what is the definition of an airway obstruction
the narrowing or blockage of airflow which can occur at different levels of respiratory tract.
what are fixed obstructions?
- does not move or change shape with breathing
- it is unaffected by airflow or by changes in transmural pressure
- it maintains a constant degree of narrowing during both inspiration and expiration
what are examples of fixed obstructions?
- tracheal stenosis from scaring
- a rigid tumor or foreign body lodged in the airway
what does the flow volume loop look like in a fixed obstruction?
both inspiratory and expiratory limbs of the loop are flattened. this occurs because the obstruction equally limits airflow in both directions
what is a variable obstruction?
- it moves or changes in diameter depending on Air flow direction
- the degree of narrowing depends on whether the pt. is inspiring or expiring
- behaviour changes depends on location (extra or intra thoracic)
extra thoracic obstruction
- found above the thoracic cavity eg. upper trachea or larynx and not surrounded by the pleura
what is the mechanics of extra thoracic obstruction during expiration?
- airway pressure rises above atmospheric pressure
- airway pressure pushes outwards on obstruction and the airway widens
- expiratory flow remains normal
what is the mechanics of extra thoracic obstruction during inspiration?
- airway pressure is less than atmospheric pressure due to negative pressure generated in the thorax
- causes the airway to collapse inward, narrowing the lumen
- results in reduced inspiratory flow
what does a flow volume loop look like if there is an variable extra thoracic obstruction
- flattened inspiratory limb
- normal expiratory limb
what are examples of variable extra thoracic obstructions?
- vocal cord dysfunction
- laryngeal tumour
- tracheomalacia (tracheal weakness above the thorax)
variable intra thoracic obstruction
- found within the thoracic cavity (lower trachea and main bronchi)
- surrounded by pleura
- effeted by pleural pressure
variable intra thoracic obstruction mechanics during expiration
- pleural pressure increases due to muscle contractions and is pleural pressure exceeds airway pressure the airway can collapse inward
- airflow becomes restricted during expiration
variable intra thoracic obstruction mechanics during inspiration
- pleural pressure becomes more negative
- this pulls airway open increasing its diameter
- inspiratory flow remains normal
what does the flow volume loop look like in variable intra thoracic obstruction
- flattened expiratory limb
- normal inspiratory limb
what are examples of variable intrathoracic obstruction?
- tumor or lesion within the lower trachea or bronchi
- tracheomalacia (if a segment collapses during expiration)
why extra thoracic airways don’t collapse during expiration
because extrathoracic regions are no surrounded by the pleura therefore they are not exposed to pleural pressures
unequal filling of alveoli during alveolar ventilation is due to differences in…
resistance - bronchiole diameter
and
compliance - alveolar wall thickness
what is the pendalift phenomenon (pendelluft effect)
during pauses between inspiration and expiration the air redistributes from fast alveoli to slow alveoli to equilibrate air between alveoli
what is work of breathing?
the amount of energy required to move air in and out of the lungs
what is minute ventilation?
tidal volume x RR
types of dead space : anatomical dead space
air in the conducting zone ie. trachea/terminal bronchial, that don’t reach the alveoli
types of dead space - alveolar dead space
alveoli that are ventilated but not perfused eg. PE
types of dead space - apparatus dead space
air volume in tubing or mask / ventilatory equipment
type of dead space - physiological dead space
alveolar + anatomical dead space
