Pulmonary Ventilation during
Exercise
Ventilation in Steady Rate Exercise
During light & moderate steady rate exercise,
VE:VO2 linear relationship.
 Ventilatory equivalent for oxygen (VE:VO2): ratio
of minute ventilation to oxygen uptake.

– Usually 25 : 1 during submaximal exercise up to 55%
max.
Ventilation in Steady Rate Exercise

Ventilatory response to fixed
level of submaximal exercise
can be divided into 4 phases.
1.
2.
3.
4.

Sudden increase at onset.
Ventilation gradually
increases to higher steadyrate level.
Steady state level of
ventilation maintained.
Recovery period gradual
return to resting levels.
Phase IV higher than resting
levels coincide with EPOC.
Ventilation in Steady Rate Exercise

Ventilatory equivalent for carbon dioxide
(VE:VO2): ratio of minute ventilation to carbon
dioxide produced.
– Remains constant during steady rate exercise because
pulmonary ventilation eliminates CO2 .
Ventilation in Non-Steady-Rate
Exercise
Minute ventilation (VE)
increases in proportion
to oxygen consumption
over range from rest to
moderate exercise.
 VE increases disproportionately to oxygen
consumption over
range from moderate
to strenuous.

Ventilation in Non-Steady-Rate
Exercise

The point at which
ventilation increases
disproportionately
with oxygen uptake
during incremental
exercise is termed:
ventilatory threshold
(VT).
Ventilation in Non-Steady-Rate
Exercise
Lactic acid generated
during anaerobic
glycolysis is buffered
in blood by sodium
bicarbonate.
Lactic acid + NaHCO3 →
Na Lactate + H2CO3 →
H20 + CO2

Ventilation in Non-Steady-Rate
Exercise
The excess, nonmetabolic CO2
stimulates ventilation.
 Recall that metabolic
CO2 is produced in
Krebs Cycle in
oxidation of acetyl
CoA.

Ventilation in Non-Steady-Rate
Exercise



The non-metabolic CO2
from buffering HLa drives
increased VE to eliminate it,
so VE: VCO2 remains
constant.
The increased in VE
exceeds increase in VO2
disproportionately.
The point at which VEO2
breaks with linearity is the
ventilatory threshold.
RER = 1 where two lines intersect. R values > 1 indicate CO2 production
exceeds O2 consumption, evidence of non-metabolic CO2 production.
Ventilation in Non-Steady-Rate
Exercise

As exercise intensity
increases, blood lactate
begins to systematically
increase over a baseline
value of 4 mM/L termed
onset of blood lactate.

Blood lactate
accumulation associated
with changes in CO2
production, blood pH,
bicarbonate, [H+], RER.
Ventilation in Non-Steady-Rate
Exercise

Although variables (CO2
production, blood pH,
bicarbonate, [H+], RER)

are
related to OBLA,
doubtful that VT can be
used to denote onset of
anaerobic metabolism.
OBLA directly assessed
by measuring lactate
level in blood.
Ventilation in Non-Steady-Rate
Exercise

Common practice to
use “bloodless”
techniques e.g. R >1,
or break in ventilatory
equivalent for oxygen
to denote anaerobic
threshold.
Does Ventilation Limit Aerobic
Capacity for Average Person?



If inadequate breathing
capacity limited aerobic
capacity, ventilatory
equivalent for oxygen
would decrease.
Actually, healthy person
tends to over-breathe in
relation to VO2.
In strenuous exercise,
decreases arterial PCO2 &
increase Alveolar PO2.
Work of Breathing

Two major factors determine
energy requirements of
breathing
1.
2.


Compliance of lungs
Resistance of airways to
smooth flow of air
As rate & depth of breathing
increase during exercise,
energy cost of breathing
increases too.
At maximal exercise when
VE= 100 L/m, oxygen cost of
breathing represents 10-20%
of total VO2.
Work of Breathing

Acute effects of 15 puffs on
a cigarette during a 5minute period
– 3 fold increase in airway
resistance
– Lasts an average 35 minutes

Smokers exercising at 80%
– Energy requirement of
breathing after smoking was
14% of oxygen uptake
– Energy requirement of
breathing no cigarettes was
only 9%.
References



Axen and Axen. 2001. Illustrated Principles of
Exercise Physiology. Prentice Hall.
Kapit, Macey, Meisami. 1987. Physiology
Coloring Book. Harper & Row.
McArdle, Katch, Katch. 2006. Image
Collection Essentials of Exercise Physiology,
3rd ed. Lippincott William & Wilkens.