Page 76 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

4 Respiration, Acid–Base Balance F. Lang

Overview of diffusion can also be caused by an increased
distance between alveoli and blood capillaries
Breathing through the lungs has two func- (→ A2; → p. 70,80). If alveoli and capillaries
tions: firstly, to supply O 2 to the blood and, are completely separated from one another,
secondly, to regulate the acid–base balance this results in both a functional dead space
via the CO 2 concentration in the blood. The (nonperfused alveoli) and an arteriovenous
mechanics of breathing serve to ventilate the shunt.
alveoli, through whose walls O 2 can diffuse Restrictive and obstructive lung disease as
into the blood and CO 2 can diffuse out. Respira- well as cardiovascular disease may affect lung
tory gases in the blood are largely transported perfusion (→ A3; → p. 80). Decreased perfu-
in bound form. The amount transported de- sion results in a reduced amount of gases
pends, among other factors, on the concentra- being transported in blood, despite adequate
tion in blood and on pulmonary blood flow O 2 saturation and CO 2 removal in the alveoli. If
(perfusion). It is the task of respiratory regula- flow resistance is increased, severe conse-
tion to adapt ventilation to the specific re- quences for the circulation are possible, be-
quirements. cause the entire cardiac output (CO) must
A number of disorders can affect breathing pass through the lungs (→ p. 80).
Breathing is also impaired in dysfunction of
in such a manner that ultimately sufficient O 2
uptake and CO 2 release can no longer be guar- the respiratory neurons (→ p. 82) as well as of
anteed. the motoneurons, nerves, and muscles that are
In obstructive lung disease (→ p. 76) flow controlled by them (→ p. 68). The changes in
resistance in the respiratory tract is raised and breathing movement that occur when the
ventilation of the alveoli is thus impaired breathing regulation is abnormal (→ Table 1)
(→ A1). The primary consequence is hypo- do not, however, necessarily lead to corre-
ventilation in some alveoli (abnormal distri- sponding changes of alveolar ventilation.
bution; → p. 72) or of all alveoli (global hypo- Consequences of inadequate breathing can
ventilation). If alveolar ventilation ceases be hypoxemia (→ A5; → p. 84), hypercapnia or
completely, a functional arteriovenous shunt hypocapnia (increased or decreased CO 2 con-
occurs. However, hypoxia leads to constriction tent, respectively; → A4; → p. 86ff.) in arterial-
of the supplying vessels, thus diminishing ized blood. The supply of O 2 to the cells as well
blood flow to the underventilated alveoli. as the removal of CO 2 from the periphery do
In restrictive lung disease (→ p. 74) the loss not only depend on adequate respiration but
of functioning lung tissue reduces the area of also on unimpaired oxygen transport in the
diffusion and in this way impairs gaseous ex- blood (→ chap. 3) and on intact circulation
change. There is also a reduced area of diffu- (→ chap. 7).
sion in emphysema (→ p. 78), a condition char-
acterized by alveoli that have a large lumen Table 2 Definition of Some Parameters
but are also diminished in number. Disorders of Ventilation
Tidal volume (V T ) volume of normal inspira-
Table 1 Terms for Various Breathing Activities tion and expiration
Hyperpnea increased breathing movement Vital capacity (VC) volume of maximal
expiration after maximal
Eupnea normal breathing movements inspiration
Hypopnea decreased breathing movements
Apnea arrested breathing Maximal breathing maximal ventilation (L/min)
Bradypnea decreased rate of breathing capacity (V ˙ max ) achieved in a short period
of time (usually 10 s)
Tachypnea increased rate of breathing
Dyspnea labored breathing Compliance (C) lung distensibility
(subjective feeling) Forced expiration volume maximal volume expired
Asphyxia inability to breathe (FEV 1 ) in 1 second
66 Orthopnea labored breathing, except in Functional residual total residual volume
the sitting or upright position capacity (FRC) after normal expiration
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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