:

• Waking with a headache, usually at the front of the head, clearing over the first hour or two
• Unrefreshing sleep — a full night in bed, exhausted on waking
• Daytime sleepiness, or falling asleep in class or at a desk
• Frequent waking through the night, often without memory of it
• Vivid or disturbed dreams
• Morning nausea or poor appetite at breakfast
• Needing more pillows, or sleeping propped up or in a recliner

That last one is worth asking about directly, because people do not volunteer it. Somebody who has quietly gone from one pillow to three, or who now sleeps in a chair, is telling you about diaphragm weakness. From the inside it does not feel like a breathing problem; it feels like being more comfortable sitting up.

The daytime signs, later: breathlessness on exertion and then while speaking or eating, a quieter voice, fewer words per breath, difficulty clearing the throat, and anxiety — which in this context is frequently a physiological response to inadequate ventilation rather than a psychological problem.

The sign that needs acting on without delay is a weakening cough. An effective cough needs a deep breath in, a closed glottis and a forceful expiration, and muscular dystrophy can compromise all three. Somebody who cannot cough properly cannot clear secretions, and a chest infection in that situation escalates fast. Cough strength matters at least as much as vital capacity and is measured far less often.

The monitoring schedule and the numbers

From the 2018 international DMD care considerations, which are also the reference point most Australian clinics use for other muscular dystrophies with respiratory involvement:

Monitoring frequency:

• Spirometry from age 5 to 6
• FVC annually while walking
• FVC every six months once not walking, with MIP, MEP, peak cough flow and oxygen saturation
• End-tidal or transcutaneous CO2 every six months in non-ambulatory patients, or whenever oxygen saturation is 95 per cent or lower on room air
• Sleep studies up to yearly in non-ambulatory patients with symptoms

The action thresholds:

Sleep study thresholds indicating ventilation: CO2 above 50 mm Hg for at least 2 per cent of sleep; a rise of 10 mm Hg above awake baseline for at least 2 per cent of sleep; oxygen saturation of 88 per cent or less for at least 2 per cent of sleep or 5 minutes continuously; or an apnoea–hypopnoea index of 5 or more per hour.

And the timing statement, which is the one worth holding onto: most or all core respiratory therapies should be in use by age 18 to 21 in Duchenne.

What to do with this. Ask at each appointment: what is my FVC, sitting and lying; what is my peak cough flow; and have any of the thresholds been reached. Write the numbers down and keep the series, because a trend is more informative than any single reading. If a threshold has been crossed and nothing has been started, that is a specific, answerable question to put to the respiratory team rather than a vague worry.

A note on the lying measurement. Sitting and supine FVC should both be taken, because a significant drop from sitting to lying indicates diaphragm weakness, sometimes before the seated figure looks abnormal. If only a seated figure is being recorded, ask for the lying one.

Cough assist, which comes before ventilation

Frequently neglected, and it should not be, because secretion clearance is what prevents the chest infections that cause the crises.

Breath stacking and lung volume recruitment. Taking several small breaths in without exhaling, to reach a larger lung volume than a single breath can achieve, then coughing from there. Taught by a physiotherapist. Recommended once or twice daily from an FVC of 60 per cent predicted or less — which is before assisted coughing is needed, and which is the point: this is a maintenance activity that preserves chest wall mobility and lung volumes.

Manual assisted cough, where a carer’s hands push on the abdomen or lower chest in time with the cough.

A lung volume recruitment bag, a simple hand-held device for assisting breath stacking where unassisted stacking is ineffective.

Mechanical cough assist (mechanical insufflation-exsufflation). A device that delivers a positive pressure breath in, then switches rapidly to negative pressure, producing an artificial cough. Indicated where assisted breath stacking is not effective, and particularly valuable during a chest infection — which is exactly when it is most needed and exactly when it is too late to start organising one. Get it before the infection.

Suction, for secretions that cannot be cleared from the mouth and pharynx.

And the practical instruction for families and support workers: learn the equipment, keep it charged and assembled, and know that during a chest infection the frequency of cough assist should increase. A machine in a cupboard is not a treatment.

Non-invasive ventilation

What it is. Air pressure delivered through a mask rather than a tube — in muscular dystrophy, almost always bilevel ventilation, a BiPAP or similar device, which gives a higher pressure on inhalation and a lower pressure on exhalation so the machine does part of the work of inflating the lungs. A respiratory physician prescribes the settings, and the settings matter.

Night first. Overnight ventilation is started when the thresholds above are met, because that is where the problem begins. The symptomatic improvement — waking without a headache, actually feeling rested, daytime energy returning — is frequently dramatic and is what carries people through the adjustment period.

Then day, as needed. Some people eventually use ventilation for most of the day, in blocks, around meals and conversation. Mouthpiece or “sip” ventilation during the day suits some people better than a mask and is worth asking about.

The masks. Nasal, nasal pillows, or full face. Mask intolerance is the commonest reason people abandon ventilation and it is a solvable technical problem, not a reason to stop. If a mask leaks, hurts, marks the bridge of the nose, or feels claustrophobic, the answer is a different mask. There are many. Ask to try others.

Humidification, which makes a substantial difference to tolerance — dry air through a mask all night causes nasal congestion, dry mouth and sore throat.

