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Chapter 10

Chapter 10. PED 304 Exercise Physiology. COMPOSITION OF AMBIENT AIR. 20.93% OXYGEN 79.04 % NITROGEN .03 CARBON DIOXIDE All exert pressure from the air column, referred to as barometric pressure (760 mmHg at sea level) Partial pressure = percent concentration of a gas x total pressure.

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Chapter 10

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  1. Chapter 10 PED 304 Exercise Physiology

  2. COMPOSITION OF AMBIENT AIR • 20.93% OXYGEN • 79.04 % NITROGEN • .03 CARBON DIOXIDE • All exert pressure from the air column, referred to as barometric pressure (760 mmHg at sea level) • Partial pressure = percent concentration of a gas x total pressure

  3. CONCENTRATION AND PRESSURE • As air travels to the alveoli, it mixes with residual air, is moistened, and heated/cooled, resulting in a reduction in the partial pressures of oxygen and an increase in the partial pressure of carbon dioxide

  4. PASSIVE DIFFUSION • Blood entering the capillaries surrounding the alveoli has an oxygen partial pressure of around 40mmHg. In the alveoli, the partial pressure of oxygen is around 100mmHg. The old move from higher to lower concentration takes place, and oxygen enters the blood.

  5. PASSIVE DIFFUSION • Carbon dioxide comes into the alveoli at around 46mmHg; the carbon dioxide in the alveoli has a partial pressure of around 40mmHg. Same thing—higher to lower concentration, except it doesn’t require as high a difference because…

  6. AT THE MUSCLE • Same thing happens at the muscle—higher to lower concentrations. Partial pressure of oxygen in the muscles is around 40 (a bunch lower if exercising), and arterial blood is around 100. • During intense exercise, partial pressures of oxygen in the muscles can go down to 3mmHg, while carbon dioxide can rise to 90mmHg.

  7. Oxygen Dissociation • Four things contribute to oxygen dissociation at the tissues: • Partial pressures of oxygen and carbondioxide • Temperature • pH • 2,3 Diphosphoglycerate

  8. Ventilation & Oxygen Transportation • Respiratory center is located in the medial medulla with influences from the hypothalamus

  9. Ventilatory control • Influenced by: • Temperature • Baroreceptors • Chemoreceptors • Proprioceptors

  10. Ventilation & Oxygen Transportation • Fick Equation (oxygen uptake) – Helps determine the difference in arterial vs mixed-venous blood • Starlings Law – A muscle which is Preloaded will provide a more forceful contraction • Henry’s Law – Movement of Gas in Air & Fluids • Pressure differential between the gas above the fluid and the gas dissolved in the fluid • Oxygen requires higher pressure gradient because it’s not very soluble in blood • Bohr Effect – Heat & pH, relatively unchanged

  11. HOW IT’S CARRIED • A very small amount of oxygen is dissolved in plasma. • Most is carried attached to hemoglobin. • The four iron atoms each bind to an oxygen to form oxyhemoglobin • It binds tightly and does not require an enzyme • The partial pressures alone help to accomplish this

  12. How much is carried? • Given an average hemoglobin of 15 g/100mL (females average around 14; males 15-16), with each Hb carrying 1.34mL of oxygen, the total oxygen carried is around 20.1 mL/100 mL of blood.

  13. Ventilation & Oxygen Transportation • Hemoglobin (Hb) – Contains four iron atoms which carry oxygen. • Myoglobin – Found in skeletal and cardiac muscle – but only contains one iron molecule • Capillaries – Gas exchanged by allowing one RBC through at a time. • Alveoli – Structure which allows gas exchange in lungs • Anatomic Dead Space vs Physiologic Dead Space

  14. Carbon dioxide pressure in arterial plasma provides the most important stimulus for increased minute ventilation at rest. • If you lower this through hyperventilation, the stimulus to breathe is reduced. • During exercise, it appears that increased acidity (and with it, carbon dioxide formed when buffering is completed) stimulates ventilation.

  15. VENTILATORY CONTROL • Neurogenic stimuli from the cerebral cortex and exercising limbs cause an initial, abrupt increase in breathing when exercise starts. (Cortical Influence pg. 253) • After a short plateau, minute ventilation gradually increases to a steady state, controlled through hypothalamus, chemoreceptors, and baroreceptors.

  16. VENTILATORY CONTROL • The final phase of control involves fine tuning through peripheral sensory feedback mechanisms (temperature, carbon dioxide, hydrogen ions)

  17. VENTILATION DURING EXERCISE • During light to moderate exercise, ventilation increases linearly with oxygen uptake, with most of the contributions from tidal volume. • The point at which ventilation increases dramatically when compared to oxygen uptake is known as the ventilatory threshold.

  18. OBLA & VT • This takeoff from oxygen uptake represents lactic acid buffering (R>1.0) • Normally occurs around 55-65% of VO2max in untrained, and more than 80% in trained. • Is considered to be 4mM per L • May be due to muscle hypoxia, inability to clear enough lactate, or production of too much lactate to clear • OBLA will increase as a function of training without an increase in VO2max

  19. Additional Terms • Physiological Dead Space – Portion of alveolar volume with poor profusion of tissue. • Anatomical Dead Space – Air that fills the nose, mouth and trachea • Tidal Volume – Volume inspired or expired per breath during normal respiration

  20. Additional Terms • Inspiratory Reserve Volume • Expiratory Reserve Volume • Total Lung Capacity – Volume in lungs after max. insp • Residual Lung Volume – Volume in lungs after max exp.

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