Integrated Control of Ventilation

• What is the primary goal of respiratory control in relation to blood pH?

  Maintain acid-base homeostasis by regulating arterial CO₂ levels (PaCO₂), which influences blood pH through the bicarbonate buffer system.
• How does the bicarbonate buffer system regulate blood pH?

  The bicarbonate buffer system maintains pH via the equilibrium:

  $CO_2\ +$$\ H_2O\ \leftrightarrow\ H_2CO_3\ \leftrightarrow\ H^+$$\ +$$\ HCO_3^-$

  • Increased CO₂ → More H⁺ ions → Lower pH (acidosis)
  • Decreased CO₂ → Fewer H⁺ ions → Higher pH (alkalosis)Respiratory control modifies CO₂ levels to stabilise pH.
• What is the role of central chemoreceptors in pH regulation?

  • Located in the medulla oblongata
  • Detect changes in CSF pH, which reflect arterial CO₂ levels
  • High CO₂ → Lower CSF pH → Increased ventilation to remove CO₂
  • Low CO₂ → Higher CSF pH → Decreased ventilation to retain CO₂
• How do peripheral chemoreceptors contribute to pH regulation?

  • Located in the carotid bodies and aortic bodies
  • Detect arterial pH directly and PaCO₂ indirectly
  • If blood pH decreases (acidosis) → Stimulate ventilation to remove CO₂
  • If blood pH increases (alkalosis) → Suppress ventilation to retain CO₂
• What is respiratory compensation for metabolic acidosis?

  • Metabolic acidosis (low pH due to excess H⁺ from non-respiratory sources, e.g., lactic acid, ketoacidosis)
  • The respiratory system compensates by hyperventilation (increased breathing rate)
  • This decreases PaCO₂, shifting the bicarbonate reaction leftward to reduce H⁺ levels and raise pH
• What is respiratory compensation for metabolic alkalosis?

  • Metabolic alkalosis (high pH due to loss of H⁺, e.g., vomiting, excess bicarbonate intake)
  • The respiratory system compensates by hypoventilation (decreased breathing rate)
  • This retains CO₂, increasing H⁺ concentration and lowering pH
• How does hypoventilation affect blood pH?

  • Hypoventilation → Reduced CO₂ exhalation
  • Increases PaCO₂, driving the bicarbonate reaction rightward
  • More H⁺ is produced → Lower blood pH (respiratory acidosis)
  • The kidneys compensate by increasing H⁺ excretion and HCO₃⁻ retention
• How does hyperventilation affect blood pH?

  • Hyperventilation → Excess CO₂ exhalation
  • Decreases PaCO₂, shifting the bicarbonate reaction leftward
  • H⁺ is consumed → Higher blood pH (respiratory alkalosis)
  • The kidneys compensate by reducing H⁺ excretion and increasing HCO₃⁻ excretion
• What is the role of the kidneys in long-term pH regulation?

  • The kidneys regulate blood pH by:
  • Excreting H⁺ (when pH is low)
  • Reabsorbing HCO₃⁻ (when pH is low)
  • Excreting HCO₃⁻ (when pH is high)
  • This provides a slower but more sustained pH correction compared to respiratory compensation
• What is the relationship between CO₂, ventilation, and blood pH?

  • CO₂ and pH are inversely related:
  • High CO₂ → Low pH (acidosis) → Increased ventilation
  • Low CO₂ → High pH (alkalosis) → Decreased ventilation
  • The respiratory system adjusts ventilation rate to regulate PaCO₂, maintaining acid-base balance
• What is respiratory acidosis?

  • An accumulation of carbon dioxide (CO₂) in the blood, leading to a decrease in blood pH.
• What causes respiratory acidosis to occur?

  Hypoventilation, where $CO_2$ is retained
• What conditions can cause respiratory acidosis?

  • COPD
  • Severe asthma
  • CNS depression
• What causes the decrease in pH during respiratory acidosis?

