against these infections among their criteria for
accepting recipients. Long-term immunosuppres-
sion carries numerous risks, including a signifi-
cantly increased likelihood for developing
LYMPHOMA, a cancer of the LY M P Hstructures.
A major complication that affects up to 50 per-
cent of lung transplant recipients is bronchiolitis
obliterans, a condition in which the bronchioles
(the smallest airways in the lungs) become
inflamed and then fibrotic. The fibrotic (SCAR) tis-
sue blocks the narrow openings of the bronchi-
oles, preventing air from reaching the alveoli. As
greater numbers of bronchioles become involved,
pulmonary function deteriorates. Bronchiolitis is
itself an indication for lung transplantation. CORTI-
COSTEROID MEDICATIONScan help limit the INFLAMMA-
TIONthough cannot prevent the condition from
developing or progressing.
Outlook and Lifestyle ModificationsMost people who receive transplanted lungs can
return to many of their regular activities, includ-
ing physical exercise, with few restrictions unless
complications develop. It is important to avoid cig-
arette smoke and other substances that may irri-
tate or inflame the lungs, and to minimize
exposure to other people who have viral or bacte-
rial infections such as sore throats and other com-
mon illnesses. Lung transplantation requires
regular medical care for follow-up and evaluation
of pulmonary function and lung health, with
immediate treatment for potential problems and
complications. About 45 percent of people who
undergo lung transplantation live five years or
longer with their donor lungs.
See alsoHEART TRANSPLANTATION; ORGAN TRANS-
PLANTATION; SURGERY BENEFIT AND RISK ASSESSMENT.
mechanical ventilation A method for providing
assisted respiration to an individual whose LUNGS
cannot maintain respiratory support on their own
(RESPIRATORY FAILURE). During mechanical ventila-
tion, a machine (the ventilator) rhythmically
pushes air into the lungs through an endotracheal
tube or TRACHEOSTOMYtube. An endotracheal tube
is a flexible plastic tube inserted through the NOSE
or MOUTHinto the TRACHEA, with an inflatable cuff
that holds it in place. A tracheostomy tube enters
the trachea through an incision in the neck,
bypassing the upper airways (including the mouth
and throat). The lungs continue to do the work of
OXYGEN–CARBON DIOXIDE EXCHANGE.
Mechanical ventilation may provide full respi-
ratory support, in which BREATHING occurs only
with the ventilator’s function, or partial respira-
tory support, in which the ventilator functions
only when the person’s natural breathing is insuf-
ficient. As with normal respiration the inhalation
phase of the RESPIRATORY CYCLEis active, with the
ventilator sending air under pressure into the
lungs, and the exhalation phase is passive, with
the ventilator allowing the thoracic cavity’s relax-
ation to expel air. The ventilator typically utilizes
continuous POSITIVE AIRWAY PRESSURE(CPAP), which
keeps the trachea, bronchi, and bronchioles from
collapsing.
There are numerous applications for, and vary-
ing levels of, mechanical ventilation. Temporary
mechanical ventilation is customary after major
cardiovascular or pulmonary operations and dur-
ing recovery from major trauma. Other circum-
stances in which mechanical ventilation is a
therapeutic option include- high-level (cervical and upper thoracic) SPINAL
CORD INJURYthat affects the nerves regulating
contraction of the DIAPHRAGM and intercostal
muscles (the muscles of breathing) - injury to the respiratory centers of the BRAIN
and brainstem - degenerative neurologic conditions that affect
respiratory function - increased respiratory demands that exceed the
lungs’ ability to deliver, such as in severe infec-
tions
The ventilator is primarily a mechanized bellows
that fills with air (and supplemental oxygen if nec-
essary) that inflates the lungs using positive pres-
sure. The doctor determines the RESPIRATORY RATE,
air volume (amount of air the ventilator delivers),
and flow pressure (pressure under which the venti-
lator delivers air to the person). In some situations
the person does not need help with breathing but
just needs an endotracheal tube or tracheostomy to
protect the airway and minimize the risk of aspirat-
ing foreign matter into the lungs. In such a situa-214 The Pulmonary System