cules follow the path of least resistance. During
inhalation the air pressure within the alveoli is
less than the air pressure outside the lungs. Oxy-
gen molecules pass across the thin alveolar mem-
brane and into the capillaries to enter the
bloodstream. During exhalation the air pressure
within the alveoli is greater than the atmospheric
air pressure, inducing carbon dioxide molecules to
cross from the capillaries into the air in the alveoli.
For further discussion of the lungs within the
context of pulmonary structure and function
please see the overview section “The Pulmonary
System.”
See also EPIGLOTTIS.
lung transplantation An OPERATIONto replace an
individual’s diseased lung with a healthy donor
lung. Doctors performed the first successful lung
transplantation in 1983 and now perform several
hundred lung transplantations each year. A lung
transplantation may involve one lung or both
LUNGS. Less commonly a lung transplantation
includes both lungs and the HEART, such as to
treat primary PULMONARY HYPERTENSIONwithHEART
FAILURE.
Donor lungs come primarily from people who
donate their organs upon death. Live lobular
donation, in which a living donor undergoes sur-
gery to have a lobe of the lung removed for trans-
plantation (lobectomy), is occasionally a viable
option for people who can find a tissue match
among two prospective donors (usually family
members) willing and medically capable of donat-
ing a healthy lung lobe (live lobular donation typi-
cally requires two lobes). Doctors most commonly
consider living lobular donation as an option for
children who have aggressive CYSTIC FIBROSIS.
Many circumstances influence whether an
individual is an appropriate candidate for lung
transplantation. Because donor lungs are in short
supply, the criteria for transplantation are strin-
gent though vary somewhat among transplant
centers. In general, lung transplantation recipients
must be under age 65, in good health except for
their pulmonary conditions, and demonstrate will-
ingness and ability to comply with the post-trans-
plantation care regimen. Transplantation criteria
nearly always exclude people who have cancer
(lung or other), immunodeficiency disorders,
active TUBERCULOSIS, neurologic or neuromuscular
disorders, LIVERdisease, or renal (kidney) disease.CONDITIONS FOR WHICH LUNG
TRANSPLANTATION IS AN OPTION
CHRONIC OBSTRUCTIVE CYSTIC FIBROSIS
PULMONARY DISEASE(COPD) BRONCHIECTASIS
bronchiolitis alpha-1-antitrypsin
primaryPULMONARY HYPERTENSION deficiency
PULMONARY FIBROSIS SARCOIDOSISSurgical Procedure
The operation for performing a lung transplanta-
tion is a THORACOTOMY, done with the person
under general ANESTHESIA. The surgery generally
takes three to six hours to complete. Typically one
surgical team removes and prepares the donor
lung and another surgical team removes the dis-
eased lung from the person receiving the lung
transplantation. A donor lung remains viable for
only four to six hours. Most people are on CAR-
DIOPULMONARY BYPASSduring the surgery, though
advances in surgical techniques are reducing the
need for this. MECHANICAL VENTILATION during
recovery and for up to 72 hours after surgery is
common. A lung transplant recipient typically
stays about 10 days in the hospital after the sur-
gery, the first three to five of them in the intensive
care unit (ICU). Recuperation and return to daily
activities takes about three to five months for
most people.Risks and Complications
The most significant risk of lung transplantation is
rejection of the transplanted lung. This risk is
highest during the first four weeks after the sur-
gery and remains a perpetual threat. The risk of
death, usually resulting from acute organ rejec-
tion, is highest during the first year after the trans-
plant. People who receive organ transplants must
take IMMUNOSUPPRESSIVE THERAPYfor the remainder
of their lives. These medications block the IMMUNE
SYSTEMfrom perceiving the transplanted organ as
foreign and attacking it. Immunosuppressive ther-
apy increases the risk for INFECTION. Infections such
as INFLUENZAor PNEUMONIAcan be life-threatening
for people with organ transplants; most transplant
programs require organ recipients to agree to
receive annual immunizations to help protectlung transplantation 213