A Diaphragm Pacer and a Ventilator Both Support Breathing — But They Are Not the Same
A Diaphragm Pacer and a Ventilator Both Support Breathing — But They Are Not the Same
When someone uses both a mechanical ventilator and a diaphragm pacer, it can be easy to assume:
They both help the person breathe, so one can simply substitute for the other.
But they do not create breathing in the same way.
And for someone with a complex high spinal cord injury, that distinction can matter tremendously.
How we normally breathe: negative pressure
Normally, when we inhale, the diaphragm contracts and moves downward.
That enlarges the chest cavity. Pressure inside the chest falls, creating the negative intrathoracic pressure that draws air into the lungs.
In simple terms:
Diaphragm contracts
↓
Chest expands
↓
Pressure inside the chest falls
↓
Air is drawn into the lungs
This is the basic mechanism our bodies normally use to breathe.
A mechanical ventilator works differently
Positive-pressure mechanical ventilation approaches breathing from the opposite direction.
Instead of diaphragm contraction creating lower pressure inside the chest and drawing air inward, the ventilator delivers gas into the lungs using positive airway pressure.
So, very simply:
Normal/diaphragm-generated breathing pulls air in.
Positive-pressure ventilation pushes air in.
Mechanical ventilation is lifesaving technology. But the two mechanisms are not physiologically identical.
Published cardiopulmonary research documents that spontaneous inspiratory effort decreases intrathoracic pressure, while positive-pressure ventilation increases intrathoracic pressure. Those differences can affect not only the lungs but also venous return and cardiovascular physiology.
What the NeuRx diaphragm pacer does
The NeuRx Diaphragm Pacing System does not simply blow air into the lungs.
The FDA explains that implanted electrodes electrically stimulate the diaphragm muscles. An external pulse generator controls the timing and amount of stimulation, causing the diaphragm to contract.
The diaphragm then creates the mechanics of a breath.
So:
Electrical stimulation
↓
Diaphragm contracts
↓
Chest expands
↓
Negative inspiratory pressure develops
↓
Air enters the lungs
The FDA describes NeuRx as allowing appropriately selected people with high spinal cord injuries to breathe without mechanical-ventilator assistance for periods of time.
That is an important distinction.
The pacer is activating the person’s diaphragm.
The ventilator is providing positive-pressure ventilation.
They can both support ventilation without being physiologically interchangeable.
And then there is CO₂
Breathing isn’t only about getting oxygen into the body.
Ventilation must also remove carbon dioxide (CO₂).
How much someone is ventilated directly affects the amount of CO₂ remaining in the blood.
And this issue is specifically documented in the diaphragm-pacing literature.
A peer-reviewed clinical paper on inspiratory-muscle pacing in spinal cord injury explains that people maintained on mechanical ventilation may receive large tidal volumes, producing chronic hyperventilation and reduced bicarbonate stores.
The authors then explain that diaphragm pacing is designed to maintain more normal physiological CO₂ levels.
Their wording is striking:
“When switched to the pacing system, which is designed to maintain normal PCO₂ levels…”
They explain that if CO₂ rises toward normal after prolonged hypocapnia, the body’s acid-base system may initially need time to adjust.
Another published review similarly states:
“Long-term mechanical ventilation often leads to chronic hyperventilation and reduction of bicarbonate stores.”
It explains that pacing systems are designed to maintain physiological CO₂ levels and recommends gradual ventilator adjustment as a person transitions toward pacing.
In other words, transitioning between these systems is not necessarily:
Turn one off. Turn the other on.
The body’s physiology may have to adapt.
We saw this in Alex
For our family, the CO₂ difference isn’t merely something described in a medical journal.
Before Alex received his diaphragm pacer, when he was supported by the ventilator alone, his measured CO₂ levels were very low.
After diaphragm pacing became part of his respiratory support, his CO₂ levels became normal.
We cannot say from that observation alone that every physiological change was caused solely by diaphragm pacing. Establishing that scientifically would require reviewing his historical blood gases, ventilator settings and other clinical variables.
But we can say something important:
Alex’s own clinical history demonstrated a measurable physiological difference between his ventilator-only period and his respiratory support after diaphragm pacing.
That matters when someone suggests:
“He has a ventilator, so he can just use the ventilator instead.”
For Alex, these aren’t simply two interchangeable machines that happen to move air.
