RESPIRATORY DISORDERS - Medicine for Mountaineering and Other Wilderness Activities - page 233

ing normal breathing volume— the tidal volume —is five to six liters per minute. Vital ca-
pacity is the total volume of air that can be forcefully exhaled after inhaling as deeply as
possible. The volume of air expired in the first second is the forced expiratory volume in
one second .Thesethreemeasuresarecommonlyusedtodescribelungfunction.Theresid-
ual volume is air in the lungs that cannot be exhaled even after a full forceful expiration.
Sleep causes a decrease in the rate and depth of breathing—hypoventilation—that may
result in a decreased blood oxygenation, particularly at high altitude. In contrast, exertion
greatlyincreasesventilationbecauseitincreasestheneedforoxygenandtheneedforelim-
inating carbon dioxide. These demands stimulate the respiratory center in the brain to in-
crease the respiratory volume toasmuch as150liters perminute duringvigorousexercise.
Even at rapid respiratory rates, the lungs supply oxygen to the blood and take up carbon
dioxide with extraordinary efficiency and precision.
A variety of disorders can affect the function of the respiratory system. Head injuries
or diseases of the brain may increase or decrease breathing. Airway obstruction can result
from aspirated material or from injuries to the throat, usually sudden, and may halt effect-
ive breathing. Injury of the chest wall producing rib fractures or open wounds can impair
the bellows action of the chest wall and diaphragm. Even chest wall injuries without rib
fractures can cause pain with inspiration that leads to splinting—not expanding the chest
as much on the injured side. Air, blood, or fluid within the chest cavity may compress the
lungs and prevent expansion during inspiration. An injury that damages the lung in such a
way that inhaled air continuously leaks into the space between the lung and chest wall but
cannot be exhaled (tension pneumothorax) is life threatening. Collections offluid in the al-
veoli due to edema or infection can block the exchange of gases between inhaled air and
blood.
Injury to the brain resulting in swelling or bleeding may depress the respiratory control
system and cause hypoventilation. Sedative or analgesic drugs may also depress the respir-
atory control system and cause hypoventilation. In contrast, hyperventilation, an increase
in the depth and rate of breathing, may occur in response to increased acid in the blood
caused by kidney disease, uncontrolled diabetes, shock, or ingested toxic chemical agents
or drugs.
SYMPTOMS
The principal symptoms produced by diseases of the lungs are shortness of breath or air
hunger, cough, pain, and fever. Each must be considered in order to diagnose the disorder
that has caused all of them.
Shortness of Breath
How and when did it begin?
How is it affected by position?
What makes it worse—or better?