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.