How do ventilators work? - Alex Gendler
In the 16th century, Flemish physician
Andreas Vesalius
described how a suffocating animal
could be kept alive
by inserting a tube into its trachea
and blowing air to inflate its lungs.
In 1555, this procedure didn’t warrant
much acclaim.
But today, Vesalius’s treatise
is recognized
as the first description
of mechanical ventilation—
a crucial practice in modern medicine.
To appreciate the value of ventilation,
we need to understand how
the respiratory system works.
We breathe by contracting our diaphragms,
which expands our chest cavities.
This allows air to be drawn in,
inflating the alveoli—
millions of small sacs inside our lungs.
Each of these tiny balloons is surrounded
by a mesh of blood-filled capillaries.
This blood absorbs oxygen
from the inflated alveoli
and leaves behind carbon dioxide.
When the diaphragm is relaxed,
the CO2 is exhaled alongside
a mix of oxygen and other gases.
When our respiratory systems
are working correctly,
this process happens automatically.
But the respiratory system can be
interrupted by a variety of conditions.
Sleep apnea stops diaphragm muscles
from contracting.
Asthma can lead to inflamed airways
which obstruct oxygen.
And pneumonia, often triggered
by bacterial or viral infections,
attacks the alveoli themselves.
Invading pathogens kill lung cells,
triggering an immune response
that can cause lethal inflammation
and fluid buildup.
All these situations render the lungs
unable to function normally.
But mechanical ventilators
take over the process,
getting oxygen into the body
when the respiratory system cannot.
These machines can bypass
constricted airways,
and deliver highly oxygenated air
to help damaged lungs diffuse more oxygen.
There are two main ways
ventilators can work—
pumping air into the patient’s lungs
through positive pressure ventilation,
or allowing air to be passively drawn
in through negative pressure ventilation.
In the late 19th century,
ventilation techniques largely
focused on negative pressure,
which closely approximates
natural breathing
and provides an even distribution
of air in the lungs.
To achieve this, doctors created
a tight seal around the patient’s body,
either by enclosing them in
a wooden box or a specially sealed room.
Air was then pumped
out of the chamber,
decreasing air pressure,
and allowing the patient’s chest cavity
to expand more easily.
In 1928, doctors developed
a portable, metal device
with pumps powered
by an electric motor.
This machine, known as the iron lung,
became a fixture in hospitals
through the mid-20th century.
However, even the most compact
negative pressure designs
heavily restricted a patient’s movement
and obstructed access for caregivers.
This led hospitals in the 1960’s to shift
towards positive pressure ventilation.
For milder cases,
this can be done non-invasively.
Often, a facemask is fitted
over the mouth and nose,
and filled with pressurized air
which moves into the patient’s airway.
But more severe circumstances
require a device that takes over
the entire breathing process.
A tube is inserted
into the patient’s trachea
to pump air directly into the lungs,
with a series of valves
and branching pipes
forming a circuit for inhalation
and exhalation.
In most modern ventilators,
an embedded computer system
allows for monitoring the patient’s
breathing and adjusting the airflow.
These machines aren’t used
as a standard treatment,
but rather, as a last resort.
Enduring this influx of pressurized air
requires heavy sedation,
and repeated ventilation
can cause long-term lung damage.
But in extreme situations,
ventilators can be the difference
between life and death.
And events like the COVID-19 pandemic
have shown that they’re even more
essential than we thought.
Because current models
are bulky, expensive,
and require extensive training to operate,
most hospitals only have a few in supply.
This may be enough
under normal circumstances,
but during emergencies,
this limited cache is stretched thin.
The world urgently needs more low-cost
and portable ventilators,
as well as a faster means
of producing and distributing
this life-saving technology.
