Mechanisms and Regulation of Breathing Flashcards
What are the pressures at the end of a normal breath?
Atmospheric pressure= alveolar pressure
What is elastic recoil?
- Having the property of returning to the original shape after being distorted
- To spring back
What happens as you breathe out?
- Elastic recoil in the lung pulls inwards
- Chest wall resists inward distortion from resting position
What does equilibrium result in?
Negative pleural pressure
Lung elastic recoil inward= chest wall elastic recoil outward
How does gas get into the lungs?
Expand chest wall creates differences in pressure- pressure gradient as atmospheric greater than alveolar
Describe the mechanism of inspiration
Expansion of chest wall, movement of ribs via external intercostal muscles
Inspiratory neural activity from brain via phrenic nerve
What happens at the end of a breath in?
Lung recoil is increased
Elastic forces act inward
No inspiratory neural activity
What is the difference between inspiration and expiration in terms of energy and time?
Inspiration= active, shorter Expiration= passive, longer
Why is forced expiration active?
Internal intercostals and abdominal muscles contract
What is Minute Ventilation?
Vt x fR (litres/min)
Vt- tidal volume, depth of breath
fR= respiratory frequency (breaths per minute)
What happens when central neural control is removed?
- Cortex and upper pons= slow gasping breaths
- Pons= return to rhythmic breathing
- Medulla= breathing stops
Which part of the brain is controlling voluntary/ involuntary respiratory?
Voluntary= cortex Automatic= pons, medulla, spinal cord
What are the groups in the brainstem?
Pontine Respiratory Group
Ventral Respiratory Group
Dorsal Respiratory Group
How is the basic rhythm of breathing generated?
Inspiratory neurones activate expiratory neurones Expiratory neurones (medullary neurones- VRG, DRG) inhibit respiratory neurones
What is the effect of large inspiration?
Large activation of expiratory neurones, expiratory neurones cause contraction of expiratory muscles
What things change the basic breathing pattern?
-Inhaled noxious substances
-Speech/ volition
-Sleep (pons neurones 15% drop to sleep)
Exercise
What are the feedback inputs to the respiratory rhythm generator?
Lung receptors= Slowly Adapting Receptors, Rapidly Adapting Receptors, C-fibre endings (afferent nerve fibres carried in vagus)
Chemoreceptors= central, peripheral (report to medulla)
How does lung receptor activity affect pattern of breathing?
Vagal nerves cut= slower
Vagal nerves stimulated= faster
Describe Slowly Adapting Receptors
- 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
Describe Rapidly Adapting Receptors
- 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
Describe bronchial C-fibres Endings
- In airway epithelium
- Unmyelinated nerve fibres
- Stimulated by increased interstitial fluid (oedema) and various inflammatory mediators (histamine, prostaglandins, bradykinins)
Describe Pulmonary C-fibres
Juxtapulmonary capillary receptors, J-receptors
Endings close to pulmonary capillaries
How do chemoreceptors respond to arterial O2 and CO2?
Peripheral- fast response to arterial pO2, pCO2, (H+)
Central- slow response to arterial pCO2
What is the terminology for different oxygen levels?
Above normal= hyperoxia
Normal= normoxia
Below normal= hypoxia (in blood= hypoxaemia)
What is the terminology for different CO2 levels?
Above normal= hypercapnia
Normal= normocapnia
Below normal= hypocapnia
How do central chemoreceptors work?
pCO2 in arterial blood crosses blood-brain barrier
pCO2 + H2O= (H+) + HC03-
Central chemoreceptors on surface of medulla send signals to medullary rhythm generator
What happens in severe chronic obstructive pulmonary disease?
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
How is neural activity involved in sleep?
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)What occurs during sleep?
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
What are the consequences of loss of wakefulness drive?
Patients with impaired ventilation (e.g. muscle weakness, severe lung disease, neuropathy or spinal deformity) first develop respiratory failure (raised arterial CO2) during sleep
What are the types of upper airway muscle activity?
Phasic
Tonic
Describe phasic activity
Contraction of upper airway muscles
Opening of upper airway
Facilitates inward airflow
Similar activity in diaphragm/ external intercostals which generate inspiration
Describe tonic activity
Continuous background activity
Tends to maintain patent airway
Varies with state of alertness
Similar to activity in skeletal muscles which maintain posture
How does phasic ad tonic activity relate during sleep?
Loss of tonic activity to upper airways Airways collapse (obstruct) to give cessation of breathing (apnoea)
Describe Obstructive Sleep Apnoea
Common
Fragments sleep causing daytime sleepiness
Important cause of traffic accidents
Risk factors: obesity, alcohol, nasal obstruction, anatomical abnormalities
What drugs in respiration are depressants?
- Anaesthetics= almost all
- Analgesics= opioids (morphine and its analogues)
- Sedatives (anti-anxiolytics, sleeping tablets)= benzodiazepines (diazepam, temazepam)
What drugs in respiration are stimulants?
Primary action= doxapram
Secondary action= beta 2 agonists (bronchodilators)
How can breathing control be disrupted?
- Airflow obstruction (lower or upper)
- Weakness or deformity of respiratory muscles
- Sedative drugs
