DISORDERS CAUSED BY ALTITUDE - Medicine for Mountaineering and Other Wilderness Activities - page 350

often—but not always—an irritated dry cough. In the late stages the cough may produce
frothy pink sputum. A person with HAPE is typically much more tired than other mem-
bers of the party, an important early symptom. Since the hypoxia of altitude is made more
severe by the fluid in the alveoli, the symptoms of AMS are often worsened. Shortness of
breath at rest is an important early sign. A dry cough may also be due to irritation from
overbreathing dry air.
The pulse rate is usually rapid (over 110 beats per minute), even after several hours of
rest, and respirations are fast and labored (over twenty per minute). The lips and nails are
bluish (cyanotic) and the skin pale and cold. Bubbling or crackling sounds may be heard
when listening to the lungs with the unaided ear or with a stethoscope. Sometimes crackles
are heard on one side only, usually in the middle of the right lung (best heard just below
the armpit); occasionally they are almost inaudible. Symptoms and signs usually become
worse during the night.
Due to the further decrease in oxygen reaching the brain, a person with HAPE does not
thinkclearlyandmaybecomeconfusedorevendelirious,whichsuggeststhatsomedegree
of HACE is also present. When this occurs, the outlook is poor. Unless treated quickly and
effectively, the person is likely to die.
HAPE is not due to heart failure or pneumonia, although years ago it was mistaken for
those disorders. HAPE does cause a fever but not usually a high one. The cause lies in
alterations in the pulmonary circulation. High altitude, sleep apnea, or hypoxia from any
cause, including heavy exercise, causes a rise in pulmonary artery blood pressure (PAP).
Normally, the smallest pulmonary arteries (arterioles) constrict, protecting capillaries from
excessive pressure and flow rates. One theory concerning the cause of HAPE is that indi-
viduals who develop HAPE may not have uniform arteriolar constriction throughout the
lungs. Arterioles constrict in some areas but not in others. Consequently, in those parts of
the lung where no constriction occurs, high pressure and flow are transmitted directly to
the capillaries, which leak fluid into the alveoli.
Probably no one is completely immune; HAPE occurs even in experienced and accli-
matized mountaineers if they go too high too fast and work too hard. Individuals who are
HAPE susceptible and have repeated episodes of HAPE have been recognized. These un-
fortunate people respond to high altitude—or to the hypoxia of sleep apnea—with an ab-
normally large increase in pulmonary artery pressure, particularly during exercise. This
susceptibility may begenetic, perhaps duetofailure ofcertain tissues togenerate nitric ox-
ide(NO),oneofthemostimportantcompoundscontrollingthetoneofsmallbloodvessels.
The defect may be an absent or abnormal gene sequence or some other defect in nitric ox-
ide formation.
Most persons going to moderate altitude accumulate a small amount of fluid between
the thin layers of the membrane lining the alveoli (interstitial edema), which hinders the
diffusion of oxygen. Such edema may also develop during strenuous exertion. Usually this