1 - Control of Respiration

Question 1

Objective: Explain the loop in control of respiration

(most basic)

Answer 1

Controlled Variable (pH, P_aCO₂, P_aO₂)

↓

Sensor (central / peripheral chemoreceptor)

↓

Central Pattern Generator (brain)

↓

Effector (muscles of respiration)

↓

Controlled Variable (repeat loop)

Question 2

Objectives: Explain the role of chemoreceptors and influence of PO2, PCO2, and pH on respiration

Answer 2

• Central Chemoreceptors: Loacted in brainstem (opposite BBB)
  
  • ​Highly sensitive to CO₂ via generation of [H⁺] when interacting with water
  • H⁺, HCO₃^- can not cross BBB
• Peripheral Chemoreceptors: Located in Carotid/Aortic Arch
  
  • Highly sensitive to pH via:
    
    • Arterial [H⁺]
    • Arterial P_aCO₂ (it changes pH)
    • Arterial P_aO₂ (only when very low ~ 60 mmHG)
• BLUF: For a normal person, fluctuations in CO₂ is the main drive for respiration!

Question 3

Objectives: Explain control mechanisms during respiratory disease

Answer 3

• Chronic Hypoxia: PO₂ Peripheral Control
  
  • Non-adapting; hyperventilation increases pH, lowers PCO₂
• Low V/Q Mismatch (COPD, Asthma) w/Hypoxemia (Low PO2) and Elevated PCO₂:
  
  • CO₂ will create increased [H+] Ions
    
    • Acidosis will be compensated via renal mechanisms
  • PO₂ will drive ventilation
    
    • ​When giving O₂ to these patients, be careful–you may shut down ventilation
  • Central Chemoreceptors have adapted; Peripheral (hypoxia) have NOT

Question 4

Objectives: Explain respiratory pattern during exercise

Answer 4

• During exercise (or lung disease patients) accessory muscles and abdominal muscles outside of phrenic/external intercostal control, will begin to be used
• During exercise, CO₂ will also increase in metabolizing tissues–this will lower blood pH
  
  • Central: CO₂ can cross BBB and increase respiration
  • Peripheral: Low pH sensed, can increase respiration

Question 5

Objectives: Define respiratory control centers and respiratory drives

Answer 5

• Respiratory Rhythm: Respiratory Center or Medulla
  
  • Dorsal Respiratory Group (DRG) - Basic rhythm of breathing
    
    • Only Inspiratory Neurons - Receptors +/- effector muscles
    • Receive Signals from: Central Chemoreceptors, Peripheral Chemoreceptors, Stretch Receptors, Higher Brain Centers
  • Ventral Respiratory Group (VRG)
    
    • Expiratory - Upper Airway Diameter
    • Inspiratory - Accessory Muscles
      
      • ​Stress, Heavy exercise
  • Apneustic Center - Pons
    
    • Continually stimulates DRG/VRG
    • Apneustic Breathing - hold in inspiration, periodically interrupted by expiration
      
      • Cause: Damage to Pneumotaxic Center (within Pons)

Question 6

Objectives: Illustrate specific ventilatory patterns

Cheyne Stokes

Biot

Central Sleep Apnea

Obstructive Sleep Apnea

Kussmaul’s

Answer 6

• Cheyne-Stokes Breathing
  
  • Waxing/Waning Breathing (disconnect between pulmonary / brain CO2 sensors)
  • Brain injury/cardiac failure
• Biot’s Respiration
  
  • Hyperapnea (rhythmic, deep respiratory movements with long respiratory pauses)
  • Meningitis, disorders of cerebral circulation
  • Damage to respiratory center (trauma, stroke, drugs)
• Central Sleep Apnea (problem in brain)
  
  • Stops to airflow and thoracic effort
  • No hyperventilation/waning
• Obstructive Sleep Apnea (problem in airway)
  
  • Stop to airflow, but not thoracic effort
  • Fat neck, other stuff blocking airway
• Kussmaul’s Respiration
  
  • Hyperventilation, gasping, deep labored respiration
  • Diabetic ketoacidosis, kidney failure, diabetic coma
  • High acidosis

Question 7

Explain adaption to CO₂ and hypoxia

Answer 7

• CO₂: Chronic exposure can cause adaptation to central chemoreceptors
• Hypoxia: Will NEVER adapt at peripheral chemoreceptors with low O₂ (<60 mmHg)

Question 8

Diagram how CO₂ enters the brain to influece central chemoreceptors

Answer 8

High CO_{<strong>2</strong>} (gas)

↓

BBB (diffusion)

↓

CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃^-

↓

Increase [H⁺] or low pH

↓

Increase Rate (Rr) or Depth (V_T) of breathing

= Minute Ventilation

Question 9

Why is the central chemoreceptor so sensitive to CO₂ changes?

How does O₂ affect central chemoreceptors

Answer 9

• Buffering Capacity of CSF is very low
  
  • ​No Hb
  • Low protein levels
  • Low HCO₃^- levels
• Hypoxia does NOT drive central chemoreceptors

Question 10

Diagram how peripheral chemoreceptors are activated?

Answer 10

Low pH, High P_aCO₂, Very low P_aO₂

↓

Peripheral Chemoreceptor Activation

↓

Respiratory Control Center

↓

Hyperventilation (non-adapting for chronic hypoxia)

• BLUF: The most powerful stimulus is [H+] in arterial blood, elevation of respiration in response to increased pH is mediated by peripheral chemoreceptors

Question 11

How is respiration controlled in the case of chronic hypoxia?

What can further influence this

Answer 11

• The main respiratory drive switches from PCO₂ to PO₂
  
  • ​Does NOT adapt
• Hyperventilation - will not stop!
  
  • Increase pH
  • Decrease PaCO2
• Hypercapnia (elevated PCO₂) and/or acidosis AMPLIFY the effects of hypoxia
  
  • ​LOW O2, HIGH CO2 (low pH) = BAD BAD COMBO; VERY ACTIVATED PERIPHERAL CHEMORECEPTORS!

Question 12

Explain nervous control of ventilation

Answer 12

• Primary: Inspiration
  
  • Phrenic: C345 - Keep Diaphragm Alive!
    
    • Muscles of Inspiration
  • Intercostal: Along thoracic spinal cord
    
    • Muscles of inspiration
• Secondary: (accessory) - Forced Exhalation
  
  • Thoraco-Lumber Nerves
    
    • Internal Intercostals / Abdominal Muscles
    • Trauma can damage these
• If solving question–Location, Location, Location!

Question 13

Clinical: Congenital Central Hypoventilation Syndrom (CCHS)

Answer 13

• Rare disorder
• Inoperative Pattern Generator - No automatic control of respiration
  
  • Insensitivity of chemoreceptors to both CO2, O2, and pH
• Voluntary breathing intact
• Must use ventilator during sleep to avoid death

Question 14

What are some major conditions that alter respiratory control in the medulla oblongata?

Decrease

Increase

Answer 14

• Decrease:
  
  • Cerebral Edema - Blocks blood flow through medulla
  • Polio
  • Drugs that depress CNS (dampen response to CO₂)
    
    • Alcohol, opiates, benzos, barbituates, anesthesia
    • Respiratory Arrest is what kills you
• Increase:
  
  • Drugs
    
    • Coke, Meth, Caffeine

Question 15

How does body temprature affect ventilation?

How does pain, panic affect ventilation?

Answer 15

• Deep Hypothermia - Depress ventilation
• Fever - Increase ventilation
• Pain / Panic - Increase ventilation (panic attack = hyperventilate)