Workshop: Respiratory System Flashcards
What is dead space?
What is right to left shunt?
What is the diffusion defect?
What is ventilation perfusion V/Q mismatch?
What are the anatomical components of respiratory system?
Draw out the airways-respiratory tree
- Lack of cartilage from terminal bronchiole- more distensible but vulnerable to compression
- Hierarchical branching
- Alveoli- exchanger unit
- Before alveoli- conduits/thoroughfare
When is airway resistance highest and when does it fall?
- Airway resistance is maximum at 5th-8th gen bronchi
- It falls beyond the 10th gen
- As increased cross section over-compensates for the progressive narrowing
What is present in lung parenchyma?
- Alveoli
- Alveolar interstitium
- Capillaries
- Alevolocapillary membranes
- Alveolocapillary interstitium
How much lung surface is there in the lungs and how many miles of airway is there?
- Both lung surface is equal to a folded tennis court
- With 1500 miles of airway running through it
What is the law of gas exchange?
- Can only occur in the alveolus
- That is both ventilated and perfused
- Alveolocapillary membrane is key
Explain insufficiencies in gas exchange
- Ventilation of non-perfused alveoli- DEAD SPACE
- Perfused unventilated alveoli- R2LS– right to left shunt- entry of deoxygenated blood from pulmonary to systemic circulation
- So, the entire conduit from nose and up to but excluding the alveoli- ANATOMICAL DEAD SPACE
- R2L Shunt- is generally not physiological/anatomical, almost always pathological
- These cause ventilation perfusion V/Q mismatch
Explain physiological inefficiencies in VQ
- Normal ratio 0.8
- But not uniform
- Base <0.8- better ventilated and perfused than apex
- Base better perfused than ventilated
- Gas exchange is also relatively inefficient but that is normal physiology
What are the functions of the lungs?
- Narrower than the functions of the respiratory system, as a whole, which also offers
- Speech and olfaction, humidification and temperature control, respiratory defence- gag, sneeze and cough
- Lungs- oxygenation, removal of waste gases e.g., CO2
What makes up respiratory failure?
- Impaired ventilation- neuromuscular defect
- Impaired perfusion- vascular defect
- Impaired diffusion- intrinsic lung alveolar defect
Causes of impaired ventilation?
- Neural- Narcotics, Motor neurone disease (MND), Encephalitis, Cerebral space occupying lesion (SOL) etc
- Mechanical- obstruction to airways, kyphoscoliosis, pleural effusion, trauma, muscle disease, gross obesity (Pickwickian syndrome)
What are some causes of impaired perfusion?
- Cardiovascular- heart failure, multiple pulmonary emboli
What is the cause of impaired diffusion?
Diffuse parenchymal fibrosis
What are the types of respiratory failure?
- Type I- Hypoxia but low CO2 (hypocapnia), as hyperventilatory drive is retained but insufficient for delivery of adequate O2 to the exchange unit
- Type II- Hypoxia and hypercapnia- lack of ventilatory drive- hypoventilation
- Acute type II RF- Respiratory acidosis
- Chronic type II RF- Compensatory metabolic alkalosis
What is respiratory failure?
- RF is defined as a condition in which there is failure in one or both of the gas exchange function of lungs
- Only O2 exchange- RF type I
- Both O2 and CO2- RF Type II
- Additionally type III- to be discussed and
- Type IV- hypoperfusion of respiratory muscles in shock patients
What are some physical signs of respiratory failure?
- Dyspnoea
- Somnolence
- Headache
- Confusion
- Coma
- Asterixis (flapping tremor/hepatic flap)
Explain V/Q mismatch
- A hyperventilating normal alveolar unit cannot compensate for the hypoxaemia due to shunt- anatomical or physiological (diversion from pathological dead space)- as the O2 loading graph plateaus off
- But it can compensate for the hypercapnia- as the CO2 unloading graph does not saturate and is linear
What are some adaptations in V/Q mismatch?
- If V falls- PAO2 reduces causing pulmonary vasoconstriction and vascular diversion to healthy segment
- If Q falls- PaCO2 reduces causing bronchoconstriction and diverting air to healthy segment
- FIRST IN LAST OUT PRINCIPLE- Air from inefficient alveoli stays in dead space and then enters efficient alveoli in the next breath (physiological redistribution of air)
A = alveolar
a - arterial
What is COPD describe?
- Chronic bronchitis and Emphysema
- Depending on the level of involvement of the airway
- Distinct pathological processes
- Almost always a degree of overlap
- By definition, diffuse and generally irreversible or fixed
- Centred on smaller airways and alveolar units
- Local obstruction is by tumour or foreign body
Explain the pathology of chronic bronchitis (in COPD)
- Chronic inflammation of airways, may have squamous metaplasia (smokers) or acute inflammation due to acute exacerbation even with bronchopneumonia (infective exacerbation)
- Bronchial associated lymphoid tissue or BALT
- Hyperplasia of goblet cells leading to mucus secretion, plugging and obstruction
- Hyperplasia of submucosal glands in larger airways
- Respiratory bronchiolitis- quintessential smoker’s lesion