Biomedical Engineering Reference
In-Depth Information
FIGURE 9-25
Simplified illustration
of a negative-
pressure ventilator.
The
iron lung
is the popular name for an ENPV device that consists of an airtight
metal cylinder called a plethysmograph that encloses the whole body from the neck down,
which is connected to a pump that can lower the internal pressure within the cylinder to
below that of the surrounding atmosphere to draw air into the lungs.
Techniques for sustained ventilatory support awaited the widespread availability of a
reliable supply of mains electricity, the development of electric motors, and a large number
of patients with chronic respiratory failure. This need arose during the polio epidemics of
the first half of the twentieth century.
In 1918, South African doctor W. Steuart developed a respirator much like the ones
that later made Drinker and Emerson famous. His machine was a sealed wooden box made
specifically for treating poliomyelitis that operated by variable-speed, motor-driven bel-
lows. Although his machine was supposedly a great success, the work was never formally
reported and therefore became largely forgotten.
In 1926, the Consolidated Gas Company of New York used its Liability Insurance Fund
to establish a committee to research resuscitation. As a business program, the executives
responsible for the development of this committee intended to improve safety standards
for the company's workers.
Among committee members was Harvard University professor Philip Drinker. Drinker
suggested that the committee consider supporting research by his brother, the chemical
engineer Cecil Drinker, and his colleague, Louis Shaw, who were already working on
artificial resuscitation at Harvard University. The committee agreed and sent a check for
$5000 in autumn 1927 to support further investigation (Gorham, 1971).
Drinker and Shaw's research was focused on the discovery of true artificial resuscita-
tion. As part of their research, they placed an anesthetized cat in a sealed box metal box
(plethysmograph) with a neck collar, allowing the body to be within a fully pressurized
environment. Under these conditions, they were able to record accurate measurements
of respiration. Inhalation increased the volume of the cat within the box and made the
pressure rise, while expiration produced the opposite effect (Shaw, 1928). A simplified
diagram of this apparatus is shown in Figure 9-26.
The men speculated that if the subject could not breathe independently then increas-
ing and decreasing the pressure in the box would induce respiration. To test this hy-
pothesis, Drinker and Shaw injected the cat with curare, a powerful muscle relaxant, to
induce respiratory arrest. They then placed the cat into the sealed box and used a hand-
operated piston to manually control the pressure. The experiment was successful, and the
cat was kept alive until the effects of the curare wore off after a few hours. They had
