Lung Ventilation Flashcards
Define ventilation
The process of inspiration and expiration
What are the parts of the respiratory tract?
- conducting portion: anatomical dead space
- respiratory portion
Outline the process of passive expiration
- muscles used in inspiration relax
- diaphragm moves up
- thoracic cavity volume reduces
- volume of lungs reduces and return to original
volume - intrapulmonary pressure increases
- air expelled
What makes up the conducting portion of the respiratory tract
Nasal cavity to the terminal bronchioles
- nasal cavity
- pharynx
- larynx
- trachea
- primary + secondary bronchi
- bronchioles
- terminal bronchioles
What makes up the respiratory portion of the respiratory tract?
- respiratory bronchioles
- alveolar ducts
- alveoli
What is anatomical dead space?
The volume of air in the conducting airways
What is alveolar dead space?
Air in alveoli which do not take part in gas exchange
e.g. damaged alveoli
What is physiological dead space?
PDS = anatomical DS + alveolar DS
How do you calculate tidal volume?
TV = anatomical dead space + alveolar ventilation
How do you calculate the total pulmonary ventilation?
TPV = tidal volume x respiratory rate
What is the pressure inside the lungs called?
Intrapulmonary pressure
Outline the process of inspiration
- external intercostal muscles contract
- diaphragm contracts + flattens
- intrathoracic volume increases
- intrapulmonary pressure decreases below atmospheric pressure
- elastic tissue in alveoli is stretched
- air pushed into lungs
What are the accessory muscles involved in forced inspiration?
- sternocleidomastoid
- scalene muscles
- serratus anterior
- pectoralis major + minor
What accessory muscles are used in forced expiration?
- internal intercostals
- abdominal wall muscles
Describe the pleural seal
- the surface tension of the pleural fluid creates a film that coats the lungs + the thoracic cavity > when chest cavity expands so do the lungs
- the film prevents the lungs from collapsing + allows for expansion and contraction when breathing
Describe the pleural membranes of the thorax
- Parietal pleura lines the inside of each hemi-thorax
- Visceral pleura lines the lungs
What does parietal pleura line?
Parietal pleura lines each hemi-thorax
What is the hemi thorax?
The bony thoracic cage, diaphragm + mediastinal surfaces
What is the intrapleural space?
Space between visceral and parietal pleura
What does visceral pleura line?
Visceral pleura lines the lungs
What is functional residual capacity?
Volume of air remaining after passive expiration
What is compliance?
A measure of how distensible the lungs are
How do you calculate compliance?
C = change in volume / change in pressure
What is emphysema?
- condition in which destruction of the terminal bronchioles + distal air spaces occurs via the breakdown of elastin
- permanent enlargement of air spaces (bullae)
What is the opposite of compliance?
Lung elastic recoil
What is elastic recoil in respiratory system?
The ability of something to return to its original size
What is elastic recoil directly related to?
- connective tissue surrounding alveoli ( elastic fibres)
- alveolar fluid surface tension
What does lungs returning to their original volume depend on?
Elastic recoil
Where do interstitial lung disease occur?
The interstitium between alveolar epithelium + capillary endothelium
What happens in pulmonary fibrosis in terms of compliance and elastic recoil?
- stiff lungs > compliance is reduced
- elastic recoil is increased > resting lung volume is smaller
- restrictive disease
What impact does surface tension have on compliance?
Surface tension decreases compliance
What issue can occur in premature babies <35 weeks in relation to the alveoli?
Surfactant respiratory distress syndrome
- not enough lung surfactant has been produced > alveoli collapse
- exogenous lung surfactants are needed
Clinical features of neonatal respiratory distress syndrome?
- grunting
- nasal flaring
- intercostal +subcostal retractions (use of accessory muscles)
- tachypneoa
- cyanosis
Treatment for neonatal respiratory distress syndrome
- surfactant replacements via endotracheal tube
- O2/assisted ventilation
At how many weeks do babies have enough surfactant?
35 weeks
How could you calculate the patient’s total pulmonary ventilation?
Tidal volume x respiratory rate
What is the negative intrapleural pressure?
- lungs have a natural inward elastic recoil
- chest wall has a natural outward elastic recoil
- opposing forces create a negative pressure in the intrapleural space
Role of negative intrapleural pressure
Keeps alveoli/lungs from fully collapsing with each expiration
How does intrapulmonary pressure change between inspiration and expiration relative to the atmosphere
- inspiration: intrapulomnary pressure in negative relative to atmosphere > air pushed in
- expiration: intrapulmonary pressure is positive relative to atmosphere
How does intrapleural pressure change during inspiration and expiration?
ALWAYS negative
What is transpulmonary pressure?
Intrapulmonary pressure - intrapleural pressure
What type of lung disease is pulmonary fibrosis?
Restrictive
How do bronchioles stay open in expiration?
Radial traction
Of the surrounding alveolar walls on bronchioles
Describe airways resistance across the lung
Individual resistance is high
Altogether is low
Is there lower resistance in the upper or lower airways?
Why?
lower airways
- connective branches create alternative routes
- combined resistance of downstream branches is less than higher up
- it’s easier for air to flow deeper into lungs
Compare the structure of a bronchus compared to a bronchiole
- bronchus: has cartilage + glands
- bronchioles: no cartilage (require radial traction to stay open) or glands
What is Gillian Barre syndrome?
Autoimmune condition where the body attacks its own peripheral nerves.
What is the function of the plerual seal?
To ensure the lungs expand as the thoracic cavity does using the surface tension of the pleural fluid
What types of cells produce surfactant?
Type II pneumocytes
What happens to compliance and elastic recoil in a patient with emphysema?
- Compliance increases
- Elastic recoil decreases
- Due to breakdown of elastin > less pull in
What is interstitial lung disease?
Umbrella term for disease that cause fibrosis + inflammation to lungs
Collagen is deposited into interstitium
What happens to compliance and elastic recoil in a patient with interstitial lung disease?
Compliance decreases
Elastic recoil increases
Function of surfactant
- decreases surface tension of alveoli
- prevents small alevoli collapsing into larger alveoli