  • The increase in CO₂ levels, which combine with water to form carbonic acid (H₂CO₃).
  • This dissociates into hydrogen ions (H⁺) and bicarbonate (HCO₃⁻), increasing the concentration of H⁺, thus lowering pH.
• What is hyperkalaemia, and how does it relate to respiratory acidosis?

  • An elevated level of potassium (K⁺) in the blood.
  • In respiratory acidosis, hyperkalaemia occurs because hydrogen ions (H⁺) move into cells to buffer the acidosis, while potassium ions (K⁺) shift out of cells to maintain electrical neutrality.
  • Leads to an increase in extracellular potassium concentration.
• Why is hyperkalaemia dangerous in respiratory acidosis?

  Can impair normal cardiac conduction, leading to arrhythmias, and in severe cases, cardiac arrest.
• What is respiratory alkalosis?

  Occurs when there is a decrease in CO₂ levels in the blood, leading to an increase in pH.
• What causes respiratory alkalosis to occur?

  Hyperventilation, where too much $CO_2$ is exhaled
• What are the conditions that respiratory alkalosis can cause?

  • Anxiety
  • Pain
  • High altitudes
  • Certain diseases like pneumonia
• What causes the increase in pH during respiratory alkalosis?

  • The decrease in CO₂ levels in respiratory alkalosis leads to less carbonic acid formation.
  • As CO₂ decreases, hydrogen ion concentration (H⁺) also decreases, resulting in an increase in pH (alkalosis).
• What is cerebral vasoconstriction, and how is it linked to respiratory alkalosis?

  • The narrowing of blood vessels in the brain. During respiratory alkalosis, the decrease in CO₂ levels causes a reduction in hydrogen ion concentration (H⁺) in the blood.
  • Leads to a constriction of cerebral blood vessels because CO₂ normally acts as a vasodilator in the brain.
  • The decreased blood flow may reduce oxygen delivery to the brain, causing symptoms like dizziness and confusion.
• How does hyperventilation lead to respiratory alkalosis?

  • Causes excessive exhalation of CO₂, leading to a drop in its concentration in the blood.
  • This results in an increase in pH, as CO₂ normally combines with water to form carbonic acid, which dissociates to release H⁺ ions.
  • Less CO₂ means fewer H⁺ ions and higher pH, resulting in alkalosis.
• What are some clinical examples where respiratory acidosis-induced hyperkalaemia is seen?

  Commonly observed in conditions like chronic obstructive pulmonary disease (COPD) or severe asthma, where airflow is obstructed, leading to CO₂ retention and the subsequent shift of K⁺ out of cells.
• What are the potential symptoms of alkalosis-induced cerebral vasoconstriction?

  • Dizziness
  • Light-headedness
  • Confusion
  • Fainting

  As the brain receives reduced blood flow and oxygen
• What is the compensatory mechanism in response to respiratory acidosis?

  Kidneys compensate by increasing the retention of bicarbonate (HCO₃⁻) to buffer the excess hydrogen ions (H⁺) and raise the blood pH back toward normal. This compensatory mechanism takes hours to days.
• What is the compensatory mechanism in response to respiratory alkalosis?

  Kidneys compensate by excreting bicarbonate (HCO₃⁻) to lower blood pH and restore balance. This process takes hours to days.
• What clinical findings would you expect in a patient with respiratory acidosis?

  • Lethargy
  • Confusion
  • Headache
  • Severe case: coma
  • Blood test show low pH, high $CO_2$ levels
  • Elevated $HCO_3^-$ after compensatory mechanisms begin
• What clinical findings would you expect in a patient with respiratory alkalosis?

  • Dizziness
  • Light-headedness
  • Tingling to extremities
  • Confusion
  • Blood test show elevated pH
  • Low $HCO_3^-$ after compensatory mechanisms begin
• How does chronic respiratory acidosis affect the body over time?

  • In chronic respiratory acidosis, such as in COPD, the kidneys gradually compensate by retaining more bicarbonate (HCO₃⁻) to neutralise the excess hydrogen ions.
  • Helps maintain pH balance, but patients may still have a slightly lower pH over time due to the persistent CO₂ retention.