Lecture 4 - Control Of Breathing

Question 1

Role of cardiovascular and respiratory systems

Answer 1

• delivery of oxygen to the tissues for metabolism
• Removal of metabolic waste - carbon dioxide
• Lungs provide means of exchanging gases between blood ant atmosphere
• circulation enable distribution and removal to active tissues
• divisions into separate systems artificialN

Question 2

Normal respiratory function

Answer 2

• breathing 7-8L/min

- Pumping 5L/min

Question 3

Definition of respiratory failure

Answer 3

• arterial oxygen pressure

Question 4

Control system

Answer 4

• brain stem: generates rhythm under autonomic control - oscillating pattern of neuronal activity
• spinal cord, phrenic nerves
• central chemoreceptors (Co2)
• peripheral chemoreceptors (O2)
• proprioceptors and others

Question 5

Partial pressures - Dalton’s law

Answer 5

• 80% N2
• 20% O2
• pressure in room is about 760mmHg -> 20% of that is O2 so about 150mmHg/
• 45 mmhg in lung, 40 in artery

Question 6

Normal blood gas measurements: arterial

Answer 6

• O2: 95-100mmHg
• CO2: 40 mmHg
• pH - 7.4
• BE - 0
• Bicarb - 26 Meq/L

Question 7

Mechanisms of a low arterial oxygen pressure

Answer 7

• Hypoventilation : 02 decreases, CO2 increases
• Ventilation/Perfusion mismatch
• Shunt: blood and air dont meet cause blood doesnt go all the way to Alveoli
• Diffusion defect: 0.35 msec for exchange to occur
• Low inspired oxygen percentage or pressure - at high altitudes

Question 8

How ventilation influences CO2 and O2

Answer 8

• if ventilation increases: arterial CO2 decreases, PaO2 increases

Question 9

Central chemoreceptors

Answer 9

• brain stem ventral surface
• CO2 and pH sensitive
• inputs to central oscillator and cardiovascular controller
• linear ventilatory response
• CO2 is very soluble, affects pH brain stem very quickly

Question 10

Peripheral chemoreceptors

Answer 10

• Carotid body (aortic arch)
• oxygen sensitive (also CO2)
• Nonlinear response/linear to oxygen saturation
• don’t respond to ocygen until saturation is 90% -> Arterial pressure 60mmHg

Question 11

Relationship between partial pressure and saturation

Answer 11

• in normal condition - all the hemoglobbin is saturated
• if you hit the 60mmHg arterial pressure - the configuration of hemoglobin drops - release the oxygen - less saturation

CO2 doesnt follow that curve because its much more diffusible

Question 12

Patterns of respiratory failure

Answer 12

• won’t breathe - pump or control problem
• Can’t breathe - ling (gas exchange) problem
• combination of both - COPD
• hypercapnic respiratory failure - will always be worse in sleep, and this will have played a key role in disease progression

Question 13

Two patterns of respiratory failure

Answer 13

• Hypoxix respiratory failure - low arterial O2 with normal or low CO2 - Type A (“Pink Puffer”)
• Hypercapnic respiratory failure - low arterial O2 with high CO2 - Type B (Blue bloater)

Question 14

Sleep and respiratory failure

Answer 14

• breathing is almost always worse during sleep
• breathing control: Wake/ Forebrain/behavioral drive
• NREM sleep - breathing controlled by brainstem
• REM sleep - Forebrain inputs/ critical role of descending motor inhibition

Question 15

Role of sleep disordered breathing

Answer 15

• any disease with respiratory failure
• not IF a problem
• it is how much of a problem
• Treatable
• oxygen therapy
• CPAP and or NIPPV

Question 16

Hypercapnic respiratory

Answer 16

• all have sleep disorder: upper airway obstruction/hypoventilation
• always worse in REM sleep
• Critical clinical message: both night and daytime hypoventilation can be reversed