Integrated control of Breathing

Question 1

Define respiratory acidosis

Answer 1

Low pH
High PaCO2
Hypoventilation is responsible for this

Question 2

Define respiratory alkalosis

Answer 2

High pH
Low PaCO2
Hyperventilation is responsible for this

Question 3

Define metabolic acidosis

Answer 3

Low pH
Low [HCO3-]
Excessive metabolic acid production and/or increased excretion of HCO3- is responsible for the decreased pH

Question 4

Define metabolic alkalosis

Answer 4

High pH
High [HCO3-]
Reduced metabolic acid production or reduced excretion of HCO3- is responsible for the increased pH

Question 5

How do respiratory control pathways and acid-base balance mechanisms interact during acidosis

Answer 5

decrease in pH ->
increase in respiratory chemoreceptor activity ->
increase in ventilation ->
increase in CO2 removal ->
decrease in PaCO2 ->
increase in pH

Question 6

How do respiratory control pathways and acid-base balance mechanisms interact during alkalosis

Answer 6

increase in pH ->
decrease in respiratory chemoreceptor activity ->
decrease in ventilation ->
decrease in CO2 removal ->
increase in PaCO2 ->
decrease in pH (to within normal range)

Question 7

What is respiratory acidosis associated with

Answer 7

Pathological states involving:

• chronic respiratory failure
• hypoventilation
• accumulation of CO2
  e. g COPD

Question 8

What is respiratory alkalosis associated with

Answer 8

pathological states involving:

• hyperventilation
• excessive removal of CO2
  e. g. anxiety or altitude-induced hyperventilation

Question 9

What is associated with metabolic acidosis

Answer 9

Pathological states involving:
- excessive acid production (sepsis, ketoacidosis)
OR
- excessive excretion of HCO3- (renal failure)

Question 10

What is associated with metabolic alkalosis

Answer 10

Pathological states involving;

• excessive consumption of basic substances e.g antacid abuse
• excessive secretion of acid from the body e.g vomiting
• deficient absorption of HCO3 from the GI tract e.g chronic diarrhoea
• excessive reabsorption of HCO3 e.g. renal dysfunction

Question 11

Describe Acidosis-induced hyperkalaemia

Answer 11

Acidosis =
↑blood [H+] =
disrupted intra/extracellular H+ gradients = ↓H+/Na+ exchange =
↓Na+/K+ exchange =
↓ cellular K+ absorption =
K+ accumulation in extracellular fluid and blood =
hyperkalaemia

K+ have critical roles in membrane potential and muscle function, cells such as skeletal muscle and cardiac pacemaker cells are adversely effect, as can be observed by the symptoms of cardiac arrhythmia and muscle weakness observed in patients with hyperkalaemia.

Question 12

Describe Alkalosis-induced vasoconstriction

Answer 12

Hyperventilation =
↓PaCO2 =
↓ CO2-induced vasodilation of cerebral arteries =
↑ cerebral vasoconstriction =
↓ cerebral blood flow =
light-headedness, headaches, seizures, loss of consciousness, etc.