Mechanisms and Regulation of Breathing

Question 1

What are the pressures at the end of a normal breath?

Answer 1

Atmospheric pressure= alveolar pressure

Question 2

What is elastic recoil?

Answer 2

• Having the property of returning to the original shape after being distorted
• To spring back

Question 3

What happens as you breathe out?

Answer 3

• Elastic recoil in the lung pulls inwards

- Chest wall resists inward distortion from resting position

Question 4

What does equilibrium result in?

Answer 4

Negative pleural pressure

Lung elastic recoil inward= chest wall elastic recoil outward

Question 5

How does gas get into the lungs?

Answer 5

Expand chest wall creates differences in pressure- pressure gradient as atmospheric greater than alveolar

Question 6

Describe the mechanism of inspiration

Answer 6

Expansion of chest wall, movement of ribs via external intercostal muscles
Inspiratory neural activity from brain via phrenic nerve

Question 7

What happens at the end of a breath in?

Answer 7

Lung recoil is increased
Elastic forces act inward
No inspiratory neural activity

Question 8

What is the difference between inspiration and expiration in terms of energy and time?

Answer 8

Inspiration= active, shorter
Expiration= passive, longer

Question 9

Why is forced expiration active?

Answer 9

Internal intercostals and abdominal muscles contract

Question 10

What is Minute Ventilation?

Answer 10

Vt x fR (litres/min)
Vt- tidal volume, depth of breath
fR= respiratory frequency (breaths per minute)

Question 11

What happens when central neural control is removed?

Answer 11

• Cortex and upper pons= slow gasping breaths
• Pons= return to rhythmic breathing
• Medulla= breathing stops

Question 12

Which part of the brain is controlling voluntary/ involuntary respiratory?

Answer 12

Voluntary= cortex
Automatic= pons, medulla, spinal cord

Question 13

What are the groups in the brainstem?

Answer 13

Pontine Respiratory Group
Ventral Respiratory Group
Dorsal Respiratory Group

Question 14

How is the basic rhythm of breathing generated?

Answer 14

Inspiratory neurones activate expiratory neurones 
Expiratory neurones (medullary neurones- VRG, DRG) inhibit respiratory neurones

Question 15

What is the effect of large inspiration?

Answer 15

Large activation of expiratory neurones, expiratory neurones cause contraction of expiratory muscles

Question 16

What things change the basic breathing pattern?

Answer 16

-Inhaled noxious substances
-Speech/ volition
-Sleep (pons neurones 15% drop to sleep)
Exercise

Question 17

What are the feedback inputs to the respiratory rhythm generator?

Answer 17

Lung receptors= Slowly Adapting Receptors, Rapidly Adapting Receptors, C-fibre endings (afferent nerve fibres carried in vagus)
Chemoreceptors= central, peripheral (report to medulla)

Question 18

How does lung receptor activity affect pattern of breathing?

Answer 18

Vagal nerves cut= slower

Vagal nerves stimulated= faster

Question 19

Describe Slowly Adapting Receptors

Answer 19

• Stretch receptors
• Mechanoreceptors situated close to airway smooth muscle
• Stimulated by stretching of airway walls during inspiration
• Help initiate expiration and prevent over inflation of the lungs
• Initiate Hering-Breuer inflation reflex (prolonged inspiration produces prolonged expiration)
• Afferent fibres= myelinated

Question 20

Describe Rapidly Adapting Receptors

Answer 20

• Irritant receptors
• Located in airway epithelium
• Primarily a mechanoreceptor so respond to rapid lung inflation
• Respond to chemicals (e.g. histamine), smoke, dust
• RARs in trachea and large bronchi initiate cough, mucus production, bronchoconstriction
• Afferent fibres= myelinated

Question 21

Describe bronchial C-fibres Endings

Answer 21

• In airway epithelium
• Unmyelinated nerve fibres
• Stimulated by increased interstitial fluid (oedema) and various inflammatory mediators (histamine, prostaglandins, bradykinins)

Question 22

Describe Pulmonary C-fibres

Answer 22

Juxtapulmonary capillary receptors, J-receptors

Endings close to pulmonary capillaries

Question 23

How do chemoreceptors respond to arterial O2 and CO2?

Answer 23

Peripheral- fast response to arterial pO2, pCO2, (H+)

Central- slow response to arterial pCO2

Question 24

What is the terminology for different oxygen levels?

Answer 24

Above normal= hyperoxia
Normal= normoxia
Below normal= hypoxia (in blood= hypoxaemia)

Question 25

What is the terminology for different CO2 levels?

Answer 25

Above normal= hypercapnia Normal= normocapnia Below normal= hypocapnia

Question 26

How do central chemoreceptors work?

Answer 26

pCO2 in arterial blood crosses blood-brain barrier pCO2 + H2O= (H+) + HC03- Central chemoreceptors on surface of medulla send signals to medullary rhythm generator

Question 27

What happens in severe chronic obstructive pulmonary disease?

Answer 27

Hypoxia and CO2 build up= chronic hypercapnia= loss of sensitivity of central chemoreceptors Drive to breathing =hypoxia, drive abolished if patient given high inspired O2= further hypoventilation= further increase in arterial pCO2= CO2 narcosis, acidosis= death

Question 28

How is neural activity involved in sleep?

Answer 28

``` Midbrain neural activity stimulates breathing during wakefulness ("wakefulness drive to breathe" Neural activity (cortex, pons, medulla) also regulates muscles in the upper airway (above the trachea) ```

Question 29

What occurs during sleep?

Answer 29

Respiratory drive increases (loss of wakefulness drive)- reduction in metabolic rate, reduced input from higher centres such as pons and cortex Loss of tonic neural drive to upper airway muscles

Question 30

What are the consequences of loss of wakefulness drive?

Answer 30

Patients with impaired ventilation (e.g. muscle weakness, severe lung disease, neuropathy or spinal deformity) first develop respiratory failure (raised arterial CO2) during sleep

Question 31

What are the types of upper airway muscle activity?

Answer 31

Phasic | Tonic

Question 32

Describe phasic activity

Answer 32

Contraction of upper airway muscles Opening of upper airway Facilitates inward airflow Similar activity in diaphragm/ external intercostals which generate inspiration

Question 33

Describe tonic activity

Answer 33

Continuous background activity Tends to maintain patent airway Varies with state of alertness Similar to activity in skeletal muscles which maintain posture

Question 34

How does phasic ad tonic activity relate during sleep?

Answer 34

``` Loss of tonic activity to upper airways Airways collapse (obstruct) to give cessation of breathing (apnoea) ```

Question 35

Describe Obstructive Sleep Apnoea

Answer 35

Common Fragments sleep causing daytime sleepiness Important cause of traffic accidents Risk factors: obesity, alcohol, nasal obstruction, anatomical abnormalities

Question 36

What drugs in respiration are depressants?

Answer 36

- Anaesthetics= almost all - Analgesics= opioids (morphine and its analogues) - Sedatives (anti-anxiolytics, sleeping tablets)= benzodiazepines (diazepam, temazepam)

Question 37

What drugs in respiration are stimulants?

Answer 37

Primary action= doxapram | Secondary action= beta 2 agonists (bronchodilators)

Question 38

How can breathing control be disrupted?

Answer 38

- Airflow obstruction (lower or upper) - Weakness or deformity of respiratory muscles - Sedative drugs