concentration (see Figure 13–41), due to the gen-
eration and release of lactic acid into the blood. This change
concentration is responsible, in part, for stimulating the
hyperventilation accompanying strenuous exercise.
A variety of other factors play some role in stimulating ven-
tilation during exercise. These include (1) reﬂ ex input from
mechanoreceptors in joints and muscles; (2) an increase in body
temperature; (3) inputs to the respiratory neurons via branches
from axons descending from the brain to motor neurons sup-
plying the exercising muscles; (4) an increase in the plasma epi-
nephrine concentration; (5) an increase in the plasma potassium
concentration due to movement of potassium out of the exercis-
ing muscles; and (6) a conditioned (learned) response mediated
by neural input to the respiratory centers. The operation of this
last factor can be seen in
. There is an abrupt
increase—within seconds—in ventilation at the onset of exer-
cise and an equally abrupt decrease at the end; these changes
occur too rapidly to be explained by alteration of chemical con-
stituents of the blood or by altered body temperature.
summarizes various factors that inﬂ u-
ence ventilation during exercise. The possibility that oscilla-
tory changes in arterial
, or H
despite unchanged average levels of these variables, and play
some role has been proposed, but this remains unproven.
Other Ventilatory Responses
A group of responses protect the respiratory system from irri-
tant materials. Most familiar are the cough and the sneeze
reﬂ exes, which originate in receptors located between airway
epithelial cells. The receptors for the sneeze reﬂ ex are in the
nose or pharynx, and those for cough are in the larynx, tra-
chea, and bronchi. When the receptors initiating a cough are
stimulated, the medullary respiratory neurons reﬂ exly cause a
deep inspiration and a violent expiration. In this manner, par-
ticles and secretions are moved from smaller to larger airways,
and aspiration of materials into the lungs is also prevented.
The effect of exercise on ventilation, arterial gas pressures, and
hydrogen ion concentration. All these variables remain constant during
moderate exercise; any change occurs only during strenuous exercise,
when the person is actually hyperventilating (decrease in
Adapted from Comroe.
Minute ventilation (L/min)
Ventilation changes during exercise. Note (1) the abrupt increase at
the onset of exercise and (2) the equally abrupt but larger decrease
at the end of exercise.
Summary of factors that stimulate ventilation during exercise.
Note: ? indicates a theoretical input.
The existence of chemoreceptors in the pulmonary artery has been
suggested. Hypothesize a function for peripheral chemoreceptors
located on and sensing the
of the blood in the
Answer can be found at end of chapter.
? Oscillatory changes