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  • 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.

In the 16th century, Flemish physician Andreas Vesalius

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B2 ventilation patient air respiratory oxygen pressure

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    林宜悉 posted on 2020/10/23
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