Ventilation and Acid Base Balance

The basic concepts and terminology relating to the acid-base balance of the blood were introduced in chapter 13. In brief review, acidosis refers to an arterial pH below 7.35, and alkalosis refers to an arterial pH above 7.45. There are two components of each: respiratory and metabolic. The respiratory component refers to the carbon dioxide concentration of the blood, as measured by the PCO2. As implied by its name, the respiratory component is regulated by the respiratory system. The metabolic component is controlled by the kidneys, and is discussed in chapter 17.

Ventilation is normally adjusted to keep pace with the metabolic rate, so that the arterial PCO2 remains in the normal range. In hypoventilation, the ventilation is insufficient to "blow off' carbon dioxide and maintain a normal Pœ2. Indeed,

Chloride Shift Rbc

Plasma

From pulmonary artery

To pulmonary vein

Plasma

From pulmonary artery

To pulmonary vein

■ Figure 16.39 The reverse chloride shift in the lungs. Carbon dioxide is released from the blood as it travels through the pulmonary capillaries. A "reverse chloride shift" occurs during this time, and carbonic acid is transformed into CO2 and H2O. The CO2 is eliminated in the exhaled air.

hypoventilation can be operationally defined as an abnormally high arterial Pœ2. Under these conditions, carbonic acid production is excessively high and respiratory acidosis occurs.

In hyperventilation, conversely, the rate of ventilation is greater than the rate of CO2 production. Arterial PCO2 therefore decreases, so that less carbonic acid is formed than under normal conditions. The depletion of carbonic acid raises the pH, and respiratory alkalosis occurs.

A change in blood pH, produced by alterations in either the respiratory or metabolic component of acid-base balance, can be partially compensated for by a change in the other component. For example, a person with metabolic acidosis will hyperventilate. This is because the aortic and carotid bodies are stimulated by an increased blood H+ concentration (fall in pH). As a result of the hyperventilation, a secondary respiratory alkalosis is produced. The person is still acidotic, but not as much so as would be the case without the compensation. People with partially compensated metabolic acidosis would thus have a low pH, which would be accompanied by a low blood PCO2 as a result of the hyperventilation. Metabolic alkalosis, similarly, is partially compensated for by the retention of carbonic acid due to hypoventilation (table 16.10).

Clinical Investigation Clues

Remember that Harry had a high arterial PCO2 and a pH of 7.15. What does the pH of 7.15 represent, and what is the relationship between this pH and the arterial PCo2? What caused these conditions to occur, and how were they corrected?

Capillary

Tissue cells

Tissue cells

Capillary

The Effect Bicarbonate Blood

■ Figure 16.40 The effect of bicarbonate on blood pH. Bicarbonate released into the plasma from red blood cells buffers the H+ produced by the ionization of metabolic acids (lactic acid, fatty acids, ketone bodies, and others). Binding of H+ to hemoglobin also promotes the unloading of O2.

Table 16.10

Effect of Lung Function on Blood Acid-Base Balance

Condition

PH

Pco2

Ventilation

Cause of Compensation

Normal

Respiratory acidosis Respiratory alkalosis

High

Hypoventilation Hyperventilation

Not applicable Cause of the acidosis Cause of the alkalosis

Metabolic acidosis

Low

Low

Hyperventilation

Compensation for acidosis

Metabolic alkalosis

High

High

Hypoventilation

Compensation for alkalosis

Test Yourself Before You Continue

1. List the ways in which carbon dioxide is carried by the blood. Using equations, show how carbonic acid and bicarbonate are formed.

2. Describe the events that occur in the chloride shift in the systemic capillaries; also describe the reverse chloride shift that occurs in the pulmonary capillaries.

3. Describe the functions of bicarbonate and carbonic acid in blood.

4. Describe the effects of hyperventilation and hypoventilation on the blood pH and explain the mechanisms involved.

5. Explain why a person with ketoacidosis hyperventilates. What are the potential benefits of hyperventilation under these conditions?

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Responses

  • orazio
    How carbonic acid is formed in humans?
    7 years ago
  • fethawit
    When carbon dioxide is released from lungs a reverse chloride shift occurs?
    7 years ago
  • lucas
    How does pulminary ventilation change acid/base balance?
    7 years ago
  • craig
    How does the hemoglobin affect blood ph?
    7 years ago
  • simona
    How hemoglobin affects the acidbase balance?
    6 years ago
  • Glen
    How does ventilation change blodd pH?
    6 years ago
  • Liberata
    How does carbon dioxide affect blood ph?
    6 years ago
  • Doda
    How does low hemoglobin affect the acid base balance?
    6 years ago
  • eglantine
    How is ventilation related to acids and bases?
    5 years ago
  • bell
    How does hypoventilation affect acid base balance?
    4 years ago
  • charles
    How does ventilation and acidbase?
    3 years ago
  • dafne
    What causes abnormally high arterial PCO2 and an arterial pH of 7.15?
    3 years ago
  • fnan luwam
    How is abnormally high arterial pco2 and an arterial ph of 7.15 related?
    2 years ago
  • sarama
    How does ventilation affect blood pH balance?
    2 years ago
  • Frazer
    What impact will the increase in ventilation have on acidbase regulation?
    2 years ago
  • Helen
    How hyper nd hypoventilation affect blood ph with examples?
    2 years ago
  • melissa pisano
    How to prevent respiratory acid base imbalance in ventilator?
    1 year ago
  • JO
    What does increading ling ventilation do to ph?
    1 year ago
  • layton
    How hyper ventillation effect the ph of the blood?
    8 months ago
  • Caden
    What is role of ventilation in acid base regulation?
    7 months ago
  • amina
    What is the effect of hypoventilation on pH?
    5 months ago
  • Tove Valo
    How ventilatory system maintains acid balance?
    3 months ago
  • Kifle Bisrat
    How does ventilator change blook pH?
    2 months ago
  • jasmine
    How does acid base balance effect high respiratory rate?
    1 month ago
  • ralf
    How increased pulmonary ventilation regulates acidbase balance?
    1 month ago
  • libby
    What vent settings will alter acid PH level?
    21 days ago

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