Transcript Chapter 10

Chapter 10
Pulmonary Function
During Exercise
The Respiratory System


Provides gas exchange between the
environment and the body
Regulates of acid-base balance during
exercise
Ventilation

Moving Air
Conducting and Respiratory Zones
Conducting zone
 Conducts air to
respiratory zone
 Humidifies, warms,
and filters air
 Components:
– Trachea
– Bronchial tree
– Bronchioles
Respiratory zone
 Exchange of gases
between air and blood
 Components:
– Respiratory
bronchioles
– Alveolar sacs
Pathway of Air to Alveoli
Mechanics of Breathing

Ventilation
– Movement of air into and out of the lungs via bulk
flow

Inspiration
– Diaphragm pushes downward, lowering
intrapulmonary pressure

Expiration
– Diaphragm relaxes, raising intrapulmonary pressure

Resistance to airflow
– Largely determined by airway diameter
The Mechanics of Inspiration and
Expiration
Pulmonary Volumes and Capacities


Measured by spirometry
Vital capacity (VC)
– Maximum amount of air that can be expired following a
maximum inspiration

Residual volume (RV)
– Air remaining in the lungs after a maximum expiration

Total lung capacity (TLC)
– Sum of VC and RV
Pulmonary Volumes and Capacities

Inspiratory Reserve volume (IRV)
– Maximum amount of air that can be inspired following
a normal inspiration

Expiratory reserve volume (ERV)
– Air remaining in the lungs after a normal expiration
A Spirogram Showing Pulmonary
Volumes and Capacities
Check measurements to find:



Norms for body sizes
Indications of healthy lung function
Indications of diseases/conditions that
affect ventilation
– Asthma
– Emphysema
.
Pulmonary Ventilation (VE)

The amount of air moved in or out of the
lungs per minute
– Product of tidal volume (VT)
and breathing frequency (FB)
.
– (looks similar to Q = SV x HR? )
.
VE = VT x FB
Respiration

Movement of gasses
Diffusion of Gases

Gases diffuse from high  low partial
pressure
– From lungs to blood and back to lungs
– From blood to tissue and back to blood
Partial Pressure of Gases


Each gas in a mixture exerts a portion
of the total pressure of the gas
The partial pressure of oxygen (PO2)
– Air is 20.93% oxygen
• Expressed as a fraction: 0.2093
– If total pressure of air = 760 mmHg, then
PO2 = 0.2093 x 760 = 159 mmHg
Partial Pressure and Gas Exchange
O2 Transport in the Blood

O2 is bound to hemoglobin (Hb) for
transport in the blood
– Oxyhemoglobin: O2 bound to Hb

Carrying capacity
– 201 ml O2•L-1 blood in males
• 150 g Hb•L blood-1 x 1.34 mlO2•g Hb-1
– 174 ml O2•L-1 blood in females
• 130 g Hb•L blood-1 x 1.34 mlO2•g Hb-1
Oxyhemoglobin Dissociation
Curve
O2-Hb Dissociation Curve:
Effect of pH


Blood pH declines during heavy
exercise
Results in a “rightward” shift of the
curve
– Bohr effect
– Favors “offloading” of O2 to the tissues
O2-Hb Dissociation Curve:
Effect of pH
10
8
6
4
2
Amount of O2
unloaded
Oxygen Content
(ml O2 / 100 ml blood)
20
18
16
14
12
O2-Hb Dissociation Curve:
Effect of Temperature


Increased blood temperature results in
a weaker Hb-O2 bond
Rightward shift of curve
– Easier “offloading” of O2 at tissues
O2-Hb Dissociation Curve:
Effect of Temperature
Oxygen Content
(ml O2 / 100 ml blood)
Amount
offloaded
O2 Transport in Muscle


Myoglobin (Mb) shuttles O2 from the cell
membrane to the mitochondria
Higher affinity for O2 than hemoglobin
– Even at low PO2
– Allows Mb to store O2
Dissociation Curves for
Myoglobin and Hemoglobin
Carbon Dioxide Transport

Not identical to oxygen transport
CO2 Transport in Blood



Dissolved in plasma (10%)
Bound to Hb (20%)
Bicarbonate (70%)
Carbonic Acid
binds to Hb
CO2 + H2O  H2CO3  H+ + HCO3Muscle
Normal Metabolism
Bicarbonate
CO2 Transport in Blood



Lung
Dissolved in plasma (10%)
Bound to Hb (20%)
Bicarbonate (70%)
Ventilation
CO2 + H2O  H2CO3  H+ + HCO3-
O2 replaces on Hb
CO2 Transport in Blood



Dissolved in plasma (10%)
Bound to Hb (20%)
Bicarbonate (70%)
Ventilation
Lung
CO2 + H2O  H2CO3  H+ + HCO3Muscle
Intense Exercise
– Also important for buffering H+
Release of CO2 From Blood
Effect of Respiratory Gases
on Ventilation

How do these gasses affect breathing?
Control of Ventilation

Respiratory control center in the
brainstem
– Regulates respiratory rate
– Receives neural and humoral input
• Feedback from muscles
• PO2, PCO2, H+, and K+ in blood
• PCO2 and H+ concentration in cerebrospinal
fluid
Effect of Arterial PO2 on Ventilation
Effect of Arterial PCO2 on Ventilation
Ventilation and Acid-Base Balance


Blood pH is regulated in part by
ventilation
An increase in ventilation causes
exhalation of additional CO2
– Reduces blood PCO2
– Lowers H+ concentration
H+ + HCO3-  H2CO3  H2O + CO2
Exhalation
Ventilatory Control During
Submaximal Exercise
Incremental Exercise

Linear increase in ventilation
.
– Up to ~50-75% VO2max


Exponential increase beyond this point
Ventilatory threshold (T
)
vent
.
– Inflection point where VE increases
exponentially
Ventilatory Response to Exercise:
Tvent
Is This Trainable?


Does an endurance trained person
breathe less?
Does an endurance trained person
need less oxygen?
Effect of Training on Ventilation

Ventilation is lower at same work rate
following training
– May be due to lower blood lactic acid levels
– Results in less feedback to stimulate
breathing
– Well trained produce less CO2 – stim. for
breathing
Effects of Endurance Training on
Ventilation During Exercise
Ventilatory Response to Exercise:
Trained vs. Untrained

In the trained runner
– Decrease in arterial PO2 near exhaustion
• more oxygen extracted
– pH maintained at a higher work rate
• less lactic acid produced – “aerobic metab.”
– Tvent occurs at a higher work rate
• lower relative intensity
Ventilatory Response to Exercise:
Trained vs. Untrained
Do the Lungs Limit Exercise
Performance?

Sub maximal exercise
– Pulmonary system not seen as a limitation

Maximal exercise
– Not thought to be a limitation in healthy
individuals at sea level
– May be limiting in elite endurance athletes
Questions?
End