Physiological Consequences of Respiratory Centre Depression and Hypoventilation

Question 1

Central chemoreceptors are located ________ and respond to

Answer 1

in the pons and medulla of the brainstem

respond to PaCO2 via CSF H+ ions

Question 2

Peripheral chemoreceptors are located in _____ and respond to

Answer 2

carotid bodies, aortic arch

PaO2, PaCO2, pH

Question 3

Ventilation is more sensitive to

Answer 3

PaCO2 (or its affects on ph): small change = big change in ventilation

PaO2 must drop significantly (<60mmHg) before ventilation increases significantly

**sensitivity varies significantly among people**

Question 4

In exercise, PaO2, PaCO2, and pH

Answer 4

are held constant by ventilation matching O2 consumption/CO2 production

Question 5

Beyond the anaerobic threshold, PaO2, PaCO2, and pH

Answer 5

PaO2 remains constant

PaCO2 and pH decline due to increase in ventilation and lactic acid, respectively

Question 6

What are causes of hypoventilation?

Answer 6

• reduced respiratory centre activity
• neuromuscular disease
• chest wall deformity (gross)
• obesity (gross)
• sleep disordered breathing

Question 7

What are the three clinical types of sleep disordered breathing?

Answer 7

• obstructive sleep apnoea
• central sleep apnoea
• obesity hypoventilation syndrome

Question 8

What distinguishes OSA from CSA on polysomnogram?

Answer 8

chest effort, measured by bands

Question 9

When does O2 decrease in OSA?

Answer 9

when the person starts to breathe again - circulatory lag between decline from apnoea and decrease in circulatory O2

Question 10

What is the management for OSA?

Answer 10

• underlying cause e.g. obesity
• application of positive airway pressure - CPAP
• lying on side
• mandibular advancement split to keep jaw and tongue forward in sleep
• surgical procedures to remove airway soft tissue

Question 11

How does CPAP work?

Answer 11

• application of constant positive airway pressure to the nose during sleep
• 4-20cm H2O pressure, n ~10cm
• positive pressure is > atmospheric pressure tf airways splinted open

Question 12

What are the causes of central sleep apnoea?

Answer 12

• major cause is Cheyne Stokes breathing
• in adults with respiratory centre damage, chronic heart failure
  
  • low CO decreases chemical stimuli to brainstem –> apnoeas
• in newborns with immature respiratory systems
• when unacclimatized to high altitudes
• manage underlying CHF, BiPAP, or CPAP

Question 13

What is obesity hypoventilation?

Answer 13

• large abdomen restricts abdomen leading to hypoventilation at night
• tx with BiPAP and weight reduction
• sensitive to supplemental O2

Question 14

What is the consequence of severe sleep disordered breathing?

Answer 14

• body comes to accept lower levels of O2 and higher levels of CO2 during sleep
• this can spill over into daytime
  
  • development of chronic hypoxia and hypercapnea in pt with COPD, severe pulmonary fibrosis, and neuromuscular disease
  • chronic compensated respiratory acidosis
    
    • slow development of hypercapnea leads to compensation, where PaCO2 and HCO3 are high, and pH low

Question 15

What happens if you give supplemental O2 to someone with chronic hypercapnea?

Answer 15

• adaptation to chronic hypercapnea is a dependency on the hypoxic drive to breathe
  
  • hypercapnia does not stimulate ventilation
• tf giving supplemental O2 can reduce the hypoxic drive to breathe, causing acute hypoventilation

Question 16

How do patients with chronic hypercapnoea present?

Answer 16

• chronically elevated CO2
• chronically low O2 due to chronic hypoventilation
• oxygen administration can lead to acute hypoventilation due to their increased reliance on the hypoxic drive to breathe (less sensitive to the CO2 drive to breathe)