The literature even describes using both systems together
Transitioning to diaphragm pacing generally requires conditioning because a diaphragm that has not been regularly used can become significantly deconditioned.
Published SCI respiratory literature describes beginning pacing gradually.
It even describes early diaphragm conditioning while the patient is still receiving mechanical ventilation.
And here’s an especially interesting detail:
The literature explains that, in assist-control ventilation, the ventilator can sometimes be triggered by the:
“negative inspiratory pressure”
created by the person’s diaphragm contraction.
Think about that.
The physiological activity produced by the diaphragm can actually interact with the ventilator.
That alone demonstrates why:
Pacer + ventilator does not mean two interchangeable breathing machines.
They can function together as parts of one respiratory-support system.
Then 2019 taught us another part of the lesson
In 2019, Alex developed a severe pleural effusion and required hospitalization at Ohio State.
We still do not know definitively what caused that illness, and I do not attribute the pleural effusion to either his diaphragm pacer or ventilator.
But the hospitalization taught me much more about respiratory pressures. I sat in the ICU where Alex was googling pleural effusions in individuals with ventilators or something to that effect.
A pleural effusion means fluid has accumulated in the space surrounding the lung.
Published research shows that a significant pleural effusion can alter pleural pressure, reduce lung volume and change the mechanical relationship among the lung, chest wall and diaphragm.
That introduced me to another important concept:
There is pressure inside the lung and pressure outside the lung.
The difference between alveolar pressure and pleural pressure is called transpulmonary pressure.
That pressure relationship helps determine how expanded the lung is.
And suddenly the difference between Alex’s two forms of respiratory support became even more meaningful.
His diaphragm pacer was activating his diaphragm and helping create negative-pressure inspiration.
His ventilator was providing positive-pressure assistance through his airway.
During the hospitalization, as Alex’s condition improved and his lung mechanics changed, I talked with his hospital staff about bringing down the ventilator pressure. I had learned from my google search about how delicate the balance between inside and outside the lung was.
It was an education in how dynamic respiratory support can be.
What is appropriate when someone is very sick may not remain appropriate as the underlying physiology changes.
Pressure matters beyond the lungs, too
Changes in intrathoracic pressure can also influence circulation.
Published cardiopulmonary physiology shows that spontaneous inspiratory effort and positive-pressure ventilation can have different effects on venous return and cardiovascular function.
That doesn’t tell us exactly how any particular ventilator adjustment will affect Alex.
His physiology is unusually complex, and those decisions belong with Alex and the clinicians who understand his individual situation.
But it reinforces an important principle:
Changing respiratory support can affect more than breathing.
That becomes especially relevant for someone whose respiratory, neurological and autonomic systems already interact in unusual ways.
This is why individualized knowledge matters
A standardized record might say:
Uses diaphragm pacer.
Uses ventilator.
Both statements are correct.
But those two checkboxes don’t tell you:
- which is Alex’s primary respiratory support;
- how the two systems work differently;
- how they interact;
- how his CO₂ responded before and after pacing;
- how changes in lung mechanics can alter the balance;
- how pressure changes may affect physiology beyond the lungs; or
- how Alex himself recognizes changes in his body.
The equipment list is accurate.
The equipment list is not the physiology.
The simplest explanation
A ventilator and diaphragm pacer can both support breathing.
But they do it differently.
A mechanical ventilator uses positive pressure to deliver air into the lungs.
A diaphragm pacer electrically activates the diaphragm, helping produce the negative-pressure breathing mechanism our bodies normally use.
Published diaphragm-pacing research specifically documents CO₂ and acid-base considerations when people transition from chronic mechanical ventilation toward diaphragm pacing.
And Alex’s own history adds something population research cannot:
Before diaphragm pacing, while using the ventilator alone, his CO₂ levels were very low. After diaphragm pacing, his CO₂ levels became normal.
Years later, a severe pleural illness taught us even more about how delicately lung mechanics, pressures and respiratory support can interact.
So when we say Alex’s ventilator and diaphragm pacer are not interchangeable, that isn’t merely a preference about equipment.
There is physiology behind it.
There is published research behind it.
And there are more than seventeen years of Alex’s individual clinical experience behind it.
Two technologies can accomplish the same broad goal—supporting ventilation—without being physiologically equivalent ways of achieving it.
The existence of one does not automatically make the other unnecessary.
We are still working to educate others and help them to understand. It’s a process for sure.
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