The adjustment period is real. Almost nobody finds it comfortable on the first night, and most people adapt over one to three weeks. Starting earlier, while somebody is less unwell and better able to adapt, is one of the arguments for not waiting until a threshold is well past.

Backup power. For somebody dependent on ventilation at home, a plan for power failure is essential — battery backup, and registration with the electricity distributor as a life-support customer, which is a real scheme and which families frequently do not know about. Ask the home ventilation service how to do it in your state.

And who pays. Ventilation equipment in Australia is frequently supplied through a state home ventilation or respiratory service rather than the NDIS, with consumables, masks and servicing sometimes coming from elsewhere again, and the support workers who assist with ventilation usually funded through the NDIS. It varies by state. Ask the neuromuscular clinic what the local arrangement is. See muscular dystrophy and the NDIS.

The oxygen warning

This belongs in every file and on a card in every wallet.

Respiratory failure in muscular dystrophy is a problem of ventilation, not oxygenation. The issue is carbon dioxide that is not being cleared, not oxygen that is not getting in. Giving oxygen alone can suppress the respiratory drive and worsen carbon dioxide retention.

Oxygen may be used for palliative breathlessness with monitoring, and alongside ventilation, but it is not a substitute for ventilation — and in an emergency department, at 2am, with staff who have never met the person, somebody needs to say so.

What to carry: a card or letter stating the diagnosis, that there is a carbon dioxide retention risk, that oxygen should not be given without ventilatory support, the current ventilation settings, and the contact details of the home ventilation service and neuromuscular clinic. Keep a copy with the person, in the house, and with any support provider.

Chest infections, and the plan that should already exist

Chest infections are the commonest acute crisis in muscular dystrophy, and the difference between a managed illness and an intensive care admission is usually preparation.

What should be written down, in advance:

• When to start antibiotics, and whether there is a standby supply at home
• When and how much to increase cough assist frequency
• When to increase ventilation use into the daytime
• What oxygen saturation or symptom triggers mean “go to hospital”
• Which hospital, and which team to contact
• The oxygen caution
• Current ventilation settings and equipment
• The corticosteroid stress dosing requirement, where the person is on long-term steroids — this is important and emergency staff do not always know it

Signs that need same-day review: new fever, a productive or wet-sounding chest, a weak cough with new secretions, increased work of breathing, falling oxygen saturation, new confusion or drowsiness, or needing substantially more ventilation than usual.

And vaccination. The care considerations recommend annual inactivated influenza vaccine — not the live attenuated nasal form — plus pneumococcal vaccination. This is cheap, effective and routinely missed.

Scoliosis, surgery and breathing

Worth connecting, because these interact.

Scoliosis reduces chest wall mobility and lung volumes, so a progressive curve worsens respiratory function independently of muscle weakness. Spinal fusion in appropriate cases can stabilise seating, posture and comfort, and the timing involves respiratory function because the surgery itself carries respiratory risk.

The care considerations recommend cardiology and respiratory consultation before any spinal surgery, and spinal orthoses are not recommended in this population. See steroids, bones and scoliosis.

And seating matters respiratorily. A slumped posture compresses the chest and abdomen and reduces vital capacity. A seating review is a legitimate response to deteriorating respiratory function, and it is a cheaper intervention than most. See equipment and home modifications.

Sleep, and the thing that gets mistaken for laziness

Worth its own section, because the most common and most reversible respiratory problem in muscular dystrophy presents as a behavioural one.

What happens. Nocturnal hypoventilation fragments sleep and raises carbon dioxide overnight. The person wakes unrefreshed, with a headache, feeling sick. By mid-morning the headache has cleared and they are merely exhausted. By afternoon they are asleep in a chair.

What it looks like from outside. A teenager who cannot get up, falls asleep in class, has stopped doing homework and seems to have lost interest in things. An adult who is unreliable at work, dozing off in meetings, irritable and apparently unmotivated. Both get read as attitude, depression, or screen time.

Both are frequently a treatable breathing problem, and the fix — nocturnal ventilation — can produce a change in function within weeks that families describe as getting the person back.

What to ask for:

An overnight oximetry study, which is a finger probe worn at home and is the cheapest way to detect nocturnal desaturation.

A full sleep study (polysomnography) with carbon dioxide monitoring, where oximetry is abnormal or symptoms are suggestive. The 2018 care considerations give specific criteria: CO2 above 50 mm Hg for at least 2 per cent of sleep, a rise of 10 mm Hg above awake baseline for at least 2 per cent of sleep, oxygen saturation of 88 per cent or less for 2 per cent of sleep or five minutes continuously, or an apnoea–hypopnoea index of five or more per hour.

And a low threshold for asking. In non-ambulatory patients with symptoms, sleep studies up to yearly are indicated. If somebody has any of the nocturnal symptoms and has never had a sleep study, that is the request to make.

Three other things that disturb sleep here and are fixable: pain from being unable to reposition, which an adjustable bed and a repositioning schedule address; needing the toilet, where a urinal, bottle or overnight arrangement helps; and anxiety, which is sometimes a physiological response to inadequate ventilation rather than a psychological problem and which improves when the ventilation does.