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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.

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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?