C H A P T E R    8
RESPIRATORY REGULATION DURING EXERCISE
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Respiration
Respiration—delivery of oxygen to and removal of carbon dioxide from the tissue
External respiration—ventilation and exchange of gases in the lung
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Internal respiration—exchange of gases at the tissue level (between blood and tissues)

External Respiration
Pulmonary ventilation—movement of air into and out of the lungs—inspiration and expiration
Pulmonary diffusion—exchange of oxygen and carbon dioxide between the lungs and blood
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RESPIRATORY SYSTEM
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INSPIRATION AND EXPIRATION
Rest
Inspiration
Expiration

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Lung Volumes


Pulmonary Diffusion
w Replenishes blood's oxygen supply that has been depleted for oxidative energy production
w Removes carbon dioxide from returning venous blood
w Occurs across the thin respiratory membrane
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RESPIRATORY MEMBRANE
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Laws of Gases
Dalton's Law: The total pressure of a mixture of gases equals the sum of the partial pressures of
the individual gases in the mixture.
Henry's Law: Gases dissolve in liquids in proportion to their partial pressures, depending on their
solubilities in the specific fluids and depending on the temperature.
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Partial Pressures of Air
w Standard atmospheric pressure (at sea level) =
760 mmHg (= Torr)
w Nitrogen (N2) is 79.04% of air; the partial pressure of nitrogen (PN2) = 600.7 mmHg
w Oxygen (O2) is 20.93% of air; PO2 = 159.1 mmHg
w Carbon dioxide (CO2) is 0.03%; PCO2 = 0.2 mmHg
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Differences in the partial pressures of gases in the aveoli and in the blood create a pressure
gradient across the respiratory membrane. This difference in pressures leads to diffusion of gases
across the respiratory membrane. The greater the pressure gradient, the more rapidly oxygen
diffuses across it.
Did You Know…?

Partial Pressures of Respiratory Gases at Sea Level
Total 100.00 760.0 760 760 706 0
H2O 0.00 0.0 47 47 47 0
O2 20.93 159.1 105 100 40 60
CO2 0.03 0.2 40 40 46 6
N2 79.04 600.7 568 573 573 0
Partial pressure (mmHg)
% in Dry Alveolar Arterial Venous Diffusion
Gas dry air air air blood blood gradient

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PO2 AND PCO2 IN BLOOD


UPTAKE OF OXYGEN INTO PULMONARY CAPILLARY
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Oxygen Transport
w Hemoglobin concentration largely determines the oxygen-carrying capacity of blood (>98% of oxygen
transported).
w Increased H+ (acidity) and temperature of a muscle allows more oxygen to be unloaded there.
w Training affects oxygen transport in muscle.
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OXYGEN-HEMOGLOBIN DISSOCIATION CURVE
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Carbon Dioxide Transport
w Dissolved in blood plasma (7% to 10%)
w As bicarbonate ions resulting from the dissociation of carbonic acid (60% to 70%)
w Bound to hemoglobin (carbaminohemoglobin)
(20% to 33%)
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wHemoglobin (Hb)—1 molecule of Hb carries 4 molecules of O2, and 100 ml of blood contains ~14–18 g
of Hb in men and ~12–14 in women.
w(1 g of Hb combines with 1.34 ml of oxygen.)
w There are ~20.1 ml of O2 per 100 ml of arterial blood in men and ~17.4 ml of O2 per 100 ml of
arterial blood in women.
w Low iron leads to iron-deficiency anemia, reducing the body’s capacity to transport oxygen—this
is more of
a problem in women than men.
The a-vO2 diff—Arterial O2 Content
–

Did You Know…?
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The increase in a-vO2 diff (difference between arterious and venous vO2) during strenuous exercise
reflects increased oxygen use by muscle cells. This use increases oxygen removal from arterial
blood, resulting in a decreased venous oxygen concentration.
–

Regulators of Pulmonary Ventilation at Rest
w Higher brain centers
w Chemical changes within the body
w Chemoreceptors
w Muscle mechanoreceptors
w Hypothalamic input
w Conscious control
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RESPIRATORY REGULATION


VENTILATORY RESPONSE TO EXERCISE
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Breathing Terminology
Dyspnea—shortness of breath.
Hyperventilation—increase in ventilation that exceeds the metabolic need for oxygen. (Voluntary
hyperventilation, as is often done before underwater swimming, reduces the ventilatory drive by
increasing blood pH.)
Valsalva maneuver—a breathing technique to trap and pressurize air in the lungs to allow the
exertion of greater force; if held for an extending period, it can reduce HR (by vagal tone). This
technique is often used during heavy
lifts.

Pulmonary Ventilation
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Ventilation (VE) is the product of tidal volume (TV) and breathing frequency (f):
VE = TV ´ f
.
.

Ventilatory Equivalent for Oxygen
w Indicates breathing economy
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w The ratio between VE and VO2 in a given time frame
.
.
w At rest—VE/VO2 = 23 to 28 L of air breathed per L VO2
per minute
.
.
.
w At max exercise—VE/VO2 = 30 L of air per L VO2
per minute
.
.
.
w Generally VE/VO2 remains relatively constant over a wide range of exercise levels
.
.

Ventilatory Breakpoint
w The point during intense exercise at which ventilation increases disproportionately to the oxygen
consumption.
w Anaerobic glycolysis increases lactate levels, which increase CO2 levels (buffering), triggering
a respiratory response and increased ventilation.
w When work rate exceeds 55% to 70% VO2max, oxygen delivery can no longer match the energy
requirements so energy must be derived from anaerobic glycolysis.
.
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VE AND VO2 DURING EXERCISE
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Anaerobic Threshold
w Point during intense exercise at which metabolism becomes increasingly more anaerobic
w Reflects the lactate threshold under most conditions, though the relationship is not always exact
w Identified by noting an increase in VE/VO2 without
a concomitant increase in the ventilatory equivalent
for carbon dioxide (VE/VCO2)
.
.
.
.
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VE/VCO2 AND VE/VO2
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ARTERIAL BLOOD AND MUSCLE pH
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