the respiratory rate as well as pressuring the net-
work of blood vessels within the lungs to cause
conditions such as PULMONARY HYPERTENSION. Con-
gestive HEART FAILUREdevelops when the heart is
not strong enough to pump blood throughout the
body, allowing fluids to seep from the bloodstream
and into the interstitial spaces in the lungs. The
resulting pulmonary congestion and PULMONARY
EDEMAfills the lungs with fluid, restricting the
oxygen–carbon dioxide exchange. Exposure to
environmental irritants and toxins also can dam-
age the lungs, particularly as a cumulative effect
over time, causing repeated INFLAMMATIONthat can
result in SCARformation (fibrosis).
Traditions in Medical HistoryAncient Western and Eastern medical traditions
alike correlated the function of the lungs with the
role of bringing life-giving air, and the NUTRIENTSit
bears, into the body. Greek physician Galen
(129–199), whose views framed the perceptions
and practices of medicine for nearly 1500 years,
postulated the lungs took in and digested air, after
which the pulmonary VEINcarried the resulting
“vapors” to the heart. Though this hypothesis held
the correct intent, its details were enough skewed
to thwart genuine understanding of cardiopul-
monary circulation for centuries.
The concepts of cardiovascular circulation and
pulmonary function finally began to converge
with William Harvey’s detailed monograph, Exerci-
tatio Anatomica De Motu Cordis et Sanguinis in Ani-
malibus, published in 1628. This work, whose title
translates as A Treatise on the Movement of the Heart
and Blood in Animals, provided the first definitive
description of the circulation of the blood through
the heart, lungs, and blood vessels. Harvey failed
to identify the capillary beds and their role in oxy-
gen–carbon dioxide exchange; yet his work estab-
lished the foundation for later researchers to make
this and other discoveries about lung function.
Once physicians understood the basic function-
ing of the lungs, heart, and blood, they could begin
to find the causes of the diseases that disrupted
these functions, often with debilitating or fatal
results. Throughout documented history, TUBERCU-
LOSIS—consumption, as early cultures called this
infection that appeared to “consume” its sufferers—
has reigned as one of the most devastating diseases
known to afflict humankind. The disease causes
inflammation, granulation, and calcification within
the inner structures of the lungs, permanently
destroying lung tissue. Unchecked, tuberculosis
spreads within the infected person to fully involve
the lungs and often other organs such as the KID-
NEYS, spinal fluid, and bones. Early explanations for
tuberculosis, which accounted for about 1 in every
20 deaths across centuries and civilizations, ranged
from dietary habits such as eating meat and drink-
ing liquor to environmental exposures such as foul
weather and smoke from burning fires. In fact,
however, tuberculosis spreads among people
through contact with bacteria in the SPUTUM(the
mucus, fluids, and debris coughed from the lungs)
of those who are infected.
Ancient Egyptian mummies demonstrate BONE
damage characteristic of tuberculosis. Even famed
Western physician of antiquity and Galen’s prede-
cessor Hippocrates (460–400 B.C.E.) wrote of the
physical wasting that accompanied tuberculosis
and warned against close contact, even by physi-
cians, with those in the end stages of the disease.
Not for nearly two millennia after him, however,
did physicians make the connection between close
contact and the contagiousness of tuberculosis. In
1882 microbiologist Robert Koch (1843–1910) dis-
covered the responsible bacillus, Mycobacterium
tuberculosis, turning the corner toward finding a
true cure for the infectious and debilitating dis-
ease. Though a cure was still another 60 years
away, isolating those who were ill became the
trend. Doctors sent those afflicted with tuberculo-
sis to sanatoriums where fresh air, rest, and nutri-
tious meals formed the core of treatment. It was
enough for some, though not most, people to
recover or at least to send the disease into inactiv-
ity—and it separated the infectious from the
healthy, helping slow contagion. Some people
underwent more dramatic therapies, such as
intentional collapse of the infected lung, to try
slow the progression of the disease by starving the
tissue of oxygen.
In 1943 biochemist Selman Waksman was able
to isolate and cultivate an effective antibiotic,
streptomycin, to kill M. tuberculosis without also
killing the person this stubborn PATHOGENinfected.
By the early 1960s researchers had developed a
regimen of multiple antibiotics to successfully cureThe Pulmonary System 179