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Respiratory Regulation 
During Exercise
Chapter 9 and 10
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Pulmonary Ventilation
process by which air is 
moved into and out 
of the lungs.
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Inspiration
 Breathing in
 Active process 
 Involves diaphragm and external 
intercostal muscles.
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Expiration
 Breathing out.
 At rest, passive process. 
 The inspiratory muscles relax and the 
elastic tissue of the lungs recoils, 
returning the thoracic cage to its smaller, 
normal dimensions.
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Ventilation During Exercise
Forced or labored inspiration and 
expiration are active processes, 
dependent on muscle actions.
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Pulmonary Diffusion
 process by which 
gases are 
exchanged across 
the respiratory 
membrane in the 
alveoli.
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The respiratory membrane 
 the amount of gas exchange that occurs 
across the membrane primarily depends 
on the partial pressure of each gas, 
though gas solubility and temperature 
are also important.
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Pulmonary Diffusion
 Gases diffuse along a pressure gradient, 
moving from an area of higher pressure 
to one of lower pressure. 
 Thus oxygen enters the blood and 
carbon dioxide leaves it.
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Partial pressure of gases
 the total pressure of a mixture of gases 
equals the sum of the partial pressures 
of the individual gases in that mix.
 PO2 and PCO2.
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Oxygen Exchange
 Oxygen diffusion capacity increases as 
you move from rest to exercise. 
 When your body needs more oxygen, 
oxygen exchange is facilitated.
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Carbon Dioxide Exchange
 The pressure gradient for CO2 exchange 
is less than for O2, but carbon dioxide’s 
membrane solubility is 20 times greater 
than that of oxygen, so carbon dioxide 
crosses the membrane easily, even 
without a large pressure gradient.
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Oxygen Transport:
 Oxygen is transported in the blood 
primarily bound to hemoglobin (as 
oxyhemoglobin), though a small part of it 
is dissolved in blood plasma.
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Hemoglobin
 Hemoglobin oxygen saturation levels 
decrease (O2 unloading at muscles is 
enhanced) when: 
» PO2 decreases,
» pH decreases, and
» temperature increases.
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Hemoglobin
 Hemoglobin is usually about 98% 
saturated with oxygen. 
 This reflects a much higher oxygen 
content than our bodies require, so the 
blood’s oxygen-carrying capacity seldom 
limits performance.
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Acid-base Buffering:
 Carbon dioxide is transported in the 
blood primarily as bicarbonate ion.
 This prevents the formation of carbonic 
acid, which can cause H+ to accumulate, 
decreasing the pH.
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Acid-base Buffering:
 Smaller amounts of carbon dioxide are 
carried either dissolved in the plasma or 
bound to hemoglobin.
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a-vO2 difference
 The a-vO2 diff is the difference in the 
oxygen content of arterial and venous 
blood. 
 This measure reflects the amount of 
oxygen uptake by the tissues.
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a-vO2 difference
 Oxygen delivery to the tissues depends 
on:
» the oxygen content of the blood, 
» the amount of blood flow to the tissues, 
» and local conditions.
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a-vO2 difference
 CO2 exchange at the tissues is similar to 
O2 exchange, except that CO2 leaves 
the muscles, where it is formed, and 
enters the blood to be transported to the 
lungs for clearance.
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Respiratory Control
 The respiratory centers in the brainstem
set the rate and depth of breathing.
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Respiratory Control
 Central chemoreceptors in the brain 
respond to changes in concentrations of 
carbon dioxide and H+.
 When either of these rise, the inspiratory 
center increases respiration.
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Respiratory Control
 Peripheral receptors in the arch of the 
aorta and the bifurcation of the common 
carotid artery respond primarily to 
changes in blood oxygen levels, but also 
to changes in carbon dioxide and H+
levels.
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Respiratory Control
 If O2 levels drop too low, or if the other 
levels rise, these chemoreceptors relay 
their information to the inspiratory 
center, which in turn increases 
respiration.
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Respiratory Control
 Stretch receptors in the air passages 
and lungs can cause the expiratory 
center to shorten respiration to prevent 
over-inflation of the lungs.
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Respiratory Control
 In addition, we can exert some voluntary 
control over our respiration.
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Respiratory Control
 During exercise, ventilation shows an 
almost immediate increase, resulting 
from increased inspiratory center 
stimulation caused by the muscle 
activity itself.
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Respiratory Control
 This is followed by a more gradual 
increase that results from the rise in 
temperature and chemical changes in 
the arterial blood that are caused by the 
muscular activity.
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Respiratory Control
 Problems associated with breathing 
during exercise include:
» dyspnea, 
» hyperventilation, 
» and the Valsalva maneuver.
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Respiration and Metabolism
 During mild, steady-state exercise, 
ventilation accurately reflects the rate of 
energy metabolism.
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Respiration and Oxygen 
Uptake
 Ventilation parallels oxygen uptake. 
 The ratio of air ventilated to oxygen 
consumed is the ventilatory equivalent 
of oxygen (VE/VO2).
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Ventilatory Breakpoint
 The ventilatory breakpoint is the point at 
which ventilation abruptly increases, 
even though oxygen consumption does 
not.
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Ventilatory Breakpoint
 This increase reflects the need to 
remove excess carbon dioxide.
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Anaerobic Threshold
 The anaerobic threshold can be 
determined by identifying the point at 
which the ventilatory equivalent of 
oxygen (VE/VO2) shows a sudden 
increase while the ventilatory equivalent 
of carbon dioxide (VE/VCO2) stays 
relatively the same.
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Anaerobic Threshold
 Anaerobic threshold has been used as a 
noninvasive estimate of lactate 
threshold.
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Energy Cost of Respiration
 More than 15% of the body’s total 
oxygen consumption during heavy 
exercise can occur in the respiratory 
muscles.
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Exercise
 Pulmonary ventilation is usually not a 
limiting factor for performance, even 
during maximal effort.
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Exercise
 The respiratory muscles seem to be 
better designed for avoiding fatigue 
during long-term activity than muscles of 
the extremities.
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Exercise
 Airway resistance and gas diffusion 
usually do not limit performance in 
normal, healthy individuals.
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Exercise
 The respiratory system can limit 
performance in people with restrictive or 
obstructive respiratory disorders.Illinois State University
COPD
 Chronic Obstructive Pulmonary Disease
» Asthma
» Bronchitis
» Emphysema
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H+ Production
 Excess H+ (decreased pH) impairs 
muscle contractility and ATP formation.
 The respiratory system plays an integral 
role in maintaining acid-base balance.
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H+ Production
 Whenever H+ levels start to rise, the 
inspiratory center responds by 
increasing respiration.
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H+ Production
 Removing carbon dioxide is an essential 
means for reducing H+ concentrations.
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H+ Production
 Carbon dioxide is transported primarily 
bound to bicarbonate.
 Once it reaches the lungs, CO2 is 
formed again and exhaled.
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H+ Production
 Whenever H+ levels begin to rise, 
whether from carbon dioxide or lactate 
accumulation, bicarbonate ion can buffer 
the H+ to prevent acidosis.
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Nasal Strips
 Do they aid in exercise performance?