Chapter Two
CARDIO-RESPIRATORY EXERCISE
PHYSIOLOGY
GAS EXCHANGE
Key Point –
Gas exchange is continuously occurring
between air, blood, and tissue. Gases move by a
passive process called diffusion along a gradient
from high pressure to low pressure. The
challenge during exercise is to ensure that the
gradient is maintained, requiring changes in
ventilation and in the cardiovascular system.

GAS EXCHANGE
Gas exchange in the lungs as well as in other body
tissues, takes place according to a passive
process known as diffusion.
 Gas will move along a gradient from an area of
higher partial pressure to lower partial pressure.
 Partial pressure is similar to concentration, but
reprents the pressure exerted by a single gas
(ex.O2) within a mixture (ex. Air, blood, tissue fluid)

GAS EXCHANGE
In the lungs, the air breathed in is high in O2
and low in carbon dioxide.
 The blood being pumped to the lungs from the
active tissue via the heart is lower in O2 and
higher in carbon dioxide.
 Meaning…oxygen will diffuse from the alveolus
into the blood and carbon dioxide will diffuse
form the blood into the alveolus.

GAS EXCHANGE
Therefore, the blood leaving the lungs, now
high in oxygen and low in carbon dioxide will be
pumped to the tissues via the heart.
 At the tissues where oxygen is being used up
and carbon dioxide produced the pressure
gradient will drive oxygen from blood into
tissues and carbon dioxide from tissues into
the blood.

GAS EXCHANGE

During exercise, the pressure gradient at the
tissues and lungs becomes greater as more
oxygen is being used up and more carbon
dioxide is being produced (refer to figure 2.3).
GAS EXCHANGE
The challenge for the lungs is to maintain
resting partial pressures in the alveoli.
 This is achieved by breathing out the air with
less oxygen and more carbon dioxide and then
breathing in fresh air to maintain the pressure
gradients for diffusion to occur.
 Otherwise exercise could not be sustained for
long.

GROUP WORK
How would you use a flow map to illustrate the
following:
1. Ventilatory system
2. Gas exhange in the lungs
In your groups discuss each of these in a
separate flow map. This will count as a quiz
grade! You may use your notes. Group
assignments are on the board.
VENTILATION DURING EXERCISE
Ve = minute ventilation and describes the
volume of air being exhaled per minute (and
inhaled since we do not store air)
 Ve is determined as the product of the size of
each breath (Vt = tidal volume) multiplied by
the number of breaths per minute (Bf = breath
frequency).
