The mean values for arterial Po2 and Pco2 do not change during exercise

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- Arterial pH does not change during moderate exercise, although it may decrease during strenuous exercise because of lactic acidosis.

3. On the other hand, venous Pco2 increases during exercise because the excess C02 produced by the exercising muscle is carried to the lungs in venous blood.

Table 4-7. Summary of Respiratory Responses to Exercise



02 consumption C02 production Ventilation rate

T (matches 02 consumption/C02 production) No change

No change in moderate exercise 4- in strenuous exercise (lactic acidosis)

Arterial Po2 and PcO; Arterial pH

Venous Pco2 Pulmonary blood flow (cardiac output) V/Q ratios

More evenly distributed in lung

V/Q = ventilation/perfusion.

4. Pulmonary blood flow increases because cardiac output increases during exercise. As a result, more pulmonary capillaries are perfused, and more gas exchange occurs. The distribution of V/Q ratios throughout the lung is more even during exercise than when at rest, and there is a resulting decrease in the physiologic dead space.

B. Adaptation to high altitude (Table 4-8)

1. Alveolar Po2 is decreased at high altitude because the barometric pressure is decreased. As a result, arterial Po2 is also decreased (hypoxemia).

2. Hypoxemia stimulates the peripheral chemoreceptors and increases the ventilation rate (hyperventilation). This hyperventilation produces respiratory alkalosis, which can be treated by administering acetazol-amide.

3. Hypoxemia also stimulates renal production of erythropoietin, which increases the production of RBCs. As a result, there is increased hemoglobin concentration, increased 02-carrying capacity of blood, and increased 02 content of blood.

4. 2,3-DPG concentrations are increased, shifting the hemoglobin-02 dissociation curve to the right. There is a resulting decrease in affinity of hemoglobin for 02 that facilitates unloading of 02 in the tissues.

5. Pulmonary vasoconstriction is another result of hypoxemia (hypoxic vasoconstriction). Consequently, there is an increase in pulmonary arterial pressure, increased work of the right side of the heart against the higher resistance, and hypertrophy of the right ventricle.

Table 4-8. Summary of Adaptation to High Altitude

Parameter Response

Alveolar Po2 Arterial Po2 Ventilation rate Arterial pH

Hemoglobin concentration 2,3-DPG concentration Hemoglobin-02 curve Pulmonary vascular resistance

4- (resulting from -1- barometric pressure) I (hypoxemia) T (hyperventilation) T (respiratory alkalosis) T (polycythemia) t

Shift to right; I affinity

DPG = diphosphoglycerate.

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  • EUAN
    Does arterial PCO2 increase during exercise?
    3 years ago
  • efrain
    Does po2 decrease during excercisee?
    2 years ago
  • mira
    Does arterial ph change during exercise?
    1 year ago
  • jorge
    What happen to pco2 during excerise?
    1 year ago
  • arto
    How decreased PO2 affects pulmonary vascular resistance?
    11 months ago
  • winta
    How does a change in po2 or pco2 stimulate ventilation?
    10 months ago
  • Benjamin
    How does pH and PCO2 change during excersie?
    6 months ago
  • Daniela
    What happens to paco2 as we exercise?
    3 months ago
  • michelle watkins
    Does pco2 increase as po2 decrease?
    2 months ago
  • Wegahta Fikru
    How do you decrease alveolar po2?
    24 days ago

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