Respiratory Regulation During Exercise

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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 dioxides 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 bloods
  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 bodys 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.

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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?