Pulmonary Function During Exercise

Chapter 10

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

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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

20

1816

1412

10 8 6

4 2

Oxy

gen

Con

tent

(ml O

2 / 1

00 m

l blo

od)

Amount of O2

unloaded

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

Amountoffloaded

Oxy

gen

Con

tent

(ml O

2 / 1

00 m

l blo

od)

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%)

CO2 + H2O H2CO3 H+ + HCO3-

MuscleNormal Metabolism

binds to HbCarbonic Acid

Bicarbonate

CO2 Transport in Blood

Dissolved in plasma (10%) Bound to Hb (20%) Bicarbonate (70%)

CO2 + H2O H2CO3 H+ + HCO3-

Lung Ventilation

O2 replaces on Hb

CO2 Transport in Blood

Dissolved in plasma (10%) Bound to Hb (20%) Bicarbonate (70%)

CO2 + H2O H2CO3 H+ + HCO3-

– Also important for buffering H+

Muscle

Lung

Intense Exercise

Ventilation

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 (Tvent)

– Inflection point where VE increases exponentially

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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